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TMI Radius Map

This map shows the 10-mile radius around Three Mile Island.

Three Mile Island experienced an alert situation Monday after an overheated motor ignited a small fire within the plant. The alert, paired with memories of the plant’s 1979 partial meltdown, may have raised curiosity among Midstate residents as to how the plant manages, identifies and handles emergency situations in general.

According to Ralph DeSantis, communications manager of Exelon Nuclear, TMI’s operator company annually sends out brochures to communities located near its plants. These brochures contain special plans developed to inform and protect the community in times of nuclear crisis.

One crucial part of emergency response is the classification of plant accidents. The National Nuclear Regulatory Commission categorizes accidents into four separate levels based on severity:

  • Unusual Event: These events involve potential degradation of the level of safety of the plant or indicate a security threat to facility protection. No releases of radioactive material requiring off-site response or monitoring are expected unless further degradation of the safety system occurs.
  • Alert: Alert events, including the Oct. 5 incident, indicate an actual or potential degradation of the safety of the plant, a security event that involves probable life-threatening risk to site personnel or damage to site equipment because of intentional malicious efforts of a hostile act. Any radioactive releases are expected to be limited to small fractions of the Environmental Protection Agency’s Protective Action Guideline exposure levels.
  • Site Area Emergency: These events involve actual or likely major failures of plant functions needed for protection of the public. They may also involve security events that result in intentional damage or malicious acts toward site personnel or equipment — as well as ones that may prevent effective access to equipment needed for the protection of the public. Any radioactive releases are not expected to result in exposure levels that exceed EPA Protective Action Guide exposure levels beyond the site boundary.
  • General Emergency: General Emergencies involve actual or imminent substantial core degradation or melting with potential for loss of containment integrity. They also include security events that result in an actual loss of physical control of the facility. Radioactive releases can be reasonably expected to exceed EPA Protective Action Guide exposure levels offsite for more than the immediate site area.

Emergency protocol is designed to give specific attention to communities located within 10 miles of a plant. Much of Cumberland County sits outside of TMI’s 10-mile radius; however, DeSantis said the radius does include New Cumberland Borough and several small parks in Lower Allen Township.

In the event of an upper level emergency that may exceed this radius, citizens are advised to listen for emergency instructions via radio and to keep their phone lines open for emergency workers. From here, evacuation measures may be suggested as the situation is handled.

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