Olkiluoto Biosphere Description 2006 (pdf) (4.1 MB) - Posiva

6Principles of Safety CaseFirst, the purpose and context of the Safety Case should be made clear and the overallsafety strategy presented. This includes strategies for the siting, design and implementationof the repository as well as the strategy for performing safety assessments (Vieno &Ikonen 2005). Next, the information and analysis tools for safety assessment must bedescribed. These are collectively termed the "assessment basis", and include:The system concept, which is a description of the repository design including theengineered barriers, geologic setting and its stability, how both engineered andnatural barriers are expected to evolve over time, and how they are expected toprovide safety.The scientific and technical information and understanding, including the detailedsupport for the expected evolution and safety of the disposal system andassessments of the uncertainties in scientific understanding.The analysis methods, computer codes and databases that are used in themodelling of the disposal system.The adequacy and reliability of the assessment basis for carrying out safety assessmentsmust also be addressed as a part of the safety case (Vieno & Ikonen 2005, Ikonen 2006).Lastly, a synthesis will be made that draws together key findings from the safety case,namely the principal evidence, analyses and arguments that quantify and substantiatea claim that the repository is safe, including an evaluation of uncertainty. This judgementis a statement of expert confidence in the safety of the disposal system recognisingthat this is expected to increase over the time of the repository development programmein the context of the assessment basis available at the current stage of the repositoryprogramme (Vieno & Ikonen 2005).Posiva Safety Case PortfolioTo benefit from the advantages of long site investigation programme and close cooperationwith the parallel programme of Swedish Nuclear Waste Management Co (SKB),and to facilitate the flexible, and gradual development of the Safety Case, a portfolioapproach will be employed in the reporting of the Safety Case. In practice, this impliesthat the main components of the Safety Case will be living, fairly independent reportsbased on supporting technical reports. At the various milestones of the programme (e.g.,interim reporting in 2006 and 2009, and the PSAR in 2012), the reports will be linkedand complemented to a Safety Case by means of additional analyses and a summaryreport (Vieno & Ikonen 2005).The Safety Case Portfolio will be compiled from a number of main reports (Vieno &Ikonen 2005) as illustrated in Figure 1-2. It is especially important to notice that thegeo-scientific and scientific reports aim to be as realistic as possible, whereas the radiationsafety-related reports are required to be conservative by the regulations.