Evaluation on review of screening level of simple measurement of radioactive iodine radioactivity in the thyroid in the case of a nuclear accident

Hokama, Tomonori ; Kimura, Masanori ; Togawa, Orihiko 

In the case of a nuclear accident, itis planned to perform simple measurement of radioactive iodine radioactivity in the thyroid of residents. The screening level for simple measurement is set at 0.20 Sv/h as a reference, and it is required to be reviewed appropriately according to the situation such as a nuclear accident. However, a specific method for reviewing the screening level is not shown. When reviewing the screening level, it is important to take into account factors related to the feasibility of simple measurement, such as the judgment level for internal exposure dose of the thyroid and the duration of the measurement period. In this study, we organized the derivation process of 0.20 Sv/h, which was set as the reference for screening level, and considered the feasibility of the reviewing of screening level. We calculated the relationship between the judgment level and the duration of simple measurement for each screening level, ranging from 0.025 to 0.50 Sv/h. Then, the feasibility of the reviewing of screening level was considered. It was found that reviewing the screening level is technically feasible, provided that the judgment level and the duration of simple measurement are appropriate. However, assuming that simple measurement will be performed in an actual nuclear accident, we assessed that it would be reasonable to review the screening level within the range of 0.030 to 0.20 Sv/h, in a situation where the duration of simple measurement must be extended.