JCO criticality accident termination operation

Kanamori, Masashi

The JCO criticality accident occurred at about 10:35 A.M. on September 30, 1999 in Tokai-mura, Ibaraki Prefecture, Japan. This year (2009) is full 10 years from that truly unfortunate accident. I was then the manager of safety section of Japan Nuclear Cycle Development Institute (JNC) Tokai Works, and engaged in the operation of the criticality accident termination in JCO sites as an expert of the disaster prevention of national government. This report is summarized the circumstances surrounding termination of the JCO criticality accident based on testimony in the Mito District Court in 2001. Since then, comments have been received and I rewritten in this tenth year with my thought not to have to forget the accident. We hope that this report will be useful in some way in preventing nuclear disaster in the future.