Lessons Learnt from Staged Dry Run of Performance Assessment and Repository Design

Nuclear Waste Management Organization of Japan (NUMO) has proceeded with repository siting, since 2002, based on an “open solicitation procedure”. While waiting for volunteer municipalities and having no specific site geological information, NUMO has been preparing for expected assessments and designs at the investigation stage. One of the efforts for preparation is the dry run using hypothetical site information. This paper introduces lessons learnt through this dry run. Introduction Nuclear Waste Management Organization of Japan (NUMO), the implementer of Japanese HLW geological disposal, has proceeded with repository siting, since 2002, based on an “open solicitation procedure”. And it proposes stepwise investigations to find the final repository: the literature survey (LS) stage, the preliminary investigation (PI) stage and the detailed investigation (DI) stage. While waiting for volunteer municipalities and having no specific site geological information, NUMO has been preparing for expected assessments and designs at these investigation stages. One of the efforts is a dry run using hypothetical site information as a hands-on training mainly for safety assessment and repository designing. It does not only train NUMO staff but also brings various suggestions to the investigation planning and R&D strategy. And dry runs of the hypothetical sites of various geoenvironment such as mountainous site, costal site, crystalline rock, sedimentary rock etc. also enable us to brainstorm the way to build a safety case and a repository concept for generic and specific sites. This paper shows suggestions to investigations and further R&D from the viewpoint of designing panel layout. The design of panel layout is one of the most important decision-making processes at the early stage of the repository designing because the location of panel directly affects the decision of locations of the following investigations. Especially the decision of panel layout in the surface-based investigation stage is very important, since the change of the location of panel after the detailed investigation stage using the underground facility would be extremely inefficient and would cause significant environmental disturbance. Firstly, we briefly introduce the method of design of panel layout. And then, it is applied to the hypothetical site based on the stepwise dataset that corresponds to the NUMO stepwise approach of repository siting. And finally, suggestions to investigations and further R&D are presented through the discussion. In the dry run, we create hypothetical site dataset by modifying a set of investigations of an actual civil engineering project.