Baldwin TD and Hicks TW, Assessment Calculations for Human ...

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0977-6Version 1Table 6.4Summary maximum calculated doses for short-duration intrusionevents for inventory Case B.Case BMaximumdose (mSv)Location(cells)Time ofmaximum(year)B1aDrilling(5 boreholes)B1bTrial pit(20excavations)B1cLaboratoryanalysis(25 samples)B3aConstructionC2Materialrecovery7.4 x 10 -4 2.4 x 10 -4 5.5 x 10 -4 2.5 x 10 -3 9.9 x 10 -4Vault 15(C10)Vault 20 (E11) Vault 15(C10)Vault 20 (E11) Vault 15(C10)2230 2230 2230 2230 2310Key pathway Inhalation Externalirradiationand inhalationDominantradionuclide(s)239 Pu and240 Pu94 Nb, 239 Pu and240 PuInhalation239 Pu and 240 PuExternalirradiation94 NbInhalation andexternalirradiation239 Pu and 94 NbTable 6.5Summary maximum calculated doses for longer-term intrusionactivities for inventory Case B.Case BMaximum annual dose(mSv)B3bHouse occupancyB7SmallholdingC1Scavenging0.24 4.7 1.1 x 10 -3Location (cells) Vault 15 (C10) Vault 17 (E10) Vault 15 (C10)Time of maximum(year)2230 2230 2310Key pathway Radon Ingestion (plants andgoat’s milk)Dominantradionuclide(s)222 Rn (from decay of226 Ra and 234 U)14 C and 36 ClInhalation and externalirradiation239 Pu and 94 NbGalson Sciences Ltd 46 21 March 2011
0977-6Version 17 ConclusionsAssessment calculations have been undertaken of the potential radiological hazardpresented by the LLWR if humans should inadvertently intrude into the facility in thefuture when controls on the site have lapsed or cease. The dose to intruders, or siteoccupants following intrusion, has been calculated using a GoldSim implementationof a human intrusion model for a range of possible intrusion events and potentialexposure pathways. Calculations for a Reference Disposal Area involving the LLWRtrenches and vaults up to the construction of Vault 14 have been reported by Hicksand Baldwin (2011). This report provides calculations for an Extended Disposal Areainvolving extra waste capacity in Vaults 15 to 20.The assessment calculations have been undertaken in support of a demonstration – tobe documented in the 2011 ESC – that the facility meets Requirement R7 of theNS-GRA. According to Requirement R7, the dose to any person during and afterassumed intrusion should not exceed a guidance level in the range of around3 mSv/year to around 20 mSv/year. Values towards the lower end of this range areapplicable to assessed exposures continuing over a period of years (prolongedexposures), while values towards the upper end of the range are applicable to assessedexposures that are only short term (transitory exposures).A representative range of possible human intrusion events has been considered for theassessment based on present-day technologies and credible future uses for the site.The identification of intrusion events derives from a substantial body of work onhuman actions undertaken in support of the previous safety case for the LLWR,including expert elicitations and consideration of possible site uses. This process hasresulted in the identification of geotechnical investigations, a housing developmentand a smallholding as requiring quantitative assessment.In addition, human intrusion events have been considered that are associated withactivities that might occur in the period during which the site is being eroded by thesea and access to the in situ waste would be possible from the beach. Coastal erosionis expected to begin to erode the disposal facility on a timescale of a few hundreds tothousands of years after present; this will reveal wastes and engineered barriermaterials, which could become targets for casual interest or exploitation. Therefore,the dose to individuals involved in activities to examine or extract materials from theeroding facility has also been evaluated.Assessment calculations take account of information on the vault waste inventoriesfor the EDA and the engineered cap design for the closed facility:• Two alternative EDA vault inventory cases have been evaluated based ondifferent assumptions about future waste arisings and management of LLW inthe UK: the Case A inventory includes LLW from Stage 3 reactordecommissioning; Case B includes solid LLW associated with new buildconstruction, operation and decommissioning. Calculations for the trenchesand vaults of the RDA have not been reproduced.Galson Sciences Ltd 47 21 March 2011
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