RSC-Programme - Interim Report. Approach and Basis for - Posiva

42fulfillment of the performance 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.Performance targets for 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 and intrusion ofglacial melt waters, thus affecting many performance targets related to chemicalcomposition of the groundwater. These high groundwater flow zones provide hardly anytransport resistance and should therefore be far enough from the deposition holes.Another reason for defining a zone as layout determining is to find the potential offuture (post glacial) zone faulting. The project of layout determining features andrespect distances concerns mainly the following performance targets and their limitvalues. Hence only consideration of layout determining features and respect distancevolumes is insufficient to fulfil these performance 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 for 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 thousand 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 performance targets for long-term safety of therepository. This volume is called respect distance volume. Defining respect distance fora layout determining feature demands an intermediate step, which is establishing aninfluence zone for the feature. Respect distance should be large enough to set a safeenvironment for disposal, taking into account the uncertainties in location and propertiesof the layout determining features. On the other hand, 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 bydeformations and are also less competent for 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 and 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.