"The Nuclear Regulatory Commission has revised a section of its emergency preparedness regulations. The revised rule requires that States with population within the 10-mile emergency planning zone of commercial nuclear power plants consider including potassium iodide (KI) as a protective measure for the general public to supplement sheltering and evacuation in the unlikely event of a severe nuclear power plant accident. Potassium iodide is a salt, similar to table salt. Its chemical symbol is KI. It is routinely added to table salt to make it iodized. Potassium iodide, if taken in time and at the appropriate dosage, blocks the thyroid gland's uptake of radioactive iodine and thus would prevent thyroid cancers and other diseases that might otherwise be caused by exposure to radioactive iodine that could be dispersed in a severe nuclear accident."
Nuclear Regulatory Commission: http://www.nrc.gov/