Experience of the JCO criticality accident

JCO臨界事故の経験

外池 幸太郎 

Tonoike, Kotaro

JCO臨界事故は1999年9月30日午前に発生し、臨界状態が19時間半にわたって継続し、総核分裂数は2.510に達した。重篤な放射線障害による2名の死者を生じた日本で最初の臨界事故である。この臨界事故に際して、核燃料物質の臨界性の判断は比較的容易であったが、一方で、公衆の避難行動の判断には困難を伴った。本発表では、事故に際してのこれらの判断を振り返る。

The JCO criticality accident occurred in the morning of September 30, 1999, where the critical condition continues for 19.5 hours and the total fission number reached 2.510. This was the first criticality accident in Japan that resulted in two fatalities due to their severe exposures to radiation. During the accident, the assessment and prognosis on the criticality of nuclear material was relatively easy. The planning and implementation of the public evacuation was, however, difficult. This presentation summarizes judgements and their processes in the day on those issues.