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Three Mile Island

The accident at Three Mile Island Unit 2 (TMI 2) in Pennsylvania in 1979 was caused by misinterpretation of equipment functioning by plant operators when assessing the reactor's condition. A gradual loss of cooling water to the reactor's heat-producing core led to partial melting of the uranium fuel and fuel rod assemblies and the release into the environment of a very small amount of radioactive material. While the TMI 2 accident caused no physical injuries or deaths, it did result in serious concerns and fear and, undoubtedly, was a source of stress to some of the people living close by. Related to the radiation, however, careful follow-up studies showed that the highest dose an individual member of the public could have received would have been about one-fourth of the dose we get each year from natural background radiation sources, even if the individual stood just outside the plant fence during the entire accident.