Fact Sheets


March 2011

Key Facts


  • The primary protective actions in the event of a nuclear plant accident are evacuation or sheltering of residents who live in the 10-mile emergency planning zone (EPZ). These actions protect the whole body from any type of radioactive exposure. Potassium iodide (KI) is an option as a secondary measure within the 10-mile EPZ to protect the thyroid gland against exposure to radioactive iodine; KI provides no other radiation protection.
  • A 2002 law states that the federal government will provide KI to state and local governments should they wish to distribute the compound in the area 10 to 20 miles from a nuclear power plant.1 The law also includes an option to waive the KI program if the federal government concludes there is a more effective way to protect the thyroid gland from radioactive iodine.2 The White House Office of Science and Technology Policy (OSTP) invoked this waiver in January 2008, saying interdiction of any contaminated food, along with the consideration of evacuation and sheltering, are more effective protective measures to use in the very unlikely event that people beyond 10 miles of a nuclear plant could be exposed to radioactive iodine.
  • The U.S. Nuclear Regulatory Commission evaluated the basis for its emergency preparedness requirements following the terrorist events of Sept. 11, 2001, and concluded that the basis remains valid.
  • In 2009, the NRC issued a proposed rule that identifies several issues the agency believes require further action in light of the potential for a terrorist event at a nuclear power plant. The proposal does not include any changes related to KI administration. However, the NRC continues to provide KI to states that request it for residents who live in the 10-mile EPZ of a nuclear power plant.

The Science of Nuclear Power Plant Emergency Planning
The NRC, the U.S. Environmental Protection Agency and other federal agencies determined in 1978 that a 10-mile radius around a nuclear power plant is an appropriate emergency planning zone in the event that a reactor releases radioactive materials. The projected radiation doses from most major reactor accidents would not be a threat to public health and safety beyond the 10-mile zone, the task force concluded.

The multi-agency task force also concluded that a 50-mile EPZ protects the public from limited exposure from consuming contaminated water, milk or food. Protection of the food chain is vital in the event of a serious reactor accident. In a 2004 report, the National Academy of Sciences concluded: “[If] contaminated milk and food had been avoided, most of the resulting thyroid cancers [around Chernobyl] would almost certainly not have occurred.”

In the United States, detailed emergency plans are in place for both the 10-mile and 50-mile EPZ, and they are tested regularly by plant staff, federal regulators, and state and local emergency management officials.

Use of KI Evaluated Beyond 10-Mile EPZ
The Public Health Security and Bioterrorism Preparedness and Response Act of 2002 states that the federal government “shall make available to state and local governments [KI] tablets for stockpiling and for distribution as appropriate to public facilities, such as schools and hospitals, in quantities sufficient to provide adequate protection for the population within 20 miles of a nuclear power plant.” The law also states that the government may waive the KI requirement if it determines there is a more effective way to protect the thyroid from exposure to radioactive iodine.

After evaluating the science and policy issues related to KI, the OSTP issued a decision on Jan. 22, 2008, invoking the waiver. “I have determined that a more effective preventive measure does exist for the extended zone covered by the Act, namely avoidance of exposure altogether through evacuation of the potentially affected population and interdiction of contaminated food,” wrote OSTP Director John Marburger. He said the probability of a release of radioactive iodine was not at issue, only the potential consequences. However, he noted, “The risk of a severe release of radioactive iodine 10-20 miles from a [nuclear power plant] is on the order of one-in-a-million to one-in-ten-million.”

NRC Reviews Requirements in Light of Terrorist Threat
The NRC evaluated the basis for its emergency preparedness requirements following Sept. 11, 2001. In a 2003 report to the commissioners, the NRC staff concluded that the emergency preparedness basis remains valid. However, the NRC staff recognized that security events differ from accidents from the standpoint of advance planning. In 2009, the NRC published a proposed rule identifying several emergency preparedness issues that it believes require further action. The proposed rule does not include any changes related to KI administration.





1 Public Health Security and Bioterrorism Preparedness and Response Act of 2002, Public Law 07-188, June 12, 2002.
2 Ibid, Section 127(f).