福島第一原子力発電所事故に関する5つの事故調査報告書の レビューと技術的課題の分析: 事故の進展と原因に焦点を当てて

摘要

本報では，炉心損傷とその後の放射性物質の放出に至った1～3号機における事故の進展と原因に着目し，技術的な側面から，5つの事故調査報告書をレビューし，それぞれの調査結果における見解の相違等について分析，整理するとともに，これらの報告書において十分な議論がなされていない課題等を明らかにした。以下では，事故調間で見解が異なるか，それらの見解に対して異論のある事項についてまとめる。%On March 11，2011, the Tohoku District-off the Pacific Ocean Earthquake and the subsequent tsunami resulted in the severe core damage at TEPCO's Fukushima Dai-ichi Nuclear Power Station Units 1-3， involving hydrogen explosions at Units1，3， and 4 and the large release of radioactive materials to the environment. Four independent committees were established by the Japanese government, the Diet of Japan, the Rebuild Japan initiative Foundation, and TEPCO to investigate the accident and published their respective reports. Also, the Nuclear and Industrial Safety Agency carried out an analysis of accident causes to obtain the lessons learned from the accident and made its report public. This article reviews the reports and clarifies the differences in their positions, from the technological point of view, focusing on the accident progression and causes. Moreover, the undiscussed issues are identified to provide insights useful for the near-term regulatory activities including accident investigation by the Nuclear Regulation Authority.