On Sept. 30, Japan commemorated the first anniversary of its worst nuclear disaster since the inception of its nuclear power industry. Tokaimura, approximately 150 km northwest of Tokyo, experienced a criticality accident around 10:30 a.m. when employees of JCO Co., a subsidiary of Sumitomo Metal Mining Company Limited, poured 16 kg of uranium into a purification tank containing nitric acid, instead of the 2.3 kg normally used.
Three workers were critically injured -- Hisashi Ouchi, Masato Shinohara and Yutaka Yokokawa -- and dozens more were irradiated, albeit at a lower degree. Ouchi and Shinohara both subsequently died as a result of complications of acute radiation exposure, while Yokokawa still is confined due to massive irradiation.
Two prominent reports have surfaced in the accident's aftermath. The International Atomic Energy Agency, a United Nations specialized agency, released its findings in a report published November 1999, while Japan's Nuclear Safety Commission released its report in December 1999. The IAEA report reiterated the agency's conclusion that the accident presented no significant off-site risk. The NSC report further validates the limited impact of the criticality accident on the residents of Tokaimura.