Emergency Preparedness at Nuclear Power Plants

Background

The Nuclear Regulatory Commission reexamined the role of emergency preparedness for 

protecting the public near nuclear power plants following the accident at the Three Mile Island nuclear 

power plant in 1979. The accident showed the need for improved planning, response, and 

communication by federal, state, and local governments to deal with reactor accidents. Although the 

NRC remained vigilant over the years, the events of Sept. 11, 2001, prompted a new focus on 

emergency preparedness and a further review of the threat environment. The NRC now considers new 

threat scenarios and protections in emergency preparedness in light of the threat of terrorist attacks.

Nuclear power plant owners, government agencies, state and local officials, as well as thousands 

of volunteers and first responders have worked together to create a system of emergency preparedness 

and response that will serve the public well in the unlikely event of an emergency. The nuclear power 

plants’ emergency plans include preparations for evacuation, sheltering, or other actions to protect the 

residents nearby in the event of a serious incident.

Since commercial nuclear power plants began operating in the United States, there have been no 

physical injuries or fatalities from exposure to radiation from the plants among members of the U.S. 

public. Even the country’s worst nuclear power plant accident at Three Mile Island resulted in no 

identifiable health impacts.

Federal Oversight

In the U.S., each commercial nuclear power reactor has onsite and offsite emergency plans to 

assure that adequate protective measures can be taken to protect the public in the event of a radiological 

emergency. Federal oversight of emergency preparedness for licensed nuclear power plants is shared by 

the NRC and Federal Emergency Management Agency. This sharing is facilitated through a 

Memorandum of Understanding. The MOU is responsive to the President's decision of Dec. 7, 1979, 

that FEMA take the lead in overseeing offsite planning and response, and that NRC assist FEMA in 

carrying out this role. The NRC has statutory responsibility for the radiological health and safety of the 

public by overseeing onsite preparedness, and has overall authority for both onsite and offsite 

emergency preparedness.

Before a plant is licensed to operate, the NRC must have “reasonable assurance that adequate 

protective measures can and will be taken in the event of a radiological emergency.” The NRC’s 

decision of reasonable assurance is based on licensees complying with NRC regulations and guidance. 

In addition, licensees and area response organizations must demonstrate they can effectively implement 

emergency plans and procedures during periodic evaluated exercises. As part of the Reactor Oversight 
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Process, the NRC reviews licensees’ emergency planning procedures and training. These reviews 

include regular drills and exercises that assist licensees in identifying areas for improvement, such as in 

the interface of security operations and emergency preparedness. Each plant operator is required to 

exercise its emergency plan with offsite authorities at least once every two years to ensure state and 

local officials remain proficient in implementing their emergency plans. Those biennial exercises are 

inspected by the NRC and evaluated by FEMA. Licensees also self-test their emergency plans regularly 

by conducting drills. Each plant's performance in exercises can be accessed through the NRC website at 

the Reactor Oversight Process page.

FEMA takes the lead in initially reviewing and assessing the offsite planning and response and in 

assisting state and local governments, while the NRC reviews and assesses the onsite planning and 

response. FEMA findings and determinations as to the adequacy and capability of implementing offsite 

plans are communicated to the NRC. The NRC reviews the FEMA findings and determinations as well 

as the onsite findings. The NRC then makes a determination on the overall state of emergency 

preparedness. These overall findings and determinations are used by the NRC to make radiological 

health and safety decisions before the issuing licenses and in the continuing oversight of operating 

reactors. The NRC has the authority to take action, including shutting down any reactor deemed not to 

provide reasonable assurance of the protection of public health and safety.

Emergency Planning Zones

For planning purposes, the NRC defines two emergency planning zones around each nuclear 

power plant. The exact size and configuration of the zones vary from plant to plant due to local 

emergency response needs and capabilities, population, land characteristics, access routes, and 

jurisdictional boundaries. The two types of EPZs are:

• The plume exposure pathway EPZ extends about 10 miles in radius around a plant. Its 

primary concern is the exposure of the public to, and the inhalation of, airborne radioactive 

contamination.

• The ingestion pathway EPZ extends about 50 miles in radius around a plant. Its primary 

concern is the ingestion of food and liquid that is contaminated by radioactivity.

Emergency Classification 

Emergency Classification is a set of plant conditions that indicate a level of risk to the public. 

Nuclear power plants use the four emergency classifications listed below in order of increasing severity.

• Notification of Unusual Event - Events are in process or have occurred which indicate 

potential degradation in the level of safety of the plant. No release of radioactive material 

requiring offsite response or monitoring is expected unless further degradation occurs.

• Alert - Events are in process or have occurred that involve an actual or potential substantial 

degradation in the level of safety of the plant. Any releases of radioactive material from the 

plant are expected to be limited to a small fraction of the Environmental Protection Agency 

protective action guides. Additional information regarding PAGs can be found on the EPA 

website at: Additional information regarding PAGs can be found on the EPA website.
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• Site Area Emergency - Events are in process or have occurred that result in actual or likely 

major failures of plant functions needed for protection of the public. Any releases of 

radioactive material are not expected to exceed the EPA PAGs except near the site boundary.

• General Emergency - Events involve actual or imminent substantial core damage or melting 

of reactor fuel with the potential for loss of containment integrity. Radioactive releases can 

reasonably be expected to exceed the EPA PAGs for more than the immediate site area.

Protective Actions

The NRC's regulations are designed to mitigate accident consequences and minimize radiation 

exposure to the public through protective actions. When a radiological emergency occurs, nuclear power 

plant personnel evaluate plant conditions and make protective action recommendations to the state and 

local government agencies on how to protect the population. Based on the recommendation and 

independent assessment of other local factors, the state or local government agencies are responsible for 

making decisions on the actions necessary to protect the public and for relaying these decisions to the 

public.

Factors that affect protective action decisions include plant conditions, competing events, 

weather, evacuation times, shelter factors, how quickly an incident develops, how short-lived a release 

of radiation may be, and other conditions.

Evacuation, Sheltering, and the Use of Potassium Iodide

Protective actions considered for a radiological emergency include evacuation, sheltering, and, as 

a supplement to these, the prophylactic use of potassium iodide (KI), as appropriate. Under most 

conditions, evacuation may be preferred to remove the public from further exposure to radioactive 

material.

Evacuation does not always call for completely emptying the 10-mile zone around a nuclear 

power plant. In most cases, the release of radioactive material from a plant during a major incident 

would move with the wind, not in all directions surrounding the plant. The release would also expand 

and become less concentrated as it travels away from a plant. Therefore, evacuations should be mapped 

to anticipate the path of the release. Generally as a minimum, in the event of a General Emergency, a 

two-mile ring around the plant is evacuated, along with people living in the 5-mile zone directly 

downwind and slightly to either side of the projected path of the release. This “keyhole” pattern (Figure 

1) helps account for potential wind shifts and fluctuations in the release path. Evacuation beyond 5 miles 

is assessed as the accident progresses. Also in response to a General Emergency, people living in the 

remainder of the 10-mile zone will most likely be advised to go indoors to monitor Emergency Alert 

System broadcasts. 

Under some conditions, people may be instructed to take shelter in their homes, schools, or 

office buildings. Depending on the type of structure, sheltering can significantly reduce a person’s dose 

compared to remaining outside. Sheltering is a protective action that keeps people indoors, such as at 

home, the office, school, or a shopping mall to reduce exposure to radioactive material. It may be 

appropriate to shelter when the release of radioactive material is known to be short-term or controlled by 

the nuclear power plant operator.
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Another protective action in the 10-mile EPZ involves KI, a compound that helps prevent the 

thyroid from absorbing radioactive iodine, one of several radioactive materials that could be present in a 

release from a nuclear power plant accident. If taken within the appropriate time and at the appropriate 

dosage, KI blocks the radioactive iodine from being absorbed by the thyroid gland and reduces the risk 

of thyroid cancers and other diseases. KI does not protect against any other inhaled radioactive 

materials, nor will it offer protection from external exposure to radiation. The Food and Drug 

Administration has determined that KI is a safe and effective drug when used for this purpose. However,

there may be risks and potential side effects in using KI, including gastrointestinal disturbances, allergic 

reactions, and iodide goiter and hypothyroidism. Please consult your physician if you have questions on 

the potential side effects.

Further information on KI is available on the NRC website at: http://www.nrc.gov/aboutnrc/emerg-preparedness/about-emerg-preparedness/potassium-iodide/ki-faq.html .

After September 2001, the NRC examined how terrorist-based events might challenge existing 

emergency preparedness. The NRC’s formal evaluation determined that, in view of the threat 

environment, the emergency preparedness planning basis remain valid. While a terrorist event might 

alter the initial response to an event, the consequences of the event will be the same whether it was 

caused by terrorism or a safety accident.

The nuclear power reactor’s emergency plans are periodically updated and are designed to be 

flexible to identify, evaluate and react to the wide spectrum of emergency conditions. The NRC 

recognized how the terrorism threat affects emergency planning when it issued orders and guidance to 

nuclear power plants after September 2001. These orders and guidance include interim measures dealing 

with how increased security affects implementation of emergency plans. Nuclear industry groups and 

federal, state, and local government agencies assisted in the prompt implementation of these measures 

and participated in drills and exercises to test these new planning elements. The NRC has reviewed 

licensees’ commitments to address these requirements and verified the implementation through 

inspections to ensure public health and safety.

Additional Information

Detailed information about emergency preparedness is contained in NRC regulations, 

specifically Appendix E to Part 50 of Title 10 in the Code of Federal Regulations and in NUREG-0654 

(FEMA-REP-1), a joint publication of the NRC and FEMA published in November 1980, entitled 

“Criteria for Preparation and Evaluation of Radiological Emergency Response Plans and Preparedness 

in Support of Nuclear Power Plants.” These documents along with additional information on the NRC’s 

Emergency Preparedness and Response programs is available on the NRC website at: 

http://www.nrc.gov/about-nrc/emerg-preparedness.html. 
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Figure 1 – Original keyhole (L) and revised keyhole following wind shift (R)

June 2018