April 26, 1986
Widely regarded as the worst nuclear disaster in historyâand the only one to be classified a level 7 "
major accident" on the International Nuclear Event Scaleâthe catastrophe occurred during a systems test at reactor No. 4 at the Chernobyl plant near the town of Pripyat in the former Ukrainian Soviet Socialist Republic. A sudden power surge led the nuclear reactor to rupture, creating a series of violent explosions and eventually sending a plume of radioactive dust into the atmosphere, covering not only Pripyat, but large parts of the western Soviet Union and Europe. Four hundred times more radioactive material was released than the atomic bombing of Hiroshima, and the Soviet government initially tried to cover up the incident. It wasn't until workers at the Forsmark Nuclear Power Plant in Swedenâapproximately 680 miles from Chernobylâfound radioactive particles on their clothes that the USSR admitted the disaster had taken place. Only 50 deathsâall reactor staff and emergency workersâhave been directly attributed to the accident, but a
U.N. report says the incident will ultimately claim as many as 4,000 deaths.
March 28, 1979
The biggest nuclear disaster in U.S. historyâ
level 5 on the International Nuclear Event Scaleâoccurred at the Three Mile Island Plant near Harrisburg, the capital of Pennsylvania. A small valve opened to relieve pressure to the nuclear reactor, but malfunctioned and would not close, causing cooling water to leak and the core to overheat. To make matters worse, the machines monitoring the core's conditions provided false information, so emergency water that would have cooled the core was not released. The core eventually overheated, reaching 4,300 degrees Fahrenheit, resulting in the release of 13 million curies of radioactive gases. The plant's designers were finally able to contact the plant operators and stabilize conditions just before the leaking water reached the core's fuel rods, which would have caused a full meltdown. Members of the U.S. Nuclear Regulatory Commission launched an investigation, and
concluded that "it led to no deaths or injuries to plant workers or members of the nearby community," but did bring about many changes concerning nuclear power plant regulation and emergency response.
October 10, 1957
After WWII, Great Britain, not wanting to be left behind in the nuclear arms race, launched a program to build an atomic bomb as fast as possible. At Windscale, Cumberland, the graphite core of a nuclear reactor caught fire. Operators feared that putting it out with water would cause a hydrogen explosion, but ultimately turned on the water and put out the fireâbut not until a substantial amount of radiation was released into the nearby countryside. Prime Minister Harold Macmillan, worried that the incident would embarrass the British government and tarnish the reputation of the country's nuclear program, tried to cover up the seriousness of the accident. But a recent study
estimated that the radiation led to 240 cases of cancer.
September 30, 1999
Up to then Japan's worst nuclear radiation accident,
ranking a level 4 on The International Nuclear Event Scale, this incident took place at a small uranium-processing facility located in the village of TĹkai, Naka District, Ibaraki Prefecture. A batch of highly enriched uranium was prepared by unqualified workers for a nuclear reactor that had not been touched in over three years, and the workers put far too much uranium in the tank, causing it to reach critical mass, and emit intense gamma and neutron radiation. All three of the workers handling the uranium were hospitalized, with two in critical condition. One died 12 weeks later, and another died seven months later due to radiation,
according to the World Nuclear Association. In addition, radiation doses for 436 others were evaluated, with 56 plant workers and 21 other workers receiving elevated doses of neutron and gamma radiation.
February 22, 1977
The Bohunice nuclear power plant in JaslovskĂŠ Bohunice, Czechoslovakia, was the first power plant in the countryâthen part of the Soviet Bloc. The plant was plagued by a series of problems, but none worst than the one that occurred in 1977,
rated a level 4 accident on The International Nuclear Event Scale. During a fuel change, some humidity absorbers covering the fuel rods were not properly removed, which caused less heat to be transmitted to coolant gas, resulting in the fuel overheating. Eventually, the nuclear reactor suffered severe corrosion, and a large quantity of radioactive gases were released into the plant area. Because the incident was largely covered up by the Soviet government, there are no adequate estimates of injured or deceased persons related to the accident. Nevertheless, the plant was decommissioned and shut down two years later.
September 13, 1987
When it happened, the 1987 Goiânia accident in Goiås, Brazil, was the worst accident involving a radioactive source that the world had ever seen. Two men scavenged a billiard ball-size capsule of highly radioactive cesium chloride from the Instituto Goiano de Radioterapia, a partially demolished former radiotherapy institute. The men, thinking it had junkyard value, opened the capsule, emitting radioactive material, and then sold it to a junkyard owner. The contaminated capsule was passed around a Brazilian scrapyard for more than two weeks before being properly identified, with many of the people going so far as applying the glittery radioactive blue powder emanating from the capsule onto their faces. About 130,000 people visited hospitals in a panic, and 250 people were found to be contaminated by radioactive residue, with 20 of them requiring treatment for radiation sickness. Four people died from exposure to radiation, including the two men who scavenged the capsule, the wife of the junkyard owner who purchased the capsule, and a 6-year-old girl who applied the blue powder to her face. "Before the 1987 accident, the regulations were weak when it came to controlling radiation used in medicine and industry worldwide,"
said Eliana Amaral, International Atomic Energy Agency director of Radiation, Transport and Waste Safety. "There was no awareness that sources must be controlled from "cradle to grave" and to prevent the public accessing them. After the accident [new] concepts were fostered."
July 4, 1961
At the height of the Cold War, the U.S. and the Soviet Union were in a precarious nuclear battle. On July 4, 1961, Russian's missile submarine K-19 was conducting exercises in the North Atlantic when radioactive energy began leaking from its main cooling circuit. To further complicate matters, the
leak occurred in an inaccessible area near a pipe that regulated pressure within the cooling circuit. There was no coolant-flooding system to prevent the nuclear reactor from overheating and causing thermal explosion, so the crew had to
force open and go inside the sealed reactor compartment to try and repair the leak. The crew was exposed to radiation from poisonous gases and steam for lengthy periods of time, and eight men suffered painful deaths as a result.
December 18, 1970
Nevada's Yucca Flat, located 65 miles from Las Vegas, is one of the four major nuclear test regions in the state. During 1970's notorious Baneberry test, a 10-kiloton nuclear device was detonated beneath the Yucca Flat. But the
plug sealing the shaft from the Flat's surface burst open, flooding the atmosphere with radioactive matter. Eighty-six workers at the site were exposed to harmful radiation.
August 10, 1985
In August 1985, the Soviet nuclear-powered submarine K-431 experienced an explosion during the sub's refueling at the Chazhma Bay naval facility near Vladivostok, Russia's largest seaport city. After the submarine was refueled,
a new reactor tank lid was incorrectly set, resulting in a steam explosion that blew up critical mechanisms on board and dispelled new fuel and radioactive particles into the air.
Ten naval personnel died in the accident, most likely during the explosion, but
49 people suffered injuries from the radiation and 10 fell ill to radiation sickness.
