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

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) andOlkiluoto site characteristics. The research, development and technical design of a spentnuclear fuel repository is an iterative process. Main components of the developmentprocess are site characterisation, technical design, safety and performance 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 and safety criteria set by authorities guiding the implementation of a spent fuelrepository. Lower levels include technical requirements for the disposal system and itscomponents.Figure 3-1 shows how the safety and performance assessment (sub-project TARGET),site characterisation (sub-project DETECT) and technical design (sub-project DESIGN)are integrated in order to define suitable rock volumes and locations for disposal use.According to general principle, requirements within the RSC-programme are alsodefined at different levels. The aim is to increase transparency and clarify the logicbehind different requirements and criteria. Documentation of the rational behind thedifferent requirements and criteria is important during the iterative process ofdeveloping the criteria. Such documentation helps to assess which part of therequirements and criteria need revision in case of design changes, new information fromthe site or performance of the barriers, or new safety assessment results. The basis forthe definition of the requirements is the function of host rock as a natural barrier, thesafety function of host rock. Performance targets considering rock properties ofrelevance for long-term safety and engineering targets regarding constructability aredefined separately from practical RSC-criteria, based on current site data and models.Figure 3-1 also shows information delivery of the results of Safety Case and layoutdesign criteria development, as well as depicting criteria testing and evaluationprocesses and feedback loops.An integral part of the implementation process is to show that set requirements will bemet. Hence, observable and measurable properties of the host rock that contribute to thelong-term safety of the repository need to be defined. A central goal of the RSCprogramme has been to clarify this link between the practical criteria and 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 for example in theterminology used. The role of the RSC-programme, to communicate requirements andfeedback from the safety case to site characterisation and layout design, is described inthe revised safety case plan (Posiva 2008) and shown in Figure 3-1.