This article lists notable civilian accidents involving nuclear material. Military accidents are listed at list of military nuclear accidents. For a general discussion of both civilian and military accidents, see nuclear and radiation accidents.

Scope of this article

In listing civilian nuclear accidents, the following criteria have been followed:

1. There must be well-attested and substantial health damage, property damage or contamination.
2. The damage must be related directly to radioactive material, not merely (for example) at a nuclear power plant.
3. To qualify as "civilian", the nuclear operation/material must be principally for non-military purposes.
4. The event should involve fissile material, fission or a reactor.

1950s

• December 12, 1952 — The first serious nuclear accident occurred at AECL's NRX reactor in Chalk River, Ontario. A reactor shutoff rod failure, combined with several operator errors, led to a major power excursion of more than double the reactor's rated output. The operators purged the reactor's heavy water moderator, and the reaction stopped in under 30 seconds. A cover gas system failure led to hydrogen explosions, which severely damaged the reactor's interior. The fission products of approximately 30 kg of uranium were released through the reactor stack. Irradiated light-water coolant leaked from the damaged coolant circuit into the reactor building; some 4,000 cubic metres were pumped via pipeline to a disposal area to avoid contamination of the Ottawa River. Subsequent monitoring of surrounding water sources revealed no contamination. No immediate fatalities or injuries resulted from the incident; a 1982 followup study of exposed workers showed no long-term health effects. Future U.S. President Jimmy Carter, then a nuclear engineer in the US Navy, was among the cleanup crew.[1][2]

• May 24, 1958 — At the NRU reactor in Chalk River, Ontario, a damaged uranium fuel rod caught fire and was torn in two as it was being removed from the core, due to inadequate cooling. The fire was extinguished, but not before releasing a sizeable quantity of radioactive combustion products that contaminated the interior of the reactor building and, to a lesser degree, an area surrounding the laboratory site. Over 600 people were employed in the clean-up.[3][4]

• July 26, 1959 — The first partial core meltdown took place when the Sodium Reactor Experiment SRE) — a sodium-cooled experimental nuclear reactor at the Rocketdyne corporation's Santa Susana Field Laboratory (in the Simi Hills northwest of Los Angeles) — experienced a power excursion that caused severe overheating of the reactor core, resulting in the melting of one-third of the nuclear fuel and significant releases of radioactive gases.[5]

1960s

• October 5, 1966 – A sodium cooling system malfunction at the Enrico Fermi demonstration nuclear breeder reactor on the shore of Lake Erie near Monroe, Michigan, caused a partial core meltdown. The accident was attributed to a piece of zirconium that obstructed a flow-guide in the sodium cooling system. Two of the 105 fuel assemblies melted during the incident, but no contamination was recorded outside the containment vessel. [6]
• May 1967 – Unit 2 at the Chapelcross Magnox nuclear power station in Dumfries and Galloway, Scotland, suffered a partial meltdown when a fuel rod failed and caught fire after the unit was refuelled. Following the incident, the reactor was shut down for two years for repairs [7] [8].
• January 21, 1969 – A coolant malfunction in an experimental underground nuclear reactor at Lucens, Canton of Vaud, Switzerland. No injuries or fatalities resulted. The cavern was heavily contaminated and was sealed. [9][10]
• May 1, 1969 – A malfunctioning check valve caused a flooding in Ågesta pressurized heavy water nuclear power plant in a suburb outside of Stockholm, Sweden. The flooding of 400 m³ coolant water into the turbine room stopped the turbine and caused short circuits in multiple control functions rendering them inoperable. The reactor was stopped manually. As a result of the accident, approximately 500 liters of heavy water leaked out through faulty check valves.

1970s

• February 22, 1977 – The Czechoslovakian nuclear power plant A-1 in Jaslovské Bohunice experienced a serious accident during fuel loading. This INES level 4 nuclear accident resulted in damaged fuel integrity, extensive corrosion damage of fuel cladding and release of radioactivity into the plant area. As result the A1 power plant was shut down and is being decommissioned. [11]
• March 28, 1979 – Equipment failures and worker mistakes contributed to a loss of coolant and a partial core meltdown at the Three Mile Island nuclear reactor in Middletown, Pennsylvania. This is the worst commercial nuclear accident in the United States to date. Site boundary radiation exposure was under 100 millirems (1 mSv) (less than annual exposure due to natural sources), with exposure of 1 millirem (10 µSv) to approximately 2 million people. There were no immediate fatalities, followup radiological studies predict at most one long-term cancer fatality. [12][13][14]

1980s

• March 1981 – More than 100 workers were exposed to doses of up to 155 millirem per day radiation during repairs of a nuclear power plant in Tsuruga, Japan, violating the company's limit of 100 millirems (1 mSv) per day. [15]
• January 25, 1982 – At Rochester Gas & Electric Company's Ginna plant in Rochester, New York, a steam generator pipe broke, spilling radioactive coolant on the plant floor. Small amounts (about 80 Ci or 3 TBq) of radioactive steam escaped into the air.[16][17][18]
• September 23, 1983 – Buenos Aires, Argentina An operator error during a fuel plate reconfiguration led to a criticality accident at the RA-2 facility in an experimental test reactor. An excursion of 3×10¹⁷ fissions followed; the operator absorbed 2000 rad (20 Gy) of gamma and 1700 rad (17 Gy) of neutron radiation which killed him two days later. Another 17 people outside of the reactor room absorbed doses ranging from 35 rad (0.35 Gy) to less than 1 rad (0.01 Gy).[19] pg103[20]

• April 26, 1986 – The worst accident in the history of nuclear power occurred at the Chernobyl nuclear power plant located approximately 100 kilometers north-northwest of Kiev, USSR (now part of Ukraine). A mishandled reactor safety test led to an uncontrolled power excursion, causing a severe steam explosion and release of radioactive material. Approximately fifty fatalities resulted from the accident and its immediate aftermath (most were cleanup personnel) and an additional nine fatal cases of thyroid cancer in children in the Chernobyl area have been attributed to the accident. Radioactive material was spread over much of Europe, with over 100,000 evacuated from the areas immediately surrounding Chernobyl in addition to 300,000 from the areas of fallout in Ukraine, Belarus and Russia. Approximately 1,000 mi² (3,000 km²) of land (the "Exclusion Zone") around the site have been deemed off-limits for humans for an indefinite period. Several studies by governments, UN agencies and environmental groups have estimated the consequences and eventual number of casualties, and their findings are subject to controversy. See Chernobyl disaster.

• May 4, 1986, – An experimental 300-megawatt THTR-300 HTGR located in Hamm-Uentrop, Germany released radiation after one of its spherical fuel pebbles became lodged in the pipe used to deliver fuel elements to the reactor. Operator actions to dislodge the obstruction during the event damaged the fuel pebble cladding, releasing radiation detectable up to two kilometers from the reactor. [21]
• December 17, 1987 – Heavy accident at Biblis Nuclear Power Plant, Hessen, Germany.
• November 24, 1989 – Near-meltdown at Greifswald, East Germany [22]
• October 19, 1989, – the Vandellos nuclear power plant near Tarragona, Spain did not result in an external release of radioactivity, nor was there damage to the reactor core or contamination on site. However, the damage to the plant's safety systems due to fire degraded the defence-in-depth significantly. The event is classified as Level 3, based on the defence-in-depth criterion. The plant was closed due to this accident, and now is in dismantling process.

1990s

• April 6, 1994 – Tomsk, Russia At the Tomsk-7 Siberian Chemical Enterprise plutonium reprocessing facility, a pressure buildup led to an explosive mechanical failure in a 34 cubic meter stainless steel reaction vessel buried in a concrete bunker under building 201 of the radiochemical works. The vessel contained a mixture of concentrated nitric acid, uranium (8757 kg), plutonium (449 g) along with a mixture of radioactive and organic waste from a prior extraction cycle. The explosion dislodged the concrete lid of the bunker and blew a large hole in the roof of the building, releasing approximately 6 GBq of Pu 239 and 30 TBq of various other radionuclides into the environment. The accident exposed 160 on-site workers and almost two thousand cleanup workers to total doses of up to 50 mSv (the threshold limit for radiation workers is 100 mSv per 5 years)[23]. The contamination plume extended 28 km NE of building 201, 20 km beyond the facility property. The small village of Georgievka (pop. 200) was at the end of the fallout plume, but no fatalities, illnesses or injuries were reported. [24]
• September 30, 1999 – Japan's worst nuclear accident to date takes place at a uranium reprocessing facility in Tokai-mura, Ibaraki prefecture, northeast of Tokyo, Japan. The direct cause of the criticality accident was workers putting uranyl nitrate solution containing about 16.6 kg of uranium, which exceeded the critical mass, into a precipitation tank. The tank was not designed to dissolve this type of solution and was not configured to prevent eventual criticality. Three workers were exposed to (neutron)radiation doses in excess of allowable limits (two of these workers died); a further 116 received lesser doses of 1 msV or greater. [25] [26] [27] For more details, see Tokai, Ibaraki and 5 yen coin.

2000s

• February 15, 2000 – The Indian Point nuclear power plant's reactor 2 in Buchanan, New York, vented a small amount of radioactive steam when a steam generator tube failed. No detectable radioactivity was observed offsite. Con Edison was censured by the NRC for not following the procedures for timely notification of government agencies. Subsequently, Con Edison is required by the NRC to replace all four steam generators. [28] NRC Information Notice 2000-09
• February 9, 2002 – Two workers were exposed to a small amount of radiation and suffered minor burns when a fire broke out at the Onagawa Nuclear Power Station Miyagi Prefecture, Japan. The fire occurred in the basement of reactor #3 during a routine inspection when a spray can was punctured accidentally, igniting a sheet of plastic. [29]
• April 10, 2003 – Radioactivity leak in Paks Nuclear Power Plant, Hungary. Rated INES-3.
• August 9, 2004 - An accident occurred in a building housing turbines for the Mihama 3 reactor, operated by Kansai Electric Power Company, in Fukui perfecture, about 320 km west of Tokyo.^[1] Hot water and steam leaking from a broken pipe killed five workers and resulted in six others being injured. The accident has been called Japan's worst nuclear power accident.^[2][3]

• April 19, 2005 – Sellafield, UK. Twenty metric tons of uranium and 160 kilograms of plutonium dissolved in 83,000 liters of nitric acid leaked undetected over several months from a cracked pipe into a stainless steel sump chamber at the Thorp nuclear fuel reprocessing plant. The partially processed spent fuel was drained into holding tanks outside the plant. [30].
• 2005 – Dounreay, UK. In September, the site's cementation plant was closed when 266 litres of radioactive reprocessing residues were spilled inside containment. [31][32]. In October, another of the site's reprocessing laboratories was closed down after nose-blow tests of eight workers tested positive for trace radioactivity. [33]
• July 25, 2006 – An electrical fault prompted shut down of the Forsmark Nuclear Power Plant, Sweden. Although there was no damage to the reactor, no radioactive release and no adverse health consequences, the incident highlighted potentially hazardous flaws in the site's reactor shutdown procedures. [34](in Swedish)[35](in Swedish)[36]
• November 2005 -- Tritium contamination of groundwater was discovered at Exelon's Braidwood station.[37] Later, in March, 2006, Attorney General Lisa Madigan and Will County State’s Attorney James Glasgow announced that they were filing a lawsuit against Exelon because of six such leaks, demanding that the utility provide substitute water supplies to residents although no well outside company property shows levels that exceed drinking water standards. The lawsuit is a class-action suit representing two communities roughly two miles away from the plant and not including the closest community to the plant.^[4][5] According to the NRC, "The inspection determined that public health and safety has not been adversely affected and the dose consequence to the public that can be attributed to current onsite conditions is negligible with respect to NRC regulatory limits." However, the chairman of the NRC, said, "They're going to have to fix it."