Three Mile Island accident, The

The Three Mile Island accident of 1979 was a partial core meltdown in Unit 2 (a pressurized water reactor manufactured by Babcock & Wilcox) of the Three Mile Island Nuclear Generating Station in Dauphin County, Pennsylvania near Harrisburg. It was the most significant accident in the history of the American commercial nuclear power generating industry, resulting in the release of an estimated 43,000 curies (1.59 PBq) of radioactive krypton, but under 20 curies (740 GBq) of the particularly hazardous iodine-131.

The accident began at 4:00 a.m on Wednesday, March 28, 1979, with failures in the non-nuclear secondary system, followed by a stuck-open pilot-operated relief valve (PORV) in the primary system, which allowed large amounts of reactor coolant to escape. The mechanical failures were compounded by the initial failure of plant operators to recognize the situation as a loss of coolant accident due to inadequate training and ambiguous control room indicators. The scope and complexity of the accident became clear over the course of five days, as employees of Metropolitan Edison (Met Ed, the utility operating the plant), Pennsylvania state officials, and members of the U.S. Nuclear Regulatory Commission (NRC) tried to understand the problem, communicate the situation to the press and local community, decide whether the accident required an emergency evacuation, and ultimately end the crisis.

In the end, the reactor was brought under control, although full details of the accident were not discovered until much later, following extensive investigations by both a presidential commission and the NRC. The "Kemeny Commission Report" concluded that "there will either be no case of cancer or the number of cases will be so small that it will never be possible to detect them. The same conclusion applies to the other possible health effects." Several epidemiological studies in the years since the accident have supported the conclusion that radiation releases from the accident had no perceptible effect on cancer incidence in residents near the plant, though these findings have been contested by one team of researchers.

Public reaction to the event was probably influenced by at least three factors: first, the release (12 days before the accident) of a popular movie called The China Syndrome, concerning an accident at a nuclear reactor; secondly, what were felt to be confusing and conflicting communications from officials during the initial phases of the accident and lastly, many of the statements made by political and social activists long opposed to nuclear power. The accident was followed by essentially a complete cessation of nuclear construction in the US.

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