Abstract
The first criticality accident in Japan occurred at Tokai plant of "JCO Company" located in Tokai-mura, Ibaraki Prefecture. The causes and consequences of the accident were examined from the viewpoint of an old-fashioned nuclear chemist. JCO Company is a subsidiary of "Sumitomo Metal and Mining Company", and the number of employee was about 150. The accident occurred due to the lack of safety consideration in the handling of concentrated aqueous solution of dangerous enriched uranium. Workers poured too much amount of the solution in a cylindrical vessel whose shape is easy to reach criticality. After careful inspection of the documents and manuscripts supplied, I consider that "Science and Technology Agency", "the Japan Cycle Development Institute" and "Sumitomo Metal and Mining Company" as well as JCO Company were responsible concerning the causes of the accident.
