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

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 and retardation ofradionuclidesFAVOURABLE, PREDICTABLE BEDROCKAND GROUNDWATER CONDITIONSSUFFICIENT DEPTHWELL-CHARACTERISED MATERIALPROPERTIESROBUST SYSTEM DESIGNOutline of safety concept for a KBS-3 type repository for spent fuel in acrystalline bedrock (adapted from Posiva 2003). The safetyconcept is based on a robust system design. Red pillars and blocks link safety featuresof the disposal system on which safety primarily depends to the overall goal of thesafety concept (safe disposal). Green pillars and blocks indicate secondary safetyfeatures that may become important in the event of radionuclide release from a canister.The functions of different barriers and 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 and containment (Vieno & Ikonen 2005, Posiva2006, Posiva 2008), the role of the geosphere is mainlyto isolate the repository from the biosphere and normal human habitat (suitabledepth),to protect the engineered barriers from potentially detrimental processes andchanges of conditions taking place above and near the ground surface,to provide favourable and predictable mechanical, geochemical andhydrogeological conditions for the engineered barriers, andto limit and retard inflow and release of harmful substances to and from therepository.