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.