RSC-Programme - Interim Report. Approach and Basis for - Posiva
RSC-Programme - Interim Report. Approach and Basis for - Posiva
RSC-Programme - Interim Report. Approach and Basis for - Posiva
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Working <strong>Report</strong> 2009-29<strong>RSC</strong>-<strong>Programme</strong> - <strong>Interim</strong> <strong>Report</strong><strong>Approach</strong> <strong>and</strong> <strong>Basis</strong> <strong>for</strong> <strong>RSC</strong> Development, Layout DeterminingFeatures <strong>and</strong> Preliminary Criteria <strong>for</strong> Tunnel <strong>and</strong>Deposition Hole ScalePirjo Hellä, ed.Antti IkonenJussi MattilaTaija TorvelaLiisa WikströmApril 2009POSIVA OYOlkiluotoFI-27160 EURAJOKI, FINLANDTel +358-2-8372 31Fax +358-2-8372 3709
Working <strong>Report</strong> 2009-29<strong>RSC</strong>-<strong>Programme</strong> - <strong>Interim</strong> <strong>Report</strong><strong>Approach</strong> <strong>and</strong> <strong>Basis</strong> <strong>for</strong> <strong>RSC</strong> Development, Layout DeterminingFeatures <strong>and</strong> Preliminary Criteria <strong>for</strong> Tunnel <strong>and</strong>Deposition Hole ScalePirjo Hellä, ed.Pöyry Environment OyAntti IkonenSaanio & Riekkola OyJussi MattilaGeological Survey of Finl<strong>and</strong>Taija Torvela, Liisa Wikström<strong>Posiva</strong> OyApril 2009Base maps: ©National L<strong>and</strong> Survey, permission 41/MML/09Working <strong>Report</strong>s contain in<strong>for</strong>mation on work in progressor pending completion.
ABSTRACT<strong>Posiva</strong> Oy, jointly owned by Teollisuuden Voima Oyj, Fortum Power <strong>and</strong> Heat Oy, isresponsible <strong>for</strong> implementing the programme <strong>for</strong> geological disposal of spent nuclearfuel in Finl<strong>and</strong>. The Olkiluoto site has been studied <strong>for</strong> this purpose <strong>for</strong> over twodecades. Since 2004, an underground research facility, ONKALO, is being constructedat the site, which will later become a part of the disposal facility. <strong>Posiva</strong> is preparing tosubmit an application to obtain a construction licence <strong>for</strong> the disposal facility by the endof 2012.To prepare <strong>for</strong> the licensing, host rock requirements are being developed to guiderepository design <strong>and</strong> layout adaptation, as required by the regulators. The RockSuitability Criteria (<strong>RSC</strong>) programme has been set up <strong>for</strong> this purpose. The aim of the<strong>RSC</strong> is to develop a classification scheme both to be applied to the repository layoutdesign <strong>and</strong> to define suitable rock volumes <strong>for</strong> the deposition holes. The classificationscheme considers both long-term safety <strong>and</strong> engineering aspects. Per<strong>for</strong>mance targets<strong>for</strong> the host rock consider rock properties relevant to safety, <strong>and</strong> there<strong>for</strong>e rockproperties contributing to the function of the host rock as a natural barrier <strong>and</strong> affectingper<strong>for</strong>mance of the engineered barrier system. Consequently they are related tochemical composition of the groundwater, groundwater flow, groundwater transportproperties <strong>and</strong> thermomechanical stability.The practical criteria, Rock Suitability Criteria (<strong>RSC</strong>) based on current site data <strong>and</strong>models, are defined on different scales, including repository, tunnel <strong>and</strong> deposition holescales. The focus has been in the repository scale. Consequently, layout determiningfeatures (LDFs) <strong>and</strong> their respect distance volumes that are to be avoided when locatingdeposition tunnels <strong>and</strong> holes have been defined. Zones defined as LDFs are potentiallymechanically instable in the current or future stress field or they are main groundwaterflow routes important <strong>for</strong> transport of solutes <strong>and</strong> chemical stability at the site. The rockconditions at repository level contribute to fulfilment of several per<strong>for</strong>mance targets likegroundwater composition, rock mechanics <strong>and</strong> non-flow related transport properties. Aninitial version of the <strong>RSC</strong>- criteria, applied in deposition hole location selection,considers LDFs <strong>and</strong> smaller scale zones <strong>and</strong> their respect distance volumes, FPI (fullperimeter intersection) fractures <strong>and</strong> inflow in the deposition hole.Rock suitability criteria <strong>and</strong> per<strong>for</strong>mance <strong>and</strong> engineering targets, which <strong>for</strong>m thebackground of the criteria, are developed in an iterative manner. Changes may beneeded based on practical testing of the criteria, evaluation of the application of thecriteria to layout design <strong>and</strong> safety case compilation, as well as new knowledge onper<strong>for</strong>mance of the engineered barriers <strong>and</strong> site. Future work includes development oftunnel <strong>and</strong> deposition hole scale criteria, identifying suitable measurement techniques<strong>and</strong> developing the predictive modelling procedure to support the application of criteria.Keywords: crystalline bedrock, nuclear waste disposal, KBS-3V, long-term safety,constructability
<strong>RSC</strong>-ohjelma - väliraportti. Kallion soveltuvuusarvioinnin perusteet, tilojensijoittelua rajoittavat piirteet ja alustavat tunneli- ja sijoitusreikäskaalankriteeritTIIVISTELMÄTeollisuuden Voima Oyj:n, Fortum Powerin ja Heat Oy:n omistama <strong>Posiva</strong> Oy onvastuussa ydinjätteiden loppusijoituksesta Suomessa. Olkiluodon aluetta on tutkittu tätätarkoitusta varten yli kahdenkymmenen vuoden ajan, ja vuonna 2004 aloitettiinmaanalaisen tutkimustilan, ONKALOn, rakentaminen. Myöhemmin ONKALOsta tuleeosa loppusijoituslaitosta. Parhaillaan <strong>Posiva</strong> Oy valmistautuu esittämään käytetyn ydinpolttoaineenrakentamislupahakemuksen vuonna 2012.Rakentamislupahakemusta varten määritetään viranomaisohjeiden mukaisesti kallioperänsoveltuvuuskriteerit, jotka ohjaavat loppusijoitustilojen suunnittelua ja tilojen sijoittelua.Tätä tarkoitusta varten on perustettu <strong>RSC</strong>-ohjelma (Rock Suitability Criteria),jonka tavoitteena on kehittää soveltuvuusluokittelu käytettäväksi loppusijoitustilojenasemoinnissa ja sijoitusreikien paikkojen valinnassa. Soveltuvuusluokittelu huomioisekä pitkäaikaisturvallisuuden että tilojen rakentamisen kannalta oleelliset seikat.Kallioperälle asetetut toimintakykytavoitteet koskevat turvallisuuden kannalta merkittäviäkallioperän ominaisuuksia, jotka vaikuttavat kallioperän toimintaan luonnollisenavapautumisesteenä ja toisaalta teknisten vapautumisesteiden toimintakykyyn. Toimintakykytavoitteetliittyvät pohjaveden kemialliseen koostumukseen, pohjaveden virtaukseensekä kulkeutumisominaisuuksiin ja lämpömekaaniseen stabiliteettiin.Käytännössä sovellettavat kriteerit, <strong>RSC</strong>-kriteerit, perustuvat tämänhetkiseen loppusijoituspaikantuntemukseen ja sitä kuvaaviin malleihin. <strong>RSC</strong>-kriteerit on määritettyloppusijoitustila-, tunneli- ja reikämittakaavoissa painopisteen ollessa työn tässä vaiheessaloppusijoitustilamittakaavassa. Loppusijoitustilojen ja -tunneleiden asemointiarajoittavat LDF-piirteet (layout determining features) sekä niiden vaikutusalueet onmääritetty. Näitä tilavuuksia tulee välttää tilojen asemoinnissa. LDF-piirteitä ovatmerkittävät de<strong>for</strong>maatiovyöhykkeet, joilla merkitystä kallioliikuntojen kannalta jokonykyisessä tai tulevassa jännityskentässä ja vyöhykkeet, jotka ovat merkittäviä pohjavedenvirtauksen ja aineiden kulkeutumisen kannalta ja vaikuttavat siten alueenkemiallisten olosuhteiden pysyvyyteen. Kallioperän ominaisuudet loppusijoitustilojentasolla ovat suotuisat useiden toimintakykytavoitteiden toteutumisen kannalta kutenpohjaveden koostumus, kalliomekaaniset ominaisuudet ja pidättymisominaisuudet.Esitetyt <strong>RSC</strong>-kriteerit huomioivat loppusijoitusreikien paikan valinnassa seuraavatkallioperän ominaisuudet; LDF-piirteet, pienemmät vyöhykkeet ja niiden vaikutusalueetja sijoitusreikää leikkaavat FPI-raot (full perimeter intersection) sekä vuoto loppusijoitusreikään.<strong>RSC</strong>-kriteerit sekä kallioperälle asetetut toimintakykytavoitteet ja tilojen rakentamiseenliittyvät vaatimukset määritetään iteratiivisesti. Muutosten perusteena voivat ollakäytännön testit, kriteerien toimivuuden arviointi sekä teknisten vapautumisesteidentoimintakyvystä ja sijoituspaikasta saatava uusi tieto. Jatkossa <strong>RSC</strong>-työ keskittyytunneli- ja loppusijoitusreikämittakaavan kriteerien ja kriteerien soveltamista tukevanennustavan mallintamisen kehittämiseen sekä kriteerien täyttymisen osoittamiseksitarvittavien mittausmenetelmien määrittämiseen.Avainsanat: kiteinen kallio, ydinjätteen loppusijoitus, KBS-3V, pitkäaikaisturvallisuus,rakennettavuus
PREFACEThis report presents the outcome of Phase 1 of the Rock suitability criteria (<strong>RSC</strong>)programme.The following individuals have contributed to the compilation of the report Pirjo Hellä(Pöyry Environment) has written Chapters 1–4 (excluding Section 2.2) <strong>and</strong> compiledChapter 7 based on contribution from the other authors as well as edited the report;Liisa Wikström (<strong>Posiva</strong> Oy) has written the Section on layout determiningfeatures (Section 5.2); Jussi Mattila (Geological Survey of Finl<strong>and</strong>) has written Section5.3 presenting development of the <strong>RSC</strong>-I criteria; <strong>and</strong> Antti Ikonen (Saanio & RiekkolaOy) has written Chapter 6 on engineering targets.Material <strong>and</strong> text was also provided by the following people: Ismo Aaltonen (<strong>Posiva</strong>Oy) has provided material <strong>for</strong> the estimation of the degree of utilisation (Section 5.3);Henry Ahokas (Pöyry Environment Oy) has provided text concerning thehydrogeological zones <strong>and</strong> their respect distance presented in Section 5.2; PetteriPitkänen (VTT) has provided text on the hydrogeochemistry in Section 5.3. JohanAndersson (Streamflow Ab) has commented on various drafts of the report <strong>and</strong> has thuscontributed significantly to the outcome.Parts of or the entire report has been commented on by the following individuals: NuriaMarcos (Saanio & Riekkola Oy), Margit Snellman (Saanio & Riekkola Oy) <strong>and</strong> PaulSmith (Sam Ltd) from the SAFCA group, Raymond Munier (SKB), Rolf Christiansson(SKB), Juhani Vira (<strong>Posiva</strong> Oy), Timo Äikäs (<strong>Posiva</strong> Oy), Johanna Hansen (<strong>Posiva</strong>Oy), Erik Johansson (Saanio & Riekkola Oy) <strong>and</strong> Pekka Anttila (Fortum NuclearServices). These comments have provided valuable help in finalising the report.Discussions with <strong>and</strong> comments from many of the reviewers <strong>and</strong> others during theprocess of defining the per<strong>for</strong>mance targets is gratefully acknowledged. EspeciallyPaula Keto (Saanio & Riekkola Oy) is thanked <strong>for</strong> helping in many questions related tobackfilling.Finally, the authors would like to thank Sofia Walker (Pöyry Environment Oy) <strong>for</strong>editing the language of this report.
1TABLE OF CONTENTSABSTRACTTIIVISTELMÄPREFACE1 INTRODUCTION .................................................................................................... 32 BACKGROUND ..................................................................................................... 72.1 Regulatory requirements ............................................................................. 72.2 Host rock classification (HRC) <strong>and</strong> its testing in ONKALO .......................... 92.2.1 General .......................................................................................... 92.2.2 Methodology <strong>and</strong> data .................................................................... 92.2.3 Results ......................................................................................... 132.2.4 Development needs ..................................................................... 152.3 SKB approach .......................................................................................... 162.4 KBS-3H work ............................................................................................ 173 GENERAL APPROACH AND METHODOLOGY .................................................. 194 LONG-TERM SAFETY RELATED REQUIREMENTS ON HOST ROCK .............. 254.1 Safety concept <strong>and</strong> safety functions.......................................................... 254.2 Repository depth....................................................................................... 274.3 Per<strong>for</strong>mance targets related to functionality of the engineered barriers ..... 284.3.1 Canister ........................................................................................ 284.3.2 Buffer ........................................................................................... 304.3.3 Backfill .......................................................................................... 324.3.4 Summary ...................................................................................... 344.4 Per<strong>for</strong>mance targets related to radionuclide transport ............................... 354.5 Other issues need to be considered.......................................................... 364.5.1 Disturbances caused by excavation <strong>and</strong> operation ....................... 364.5.2 Mutual compatibility of <strong>and</strong> interfaces between the barriers .......... 374.5.3 Groundwater flow regime ............................................................. 374.6 Summary of the host rock per<strong>for</strong>mance targets ........................................ 375 DEVELOPMENT OF THE ROCK SUITABILITY CRITERIA ................................. 415.1 <strong>Approach</strong> to the criteria development ........................................................ 415.2 Layout-determining features <strong>and</strong> respect distance volumes ...................... 415.2.1 Introduction .................................................................................. 415.2.2 Methodology ................................................................................. 435.2.3 Data <strong>and</strong> models .......................................................................... 545.2.4 Results ......................................................................................... 575.2.5 Uncertainties in layout determining features <strong>and</strong> respectdistance volumes ......................................................................... 735.3 Rock suitability criteria, <strong>RSC</strong>-I................................................................... 745.3.1 Site characteristics of relevance to the per<strong>for</strong>mance targets ......... 745.3.2 Evolution of the Olkiluoto site <strong>and</strong> its impact on the criteria .......... 825.3.3 Criteria related to the hydrogeological properties of the rock ........ 845.3.4 Criteria related to the mechanical properties of the rock ............... 865.3.5 Aspects related to the application of the <strong>RSC</strong> in practice .............. 875.3.6 Discussion <strong>and</strong> development needs ............................................. 97
26 ENGINEERING TARGETS ON HOST ROCK ...................................................... 996.1 Activities ................................................................................................... 996.2 Development needs ................................................................................ 1017 CONCLUSIONS AND FUTURE WORK ............................................................. 1037.1 Main achievements ................................................................................. 1037.2 Summary of h<strong>and</strong>ling the regulatory requirements in the <strong>RSC</strong> ................ 1047.3 Future work ............................................................................................. 107REFERENCES .............................................................................................................. 113
31 INTRODUCTIONBackground<strong>Posiva</strong> Oy, jointly owned by Teollisuuden Voima Oyj, Fortum Power <strong>and</strong> Heat Oy, isresponsible <strong>for</strong> implementing the programme <strong>for</strong> geological disposal of spent nuclearfuel in Finl<strong>and</strong>. The programme consists of research, technical design <strong>and</strong> developmentactivities, as well as construction <strong>and</strong> operation of the disposal facility. In 2000,Government made the Decision in Principle (DiP) <strong>for</strong> the disposal of spent fuel fromTVO <strong>and</strong> Fortum's reactors on Olkiluoto Isl<strong>and</strong> in Eurajoki. <strong>Posiva</strong> plans to construct aKBS-3 type repository, designed to be situated at a depth of 400 m to 700 m in thebedrock at Olkiluoto. By decision of the Ministry of Trade <strong>and</strong> Industry (KTM, atpresent Ministry of Employment <strong>and</strong> Economy, TEM) made in 2003, <strong>Posiva</strong> is tosubmit an application to obtain a construction licence <strong>for</strong> the disposal facility by theend of 2012.As the programme is approaching the licensing phase, the Safety Case needs to cover allaspects from design, manufacturing <strong>and</strong> installation to quality control <strong>and</strong> long-termper<strong>for</strong>mance (see e.g. <strong>Posiva</strong> 2008). An aspect emphasised in developmental work, issetting up the requirements <strong>for</strong> design, manufacturing <strong>and</strong> implementation of technicalbarriers. Also aspects related to operation of the facilities need to be considered.Appropriate quality assurance measures need to be developed to verify that therequirements will be met. Consequently, host rock requirements are being developed toguide repository design <strong>and</strong> layout adaptation, as required by the regulator.Olkiluoto siteDuring the past two decades, various investigations have taken place at the Olkiluotosite (see Figure 1-1). Currently, construction of the underground research facilityONKALO provides opportunities to carry out investigations underground. Theseinvestigations enable the collection of more detailed in<strong>for</strong>mation of the rock atrepository depth <strong>and</strong> confirmation of site underst<strong>and</strong>ing obtained during previoussurface-based investigations, as well as making testing <strong>and</strong> demonstration of thedisposal technology possible. Existing site underst<strong>and</strong>ing is summarised in the series ofSite Descriptive Model reports (<strong>Posiva</strong> 2005, Andersson et al. 2007 <strong>and</strong> <strong>Posiva</strong> 2009a)compiled by the Olkiluoto Modelling Task Force (OMTF). Based on this currentunderst<strong>and</strong>ing, the bedrock will generally provide suitable <strong>and</strong> sufficiently stableconditions <strong>for</strong> a repository, although there are certain site specific features, such asextensive de<strong>for</strong>mation zones, volumes of relatively low mechanical strength in relationto rock stress, sparse occurrence of highly transmissive fractures or saline groundwater,which may affect safety of the repository.
4Reference DesignThe discussion in this report is based on the design as described in the facilitydescription 2006 (Tanskanen 2007). The design of the disposal facility is based on theKBS-3V concept (vertical disposal). The release barriers include canister, buffer <strong>and</strong>deposition tunnel backfill <strong>and</strong> the host rock around the repository. The repository islocated at depth of -420 m. The canisters are made of copper with an iron insert. Thebuffer material is bentonite with MX-80 as reference material or another bentonite withsimilar properties. The backfilling option is based on blocks <strong>and</strong> pellets. The blocks aremade either of bentonite or clay (Friedl<strong>and</strong> clay is the reference material). Alternativebackfill material is a mixture of bentonite <strong>and</strong> crushed rock <strong>and</strong> also in situ compactionis considered as an option.<strong>RSC</strong> programmeIn the research <strong>and</strong> development programme TKS-2006 (<strong>Posiva</strong> 2006), <strong>Posiva</strong>acknowledged the need <strong>for</strong> further development of requirements on the host rock <strong>and</strong><strong>for</strong> ensuring their applicability <strong>and</strong> reliability of these requirements during the actualrepository implementation. The Rock Suitability Criteria (<strong>RSC</strong>) programme has beenset up <strong>for</strong> this purpose. The <strong>RSC</strong> is based on work done in the Host RockCharacterisation (HRC) project (Hagros et al. 2005, Hagros 2006) which produced thepreliminary Olkiluoto-specific criteria.
5The aim of the <strong>RSC</strong> is to develop a classification scheme to be applied <strong>for</strong> the repositorydesign <strong>and</strong> construction. This scheme includes definition of rock volumes suitable <strong>for</strong>the repository panels, assessment of whether deposition tunnels or tunnel sections aresuitable <strong>for</strong> locating deposition holes <strong>and</strong> acceptance of a deposition hole <strong>for</strong> disposalbased on the rock properties. The developed criteria should be based on observable <strong>and</strong>measurable properties of the host rock. Together with interpretation, modelling <strong>and</strong>general underst<strong>and</strong>ing of site properties, the criteria can then be used to show thatrequirements set on the rock can be fulfilled. By applying the classification scheme, theaim is to avoid features of the rock that may be detrimental <strong>for</strong> safety of the repository.The focus of these investigations has been on the reference concept KBS-3V withvertical deposition holes. Related work was also done <strong>for</strong> the alternative conceptKBS-3H with horizontal deposition drifts, although its emphasis has been on adeposition drift scale <strong>and</strong> the engineered barrier design.The <strong>RSC</strong>-programme is divided into three sub-projects which in turn include severaltasks:Definition of the per<strong>for</strong>mance targets on the host rock (TARGET)Development <strong>and</strong> testing of the criteria (DETECT)Definition of the engineering targets on the host rock (DESIGN)Sub-project TARGET is responsible <strong>for</strong> defining per<strong>for</strong>mance targets i.e. requirementson rock properties arising from the long-term safety. These are the basis <strong>for</strong> the practicalcriteria. It includes the tasks of reviewing proposed criteria against the per<strong>for</strong>mancetargets, <strong>and</strong> of evaluating how application of suggested criteria will contribute to thesafety case. Application of the rock suitability criteria will define the potential range ofinitial conditions <strong>for</strong> the host rock <strong>and</strong> <strong>for</strong>ms thus basis also <strong>for</strong> the assessment of theconditions in the canister near field during repository <strong>and</strong> site evolution. Sub-projectDESIGN considers the engineering requirements <strong>and</strong> tracks how the criteria are appliedin layout design. Finally, the main work is carried out under sub-project DETECT. It isresponsible <strong>for</strong> defining the practical criteria based on observable <strong>and</strong> measurable siteproperties, testing the criteria, <strong>and</strong> applying the criteria <strong>for</strong> example in layout planning.The programme was started in 2007 <strong>and</strong> is planned to continue until 2012. During thePhase 1 of the project, from 2007 until the end of 2009, the focus has been on defininglong-term safety related <strong>and</strong> engineering requirements, as well as defining volumessuitable <strong>for</strong> locating panels of several deposition tunnels. However, as the long-termsafety mainly depends on the properties of the near field of the deposition hole <strong>and</strong> thelong-term safety related requirements mainly consider these properties, also preliminarycriteria <strong>for</strong> the deposition tunnel <strong>and</strong> deposition hole scale has been developed. Thefocus during 2010–2012 will be on further development of deposition hole scalecriteria, as well as on testing <strong>and</strong> demonstrating the use of the criteria in ONKALO.Posterior, specific features related to the KBS-3H alternative will be taken into account.Objectives <strong>and</strong> scope of the reportThe aim of this report is to summarise the work done so far during Phase 1 (2007-2008)of the <strong>RSC</strong> programme. Chapter 2 presents background <strong>for</strong> the <strong>RSC</strong>-development; theregulatory requirements, the HRC-classification <strong>and</strong> its testing with ONKALO data, aswell as related work done by SKB <strong>and</strong> within the KBS-3H project. The general
6approach is presented in (Chapter 3), <strong>and</strong> setting up the per<strong>for</strong>mance targets, theoutcome of the sub-project TARGET (Chapter 4). As this work concentrates on the hostrock properties, the long-term safety related requirements, the per<strong>for</strong>mance targets, <strong>for</strong>the other main barriers, namely the canister <strong>and</strong> the buffer, are not defined within thisprogramme. They are however considered to the extent to which they affect the requiredproperties of the host rock by referring to other studies.Chapter 5 summarises the outcome of the DETECT sub-project. As the main focusduring Phase 1 of the programme has been in defining suitable volumes to host tunnels,the definition of the layout determining features <strong>and</strong> their respect distance volume is theother main outcome this work. Preliminary criteria <strong>for</strong> the deposition tunnel <strong>and</strong>deposition hole scale, along with practical aspects of applying the criteria, are alsopresented. The criteria development is an iterative process <strong>and</strong> it is clear that, especiallythe deposition hole scale criteria will still change. It is expected that ONKALO datafrom the relevant depths will bring new valuable in<strong>for</strong>mation in this respect. Thisin<strong>for</strong>mation will be considered in the next development phase 2010-2012.The requirements related to the constructability of the repository, <strong>and</strong> how the criteriaare applied <strong>for</strong> the layout planning, are discussed in Chapter 6. Discussion, includingcomparison with the regulatory requirements <strong>and</strong> identification of the furtherdevelopment needs, is presented in Chapter 7.Testing of the suggested criteria in ONKALO is planned <strong>and</strong> estimation of the degree ofutilisation is being carried out. These will be reported separately.
72 BACKGROUND2.1 Regulatory requirementsRegulatory requirements related to the host rock are presented in the YVL Guide 8.4(STUK 2001). This guide will soon be replaced by the guide STUK-YVL E.5. In thefollowing, regulatory requirements are presented according to the YVL Guide 8.4. Thetwo guides are to great extent consistent with each other. Any changes due to revision ofthe regulatory guides are commented on below, as based on the currently available draft(draft 3, dated 15.1.2009, in Finnish) of the guide STUK-YVL E.5.According to the Government Decision VNA 736/2008 “the long-term safety ofdisposal shall be based on redundant barriers so that deficiency in one of the barriersor a predictable geological change does not jeopardise the long-term safety.”According to the YVL-guide, barriers include both engineered barriers <strong>and</strong> naturalbarriers.“Natural barriers may consist ofthe intact rock around the disposal tunnels, which limits groundwater flowaround waste canistersthe host rock where low groundwater flow, reducing <strong>and</strong> even otherwisefavourable groundwater chemistry <strong>and</strong> retardation of dissolved substances inrock limit the mobility of radionuclidesthe containment provided by the host rock against natural phenomena <strong>and</strong>human actions. ”Further on, the guide requires definition of the per<strong>for</strong>mance targets <strong>for</strong> each barrier, thusincluding the repository host rock. The regulatory guide YVL 8.4 (STUK 2001) requiresthat “Targets <strong>for</strong> the long-term per<strong>for</strong>mance of each barrier, shall be determined basedon best available experimental knowledge <strong>and</strong> expert judgement. The per<strong>for</strong>mance of abarrier may diverge from the respective target value due to rare incidental deviationssuch as manufacturing or installation failures of engineered barriers, r<strong>and</strong>omvariations in the characteristics of the natural barriers or erroneous determination ofthe characteristics. However, the per<strong>for</strong>mance targets <strong>for</strong> the system of barriers as awhole shall be set so that the safety requirements are met notwithst<strong>and</strong>ing thedeviations referred to above. The determination of the per<strong>for</strong>mance targets <strong>for</strong> thebarriers shall be based on an assumption that, due to some unpredicted phenomenon,the per<strong>for</strong>mance of a single barrier as a whole may be significantly lower than therespective target value. The safety requirements shall be met even in such case. Thedetermination of the per<strong>for</strong>mance of barriers shall take account of changes <strong>and</strong> eventsthat may occur in various assessment periods.” In the regulatory guide STUK-YVLE.5, this is altered so that the safety functions <strong>for</strong> each barrier should be defined <strong>and</strong> thatthe per<strong>for</strong>mance targets are defined <strong>for</strong> safety functions instead of barriers as earlier.The guide requires that the host rock characteristics are such that they act as a naturalbarrier <strong>and</strong> that they are favourable with respect to long-term per<strong>for</strong>mance of engineeredbarriers. “Such conditions in the host rock as are of importance to long-term safetyshall be stable or predictable up to at least several thous<strong>and</strong>s of years. The range ofgeological changes which occur thereafter due to e.g. the large scale climate changes,
8shall be estimable <strong>and</strong> be considered in the determination of the per<strong>for</strong>mance targets<strong>for</strong> the barriers.” Features indicating unsuitability of the site are as follows:”proximity of exploitable natural resourcesabnormally high rock stressespredictable anomalously high seismic or tectonic activityexceptionally adverse groundwater characteristics, such as lack of reducingbuffering capacity <strong>and</strong> high concentrations of substances which mightsubstantially impair the per<strong>for</strong>mance of barriers.”The YVL guide continues with requirements of location <strong>and</strong> depth of the repository:“The location of the repository shall be favourable with regard to the groundwater flowregime at the disposal site.The disposal depth shall be selected with due regard to long-term safety, taking intoaccount at leastthe geological structures <strong>and</strong> lithological properties of the host rockthe trends in rock stress, temperature <strong>and</strong> groundwater flow rate with depth.To ensure that the effects of above ground natural phenomena, such as glaciation, <strong>and</strong>human activities will be adequately mitigated, the repository shall be located at thedepth of several hundreds of meters.”Regarding the host rock, special emphasis should be put on geological structures. TheYVL 8.4 (STUK 2001) states “The structures of the host rock of importance togroundwater flow, rock movements or other factors relevant to long-term safety, shallbe defined <strong>and</strong> classified. The waste canisters shall be emplaced in the repository sothat adequate distance remains to such major structures of the host rock which mightconstitute fast transport pathways <strong>for</strong> the disposed radioactive substances or otherwiseimpair the per<strong>for</strong>mance of barriers.”The new guide STUK-YVL E.5 also includes new requirements which influencedevelopment of the scheme <strong>for</strong> rock classification <strong>and</strong> evaluation of its suitability <strong>for</strong>disposal use:safety classification (“turvallisuusluokitus”) of the repository system, structures<strong>and</strong> equipment on the basis of long-term safety should consider layout of therepository (E.5 5.9)carrying out a programme <strong>for</strong> research, testing <strong>and</strong> monitoring duringconstruction <strong>and</strong> operation of the repository. This programme aims to confirmthe suitability of excavated rooms <strong>for</strong> disposal use, define the rock properties ofimportance <strong>for</strong> safety, <strong>and</strong> confirm the long-term per<strong>for</strong>mance of the barriers(E.5 5.11).preparedness to change the layout of the underground facilities in case rockquality is significantly poorer than the design premises (E.5 5.11)
9production of the documentation <strong>for</strong> quality assurance of the canisteremplacement (E.5 6.10) <strong>and</strong> acceptance of disposal locations by STUK (E.58.11)construction of the repository should be done stepwise so that the investigationsneeded to estimate suitability of the rock volume <strong>for</strong> disposal <strong>and</strong> classificationof important rock structures <strong>for</strong> long-term safety can be carried out (E.5 8.9)These points are not explicitly considered in current criteria; however they have to betaken into account in the coming development phases.2.2 Host rock classification (HRC) <strong>and</strong> its testing in ONKALO2.2.1 General<strong>Posiva</strong> has carried out a programme to evaluate existing rock classification schemesused <strong>for</strong> rock construction purposes, also having developed a new host rockclassification system (HRC; Hagros et al. 2005, Hagros 2006). Hagros (2006) includesan extensive summary of the influence of the host rock properties on long-term safety,repository layout <strong>and</strong> constructability. The proposed HRC classification system is basedon a preliminary assessment of the rock properties that are important <strong>for</strong> long-termsafety on the basis of contemporary site models. Constructability of the bedrock wasalso considered. Ultimately, the HRC classification aims to provide relevant in<strong>for</strong>mation<strong>for</strong> deciding whether to excavate deposition tunnels or deposition holes at givenlocations.The HRC-programme has served as the foundation of the current <strong>RSC</strong>-programme,which demonstrates the iterative nature of classification <strong>and</strong> criteria development.Consequently, the current <strong>RSC</strong> program was established to revise the HRC systembased on existing underst<strong>and</strong>ing of the bedrock <strong>and</strong> the requirements on long-termsafety. Testing <strong>and</strong> developing HRC using ONKALO data is described in more detail byLampinen (2008). The testing concerned practical application of the system instead ofits adequacy with respect to repository per<strong>for</strong>mance. The testing was per<strong>for</strong>med byexecuting the tunnel scale procedure described in the HRC, using data from pilot holes(ONK-PH2…ONK-PH5 reaching the maximum depth of 130 m below the surface) <strong>and</strong>their respective tunnel sections in ONKALO. Results were also evaluated together withnew in<strong>for</strong>mation from recent site investigations. The main objectives of the testing wereto assess the practicality, quality <strong>and</strong> development needs of the HRC procedure byclassifying the tunnel sections according to the HRC <strong>and</strong> evaluating gathered results.Testing methodologies, results <strong>and</strong> HRC development needs concluded from the resultsare briefly described in Sections 2.2.2-2.2.4.2.2.2 Methodology <strong>and</strong> dataThe HRC is designed to evaluate the Olkiluoto site on three scales: the repository scale,the tunnel scale <strong>and</strong> the canister scale (Table 2-1).The repository scale considers large-scale characteristics of the rock mass, <strong>for</strong> examplelocation <strong>and</strong> geometry of major fracture zones, <strong>and</strong> is intended to define suitablevolumes <strong>for</strong> the repository. Parameters examined in this scale include fracture zones,rock strength/stress ratio, hydraulic conductivity of the rock, <strong>and</strong> groundwater TDS(total dissolved solids). These parameters are primarily determined on the basis of direct
10ScaleParametersRepository scaleLarge-scale properties: fracture zones(de<strong>for</strong>mation zones), rock strength/stress,hydraulic conductivity,hydrogeochemistry.Tunnel scaleHydraulic conductivity, Q'-value, fracturezones.Canister scaleFractures <strong>and</strong> fracture zones, fracturewidth <strong>and</strong> trace length, rock hydraulicconductivity, Q'-value.data from deep drillholes, but also some indirect data sources, such as geophysical data<strong>and</strong> their interpretations, have been used.The tunnel scale parameters <strong>for</strong> host rock classification include hydraulic conductivity,rock mass quality (Q') <strong>and</strong> fracture zones. Parameters are primarily based on geological<strong>and</strong> hydrogeological data from pilot holes that are drilled in the access tunnel prior tothe actual construction of a tunnel section. Determination of spatial, geological <strong>and</strong>hydraulic properties of fractures <strong>and</strong> fracture zones in the pilot hole are used inclassifying the fracture zones <strong>and</strong> the rock mass that the pilot hole represents. Accordingto the HRC, the relation of fracture zones encountered in a pilot hole to the current sitemodel needs to be assessed. Suitability of the rock mass <strong>for</strong> construction of a tunnelwould be preliminarily determined on the basis of data obtained from the pilot holes.For this purpose, the HRC includes a suitability classification, according to which rockmass on the tunnel scale would be classified as having high, moderate, low or very lowsuitability <strong>for</strong> deposition hole construction, The location <strong>and</strong> hydraulic properties offracture zones concluded from the pilot hole data would then be verified duringconstruction of the tunnel section (the so-called prediction-outcome approach, or P/O).The canister scale HRC (called the deposition hole scale in the <strong>RSC</strong>) aims to evaluatethe suitability of individual deposition holes <strong>for</strong> long-term disposal. High resolution ofthe bedrock model is needed on this scale. In selecting canister locations, the presenceof large fractures <strong>and</strong> local fracture zones are considered. The determination of fracturelocations is, as suggested in the HRC, to be based mainly on three things. Firstly ondetailed mapping of the tunnel floor. Secondly on geological logging of <strong>and</strong>hydrogeological measurements along the probe hole drilled in the middle of the planneddeposition hole. Thirdly on interpretation of the results of ground-penetrating radar or
11other geophysical methods that study the fracture network beneath the tunnel. Proposedparameters <strong>for</strong> canister scale classification include hydraulic conductivity, Q', fracturezones, fracture width (aperture + filling) <strong>and</strong> fracture trace length. Results of thecanister scale HRC should ultimately lead to a decision as to whether or not thedeposition hole can actually be constructed in the planned location. If the decision isaffirmative <strong>and</strong> the deposition hole is made, the HRC will be confirmed by detailedgeological <strong>and</strong> hydrological investigations in the deposition hole be<strong>for</strong>e approving thehole <strong>for</strong> deposition.HRC testing was per<strong>for</strong>med on the tunnel scale in two stages. During the first stage,data was collected from the pilot holes (ONK-PH2…ONK-PH5). After the tunnelsection corresponding to each pilot hole was excavated, data obtained from the pilotholes was compared to data collected from the tunnel section (stage 2). Several datasources <strong>and</strong> methods were used <strong>for</strong> the HRC testing. Data sources include geologicalmodels, geological core loggings of pilot holes, geological tunnel mapping, <strong>and</strong>hydrogeological measurements from both the pilot holes <strong>and</strong> corresponding tunnelsections. Data from probe holes is also suggested to be utilised in the HRC. A shortaccount of these is given below; <strong>for</strong> a more detailed description, the reader is referred toLampinen (2008) <strong>and</strong> references therein.Geological modelsThe site models published up to 2003 classified repository scale geological structuresmainly according to their constructability <strong>and</strong> hydraulic properties, the most importantparameters being fracture frequency, RG-classification (engineering geological mappingdata of the core samples), <strong>and</strong> fracture hydraulic properties. The Olkiluoto bedrockmodel 2003/1 (Vaittinen et al. 2003) classified modelled structures as fractured zones,crushed zones, or hydraulic features based on the observed properties in the drillholes.The classification followed the RG-classification (RiI-RiV) according to FinnishEngineering Geological Classification. Naming convention distinguished R / RH / H -structures.The methodology of structural modelling changed in 2006. Models now aim atthorough site underst<strong>and</strong>ing, where any geological features deviating from the averagehost rock can be detected <strong>and</strong> classified. The modelling approach utilises bothgeological <strong>and</strong> geophysical data. The Olkiluoto geological site model 2006 v.0(Paulamäki et al. 2006) is divided into the lithological model, the alteration model, thebrittle de<strong>for</strong>mation model <strong>and</strong> the ductile de<strong>for</strong>mation model. Of these, the brittlede<strong>for</strong>mation model corresponds most closely to the older bedrock models. R-structuresof the previous structural models were partly re-modelled <strong>and</strong> re-named as brittle faultzones (BFZ) or brittle joint zones (BJZ).The approach <strong>for</strong> hydrogeological modelling has also evolved. Since the 2006 sitemodel (Andersson et al. 2007), hydrogeological zones are identified using hydraulicdata, mainly measured transmissivity by the <strong>Posiva</strong> Flow Log (PFL) <strong>and</strong> pressureresponses. The hydrogeological model is then compared with the modelled brittlede<strong>for</strong>mation zones (BDZ). These comparisons generally show a good overallconsistency. Although some differences exist as some brittle de<strong>for</strong>mation zones may notbe hydraulically important <strong>and</strong>, vice versa, there may be hydraulically importantfeatures outside the modelled BDZs.
12Pilot hole dataThe logging of pilot hole cores takes place immediately after the drilling of the hole. Ofthe attributes recorded during logging, those relevant to the HRC are:FracturingFracture frequency <strong>and</strong> RQD (Rock quality designation)Rock quality (Q'-classification; includes e.g. alteration, joint roughness, etc)Fracture zones <strong>and</strong> core lossDe<strong>for</strong>mation zone intersectionsThe pilot holes ONK-PH2…ONK-PH5 were investigated using geological logging <strong>and</strong>hydrogeological measurements. Brittle de<strong>for</strong>mation zone (called fracture zones in theearly bedrock models) intersections in the pilot holes were first characterised accordingto site models 2003/1 <strong>and</strong> 2006 v.0. The zones were then classified according to HRCtunnel scale classification (<strong>for</strong> details, see Hagros et al. 2005). Q'-values were alsodetermined from each pilot hole. Different flow measurements were per<strong>for</strong>med in orderto define transmissivities <strong>for</strong> the de<strong>for</strong>mation zones <strong>and</strong> hydraulic conductivity of therock mass surrounding the zones.Probe hole dataProbe holes are c. 25 m long boreholes bored at approximately 20 m intervals along thetunnel, or, later when the repository itself is excavated, shorter core drilled probe holeswill be drilled in the centre of the planned deposition hole. Tunnel probe holes are boredin four corners of the tunnel face be<strong>for</strong>e excavation. Water loss measurements werecarried out in the tunnel probe holes during HRC testing, although the results of thesemeasurements are mainly used <strong>for</strong> estimating the need <strong>for</strong> grouting. At the time oftesting, hydrogeological measurements from the tunnel probe holes were not used <strong>for</strong>HRC purposes due to technical difficulties, despite the recommendations of the HRCprocedure. For the same reason, the planned probe hole optical imaging, in order todefine the Q'-value in the probe hole, proved impossible to per<strong>for</strong>m at the time oftesting as no images currently exists from the holes. Probe hole data is there<strong>for</strong>e notincluded in the HRC testing of Lampinen (2008).Geological tunnel mappingAccording to the HRC procedure, Q'-values determined from the pilot holes should bechecked against the data from the respective tunnel section after excavation of thetunnel. Consequently, results from geological mapping (systematic mapping stage) areutilised in the P/O studies <strong>and</strong> HRC testing.Tunnel mapping is per<strong>for</strong>med in stages. The first stage, "round mapping", is carried outafter excavation of each round when the tunnel section has been secured. Basicgeological features <strong>and</strong> rock quality are mapped during this stage, as round mappingprimarily serves rock support <strong>and</strong> engineering purposes. The second stage, "systematicmapping", follows construction work generally c. 100-200 m behind the tunnel face.During systematic mapping, the tunnel walls <strong>and</strong> roof are investigated more carefully
13with respect to geological parameters such as rock types, fracture/de<strong>for</strong>mation zoneintersections, fault properties <strong>and</strong> kinematics, foliation, lineation, folding, weathering,etc. This data serves geological modelling, detailed geological characterisation <strong>and</strong>decisions on final rock support.Hydrogeological tunnel observationsThe significance of mapped <strong>and</strong> modelled geological <strong>and</strong>/or hydrogeological zones tothe HRC is to a great extent determined by the hydrogeological properties of the zonesobserved in pilot holes. There<strong>for</strong>e, hydrogeological investigations per<strong>for</strong>med in thetunnel pilot holes were checked against water leakage observations in the correspondingsection of excavated tunnel. The HRC suggests the usage of Lugeon tests (water lossmeasurement from the probe holes) <strong>and</strong> water leakage mappings <strong>for</strong> testing of pilot holedata in the tunnel. The applicability of the Lugeon tests was, however, poor.Furthermore, water leakage observations at the time of testing are affected by theextensive grouting in the tunnel sections used <strong>for</strong> testing.2.2.3 ResultsFor a detailed description of the testing results, see Lampinen (2008). An example of theclassification results is given in Figure 2-1.Results from the pilot holesFor all tested pilot holes, a rock suitability classification map was constructed (<strong>for</strong> anexample, see Figure 2-1), based on the core loggings <strong>and</strong> hydrogeological data, in orderto test the implementation of the HRC procedure (Lampinen 2008). The suitability mapdivides each pilot hole into suitability classes suggested in the HRC (see Section 2.2.2).Site models 2003/1 (hydrogeological model, Vaittinen et al. 2003) <strong>and</strong> 2006 v.0(geological model, Paulamäki et al. 2006) were used in the characterisation of brittlede<strong>for</strong>mation zones in order to compare the applicability of the two site models <strong>for</strong> HRC.According to pilot hole data from ONK-PH2…ONK-PH5, c. 42–83% of the rock masscould be classified as suitable <strong>for</strong> spent fuel disposal according to the HRC. Theclassification results based on the two site models gave similar results. In pilot holeONK-PH5, the difference was largest as the proportion of rock mass suitable <strong>for</strong>deposition varied from c. 42% (model 2006 v.0) to 49% (model 2003/1). Thedifferences between the two models are mainly due to differences in the definition ofthe de<strong>for</strong>mation zones in the pilot holes. According to current views, the use of both(hydrogeological <strong>and</strong> geological models) is suggested <strong>for</strong> the purposes of the <strong>RSC</strong>, anapproach now occupied in the development of new criteria.Suitability of the rock mass <strong>for</strong> spent nuclear fuel disposal was primarily reduced by thepresence of brittle de<strong>for</strong>mation zones with high hydraulic conductivities. However, Q'-value appear to be an inadequate parameter <strong>for</strong> detecting zones significant from thelong-term safety point of view. Good rock constructability does not cover all rockproperties affecting the suitability of the rock <strong>for</strong> disposal of spent fuel. In other words,pilot hole sections may, despite giving a high Q'-value, contain geological orhydrogeological intersections that within the repository would be considered significant<strong>for</strong> long-term safety of the repository. In addition, Q'-values obtained from the pilotholes did not always correspond to Q'-values observed in the corresponding tunnelsection. The suitability classification according to HRC procedure was there<strong>for</strong>e mainly
14determined on the basis of hydraulic conductivities <strong>and</strong> geological core logging(locations of the fractured zones).Results from the tunnelSimilar to the pilot holes, a rock suitability map was constructed <strong>for</strong> each tunnel sectioncorresponding to the investigated pilot holes (<strong>for</strong> an example, see Figure 2-1). Thesuitability map divides each pilot hole into suitability classes suggested in the HRC (seeSection 6.2.1). Results show that the rock volume percentage estimated suitable <strong>for</strong>disposal is generally lower on the basis of tunnel data than on the basis of pilot holedata. In ONK-PH4 <strong>and</strong> ONK-PH5, the suitability based on the tunnel data wasconsiderably lower than the estimation based on the pilot hole data (33% vs. 47% <strong>and</strong>34% vs. 42%, respectively). Geometrical uncertainty was quite high <strong>for</strong> the low-anglede<strong>for</strong>mation zones observed in ONK-PH5. Only <strong>for</strong> ONK-PH3 the same proportion ofsuitable rock was observed both in the pilot <strong>and</strong> in tunnel. Results show that the angle ofthe de<strong>for</strong>mation zone with respect to the tunnel has a great influence on reliability of thepilot hole estimations, since zones that are vertical <strong>and</strong>/or perpendicular to the tunnelseem to have the highest consistency between pilot hole <strong>and</strong> tunnel data. Furthermore,presence of the site-scale de<strong>for</strong>mation zone with high transmissivity, "R19" (HZ19according to current nomenclature), apparently complicated measurements in ONK-PH5. Similar de<strong>for</strong>mation zones are not expected within the repository.Site modelsThere were several differences in the HRC testing results depending on which sitemodel was used <strong>for</strong> classification. Overall, the site model 2006 v.0 seems to have ahigher capability of classifying the rock mass compared to the older model 2003/1.Differences between the models were small where rock quality is relatively good(ONK-PH2…ONKPH4), but the site model 2006 per<strong>for</strong>med better in the pilot holeONK-PH5 where a significant, low-angle de<strong>for</strong>mation zone (OL-BFZ056) exists. Thiszone coincides with the hydrogeological zone HZ19 (Vaittinen et al. 2009) <strong>and</strong> the R19in Vaittinen et al. 2003.
152.2.4 Development needsFrom a long-term safety point of view, estimating rock mass suitability based on Q'-value is unsatisfactory. It is evident that the Q'-value is inadequate <strong>for</strong> classifyinggeological <strong>and</strong> hydrogeological features significant to nuclear waste disposal.According to current view, resolution of the Q’-system itself is not a problem, but ratherthe general inadequacy of it to detect significant safety features. There<strong>for</strong>e, anotherparameter to describe rock quality <strong>and</strong>/or de<strong>for</strong>mation intensity may there<strong>for</strong>e beneeded. Classification based on hydrogeological data (hydraulic conductivity) frompilot holes is not fully satisfactory either due to uncertainties <strong>and</strong> difficulties incorrelating pilot hole data with tunnel inflow data. In addition, correlating Lugeonvalues <strong>and</strong> different flow measurements proved problematic. Furthermore,hydrogeological zones do not always coincide with the modelled site-scale geologicalstructures 1 , which further complicates the interpretation of pilot hole data. Interpretationof overall hydrogeological conditions of the studied area also dem<strong>and</strong>s extensive1 Highly transmissive features, defined as layout-determining features based on hydrogeologicalproperties, may on some occasions appear as single large fractures <strong>and</strong> are there<strong>for</strong>e not defined asgeological layout-determining features.
16underst<strong>and</strong>ing of site hydrogeology. Finally, there were significant difficulties in takingdifferent flow measurements, particularly in the tunnel probe holes. The hydrogeologicaldata is, nevertheless, important <strong>for</strong> rock suitability classification, thoughusability of the data could probably be increased with method development.The geometrical variations <strong>and</strong> uncertainties of many de<strong>for</strong>mation zones have a greatimpact on implementation of the HRC, especially if the zones are only modelled on sitescale as is currently the case at Olkiluoto. A 3D tunnel-scale de<strong>for</strong>mation zone modelthat integrates both the hydrogeological <strong>and</strong> geological models <strong>and</strong> takes the variablezone geometries into account is there<strong>for</strong>e needed. Large fractures are not considered inthe HRC tunnel scale process, although fracture trace length is an important parameter<strong>for</strong> a nuclear waste repository on the canister scale. There<strong>for</strong>e, it is necessary to exp<strong>and</strong>the tunnel-scale parameters to consider properties <strong>and</strong> orientations of fractures with longtrace lengths. The relationship between the tunnel cross-cutting fractures <strong>and</strong> slickensidedfractures in pilot holes needs to be investigated. Furthermore, the ductilede<strong>for</strong>mation zones <strong>and</strong> rock mechanics issues are not sufficiently taken into account inthe tested HRC. The ductile de<strong>for</strong>mation model describes the variations in the foliationintensity <strong>and</strong> direction, which are in turn directly related to the rock mechanical stability<strong>and</strong> repository planning.The division suggested in the HRC into four suitability classes on tunnel scale seemssomewhat difficult in practice. There<strong>for</strong>e, the procedure <strong>for</strong> determining suitability ofthe rock mass <strong>for</strong> disposal needs to be revised.At present, systematic mapping takes place too far from the excavation front withrespect to availability of the P/O results when planning the excavation. Some practicalarrangements could help to at least partially solve this problem. On the other h<strong>and</strong>, theexcavation time-table within the repository will most likely be looser than withinONKALO.Summarising, in addition to a great need <strong>for</strong> validation <strong>and</strong> st<strong>and</strong>ardisation of sourcedata used in the HRC process, a tunnel-scale 3D model that integrates the geological<strong>and</strong> hydrogeological models is also needed. Also, additional tools <strong>for</strong> data collection areneeded. Furthermore, it is noted that, while the HRC testing revealed severaldevelopments needs concerning the practical applicability of the HRC, it is alsonecessary to improve the link between long-term safety targets <strong>and</strong> the actual criteria.This latter aspect is the focus of development of the <strong>RSC</strong> criteria described in Section5.3.2.3 SKB approachThe disposal concept to be used in Sweden <strong>and</strong> in Finl<strong>and</strong> is the same. There<strong>for</strong>e,especially requirements of the host rock related to long-term per<strong>for</strong>mance of engineeredbarriers will, to a large extent, be similar. Still, there are site specific features <strong>and</strong>differences in available site data to be considered in development of the practicalcriteria. Due to the similarities, the concept of safety functions, safety functionindicators <strong>and</strong> safety function indicator criteria presented by SKB in SR-Can (SKB2006) is highly relevant to this work. By introducing these concepts, transparencybetween long-term safety <strong>and</strong> any practical criteria can be enhanced. The concepts aredefined as follows:
17A safety function is a role through which a repository component contributes tosafety.A safety function indicator is a measurable or calculable property of a repositorycomponent, which indicates the extent to which a safety function is fulfilled.A safety function indicator criterion is a quantitative limit, such that if therelevant safety function indicator fulfils the criterion, the corresponding safetyfunction is maintained.Fulfilment of the safety function indicator criteria implies that safety functions of thecomponent are maintained. On the other h<strong>and</strong>, if the criteria <strong>for</strong> one or more safetyfunction indicators are not fulfilled, then consequences of loss or degraded per<strong>for</strong>manceof the corresponding safety function will be further analysed <strong>and</strong> potentially evaluatedin the safety assessment.As part of the preparation <strong>for</strong> its upcoming licence application, SKB is currentlydeveloping design premises of a KBS-3V repository <strong>for</strong> spent nuclear fuel from a longtermsafety point of view. The design premises is based on the experience from SKB’slatest published safety assessment, SR-Can, <strong>and</strong> some subsequent analyses. Thedevelopment work by SKB presents an elaboration of the design basis cases, <strong>and</strong> thefeedback to the canister <strong>and</strong> repository design in sections 13.4–13.6 of the SR-Can mainreport (SKB 2006). The purpose is to provide more detailed material in order to<strong>for</strong>mulate requirements on the barriers <strong>for</strong> actual design decisions, includingrequirements on the host rock <strong>and</strong> underground excavation. Examples of requirementswith regard to the rock include maximum permitted inflow to deposition tunnels <strong>and</strong>holes, minimum distances from deposition holes to large de<strong>for</strong>mation zones, a need toavoid large fractures in deposition holes to ensure mechanical stability (see e.g. Munier2006a, 2006b) <strong>and</strong> minimum distances between canisters to control buffer temperature.These design premises are key inputs to the SKB reference design, which will bepresented in the “production reports” <strong>for</strong> the final repository. The production reportsshould verify that the chosen design complies with given design premises, whereas thedesign premises report takes the burden of justifying why these design premises arerelevant.2.4 KBS-3H workSKB <strong>and</strong> <strong>Posiva</strong> have carried out a joint project <strong>for</strong> developing the KBS-3H repositoryalternative. The approach based on safety functions <strong>and</strong> safety function indicatorspresented in the SR-Can <strong>and</strong> applied <strong>for</strong> the Swedish c<strong>and</strong>idate sites (SKB 2006, seealso Section 2.3), was applied <strong>for</strong> Olkiluoto in compiling the safety case <strong>for</strong> KBS-3H(Smith et al. 2007a, b, c). It is noted that work carried out by Smith et al. (2007a) wasnot a full safety case, as the focus was mainly in differences between the features ofKBS-3V <strong>and</strong> KBS-3H. Accordingly, the emphasis in the KBS-3H work was on safetyfunctions, indicators <strong>and</strong> criteria <strong>for</strong> the engineered barrier system, rather than thegeosphere. Some modifications were done by Smith et al. (2007c) to the safetyfunctions, safety function indicators <strong>and</strong> safety function indicator criteria given in SR-Can (SKB 2006) to make them applicable <strong>for</strong> KBS-3H.Smith et al. (2007c) also distinguished between design requirements on the components<strong>and</strong> the safety function indicators, although the two are often closely related. Smith etal. (2007c) defines the design requirements to be “attributes that the repository is
18ensured to have by design at the time of emplacement of the first canister, or during theearly evolution of the repository in the period leading up to saturation”. Still, there is alink between the design requirements <strong>and</strong> long-term evolution of the system, sincedesign requirements are set to contribute to fulfilment of the safety function indicatorcriteria over a prolonged period of time. For example, the design requirement onthickness of the copper shell is set to ensure that the safety function indicator criterionof a copper shell with thickness greater than zero will likely be met in the long-term,taking into account general <strong>and</strong> localised corrosion processes. Design requirements arealso established to guide engineering dimensioning <strong>and</strong> feasibility. For example,mineral alteration of the buffer due to high temperature may lead to situations where thesafety functions of the buffer, which are to protect the canister <strong>and</strong> to limit <strong>and</strong> retardradionuclide releases in the event of canister failure, may not be fulfilled. There<strong>for</strong>e arequirement of maximum temperature less than 100ºC of the buffer is taken. is therequirement is satisfied by ensuring adequate spacing between canisters along thedeposition tunnel, as well as adequate spacing between deposition tunnels. Otherexamples are the need to limit disturbances at the buffer-rock interface, leading torequirements on hydraulic conductivity, thickness <strong>and</strong> extent of the affected buffer.
193 GENERAL APPROACH AND METHODOLOGYSetting up the host rock requirementsThe basis of development work is the safety concept (see Section 4.1), which showshow safe disposal can be achieved given the repository concept (KBS-3V) <strong>and</strong>Olkiluoto site characteristics. The research, development <strong>and</strong> technical design of a spentnuclear fuel repository is an iterative process. Main components of the developmentprocess are site characterisation, technical design, safety <strong>and</strong> per<strong>for</strong>mance assessment.An integral part of the process is management of requirements at several hierarchicallevels. At the highest level there are stakeholder requirements set by producers of spentfuel <strong>and</strong> safety criteria set by authorities guiding the implementation of a spent fuelrepository. Lower levels include technical requirements <strong>for</strong> the disposal system <strong>and</strong> itscomponents.Figure 3-1 shows how the safety <strong>and</strong> per<strong>for</strong>mance assessment (sub-project TARGET),site characterisation (sub-project DETECT) <strong>and</strong> technical design (sub-project DESIGN)are integrated in order to define suitable rock volumes <strong>and</strong> locations <strong>for</strong> disposal use.According to general principle, requirements within the <strong>RSC</strong>-programme are alsodefined at different levels. The aim is to increase transparency <strong>and</strong> clarify the logicbehind different requirements <strong>and</strong> criteria. Documentation of the rational behind thedifferent requirements <strong>and</strong> criteria is important during the iterative process ofdeveloping the criteria. Such documentation helps to assess which part of therequirements <strong>and</strong> criteria need revision in case of design changes, new in<strong>for</strong>mation fromthe site or per<strong>for</strong>mance of the barriers, or new safety assessment results. The basis <strong>for</strong>the definition of the requirements is the function of host rock as a natural barrier, thesafety function of host rock. Per<strong>for</strong>mance targets considering rock properties ofrelevance <strong>for</strong> long-term safety <strong>and</strong> engineering targets regarding constructability aredefined separately from practical <strong>RSC</strong>-criteria, based on current site data <strong>and</strong> models.Figure 3-1 also shows in<strong>for</strong>mation delivery of the results of Safety Case <strong>and</strong> layoutdesign criteria development, as well as depicting criteria testing <strong>and</strong> evaluationprocesses <strong>and</strong> feedback loops.An integral part of the implementation process is to show that set requirements will bemet. Hence, observable <strong>and</strong> measurable properties of the host rock that contribute to thelong-term safety of the repository need to be defined. A central goal of the <strong>RSC</strong>programme has been to clarify this link between the practical criteria <strong>and</strong> the long-termsafety. For this reason, the approach presented by SKB (2006, see also Section 2.3) isfollowed to a great extent, although there are some differences <strong>for</strong> example in theterminology used. The role of the <strong>RSC</strong>-programme, to communicate requirements <strong>and</strong>feedback from the safety case to site characterisation <strong>and</strong> layout design, is described inthe revised safety case plan (<strong>Posiva</strong> 2008) <strong>and</strong> shown in Figure 3-1.
20SafetyconceptSiteReferenceDesignTARGETDETECTDESIGNPERFORMANCETARGETSDATA ANDMODELSENGINEERINGTARGETSCRITERIAASSESSMENTAgainst targetsImplication <strong>for</strong>Safety CaseSafety CaseAPPLICATIONsuitable volumesdegree of utilisationTESTING ANDDEMONSTRATIONASSESSMENTRepositoryDesignTo summarise the above discussion, the following levels of requirements are used:To meet the requirements related to long-term per<strong>for</strong>mance of barrierso A safety function is defined as the contribution of specific barrier tosystem safety.o per<strong>for</strong>mance targets are defined as the target values or range of values<strong>for</strong> parameters describing safety relevant properties of the barriers that, ifupheld over relevant time windows, ensure that the barriers will fulfiltheir respective safety functions.To show that the host rock will meet set requirementso rock suitability criteria define observable, measurable, present-day rockproperties, which are used to locate rock volumes where it is highlylikely per<strong>for</strong>mance targets <strong>and</strong> thereby the safety functions will beupheldThe engineering targets consider the rock constructability <strong>and</strong> the layoutadaptation according to the rock suitability criteria (<strong>RSC</strong>) thus contributing thefulfilment of the per<strong>for</strong>mance targets <strong>and</strong> safety functionsSafety functions <strong>for</strong> the barriers are derived from the disposal concept, whereasper<strong>for</strong>mance targets already take into account design <strong>and</strong> site specific issues. For
21example, material selection (e.g. buffer <strong>and</strong> backfill material) can lead to morerequirements on the rock environment <strong>and</strong> thus needs to be considered when settingper<strong>for</strong>mance targets. The per<strong>for</strong>mance targets <strong>for</strong> barriers are defined as conditionsunder which the safety functions are fulfilled, i.e. if target values are met then the safetyfunctions of barriers are maintained. If, during certain time frames of the assessmentperiod, deviations from target values occur <strong>and</strong> indicate that the corresponding safetyfunctions may not be provided in full, overall system safety assessment must be carriedout. A per<strong>for</strong>mance target is a property of the system component, including a preferablyquantitative limit or range <strong>for</strong> this property. There<strong>for</strong>e, per<strong>for</strong>mance targets correspondto safety function indicators <strong>and</strong> criteria in SKB notation (see also Section 2.3). As anexample, Figure 3-2 shows the steps in defining rock suitability criteria from safetyfunctions <strong>and</strong> per<strong>for</strong>mance targets. A more detailed discussion on definition of safetyfunctions <strong>and</strong> per<strong>for</strong>mance targets is given in Chapter 4.Rock suitability criteria are site-specific. For example, they judge the most relevantparameters <strong>and</strong> confidence in models at the site which affect the per<strong>for</strong>mance targets<strong>and</strong> engineering targets set. Interpretation <strong>and</strong> modelling are required to underst<strong>and</strong> theimportance of these observations in the context of general site underst<strong>and</strong>ing. The linkbetween the site property used in criteria definition <strong>and</strong> the given per<strong>for</strong>mance orengineering target needs to be shown. In many cases, modelling of underlying processes<strong>and</strong> laboratory or in situ tests on barrier per<strong>for</strong>mance is needed. In defining the criteria,there is a need to assess whether the rock characterisation in current conditions willprovide sufficient in<strong>for</strong>mation about future conditions. The challenge is to have thispredictive capacity in models, as well as the ability to observe <strong>and</strong> measure the mostrelevant site properties under disturbed conditions. Part of this work is the selection ofproper measurement techniques. Preliminary testing at the site will not only provideimportant in<strong>for</strong>mation on the practical aspects of applying such criteria, but also help inestimating observational uncertainties. To estimate the effectiveness of the criteria, theinitial state defined by the criteria <strong>and</strong> potential <strong>for</strong> the perturbing processes <strong>and</strong> eventsduring the evolution of the repository <strong>and</strong> site needs to be considered. Further on, theconsequences on the safety needs to assessed.Definition of the rock suitability criteria is presented in more detail in Chapter 5. It isnoted, that the rock suitability criteria are often set conservatively. This means thatsome of the criteria can be overly strict <strong>for</strong> example to cope with the uncertainties in thedetermination of the parameter value <strong>and</strong> still giving confidence in the fulfilment of theper<strong>for</strong>mance target. Thus the criteria could be referred to as indicators rather thancriteria. In any case, the criteria will be used in deciding whether to construct tunnels incertain volume during tunnel excavation <strong>and</strong> <strong>for</strong> acceptance of the deposition hole <strong>for</strong>disposal use. There<strong>for</strong>e, due to the fact that <strong>RSC</strong> is a tool in this decision makingprocess, it is considered justified to call them criteria rather than just indicators.
22Safety functionsPer<strong>for</strong>mancetargetsRock suitabilitycriteriaDerived from thedisposal conceptHow do the barrierscontribute to thesafety ?Property of a barrierindicating its abilityto provide the safetyfunctionGuide design <strong>and</strong>selection ofdisposal locations,analysed in SATake into accountdesign <strong>and</strong> sitespecific issuesaffectingper<strong>for</strong>mance ofbarriersObservable sitepropertiescontributing tofulfilment of safetyfunctions <strong>and</strong>per<strong>for</strong>mance targetsTool <strong>for</strong> selectingrock volumes <strong>for</strong>disposal, esp.deposition holesConsider sitespecific propertiesStepwise identification of suitable rock volumesThe amount <strong>and</strong> resolution of site characterisation data, as well as the needed level ofdesign detail, is increasing along with repository design phases <strong>and</strong> construction.There<strong>for</strong>e a stepwise approach considering different scales, as already suggested by theHRC, has been adopted. This approach aims to provide adequate resolution <strong>for</strong> thevarious stages of the classification process. The starting point in criteria development isthe requirements on host rock close to the deposition hole. The stepwise approachconsiders three scales; repository, tunnel <strong>and</strong> deposition hole scale.At the first step, in the repository scale, the aim is to identify larger rock volumes <strong>for</strong>hosting panels of several tunnels. The focus is on classification of the host rockstructures which are of importance to groundwater flow, rock movements or otherfactors relevant to long-term safety. Furthermore ensuring adequate distance ismaintained between canisters <strong>and</strong> structures that may <strong>for</strong>m fast transport paths orotherwise impair the per<strong>for</strong>mance of barriers, is to be achieved, as required by theregulatory guide (see Section 2.1). For this purpose the layout determining features <strong>and</strong>a respect volume to them is defined (see Section 5.2). Layout determining features can
23be mechanically instable especially during glaciations or they are main groundwaterflow routes <strong>and</strong> thus of importance <strong>for</strong> transport of solutes <strong>and</strong> chemical stability at thesite. Between these features the host rock properties are such that is suitable <strong>for</strong> hostingdeposition holes with local exceptions.Tunnel scale criteria address the selection of suitable rock volumes within each panellocated in the rock volume between the layout determining features. The rock volumeconsidered suitable based on the repository scale classification may still contain featureslike local scale de<strong>for</strong>mation zones <strong>and</strong> large <strong>and</strong> highly transmissive fractures whichaffect the suitability of the host rock locally (see Section 5.3 <strong>for</strong> a more detaileddiscussion). These are addressed by the tunnel <strong>and</strong> deposition hole scale criteria. Theapplication of the repository <strong>and</strong> tunnel scale criteria consider also whether in the givenvolume there is enough potential locations <strong>for</strong> the deposition holes so that excavatingthe tunnel(s) is economical. The final acceptance of the deposition hole, is based on theassessment of the suitability of the host rock defined by the deposition hole scaleclassification, but also on quality assurance of the engineering <strong>for</strong> example holestraightness. Figure 3-3 presents the scaled approach <strong>for</strong> identifying potentially suitablerock volumes <strong>and</strong> canister positions.
254 LONG-TERM SAFETY RELATED REQUIREMENTS ON HOST ROCKThe definition of per<strong>for</strong>mance targets is realised from a long-term safety point of view.Parallel design-related requirements are discussed in Chapter 6. The starting points indefining host rock per<strong>for</strong>mance targets are safety functions of the host rock <strong>and</strong>requirements arising from the per<strong>for</strong>mance targets set <strong>for</strong> the engineered barriers. Whendefining the per<strong>for</strong>mance targets <strong>for</strong> the host rock, it is necessary to take into accountsite evolution, possible detrimental impacts on safety due to disturbances caused byexcavation <strong>and</strong> operation (including the introduction of <strong>for</strong>eign materials, such ascement <strong>and</strong> metal structures) <strong>and</strong> finally the host rock properties affecting transport. Inaddition, properties considered to be favourable, though not required, <strong>for</strong> long-termsafety are mentioned.4.1 Safety concept <strong>and</strong> safety functions<strong>Posiva</strong>'s concept of spent fuel disposal is based on the KBS-3 design of a geologicrepository <strong>and</strong> the characteristics of Olkiluoto site (see e.g. <strong>Posiva</strong> 2008). <strong>Posiva</strong>’ssafety concept is illustrated in Figure 4-1. According to this concept, safety rests first<strong>and</strong> <strong>for</strong>emost on the long-term isolation <strong>and</strong> containment of radionuclides within thecopper-iron canisters. A clay buffer protects the canisters from rock movements <strong>and</strong>potential detrimental substances, limits groundwater flow around the canisters, alsolimiting <strong>and</strong> retarding radionuclide releases in the event of canister failure. Long-termcontainment within the canisters in turn depends primarily on proven technical qualityof the engineered barrier system (EBS) <strong>and</strong> favourable near-field conditions <strong>for</strong> thecanisters. The technical quality of the EBS is favoured by the use of components withwell-characterised material properties <strong>and</strong> by the development of appropriateacceptance specifications <strong>and</strong> design criteria. Favourable <strong>and</strong> predictable bedrock <strong>and</strong>groundwater conditions are requirements <strong>for</strong> selecting a waste disposal site.The EBS includes the canisters <strong>and</strong> a surrounding clay buffer that protects the canistersfrom rock movements <strong>and</strong> from potential detrimental substances in the groundwater.The EBS also includes other components, such as the backfill of the deposition tunnelas well as the backfill, plugs <strong>and</strong> seals of other cavities (central tunnels, shafts, accesstunnel, research boreholes). These are designed to be compatible with, <strong>and</strong> support thesafety functions of, the canister, the buffer <strong>and</strong> the host rock. For example, backfilling<strong>and</strong> sealing of the repository cavities (including tunnels, shafts <strong>and</strong> boreholes) supportthe safety functions of the host rock by giving mechanical support to the rock <strong>and</strong>preventing the <strong>for</strong>mation of transport pathways (water conductive flow paths). Theycontribute also to discourage inadvertent human intrusion into the repository. Thesurface environment does not have any barrier role <strong>and</strong> is thus not assigned any safetyfunctions or targets.Besides providing a protective environment <strong>for</strong> the canisters, situation <strong>and</strong> design of thedisposal system ensure that the transport of radionuclides released from an initiallydefective or subsequently failed canister will be effectively retained <strong>and</strong> retarded byother barriers. These are illustrated by the secondary set of safety pillars in Figure 4-1,spanning slow release from the spent fuel matrix, slow diffusive transport in thebuffer, <strong>and</strong> slow radionuclide transport in the geosphere.
FAVOURABLE NEAR-FIELDCONDITIONS FOR THECANISTERSlow transport in thegeosphereSlow release from thespent fuel matrixSlow diffusivetransport in the bufferPROVEN TECHNICAL QUALITYOF THE EBS26SAFE DISPOSALLONG-TERM ISOLATION AND CONTAINMENTRetention <strong>and</strong> retardation ofradionuclidesFAVOURABLE, PREDICTABLE BEDROCKAND GROUNDWATER CONDITIONSSUFFICIENT DEPTHWELL-CHARACTERISED MATERIALPROPERTIESROBUST SYSTEM DESIGNOutline of safety concept <strong>for</strong> a KBS-3 type repository <strong>for</strong> spent fuel in acrystalline bedrock (adapted from <strong>Posiva</strong> 2003). The safetyconcept is based on a robust system design. Red pillars <strong>and</strong> blocks link safety featuresof the disposal system on which safety primarily depends to the overall goal of thesafety concept (safe disposal). Green pillars <strong>and</strong> blocks indicate secondary safetyfeatures that may become important in the event of radionuclide release from a canister.The functions of different barriers <strong>and</strong> their role in contributing to repository safety aresummarised in Figure 4-2. According to the adopted safety concept (Figure 4-1),emphasising the long-term isolation <strong>and</strong> containment (Vieno & Ikonen 2005, <strong>Posiva</strong>2006, <strong>Posiva</strong> 2008), the role of the geosphere is mainlyto isolate the repository from the biosphere <strong>and</strong> normal human habitat (suitabledepth),to protect the engineered barriers from potentially detrimental processes <strong>and</strong>changes of conditions taking place above <strong>and</strong> near the ground surface,to provide favourable <strong>and</strong> predictable mechanical, geochemical <strong>and</strong>hydrogeological conditions <strong>for</strong> the engineered barriers, <strong>and</strong>to limit <strong>and</strong> retard inflow <strong>and</strong> release of harmful substances to <strong>and</strong> from therepository.
27The above are referred to as the safety functions of the geosphere. A loss ordegradation of the protective role of the host rock could occur if chemical conditions(groundwater chemistry) become unfavourable to buffer <strong>and</strong> canister longevity, if highwater flow occurs around the deposition holes, in part contributing to changes inchemical conditions, or if a fracture intersecting a deposition hole slips sufficiently tocause rupturing of the canister. Mechanical disturbances due to excavation <strong>and</strong> thermalload due to presence of the spent fuel may damage the rock surrounding the depositionhole <strong>and</strong> consequently water flow around the canisters may increase.The following sections contain a more detailed discussion on factors affecting the safetyfunctions of the geosphere, which need thus to be considered in defining per<strong>for</strong>mancetargets on the host rock. Resulting per<strong>for</strong>mance targets <strong>for</strong> the host rock are summarisedin Table 4-3 in Section 4.6.4.2 Repository depthThe repository should be located at a sufficient depth <strong>for</strong> the host rock to be capable ofprotecting the canisters <strong>and</strong> other components of the EBS against climate-related eventse.g. penetration of the permafrost to repository depth <strong>and</strong> reducing the likelihood ofhuman intrusion. Climate-related processes affecting the surface <strong>and</strong> biosphere includethose related to glacial cycles, According to the YVL 8.4 (STUK 2001), the repositoryshould be located at a depth of several hundred meters. However, repository depth is
28constrained by rock properties at those depths, <strong>for</strong> example higher stresses <strong>and</strong>unfavourable chemical environment (e.g. salinity), which affect both safety <strong>and</strong>construction procedures (<strong>for</strong> discussion see e.g. Äikäs et al. 2000). The current plannedrepository depth is between 400–500 meters, the lowest point of the repository layoutbeing at -437 m (Anttila et al. 2009).4.3 Per<strong>for</strong>mance targets related to functionality of the engineeredbarriersSafety of the repository rests first <strong>and</strong> <strong>for</strong>emost on the long-term isolation <strong>and</strong>containment of radionuclides in the copper canisters, provided by the engineered barriersystem (EBS), <strong>and</strong> on favourable site properties. As interactions between the systemcomponents are also important <strong>for</strong> safety, requirements related to the per<strong>for</strong>mance of theEBS are briefly summarised in the following sections. The discussion is based oncurrent knowledge <strong>and</strong> it is expected that further studies, <strong>for</strong> example of bufferper<strong>for</strong>mance, will bring new in<strong>for</strong>mation that may lead to a revision of the presentedtargets. For a detailed account of EBS per<strong>for</strong>mance targets, see e.g. <strong>Posiva</strong> 2006, SKB2006, Smith et al. 2007c.4.3.1 CanisterContainment provided by the canister plays a key role in system safety. A basicrequirement is that the spent fuel inside the canister remains sub-critical. Theper<strong>for</strong>mance target or design lifetime of the canister is to retain integrity over a periodof at least 100 000 years. There<strong>for</strong>e canisters shouldhave low probability of initial penetrating defects,be resistant to corrosion, <strong>and</strong>have high mechanical strength.The canister’s susceptibility to corrosion is dependent on the chemical environment inthe near field of the canister. The mechanical load on a canister results from hydrostaticpressure that depends on repository depth, ice sheet thickness during future glaciations,<strong>and</strong> swelling pressure of the bentonite. Shear stress on a canister can result from unevenswelling of the buffer <strong>and</strong>/or shear displacement caused by earthquakes (most likelyinduced by glaciation).The ability of the canister to withst<strong>and</strong> shear loads is strongly dependent on the bufferdensity. According to results by Börgesson et al. (2004) based on laboratory tests <strong>and</strong>modelling (ABACUS software), where canister <strong>and</strong> buffer dimensions according tocurrent design were applied, the impact of shear displacements up to 10 cm on theplastic strain of the canister is minimal (1,6 %) if the buffer densities are in range of2000 kg/m 3 . With higher buffer densities or larger displacements, strain on the canisteris increased; at buffer density 2100 kg/m 3 <strong>and</strong> shear displacement 20 cm, the cast ironinsert is already strongly affected. Also velocity of the shear movement <strong>and</strong> location ofthe shear plane both affect the severity of consequences on the canister. Shear rates ofup to 1 m/s have been considered in the modelling. The rock shear criterion may have tobe reconsidered in case of new essential results from the ongoing studies on the canister<strong>and</strong> buffer behaviour under shear load become available.
29A summary of safety function indicators <strong>and</strong> associated criteria according to SKB(2006) <strong>and</strong> KBS-3H work (Smith et al. 2007c) is summarised in Table 4-1. Thepresented criteria set the following requirements <strong>for</strong> the geosphere:chemical environment that inhibits corrosionsuitable repository depth with respect to the isostatic loadlow probability of (large) shear movements in the vicinity of the repositoryTable 4-1Per<strong>for</strong>mance target Target value RationaleCopper thickness shouldbe higher than the targetvalue.Isostatic pressure oncanister should be lessthan the pressure <strong>for</strong>isostatic collapse.> 0 mm Zero copper thickness anywhere on thecopper surface would allow the relativelyrapid water ingress to the canister interior<strong>and</strong> radionuclide release.< 44 MPa The limit varies between the canisters, butprobability of collapse at 44 MPa isvanishingly small.An isostatic pressure on the canister greaterthan 44 MPa would imply an increasedpossibility of failure due to isostaticcollapse.44 MPa is the design isostatic loadincluding evenly distributed hydrostaticpressure (7 MPa corresponding 700 mdepth), swelling pressure of bentonite (7MPa, dry bentonite density of 1590 kg/m 3or a saturated density of 2020 kg/m 3, Werme1998, Karnl<strong>and</strong> 1998) <strong>and</strong> 30 MPa load,estimated maximum load from a 3 km icesheet.Shear stress on canistershould be less thanrupture limit.A shear stress on the canister greater thanthe rupture limit would imply failure due torupture.
304.3.2 BufferThe most important safety function of the buffer is to protect the canisters fromprocesses that could compromise the safety function of complete containment of spentfuel. The buffer will also retard the transport of radionuclides in case of canister failure.To protect the canister, the buffer should besufficiently plastic (or ductile) to protect canisters from small rock movements,including shear displacements at canister locations,sufficiently stiff to maintain canisters in a vertical position,sufficiently dense so that microbes are not active in the buffer <strong>and</strong> do not giverise to unfavourable chemical conditions at canister surface, <strong>and</strong>impermeable enough that the movement of water is insignificant <strong>and</strong> diffusion isthe dominant transport mechanism <strong>for</strong> corrosive agents present in thegroundwater that may degrade the canisters.The buffer should have a swelling pressure <strong>and</strong> self-sealing capability, which mean thatany potential advective pathways <strong>for</strong> flow <strong>and</strong> transport that may arise, <strong>for</strong> example, asa result of piping <strong>and</strong> erosion, sudden rock movements or the release of gas <strong>for</strong>med in adamaged canister are rapidly closed. Its impermeability should limit <strong>and</strong> retard therelease of any dissolved radionuclides from the canisters, should any be damaged.Furthermore, it should have a fine pore structure such that microbes <strong>and</strong> colloids areimmobile (filtered) <strong>and</strong> microbe- or colloid-facilitated radionuclide transport will notoccur.Loss or redistribution of buffer mass or mineral alteration can lead to a reduction inswelling pressure, increase in hydraulic conductivity of the buffer, <strong>and</strong> to possiblechanges in buffer density (described in more detail by Smith et al. 2007c <strong>and</strong> Miller &Marcos 2007). These will in turn have a detrimental effect on the functionality of thebuffer. Buffer freezing would only occur at low temperatures (less than –5 C, see e.g. p.477 in SKB 2006) <strong>and</strong> the consequences may not be dramatic even if the buffer freezes.Furthermore, according to existing knowledge, freezing is not expected at repositorydepth (Hartikainen 2006), however, further studies on this issue are in process.Loss or redistribution of buffer mass can result, <strong>for</strong> example, from piping <strong>and</strong> erosion byflowing water. There are a number of factors affecting the loss of bentonite, <strong>for</strong> exampleinflow, erosion rate <strong>and</strong> duration of the erosion process <strong>and</strong> the properties of thebentonite like the self sealing. According to Börgesson & Hernelind (2006), the amountof eroded bentonite in one deposition hole can be in the order of 100 kg withoutdetrimental effects on the barrier safety function. This amount of erosion will result inreduced density at the buffer/rock interface but swelling pressure will remain above1 MPa, which is required <strong>for</strong> tightness <strong>and</strong> self-sealing. Based on results presented byBörgesson & Hernelind (2006), also summarised in SR-Can (SKB 2006), the buffer cantolerate inflow to the deposition hole in the order of 0.1 L/min eroding 10 g dry weightof bentonite per litre water during <strong>and</strong> after installation. The amount of eroded bentonitedepends on the duration of erosion, assumed by Börgesson & Hernelind (2006) to last<strong>for</strong> 12 weeks until the tunnel is plugged <strong>and</strong> sealed. For reference, at Olkiluoto theoperation of the tunnel will last <strong>for</strong> some 7 to 10 months (Section 4.1, Saanio et al.2006).
31The results by Börgesson <strong>and</strong> Hernelind (2006) are based on calculations using the codeABAQUS. The bentonite has been modelled as completely water-saturated. Mechanicalproperties of the buffer controlling swelling <strong>and</strong> consolidation phases are based onmodels <strong>and</strong> properties derived <strong>for</strong> MX-80 bentonite. The authors acknowledgeuncertainties in the material model since strong swelling of the bentonite makes theresults somewhat uncertain, especially at high porosities, suggesting that the results bechecked using laboratory swelling tests. Thus re-evaluation of the results may changethe suggested inflow limit of 0.1 L/min to avoid erosion of bentonite during earlyphases. Piping has been observed in two field tests in Äspö HRL (LOT <strong>and</strong> the fullscale test LASGIT, see e.g. Miller & Marcos 2007 with reference to Börgesson &S<strong>and</strong>én 2006). In LASGIT, flow rate was about 0.1 L/min <strong>and</strong> erosion rate about 1 g/L.If the inflow of 0.1 L/min originates from a single fracture, the correspondingtransmissivity of the fracture is roughly in the order of 10 -9 –10 -8 m 2 /s (see e.g. scopingcalculations in Appendix B in Smith et al. 2007c).Groundwater salinity affects the swelling pressure of the bentonite. The impact ofsalinity on swelling pressure decreases with increasing buffer (saturated) density.According to SR-Can (SKB 2006), the swelling pressure of both MX-80 <strong>and</strong> DeponitCa-N bentonites with buffer saturated densities above 1890 kg/m 3 remains at about1 MPa when exposed to salinities of 3 mol/L (M) of NaCl <strong>and</strong> CaCl 2 . Such salinitiesexpressed as TDS (g/L) would mean salinities notably higher than 100 g/L, which arenot expected at repository depth.Chemical erosion of the buffer is possible if it is comes in contact with highly dilutedglacial meltwaters, in which case colloid <strong>for</strong>mation is possible (SKB 2006). Mineralalteration of the buffer can result from influence of high temperatures, from interactionof the bentonite with a high pH leachate plume from cementitious materials or frominteraction with iron corrosion products. Long-term stability of montmorillonite mayalso be affected by evolving groundwater conditions which may lead to the change of aNa-type montmorillonite to a Ca-type montmorillonite. Mineral alteration due totemperature effects have been ruled out because the high temperatures (>120 o C)required <strong>for</strong> such a trans<strong>for</strong>mation are not relevant to the repository conditions (seeSection 5.2.6 in Miller & Marcos 2007). The highest temperatures at the repository willremain below 100 o C (see e.g. Figure 6-1 in Pastina & Hellä 2006), the value which isused as the target value. Alteration of the buffer due to interaction with metallicstructures (in particular Fe-bearing structures) is also possible. The impact of iron onclay is especially relevant <strong>for</strong> the horizontal emplacement alternative (KBS-3H) due tothe use of the supercontainer (a steel shell surrounding the buffer) which will corrode<strong>and</strong> the resulting iron corrosion products will interact with the buffer. Studies areongoing to further develop the underst<strong>and</strong>ing of the Fe-clay interaction process. Overallthe development of the underst<strong>and</strong>ing of mineral trans<strong>for</strong>mation <strong>and</strong> cementation is amajor issue being addressed in <strong>Posiva</strong>´s TKS-programme <strong>for</strong> the next three years.The impact of grout leachates transported by groundwater to deposition holes also needsto be considered. <strong>Posiva</strong> has carried out a programme related to the development oflow-pH grouts (R20-programmme, Arenius et al. 2008). According to the results,bentonite degradation rate is greatly decreased below pH 10, there<strong>for</strong>e this is set as theupper limit <strong>for</strong> the pH of groundwater flowing to deposition holes. Cements used mayhave higher leachate pH up to 11. pH of the cementitious waters will be likely loweredas the waters will be mixed with flowing groundwater around/through the grouted area<strong>and</strong> further buffering <strong>and</strong> dilution will take place during the transport of waters in the
32geosphere (Miller & Marcos 2007). This is supported by observations from theONKALO control holes <strong>for</strong> grouting, which show that the pH decreases rather quickly(<strong>Posiva</strong> 2009a, Pitkänen et al. 2008). The effect of high pH water on the buffer can beexpected to be limited considering the amount bentonite in the deposition holecompared to the potential amount of high pH water. It is however recommended thatsome distance be kept between the deposition holes <strong>and</strong> the tunnel sections containingeven lower-pH cementitious material, <strong>for</strong> example in the <strong>for</strong>m of grouts.A summary of the per<strong>for</strong>mance targets <strong>and</strong> target values (safety function indicators <strong>and</strong>associated criteria according to SKB) <strong>for</strong> the buffer according to SKB (2006) <strong>and</strong> KBS-3H work (Smith et al. 2007c) is given in Table 4-2. Future development of therequirements will likely address whether, <strong>for</strong> example, density <strong>and</strong> swelling pressurerequirements apply to the average properties of the buffer (bulk of buffer), allowingsome local deviations, such as at the buffer-rock interface. Given the buffer material, therequirements related to hydraulic conductivity, swelling pressure, density given in Table4-2 can be also given as a (saturated) density range. The per<strong>for</strong>mance of the buffer isbased on the following assumptions of the host rock <strong>and</strong> these assumptions need to beconsidered in setting up the per<strong>for</strong>mance targets <strong>for</strong> the host rock:chemical environment that is favourable to buffer functionalitylow groundwater inflows <strong>and</strong> low groundwater flow rates in long-term so thaterosion will not take place or change the chemical environmentlimited shear displacementssufficient repository depth in order to avoid freezing of the buffer orminimise any adverse impact of freezing on the bufferto4.3.3 BackfillThe function of the backfill together with plugs is to support the safety functions of thecanister, buffer <strong>and</strong> rock. The backfill prevents <strong>for</strong>mation of transport paths, contributesto mechanical stability of the tunnels, <strong>and</strong> prevents inadvertent human intrusion to therepository. Furthermore, the backfill should provide enough counter-pressure againstthe buffer swelling pressure so as to prevent the buffer from swelling out of thedeposition hole.Currently, the refence backfill option is block backfill with Friedl<strong>and</strong> clay blocks(Tanskanen 2007). In this concept, most of the tunnel is filled with pre-compactedblocks of clayish material <strong>and</strong> the remaining space between the blocks <strong>and</strong> rock withbentonite pellets (Gunnarsson et al. 2007, Keto & Rönnqvist 2006). Alternative conceptof in-situ backfilling is being studied as well as alternative backfill materials includingbentonite <strong>and</strong> a mixture of bentonite <strong>and</strong> crushed rock are still under study (Gunnarssonet al. 2007, Keto 2006, Keto et al. 2009).
33Per<strong>for</strong>mance target Target value RationaleBulk hydraulicconductivity should beless than the targetvalue.Swelling pressure atdrift wall should behigher than the targetvalue.< 10 -12 m s -1 Avoid advective transport in buffer.> 1 MPa Ensure tightness, self sealing.This target applies after a limited timeneeded <strong>for</strong> swelling pressure to develop.Swelling pressure inbulk of buffer should behigher than the targetvalue.> 2 MPa> 0.2 MPaPrevent significant microbial activity.Prevent canister sinking.These target values applies after a limitedtime needed <strong>for</strong> swelling pressure todevelop.Saturated density shouldbe higher than theminimum <strong>and</strong> less thanthe maximum density.Mineralogicalcomposition should notchange in a way thatwould result insignificant perturbationsto the rheological <strong>and</strong>hydraulic properties ofthe buffer.Buffer temperatureshould be less than thetarget value.minimum density Prevent both colloid-facilitated radionuclidetransport (> 1650 kg m -3 ) <strong>and</strong> siginificant> 1890 kg m -3microbial acitivity.maximum density Ensure protection of canister against rockshear.< 2050 kg m -3This is not applicable to frozen buffer.Ensure swelling pressure, self healing <strong>and</strong>plasticity of the buffer.Processes that may perturb the buffer arerelated to e.g. iron or cement interaction orrelated to temperature.< 100 °C Avoid chemical alteration.Sufficient swelling pressure (100–200 kPa, see e.g. Miller & Marcos 2007) is needed<strong>for</strong> the backfill to provide the functions described above. Swelling pressure depends onthe material properties of the backfill, most importantly on swelling material content<strong>and</strong> density. Salinity also affects swelling pressure. The design value <strong>for</strong> salinity hasbeen 35 g/L, similar to the salinity of ocean water, which is the upper limit of
34infiltrating water. Upconing of the deep saline water due to disturbances caused by theconstruction or during glacial periods is possible. According to a description of siteevolution (Pastina & Hellä 2006), maximum salinities at the repository level areexpected to remain below 20–25 g/L, with occasional higher values possible. Also,higher salinities may be permitted depending on material selection, as some backfillmaterials studied by Johannesson & Nilsson (2006) could provide enough swellingpressure even in higher salinities (7%).In addition to per<strong>for</strong>mance of the backfill material, emplacement of the backfill maycreate further requirements on the rock. These requirements may consider the salinity<strong>and</strong> inflow to a certain tunnel section as well to the point inflow. Per<strong>for</strong>mance tests onthe backfill concept have been carried out using maximum salinity of 35 g/L. Thedevelopment of backfilling materials <strong>and</strong> concept needs to be considered in the futurerevisions of per<strong>for</strong>mance targets <strong>and</strong> criteria.As the backfill will contain swelling material (either bentonite or Friedl<strong>and</strong> clay,Tanskanen 2007, see also Keto et al. 2009), the backfill material will pose similar hostrock requirements as the buffer:chemical environment that is favourable to backfill functionalitylow groundwater flow so that erosion will not take place or change the chemicalenvironmentsufficient repository depth in order to avoid freezing of the backfill or tominimise any adverse impact of the freezing of the backfill4.3.4 SummaryEBS functionality depends on the geochemical, hydrogeological <strong>and</strong> mechanicalconditions at the repository depth.With respect to the chemical environment, reducing conditions with no dissolvedoxygen (O 2 ) are required to avoid canister corrosion. Other corroding agents includesulphide (HS - ) <strong>and</strong> chloride (Cl - ) as well as nitrates <strong>and</strong> ammonia. Sulphide, present ingroundwater, the buffer <strong>and</strong> the backfill, is produced by sulphate-reducing bacteria inthe presence of organic matter, <strong>and</strong> by anaerobic methane oxidation involving bothmethane-oxidising bacteria <strong>and</strong> sulphate-reducing bacteria (sees e.g. Chapters 6 <strong>and</strong> 11in Pastina & Hellä 2006). To avoid chloride corrosion, the pH of groundwater must behigh enough, i.e. pH > 4 (SKB 2006).Chemical erosion of buffer can take place in the presence of groundwater with very lowionic strength. High salinity can impair buffer <strong>and</strong> backfill properties, especiallyswelling pressure <strong>and</strong> hydraulic conductivity. The presence of potassium can lead toillitisation of the buffer <strong>and</strong>, consequently, to a decrease in swelling pressure <strong>and</strong>increase in hydraulic conductivity (Pastina & Hellä 2006, SKB 2006). Iron is alsoconsidered to be detrimental to the long-term behaviour of the buffer as it may lead tochloritisation <strong>and</strong> other mineral alterations <strong>and</strong> to a reduced swelling pressure.Erosion of the buffer can take place when there is high inflow in the deposition hole ortunnel section. Currently, maximum allowable inflow to the deposition hole is estimatedto be in the order of 0.1 L/min (SKB 2006, Smith et al. 2007c, see also Section 5.2).
35Even this inflow would need to continue <strong>for</strong> several weeks in order to erode harmfulamounts of bentonite, assuming the erosion rate given by Börgesson & Hernelind(2006). This amount of inflow corresponds to a transmissivity of approximately10 -9 …10 -8 m 2 /s, if the flow originates from a single fracture. According to Smith et al.(2007c) this transmissivity is coincident with the fracture flow properties that provideadequate geosphere transport resistance <strong>for</strong> any released radionuclides (see Section 4.4).Low flow rate around the deposition holes in the long-term is also favourable <strong>for</strong>functionality of the buffer <strong>and</strong> backfill, since it will limit geochemical changes in thenear field.The ability of the canister to withst<strong>and</strong> shear loads is dependent not only on mechanicalproperties of the canister itself, but also on the ability of the buffer to mitigate theeffects of shear displacements. Maximum allowable shear displacements are in the orderof 10 cm (Börgesson et al. 2004, see also discussion in Section 4.3.1) at buffer densitiesof about 2000 kg/m 3 . This target is suggested to be applied <strong>for</strong> all canister positions.Displacements of several centimeters across the deposition hole are possible only if thedeposition hole is intersected by a large enough fracture which can undergo thesedisplacements of several centimetres. Such displacements are thought to be possiblemainly in connection to earthquakes occurring during or after a deglaciation. Thelikelihood of events causing such displacements is very low (see e.g. LaPointe &Hermansson 2002 Saari 2000). Saari (2008) discusses the seismicity of the Olkiluotoarea in relation to the general seismicity of the Fennosc<strong>and</strong>ian Shield <strong>and</strong> the region ofsouth-western Finl<strong>and</strong>. The conclusions of the study by Saari (2008) include that thehistorical earthquakes in the area within a radius of 100 km from Olkiluoto are small(M
36radionuclide transport are much more sensitive to changes in the hydrodynamic controlof retention than to changes in rock porosity <strong>and</strong> diffusion. Consequently, flowproperties around the deposition hole are of importance in limiting radionuclidetransport. Based on the results of TILA-99 (Vieno & Nordman 1999, see also Smith etal. 2007b <strong>and</strong> Nykyri et al. 2008), it can be concluded that the geosphere transportresistance parameter (WL/Q) in the order of few thous<strong>and</strong>s years per metre will providean effective transport barrier. Assuming gradient (i 0 ) of 1% (see e.g. TILA-99, Smith etal. 2007b, c <strong>and</strong> Nykyri et al. 2008), transport distance (L) of 10 m <strong>and</strong> fracturetransmissivity (T) of 3 ∙10 9 m 2 /s, the transport resistance (WL/Q) would be:WL/Q = L / (T∙i 0 ) = 10 m / (3∙10 -9 m 2 /s ∙ 0.01) = 11 000 year/m,i.e. in the order of 10 000 years/m, (See also Appendix B in Smith et al. 2007c) Thusfractures with T in the order of 10 -9 … 10 -8 m 2 /s <strong>and</strong> transport distance in the order offew tens of metres would result in a transport resistance of approximately 10 000year/m. Nykyri et al. 2008 present a more elaborate discussion on the issue pointing outthat the WL/Q is better correlated to the flow rate than the transmissivity of the fracture.Flow rates in the order of 1 L/year indicate transport resistance in the order of tenthous<strong>and</strong>s of years per metre (Section 4.2.9 in Nykyri et al. 2008).The retardation properties (solubility, speciation, sorption <strong>and</strong> diffusivity) of manyradionuclides are affected by the chemical environment, including salinity, pH,dissolved carbonate content <strong>and</strong> redox conditions. A summary of the contributingfactors can be found in Appendix 1 in Hagros (2006). No specific requirements on thechemical environment are set based on impact of the chemical environment onretardation properties. The chemical environment favourable <strong>for</strong> retardation is partlyprovided by the requirements arising from canister <strong>and</strong> buffer per<strong>for</strong>mance. Similarly,fracture properties like filling minerals affect the diffusion <strong>and</strong> sorption properties. Atthe current stage, only a general per<strong>for</strong>mance target <strong>for</strong> an environment favourable <strong>for</strong>matrix diffusion <strong>and</strong> sorption is defined (Table 4-3).4.5 Other issues need to be considered4.5.1 Disturbances caused by excavation <strong>and</strong> operationExcavation of <strong>and</strong> operation within the repository will cause changes in host rockproperties. The excavated spaces will act as a sink, thereby changing the flow regime inadjacent rock volumes. As a result, mixing of groundwaters will cause changes in thechemical conditions, which could be further disturbed by the introduction of structural<strong>and</strong> residual materials such as cementitious materials, organics, or nitrogen oxides.Despite these changes, the host rock should be able to fulfil the criteria summarised inTable 4-3, thus retaining its functionality in providing favourable <strong>and</strong> predictable nearfieldconditions, as well as its retardation function in case of canister failure.Mechanical changes in the geosphere already begin during the repository construction<strong>and</strong> continue during subsequent phases. The main active processes in the operationalphase are related to stress changes caused by construction <strong>and</strong> operation of therepository. In addition it has also been observed that minor seismicity (magnitude of-0.9) can be induced due to blasting ( Damage related to rockmechanics, such as the <strong>for</strong>mation of an EDZ or spalling of the excavated rooms, canhave an impact on hydraulic characteristics in the near field <strong>and</strong> thereby affect transportproperties of the rock. To be meaningful <strong>for</strong> long-term safety the EDZ would need to
37<strong>for</strong>m a continuous path along the tunnels of elevated transmissivity. There are actuallyfew proofs that the EDZ <strong>for</strong>ms a continuous path along the tunnels of elevatedtransmissivity. Even if continuous paths were <strong>for</strong>med, scoping calculations suggests thata continuous EDZ only has limited impact on per<strong>for</strong>mance (e.g. SR-Can, SKB 2006).Nevertheless, the impact of the mechanical changes on long-term safety requires furtherstudy. There<strong>for</strong>e a requirement of keeping any damage to a tolerable level is being<strong>for</strong>mulated. The mechanical disturbances can be mitigated by the repository design e.g.by the orientation <strong>and</strong> shape of the underground openings.Thermal properties of the rock <strong>and</strong> their potential variation within the site should beknown, as they need to be taken into account in the thermal dimensioning of therepository by adjusting canister spacing <strong>and</strong> repository layout design. This is to ensurethat the temperature in the near field of the canister does not have any detrimentaleffects on the canister, buffer or host rock.4.5.2 Mutual compatibility of <strong>and</strong> interfaces between the barriersThe various barriers should be mutually compatible <strong>and</strong> should have no detrimentaleffect on the functionality of each other. Also, the interfaces between barriers shouldhave properties compatible with the safety of the whole system. Notably,no component should have chemical characteristics having significant negativeeffects on other barriers,swelling pressure of the buffer (<strong>and</strong> the backfill) should not generate stressesthat could impair the functionality of other barriers, <strong>and</strong>volume changes of the components should be limited during the repositoryevolution.Furthermore, according to current underst<strong>and</strong>ing, it is important that the buffer reaches asufficient swelling pressure <strong>and</strong> thereby <strong>for</strong>ms a tight interface with the host rock withinreasonable time. This is required in order to prevent <strong>for</strong>mation of a flow path along thedeposition hole or deposition tunnel, <strong>for</strong> example due to spalling, <strong>and</strong> to enhance heattransfer from the buffer to the host rock.4.5.3 Groundwater flow regimeThe repository facilities should be located within a favourable groundwater flow regimeat the site. This needs to be considered especially when locating panels consisting ofseveral tunnels. Also on a smaller scale, hydraulically conductive features, that couldimply rapid transport paths or a potential connection to saline water <strong>and</strong> otherunfavourable features, should be taken into account. This is important because of theevolution of hydrogeological <strong>and</strong> hydrogeochemical site characteristics <strong>and</strong> their impacton EBS functionality <strong>and</strong> transport of solutes.4.6 Summary of the host rock per<strong>for</strong>mance targetsA summary of the current host rock per<strong>for</strong>mance targets <strong>and</strong> associated criteriamodified from SKB (2006) <strong>and</strong> KBS-3H work (Smith et al. 2007c) as discussed in theprevious sections of this chapter is presented in Table 4-3. The per<strong>for</strong>mance targets willbe revised along with improved knowledge of the site, design development <strong>and</strong> progress
38in Research, Development <strong>and</strong> Technical Design (RTD) activities. For example, thestudies on bentonite buffer are likely to provide new in<strong>for</strong>mation on buffer behaviourunder different flow conditions <strong>and</strong> chemical environments. Furthermore, developmentof the backfill concept <strong>and</strong> selection of the backfill material may cause changes toper<strong>for</strong>mance targets <strong>for</strong> geosphere.An area that requires further evaluation is that of mechanical disturbances in tunnels <strong>and</strong>deposition holes. Prediction of the probability of rock damage along the tunnel ispresented in the latest Site Descriptive Model report (<strong>Posiva</strong> 2009a), <strong>and</strong> estimates onthe spalling are reported by Hakala et al. (2008). In the current state, resolution of thesepredictions is not yet such that numerical tunnel or deposition hole scale criteria can beproposed. It might be possible to suppress the initiation of thermally induced spalling byengineering solutions <strong>and</strong> even if such spalling was to occur it may still be acceptablefrom a safety point of view. Furthermore, the uncertainties in spalling strength, reflectedby uncertainty in the estimated extent of spalling (both depth <strong>and</strong> area of the damages aswell as potential number of deposition holes affected), call <strong>for</strong> further study. Theongoing construction of ONKALO will provide data at relevant depths. Predictions onmechanical damage are also being developed. Currently, further development of thecriteria <strong>for</strong> buffer/rock <strong>and</strong> backfill/rock interfaces is taking place, however theserequirements are likely to concern mainly the buffer <strong>and</strong> are not expected to affect therequirements on the host rock to great extent. Properties at the buffer rock interfacewere a key issue in the KBS-3H safety assessment (Smith et al. 2007a, c).The per<strong>for</strong>mance targets defined here <strong>for</strong>m a basis in developing rock suitability criteria<strong>for</strong> the host rock (see Chapter 5). The rock suitability criteria translate these generalrequirements to observable <strong>and</strong> measurable (either directly or indirectly) properties ofthe host rock that can be verified by means of interpretation <strong>and</strong> modelling. Consideringthe set of per<strong>for</strong>mance targets listed in the Table 4-3, the following are taken asguidelines <strong>for</strong> criteria development:per<strong>for</strong>mance targets affecting the criteria <strong>for</strong> deposition holes are essentiallyones related to inflow, i.e. low flow rate around the deposition holes which isalso linked to transport resistance, <strong>and</strong> to limited rock shear in the depositionholes,criteria related to groundwater chemistry, retention <strong>and</strong> thermal propertiesshould be considered <strong>for</strong> rock volumes hosting the deposition tunnels, <strong>and</strong>criteria related to limited mechanical disturbances need to be developed whenmore in<strong>for</strong>mation is gained from ONKALO at relevant depths.
39Per<strong>for</strong>mance targets related to chemical composition of the groundwaterPer<strong>for</strong>mance target Target value RationaleRedox conditions shouldbe reducing.No dissolvedoxygenThe presence of measurable O 2 wouldimply oxidising conditions. Avoid canistercorrosion.Ionic strength should behigh enough; Totaldivalent cationconcentration should behigher than the targetvalue.> 10 -3 M Avoid buffer erosion.pH should be higherthan the target value.[Cl - ] should be less thanthe target value.> 4< 3 MAvoid chloride corrosion of canister.pH < 10 Avoid dissolution of buffer smectite.Refers to emplacement time, initially higherpH up to 11 is allowed.Salinity should be lessthan the target value.Concentration ofdetrimental agents, HS - ,K + , Fe tot , nitrates (NO 3 )<strong>and</strong> ammonia (NH 4 + )should be limited.Colloid <strong>and</strong> organiccontent should be low.Methane should bebelow saturation level.< 70 g/L (TDS,total dissolvedsolids)Avoid detrimental effects, in particular onswelling pressure of backfill (depends onbackfill option).The target is based on that the knowledgethat with the optional materials the swellingpressure will be reached <strong>and</strong> retained insalinities up to the target value.Avoid canister corrosion (HS - , NO 3 - , NH 4 + );avoid illitisation (K + ) <strong>and</strong> chloritisation(Fe tot ) of buffer <strong>and</strong> backfill.Limit microbial activity <strong>and</strong> RN transport.Avoid gas <strong>for</strong>mation <strong>and</strong> limit RNtransport.
40Per<strong>for</strong>mance targets related to groundwater flow <strong>and</strong> solute transportPer<strong>for</strong>mance target Target value RationaleInflow to depositionholes should be less thanthe target value.Flow rate arounddeposition hole shouldbe limited.Transport resistance(WL/Q) in the vicinityof the deposition holesshould be high enough.Environment should befavourable <strong>for</strong> matrixdiffusion <strong>and</strong> sorption.< 0.1 L/min(corresponding toT ~ 10 -9 …10 -8 m 2 /s<strong>for</strong> single fracture)in the order of1 L/year(over width of 1 m)In the order of fewthous<strong>and</strong>s of yearsper metreEnsure buffer <strong>and</strong> backfill functionality <strong>and</strong>provide transport resistance.Applies only <strong>for</strong> unsaturated conditions.Ensure EBS functionality <strong>and</strong> limitradionuclide transport.Applies only <strong>for</strong> saturated conditions.Limit transport of corroding agents <strong>and</strong>RNs.Limit RN transport.Per<strong>for</strong>mance targets related to thermomechanical stabilityPer<strong>for</strong>mance target Target value RationaleRock shear in depositionhole should be less thanthe target value.Mechanical disturbances(EDZ, spalling) aroundexcavations should belimited.Sufficient heat transfercapability.< 10 cm* Avoid canister failure due to rock shear indeposition hole.Related to hydraulic properties. Ensurebuffer functionality <strong>and</strong> limit RN transport.Impact can be mitigated by design <strong>and</strong>proper excavation methods.To avoid an increase in the buffer <strong>and</strong>canister temperatures to an unacceptablelevel. Related to tunnel <strong>and</strong> canisterspacing.* The target value is based on the work by Börgesson et al. (2004). It is noted that based on ongoingstudies the target value may be changed.
415 DEVELOPMENT OF THE ROCK SUITABILITY CRITERIA5.1 <strong>Approach</strong> to the criteria developmentThe following sections present the revised, preliminary criteria (<strong>RSC</strong>-I). The criteriaconsider three scales, the repository scale, the deposition tunnel scale <strong>and</strong> the depositionhole scale. The rock suitability criteria suggested here concentrate on the repositoryscale criteria, applied on the layout-determining features i.e. features affecting theplacement of repository <strong>and</strong> panels. The deposition tunnel <strong>and</strong> deposition hole scalecriteria are still subject to further testing <strong>and</strong> development. The smaller scale criteriaare, nevertheless, briefly addressed <strong>and</strong> some preliminary criteria suggested, althoughthese will be more thoroughly considered during the next phase of <strong>RSC</strong> (<strong>RSC</strong>-II).5.2 Layout-determining features <strong>and</strong> respect distance volumes5.2.1 IntroductionDefinition of layout-determining features <strong>and</strong> respect distance volumes has been guidedabove all by requirements <strong>for</strong>mulated by the Finnish regulatory body, the FinnishRadiation <strong>and</strong> Nuclear Safety Authority (STUK), in Guide YVL 8.4 (STUK 2001), asdescribed in Chapter 2.1. The Guide YVL 8.4 <strong>for</strong>mulates that the structures of the hostrock of importance in the terms of groundwater flow, rock movements or other factorsrelevant to long-term safety, shall be defined <strong>and</strong> classified. The waste canisters shallbe emplaced in the repository so that an adequate distance remains to such majorstructures of the host rock which might constitute fast transport pathways <strong>for</strong> thedisposal <strong>for</strong> the radioactive substances or otherwise impair the per<strong>for</strong>mance of thebarriers. Accordingly, relevant structures called layout determining features need to bedefined together with a respect volume surrounding the feature so that an adequatedistance remains between the relevant structure <strong>and</strong> the deposition holes.Thus, as part of the definition of suitable rock volumes to host the repository, layoutdetermining features <strong>and</strong> their respect volumes are defined as volumes to be avoided bycertain parts of the repository. The rock properties in layout determining features <strong>and</strong>their respect volumes do not meet the per<strong>for</strong>mance targets set with respect to long-termsafety are defined in Chapter 4. In sub-project DETECT-4, The Layout determiningfeatures <strong>and</strong> their respect distances, the main focus has been to define the layoutdetermining features, their influence zones <strong>and</strong> respect volumes (see Figure 3-3 inChapter 3), with respect to these targets. The work was done in close co-operation withsub-project DETECT-3, The Rock Suitability Criteria, where rock suitability criteria <strong>for</strong>the repository host rock were defined (Section 5.3).Layout determining features, including faults, hydrogeological zones <strong>and</strong> boundinglineaments, are usually large in size <strong>and</strong> may have high transmissivity. In the centralpart of the isl<strong>and</strong>, layout determining features have been detected in many boreholes,representing the most certain features at the Olkiluoto site. However, smaller scalede<strong>for</strong>mation zones <strong>and</strong> single, large, hydraulically well conductive fractures also existoutside layout determining features <strong>and</strong> their respect volumes. There are moreuncertainties in the existence, orientation <strong>and</strong> properties of these local featurescompared to layout determining features. The features are not considered to have amajor impact on groundwater flow <strong>and</strong> chemistry, mechanical stability or radionuclidetransport on the site scale. However, locally on the deposition hole scale, they affect
42fulfillment of the per<strong>for</strong>mance targets presented in Table 4.3 in Chapter 4. Thus thesefeatures are considered as part of the rock suitability criteria presented in Section 5.3.Per<strong>for</strong>mance targets <strong>for</strong> the host rock were presented in Chapter 4, Table 4-3. Layoutdetermining features are those where high groundwater flow can cause unfavourablechanges in groundwater chemistry, such as upconing of saline water <strong>and</strong> intrusion ofglacial melt waters, thus affecting many per<strong>for</strong>mance targets related to chemicalcomposition of the groundwater. These high groundwater flow zones provide hardly anytransport resistance <strong>and</strong> should there<strong>for</strong>e be far enough from the deposition holes.Another reason <strong>for</strong> defining a zone as layout determining is to find the potential offuture (post glacial) zone faulting. The project of layout determining features <strong>and</strong>respect distances concerns mainly the following per<strong>for</strong>mance targets <strong>and</strong> their limitvalues. Hence only consideration of layout determining features <strong>and</strong> respect distancevolumes is insufficient to fulfil these per<strong>for</strong>mance targets, but smaller scale criteriapresented in Section 5.3 are also required.Salinity should be less than the target valueo < 70 g/L (TDS, total dissolved solids)Inflow to deposition holes should be less than the target valueo < 0.1 L/min (corresponding to T ~ 10 -9 ...10 -8 m 2 /s <strong>for</strong> single fracture)Flow around deposition holes should be limitedo in the order of 1 L/year (defined as flow over width of 1 m)Transport resistance (WL/Q) in the vicinity of the deposition holes should behigh enougho in the order of few thous<strong>and</strong> of years per metreRock shear in deposition hole should be less than the target valueo < 10 cmRespect distance determines a volume surrounding the layout determining feature thatshould be avoided in order to maintain per<strong>for</strong>mance targets <strong>for</strong> long-term safety of therepository. This volume is called respect distance volume. Defining respect distance <strong>for</strong>a layout determining feature dem<strong>and</strong>s an intermediate step, which is establishing aninfluence zone <strong>for</strong> the feature. Respect distance should be large enough to set a safeenvironment <strong>for</strong> disposal, taking into account the uncertainties in location <strong>and</strong> propertiesof the layout determining features. On the other h<strong>and</strong>, it should be optimised so thatgood rock volumes are not unnecessarily lost. This work is based on the assumption thatvolumes around the faults or hydrogeological zones are the most influenced byde<strong>for</strong>mations <strong>and</strong> are also less competent <strong>for</strong> hosting the deposition holes. This volumeof rock is called an influence zone. The respect distance volume around the fault orhydrogeological zone is basically defined by the influence zone, with a few exceptions.In addition, single faults <strong>and</strong> large fractures, either transmissive or prone to slipping,should be avoided outside the influence zone. This is considered as part of the rocksuitability criteria presented in Section 5.3.
43The objectives <strong>and</strong> the scope of the Section 5.2.2 are to explain the methodology of a)defining the layout determining features, b) defining the influence zone <strong>and</strong> c) definingthe respect distance volumes. The avoidance of large fractures is explained in Section5.3. Section 5.2.3 explains the data <strong>and</strong> models used in this study, while 5.2.4 presentsthe results. Section 5.2.5 discusses uncertainties <strong>and</strong> confidence level in addition tofuture work on this subject.5.2.2 MethodologyThe methodology is based on three steps which are explained in this chapter. The stepsare 1) defining the layout determining features, 2) defining the influence zone <strong>for</strong> them<strong>and</strong> 3) defining the respect volume.Layout determining featuresWithin this work, the term layout determining feature is used to describe a geological orhydrogeological feature in the bedrock which may affect the long-term safety ofdeposition, <strong>and</strong> should there<strong>for</strong>e be avoided by deposition tunnels <strong>and</strong> deposition holes.Central tunnels <strong>and</strong> the access tunnel may however intersect these features. Duringexcavation, engineering measures, like rock support to stabilise the rock <strong>and</strong> grouting tolimit inflow, may be needed. In the long-term, per<strong>for</strong>mance of the backfill may belocally weakened due to <strong>for</strong> example increased flow as a result of grout degradation.Locally weakened backfill per<strong>for</strong>mance in the central <strong>and</strong> access tunnel far away fromdeposition holes is allowed. Also, the impact of engineering measures will not affect thedeposition holes because of distance to the deposition holes <strong>and</strong> limited flow aroundthem.Layout determining features due to mechanical reasonsLayout determining features are generally large enough in size to host an earthquake,which may cause primary or secondary movements in the repository volume. Anearthquake can cause shear displacement of the canister through an existing fracture orde<strong>for</strong>mation zone or the <strong>for</strong>mation of a new shear fracture cutting through thedeposition hole. Based on per<strong>for</strong>mance targets (Table 4-3), these are two of the maingeological hazards <strong>for</strong> the safety of the repository. It is noted that, new fractures are notanticipated to <strong>for</strong>m outside the influence zone Mechanical <strong>for</strong>ces able to produce suchseismic events in the area include the continuous ridge-push by the Mid-Atlantic riftvalley, as well as changes in glacial loads, mainly post-glacial rebound. Olkiluoto is, atpresent, a seismically quiet area based on microseismic monitoring <strong>and</strong> historicalseismic measurements. However it is known that isostatic uplift has been occuring afterthe last glaciation <strong>and</strong> that seismicity has increased immediately post deglaciation (Hutri2007; Bödvarsson et al. 2006). During the operational phase <strong>and</strong> <strong>for</strong> several thous<strong>and</strong>years after the closure of the repository, the main stress field has been considered stable.However, future glaciations will cause changes in the stress field.According to published relationships between earthquake magnitude <strong>and</strong> displacement(e.g. Wells <strong>and</strong> Coppersmith 1994), displacement of the primary fault does not exceedthe threshold value of 0.1 m <strong>for</strong> earthquakes of magnitude equal to or less than 5. Theseresults mean that, even if the earthquake originated on a fault intersecting one or moredeposition holes, no canisters would be damaged. There<strong>for</strong>e, analysis of smallearthquakes is not meaningful (Munier <strong>and</strong> Hökmark 2004). Concluding, a largeearthquake able to cause shear displacement larger than 10 cm is defined as an
44earthquake M>6 by Bödvarsson et al. (2006) <strong>and</strong> Fälth <strong>and</strong> Hökmark (2006), also thebasic assumption in the <strong>RSC</strong>-project. This means that all de<strong>for</strong>mation zones orlineaments larger than 8 km could act as hosts <strong>for</strong> a large earthquake (Fälth <strong>and</strong>Hökmark 2006). These zones <strong>and</strong> lineaments are there<strong>for</strong>e being defined as a layoutdetermining features.GPS measurements (Ahola et al. 2008) <strong>and</strong> precise levelling campaigns (Lehmuskoski2008) on Olkiluoto Isl<strong>and</strong> suggest that certain areas are moving in relation to oneanother. Mattila et al. (2007b) hypothesised that in certain places, movement could beconnected to de<strong>for</strong>mation zones or lineaments. These zones are here defined as layoutdetermining features, although movement seems very slow <strong>and</strong> incomparable to that oflarge earthquakes. According to Mattila et al. (2007b), further studies are required inthis area.An ice load covering the site during the glacial period will cause local changes in thestress field depending on geometry of the faults at the site. To be able to further definewhich zones <strong>and</strong> lineaments might move in the changing stress field, two types ofanalyses of different ice loads were conducted (Appendices in Wikström et al. 2009). Inboth cases, the main sets of data have been stress data from Olkiluoto Isl<strong>and</strong>, calculatedstress changes due to glaciation <strong>and</strong> the geometry of the main geological brittlede<strong>for</strong>mation zones <strong>and</strong> lineaments. Analyses were conducted using the 3 DEC -programme <strong>and</strong> the Poly3D -programme (presented in the Appendices in Wikström etal. 2009). Based on these analyses, a few of the brittle de<strong>for</strong>mation zones wereconsidered layout determining features. However, these zones slipped under veryconservative assumptions <strong>and</strong> if more realistic values were used, no slippage wouldprobably occur. Nevertheless, results indicated that these zones are favourably oriented<strong>for</strong> slippage to occur under modelled stress states. The lineament interpretation is basedon observed geophysical anomalies (Korhonen et al. 2005). The geologicalcharacteristics of these zones are not known at the moment, but they are assumed topresent mainly possible de<strong>for</strong>mation zones <strong>and</strong> thus, due to their size, layoutdetermining features. These features are located mainly in the straits surroundingOlkiluoto Isl<strong>and</strong>, but also in the eastern part of the isl<strong>and</strong>. Those features must becharacterised in more detail if located close to the planned deposition tunnels.Layout determining feature due to hydraulic propertiesThe layout determining feature may not always be very significant in terms of geologyor rock mechanics. However, a feature with high transmissivity (T > 10 -5 m 2 /s) <strong>and</strong> oflarge size or connected to a high-transmissive feature may diminish the radio nuclidetransport time significantly, hence affecting long-term safety of the repository. Theeffect of up-coning of saline groundwater <strong>and</strong> other potential changes in thegroundwater chemistry enhanced by the high flows have also been taken into account indefining hydrogeologically important zones. Thus it is not solely the T-value, but ratherthe underst<strong>and</strong>ing of site hydrogeology <strong>and</strong> geochemistry in general that determinescertain zones as more important than the others.In Ahokas et al. (2007) <strong>and</strong> in Vaittinen et al. (2009) zones estimated to be hydraulicallysignificant in the site scale are modeled. These hydrogeological zones have large aerialextension <strong>and</strong> high transmissivity <strong>and</strong> thus need to be avoided by deposition tunnels <strong>and</strong>holes. These hydrogeological zones are included in the layout determining features.Nevertheless, many of the hydrogeological per<strong>for</strong>mance targets (Table 4-3) suggest that,
45not only should high transmissive zones be avoided in the vicinity of deposition holes,but neither should deposition tunnels pass through layout determining features.Layout determining feature based on expert judgmentCertain zones, although not strictly fulfilling criteria <strong>for</strong> layout determining features, butthat are considered mechanically, hydrogeologically or hydrogeochemically importantaccording to current site underst<strong>and</strong>ing, are also defined as layout determining featuresbased on expert judgment. These zones are considered to cause mechanical instability,have high flow <strong>and</strong> thus cause changes in groundwater chemistry. Expert judgmentreasoning, when used, is presented <strong>for</strong> each layout determining feature in Table 5-2.Expert judgment represents conservatism, meaning taking into account uncertainty ofthe properties of these features. Expert judgment has been used <strong>for</strong> a few zones in theeastern investigation area <strong>and</strong> the bounding lineaments.SummaryTo summarise the above, any feature can be defined as a layout determining feature if itfulfils one or more of the following criteria:a) The length of the zone is 8 km or longer.b) The zone is "moving" in the present stress field.c) The zone is moving or slipping based on earthquake analysis in changing stress field(glaciation).d) The zone is a large scale (assumed lateral extension several hundred of metres)hydraulically significant zone (T > 10 -5 m 2 /s).e) The zone is judged to be a layout determining feature based on expert judgment <strong>and</strong>geoscientific knowledge of the site.Nevertheless, one should remember that these indicators are more or less guidelines,which will be developed further during the <strong>RSC</strong>-process. There remain many openquestions to be cleared with regard to each indicator. At this point, the achievement ofbetter knowledge <strong>and</strong> underst<strong>and</strong>ing of the site is needed in order to define what is <strong>and</strong>is not important.Influence zones of the layout determining featuresDefining the influence zone <strong>for</strong> zones with direct observationsIn geology, it is generally known that when a fault is <strong>for</strong>med, it consists of a welldefinedcore section of broken rock surrounded by fracture system i.e. the fault damagezone. The core <strong>and</strong> the damaged zone were developed simultaneously. Characteristicsof the damage zone, including width, type of fracturing <strong>and</strong> other special characteristics,depend, among other things, on the type of faulting, length of the zone <strong>and</strong> locationalong the fault (Kim et al. 2004). In addition, lithology <strong>and</strong> existing fabric are alsoimportant in the case of Olkiluoto.
46In this study, the term influence zone is used instead of fault damage zone <strong>for</strong> severalreasons. An influence zone is based on borehole in<strong>for</strong>mation. Data used <strong>for</strong> theinfluence zone includes, not only fracturing but also different types of geological <strong>and</strong>hydrogeological data presented in the WellCad logs <strong>for</strong> each drillhole (see Figure 5-5).Hence the term influence zone includes more in<strong>for</strong>mation, especially thehydrogeological <strong>and</strong> also hydrogeochemical, than that is generally defined in thegeological context of a fault damage zone. Furthermore, in the nuclear wastecommunity, as well as in mechanical engineering, the term damage zone describes manmadedamage to the host rock, usually fracturing, caused <strong>for</strong> instance by drilling orblasting. To avoid confusion between man-made artificial damage zones <strong>and</strong> naturalfault damage zones, the word influence zone is used <strong>for</strong> the latter. As a summary theterm influence zone is as follows:"Influence zone is used <strong>for</strong> the 3D volume around a fault or a hydrogeologicallysignificant feature. It is affected by the existence of the fault or hydrogeologicalfeature, <strong>and</strong> hence considered as a weak or transmissive part of the host rock".More details of influence zone concepts are described in Wikström et al. (2009). Theterm fault damage zone is almost synonymous with influence zone.Areas of the bedrock affected by changing stress field are faults, fault damaged zonearound the fault, local de<strong>for</strong>mation zones <strong>and</strong> large fractures. The Fennosc<strong>and</strong>iancrystalline bedrock is very old, 1.8 to 1.9 billion years at the Olkiluoto site, <strong>and</strong> has beende<strong>for</strong>med, altered <strong>and</strong> fractured in many phases. Existing faults <strong>and</strong> fractures could havebeen reactivated during the geological history (Mattila et al. 2007b). However, no newfaults <strong>for</strong>med after the last glaciations have been found in the Olkiluoto vicinity(Lindberg 2007). This hypothesis of the possible reactivation of existing structures hasbeen the basic assumption when defining the rock suitability criteria <strong>and</strong> respectdistance volumes <strong>for</strong> main bedrock features. If faults <strong>and</strong> fault damage zone (theinfluence zone), which is already influenced <strong>and</strong> having increased fracturing as well aslarge fractures, the seismic disturbance to deposition hole is avoided. Moreover, adamaged zone is often more transmissive than a so called averagely fractured or intactrock, which also helps to fulfil the target <strong>for</strong> radionuclide retention.In the central investigation area, not only is the amount of in<strong>for</strong>mation vast, but the sitemodel (<strong>Posiva</strong> 2009a), including geological <strong>and</strong> hydrogeological models, has alsoattained a level where interpretation of major features is consistent from one modelversion to another. Furthermore, models from different disciplines support each other.For the layout determining features in the central area (Figure 5-6), due to numerousborehole intersections through each zone <strong>and</strong> sufficient existing in<strong>for</strong>mation oncharacteristics of the zone, an influence zone can be definedThe influence zone is defined following geological, hydrogeological or geophysicalmeasurements taken from the core along the borehole in both directions. Whileinvestigating all borehole intersections of one zone, certain characteristics, such asslickenside fractures or alteration, are more distinct in certain zones, but may be missingin or less characteristic of others. Geophysical anomalies seem to be typical of somezones <strong>and</strong> are believed to represent certain properties like porosity, alteration, sulphidesor water content, unobservable in core logging. All data characterising the influencezone is evaluated together <strong>and</strong> a limit <strong>for</strong> the influence zone defined. This process isdescribed in more detail in Wikström et al. (2009) <strong>and</strong> example is shown in Figure 5-5.This work includes expert judgment. More rules <strong>for</strong> definition will be developed in the
47next stage of the project, though expert judgment is also needed <strong>and</strong> will not becompletely ab<strong>and</strong>oned.To increase transparency, an influence zone description table, including depth of thecore, limit of the hanging wall <strong>and</strong> footwall influence zones, <strong>and</strong> a verbal description ofthe whole influence zone intersection along the borehole, have been compiled <strong>for</strong> eachdeterministic brittle de<strong>for</strong>mation zone. This table includes reasoning <strong>for</strong> upper <strong>and</strong>lower limits of the influence zone intersection, especially in unclear cases. An exampleof part of the influence zone description table <strong>for</strong> brittle de<strong>for</strong>mation zone BFZ002 ispresented in Table 5-3.Modelling of the influence zone geometry is then based on values defined in theinfluence zone description table. The influence zone’s top <strong>and</strong> bottom surfaces are firstmodelled separately <strong>and</strong> later combined to one solid. However, the outskirts of mainde<strong>for</strong>mation zones have only few or no boreholes, <strong>and</strong> in these areas average width,based on description table values <strong>for</strong> both upper <strong>and</strong> lower influence zones <strong>for</strong> therespective zone, are used. Observations at Olkiluoto indicate an asymmetry of upper <strong>and</strong>lower influence zones, similar to observations given in literature (Kim et al. 2004).Width of the influence zone on either side of the fault core is not equally divided butvaries, usually being clearly wider on one side.Defining the influence zone <strong>for</strong> zones with no direct observationsOnly part of Olkiluoto Isl<strong>and</strong>, the central area, has been investigated well enough inorder to define the deterministic influence zone. Nevertheless, the eastern Olkiluoto area<strong>and</strong> bounding features have been included in this study because of planned repositoryextension to the eastern area. However, in this case another type of approach has beentaken to define the influence zone. These definitions will of course be revised after theeastern area is characterised in more detail. The approach is based on a simplifiedhypothesis that the longer the fault is the wider is the damages zone. Scholz (2002) haspresented typical values of fault scaling parameters where length of the fault,displacement of the fault, process zone width (influence zone) <strong>and</strong> cataclasite zonewidth (core) are in a reciprocal relation (Table 5-1). Based on Scholz (2002), thesemacroscopic scaling relationships show that, as slip accumulates on them, faultsprogressively grow in lateral extent <strong>and</strong> thickness. He notes, however, that individualcases may vary widely from these typical values.It is acknowledged that the scaling laws are only trendsetting. Olkiluoto site has hadquite a complicated geological evolution <strong>and</strong> there are many parameters affecting thegrowth of the influence zone. Also, uncertainties in defining length of the surfacelineament will affect these results.Length of the surface lineament has been the decisive factor in defining width of theinfluence zone <strong>for</strong> the zones with no direct observations. The scaling laws in the Table5-1 have been used to define influence zone width (in Table 5-1 process zone), which isthen divided equally to both sides of the core. Scaling laws can also be used to definewidth of the core of the lineaments.Defined influence zones <strong>for</strong> both modelled brittle de<strong>for</strong>mation zones in the easterninvestigation area <strong>and</strong> <strong>for</strong> bounding lineaments are presented in Table 5-6.
48Length Displacement Process zonewidthCataclasitezone widthLength 1 10 2 10 2 10 4Displacement 10 -2 1 1 10 2Process zonewidthCataclasitezone width10 -2 1 1 10 210 -4 10 -2 10 -2 1Defining the influence zone <strong>for</strong> hydrogeological featuresDetermination of the intersection length of hydrogeological zone in a drillhole is basedon observation of transmissive fractures <strong>and</strong> supported by the fracture frequency,hydraulic conductivity of the intersection <strong>and</strong> expert judgement (Vaittinen et al. 2009).Determination of influence zones in hydrology is based on occurrence of transmissivefractures along the borehole with respect to the core of the zone i.e. most transmissivefractures. In some zones there are several high transmissive fractures <strong>and</strong> the study iscarried out to both directions (hanging wall <strong>and</strong> footwall), starting separately from ahanging wall core <strong>and</strong> a footwall core. The procedure <strong>for</strong> defining the hydrogeologicalinfluence zones is described in more detail in Wikström et al. (2009).For the hydrogeological zone intersections in drillholes, the sum of transmissivity offractures on five metre intervals (0-5, 5-10, 10-15 m etc.) with increasing distance fromthe core was calculated. The distribution of the sum of the transmissivity at differentintervals is shown in Figure 5-1. Furthermore, the transmissivity value corresponding to90% in the cumulative plot was used to compare the different depth intervals, tocompare the results to hydraulic conductivity of the background rock <strong>and</strong> further todefine the influence zone
cumulative percent49100908070Tsum0-5m allTsum5-10m allTsum10-15m allTsum15-20m all60Tsum20-25m allTsum25-30m allTsum30-35m allTsum35-40m all50-11 -10 -9 -8 -7 -6 -5log TPFL- (<strong>Posiva</strong> Flow Log) <strong>and</strong> HTU- (Hydraulic Testing Unit) data were both usedseparately <strong>for</strong> analysis <strong>and</strong> later compared. According to this analysis, some differencesbetween PFL- <strong>and</strong> HTU-data are present, which is partly explained by the differentamount <strong>and</strong> origin of data. However, final results <strong>for</strong> defining the influence zonesupport each others (Figure 5-2). As a conclusion based on both types of data, the sameupper <strong>and</strong> lower influence zone of 20 m, totally 40 m, was defined <strong>for</strong> allhydrogeological zones.
log T50-12-11-10-9-8-7-690% PFL-HZ20down90% PFL-HZ20up90%HTU-HZ20Bd90%HTU-HZ20Au90%HTU-HZ20Au+Bd0 5 10 15 20 25 30 35 40 45 50distance (m) from max T of a zoneRespect distance of the layout determining featuresSKB has investigated the subject of respect distance, concerning seismic activity of thesites, magnitude of the possible earthquake, the amount of slip, the fracture hosting asecondary slip <strong>and</strong> observation of fractures in the tunnel, <strong>and</strong> included sensitivityanalyses of these in Fälth <strong>and</strong> Hökmark (2006), Bödvarsson et al. (2006), Munier(2006a), Munier (2006b) <strong>and</strong> Munier <strong>and</strong> Hökmark (2004). All in<strong>for</strong>mation has beenutilised in this project, although a more robust approach to meet the dem<strong>and</strong>s ofper<strong>for</strong>mance targets was adopted, including <strong>for</strong> the hydrogeological influence on therespect distance.First Munier <strong>and</strong> Hökmark (2004) have defined the term respect distance as follows:“The respect distance is the perpendicular distance from a de<strong>for</strong>mation zone thatdefines the volume within which deposition of canisters is prohibited, due toanticipated, future seismic effects on canister integrity”.According to Munier <strong>and</strong> Hökmark (2004), it appears that seismic influence on canisterintegrity dominates the mechanical, thermal <strong>and</strong> hydraulic aspects. However, accordingto Wikström et al (2009), also the major hydrogeological zones are considered as layoutdetermining, because of the higher flows causing potentially changes in the groundwaterchemistry <strong>and</strong> because such zones may provide rapid transport routes <strong>for</strong> radionuclides.The hydrogeological influence zone is defined so that outside that the number offlowing features <strong>and</strong> the potential <strong>for</strong> connected fracture network are reduced. Byavoiding the influence zone the inflow in the deposition holes is limited <strong>and</strong> highertransport resistance is provided. Nevertheless, this study has indicated that the distanceis probably smaller than the mechanical influence zone (Wikström et al. 2009).
51Based on the reasoning above, the respect distance is here defined as follows (Wikströmet al. 2009):“The respect distance is the perpendicular distance from a de<strong>for</strong>mation zone thatdefines the volume, the respect distance volume, which should be avoided bydeposition tunnels <strong>and</strong> deposition holes, due to potential seismic effects oncanister integrity <strong>and</strong> further to create a desirable transport resistance <strong>for</strong> theradionuclides”.To match the respect distance definition, features to consider include the mainhydrogeological zones <strong>and</strong> large de<strong>for</strong>mation zones together with the local de<strong>for</strong>mationzones <strong>and</strong> large fractures able to host an earthquake <strong>and</strong>/or slip. The main features, i.e.the largest <strong>and</strong> best-known, of de<strong>for</strong>mation zones <strong>and</strong> hydrogeological zones aredetected at the Olkiluoto site with good certainty. However, one of the main concernsthat arose in the <strong>RSC</strong>-work, both in modelling <strong>and</strong> in tunnel mapping versus drill coremapping, is how to define which of the local de<strong>for</strong>mation zones <strong>and</strong> large fractures aresignificant. Some current local zones may be classified as layout determining features inthe future when site in<strong>for</strong>mation increases.The methodology of defining respect distance volumes includes three steps, described indetail in Wikström et al. (2009). These steps are:1. The layout determining features are zones identified with the help oftransmissivity, length/size of the zone, hydrogeochemical characteristics of thezone <strong>and</strong> geomechanical slip analysis. The main de<strong>for</strong>mation zones <strong>and</strong>hydrogeological zones can be detected <strong>and</strong> defined with good certainty based ona vast amount of data.2. The influence zone is the rock volume surrounding a layout determining featurewhere any future slip or growth of the fault are expected to take place or wherefractures with high transmissivity occur.3. Definition of the respect distance volumes is based on geological <strong>and</strong>hydrogeological influence zones. The basic assumption has been that aninfluence zone defines a respect distance. In addition, the respect distancevolume can include certain volumes outside the influence zone defined by expertjudgment. Influence zones of certain areas, namely fault pairs withhydrogeological zones at equal volume, have been combined to one respectdistance volume covering many layout determining features.A fourth step in this methodology is the avoidance of large fractures <strong>and</strong> localde<strong>for</strong>mation zones. However, this is related to finding suitable volumes with additional<strong>RSC</strong> criteria, <strong>and</strong> so is described further in Section 5.3.The Figure 5-3 schematically presents the concepts of influence zone <strong>and</strong> respectdistance. The figure is modified from Mattila et al. (2007a), presenting the idea in 2D (asurface cut), showing fracturing in a more simplistic way. The aim of the figure is todepict the difference between influence zone <strong>and</strong> respect distance.
52The basic assumption is that the affected part of the host rock is the fault core <strong>and</strong> theinfluence zone <strong>and</strong> the leaving the rest of the rock mass intact. This assumption leads tothe conclusion that in general, the respect distance is equal to the influence zone,providing that large fractures <strong>and</strong> local de<strong>for</strong>mation zones in the so called intact or
53averagely fractured rock are avoided (see also Section 5.3). This is valid <strong>for</strong> mechanicalprotection because no significant rock movement is expected outside the influencezones (Scholz 2002; Kim et al. 2004), except in large fractures <strong>and</strong> local de<strong>for</strong>mationzones. This means that the respect distance volume around the fault or hydrogeologicalzone is somewhat smaller than that proposed by SKB (Munier <strong>and</strong> Hökmark 2004).However, relatively small fractures, i.e. tunnel crosscutting fractures, all over therepository rock volume, need to be avoided. In addition, the retention properties of theflow paths are determined by mainly by the flow rate <strong>and</strong> transmissivity of the fracturesin the deposition holes. The simulations carried out showed that the distance from thedeposition hole to the largest de<strong>for</strong>mation zones is a poor indicator of the retentionproperties (<strong>for</strong> more detailed discussion, see Wikström et al. 2009). There<strong>for</strong>e, theretention properties are not specifically considered in the definition of the influencezone. This issue is covered by taking into account the hydraulic properties of theinfluence zone <strong>and</strong> to avoid transmissive features in the deposition holes. However,uncertainties in locating the influence zone need to be considered.Bounding lineamentsBounding lineaments of Olkiluoto isl<strong>and</strong> match the general case where respect distanceis exactly the same as the lineament’s influence zone.De<strong>for</strong>mation zones in the eastern areaThe same general idea, where respect distance equals influence zone, is also used <strong>for</strong>brittle de<strong>for</strong>mation zones in the eastern area. However, some concerning the extensionof significant zones need to be made. Truncation of the zone is re-evaluated in the tipareasif geomechanical analyses (Wikström et al. 2009) indicate a slipping zone. Inuncertain cases, the zone has been extended over the uncertain area. These casesdem<strong>and</strong> additional investigations as soon as possible to avoid unnecessary rejection ofthese rock volumes <strong>for</strong> disposal. The hydrogeological influence zone has not been takeninto account in the eastern area because of lacking hydrogeological data.Brittle de<strong>for</strong>mation zones <strong>and</strong> hydrogeological zones in the central areaFor deterministic zones <strong>and</strong> hydrogeological zones in the central area, the same generalidea of respect distance being equal to influence zone was applied. In the central area,geological <strong>and</strong> hydrogeological zones usually coincide. Here, the hydrogeological zones<strong>and</strong> the geological faults spread over one another in a disorderly way, creating acomplicated picture. In addition, the faults seem to exist in pairs. A solution has been totreat fault pairs as one system, which in fact seems to find support from thehydrogeological <strong>and</strong> hydrogeochemical data (<strong>Posiva</strong> 2009a). Also, the fault pairs arecovered by one respect distance. Upper <strong>and</strong> lower limits <strong>for</strong> respect distance are definedbased on the uppermost <strong>and</strong> lowermost influence zones, respectively, of the fault orhydrogeological zone. In places these alternate.Areas not included in any of the influence zones but considered to comprise manyuncertainties are included in the respect distance volume by expert judgement.Volumes between two splays (branches) of the fault, especially if they are closeto each other <strong>and</strong> be<strong>for</strong>e amalgamating the rock is fractured <strong>and</strong> contains localfeatures which are difficult to interpret <strong>and</strong> model
54Volumes where a hydrogeological zone ceases, but geological fault continuesVolumes, usually minor, between faults <strong>and</strong> hydrogeological zones that arebounded by influence zones in many directions.So far, definition of the influence zone is most uncertain close to the surface. There<strong>for</strong>e,<strong>for</strong> transparency, it has been considered appropriate to present features close to thesurface as single ones, even though in the future they might be combined with others. Inaddition few single hydrogeological zones are also unaccompanied by faults. Forexample the hydrogeological zones HZ19 are not combined with the fault BFZ056 to<strong>for</strong>m one respect distance volume but kept separate. This is not considered significantbecause the repository is located deeper.Initially, respect distance volumes show volumes which should not be used <strong>for</strong>deposition tunnels <strong>and</strong> holes, leaving the remaining rock to be possible repository hostrock. In the next step of the process, the avoidance of large fractures <strong>and</strong> the rocksuitability criteria (<strong>RSC</strong>-I) will be applied <strong>for</strong> the host rock, as explained in Section 5.3.Respect distance volumes together with <strong>RSC</strong>-I criteria will be used <strong>for</strong> layout planning<strong>and</strong> definition of the degree of utilisation of the repository volume.5.2.3 Data <strong>and</strong> modelsThe foundations <strong>and</strong> sources of this sort of study are site knowledge, data availablility<strong>and</strong> different site models. However, knowledge increases <strong>and</strong> models develop, there<strong>for</strong>ethe system <strong>for</strong> defining respect distance volumes needs to be flexible <strong>for</strong> those changes.Present modelling of the entire Olkiluoto isl<strong>and</strong> consists of two separate areas due to thedifferent amounts of data from these areas. They are called the central area, which is thethoroughly investigated area, <strong>and</strong> the eastern area, which is an extension area. Both aredepicted in Figure 5-4.The extensive amount of data from the Olkiluoto site is an excellent source <strong>for</strong> thestudy; however this also dem<strong>and</strong>s more attention to create an equal quality data set to beused. Much attention was paid when choosing data sets which were as comparable <strong>and</strong>transparent as possible. Data sets from boreholes, investigation trenches, outcropmapping <strong>and</strong> tunnel were compared. Finally, the borehole data was evaluated to be themost appropriate data <strong>for</strong> the first stage of the study, as it is the most extensive <strong>and</strong>consistent data set. It can also be compared with data sets from the tunnel later on. Thesurface investigation outcrop TK11 also provided excellent data, but it is difficult tocompare with the borehole data <strong>and</strong> was there<strong>for</strong>e not used directly in this study. TheTK11 data <strong>and</strong> Storage Hall intersections data will be studied more in the next phase ofthis programme. The aim of influence zone modelling is to define comparable influencezones based both on borehole <strong>and</strong> tunnel data. Also, much thought was paid totransparency <strong>and</strong> reiteration of influence zone modelling by creating rules <strong>for</strong> data sets.Although this has not yet been fully achieved, much expert judgment has been included.This has been set as a final project goal after evaluating the results of this study usingtunnel data.
55The utilised borehole data consists of geological, hydrolgeological <strong>and</strong> geophysicalmeasurements in boreholes KR1 to KR40 (depth varying between 0 to 1050 metres),also including B-boreholes if they exists.The used data sets were h<strong>and</strong>led with the well data management tool WellCad. Eachborehole is presented in a log with all data taken into account. One log consists ofgeological in<strong>for</strong>mation like lithology, mapped core sections, foliation, fractures,alteration, hydraulic conductivity, geophysical measurements like P-wave velocity, long<strong>and</strong> short normal anomalies, single point resistance, hydrogeochemical measurement <strong>for</strong>electrical conductivity <strong>and</strong> finally a defined influence zone. Each log is attached withthe reference list of data reports used to create the log. An example of WellCad log ispresented in Figure 5-5.
56A basic model description of the integrated underst<strong>and</strong>ings of Olkiluoto site by variousscientific disciplines is presented in the Olkiluoto Site Description 2008 (<strong>Posiva</strong> 2009a).The geological model version utilised in this study, mainly the brittle de<strong>for</strong>mationmodel, is presented in the Olkiluoto Site Description 2008 (<strong>Posiva</strong> 2009a). However,the idea of an influence zone was already previously introduced in both the geologicalmodel version 1.0 (Mattila et al. 2007b) <strong>and</strong> in the geological data acquisition report(Milnes et al. 2007). The geological model consists of four sub-models, these beinglithological, ductile de<strong>for</strong>mation, brittle de<strong>for</strong>mation <strong>and</strong> alteration models. In thisstudy, the brittle model has been the principal model <strong>for</strong> influence zone modelling,though in<strong>for</strong>mation from both the alteration <strong>and</strong> lithological models has been usedfrequently.Significant lineaments bounding Olkiluoto isl<strong>and</strong> have also been included in influencezone modelling. These lineaments are described in Korhonen et al. (2005) <strong>and</strong> inPaananen <strong>and</strong> Kuivamäki (2007). Lineaments were later re-interpreted in anothergeological model (Mattila et al. 2007b).The hydrogeological model is first reported in Ahokas et al. (2007) <strong>and</strong> furtherdeveloped in Vaittinen et al. (2009). The latest version is presented in the SiteDescription 2008 (<strong>Posiva</strong> 2009a). In Vaittinen et al. (2009), zones estimated to behydraulically significant <strong>for</strong> numerical flow modelling are modelled <strong>and</strong> the definitionof hydrogeological zones to be avoided by deposition tunnels <strong>and</strong> holes is presented.These zones are included into the influence zone modelling as such.
575.2.4 ResultsLayout determining featuresSome layout determining features can be established through direct observations bydrillhole or the ONKALO access tunnel intersections. Occasionally, significantgeophysical anomalies are interpreted as a lineament <strong>and</strong> inferred as a significant sitefeature through expert judgment. To this point, 21 layout determining features havebeen defined, <strong>and</strong> each can be dealt with separately to both ensure repository safety <strong>and</strong>effective use of rock volume.Bounding lineaments, de<strong>for</strong>mation zones in the eastern investigation area <strong>and</strong> brittlede<strong>for</strong>mation zones or hydrogeological zones in the central investigation area can bedefined as layout determining features if they fulfil one or more of the necessaryindicators (presented in Section 5.2.2).Based on these indicators, the following features presented in the Table 5-2 are definedas layout determining features.ZoneBFZ002BFZ056BFZ080BFZ098BFZ099BFZ146Reason <strong>for</strong> being layout determining featureDeterministic brittle de<strong>for</strong>mation zone. Lower splay of BFZ099, whichmight be moving based on GPS measurements (Mattila et al. 2007b).Coincides partly with HZ21.Deterministic brittle de<strong>for</strong>mation zone close to surface. Coincides with thehydrogeological zones HZ19B <strong>and</strong> HZ19C. Dipping towards the easternarea <strong>and</strong> probably continues there based on 3D seismic data. BFZ018coinciding with HZ19A is located close to surface <strong>and</strong> the<strong>for</strong>e there areuncertainties in the definition of the zone <strong>and</strong> its influence zone. This zoneis not presented as a single layout determining feature but considered as aupper slay of BFZ056 (<strong>for</strong> example in Table 5-4).Deterministic brittle de<strong>for</strong>mation zone. Significant geological fault, whichcoincides with the HZ20B.Deterministic brittle de<strong>for</strong>mation zone. Significant geological fault, whihcoincides with the HZ20A.Deterministic brittle de<strong>for</strong>mation zone, upper splay of BFZ002. Might bemoving based on GPS- <strong>and</strong> precise leveling measurements. The fault slipanalysis indicates slipping may occur in changing stress field caused byglaciation.Brittle de<strong>for</strong>mation zone in the eastern area. Overprints the large ductilefeature called Liikla shear zone.
58ZoneBFZ147BFZ148BFZ159LINKED0320LINKED0166LINKED0477LINKED0257LINKED0112LINKED0072HZ19AHZ19BHZ19CHZ20AHZ20BHZ21Reason <strong>for</strong> being layout determining featureBrittle de<strong>for</strong>mation zone in the eastern area. The fault slip analysis indicatesslipping may occur in changing stress field caused by glaciation.Brittle de<strong>for</strong>mation zone in the eastern area. The fault slip analysis indicatesthat slipping may occur in changing stress field caused by glaciation.Brittle de<strong>for</strong>mation zone in the eastern area. Based on expert judgement, ina same cluster (orientation) with BFZ147 <strong>and</strong> BFZ148, even though notmoving based on fault slip analysis.Bounding lineaments in the western part of the isl<strong>and</strong>. Lineaments are lessthan 8 km long, hence included by expert judgment because seems totruncate the brittle de<strong>for</strong>mation zones BFZ002 <strong>and</strong> BFZ099 <strong>and</strong> acts as aborder to the west.Bounding lineament over 8 km long.Bounding lineament over 8 km long.Bounding lineament over 8 km long.Bounding lineament over 8 km long.Significant hydrogeological zone, based on expert judgement, if extendedeast whereas indications from the 3D-seismic measurements.Significant hydrogeological zone.Significant hydrogeological zone.Significant hydrogeological zone.Significant hydrogeological zone.Based on expert judgment (see BFZ002 above) <strong>and</strong> geochemical bases,because possible route <strong>for</strong> upconing (intrusion) of saline groundwater.Brittle de<strong>for</strong>mation zones, i.e. faults classified as layout determining features, in thecentral <strong>and</strong> eastern investigation areas are presented in Figure 5-6. Figure 5-6 is asurface profile, there<strong>for</strong>e only those features reaching the surface are presented.Hydrogeological zones following the faults <strong>and</strong> their surface sections are located at orclose to the faults.
59The brittle de<strong>for</strong>mation zones BFZ002 <strong>and</strong> BFZ099 are the splays of main faultbounding the repository block underneath. The hydrogeological zone HZ21 coincideswith these de<strong>for</strong>mation zones. The splays amalgamate close to boreholes OL-KR2 <strong>and</strong> -KR12, <strong>and</strong> <strong>for</strong>m a single fault in boreholes OL-KR4 <strong>and</strong> -KR7. It is proposed, based onthe location of its surface section which is between two GPS-stations moving apart fromeach other, that BFZ099 is a moving fault (Mattila et al. 2007b). In addition, based onfault slip analysis, BFZ099 seems to slip in a changing stress field (Wikström et al.2009). BFZ002 is one of the earliest known faults at the Olkiluoto site. Based onhydrogeochemical <strong>and</strong> hydrogeological data, this fault <strong>and</strong> the hydrogeological featureHZ21 seem to act as a border between less saline <strong>and</strong> deep saline groundwater, alsoprobably acting as a route <strong>for</strong> the upconing of the deep saline water.The brittle de<strong>for</strong>mation zones BFZ098 <strong>and</strong> BFZ080 <strong>for</strong>m a well-determined fault pairvolume. The main characteristic of this volume is high hydraulic transmissivity, sohydrogeological zones HZ20A <strong>and</strong> HZ20B are the main features. The fault pair isbounding the upper limit of the repository block. In terms of radionuclide transport, thisvolume is believed to be very important because of its location above the repository <strong>and</strong>the high transmissive features. Although to reach the repository this volume needs to be
60passed by the access tunnel, it is considered acceptable provided effective engineeringmethods of grouting to avoid both leakages to the tunnel <strong>and</strong> further upconing of salinewater.As faults close to the surface, brittle de<strong>for</strong>mation zones BFZ018 <strong>and</strong> BFZ056, <strong>and</strong>hydrogeological zones HZ19A, HZ19B <strong>and</strong> HZ19C, are included as layout determiningfeatures. Based on 3D-seismic data these features extend to the eastern investigationarea. This new in<strong>for</strong>mation will be considered in the next update of the model <strong>and</strong> incase these features are extended to the eastern area, they will <strong>for</strong>m the upper boundingfeatures <strong>for</strong> the repository block. As the current observations from these zones are allfrom close to surface part of the rock, there are uncertainties related to definition ofthese zones due to increased fracturing <strong>and</strong> frequency of hydraulic transmissivefractures typical <strong>for</strong> near surface part of the rock.The brittle de<strong>for</strong>mation zones BFZ147, BFZ148 <strong>and</strong> BFZ159 appear in a cluster.Geophysical 3D-seismic data showed a clear picture of vertically faulted reflectors.When the vertical faults were brought to the surface, they coincided well with thesurface lineaments, resulting in faults BFZ147 <strong>and</strong> BFZ148 being created. In addition,these two faults may slip in changing stresses as shown by the fault slip analysis.Because of the identical orientation of BFZ159, this was also included as a layoutdetermining feature.The eastern part of the investigation area is divided by the ductile de<strong>for</strong>mation zonecalled Liikla Shear Zone. Based on surface magnetic data, the zone is a large featurecontinuing outside Olkiluoto isl<strong>and</strong>. So far, due to lack of data from the easterninvestigation area, only part of it, the BFZ146, is known to be a brittle de<strong>for</strong>mationzone. Because BFZ146 most likely represents part of a larger zone, it was included as alayout determining feature.Bounding lineaments, shown in Figure 5-7, are defined based on lineament interpretations(Mattila et al. 2007b; Paananen <strong>and</strong> Kuivamäki 2007; Korhonen et al. 2005).The naming LINKED refers to the <strong>for</strong>mation of a lineament by linking togetherdifferent types of lineaments, like geophysical <strong>and</strong> topographic ones. Lineamentsincluded here are the largest, with higher certainty <strong>and</strong> closest to or passing OlkiluotoIsl<strong>and</strong>, meaning they are believed to be bounding the repository block. Almost allbounding lineaments are longer than 8 km <strong>and</strong> possible hosts <strong>for</strong> large earthquake. Inthe western part of the isl<strong>and</strong>, the bounding lineament consists of two separately namedlineaments, which do not exceed the 8 km length. However, by expert judgment, theyare believed to be bounding lineaments due to modelled truncation of the mainde<strong>for</strong>mation zones BFZ099 <strong>and</strong> BFZ002. In the north of the isl<strong>and</strong>, there are severalequally likely lineaments close to each other, though only the closest one has beenincluded here. To this point there are no direct observations on the existence orcharacteristics of the bounding lineaments. Hence these lineaments are considered aslayout determining features because, based on geophysical in<strong>for</strong>mation <strong>and</strong> indirectobservations from outcropping isl<strong>and</strong>s, they are believed to represent either ductile orbrittle de<strong>for</strong>mation zones. Also at one of the lineament locations, interpretation ofacoustic-seismic data indicates disturbances of sea-floor sediments, which areinterpreted to have been caused by a postglacial earthquake (Hutri 2007).
61In the future, after increased in<strong>for</strong>mation <strong>and</strong> developed modelling <strong>and</strong> geomechanicalanalysis, some of these zones may be excluded <strong>and</strong> new ones included as layoutdetermining features.Influence zoneThe process of defining influence zones <strong>for</strong> brittle de<strong>for</strong>mation features with manyborehole intersections in the central investigation area begins by looking at the WellCadlog of each borehole intersection at the zone (Figure 5-5). Parameters like fracturing,alteration, lithology, hydraulic conductivity <strong>and</strong> geophysical anomalies are allconsidered. The upper (hanging wall) <strong>and</strong> lower (footwall) limit of the influence zone isdefined in relation to the main core section. These limit values <strong>and</strong> other influence zonedescriptions are described in the influence zone description table prepared <strong>for</strong> eachzone. Table 5-3 is an example of part of the influence zone description table <strong>for</strong> zoneBFZ002. All WellCad logs <strong>and</strong> influence zone description tables <strong>for</strong> each zone arepresented in Wikström et al. (2009).At this stage upper <strong>and</strong> lower influence zones are modelled separately, <strong>and</strong> are latercombined to one solid. The outskirts of zones without borehole intersections aremodelled using the average value <strong>for</strong> the upper respective lower limit of influence zonescalculated, from the influence zone description table.
62BFZ002Upper limit Lower limit Upper limit Lower limit Width of Width of Width of Width ofHole to core to core to inf.zone to inf.zone upper inf.zone core lower inf.zone whole inf.zone Description of the zone of influence RemarksKR1 611 618 593 649 18 7 31 56 The zone is described by increasing fracturing <strong>and</strong> alteration. The rock types of the zone changes from theupper limit of the influence zone downwards from veined gneiss to diatexitic gneiss to TTG gneiss <strong>and</strong> againveined gneiss. The main modelled zone consists of RiIII-section with core loss, increased fracturing,elevated hydraulic conductivity <strong>and</strong> pervasive illitisation <strong>and</strong> kaolinisation. While major part of the main coreis missing, consequently also geological section interpretation is missing. Slickensided fractures areexceptionally rare <strong>for</strong> the upper part of the influence zone, but occuring mainly close to the cores <strong>and</strong> in thelower part of the influence zone in the altered section. The upper RiIII-section at 594 m with core loss is alsoslightly hydraulically conductive. Another BFI-section at 640-642 m coincides with RiIII-section. This sectionis covered by section of pervasive kaolinisation, illitisation <strong>and</strong> fracture controlled sulphidisation at 636-648m. This altered section covers also two other RiIII-sections, one in the beginning of the altered section <strong>and</strong>one at 645 m. Finally, at the end of altered section a concentration of slickensided fractures occur. Theinfluence zone is visible in long normal <strong>and</strong> short normal anomalies as well in P-wave veocity anomaly, butthe P-wave velocity anomaly describes the lower part of the influence zone better. A special phenomenom isthe decreasing borehole water TDS-value from the beginning of the influence zone to the end of the zone. Inthe beginning of the influence zone the orientation of the foliation dip seems to change when approachingthe RiIII-section. Changes in the foliation orientation occur also at the end of the influence zone around theRiIII-cores.KR2 600 607 568 643 32 7 36 75 The main rock type of the zone is diatexitic gneiss, but short sections of pegmatitic granite exists at <strong>and</strong>close to the main core section.The main core, at 600-607 m, consists of BFI-section coinsiding with two RiIIIsections,clearly increased fracturing, pervasive illitisation <strong>and</strong> fracture controlled kaolinitisation at 598-622m <strong>and</strong> increased hydraulic conductivity. The whole influence zone is determined based on increasednumber of slickensided fractures <strong>and</strong> slightly elevated hydraulic conductivity not only in cores but also in theinfluence zone. Based on long normal <strong>and</strong> short normal anomalies the zone is from 502 to 715 m, but hasbeen cut off based on slickensided fractures <strong>and</strong> elevated hydraulic conductivity. Additional core sectionexists at 631-633 m (RiIII-section <strong>and</strong> elevated hydraulic conductivity). The dip of foliation seems to changea little around the lowest RiIII-section. A special phenomenom <strong>for</strong> the zone is decreasing borehole waterTDS-values along the influence zone. The limiting factor <strong>for</strong> the both upper <strong>and</strong> lower influence zones is thehydrological conductivity in addition to slickensided fractures. The upper limit of the influence zone is quiteartificial!KR3 470 473 462,5 474 7,5 3 1 11,5 The upper limit of the influence zone begins right under the pegmatitic unit being totally in a veined gneiss.The modelled main core includes a short sections of HSI- <strong>and</strong> BJI-sections, increased number ofslickensided fractures, pervasive kaolinitisation <strong>and</strong> fracture controled illitisation. Both alteration typescontinue <strong>and</strong> cover a large area of 430-502 m. However, this influence zone has not been extended to coverthe whole area, hence the part of the core sections <strong>and</strong> slickensided fractures. Reasoning <strong>for</strong> the shortinfluence zone is cease of slickensided fractures, which are interpreted as the main characteristic <strong>for</strong> thiszone. Geophysical anomalies are fluctuating a lot <strong>and</strong> are probably affected by the large altered area.however the influence zone is visible in the short normal, long normal <strong>and</strong> P-wave velocity measurements.Sameintersectionwith BFZ099
63Widths of the deterministic influence zones are presented in Table 5-4. Thesedeterministic faults seem to appear in pairs <strong>and</strong> their influence zones behave similarly interms of width. Zones of the uppermost fault pair, BFZ018 <strong>and</strong> BFZ056, both havewider footwall than hanging wall influence zone, as do zones of the lowermost faultpair, BFZ099 <strong>and</strong> BFZ002. The relationship between influence zones of the middle faultpair, BFZ098 <strong>and</strong> BFZ08, is vice versa. Total width of the influence zone seems tofollow the scaling laws by Scholz (2002), meaning the larger or longer the zone thewider the influence zone. The modelled deterministic influence zones in the centralinvestigation area are presented in Figure 5-8.The procedure <strong>for</strong> determination of influence zones in hydrology is explained in moredetailed in Wikström et al. (2009). In the first phase of analysis, flow logging data(PFL) above <strong>and</strong> below zones HZ20A, HZ20B, HZ21, HZ21 <strong>and</strong> HZ099 was analysed<strong>and</strong> cumulative plots of transmissivity sums were classified into distances (0-5, 5-10,10-15 m etc.) from cores. Transmissivities are usually below detection limit (ca10 -9 m 2 /s) of the PFL-tool, though some differences along the stretch can be seen. It isinteresting to note that most transmissive sections are observed at a 5-10 m distancefrom the core, meaning that volumes closest to the core are not the most transmissive aswas expected. According to a study, there seems to be decreasing linear trend betweentransmissivity versus distance. However, values over 10 m distance show a somewhatstabilised condition, which indicates that average width of the hydrogeologicalinfluence zone <strong>for</strong> all data is on the order of 10 m. The same conclusion can be madewhen cumulative percent of transmissivity smaller than 10 -8 m 2 /s <strong>for</strong> different distanceclasses is plotted against distance from core. For over 10 m distances more than 90 % oftransmissivities are smaller than 10 -8 m 2 /s. Immediately (0-5 m) outside a core thispercentage is almost 90 %, whereas 5-10 m from a core this percentage is clearlysmaller being a bit over 80%.Brittlede<strong>for</strong>mationzoneWidth ofhanging wallinfluence zone(m)Width offootwallinfluencezone (m)Width ofwholeinfluencezone (m)RemarksBFZ018 7.9 8.5 17.4 Upper part of the BFZ056BFZ056 7.9 11.1 19.8 Lower part of the BFZ018BFZ080 15.2 12.8 29.1 Lower part of BFZ098BFZ098 15.6 11.2 28.4 Upper part of BFZ080BFZ099 14.0 24.0 42.9 Upper splay <strong>for</strong> the BFZ002BFZ002 17.4 24.5 42.9 Lower splay <strong>for</strong> the BFZ099
64PFL-data <strong>for</strong> different zones was studied separately <strong>and</strong> then compared to data <strong>for</strong> allzones. Due to the limited amount of zone intersections data was limited to the followingdatasets:HZ20 footwallHZ20 hanging wallHZ21 <strong>and</strong> HZ21B both sidesHZ099 both sidesEffects of the HZ20A <strong>and</strong> HZ20B footwalls can be clearly seen as they are the mosttransmissive <strong>and</strong> show high variability over long distances. It is evident that the footwallof zones HZ20A <strong>and</strong> HZ20B has strongly affected all data. The hanging wall of HZ20-zones is hydraulically non-conductive <strong>for</strong> distances equal to or greater than 10 m(Figure 5-2), where all transmissivities are below detection limit of the PFL-tool (ca10 -9 m 2 /s). The same behaviour is present on both sides of zones HZ21 <strong>and</strong> HZ21B,beginning from a distance of 15 metres. Data <strong>for</strong> zone HZ099 shows similar behaviouras the hanging wall of HZ20-zones near the core, though it differs in having hightransmissivities at distance class of 30-35 m. The behaviour of transmissivities near thecore section, where transmissivities are small just outside the core <strong>and</strong> high in thedistance class 5-10 m, is similar <strong>for</strong> several zones <strong>and</strong> requires further detailed study inthe future (Figure 5-2).Some boreholes have been measured by the HTU-tool to have a lower detection limit oftransmissivity in the order of 10 -11 m 2 /s. Several differences between this <strong>and</strong> PFL-dataare present, partly explained by the different amounts <strong>and</strong> origin of the data gathered.According to HTU-data, which divides into distance classes 0-6 m, 6-12 m etc due tothe tool’s 2 m section length, transmissivities around HZ20-zones show relatively highvalues in distance classes 0-6 m <strong>and</strong> 6-12 m, with a sharp decrease in classes 12-18 m<strong>and</strong> further. Thus it is clear that a strong change takes place around 12 m. Thedifferences between HTU-data <strong>and</strong> PFL-data <strong>for</strong> distances greater than ca 10-15 m <strong>for</strong>the footwall area of HZ20-zones are significant <strong>and</strong> will be studied in the future.Based on HTU-data, the transmissivities behave rather ideally <strong>and</strong> show ca 20 m longinfluence zone, while the variation based on PFL-data is larger. A summary of analysedhydrogeological influence zones is shown in Table 5-5. Resulting, a 20 mhydrogeological influence zone <strong>for</strong> each side of the hydrogeological zone is defined.The suggested value <strong>for</strong> the influence zone covers both types of data <strong>and</strong> theuncertainties remaining in the results of this preliminary study. Modelledhydrogeological influence zones are presented in Figure 5-8. In the next stage of thisinvestigation, study will be taken further by defining individual hanging wall <strong>and</strong>footwall influence zones <strong>for</strong> hydrogeological zones.Comparison of widths of the hydrogeological <strong>and</strong> geological influence zones <strong>for</strong> thesefeatures show that they are on the same order. HZ20A <strong>and</strong> HZ20B are related toBFZ098 <strong>and</strong> BFZ080; <strong>and</strong> HZ21 related to BFZ002. The difference between HZ099<strong>and</strong> BFZ099 can be partly explained by the fact that BFZ099 is a distinct geologicalfault, though quite an insignificant hydrogeological feature.
65Determining the influence zone of de<strong>for</strong>mation zones in the eastern investigation area<strong>and</strong> of bounding lineaments is based purely on scaling laws by Scholz (2002) <strong>and</strong> lengthof the surface lineament. The entire influence zone is then divided equally <strong>for</strong> eitherside of the core/zone/lineament. In Table 5-6, widths of the influence zones <strong>for</strong>de<strong>for</strong>mation zones in the eastern investigation area <strong>and</strong> <strong>for</strong> bounding lineaments arepresented. Figure 5-9 depicts influence zones in the eastern area <strong>and</strong> Figure 5-10influence zones <strong>for</strong> bounding lineaments. Due to missing in<strong>for</strong>mation on the depth <strong>and</strong>orientation of bounding lineaments, the surface lineament has simply been modelled asa vertical feature continuing to a depth of 1 km.HydrogeologicalfeatureWidth ofhanging wallinfluence zone(m)Width offootwallinfluencezone (m)Width ofwholeinfluencezone (m)RemarksHZ20A+HZ20B 10-15 10-15 20-30 Footwall of HZ20B partlyclearly more transmissivethan other zonesHZ099 10 10 20 Footwall <strong>and</strong> hangingwall are not analysedseparatelyHZ21 (+HZ21B) 15-20 15-20 30-40 Footwall <strong>and</strong> hangingwall are not analysedseparately
66ZoneLineamentlength (m)Width ofhanging wallinfluence zone(m)Width offootwallinfluence zone(m)Width of wholeinfluence zone(m)BFZ146 2 210 11.05 11.05 22.1BFZ147 3 830 19.15 19.15 38.3BFZ148 2 895 14.5 14.5 28.9BFZ159 3 470 17.35 17.35 34.7LINKED0320LINKED01666 519 32.6 32.6 65.2LINKED0477 10 004 50.05 50.05 100.0LINKED0257 8 278 41.4 41.4 82.8LINKED0112 8 125 41.15 41.15 82.3LINKED0072 13 834 69.15 69.15 138.3LINKED0069 9 813 49.06 49.06 98.13
68Respect distance volumeFault pair BFZ098 <strong>and</strong> BFZ080 <strong>and</strong> hydrogeological zones HZ20A <strong>and</strong> HZ20B have allbeen included into one respect distance volume, where the upper <strong>and</strong> lower limitalternate, following either the fault influence zone or the hydrogeological influence zone(Figure 5-11). Here the volume has been called here the R20 respect distance volume. Inaddition, a volume not included in any influence zones, but considered to contain manyuncertainties, is included in the respect distance volume. A special volume, where themain transmissive features HZ20A <strong>and</strong> HZ20B cease while the geological fault BFZ098continues, has been considered uncertain, thus respect distance there has been extendedinstead of a very sharp edge following the end of hydrogeological zones. This is the socalled tip area of hydrogeological zones <strong>and</strong> special caution needs to be taken here.Total respect distance volume is shown in Figure 5-11 B).The lowermost fault pair, splays of BFZ099 <strong>and</strong> BFZ002 <strong>and</strong> hydrogeological zonesHZ99 <strong>and</strong> HZ21, <strong>for</strong>ms a volume, combined together to be called R21 respect distancevolume. A local hydrogeological zone, HZ001, is also within this respect distancevolume.The splays of R21-structures, BFZ099 <strong>and</strong> BFZ002, amalgamate in the middle of thecentral investigation area <strong>and</strong> stay connected throughout the southern part of the isl<strong>and</strong>.In the northern part of the central investigation area they separate, thus this area is notentirely included in the influence zone of either splay. Due to many uncertainties in thearea between the splays, it was decided to be included in respect distance volume of theR21-structures. The R21-structures’ respect distance volume also includes the volumesbetween hydrogeological zones <strong>and</strong> geological faults (Figure 5-12).All features other than the above mentioned, mainly ones close to the surface, have beenpresented alone, though in the future they may be combined with other features. So fardefinition of the influence zone is most uncertain close to the surface, there<strong>for</strong>e it hasbeen considered appropriate <strong>for</strong> the respect distance concept to present these features assingle ones <strong>for</strong> transparency. All respect distance volumes in the central area are shownin Figure 5-13.The same basic idea, respect distance of the zone equals influence zone, is also used <strong>for</strong>brittle de<strong>for</strong>mation zones in the eastern area except in special cases. Here, lack ofhydrogeological data is restricting the analysis of hydrogeological zones <strong>and</strong> only faultsare considered.Zones BFZ147 <strong>and</strong> BFZ148 have been considered to be significant as they might, basedon geomechanical analysis, slip in the changing stress field (Wikström et al. 2009).Modelling of the zones is based on offsets in seismic reflectors hence observed faultingmay be very old <strong>and</strong> related to a totally different stress conditions to those applied inthis analysis (Appendix in Wikström et al. 2009). However, the extent of these zones<strong>and</strong> their truncation in the central area is uncertain. In these cases, tip area <strong>for</strong> respectdistance of both zones has been extended over the central area <strong>and</strong> truncated towardsBFZ099. This is considered important in order to fulfil the safety aspect of avoidingpossible seismic hazards by avoiding the layout determining features <strong>and</strong> their respectdistance volumes. The suitable volume <strong>for</strong> the repository is affected, there<strong>for</strong>e extension<strong>and</strong> characteristics of the zone need to be investigated to evaluate if respect distancecould be reduced.
71Respect distance <strong>for</strong> bounding features follows the same principle of respect distancebeing equal to influence zone. At present no related modifications have occurred.Respect distance results will be used in layout planning. Respect distance volumes showthe volumes which should not be used <strong>for</strong> deposition, providing that large fractures <strong>and</strong>local de<strong>for</strong>mation zones are also avoided in locating deposition holes. In the Figure 5-14the available areas <strong>for</strong> the repository at -420 m depth are shown.A few bounding lineaments are very long <strong>and</strong> their influence zone may become verywide. The longer the zone, the larger the possibility is <strong>for</strong> the zone being host to a largeearthquake. These long bounding lineaments will be studied further <strong>and</strong> analysis of howlarge earthquakes they can host will be studied. In addition, a revised definition ofpossibly larger respect distances will be made.
735.2.5 Uncertainties in layout determining features <strong>and</strong> respect distancevolumesConfidence level <strong>and</strong> reliability in terms both existence <strong>and</strong> detailed geometry of thelayout determining features varies a lot. Deterministic features are proven by differenttypes of investigations. In addition, models based on different disciplines support theexistence, orientation <strong>and</strong> characteristics of major deterministic zones. It is believed thatthe most significant features have been established with quite a high level of confidence.On the other h<strong>and</strong>, bounding features are only lineaments <strong>and</strong> may not even exist, henceall interpretations or definitions concerning these are not as reliable, even thoughbounding lineaments represent the highest certainty class of lineaments. The reliabilityof de<strong>for</strong>mation zone in<strong>for</strong>mation in the eastern area is only moderate.Development of the definition of influence zone is, so far, strongly based on literature<strong>and</strong> the one method of borehole interpretation. However, knowledge on how to definethe influence zone has increased from previous literature Mattila et al. (2007b), <strong>and</strong> dataacquired from the boreholes is very good. Next, developing the influence zonedefinition <strong>for</strong> tunnel data <strong>and</strong> further comparison of borehole <strong>and</strong> tunnel data arebelieved to improve confidence of the whole study. In addition, a study on influencezone width, comparing data from the Storage Hall fault at the surface (TK11) (Mattila etal. 2007a) <strong>and</strong> in several tunnel intersections, will be done. The Storage Hall fault isconsidered an important example, even though it is not a layout determining feature,because it has been intersected in many places including the surface outcrop, pilot holes<strong>and</strong> tunnel. Hence natural variability of the strike-slip fault influence (Mattila et al.2007a) will be studied. From both literature <strong>and</strong> this study, it is known that the influencezone <strong>for</strong> thrust faults, represented by main layout determining features in the centralarea, varies (Wikström et al. 2009). How to cope with the uncertainty arising fromnatural variation will be studied further.The basis <strong>for</strong> influence zone modelling is the underlying geological <strong>and</strong>geohydrological models <strong>and</strong> definition of the core of the modelled zones. In bothgeological <strong>and</strong> hydrogeological modelling, geophysical measurements play animportant role in determining how to combine different drillhole intersections,especially those with large distances between intersections, such as boreholes have.However, a geophysical measurements may not always coincide with the main coresection, i.e. the section which has experienced most strain, been most intensely orextensively fractured <strong>and</strong> been most influenced consisting, <strong>for</strong> instance of gaugematerial <strong>and</strong> cataclasites. There<strong>for</strong>e, in many cases the geophysical anomaly follows atransmissive fracture, especially saline, or a vein containing sulphides. Although thesephenomena usually relate to the de<strong>for</strong>mation zones, it is considered important <strong>for</strong>influence zone modelling to build the influence zone around the real core section. If thecore is at the edge of the influence zone, which may be a natural case, it will affectdefinition of the influence zone, especially width. In the next stage, it will also have aneffect on interpretation of the type or part of the influence zone in question by giving afaulty image of the width of upper (hanging wall) <strong>and</strong> lower (footwall) influence zones.This problem has been tackled by intense discussion between brittle modellers <strong>and</strong>influence zone modellers. Usually these cases arise while the influence zone is beingmodelled, <strong>and</strong> in some cases a brittle model has to be checked <strong>and</strong> redefined. In othercases the main modelled core section is kept as it is, while the influence zone model isadjusted accordingly <strong>and</strong> mentioned in the description tables <strong>for</strong> influence zoneintersection.
74Defining influence zones at the surface or surface part of the bedrock down toapproximately 100 metres is challenging as the rock is usually relatively fractured. Also,continuous increases in hydraulic conductivity are disturbing borehole loginterpretation. This surface phenomenon conceals the effect of the influence zone <strong>and</strong> insome cases it has been impossible to define the zone. However, this has not haddramatic effect on the study because, at the moment, the volume close to the repositorylevel is most important.By increasing transparency, <strong>for</strong> instance by influence zone description tables, a repeat ofinfluence zone modelling is possible. It is important to create guidelines <strong>for</strong> others to beable to per<strong>for</strong>m identical modelling. So far this is not been achieved, however it isplanned to be developed by checking zones using tunnel data <strong>and</strong> working with thoseguidelines.The existence <strong>and</strong> extension of de<strong>for</strong>mation zones BFZ147 <strong>and</strong> BFZ148 will beinvestigated in the near future. Potentially zone BFZ147 is found in the ONKALOtunnel, otherwise it must be examined by drilling. In addition, investigations <strong>for</strong> thecharacterisation of bounding lineaments <strong>and</strong> de<strong>for</strong>mation zones in the eastern areashould be planned. At least one bounding lineament needs to be characterised bydrilling to obtain a better underst<strong>and</strong>ing of what these types of lineaments represent.5.3 Rock suitability criteria, <strong>RSC</strong>-IThe scale division applied in Hagros et al. (2005) <strong>and</strong> Hagros (2006) is consideredpractical <strong>for</strong> <strong>RSC</strong> classification purposes, <strong>and</strong> is consequently implemented into thecurrent version of the <strong>RSC</strong>. There<strong>for</strong>e, the <strong>RSC</strong> <strong>and</strong> classification process presented inthe following sections are examined at repository scale, deposition tunnel scale <strong>and</strong>deposition hole scale (canister scale in the HRC). However, the preliminary rocksuitability criteria suggested in this report concentrate on repository scale criteria astunnel <strong>and</strong> deposition hole scale criteria are still subject to further testing <strong>and</strong>development. The smaller scale criteria are, nevertheless, briefly addressed <strong>and</strong> somepreliminary criteria suggested.The fact that Olkiluoto has already been selected as an investigation site <strong>for</strong> the finaldisposal inherently assumes that the site is generally suitable <strong>for</strong> the purpose. In additionit assumes that its geological, geochemical <strong>and</strong> hydrogeological site properties, whichcould be harmful <strong>for</strong> long-term safety, can be avoided. In Section 5.3.1, the sitecharacteristics relevant to long-term safety are discussed in relation to the per<strong>for</strong>mancetargets established in Chapter 4. The impact of modelled site evolution on sitecharacteristics <strong>and</strong> safety assessment is summarised in Section 5.3.2. Proposedsuitability criteria of the classification system, focusing on the avoidance of harmfulbedrock properties, will be introduced in Sections 5.3.3–5.3.4. This will be followed bya discussion on practical application (Section 5.3.5), uncertainties <strong>and</strong> developmentneeds of the criteria (Section 5.3.6).5.3.1 Site characteristics of relevance to the per<strong>for</strong>mance targetsThis section identifies site characteristics related to the geosphere per<strong>for</strong>mance targetslisted in Table 4-3. This <strong>for</strong>ms the basis <strong>for</strong> <strong>for</strong>mulating criteria in different scales.
75Hydrogeological propertiesPer<strong>for</strong>mance target: Inflow to deposition holes < 0.1 L/minPer<strong>for</strong>mance target: Low flow rate around deposition hole in saturated conditions (inthe order of 1 L/year)Per<strong>for</strong>mance target: Transport resistance in the order of few thous<strong>and</strong>s of years permetre in the vicinity of deposition holeThe hydrogeological per<strong>for</strong>mance targets are mainly related to groundwater flow rate inthe vicinity of the deposition holes. At Olkiluoto, high groundwater flow rates deep inthe rock are predominantly related to hydraulically connected, transmissive, SE-dippingsite-scale fracture zones. However, it should be noted that these fractures withsignificant transmissivities occur even outside the main hydrogeological zones. Highgroundwater flow rates in the vicinity of a deposition hole can have detrimental effectson the buffer (erosion). In addition, advection of groundwater within crystalline bedrockfunctions as the primary transport medium <strong>for</strong> released radionuclides in the case ofcanister failure. There<strong>for</strong>e, the repository facilities should be located within rockvolumes with favourable groundwater flow regimes, which in practice means avoidingrock volumes that have a high frequency of fractures with elevated transmissivities. Thehydrogeological suitability criteria presented in Section 5.3.3 are developed on the basisof this requirement.Hydrogeochemical propertiesChemical composition <strong>and</strong> properties of the groundwater are not, as such, properties ofthe rock, although rock geochemistry does have a significant effect on groundwatercomposition. The variations in local bedrock groundwater properties are in the longterm,however, mostly dependent on groundwater flow, external factors like infiltration<strong>and</strong> glaciation, <strong>and</strong> disturbances caused by the repository construction <strong>and</strong> operation.Consequently, the suggested targets <strong>for</strong> groundwater geochemical composition apply onrepository scale. Smaller scale deposition tunnel <strong>and</strong> deposition hole observations willonly serve as validation of an appropriate repository-scale groundwater compositionexpected at the repository depth. In addition, the mechanical <strong>and</strong> hydrogeologicalcriteria (sections 5.3.4 <strong>and</strong> 5.3.3) dictate that canister sites will not be located withinrock volumes with high water conductivity. It follows that, possible changes in thegroundwater flow patterns <strong>and</strong>/or composition will have a minimal effect ongroundwater composition <strong>and</strong> thereby on buffer <strong>and</strong> canister per<strong>for</strong>mance.It is noted here, although the hydrogeochemical properties are favourable <strong>for</strong> finaldisposal, i.e. the per<strong>for</strong>mance targets are fulfilled, final proof of the suitability <strong>for</strong> finaldisposal can only come from the safety assessment <strong>and</strong> its evaluation of repositoryevolution <strong>for</strong> different scenarios. The site’s hydrogeochemistry will be activelymonitored <strong>and</strong> its evolution simulated continuously as new data <strong>and</strong> models areacquired. Any changes in underst<strong>and</strong>ing need to be taken into account in the selectioncriteria if necessary.Per<strong>for</strong>mance target: Redox conditions - no dissolved oxygenA basic assumption of the site, proven by practical measurements <strong>and</strong> analyses, is thatredox conditions are reducing at depth at Olkiluoto, <strong>and</strong> there<strong>for</strong>e there is no need to
76include this parameter in classification. This approach was already used by Hagros(2006) <strong>and</strong> is still considered valid. Possible oxidising conditions may occur during theconstruction <strong>and</strong> operational phase due to oxygen access during construction via theopen tunnels. But natural reducing conditions will re-establish as soon as theconstructed section is closed, though oxygen will still be present in barriers like pores ofbuffer <strong>and</strong> backfill, <strong>and</strong> it does take time be<strong>for</strong>e these are consumed. On the other h<strong>and</strong>,it has been proposed that glacial melt waters reaching the repository may be rich inoxygen, still a conservative assumption. The melt water intrusion phase is howeverconsidered a transient event, simply crossing of the repository by moving ice sheet(Pastina & Hellä 2006). There<strong>for</strong>e, any oxygenating event is likely to be relativelyshort-lived. Furthermore, in order <strong>for</strong> the oxygenated water to cause harmful effects tothe repository, direct hydraulic connections to the repository are required. Due to thehydrogeological criteria discussed in Section 5.3.3, deposition in a rock volume withhydraulic connections will be avoided, thus it is very unlikely that the redox conditionswill become an issue. At present there is no evidence of oxygen intrusion at repositorydepth according to geochemical interpretation see Chapter 7 in <strong>Posiva</strong> 2009a.Per<strong>for</strong>mance target: Total divalent cation concentration > 10 -3 MField investigations have shown that this target is generally met at depth (Andersson etal. 2007, <strong>Posiva</strong> 2009a) <strong>and</strong>, consequently, there is no need to add specific criteria to theclassification. In the current hydrogeochemical database, the target limit is reached onlyin a few shallow boreholes drilled on outcrops. Divalent cation concentrations below thetarget limit indicate a direct hydraulic connection to the ground surface. Again, suchlocations are, in any case, discarded based on other criteria.Per<strong>for</strong>mance target: pH(GW) > 4 or [Cl - ] GW < 3 MGroundwater pH-values below 4 have not been observed at Olkiluoto. Low pH mayoccur in strongly oxidising conditions due to oxidation of mineral sulphides. However,strongly oxidising conditions are not expected within the repository (see above). Presentmaximum observed [Cl - ] GW concentrations at Olkiluoto are c. 50 g/L , i.e. 1.5 M (seee.g Chapter 7 in <strong>Posiva</strong> 2009a). There<strong>for</strong>e, target conditions are in both cases considereda basic site property. Nevertheless, groundwater chemistry will be monitoredcontinuously to track the validity of this assumption. Elevated salinities indicate anotable hydraulic connection to the deepest parts of Olkiluoto bedrock, but suchhydrogeological zones are avoided based on other criteria. Note also that the TDScriterion given below is much stricter than the criterion <strong>for</strong> Cl - concentration.Per<strong>for</strong>mance target: pH(GW) < 10In natural conditions, pH values higher than 9 are not probable at Olkiluoto (pH above 9has been measured only in EP shallow boreholes <strong>and</strong> in some boreholes which havebeen strengthened by cement during drilling). Equilibrium between water <strong>and</strong> calcitecontrols the pH-value, <strong>and</strong> may slightly exceed 9 if pure water equilibrated withatmosphere is used in calculations. The ionic strength is derived from calcite dissolutiononly <strong>and</strong> Ca 2+ 2-<strong>and</strong> CO 3 ions from other sources do not limit the pH increase(Luukkonen 2004). There<strong>for</strong>e, the target condition is considered a basic site property,<strong>and</strong> there is no need to make this target a criterion in the classification. However, highpH values may occur locally due to the interaction of groundwater <strong>and</strong> grout duringconstruction. This aspect should be considered in the final classification, taking intoaccount both the <strong>RSC</strong> <strong>and</strong> engineering effects on tunnel <strong>and</strong> canister scale.
77Per<strong>for</strong>mance target: Limited concentration of detrimental agents incl. HS - , K + <strong>and</strong> Fe totPotassium <strong>and</strong> iron concentrations are naturally low at Olkiluoto <strong>and</strong> could only beincreased in extreme conditions, such as in very low pH-conditions (see above). Theamount of dissolved sulphide depends on availability of a SO 4 source (abundant inLittorina sea derived brackish-SO 4 type groundwater above 300 m depth at Olkiluoto)<strong>and</strong> organic carbon or CH 4 gas (which are oxidised in the microbially catalysed process<strong>for</strong> reduction of sulphate to sulphide). Groundwater at the planned repository depthcontains notable amounts of dissolved CH 4 at present. Some organic carbon will beavailable in the EBS, <strong>for</strong> example small amounts in the buffer <strong>and</strong> backfill, althoughthese should be restricted. The main sources of sulphide are from groundwatercomposition, there<strong>for</strong>e the sulphide issue is examined with respect to availability of SO 4<strong>and</strong> methane in the groundwater. No criteria have been proposed here due to lack ofdata. The issue will be further studied <strong>and</strong> addressed in <strong>RSC</strong>-II.Per<strong>for</strong>mance target: Methane below saturation levelThe potential repository depth of -400 to -700 m is well above the saturation level ofmethane, which occurs approximately at a -900 metre level. New investigations onmethane saturation are occurring. Results should be checked be<strong>for</strong>e applying any targetcriterion. Overall, the basic assumption is that methane saturation is not considered aproblem at the planned repository level <strong>and</strong> no practical criterion is needed to fulfil thetarget unless new analyses provide contrary evidence.Per<strong>for</strong>mance target: TDS < 70 g/LCurrent salinities at depths of 400 to 500m at Olkiluoto generally vary from 10 to20 g/L (<strong>Posiva</strong> 2009a). Higher values have also been observed in boreholes OL-KR8,OL-KR10 <strong>and</strong> OL-KR19 at around 500 m depth (Figure 5-15). The highest measuredsalinity is 35 g/L in OL-KR19, which is located far from ONKALO near the isl<strong>and</strong>’snorthern coastline. There is no difference between major hydrogeological zones <strong>and</strong>single transmissive fractures at depths of 400 to 500m.Differences or any systematic trends in salinity changes between baseline data <strong>and</strong>monitoring data have not been observed at these depths. Monitoring data in some casesshow increasing salinity, <strong>for</strong> instance OL-KR23_T424. The observed enrichment,however, corresponds to typical salinities in those depths. Thus the observed increase insalinity indicates a recovery of salinity level after dilution occurred during openborehole conditions. These kinds of changes are believed to occur also elsewhere atOlkiluoto, because many boreholes have been open over several years. Hydraulic headmeasurements show, that groundwater tends to inflow from shallow depth fractures, <strong>and</strong>then descends along open boreholes until outflow to fractures located at a great depth.This may confuse interpretation of potential upconing from monitoring data.
78Current in<strong>for</strong>mation indicates that groundwater salinity at Olkiluoto may slightly exceed20 g/L at repository depth of 400 to 500 m . High salinities are not expected if waterleakages into the tunnel will be low <strong>and</strong> vertical hydrogeological zones have lowtransmissivities as indicated in Site Description 2008 (<strong>Posiva</strong> 2009a). Monitoring ofsuch features by groundwater sampling <strong>and</strong>/or EC monitoring, should be strengthenedin the future <strong>for</strong> depths below 500 m. In addition, underst<strong>and</strong>ing of vertical zones <strong>and</strong>their hydraulic connections will be improved be<strong>for</strong>e the revised Site Description due in2011. This improvement will increase confidence on simulations of salinity evolution.Taking into account expected hydrogeochemical evolution (see Section 5.3.2), thepresented results show that the given per<strong>for</strong>mance target value is not expected to beexceeded, <strong>and</strong> that favourable TDS-values can be considered a basic site property at theplanned repository depth.Per<strong>for</strong>mance target: Low colloid <strong>and</strong> organic contentIf inflows into a deposition hole are lower than 0.1 L/min (see below), the amount o<strong>for</strong>ganic material introduced into the hole is considerably less than the organic content ofthe buffer itself. In such conditions, organic material in the groundwater does not have
79any influence on the behaviour of the buffer. There<strong>for</strong>e, no specific criterion <strong>for</strong> theconcentration of organic substances in groundwater is needed.With respect to colloid <strong>for</strong>mation, extremely diluted conditions may enhance colloidstability, though at TDS values above 1 g/L, colloids are unstable (Missana et al. 2003,Degueldre et al. 2000). This requirement is related to divalent cation concentration. Asalready stated in the preceding text, total divalent cation concentration based on fieldinvestigations are over 10 -3 M (Andersson et al. 2007), thus preventing colloid<strong>for</strong>mation. Extremely diluted conditions are not expected at the Olkiluoto repositorydepth as long as highly conductive features are avoided (Pastina & Hellä 2006, <strong>and</strong>Section 5.3.2). Consequently, there is no need to add specific criteria <strong>for</strong> colloid<strong>for</strong>mation.Rock mechanics propertiesPer<strong>for</strong>mance target: Limited mechanical disturbancesPer<strong>for</strong>mance target: Rock shear in deposition hole < 10 cmFracturing is of great significance <strong>for</strong> repository safety, both from an engineering <strong>and</strong> a(hydro)geological point of view. Natural fractures <strong>and</strong> brittle de<strong>for</strong>mation zones thatmay be reactivated during earthquakes exist at all scales within the site volume, <strong>and</strong> aretaken into account when developing the criteria. At tunnel <strong>and</strong> deposition hole scales,the most important fracture type <strong>for</strong> the <strong>RSC</strong> is a large fracture. As it is either difficultor impossible to accurately define the true size of a fracture, Munier (2006a) developedthe so-called FPI criterion (full perimeter intersection), which assumes that any fractureintersecting a tunnel or deposition hole perimeter, determined by the fact that it isvisible in all walls, may be large enough to slip more than 10 cm <strong>and</strong> should there<strong>for</strong>ebe avoided by deposition holes. An example of a FPI fracture is shown in Figure 5-16.Hagros et al. (2005) applied a trace length criterion in the HRC at deposition hole scaleto identify possible large fractures. This approach was similar to that by Munier(2006a), although with a slightly different practical implementation. The FPI-criterionis adopted in <strong>RSC</strong> work (Sections 5.2.1 <strong>and</strong> 5.3.4).During the <strong>RSC</strong>-II phase, it will be investigated whether large fractures can, withreasonable, confidence be identified. Investigation could be carried out by geologicalmapping of pilot holes <strong>and</strong>/or tunnel or by other means like using geophysics.Identification of large fractures would aid in direct estimation of the degree ofutilisation of the repository volume represented by the pilot hole. Investigatedparameters include fracture orientation, fracture type(s), fracture fill mineralogy, <strong>and</strong>orientation of the slip lineation <strong>and</strong> senses of movement (when present). Pilot hole datais to be compared with FPI data from ONKALO. The relationship between FPIs <strong>and</strong>observed de<strong>for</strong>mation zones will also be studied further. A prediction/outcome of studytackling these issues is being <strong>for</strong>mulated.
80In Hagros et al. (2005) <strong>and</strong> Hagros (2006), strength/stress ratio of 4 was used as acritical value limiting suitability of the bedrock <strong>for</strong> final disposal at Olkiluoto (<strong>for</strong>thorough discussion of the effects of the ratio, see e.g. Hagros 2006). According toHagros (2006), approximately 25 % of the rock mass has a strength/stress -ratio lessthan 4 at depth interval of -400 to -440, indicating a risk of severe spalling <strong>and</strong>fracturing. On the basis of more recent analyses, Hakala et al. (2008) concluded that atthe -420 level the probability of spalling in deposition holes is approximately 14%,indicating that the stress state is likely to have harmful effects at the planned repositorydepth. Spalling effects can be mitigated by design. As more stress data becomesavailable, it may be possible to assess which volumes have high spalling potential.These areas can then be avoided.It is noted that issues related to basic rock mass stability are not currently discussedwithin the <strong>RSC</strong>, but will be addressed in <strong>RSC</strong>-II phase. Various rock massclassifications have been employed at Olkiluoto, <strong>for</strong> example Q <strong>and</strong> GSI, to estimatestability of the rock mass. This in<strong>for</strong>mation will be applied in development of thecriteria. Prior to the development, decisions on excavation methods <strong>and</strong> allowed rocksupport methods, in terms of long-term safety, need to be made as these provide theactual constraints <strong>for</strong> the criteria. As proven through experience, stabilisation methodsare dependant on the excavation method used, such as TBM <strong>and</strong> blasting, <strong>and</strong> there<strong>for</strong>ethis in<strong>for</strong>mation is required. Based on current in<strong>for</strong>mation from Olkiluoto, in addition toactual rock mass classifications, in<strong>for</strong>mation on stress conditions is also required tocharacterise rock mass stability. This issue will be elaborated in the <strong>RSC</strong>-II phase.Preliminary review: FPI properties as observed from the ONKALO tunnelAccording to <strong>Posiva</strong>’s fracture database, a total of 333 FPI fractures have been mappedat ONKALO (chainages 150-3000). Locations of these fractures are shown in Figure 5-17. Frequency of FPI-fractures varies from 1 fracture to 26 fractures per 100 metres oftunnel (Figure 5-18). Most of the FPI fractures are undulating slicken-sided fractures,undulating smooth fractures or undulating rough fractures. The FPI-fractures are mainlyvertical to sub-vertical with approximately N-S strikes, or sub-horizontal to horizontal,dipping gently to N-NE (Figure 5-19). A small group of sub-vertical FPIs strike E-W.Some FPIs have measurable slip lineations (slickensides). Measured slip lineationsindicate a strong strike-slip component, even <strong>for</strong> the sub-horizontal fractures.
81~ 350 m30252425262320FPIs/100 m151050512971391295141014181412 14 10 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2100 2200 2300 2400 2500 2600 2700 2800 2900Chainage481217111719
820°N = 331270° 90°Maximum density = 5.29Minimum density = 0.00Mean density = 1.00Density calculation: Small circle countSmall circle area = 20 ‰Contour intervals = 10180°5.3.2 Evolution of the Olkiluoto site <strong>and</strong> its impact on the criteriaEvolution of the geosphere at Olkiluoto during <strong>and</strong> after the operational phase of therepository is described in Pastina & Hellä (2006). The report addresses the impact ofboth short <strong>and</strong> long-term events on rock <strong>and</strong> groundwater properties within therepository <strong>and</strong>, accordingly, on canister <strong>and</strong> buffer per<strong>for</strong>mance. A brief summary of themain thermal, mechanical, hydraulic <strong>and</strong> chemical evolutionary aspects presented in thereport are described in the following text (see Pastina & Hellä (2006) <strong>for</strong> details <strong>and</strong>references). Site evolution is being modelled further <strong>and</strong>, if necessary, criteria will beadjusted in accordance with the results. However, final proof of suitability with respectto long-term evolution can only come from the safety assessment <strong>and</strong> its evaluation ofthe repository <strong>for</strong> different scenarios, not by selection criteria.Thermal <strong>and</strong> mechanical evolutionDuring the operational phase, heat transported from the canister to the surroundingbedrock induced rock volume expansion, potentially causing thermal spalling. Thermalspalling effect is reduced by the counter-pressure of the swelling buffer <strong>and</strong> backfill.Other harmful thermal effects can also be mitigated by design aspects such asdeposition hole spacing <strong>and</strong> repository layout. During glacial phases, the main thermaleffect is related to the generation of permafrost, which according to analyses would notreach repository depth.Thermal evolution does not directly affect the rock suitability criteria as mitigation ofthe effects is mainly a design issue.The main mechanical disturbances expected during the operational stage are thedevelopment of an EDZ (excavation-damaged zone) <strong>and</strong> spalling, caused by changingstress conditions due to excavation. Stress concentrations may be reduced throughrepository layout adaptation.
83In the post-closure <strong>and</strong> glacial phases, movements along pre-existing fractures <strong>and</strong>brittle de<strong>for</strong>mation zones may take place due to changing stress conditions <strong>and</strong>glaciation-induced loading-unloading cycles. There<strong>for</strong>e, from the perspective of longtermsafety, the repository cannot be constructed in the vicinity of major brittlede<strong>for</strong>mation zones or the deposition holes be intersected by large fractures with apotential to slip. Criteria related to the movements in pre-existing geologicaldiscontinuities is included in classification <strong>and</strong> described in the following sections (seealso Section 5.2).Hydrogeological evolutionExcavation of the ONKALO tunnel <strong>and</strong> repository will affect groundwater flowconditions at depth at Olkiluoto. In particular, changes are also anticipated in thegroundwater table <strong>and</strong> salinity distribution within <strong>and</strong> in the vicinity of the tunnel <strong>and</strong>the repository. However, changes can be moderated by grouting. An EDZ may create apreferential transport pathway <strong>for</strong> water from the fracture intersections that are parallelto the tunnel, whose effects need to be taken into account in classification. At themoment, EDZ effects have not been taken into account in the development of criteria,but will be assessed in the <strong>RSC</strong>-II.Modelling results show that, once excavated, open tunnels start to draw water from alldirections, especially from the most transmissive zones intersecting the tunnels. Inflowrates evolve over time, but depend in particular on whether transmissive bedrockfeatures intersect tunnels. Hydogeological disturbances caused by evolution of thesystem are minimised by avoiding such features. In certain cases, hydrogeologicaleffects may also be controlled by grouting (see below). Consequently, inflow to thoseparts of the repository that do not intersect transmissive features will be minimal.Hydrogeochemical evolutionDuring the operational phase, upconing of saline groundwater may take place due toopen excavations. According to models considering the impact of ONKALO (reachingappr. 540 m depth), the maximum salinities (TDS, Total Dissolved Solids) at therepository depth of -440 m would be between 15–20 g/L (Löfman et al. 2009). Theincrease from the baseline level is about 5 g/L during the time open tunnels are present(Löfman et al. 2009). At -540 m level the salinities increase from the present value ofaround 20 g/L to 50 g/L <strong>and</strong> up to 80 g/L depending on the model assumptions (Löfmanet al. 2009). The observed maximum salinities at repository level are 35 g/L, seediscussion in Section 5.3.1. During the temperate phase, the salinity of the groundwaterwill decrease due to infiltration of the fresh water resulting from the continued l<strong>and</strong>uplift. According to Pastina & Hellä (2006), the maximum TDS values to be expected atthe deposition holes <strong>and</strong> tunnels are approximately 25 g/L. It can thus be concluded, thataccording to current knowledge, the salinity at the repository depth is expected to beless than the target value of 70 g/L.During a glacial melting period, glacial melt water intrusion may take place such thatdiluted waters may reach repository depth, which in turn may affect the chemicalenvironment within the repository. However, hydrogeochemical evidence fromOlkiluoto indicates that glacial melt waters did not dominate groundwater compositionsat the repository depths during the last glaciation. Current evidence suggests that themaximum dilution of groundwater was in the order of 10–20 % to the depth of -400 m(<strong>Posiva</strong> 2009a). There<strong>for</strong>e, extremely diluted conditions are not expected at Olkiluoto
84repository depth, provided highly conductive features are avoided (Pastina & Hellä2006).5.3.3 Criteria related to the hydrogeological properties of the rockPer<strong>for</strong>mance target: Inflow to deposition holes
85the cores of the zones, the T-values drop down to background value indicating the endof the IZ <strong>for</strong> the zones (Wikström et al. 2009).There<strong>for</strong>e, the hydrogeological criterion at repository scale is to avoid the influencezones of site-scale hydrogeological zones at Olkiluoto, which in practice meansavoiding rock volumes with elevated transmissivities (water-conducting fractures)around the hydrogeological zones. Consequently, taking geometrical uncertainty of thezones into account, 20 metres is currently held as an adequate RD <strong>for</strong> thehydrogeological zones, measured perpendicular from the core of the zone (see alsoSection 5.2).Currently, the <strong>RSC</strong> does not give any specific inflow criteria <strong>for</strong> deposition tunnel scale.The total inflow to the open tunnels in the repository needs to be limited to avoid sitescale disturbances to ground water table, mixing of different groundwater types <strong>and</strong>upconing of saline water. Currently the limit to inflow to ONKALO has been set to140 l/min (Ahokas et al. 2006) based on the estimated recharge, recharge area <strong>and</strong>precipitation. At a specific time, when certain repository tunnels/spaces aresimultaneously open, total inflow must not exceed the limit set <strong>for</strong> ONKALO. It isnoted that the estimate <strong>for</strong> maximum inflow to ONKALO is being updated based onnew in<strong>for</strong>mation on recharge <strong>and</strong> tunnel observations. Major part of the inflow isexpected to come from the access <strong>and</strong> central tunnels. Need to limit inflow to depositiontunnels is mainly related to limited inflow to deposition hole <strong>and</strong> to per<strong>for</strong>mance ofbackfill. Piping <strong>and</strong> erosion of the backfill is depending on the selected backfillmaterial, concept (reference concept currently is block filling with pellets) <strong>and</strong>installation of the backfill. Based on preliminary results from tests simulating waterinflow into a deposition tunnel (Dixon et al. 2008a, 2008b, Keto et al. 2009, Riikonen etal. 2009), the backfill can tolerate a point-wise inflow between 0.1-0.5 l/min withoutsignificant erosion. These tests were per<strong>for</strong>med using either Friedl<strong>and</strong> clay blocks(Dixon et al. 2008a, 2008b, Keto et al. 2009) or crushed rock / bentonite (60:40)mixture combined with bentonite pellets. As the backfill testing continues, requirements<strong>for</strong> tunnel inflow can be defined on a more firm basis <strong>and</strong> they will be implemented inclassification as specific tunnel scale criteria.At the deposition hole scale, if measured inflow to a hole exceeds 0.1 L/min, theposition needs to be rejected. If a hydrogeological feature (a water-conducting minorzone or a fracture) is observed in the excavated deposition tunnel, adjacent depositionholes need to be positioned avoiding the intersection of these features. No specific RDis determined <strong>for</strong> such features, but the hydrogeological IZ of these features needs to beavoided. It is noted, however, that at this stage there is no proper definition <strong>for</strong> thehydrogeological IZ at this scale. The general idea, subject to further development, is toindividually identify rock volumes that are affected by the hydrogeological featuresconsequently <strong>for</strong>ming potential transport paths <strong>for</strong> radionuclides, <strong>and</strong> to avoid suchvolumes. On the basis of experience gained from ONKALO, these volumes can in manycases be identified once the tunnel is excavated. However, identification of subhorizontalfeatures below the tunnel floor is practically impossible until pilot holes aredrilled to characterise deposition hole positions. It is preliminarily suggested here that ifa sub-horizontal hydrogeological feature is found to crosscut a canister position, theposition needs to be rejected.Hydrogeological criteria presented here are still under development, especiallyregarding the deposition hole scale. At the repository scale, the concept of
86hydrogeological IZ seems to provide a promising approach to defining suitable rockvolumes. At smaller scales, the usability of IZ concept needs to be further investigatedin the testing phase in order to determine how the IZ of a hydrogeological feature isdefined in practice. As the requirements are refined, corresponding criteria need to bedeveloped as well. In addition, the possibility to accurately predict tunnel inflows frompilot holes needs to be investigated. Prediction/outcome studies utilising existing tunnelpilot hole <strong>and</strong> tunnel data are being initiated. Further issues to be taken into account arethe possible effects of grouting, tunnel support <strong>and</strong> EDZ to the hydrogeologicalenvironment <strong>and</strong>, consequently, to the hydrogeological criteria. These matters will beassessed in the <strong>RSC</strong>-II.5.3.4 Criteria related to the mechanical properties of the rockPer<strong>for</strong>mance target: Limited mechanical disturbancesPer<strong>for</strong>mance target: Rock shear in deposition hole < 10 cmThe suggested criteria related to rock mechanical properties, presented in Table 5-8, arefurther discussed in the following text.At the repository scale, the greatest 'natural' mechanical risk arises from possibleearthquakes <strong>and</strong> earthquake-induced lateral slips along fault surfaces. There<strong>for</strong>e, anadequate respect distance (RD) to site-scale brittle de<strong>for</strong>mation zones needs to be keptby avoiding the influence zones (IZ) of brittle zones, because faulting may, in additionto the core part of the zone, occur within the IZ during reactivation of the zone. Munier& Hökmark (2004) conclude that minimum RD to a core of a fault zone should equalthe damage zone of the fault zone. This approach is adopted in this classification, withthe distinction that 'influence zone' is used instead of 'damage zone' (see Section 5.2.2).Furthermore, geometrical uncertainties of the zones need further assessment be<strong>for</strong>e theirRD can be defined (see Section 5.2.2).At tunnel <strong>and</strong> the deposition hole scales, per<strong>for</strong>mance targets related to long-term safety<strong>and</strong> canister per<strong>for</strong>mance require that no deposition hole be intersected by a fracture thatmay experience lateral slip of >10 cm. Such fractures may exist outside earthquakehostingde<strong>for</strong>mation zones <strong>and</strong>, obviously, need to be avoided. According to themodelling by Munier & Hökmark (2004) <strong>and</strong> further elaborated within SKB’s safetyassessment SR-Can (SKB 2006, Section 9.5), within 100 metres to site-scale potentiallyearthquake-hosting fault zones, fractures exceeding 75 metres in radius may slip morethan 10 cm. Respectively within 200 metres, fractures exceeding 150 metres in radiusmay slip more than 10 cm. As in <strong>Posiva</strong>’s approach, the IZ is considered to be anadequate respect distance. Fracture sizes to be avoided may be considerably shorter than75 metres, although further analyses are needed in order to determine the discriminatingfracture size <strong>for</strong> distances less than 100 metre from the IZ. However, in practice, it isextremely difficult to, with certainty, determine the size of a fracture. It is there<strong>for</strong>esuggested, that a deposition hole cannot intersect a FPI fracture (Section 5.3.1).The FPI criterion applies primarily to deposition holes. It is clear that, although aspecific criterion <strong>for</strong> FPIs at the deposition tunnel scale is unnecessary, the FPIs mustalready have been observed <strong>and</strong> characterised in the tunnel to be able to plan depositionhole locations. However, it is possible that, once bored, one or more deposition holesmay be found to intersect an unobservable FPI in the tunnel, in which case they all needto be rejected. Using the scaling laws of Scholz (2002), an FPI with a radius of, <strong>for</strong>
87example, 100 metres would have an IZ in the order of 1.0 metre, so 0.5 metres on bothsides of the fracture. There<strong>for</strong>e, a perpendicular distance of 0.5 metres needs to be keptto any FPI if the actual fracture size is unknown. This value must however be reassessedagainst tunnel data of observed FPIs. These issues are under further study <strong>and</strong>will be h<strong>and</strong>led in more detail in <strong>RSC</strong>-II.Repository scaleDeposition tunnel scaleDeposition hole scaleAvoid the influence zones ofsite-scale brittle de<strong>for</strong>mationzonesNo additional criteria (seetext)Deposition hole must notintersect an FPI fracture; apreliminary respect distanceof 0.5 metres is suggestedDeposition hole cannotintersect minor brittlede<strong>for</strong>mation zones <strong>and</strong> theinfluence zones of these mustbe avoidedAnother requirement, besides the FPI criterion at the deposition hole scale, is that IZs ofminor (i.e. not layout-determining) de<strong>for</strong>mation zones need to be avoided in order tomaintain the integrity of the canisters. The procedure of determining thicknesses of theIZ of minor de<strong>for</strong>mation zones (Section 5.2.2) is currently under investigation.Preliminarily, the scaling laws of Scholz (2002) can be utilised as a rough estimate, inwhich case a zone trace length of 1 km would correspond to c. 5 metres of IZ on bothsides of the fault core. The actual width of an IZ should be defined individually <strong>for</strong> eachzone once intersected by the tunnel or a pilot hole.Spalling that is expected at the repository level due to decreasing rock strength/stressratios may cause difficulties <strong>for</strong> construction work, though at this stage they areexpected to be dealt with by engineering measures. More data is, however, beingcollected <strong>and</strong> analysed. Rock mechanical issues will be discussed more thoroughlyduring the <strong>RSC</strong>-II phase, taking possible effects of foliation, alteration, <strong>and</strong> new stressdata into account.5.3.5 Aspects related to the application of the <strong>RSC</strong> in practiceThe preliminary criteria presented in the following sections are summarised inTable 5-9.Per<strong>for</strong>mance targets, practical criteria <strong>and</strong> their application are still under development,especially with respect to the tunnel <strong>and</strong> deposition hole scales, <strong>and</strong> will be addressed in
88more detail in <strong>RSC</strong>-II. However, preliminary considerations regarding application of the<strong>RSC</strong> are presented in the following sections.Application of existing modelsModel scalesSite models, by definition, focus on description of the site-scale structures <strong>and</strong>properties of the bedrock, i.e. structures with a diameter in the order of hundreds ofmetres or specific attributes with a resolution of a few tens to hundreds of metres.Model resolution is mainly determined by the density of drillholes. With respect to faultzones, locations of the zones in drillholes have high confidence. Geometries of thezones between the drillholes <strong>and</strong> outside drilled volumes are more uncertain. Someindirect geophysical data exists, which can be applied in the modelling. Similaruncertainties <strong>for</strong> other site models exist as well.Modelling of local scale features, i.e. structures or specific bedrock conditions with adiameter or scale of less than a few hundred metres, is difficult with existing datadensity within the site model framework. Some ef<strong>for</strong>ts to provide models at smallerscales have been made in the geological site model <strong>and</strong> ONKALO area model, butmodelling is restricted to volumes in the vicinity of drillholes <strong>and</strong> the ONKALO tunnel.However, local scale features exist in the volumes with less data. At present, thesefeatures are described statistically by a DFN-model (<strong>Posiva</strong> 2009a). Nevertheless,existing data may be partially applied when estimating properties of the volumes withless data, by assuming similar conditions as <strong>for</strong> volumes with higher data density. Astunnelling proceeds, data will become available from the white volumes as well.Application of the site models at the repository scaleThe main focus at this stage is to locate the layout-determining features, which, bydefinition, are hundreds of metres in scale. There<strong>for</strong>e, <strong>for</strong> the purposes of definingsuitable repository volumes, the scale of the site models is adequate. Each model can betreated separately, taking into account the restrictions of each model, <strong>and</strong> respectdistances (RD) applied to the layout-determining features. In the case of overlappingRDs, the most conservative RD should be applied.Application of the site models at the deposition tunnel <strong>and</strong> deposition hole scalesThe scale of deposition tunnels <strong>and</strong> deposition holes is in the order of less than a coupleof hundred metres <strong>and</strong> ten metres, respectively. Resolution of the site models issufficient <strong>for</strong> planning deposition tunnel panels, though <strong>for</strong> placement of the actualdeposition tunnels <strong>and</strong> holes, resolutions of the model is inadequate. More detailedcharacterisation work is needed in order to obtain models focusing on the scale of sometens of metres to some hundreds of metres. The models will be updated periodicallywith new data prior to advancing with excavation. The focus of the models will be oncharacterisation of specific tunnel sections based mainly on pilot hole data. Amethodology <strong>for</strong> the characterisation <strong>and</strong> models is being established.DFN (discrete fracture network) modelsExisting DFN models may be applied to the first assessment of geological conditions inthe characterised volumes, i.e. to the evaluation of the degree of utilisation based on
89proposed criteria <strong>and</strong> to the evaluation of the density of structures with specific lengthor T-values. The applied DFN models should be based on the latest existing data <strong>and</strong>, atthe repository scale, should focus on providing in<strong>for</strong>mation about specific parts ofpanels or groups of deposition tunnels. For an individual deposition tunnel, it is possibleto provide a deterministic fracture description based on tunnel <strong>and</strong> pilot holeobservations. There<strong>for</strong>e, DFN descriptions at this scale could be aimed at testing themodel against observed data <strong>and</strong>, subsequently, <strong>for</strong> refining the model.Per<strong>for</strong>mance target Scale CriteriaInflow to depositionholes < 0.1 L/minLow flow rate arounddeposition hole insaturated conditions (inthe order of 1 L/year)Transport resistance inthe order of fewthous<strong>and</strong>s of years permetre in the vicinity ofdeposition holeLimited mechanicaldisturbancesRock shear in depositionhole < 10 cmRepository scaleTunnel scaleDeposition hole scaleRepository scaleTunnel scaleDeposition hole scaleAvoid the influence zones of the site-scalehydrogeological zones. In general, 20metre is considered as an adequatedistanceNo additional criteriaDeposition hole cannot be positionedwithin the influence zone of ahydrogeological structure (a zone or afracture)Maximum allowed inflow to a depositionhole is 0.1 L/minAvoid the influence zones of site-scalebrittle de<strong>for</strong>mation zonesNo additional criteria (however, FPIs needto be taken into account in the degree ofutilisation)Deposition hole must not intersect an FPIfracture; a preliminary respect distance of0.5 metres is suggestedDeposition hole cannot intersect minorbrittle de<strong>for</strong>mation zones <strong>and</strong> the influencezones of these must be avoided
90Suitability classesSuitability classes with respect to different scales <strong>and</strong> investigation phases are shown inTable 5-10. The classification system consists of three general suitability classes that arerelated to specific scales <strong>and</strong> phases of the suitability investigations:Suitable (sub-index s)Possibly suitable (sub-index ps)Not suitable (sub-index ns)Each suitability class is applicable to either the entire rock volume being investigated orto parts of it, so that a rock volume may consist of sub-volumes with different suitabilityclassifications. In addition, each suitability class is defined specifically <strong>for</strong> each scale:repository (REP), deposition tunnel (TUN), deposition hole (CAN). It is emphasisedthat the proposed classification system is very preliminary <strong>and</strong> apt to changes on thebasis of testing results <strong>and</strong> practical experiences.Class “Suitable (s)” is self-explanatory, corresponding to a situation where, be<strong>for</strong>emoving on to the next investigation scale, all criteria are met <strong>and</strong> the investigatedvolume is considered suitable <strong>for</strong> the specific scale under assessment (e.g. REPs, TUNs,CANs). Suitability classification during the last investigation phase (the deposition holescale) will finally determine whether or not the hole being investigated is suitable <strong>for</strong>deposition. Class “Not suitable (ns)” is also self-explanatory, referring to volumesunable to fulfil the criteria (e.g. REPns, TUNns, CANns). Suitable deposition holelocations (CANs) may only be located within suitable repository volumes (REPs),whereas suitable repository volumes may contain unsuitable deposition hole locations(CANns) or unsuitable deposition tunnel sections (TUNns). Overall, it is emphasisedthat, ultimately, suitable deposition hole locations (CANs) define the final suitability ofa specific volume to waste disposal, whereas suitable repository volumes (REPs) <strong>and</strong>deposition tunnel sections (TUNs) are only indicators of suitable volumes <strong>for</strong> finaldisposal.“Possibly suitable (ps)” refers to a situation, where preliminary investigations of aspecific volume indicate suitability, but the suitability can only be confirmed afterexcavation of the volume or by further studies. This case corresponds to theinvestigations carried out within the deposition tunnel or deposition hole volumes(Table 5-10, e.g. TUNps, CANps), especially with respect to the data gained from pilotholes. Pilot hole data, complemented by other data, may indicate a suitable volume, butsuitability can only be confirmed by detailed investigations after excavation of thetunnel section represented by the pilot hole. There<strong>for</strong>e, the tunnel section or depositionhole cannot be defined suitable until excavation has taken place. In addition, this class isused if, <strong>for</strong> example, engineering measures are allowed to improve the bedrock qualityin order to maintain constructional stability of the tunnel or limit inflow into deeperparts of the tunnel. The engineering measures may only be allowed in cases where thesuitability criteria arising from long-term safety are fulfilled <strong>and</strong> remain unchanged afterimplementation of the measures. The class is introduced because local bedrockconditions may change due to tunnel excavation. Effects of the possible engineeringmeasures will be considered in more detail in the <strong>RSC</strong>-II phase. However, it can alreadybe stated that prior to the application of engineering measures, thorough analyses are
91needed in order to assess effects of the measures on long-term safety <strong>and</strong> repositoryper<strong>for</strong>mance.<strong>RSC</strong> classification processIn the following text, a preliminary classification process <strong>and</strong> guidelines are introducedon a scale-to-scale basis. Parameters used in the <strong>RSC</strong> classification are summarised inTable 5-11, along with comments related to development of the criteria. The suitabilitycriteria <strong>and</strong> classification process presented in this report are preliminary, <strong>and</strong> testing ofthe system will be conducted during the <strong>RSC</strong>-II phase. During testing, characterisationmethodology will continue to develop <strong>and</strong> the classification process will be documentedin detail <strong>and</strong> implemented as a quality assurance system. Also the acquisition of relevantdata will be further discussed in the <strong>RSC</strong>-II.Investigation scale Investigation phase Suitability classRepository scaleREPsREPnsDeposition tunnel scaleBe<strong>for</strong>e tunnel excavation(pilot hole data)After tunnel excavationTUNpsTUNnsTUNsTUNnsDeposition hole scaleBe<strong>for</strong>e the boring of the hole(pilot hole data)After the boring of the holeCANpsCANnsCANsCANns
92Scale Parameters CommentsRepository scaleLayout-determining brittlede<strong>for</strong>mation zones <strong>and</strong>hydrogeological zonesStatistical estimates of loss ofdeposition holes at specificvolumes can be used to assesswhether the use of the volume iseconomical <strong>and</strong> effectiveThe strength/stress ratio <strong>and</strong> itsdistribution <strong>and</strong> effect to the degreeof utilisation will be considered inmore detail in the <strong>RSC</strong>-II phase.Deposition tunnel scale No specific criterion Further inflow criteria related tobackfill requirements will beimplemented in the classificationonce the requirements aredeveloped.The degree of utilisation will affectthe final decision on the usabilityof specific tunnel section. Thedegree of utilisation is determinedby the number of suitabledeposition holes in respect totheoretical number <strong>and</strong> is related towhether the use of the volume iseconomical <strong>and</strong> effective. Oneissue is <strong>for</strong> example how many FPIfractures are intersected by thetunnel <strong>and</strong> whether it is economicalto use a tunnel with large numberof FPI fractures. In this case,further studies of the safety areneeded.Tunnel stability will also be takeninto account in <strong>RSC</strong>-II phase <strong>and</strong>will determine in part whether aspecific tunnel or tunnel section isacceptable both from economical<strong>and</strong> long-term safety point ofview,.Deposition hole scaleLarge fractures (FPIcriterion),inflow, local-scalede<strong>for</strong>mation zonesThe effect of thermal spalling onthe classification will be furtherconsidered in the <strong>RSC</strong>-II phase
93The classification process <strong>and</strong> the investigations at different steps of the process <strong>and</strong>how they are co-ordinated with the construction work are discussed in more detail inAnttila et al. (2009). That report also discusses plans <strong>for</strong> testing of the rock suitabilitycriteria <strong>and</strong> the investigation methods in ONKALO that can be utilised in developmentof the <strong>RSC</strong>-II. The work aims at the demonstration at the repository depth in 2011.Repository scale classificationPrior to application of the classification at the repository scale, it is necessary to updateexisting site models with newly acquired data <strong>and</strong>, if necessary, to re-assess layoutdeterminingfeatures based on the updated models. Layout-determining features aresubsequently incorporated in the repository scale classification. The emphasis of themodelling is on determining the brittle de<strong>for</strong>mation zones that may reactivate <strong>and</strong> slipduring loading-unloading cycles caused by ice-sheet dynamics <strong>and</strong> the hydrogeologicalzones that may impose a risk to long-term safety of the repository. In order to estimatesuitable repository volumes, the influence zone (IZ) is defined <strong>for</strong> each layoutdeterminingbrittle de<strong>for</strong>mation zone <strong>and</strong> hydrogeological zone. Volumes within the IZare not suitable <strong>for</strong> deposition holes.The repository scale classification is highly dependent on quantity <strong>and</strong> quality of theavailable data. New data is continuously being generated <strong>and</strong> will be utilised indevelopment <strong>and</strong> refinement of the criteria. As <strong>for</strong> existing models, further criticalevaluation is needed <strong>and</strong> uncertainties in the models need to be clearly stated. If theuncertainties in a model volume are high, classification <strong>for</strong> that volume may bequestionable. Model volumes with high uncertainties should be targets <strong>for</strong> furtherstudies if they are to be used in repository planning. Statistical estimates of loss ofdeposition holes based on the deposition hole scale criteria should be employed at thisstage to define volumes with low degree of utilisation. Although a specific degree ofutilisation is not a long-term safety requirement, these volumes may be avoided due toeconomical issues.Deposition tunnel scale classificationDeposition tunnels may be planned within volumes defined suitable at the repositoryscale (REPs). After the preliminary decision of where a deposition tunnel can bepositioned, a pilot hole needs to be drilled along the planned tunnel profile. St<strong>and</strong>ardgeological, geochemical, hydrogeological <strong>and</strong> geophysical measurements <strong>and</strong>observations are conducted in the hole. Currently there are no specific criteria related totunnel scale. FPI fractures possibly observed in the tunnel need to be mapped <strong>and</strong>characterised <strong>for</strong> planning purposes, so that if fracture density is sufficiently high, thecorresponding tunnel section is not used <strong>for</strong> deposition holes (Sections 5.3.1 <strong>and</strong> 5.3.4).It is, however, emphasised that at the deposition tunnel scale, even a high amount ofFPI-fractures may be allowed if these do not crosscut deposition holes. The decision touse deposition tunnels with low degree of utilisation is an economical issue, not longtermsafety related. If, by all observations, the tunnel section seems suitable, it isclassified as “possibly suitable, TUNps” <strong>and</strong> excavation can commence. If, on the otherh<strong>and</strong>, the pilot hole intersects <strong>for</strong> example a layout-determining feature, acquired dataneeds to be analysed <strong>and</strong> repository scale classification re-assessed <strong>for</strong> the volume inquestion. In addition to pilot holes, probe holes should be utilised to estimate possibleinflows to the tunnel, although similarly to pilot hole data, the relation between inflowsto probe holes <strong>and</strong> inflows to the corresponding excavated tunnel section needs to betested. At present, estimating inflows to a tunnel section from pilot <strong>and</strong> probe hole data
94contain high uncertainties, but testing the possibility to more accurately assess inflowsfrom hole data is being planned. It is also uncertain how <strong>and</strong> if pre-grouting will affectlocal groundwater chemistry <strong>and</strong> water flow patterns in the rock. These issues will bestudied further <strong>and</strong> addressed in more detail in <strong>RSC</strong>-II.After excavation, a detailed characterisation of the tunnel is conducted <strong>and</strong> suitabilitydetermined. Tunnel-scale models will continuously be updated with newly acquireddata from the tunnels <strong>and</strong> pilot holes as excavation proceeds. Tunnel mapping shouldtake place during excavation <strong>and</strong> suitability of the tunnel be constantly evaluated againstthe suitability criteria <strong>and</strong> utilisation ratio. According to the classification schemepresented in the sections above, if suitability criteria <strong>for</strong> the tunnel are fulfilled, thetunnel is classified as “suitable, TUNs”. If a limit value is exceeded, the tunnel isclassified as “not suitable, TUNns” or “possibly suitable, TUNps”, which means thetunnel is either rejected or engineering measures to meet suitability criteria may betaken, respectively. A tunnel or tunnel section may also be classified as “not suitable,TUNns" if the tunnel, after detailed characterisation, has a very low degree ofutilisation, <strong>for</strong> example due to high density of FPI fractures. For possibly suitabletunnels or tunnel sections, it may there<strong>for</strong>e be feasible to estimate the number ofsuitable deposition hole locations at an early stage. For suitable tunnels or tunnelsections with an adequate utilisation ratio, a preliminary positioning of deposition holescan be carried out.Deposition hole scale classificationDeposition holes may be initially positioned in locations determined “suitable, TUNs”at the deposition tunnel scale, with respect to suitability criteria <strong>and</strong> thermalrequirements (determined by design <strong>and</strong> constructional safety). Each chosen locationneeds to be investigated by a pilot hole. A location is thereafter classified as “possiblysuitable, CANps” or “not suitable, CANns” <strong>for</strong> final disposal if data acquired from thepilot hole indicates that the suitability criteria are or are not met, respectively. Theclassification “not suitable, CANns" comm<strong>and</strong>s rejection of the planned depositionhole. New locations may be investigated close to the rejected location though, if the newlocation is classified "suitable" at the tunnel scale <strong>and</strong> if the relocation is acceptablefrom a design point of view, so not too close to other canisters due to thermal effects. At“possibly suitable” locations, boring of the deposition holes takes place after theinvestigations from pilot holes, <strong>and</strong> final suitability is determined by a detailedcharacterisation of the bored deposition hole with respect to the criteria. The bored holesare then classified either as “not suitable, CANns” <strong>and</strong> rejected, or as “suitable, CANs”<strong>and</strong> used <strong>for</strong> final disposal. Again, design requirements <strong>and</strong> suitability criteria allowing,new locations may be investigated close to rejected positions.H<strong>and</strong>ling of overlapping criteriaIn situations where proposed criteria are overlapping, the most conservative criterionmust be used. As an example, if an FPI fracture is leaking, the respect distance to beapplied is determined either by the hydrogeological criteria or the mechanical criteria,depending on which is more conservative.Degree of utilisation - preliminary estimatesDegree of utilisation based on the proposed criteria has been preliminarily estimated inthe DETECT task. The degree of utilisation estimation, when applying the FPI criterion,
95was based on the latest DFN description (<strong>for</strong> a summary see <strong>Posiva</strong> 2009a) <strong>and</strong> includedthree different DFN models variants. In the estimates, it was assumed that criticalfractures were neither observed nor avoided during disposal, all fractures are rounddisks <strong>and</strong> deposition hole locations are r<strong>and</strong>omly distributed. According to theestimates, percentage losses of deposition hole locations were 23.6 %, 15.5 % <strong>and</strong>3.9 %, the result depending on the DFN model used in calculations. Due to theassumptions, results are considered overly conservative.Observations of FPI fractures in ONKALO tunnel were also considered a practicalapplication of FPI criterion. Imaginary deposition holes were located in tunnel chainage2427–2877 m (Figure 5-20), with a minimum distance of 10 metres between the holes.Each hole was visually positioned to avoid FPI fractures <strong>and</strong> observed de<strong>for</strong>mationzones. In the investigated tunnel section, ideal deposition hole number was 45, <strong>and</strong>realisation, using FPI criterion, was 35. Thus the loss of locations is 22 %.A new hydrogeological DFN model of the Olkiluoto Site has been recently compiled(<strong>for</strong> a summary see <strong>Posiva</strong> 2009a). Based on the model, he also estimated the amount oflost deposition holes by rejecting each location that is crosscut by a transmissivefracture. At depth level from –400 m to –1000 m, percentage of lost deposition holeswas 4 %, assuming the holes are r<strong>and</strong>omly located <strong>and</strong> critical fractures are neitherobserved nor avoided, i.e. presenting a conservative estimate.Leakages from pilot holes, probe holes, <strong>and</strong> grouting holes between zones HZ19C <strong>and</strong>HZ20A (chainage range 1200–3000 m) showed total leakage 1.6 L/min, of which1.4 L/min occurred between 1200–2000 m <strong>and</strong> 0.2 L/min between 2000–3000 m.Leakages between 2000–3000 m were concentrated to "individual" fractures at chainage2212 m, 2382 m, 2481 m <strong>and</strong> possibly 2486 m. At chainage 2382 m leakage from oneprobe-hole was 0.11 L/min, though in other places clearly less. Between 1200–2000 mleakages over 0.1 L/min were measured at 1248 m <strong>and</strong> 1505 m. Figure 5-21 shows theFPI fractures <strong>and</strong> the leakage points in tunnel chainage 2360 m–2530 m. It can beconcluded that only to a small number of FPIs are related with observable flow.The estimates given are very preliminary <strong>and</strong> conservative, <strong>and</strong> will be updated as newmodels <strong>and</strong> data are acquired. The possibility to adjust deposition hole locations toavoid critical intersections will be implemented in future assessments in order toprovide more realistic utilisation estimates. Effects of foliation (thermal properties),rock mechanics (spalling) <strong>and</strong> hydrothermal alteration will also be accounted <strong>for</strong> infuture estimations in case criteria related to these properties are developed. In addition,new tools <strong>for</strong> estimation will be developed <strong>and</strong> these used side by side with the toolsdeveloped by SKB.
975.3.6 Discussion <strong>and</strong> development needsThe main goal of the classification system is to provide criteria that are both relevant<strong>and</strong> efficient from a long-term safety point of view <strong>and</strong> have high practical usability.Usability of the proposed criteria can only be evaluated through active testing of theclassification system. With respect to the hydrogeological criteria, estimating inflows toa tunnel section from pilot <strong>and</strong> probe hole data have high uncertainties at present. Alsothe methods <strong>for</strong> FPI <strong>and</strong> fracture zone prediction from pilot hole data need furtherdevelopment. Extensive testing is planned both within ONKALO <strong>and</strong> demonstrationfacilities at repository depth in order to assess the possibility of estimating the whetherthe rock parameters from pilot <strong>and</strong> probe hole data are representative. The classificationsystem will subsequently be refined on the basis of testing results. In addition to thetesting results, the possible revisions of per<strong>for</strong>mance targets need to be taken intoaccount in development of the criteria. Rock mass stability estimations also need to beincorporated in classification, which is to be addressed thoroughly in the <strong>RSC</strong>-II phase.While reliability of the classification system with respect to the deposition tunnel <strong>and</strong>deposition hole scales can be assessed by testing the system in demonstration facilities,at the repository scale system reliability is linked to the confidence of used site models.There<strong>for</strong>e, if the confidence of site models in some volumes is considered poor,suitability estimation of these volumes, derived from the repository scale classification,has to be reassessed also. Further investigations within these volumes will be conducted,as more data is collected <strong>and</strong> as excavations proceed, in order to increase the confidenceof models <strong>and</strong> classification results. Deposition tunnels <strong>and</strong> deposition holes shouldonly be constructed in volumes where the site models are deemed to have highconfidence.Current development of the classification system needs to include the definition ofgeometrical uncertainties of influence zones (IZ), both <strong>for</strong> the site-scale brittlede<strong>for</strong>mation zones <strong>and</strong> the hydrogeological zones (layout-determining features). Thisdevelopment can at least partly be accomplished by tunnel observations. Definition ofthe IZs is also highly dependent on drillhole data that is used in modelling of the zones.By comparing the modelling results to tunnel data near zone intersections, validity ofthe modelling approach <strong>and</strong> model uncertainties can be estimated. As tunnelintersections only represent a limited zone section <strong>and</strong> a limited rock volume, statisticalmethods may be employed in the estimation of uncertainties. Once the uncertainties arequantified, the proposed criteria has to be assessed against the results <strong>and</strong>, if necessary,definition of the IZ adjusted to take geometrical uncertainties of the zones into account.The definition of the IZ <strong>for</strong> minor de<strong>for</strong>mation zones <strong>and</strong> FPI-fractures will be testedagainst tunnel data <strong>and</strong> applicability of the scaling laws validated. Furthermore,hydrogeological avoidance criteria <strong>for</strong> leaking features need to be developed on thebasis of observations from the tunnel <strong>and</strong> drillholes. Possible effects of foliation <strong>and</strong>alteration on the rock mechanical criteria need also to be further discussed in the <strong>RSC</strong>-II.The effect of engineering measures (i.e. rock support, grouting) on long-term safetyneeds to be discussed in the <strong>RSC</strong>-II phase <strong>and</strong> any long-term safety requirementsresulting from this discussion must be taken into account in the criteria. It is estimatedthat at least rock support will be needed at the repository depth. Preliminarily, the use ofengineering measures is considered possible at the deposition tunnel scale <strong>and</strong>,there<strong>for</strong>e, suitability class “Possibly suitable” is included in the classification system
98described above. After a discussion on the effects, applicability of this class should bereassessed.
996 ENGINEERING TARGETS ON HOST ROCK6.1 ActivitiesCriteria related to constructabilityOf particular interest during Phase 1 were criteria related to layout determining featuresi.e. repository scale (features affecting the emplacement of panels, see Section 5.2), aswell as estimation of the utilisation degree. The degree of utilisation estimates theproportion of the usable canister positions of total number of potential canisterpositions. Often the proportion of lost canister positions is given. Tunnel <strong>and</strong> depositionhole scales will be in focus during Phase 2 (years 2010-2012).Further development of the HRC (Hagros et al. 2005, Hagros 2006) is accomplishedthrough the <strong>RSC</strong>-program. In the task “Definition of the engineering targets <strong>for</strong> the hostrock”, engineering targets were defined through a re-evaluation of the HRCclassification.When re-evaluating the HRC-classification system, it was confirmed that there is onlyone parameter where the limit value is determined solely by constructabilityrequirements. That is the strength-stress ratio ensuring mechanical stability. The ratio ofUCS/ 1 (peak strength/in situ stress), which was used in the original HRC classificationat repository scale, can still be considered quite practical considering the excavationstage. However, this parameter does not consider thermally induced effects, which takeplace after the emplacement of the canisters (See Section 5.3.2). HRC specifies the limitvalue to be 4 over large areas of the host rock, but states that ratios less than 4 (probablyindicates some damage in rock) in limited rock mass do not affect constructability of therepository.It is well known that, due to the heterogeneity <strong>and</strong> anisotropy (foliation) of the rock,strength values have some scatter. Foliation in<strong>for</strong>mation is thus included in the strengthvalues. Rock stress values show large scattering, considered to be due mainly to thedifficulties in measurement rather than to the rock mass itself.Strength-stress ratio is still a justified parameter to ensure mechanical stability, <strong>and</strong> isincluded in <strong>RSC</strong> I. There are no other parameters where the limit values are determinedsolely by the requirements of constructability. In these cases, if a volume of rock meetsthe <strong>RSC</strong> I criterion (See Chapter 5), it is automatically acceptable from a constructionpoint of view. In terms of engineering, there are rarely criteria issues about whethersomething is “suitable” or “not suitable”. Here it is more a question of what actions willbe taken (tunnel orientation <strong>and</strong> shape, ground support, grouting etc.) <strong>and</strong> whether theyare cost effective. It is important to remember that in addition to <strong>RSC</strong>, <strong>Posiva</strong> will set upadditional criteria. For example, there will be economic criteria which define aminimum degree of utilisation <strong>for</strong> deposition tunnels; it is not reasonable to excavate adeposition tunnel that includes only one or two potential deposition holes if there isbetter host rock available.Layout adaptationFigure 5-7 shows the bounding lineaments of the repository. These bounding lineamentsare not assumed to be penetrated by tunnels or shafts. Layout determining features areavoided with deposition holes <strong>and</strong> deposition tunnels if possible, though other tunnels
100<strong>and</strong> shafts can pass through (as presented in sections 5.2.2 <strong>and</strong> 5.3.5). In these casesnecessary engineering actions are taken to ensure long-term <strong>and</strong> operational safety, <strong>for</strong>instance effective grouting <strong>and</strong> ground support. Summarising, the following principlesare followed on repository scale when adapting the repository to <strong>RSC</strong>-I:- bounding lineaments are not penetrated- deposition holes are not located within layout determining features or theirinfluence zones <strong>and</strong> respect distances- deposition tunnels are not planned to penetrate layout determining features ortheir respect distances, although occasionally the tunnels may penetrate therespect distance, in such a case further action needs to considered based on theavailable in<strong>for</strong>mation of the zone <strong>and</strong> its characteristics- other tunnels <strong>and</strong> shafts (except deposition tunnels) can be planned to penetratelayout determining features- other tunnels <strong>and</strong> shafts (except deposition tunnels) can be planned to runparallel right next to the layout determining feature <strong>and</strong> its influence zone <strong>and</strong>respect distance; occasional penetration of the inside the influence zone orrespect distance is allowed- in repository scale layout design, deposition hole locations will be assessedthrough utilisation degree later in 2009Foliation in<strong>for</strong>mation needs to be gathered <strong>for</strong> design purposes. Foliation <strong>and</strong> principalstress orientation will be taken into consideration when designing the direction oftunnels <strong>and</strong> selecting individual deposition hole positions (foliation affects the thermalconductivity). However, from a construction point of view, foliation is not directlyneeded in the classification system.An interim application of the criteria was done to gain in<strong>for</strong>mation in order to determinesuitable areas <strong>for</strong> the requirements of the repository (scale) layout due in 2009. Thiswork included the co-ordination of TARGET <strong>and</strong> DETECT aspects with repositorydesign issues. Coordination ensures that the 2009 layout will be acceptable whencompleted.In the 2009 layout, new in<strong>for</strong>mation on stress field (<strong>Posiva</strong> 2009a) will be considered<strong>and</strong> tunnels will be re-oriented to a direction parallel to the assumed principal stressdirection. These facts <strong>and</strong> drafts have already been presented <strong>and</strong> discussed with thelayout designers <strong>and</strong> the core group of the <strong>RSC</strong>-program.The location <strong>and</strong> uncertainties of defined layout-determining features <strong>and</strong> theirinfluence zones were provided <strong>for</strong> the repository design as a single, combined 3D modelat the end of 2008. From an integrative point of view, it was found advantageous torepresent the layout determining features <strong>and</strong> their respect volumes as integrated solidsrather than representing them as separate modelling objects. Current background data onutilisation degree is readily used (see Section 5.3.5) compared to previously utilisedexpert judgement. This model in<strong>for</strong>mation will be used in the 2009 repository layoutdesign.
101The coordination of TARGET <strong>and</strong> DETECT aspects with repository design issues havebeen found to be a successful <strong>and</strong> straight<strong>for</strong>ward method to work with. For example,quick studies have been drafted <strong>for</strong> different approaches to earthquake related respectdistance. Most of the practical feedback has been applicable to the layout-determining3D-model.6.2 Development needsPhase 1 focused on repository scale issues, which will be adjusted in Phase 2. In Phase2, tunnel <strong>and</strong> deposition hole scales, as well as thermally induced effects, will beconsidered more thoroughly. Rock damages like <strong>for</strong>mation of the excavation damagedzone <strong>and</strong> spalling (also thermally induced spalling) can affect the groundwater flow <strong>and</strong>transport routes in the vicinity of the deposition hole <strong>and</strong> may thus impact the long-termsafety. There<strong>for</strong>e criteria related to rock damage need to be defined. The focus will beon testing the criteria so that they can be applied in practice to make decisions related tothe construction <strong>and</strong> usability of tunnels <strong>and</strong> deposition holes.The location <strong>and</strong> uncertainties of defined layout-determining features, respect distances<strong>and</strong> influence zones will be updated within DETECT-project. These updates will beprovided <strong>for</strong> repository design as in Phase 1. The same applies <strong>for</strong> utilisation degreedata. This in<strong>for</strong>mation will then be used <strong>for</strong> the repository layout-design in 2011. Forexample, there are several uncertain layout-determining fracture zones (BFZ 147 &BFZ148, see Section 5.3.5) in present model, whose existence will be confirmed in thenear future. The coordination of TARGET <strong>and</strong> DETECT aspects with repository designissues will be continued.In situ rock stress values (magnitude <strong>and</strong> orientation) show fairly large scatter.There<strong>for</strong>e, rock stress measurements will be continued in ONKALO with direct stressmeasurements, rock response measurements, <strong>and</strong> tunnel observations during excavation.The objective is to obtain a more accurate underst<strong>and</strong>ing of the stress state whenreaching the main characterisation level. This would result in a less scattered stress/strength ratio <strong>and</strong> a single updated source of measurement results available <strong>for</strong> therepository layout-design in 2011.No classification parameter <strong>for</strong> stress-strength is given in the original HRC <strong>for</strong>thermally affected situations. In Phase 2 of the <strong>RSC</strong> program, the possible need <strong>for</strong> astress-strength parameter <strong>for</strong> thermally affected situations will be considered.It is important to be able to predict the extent to which rock spalling may occur in therepository <strong>and</strong> especially in deposition holes. The prediction is required <strong>for</strong> repositorydesign <strong>and</strong> safety analysis. Rock spalling (failure <strong>and</strong> flaking of the rock at theexcavation surfaces) occurs when the concentrated rock stress around an excavationreaches the rock spalling strength. However, both rock stress <strong>and</strong> rock strength cannotbe specified as single values but rather as distributions. Thus, the assessment of spallinginvolves, first establishing rock stress <strong>and</strong> rock strength values <strong>and</strong> then comparing thetwo <strong>for</strong> the various depths <strong>and</strong> orientations of the repository excavations. Thisassessment needs to cover both excavation-induced <strong>and</strong> thermally-induced spalling(Hakala et al. 2008).To estimate the potential <strong>for</strong> rock damage, the ratio SPALLING/ (spallingstrength secondary stress) could be used. The estimation would take into account tunnel
102orientation in terms of principal stress <strong>and</strong> tunnel shape. Tunnel orientation is anotherdesign issue, <strong>and</strong> is affected by available bedrock resources <strong>and</strong> rock conditions.There are generally two ways to express potential <strong>for</strong> spalling:- data distributions <strong>for</strong> strength (this is quite well known <strong>and</strong> includes foliationin<strong>for</strong>mation) <strong>and</strong> stress are used e.g. with Monte Carlo simulations. The outcomeis spalling probability expressed as a percentage.- mean strength <strong>and</strong> stress values are used. Probability is estimated with the Factorof Safety (FOS).It should be noted that the spalling strength <strong>for</strong> Olkiluoto migmatitic rock is not known,however a plan to conduct an in situ strength test at 370 m does exist to tackle this issue.Also, tunnel observations are continuously per<strong>for</strong>med to obtain additional in<strong>for</strong>mationabout in situ strength.Emplacement of the canisters in the repository causes thermally-induced spalling(Hakala et al. 2008). Estimates of combined stress state around the deposition holes, dueto both in situ stress <strong>and</strong> thermally induced stress, indicate that spalling will occurunless sufficient confining pressure from the bentonite is applied. An active swellingpressure is also required to prevent stress induced spalling in the deposition tunnels <strong>and</strong>central tunnels.Although the practical criteria can only be based on the observation from the conditionwhere the only the impact of the excavation is present, also the thermal evolution <strong>and</strong>thermally induced stresses in stress-strength analyses need to be considered. Assessmentof excavation-induced <strong>and</strong> thermally-induced spalling will be per<strong>for</strong>med <strong>for</strong> the nextrepository design using spalling strength data from the future test at 370 m level.According to the assessment, necessary measures will be determined <strong>for</strong> future layoutdesign. Thermally-induced spalling can be restricted in open tunnels <strong>for</strong> example withthe right tunnel orientation, profile shape <strong>and</strong> proper operation order. TARGET-projectwill determine the acceptable level of spalling <strong>for</strong> backfilled tunnels <strong>and</strong> depositionholes.
1037 CONCLUSIONS AND FUTURE WORKIn the programme <strong>for</strong> research <strong>and</strong> development TKS-2006 (<strong>Posiva</strong> 2006), <strong>Posiva</strong>acknowledges the need <strong>for</strong> further development of requirements on the host rock <strong>and</strong> <strong>for</strong>ensuring their applicability <strong>and</strong> reliability during the actual repository implementation.The Rock Suitability Criteria (<strong>RSC</strong>) programme has been set up <strong>for</strong> this purpose. The<strong>RSC</strong> programme is based on work done in the Host Rock Characterisation (HRC)project (Hagros et al. 2005, Hagros 2006), which produced the preliminary Olkiluotospecificcriteria.The aim of the <strong>RSC</strong> is to develop a classification scheme, which will be applied <strong>for</strong> therepository layout <strong>and</strong> <strong>for</strong> defining suitable rock volumes <strong>for</strong> deposition holes.Classification will be done in stepwise; first defining suitable rock volumes to hostrepository panels, then assessing whether deposition tunnels or tunnel sections aresuitable <strong>for</strong> deposition holes <strong>and</strong> finally, <strong>for</strong> deciding whether a deposition hole isacceptable <strong>for</strong> disposal. The developed criteria should be based on observable <strong>and</strong>measurable properties of the host rock. Supported by interpretation, modelling <strong>and</strong>general underst<strong>and</strong>ing of the site properties, the criteria can then be used to show thatthe per<strong>for</strong>mance targets <strong>and</strong> engineering requirements set on the rock can be fulfilled.This report summarises the work done within the <strong>RSC</strong>-programme related to setting upof the per<strong>for</strong>mance targets concerning the long-term safety <strong>and</strong> engineering targetsconcerning rock constructability. A first version of the rock suitability criteria, <strong>RSC</strong>-I ispresented, as well as its application <strong>for</strong> determining the rock volumes <strong>for</strong> the layoutadaptation.7.1 Main achievementsThe main achievements of the Phase 1 of the programme are discussed below.A methodology <strong>for</strong> deriving host rock requirements has been established. This is basedon deriving long-term safety related criteria, called per<strong>for</strong>mance targets, from safetyfunctions defined <strong>for</strong> the barriers. The per<strong>for</strong>mance targets will <strong>for</strong>m the basis <strong>for</strong>development of the rock suitability criteria necessary <strong>for</strong> deciding on the use of certainrock volumes <strong>for</strong> disposal.All these requirements are continuously developed.Per<strong>for</strong>mance targets <strong>for</strong> the host rock have been defined. Per<strong>for</strong>mance targets considerhost rock properties that affect the function of the host rock as a natural barrier <strong>and</strong> thefunctionality of the engineering barriers. Several per<strong>for</strong>mance targets related tochemical composition of the groundwater, groundwater flow, transport properties <strong>and</strong>thermomechanical stability are defined.Layout determining features <strong>and</strong> their respect distance volume have been defined.Layout determining features are de<strong>for</strong>mation zones that may be potentially unstable;being of extensive length greater than 8 km, having the potential to move either inpresent or future stress field or being hydraulically significant (T higher than 10 -5 m 2 /s).Additionally, features considered unstable or of hydraulical importance based on currentsite underst<strong>and</strong>ing, although not rigorously fulfilling the criteria, can also be defined aslayout determining features. Respect distance <strong>for</strong> these zones is defined to equal the
104influence zone of the structure. Influence zone is generally defined based on directobservations, <strong>for</strong> example increased fracturing or different type of geological,hydrogeological <strong>and</strong> geophysical data. However, if no direct observation is available,influence zone can also be defined based on theoretical scaling laws.The first version of the tunnel scale <strong>and</strong> deposition hole scale criteria, <strong>RSC</strong>-I has beenpresented along with aspects related to practical application of the criteria <strong>and</strong> theclassification process. The link between criteria, <strong>RSC</strong>-I <strong>and</strong> long-term safetyrequirements, per<strong>for</strong>mance targets has been made apparent. These practical criteriaconsider the following rock properties: groundwater salinity, avoidance of the brittlede<strong>for</strong>mation <strong>and</strong> hydrogeological zones <strong>and</strong> their influence zone, FPI (full perimeterintersection) fractures in deposition holes, <strong>and</strong> inflow in the tunnel/deposition hole. It isnoted that the revision of criteria in the tunnel <strong>and</strong> deposition scale is a majordevelopment issue.The rock volumes suitable <strong>for</strong> the hosting repository tunnels, based on the definition oflayout determining features <strong>and</strong> their respect distance volumes, have been produced <strong>for</strong>the layout planning. Experiences of the coordination of the TARGET <strong>and</strong> DETECTaspects with the repository design issues have been a successful <strong>and</strong> straight<strong>for</strong>wardway to work. Most of the feedback has been applicable to the layout-determining 3Dmodel.Layout determining features <strong>and</strong> corresponding respect distance volumes werepresented to the repository design as a combined 3D model. From designer’s point ofview, this single model was an improvement compared to the previous practice ofdelivering layout determining features <strong>and</strong> their respect distances separately. Currentbackground data on utilisation degree can also be utilised instead of previously usedexpert judgement.7.2 Summary of h<strong>and</strong>ling the regulatory requirements in the <strong>RSC</strong>YVL guides are currently being updated. The YVL guide 8.4 will be replaced by theSTUK-YVL guide E.5 as discussed in Section 2.1. Requirements in the new <strong>and</strong> oldguides are to a great extent consistent with each other <strong>and</strong> the presented approachalready partly coheres with new requirements. Examples include definition of the safetyfunctions <strong>for</strong> each barrier, definition of per<strong>for</strong>mance targets related to the safetyfunctions (E.5 4.6 <strong>and</strong> 4.7), taking into account the safety classification in theengineering targets (E.5 5.9), <strong>and</strong> stepwise characterisation <strong>and</strong> identification of suitablevolumes (E.5 5.11, E.5 8.9). The main development needs <strong>for</strong> the <strong>RSC</strong> arising from thenew regulations are related to monitoring <strong>and</strong> production of the documentation required<strong>for</strong> quality assurance <strong>and</strong> acceptance by the regulator. These development needs areconsidered mainly to be an issue of the practical procedure to be applied.A summary of the regulatory requirements that are h<strong>and</strong>led in the <strong>RSC</strong> is given in Table7-1.
105Requirement in the E.5 (Draft 3)4.6 The natural barriers <strong>and</strong> their safetyfunctions may consist ofthe intact <strong>and</strong> stable rock, wheregroundwater flow is limited, around thecanister or other package containing thewastethe host rock where low groundwater flow,reducing <strong>and</strong> even otherwise favourablegroundwater chemistry <strong>and</strong> retardation ofdissolved substances in rock limit themobility of radionuclidesthe containment provided by the host rockagainst natural phenomena <strong>and</strong> humanactions.4.7 Targets <strong>for</strong> the long-term per<strong>for</strong>mance ofthe safety function shall be defined. Thedetermination of the per<strong>for</strong>mance targets shalltake account of changes <strong>and</strong> events that mayoccur during the various assessment periods.The characteristics of the host rock can beassumed to remain in their present state up toan assessment period of several thous<strong>and</strong>years. However the effect of predictableprocesses such as l<strong>and</strong> uplift <strong>and</strong> disturbancesdue to the excavations <strong>and</strong> the waste disposal,shall be taken into account.How h<strong>and</strong>led in the <strong>RSC</strong>Safety functions are defined in accordancewith this requirement. The per<strong>for</strong>mancetargets based on the safety functions havebeen defined <strong>and</strong> they define the conditionswhere the safety functions are likely to be met,taking into account the design solution, thesite properties <strong>and</strong> processes <strong>and</strong> events duringthe site <strong>and</strong> repository evolution. Theper<strong>for</strong>mance targets are related to groundwaterchemistry, groundwater flow <strong>and</strong> transport <strong>and</strong>thermomechnical stability.The rock suitability criteria (<strong>RSC</strong>) in differentscales are defined <strong>for</strong> the locating suitablerock volumes in practice. Particularly byavoiding the major de<strong>for</strong>mation zones <strong>and</strong>significant hydrogeological zones (defined aslayout determining features) <strong>and</strong> theirinfluence zones <strong>and</strong> limiting the groundwaterflow <strong>and</strong> occurrence of large fracture in thedeposition hole contribute to fulfilment of thisrequirement.Per<strong>for</strong>mance targets are defined based on thesafety functions. Definition of theper<strong>for</strong>mance targets considers the mutualcompatibility of the barriers <strong>and</strong> also theevents <strong>and</strong> processes during the site evolutionthat will change these conditions.The practical criteria, <strong>RSC</strong>, are defined, whichwill define the initial state of the system. Thepractical criteria are defined so that this initialstate will contribute to fulfilment of theper<strong>for</strong>mance target in the long-term. There<strong>for</strong>ecriteria consider groundwater salinity,avoiding de<strong>for</strong>mation zones <strong>and</strong> hydraulicallyconductive zones which may lead to changesin the groundwater chemistry or mechanicalinstability. Criteria related to disturbances dueto excavation <strong>and</strong> operation will be consideredin the next phase of the development work.An integral part of the development work isthe evaluation whether the initial state defined
106Requirement in the E.5 (Draft 3)How h<strong>and</strong>led in the <strong>RSC</strong>by the <strong>RSC</strong> criteria provides sufficient bounds<strong>for</strong> the future evolution <strong>and</strong> maintaining thesafety.4.9 Design of the safety functions should aimthat the system as a whole is insensitive tochanges in host rock. Further, the aim is thatno adverse physico-chemical processes mayoccur inside the waste containers nor in thedisposal facilities, or that these processes donot affect significantly the safety functions.4.10 Factors indicating the unsuitability of adisposal site may includeproximity of exploitable natural resourcesabnormally high rock stressespredictable anomalously high seismic ortectonic activityexceptionally adverse groundwatercharacteristics, such as lack of reducingbuffering capacity <strong>and</strong> high concentrationsof substances which might substantiallyimpair the per<strong>for</strong>mance of barriers.4.11 The characteristics of the host rock shallbe favourable with respect to the long-termper<strong>for</strong>mance of the engineered barriers.4.12 The location of the repository shall befavourable with regard to the groundwaterflow regime at the disposal site. The disposaldepth shall be selected with due regard tolong-term safety taking into account thegeological structures <strong>and</strong> the trends in waterconductivity, groundwater chemistry <strong>and</strong> rockstress as a function of increasing depth. Toensure that the effects of above ground naturalphenomena, such as glaciation, <strong>and</strong> humanactivities will be adequately mitigated, therepository shall be located at the depth ofseveral hundreds of metres.Rock suitability criteria define the rockvolumes suitable <strong>for</strong> disposal use so that,de<strong>for</strong>mation zones <strong>and</strong> major hydrogeologicalzones are avoided <strong>and</strong> inflows into depositionhole are limited. All these aim to mitigate thechanges around the deposition hole.Per<strong>for</strong>mance targets <strong>for</strong>ming the basis <strong>for</strong> thecriteria define the range of conditions underwhich the likelihood of adverse processes islimited.These are not explicitly considered in thecurrent criteria as the site selection has beendone. Anyhow, in the iterative development ofthe per<strong>for</strong>mance targets <strong>and</strong> practical criteria,<strong>RSC</strong>, new in<strong>for</strong>mation obtained from the siteis constantly evaluated <strong>and</strong> also checked thatthis requirement is fulfilled.Characteristics of the host rock that affect theper<strong>for</strong>mance of the engineered barriers aretaking into account in setting the per<strong>for</strong>mancetargets <strong>and</strong> thereby in the <strong>RSC</strong>-criteria.Significant hydrogeological zones are definedas layout determining features <strong>and</strong> avoided inlocating the disposal facilities.The repository scale criteria include alimitation of the salinity which affects therepository depth. Limitation on inflows todeposition hole inherently takes into accounttrends in water conductivity.Trend of rock stresses is considered by settingthe engineering target on rock peak strength/insitu stress).
107Requirement in the E.5 (Draft 3)5.11 The structures of the host rock ofimportance to groundwater flow, rockmovements or other factors relevant to longtermsafety, shall be defined <strong>and</strong> classified.Preparedness to change the layout of theunderground facilites in case rock quality issignificantly weaker than the design premiseshas to be maintained.5.9 Safety classification(“turvallisuusluokitus”) of the repositorysystem, structures <strong>and</strong> equipment on the basisof long-term safety should consider layout ofthe repository.5.10 Carrying out a programme <strong>for</strong> research,testing <strong>and</strong> monitoring during construction <strong>and</strong>operation of the repository. This programmeaims to confirm the suitability of the excavatedrooms <strong>for</strong> disposal use, define the rockproperties of importance <strong>for</strong> safety <strong>and</strong>confirm the long-term per<strong>for</strong>mance of thebarriers.6.10 production of the documents <strong>for</strong> thequality assurance of the canister emplacement<strong>and</strong>8.11 acceptance of disposal locations by theregulator.7.9 Construction of the repository should bedone stepwise so that the investigations neededto estimate the suitability of the rock block <strong>for</strong>the disposal <strong>and</strong> classification of the rockstructures of importance <strong>for</strong> the long-termsafety can be carried out.How h<strong>and</strong>led in the <strong>RSC</strong>This is achieved by defining the layoutdetermining features <strong>and</strong> respect distances. Insmaller scales also minor brittle de<strong>for</strong>mationzones <strong>and</strong> large fractures are avoided.The stepwise approach adopted <strong>for</strong> definingsuitable rock volumes <strong>for</strong> disposal use <strong>and</strong>using the <strong>RSC</strong> <strong>for</strong> defining the areas suitable<strong>for</strong> layout is addressing the needs on preparing<strong>for</strong> layout changes.Safety classification is considered as part ofthe engineering targets.The monitoring aspect will be developed inthe <strong>for</strong>thcoming phases of the <strong>RSC</strong>development based on the experiences gainedin the <strong>RSC</strong> demonstration at the repositorydepth. Preliminary plans <strong>for</strong> monitoring inconnection of the demonstration of <strong>RSC</strong> inONKALO demonstration facilities have beenpresented (Anttila et al. 2009).This will be considered as part of the practicalapplication of the <strong>RSC</strong> system <strong>and</strong> needs to bedeveloped during the late phases of thedevelopment work.Rock suitability criteria are based on astepwise approach. Development of the <strong>RSC</strong>includes identifying the needed investigations<strong>and</strong> co-ordination of these with the design <strong>and</strong>excavation works. This will be tested duringthe demonstration of the criteria indemonstration facilities in ONKALO.7.3 Future workThe next steps of the <strong>RSC</strong> programme include testing suggested criteria in theONKALO access tunnel <strong>and</strong> proposed investigation niches. Tests aim at assessingapplicability of the rock characterisation <strong>and</strong> classification procedure <strong>and</strong> methods priorto reaching the disposal depth. Later a demonstration of the classification procedure will
108be carried out at repository level (Anttila et al. 2009). Also, degree of utilisation is beingestimated by applying the proposed criteria on to site models (fracture network modelsbased on geological <strong>and</strong> hydrogeological data) <strong>and</strong> evaluating available data from theONKALO tunnel, site model <strong>and</strong> tunnel. Evaluation of the criteria <strong>and</strong> its indications<strong>for</strong> safety assessment will be carried out. Feedback from the layout design will begathered. All this in<strong>for</strong>mation will be utilised in the iterative development process of theper<strong>for</strong>mance <strong>and</strong> engineering targets <strong>and</strong> the <strong>RSC</strong>-criteria. Plans <strong>for</strong> the next phase ofthe programme will be presented in the TKS-2009 programme.In the following, conclusions <strong>for</strong> the future phases of criteria development aresummarised.Development of the deposition hole criteria, <strong>RSC</strong>-IIA key task is the revision of preliminary criteria <strong>RSC</strong>-I, developed during the Phase 1 ofthe <strong>RSC</strong>-programme. The <strong>RSC</strong>-II criteria development will concentrate on depositionhole scale criteria, which will guide the selection of the deposition hole locations alongthe tunnel <strong>and</strong> the acceptance of the hole <strong>for</strong> disposal use. In revising the criteria,attention has to be paid specifically to:exploring the need <strong>and</strong> potential of setting criteria in deposition hole <strong>and</strong> tunnelscale related to thermal <strong>and</strong> mechanical stability of the rock. Excavation of therepository <strong>and</strong> the spent fuel will cause mechanical <strong>and</strong> thermal disturbances, adevelopment of EDZ <strong>and</strong> (thermal) spalling, to surrounding rock. Due to thesedisturbances, it is possible that flow paths <strong>for</strong>m at buffer/rock <strong>and</strong> backfill/rockinterface, which can affect per<strong>for</strong>mance of buffer <strong>and</strong> weaken transportresistance. Stability issues are also of importance from a rock engineering <strong>and</strong>operational safety point of view. They will, to a great extent, be h<strong>and</strong>led <strong>and</strong>controlled by design <strong>and</strong> engineering means, <strong>for</strong> example excavation techniques<strong>and</strong> orientation <strong>and</strong> spacing of tunnels <strong>and</strong> deposition holes. At the present stage,it remains an open question as to what extent these effects can be mitigated byselecting suitable location of the deposition holes. This uncertainty is due to lackof data <strong>and</strong> observations of rock responses at relevant depths. Investigations onrock mechanics properties <strong>and</strong> spalling strength are planned in the ONKALOinvestigation niche at a 370 m level (<strong>Posiva</strong> 2009b). These experiments <strong>and</strong> anyother in<strong>for</strong>mation on potential rock damages along the ONKALO (see e.g.Hakala et al. 2008) are of high interest <strong>for</strong> development of tunnel <strong>and</strong> depositionhole scale criteria concerning stability of the rock.new in<strong>for</strong>mation obtained on the per<strong>for</strong>mance of the engineered barrier.Rational <strong>for</strong> inflow <strong>and</strong> salinity requirements is mainly related to buffer <strong>and</strong>backfill per<strong>for</strong>mance, which will remain a subject of main research ef<strong>for</strong>ts. Thisnew in<strong>for</strong>mation may dem<strong>and</strong> new requirements concerning chemistry <strong>and</strong>revision of existing criteria. Potential <strong>for</strong> high pH waters at the deposition holesmust also be considered.assessing whether current preliminary criteria need to be revised <strong>and</strong> if sorevise them. The current criteria suggest limiting salinity, avoiding brittlede<strong>for</strong>mation <strong>and</strong> hydrogeological zones <strong>and</strong> their influence zone(s), avoidingintersections of large fractures, <strong>and</strong> limiting inflow in(to) deposition holes.While such criteria will certainly be part of the final <strong>RSC</strong>, the precise<strong>for</strong>mulation will be revisited in order to ensure that 1) they are efficient in terms
109of ensuring a safe repository <strong>and</strong> 2) they are economical in the sense thatpotential deposition tunnels <strong>and</strong> deposition holes are not unnecessarily excluded.Prediction of the host rock propertiesEssential <strong>for</strong> the application of <strong>RSC</strong> is to have good predictive capability of rockproperties at different scales. Prediction/outcome (P/O) studies have been carried out aspart of site descriptive modelling (e.g. <strong>Posiva</strong> 2009a). Predictions of geologicalproperties, rock stability <strong>and</strong> both hydrogeological <strong>and</strong> hydrogeochemical impacts ofONKALO construction are made. In general, there is a good to fair agreement betweenpredictions <strong>and</strong> outcomes (<strong>Posiva</strong> 2009a), <strong>and</strong> thus confidence in the modellingcapability of, <strong>for</strong> example, de<strong>for</strong>mation <strong>and</strong> hydrogeological zones on site scale.However, prediction/outcome studies need to be developed <strong>for</strong> purposes of the <strong>RSC</strong>procedure. The development includes:resolution of the predictions. Predictions can be made both on stochastic <strong>and</strong>deterministic bases along with in<strong>for</strong>mation from pilot holes, tunnels <strong>and</strong>deposition holes. Predictions will account <strong>for</strong> properties considered in thecriteria, these being de<strong>for</strong>mation <strong>and</strong> hydrogeological zones in different scalesdown to single extensive <strong>and</strong> well conductive fractures, as well as distribution ofthe inflow along the tunnel <strong>and</strong> to a deposition hole. Better estimates of salinitydistribution <strong>and</strong> expected maximum salinity at repository level are needed.However, when predicting conditions related to groundwater, inflows <strong>and</strong>salinity, it is also important to consider the disturbance created by construction<strong>and</strong> whether data obtained both during testing <strong>and</strong> at the time of accepting adeposition hole are relevant in relation to the long-term safety. Stochasticpredictions can be used to estimate the degree of utilisation <strong>for</strong> certain a rockvolume or tunnel. Deterministic prediction should be possible using in<strong>for</strong>mationfrom the nearby tunnels, holes <strong>and</strong> pilot hole. Tools <strong>and</strong> methods will bedeveloped <strong>for</strong> predictive modelling <strong>and</strong> presentation of the acquiredinvestigation data in the scales (tunnel <strong>and</strong> deposition hole) relevant to practicalapplication of the classification procedure.enhancing the agreement of data obtained from the pilot hole with thecorresponding tunnel section. There are discrepancies between certain data, <strong>for</strong>example fracture frequency obtained in the pilot hole compared to that observedin the tunnel wall. The observed differences are most likely related to scale ofobservations. Better underst<strong>and</strong> of the relationship between pilot hole data <strong>and</strong>properties mapped in the tunnel is needed. Furthermore, techniques to predicttunnel scale properties from pilot hole mapping <strong>and</strong> measurements needs to bedeveloped.Identifying the measurement techniques <strong>and</strong> proceduresEssential <strong>for</strong> <strong>RSC</strong> application is to identify the relevant measurement, interpretation <strong>and</strong>modelling techniques <strong>for</strong> each criterion. Related to this is the development of workingprocedures <strong>and</strong> co-ordination with tunnel excavation work. The focus of thisdevelopment work is on:identifying suitable characterisation techniques <strong>and</strong> procedures. These focus onsmall scale de<strong>for</strong>mation zones <strong>and</strong> single fractures with extensive size or of
110hydraulical importance that should not be penetrated by a pilot/tunnel or adeposition hole,evaluating the predictive capability of characterisation methods, especiallyin<strong>for</strong>mation gained from the pilot hole compared to tunnel observations, <strong>and</strong>measurement of inflows.A specific issue to be considered is disturbed conditions caused by excavation, whichresults in EDZ, spalling, high pH waters, <strong>and</strong> their impact on measurement results.Evaluation of the effectiveness <strong>and</strong> the economy of the <strong>RSC</strong> (taking into accountsite evolution)The applicability of the <strong>RSC</strong> with respect to long-term safety needs to be evaluated.This work will include studies of the potential evolutionary paths given the initial statedefined by the <strong>RSC</strong> <strong>and</strong> assessment of whether deviations out of the boundaries set <strong>for</strong>the mechanical <strong>and</strong> thermal disturbances or the hydrogeological, hydrochemicalconditions will occur. If this is not the case, it can be expected that the EBS retains itsper<strong>for</strong>mance <strong>and</strong> that transport is limited. This evaluation needs to be carried out inclose co-operation with the scenario development as part of safety case compilation.Similarly, it is important to assess to what extent the <strong>RSC</strong> rejects potential depositiontunnels <strong>and</strong> deposition holes. If too many are unnecessarily rejected, it will be exploredwhether slight alterations of the criteria would enhance economy without beingdetrimental to safety.Conclusions related to site characterisation <strong>and</strong> modellingIn addition to the above discussion on feedback to current site characterisation <strong>and</strong>modelling, the following conclusions can be drawn <strong>and</strong> need to be considered inupcoming site characterisation activities:Confirming studies of certain layout determining features; the existence <strong>and</strong>properties of bounding lineaments; de<strong>for</strong>mation zones in the eastern area; <strong>and</strong>existence <strong>and</strong> extension of brittle de<strong>for</strong>mation zones BFZ147 <strong>and</strong> BFZ148.Obtaining more site specific data <strong>for</strong> influence zone definition. For this purpose,the influence zone of de<strong>for</strong>mation zones in the tunnel will be studied, surface<strong>and</strong> tunnel data on the influence zones will be compared with each other <strong>and</strong>underst<strong>and</strong>ing of the location of observed geophysical anomalies with respect tocore of the zone will be evaluated. Data needs to be collected <strong>for</strong> both large scalefeatures <strong>and</strong> smaller scale features affecting the suitability of certain tunnelsections.Further studies on relation of the foliation <strong>and</strong> alteration to rock mechanicalproperties <strong>and</strong> stress <strong>and</strong> thermally induced failures. This in<strong>for</strong>mation is neededas background <strong>for</strong> developing potential criteria concerning rock stability intunnel <strong>and</strong> deposition hole scales.
111Conclusions related to design <strong>and</strong> safety caseThe main topics related to design <strong>and</strong> safety are excavation <strong>and</strong> thermally induced rockdamage, as well as studies on per<strong>for</strong>mance of the buffer <strong>and</strong> backfill takingemplacement procedures into account. Considering the rock damage, studies are relatedto extent of the excavation <strong>and</strong> thermally-induced rock damage <strong>and</strong> ways to mitigate theimpact of such damage on long-term safety <strong>and</strong> on operational safety in the opentunnels.Considering the buffer <strong>and</strong> backfill, although there are alternative materials that willmeet the per<strong>for</strong>mance targets, there are still open questions related to emplacement ofthe buffer <strong>and</strong> backfill <strong>and</strong> the emplacement procedure. The necessary conditions <strong>for</strong> theemplacement may pose requirements also on host rock.Based on experiences from the first phase of the programme, there is still need todevelop procedures, submit input data from the <strong>RSC</strong> process to the design <strong>and</strong> aligninvestigations with the excavation.
112
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