A stepwise site selection process has been adopted for geological disposal of HLW in Japan. Literature surveys, followed by preliminary investigations (PI) and, finally, detailed investigations in underground facilities will be carried out in the successive selection stages. In the PI stage, surface-based investigations such as borehole surveys and geophysical prospecting will be implemented. In order to conduct the PI appropriately and efficiently within a restricted timeframe and budget, planning and management of PI are very important. NUMO therefore compiled existing knowledge and experience in the planning and managing of investigations in the form of manuals to be used to improve and maintain internal expertise. The first editions of the two manuals were prepared on the basis of experience overseas, and then they were revised by taking geological environment, laws and regulation in Japan into consideration. This paper introduces the procedure of PI planning using the manual as well as the results of the dry-run, with the Yokosuka area as a hypothetical PI area, where the demonstration study is under way. Based on the dry-run, applicability of the manual is checked and, at the same time, further revisions are made to improve the content.

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