Stable iodine prophylaxis

Despite rigorous safety systems in a nuclear reactor, there remains a finite probability that an accident can occur that can lead to the fuel in the core overheating or melting. If such an event were to occur, there is a chance that radioactive fission products may be released to the environment. The potential radiation exposure of the population will be influenced by many parameters such as: the amounts of the radionuclides released, the meteorological conditions affecting the dispersion and deposition of the released radioactive material, human and environmental factors and the effectiveness of any protective actions taken.

Isotopes of iodine particularly I-131, is likely to be important components of the release from a severe accident. Radioactive iodines can give rise to both external exposure and internal exposure (from inhalation and ingestion). Stable iodine prophylaxis is a protective action, for which preparedness arrangements can be made as part of the overall emergency response plan. This step can protect specifically against internal exposure from inhalation, and ingestion of radioiodines by consumption of I-131 contaminated milk/milk products. It should be noted that the term “iodine prophylaxis” refers to the blocking of the uptake of radioiodine by the thyroid gland after nuclear accidents.

The selective and rapid concentration and storage of radioactive iodine in the thyroid gland results in internal radiation exposure of the thyroid, Deterministic effects from thyroid exposure are hypothyroidism and acute thyroiditis. Stochastic effects from thyroid exposure are thyroid cancer and benign thyroid nodules.

As per the WHO document on iodine prophylaxis (update-1999), it recommended that in the management of nuclear reactor accidents, stable iodine prophylaxis for children up to the age of 18 years and for pregnant and lactating women be considered at 10 mGy dose, that is 1/10th of the generic intervention level dose of 100mGy for adults recommended in the IAEA International Basic Safety Standards for Protection against Ionizing Radiation.

The recommended single dosage of stable iodine for prompt administration for adults over 12 years is 130 mg of KI or 170 mg of KIO3, for children (3 to 12 years), the dose recommended is 65mg of KI and 85mg KIO3 and for infants (1 month to 3 years) the dose is 32 mg of KI and 42 mg of KIO3.