Here are some notable accidents involving nuclear facilities in the United States and abroad. The list includes accidents at weapon production facilities as well as power-generating plants.
The information was compiled by The Washington Post from a variety of sources, including a 1980 report for the Senate Environment and Public Works Committee, the Congressional Research Service, the Critical Mass Energy Project, the Oak Ridge National Laboratory and news reports.
*Dec. 2, 1952. Chalk River, an experimental nuclear power reactor 120 miles from Ottawa, Canada. An employe mistakenly lifted four of the system's 12 control rods out of the fuel core, causing a chain reaction that melted part of the uranium. A million gallons of radioactive water accumulated inside the reactor and took six months to clean up.
*November 1955. The EBR-1 experimental enriched uranium breeder reactor in Idaho Falls, Idaho. The reactor went out of control during tests because of misshapen fuel rods and human error.
*Oct. 7-10, 1957. Windscale Pile No. 1, a plutonium production reactor on the edge of the Irish Sea on the English coast. A fire resulted in release of as much as 20,000 curies of radioactive iodine in a 42-hour period, the largest known release of radioactive gases and a thousand times the amount estimated to have been released at Three Mile Island in 1979. Britain declared a general emergency and eventually destroyed half a million gallons of milk from dairy farms in a 200-square-mile area. The reactor was permanently shut down.
*Winter 1957-58. A major nuclear accident at Kyshtym, in the Ural Mountains in the Chelyabinsk province of the Soviet Union. The Soviets have released little information on the accident, which is thought to have occurred at a nuclear weapons facility, but scientists believe it resulted in contamination of as much as 400 square miles. There are no reliable estimates of how many people were killed, injured or relocated. A river had to be rerouted to avoid contamination.
*May 23, 1958. A second accident at the Chalk River facility in Canada, this time involving a larger unit. A defective fuel rod overheated during removal. Some radioactivity was released to the environment, and another long cleanup followed.
*July 24, 1959. An experimental power reactor at Santa Susana, Calif., in the greater Los Angeles area. Blockage of the coolant system caused 12 of the 43 fuel elements to melt. Radioactivity was contained.
*Jan. 3, 1961. The SL-1 military experimental reactor near Idaho Falls, Idaho. Control rods were mistakenly removed from the core, creating a steam explosion that hurled radioactive debris through the reactor. Three servicemen were killed, the only fatalities in U.S. reactor operations.
*Oct. 5, 1966. Enrico Fermi plant, a government-backed demonstration breeder reactor in southeast Michigan 30 miles from Detroit. A malfunction caused part of the fuel core to melt. Radioactive gases were contained in the reactor building. The plant was closed in 1972.
*June 5, 1970, Commonwealth Edison's Dresden II plant in Morris, Ill. The reactor went out of control for two hours after a meter gave a false signal. Radioactive iodine accumulated in the containment vessel at 100 times the permissible level, but was not released into the environment.
*Nov. 19, 1971. The Northern States Power Co.'s reactor in Monticello, Minn. When the reactor's waste storage space filled to capacity, more than 50,000 gallons of radioactive waste water spilled into the Mississippi River. Some was taken into the St. Paul water supply.
*March 22, 1975. Brown's Ferry reactor, a Tennessee Valley Authority facility near Decatur, Ala. A worker using a candle to check for air leaks around electrical cable set fire to insulation, destroying cables controlling key safety equipment. Operators resorted to a makeshift system to cool the reactor's fuel. Cleanup costs were $150 million.
*March 28, 1979, Three Mile Island No. II, a Metropolitan Edison Plant on the Susquehanna River near Harrisburg, Pa. The pressurized-water reactor lost its coolant, and its radioactive fuel overheated in what many consider the worst U.S. commercial nuclear power accident. Some radioactivity was released into the air, but government scientists estimated that human health effects would be minimal. According to a Nuclear Regulatory Commission investigation, the plant got within an hour of a catastrophic meltdown.
*Feb. 11, 1981. Sequoyah I, a Tennessee Valley Authority power plant in Tennessee. At least eight workers were contaminated when 110,000 gallons of radioactive coolant leaked into the containment building. The accident threatened to expose the core of the reactor.
*Jan. 25, 1982. Rochester Gas & Electric Co.'s Ginna plant near Rochester, N.Y. A major steam-generator tube ruptured, spilling radioactive water into the containment vessel. Some radioactive steam escaped into the air.
*Feb. 22 and 25, 1983. Salem I, a Public Service Electric and Gas Co. plant in southern New Jersey. The plant's automatic shutdown system failed twice after water levels in the core dropped. Plant operators were able to shut down the plant manually.
*April 19, 1984. Another accident at TVA's Sequoyah I. A gusher of superheated, radioactive water erupted during a maintenance operation. No radioactivity was released and eight workers in the area escaped injury.
*June 9, 1985. Toledo Edison's Davis-Besse plant in Oak Harbor, Ohio. In the most serious of several 1985 nuclear plant accidents that involved equipment failures or employe errors, at least 16 pieces of equipment failed and plant operators pushed the wrong button at least once. While the "incidents" were similar to those that confronted Three Mile Island's operators, auxiliary cooling pumps were started and damage to the fuel core apparently was averted.