Abstract
The second progress report, H12, documented research and development progress for the high-level waste disposal made since the publication of the earlier the first progress report (H3) in 1992. The concept of geological disposal in Japan is similar to that considered in other countries, being based on a system of multiple passive barriers consisting of the geological environment and an engineered barrier system. The disposal system considered is generic, in the sense that no single rock type and no siting area have so far been identified. H12 performance assessment provided a test for the robustness of the system concept based on intentional siting and design, taking account of a wide range of Japan's geological environment. The assessment included a comprehensive evaluation of uncertainty and potentially detrimental factors, including perturbations due to external events and processes. Despite the considerable uncertainty at the current stage of the Japanese program, a safety case that is adequate for the aims of the assessment can be made by a strategy of employing conservatism where there is uncertainty and stressing the reliability and effectiveness of the performance of the near field. The aim of this paper is to summarize arguments that should build confidence in the findings of the H12 assessment.
