Japans worst nuclear radiation accident took place at a uranium reprocessing facility in Tokaimura northeast of Tokyo on 30 September 1999. The direct cause of the accident was cited as the depositing of a uranyl nitrate solutioncontaining about 16.6 kg of uranium which exceeded the critical massinto a precipitation tank. Three workers were exposed to extreme doses of radiation. Hiroshi Ouchi one of these workers was transferred to the University of Tokyo Hospital Emergency Room three days a