Development of evaluation method for the effect of reducing equivalent doses to the thyroid by implementing iodine thyroid blocking

To consider the method of implementing urgent protective actions in a nuclear accident appropriately, the authors have been assessing the effects of reducing doses by taking such actions using a Level 3 Probabilistic Safety Assessment (PSA) code, the OSCAAR, developed by the JAEA. Iodine thyroid blocking is an effective urgent protective action to reduce the equivalent doses to the thyroid due to inhalation of radioactive iodine. However, the timing of the administration of stable iodine is important to maximize the effectiveness for thyroidal blocking. Therefore, the careful consideration should be given to the most effective way of iodine thyroid blocking when preparing off-site emergency plans. In the present study, the authors introduced a metabolic model of iodine into the OSCAAR for evaluating the effect of the administration of stable iodine for reducing equivalent doses to the thyroid depending on the its timing. Then, examined the effectiveness of iodine thyroid blocking combined with sheltering or evacuation in the containment bypass scenario with large radioactive release to the environment. (author)