KOSEN 한인과학기술자네트워크

The NEA Performance Assessment Advisory Group (PAAG) set up the Working Group on Integrated Performance Assessments of Deep Repositories (IPAG) in 1994. The overall aim of the IPAG is to provide a forum for safety cases and their wupporting integrated performance assessment (IPA) studies. The work is carried out in several phases where the membership and tasks of the group change between phases. In the first phase [NEA 1997], the goal was to examine recently completed IPAs as a practical body of evidence that would indicate the current status of PA and could shed light on possible improvements for future studies. In the second phase [NEA, 2000-a], the goal was to examine the experience of peer review of IPAs, and especially reviews performed in support of regulatory assessment, from both the implementer and regulator points of view. The third exercise, named IPAG-3, is documented in this report. IPAG-3 was carried out mainly between June 1999 and November 2000. The group evaluated the approaches and arguments that have been used to establish and communicate confidence in safety and the overall results of IPAs. The objectives of IPAG-3 were to evaluate the state of the art for obtaining, presenting and demonstrating confidence in long-term safety, and make recommendations on future directions and initiatives for improving confidence. Twenty national organisations participated in Phase 3, where each had either carried out or reviewed a recent safety case or IPA. As in the previous phases, a questionnaire was used to focus the discussion. The main text describes the findings of IPAG-3 with regard to (i) setting the stage for making confidence arguments, and (ii) developing and documenting confidence arguments. The report also presents some final considerations including a comparison of the findings of IPAG-3 with those from previous phases and other NEA initiatives [NEA, 1999]. The IPAG-3 questionnaire and a compilation of the answers to the questionnaire are provided in appendices to this report. Summary observations and recommendations from IPAG-3 are presented below. Where recommendations are made, these are addressed primarily to organisations carrying out or reviewing safety cases and IPAs. The development of a deep geologic repository is characterised by several decades for completion. The long duration of this process reflects the novelty and complexity of the tasks of elaborating a repository concept as well as the sensitivity of such projects in society, and the desire to proceed by cautious steps with due regard to technical issues and social acceptance. At the end of each development stage a decision is taken whether to move forward, and whether the requirements for the next development stage need to be adjusted. It is important to communicate, for each development stage, the basis for the current level of confidence, and clearly indicate the strategy for resolving the outstanding issues.