Three Mile Island

An island in the Susquehanna River in southeast Pennsylvania southeast of Harrisburg. It was the site of a major nuclear accident on March 28, 1979, when a partial meltdown released radioactive material and forced the evacuation of thousands of nearby residents.

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The location of an accident in 1979 in a nuclear power plant — an electrical generator powered by a nuclear reactor — in Pennsylvania. The plant underwent a partial meltdown that resulted in very little leakage of radiation into the atmosphere, panic among nearby residents, losses of billions of dollars, and intense criticism of nuclear power programs in general. (Compare Chernobyl.)

The most serious nuclear reactor accident to date in the United States occurred at 4 A.M. on March 28, 1979, at the Three Mile Island nuclear power plant outside Middletown, Pennsylvania. Operator errors in dealing with a pump that had shut down caused the Unit 2 pressurized-water reactor to lose coolant and overheat. The temperature of the reactor core then rose to the point at which some of the zirconium-alloy fuel cladding failed, fuel itself partially melted, and cladding reacted with steam to produce bubbles of vapor and hydrogen, which then escaped into the reactor building, along with fission products from the reactor core. As a result of the failure to close a backup valve that could be operated manually, coolant was not restored to the reactor core until more than six hours after the accident, by which time enough hydrogen had accumulated in the building to pose the treat of a low-level explosion. The building had been designed to seal automatically in the event of a pressure rise, but no rise occurred, and four hours were allowed to elapse before the building was sealed, during which time radioactive gases escaped into the atmosphere.

Within three hours after the first sign of trouble, elevated radiation levels were detected by monitors in the reactor auxiliary building. A site emergency was declared, and officials enlisted the aid of local, state, and federal emergency personnel. The presence of a large hydrogen bubble in the reactor vessel prompted widespread fear that the reactor might explode, a concern that experts failed to allay although they knew it to be a misapprehension. Adding to the fear, dosimeter readings made in a helicopter three hundred feet above the auxiliary building's ventilation stack were misinterpreted by officials to signify elevated ground levels of radiation, prompting the governor of Pennsylvania to recommend the evacuation of all pregnant women and preschool children residing within five miles of the plant, who then complied.

Although large amounts of radiation were released, the resulting exposure of the public was relatively slight, resulting mainly from xenon-133 that was present in the gaseous plume. The largest dose of radiation any member of the public may have received is estimated to have been smaller than his or her annual dose from natural background irradiation, and the average dose to those living within fifty miles of the reactor is estimated to have been 40 to 50 times smaller than that. Because of the small magnitude of the doses that were received, no demonstrable injuries from the radiation were expected, nor have any actually been observed. Nevertheless, the legacy of fear and resentment left by the accident has adversely affected the well-being of those living nearby, and it has heightened negative attitudes toward nuclear energy.

(SEE ALSO: Energy; Environmental Determinants of Health; Nuclear Power)

Bibliography

Baum, A.; Gatchel, R.; and Schaeffer, M. (1983). "Emotional, Behavioral, and Psychological Effects of Chronic Stress at Three Mile Island." Journal of Consulting and Clinical Psychology 51:565–572.

Kemeny, J.G. (1979). The President's Commission on the Accident at Three Mile Island. New York: Pergamon Press.

Moss, T. H., and Sills, D. L., eds. (1981). "The Three Mile Island Nuclear Accident: Lessons and Implications." In Annals of the New York Academy of Sciences 365. New York: New York Academy of Sciences.

— ARTHUR C. UPTON

For more information on Three Mile Island, visit Britannica.com.

Three Mile Island, the site of the worst civilian nuclear power program accident in the United States, is located in the Susquehanna River near Harrisburg, Pennsylvania. In the early 1970s, Metropolitan Edison built two reactors on Three Mile Island for commercial energy production. On 28 March 1979, a faulty valve allowed water coolant to escape from Metropolitan Edison's second reactor, Unit 2, during an unplanned shutdown. A cascade of human errors and technological mishaps resulted in an overheated reactor core with temperatures as high as 4,300 degrees and the accidental release of radiation into the atmosphere. Plant operators struggled to resolve the situation. Press reporters highlighted the confusion surrounding the accident, while Governor Richard L. Thornburgh of Pennsylvania and President Jimmy Carter visited the stricken plant, urging the nation to remain calm. On 30 March, state officials evacuated pregnant women and preschool children from the immediate area as a safety measure. On 2 April, temperatures decreased inside the Unit 2 reactor, and government officials declared the crisis over on 9 April.

A commission authorized by President Carter investigated the calamity. Government analysts calculated that, at the height of the crisis, Unit 2 was within approximately one hour of a meltdown and a significant breach of containment. The lessons learned at Three Mile Island led to improved safety protocols and equipment overhauls at commercial reactors across the country. Three Mile Island also contributed to rising public anxiety over the safety of nuclear energy, anxieties fueled by the coincidental release of The China Syndrome, a fictional movie about the cover-up of a nuclear plant accident, just twelve days before the disaster at Three Mile Island. The Three Mile Island accident became a rallying cry for grassroots antinuclear activists. Wary of sizable cost overruns and public resistance, electrical utilities shied from constructing new nuclear plants in the years that followed. Over an eleven-year period, the cleanup of Three Mile Island's severely damaged reactor cost in excess of $1 billion.

Bibliography

Cantelon, Philip L., and Robert C. Williams. Crisis Contained: The Department of Energy at Three Mile Island. Carbondale: Southern Illinois University Press, 1982.

President's Commission on the Accident at Three Mile Island. Report of the President's Commission on the Accident at Three Mile Island: The Need for Change: The Legacy of TMI. Washington, D.C.: Government Printing Office, 1979.

Stephens, Mark. Three Mile Island. New York: Random House, 1980.

The location of an accident in 1979 in a nuclear power plant in Pennsylvania. The plant underwent a partial meltdown that resulted in some radiation leakage into the atmosphere, panic among nearby residents, losses of billions of dollars, and intense criticism of nuclear power programs in general.