44. Determination of ³²P in Urine for Early Dose Estimation of Three Victims in the JCO Criticality Accident

Yoshikazu Nishimura, Hiroshi Takeda, Kiriko Miyamoto, Yoshito Watanabe, Fuyuki Kouno, Noriko Kuroda, Hee Sun Kim and Masae Yukawa

Keywords: JCO, early dose estimation, P-32, urine

On September 30^th, 1999, a criticality accident occurred at a uranium conversion facility in Tokai-mura, Ibaraki, Japan. Three workers, who were severely exposed to neutrons and gamma-rays, were transferred to the National Institute of Radiological Sciences for medical treatment. The doses were estimated preliminarily by prodromal symptoms, lymphocyte counting, chromosomal analysis, and ²⁴Na activity in blood. For apparent dose estimation, biological materials such as blood, hair and urine were analyzed by measuring neutron-induced radionuclides. We measured the beta emitters induced by neutron activation in the biological samples in order to obtain as much information as possible from the irradiated individuals, and we detected ³²P in urine samples. ³²P generated by thermal neutron activation of stable phosphorous in the whole-body should be excreted into the urine. As yet, definite methods for the estimation of the neutron dose by measurement of ³²P in urine have not been established. Urine requires a less invasive sampling procedure, and it may possibly provide a convenient means of measuring neutron dose immediately after exposure. Table 3 shows the concentration of ³²P in urine from 5 h to 20 h after the accident and the relative concentration ratios for the three workers, together with the ²⁴Na concentrations in blood corrected to the time of the accident. The concentration ratios of ³²P in urine of three workers showed a similar tendency to the concentration ratios of ²⁴Na in the blood. Therefore the radioactivity of ³²P in urine could be used to determine the neutron exposure dose. Collecting blood is not only sometimes difficult to carry out, but also puts physical burdens on patients at a crucial time. Urine can be collected easily, and it may provide a convenient means of measuring neutron dose immediately after the exposure. We obtained similar urinary data from measurements of ³²P with a liquid scintillation counter. If ³²P in urine can be detected rapidly and easily, it could become a good indicator for estimating the neutron dose.

Table 3. Concentration of ³²P in urine on the first day after the accident, and relative concentration ratio for the workers.

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