放射性廃棄物の余裕深度処分における埋設深度の妥当性評価の考え方について

摘要

This paper describes the objectives and specific applicational issues of the document authorized by the Nuclear Safety Commission entitled "Policy of the safety assessment of subsurface disposal after the period for active control", focusing on the policy of assessment for the appropriateness of burial depth. Concerning the burial depth of subsurface disposal, the proposal of 50-100 m from the surface has been made by the Atomic Energy Commission as a sufficient depth to avoid general usage of the underground environment, furthermore, taking into account these circumstances, the above document stipulates the new policy of assessment for the appropriateness of burial depth considering uplift/erosion noted in the safety assessment for long-lived radioactive materials. In the case of considering uplift/erosion, the isolation from the living environment planned in the original scheme will be gradually lost, the disposal facility will come close to the surface and become near-surface disposal in the long term. This paper describes the required roles of burial depth for subsurface disposal considering the long-term evolutional changes, introduces the physical protection capability to human intrusion as one of the protective functions of engineered barriers, and discusses the specific important issues related to the actual application.%余裕深度処分の概念は，公衆の安全を確保することおよび将来世代に負担を残さないという観点も踏まえ，処分場跡地については，一般的であると考えられる土地利用が制約されないようにする概念として誕生した。北欧においては，地下数十mの深度に低?中レベル放射性廃棄物を埋設する施設はすでに操業中であるが，一般的な地下利用に対して十分な余裕を取った深さに放射性廃棄物を埋設することを明確に述べた余裕深度処分の概念は，日本固有の概念である。