The behavior of radioactive iodine at the time of reactor accident and its counterplan

When an accident occurs in a reactor, very volatile radioactive iodine is most dangerous among fission products. Among the isotopes of radioactive iodine, 131I which has longer half-life is harmful. Supposing one-tenth of the radioactivity of 108 Ci in a reactor of 106 Kw heat output is due to 131I, it weights about 100g. The behavior of the radioactive iodine is greatly subjected to the influence of inside temperature and other conditions. Therefore, very prudent policies are adopted by installing emergency core cooling system, containment vessels, and activated carbon filters. For the emergency core cooling system, water spraying, flooding with low pressure water, and maintaining of water level by high pressure water injection are adopted, while in the containment vessels, measures are taken so as to lower the inside pressure and minimize leakage. (Kobatake, H.)