HUMAN FACTOR ANALYSIS ON CRITICALITY ACCIDENT

At 10:35 am local time (01:35GMT), September 30 , 1999, a criticality accident occurred in a conversion building of a uranium processing plant of JCO Company Limited in Tokai-mura, Ibaraki prefecture in Japan during a job to make uranium solution. 150 people were exposed to the radiation. One of three workers who have engaged in the job and exposed to a massive dosage of radiation died of multi organ failure on 83 days after the accident, becoming the first such causality in Japan. A Japanese Governmental Investigation Committee under the Nuclear Safety Commission conducted investigation focusing on causes of this accident. Ibaraki Prefectural Police are also seeking criminal charges. These investigations have revealed that a deviation from a government-authorized processing method and a negligence of its illegal procedure manual, etc. had contributed to the accident. This accident broke the people’s trust in the nuclear industry. The authors analyse causes of this accident from the viewpoint of human factors with focusing on two behavior. One is “pouring some 16kg-U with an enrichment of 18.8% to the precipitation”. The other is “using the modified procedure manual which describes the dissolution of uranium oxide powder with nitric acid in stainless steel buckets”. From the analysis, the authors find some latent factors behind this accident. This paper summarizes what had been happening in the uranium processing plant and the results of the author’s analysis.