Estimation of radiation doses by determining radionuclides produced in heavily exposed patients of the Tokai-mura critically accident.

On September 30, 1999 three workers were carrying out a purification procedure in the uranium conversion building of JCO Company Limited, Tokai-mura, which resulted in the criticality accident. They had mixed uranium oxide powder (enrichment of 235U: 18.8%) with nitric acid and were pouring the solution, by hand, into a precipitation tank. These procedures were not permitted legally. About 16 kg of U were added to the tank, causing the nuclear fission chain reaction to start (at 10:35). The three workers were heavily exposed to neutrons and gamma-rays produced by the fission event. They were transported by ambulance, at first to a local hospital, then by helicopter to the National Institute of Radiological Sciences (NIRS), Chiba, about 120 km from Tokai-mura, which is the tertiary care center for radiation injuries. Immediately after their arrival at NIRS, radiological surveys were performed for the three patients in addition to intensive medical care. We carried out analyses of activation products such as 24Na in biological samples collected from the three patients and estimated the radiation doses for them. In this paper, we have summarized our results on the radioactivity measurements and dose estimations based on 24Na (Muramatsu et al.; Ishigure et al. ).[from Introduction