The construction and operation of these facilities is closely monitored and regulated to prevent incidents. If the primary and secondary systems fail, emergencies are possible, including those with a radioactive release that could affect public health and safety. As a result, federal, state and local officials, in addition to these utilities are required to have comprehensive emergency plans in place to protect against and respond to incidents at these facilities. Through oversight provided by both the U.S. Nuclear Regulatory Commission (NRC) and the Federal Emergency Management Agency (FEMA), these plans are reviewed, drilled and evaluated regularly to ensure they meet regulatory standards.

The State of New Hampshire has one nuclear power plant within its borders, Nextera Energy Seabrook Station. This plant generates approximately 1,244 million watts of electricity per year, enough power to supply the annual needs of approximately 1.2 million families. It is the responsibility of the New Hampshire Division of Homeland Security and Emergency Management's Radiological Emergency Preparedness (REP) Section to maintain the state's nuclear power plant off-site emergency plans, including annual reviews and updates, conduct trainings, and conduct biennial exercises per FEMA and NRC requirements.

In case of an emergency at the Nextera Energy Seabrook Station Nuclear Power Plant, Radiological Emergency Plans define two "emergency planning zones" (EPZs) to prepare for and recover from incidents at a nuclear power plant. The first zone is the Plume Exposure Pathway EPZ that covers an area of a 10-mile radius around the plant. Communities within this area have plans that are designed to avoid or reduce the dose from potential exposures such as inhaling radioactive particles. These actions include sheltering, evacuation, and the use of potassium iodide (KI) pills when appropriate. There are seventeen (17) New Hampshire communities within the 10-mile EPZ around Nextera Energy Seabrook Station: Brentwood, East Kingston, Exeter, Greenland, Hampton, Hampton Falls, Kensington, Kingston, New Castle, Newfields, Newton, North Hampton, Portsmouth, Rye, Seabrook, South Hampton and Stratham. There are also six Massachusetts towns in the Seabrook 10-mile EPZ.

The second planning zone is the Ingestion Exposure Pathway EPZ that covers a broader area, usually up to a 50-mile radius around the plant. Protective action plans for this area are designed to avoid or reduce dose from eating or drinking radioactive materials. These actions include a ban of contaminated food and water.

The potential danger from an accident at a nuclear power plant is exposure to radiation. This exposure could come from the release of radioactive material from the plant into the environment, usually characterized by a plume of radioactive particles. The major hazards to people in the vicinity of the plume are radiation exposure to the body from the particles in the air, and those that are deposited on the ground.

Nuclear Power plants use Emergency Classifications Levels (ECLs) to categorize incidents and coordinate appropriate responses based on the consequences and effects from the event. The four ECLs, in order of increasing severity are: Unusual Event, Alert, Site Area Emergency, and General Emergency.
 

• Unusual Event: An Unusual Event means a minor problem has occurred at the plant. Public officials would be notified, but people in the area would not need to take any special actions.

• Alert: An Alert means plant safety could be affected. As a precaution, public officials may transfer school children to host facilities outside the area and clear state parks and waterways. Radio or news broadcasts would inform the public of these actions.

• Site Area Emergency: Site Area Emergency means a more serious problem has occurred. State and local officials will use the emergency alert system to keep people in the area fully informed. Sirens and CodeRed would notify persons in the area if the public needs to take any action.

• General Emergency: General Emergency is the most serious type of emergency. It could involve serious damage at the plant and the release of radioactive materials. Sirens and CodeRed would notify persons in the area. State and local officials will use the emergency alert system to issue public safety instructions to those in the area.
  
  https://www.hsem.dos.nh.gov/preparedness/radiological-emergency-preparedness