Here is a chronology of notable nuclear accidents worldwide.
Dec. 2, 1952: At Chalk River near Ottawa, Canada, an employee error leads to 1 million gallons of radioactive water leaking inside an experimental nuclear reactor. It took six months to clean it up.
Oct. 7-10, 1957: At Windscale Pile, a plutonium production reactor north of Liverpool, England, a fire leads to the largest known accidental release of radioactive material. Government later attributes 39 cancer deaths to mishap.
1957: A nuclear accident, probably at a weapons facility, occurs in the Ural Mountains in the Soviet Union. Little information exists, but it is believed that hundreds of square miles had to be evacuated.
May 23, 1958: A second accident at Chalk River sparked by an overheated fuel rod leads to another long cleanup.
Jan. 3, 1961: A steam explosion at a military experimental reactor near Idaho Falls, Ida. kills three servicemen.
Oct. 5, 1966: At the Enrico Fermi plant, an experimental breeder reactor near Detroit, part of fuel core melts. No injuries, but radiation levels are high inside the plant. Plant was closed in 1972.
Oct. 17, 1969: At a reactor in Saint-Laurent, France, fuel loading error leads to partial meltdown. No injuries and only small amount of radioactive material escapes.
Nov. 19, 1971: Over 50,000 gallons of radioactive waste water spills into the Mississippi River when the waste storage space at the Northern States Power Co.'s reactor in Monticello, Minn., overflows.
March 22, 1975: A worker using a candle to check for air leaks at the Brown's Ferry reactor in Decatur, Ala., causes a $150 million fire, which lowers cooling water to dangerous levels. No injuries or release of radioactivity.
March 28, 1979: Three Mile Island in Middletown, Pa., has a partial meltdown and some radioactivity is released into the atmosphere in what many consider the worst U.S. commercial nuclear accident. Reactor is still being decontaminated.
Aug. 7, 1979: The accidental release of enriched uranium at a top-secret fuel plant near Erwin, Tenn., exposes about 1,000 people to above-normal doses of radiation.
Feb. 11, 1981: At least eight workers are exposed to radiation at Sequoyah I, a Tennessee Valley Authority power plant, when more than 100,000 gallons of radioactive coolant leaks into the containment building.
April 25, 1981: Workers are exposed to radioactive material at a nuclear plant in Tsuruga, Japan, during repairs.
Jan. 25, 1982: At the Ginna plant near Rochester, N.Y., a tube ruptures and a small amount of radioactive steam escapes into the atmosphere.
April 19, 1984: Sequoyah I has a second accident when superheated radioactive water erupts during maintenance procedure. No injuries.
June 9, 1985: Davis-Besse plant near Oak Harbor, Ohio, loses cooling-water supplies due to human and equipment error. Problem is caught in time to prevent meltdown.