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This article lists notable civilian accidents involving fissile nuclear material or nuclear reactors. Civilian incidents not serious enough to be accidents are listed at List of civilian nuclear incidents.

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 or a reactor.


  • December 12, 1952 — INES Level 5 - Chalk River, Ontariomarker, Canada - Reactor core damaged
    • 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 at AECL's NRXmarker reactor. 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 core. The fission products from 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 meters 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.
  • May 24, 1958 — INES Level needed - Chalk River, Ontariomarker, Canada - Fuel damaged
    • Due to inadequate cooling a damaged uranium fuel rod caught fire and was torn in two as it was being removed from the core at the NRU reactor. The fire was extinguished, but not before radioactive combustion products 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.
  • October 25, 1958 - INES Level needed - Vinčamarker, Yugoslavia - Criticality excursion, irradiation of personnel
    • During a subcritical counting experiment a power buildup went undetected at the Boris Kidrich Institute's zero-power natural uranium heavy water moderated research reactor . Saturation of radiation detection chambers gave the researchers false readings and the level of moderator in the reactor tank was raised triggering a criticality excursion which a researcher detected from the smell of ozone . Six scientists received radiation doses between 200 to 400 rems (p.96). An experimental bone marrow transplant treatment was performed on all of them in France and five survived, despite the ultimate rejection of the marrow in all cases. A single woman among them later had a child without apparent complications. This was one of the first nuclear incidents investigated by then newly-formed IAEAmarker.


  • October 5, 1966 — INES Level needed - Monroe, Michiganmarker, United States - Partial meltdown
*A sodium cooling system malfunction caused a partial meltdown at the Enrico Fermi demonstration nuclear breeder reactormarker (Enrico Fermi-1 fast breeder reactor). The accident was attributed to a zirconium fragment 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.
  • Winter 1966-1967 (date unknown) – INES Level needed – location unknown – loss of coolant accident
    • The Soviet icebreaker Lenin, the USSRmarker’s first nuclear-powered surface ship, suffered a major accident (possibly a meltdown — exactly what happened remains a matter of controversy in the West) in one of its three reactors. To find the leak the crew broke through the concrete and steel radiation shield with sledgehammers, causing irreparable damage. It was rumored that around 30 of the crew were killed. The ship was abandoned for a year to allow radiation levels to drop before the three reactors were removed, to be dumped into the Tsivolko Fjord on the Kara Seamarker, along with 60% of the fuel elements packed in a separate container. The reactors were replaced with two new ones, and the ship re-entered service in 1970, serving until 1989.

*Graphite debris partially blocked a fuel channel causing a fuel element to melt and catch fire at the Chapelcross nuclear power stationmarker. Contamination was confined to the reactor core. The core was repaired and restarted in 1969, operating until the plant's shutdown in 2004. .

*A total loss of coolant led to a power excursion and explosion of an experimental nuclear reactor in a large cave at Lucens. The underground location of this reactor acted like a containment building and prevented any outside contamination. The cavern was heavily contaminated and was sealed. No injuries or fatalities resulted.


*Operators neglected to remove moisture absorbing materials from a fuel rod assembly before loading it into the KS 150 reactor at power plant A-1. The accident resulted in damaged fuel integrity, extensive corrosion damage of fuel cladding and release of radioactivity into the plant area. The plant was decommissioned following this accident.

* Equipment failures and worker mistakes contributed to a loss of coolant and a partial core meltdown at the Three Mile Island Nuclear Generating Stationmarker 15 km (9 miles) southeast of Harrisburgmarker. While the reactor was extensively damaged on-site radiation exposure was under 100 millirems (less than annual exposure due to natural sources), with exposure of 1 millirem (10 µSv) to approximately 2 million people. There were no fatalities. Follow up radiological studies predict at most one long-term cancer fatality.


  • March 13, 1980 - INES Level 4 - Orléansmarker, France - Nuclear materials leak
*A brief power excursion in Reactor A2 led to a rupture of fuel bundles and a minor release (8 x 1010 Bq) of nuclear materials at the Saint-Laurent Nuclear Power Plantmarker. The reactor was repaired and continued operation until its decommissioning in 1992.

  • March, 1981 — INES Level 2 - Tsuruga, Japan - Overexposure of workers
*More than 100 workers were exposed to doses of up to 155 millirem per day radiation during repairs of a nuclear power plant, violating the company's limit of 100 millirems (1 mSv) per day.

*An operator error during a fuel plate reconfiguration in an experimental test reactor led to an excursion of 3×1017 fissions at the RA-2 facility. 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). pg103

  • April 26, 1986 — INES Level 7 - Prypiatmarker, Ukrainemarker (then USSRmarker) - Power excursion, explosion, complete meltdown
*A mishandled reactor safety test led to an uncontrolled power excursion, causing a severe steam explosion, meltdown and release of radioactive material at the Chernobylmarker nuclear power plant located approximately 100 kilometers north-northwest of Kievmarker. Approximately fifty fatalities (mostly cleanup personnel) resulted from the accident and the immediate aftermath. An additional nine fatal cases of thyroid cancer in children in the Chernobyl area have been attributed to the accident. The explosion and combustion of the graphite reactor core spread radioactive material over much of Europe. 100,000 people were evacuated from the areas immediately surrounding Chernobylmarker in addition to 300,000 from the areas of heavy fallout in Ukraine, Belarusmarker and Russia. An "Exclusion Zone"marker was created surrounding the site encompassing approximately 1,000 mi² (3,000 km²) and deemed off-limits for human habitation for an indefinite period. Several studies by governments, UN agencies and environmental groups have estimated the consequences and eventual number of casualties. Their findings are subject to controversy.

*A spherical fuel pebble became lodged in the pipe used to deliver fuel elements to the reactor at an experimental 300-megawatt THTR-300marker HTGR. Attempts by an operator to dislodge the fuel pebble damaged its cladding, releasing radiation detectable up to two kilometers from the reactor.

*Operators disabled three of six cooling pumps to test emergency shutoffs. Instead of the expected automatic shutdown a fourth pump failed causing excessive heating which damaged ten fuel rods. The accident was attributed to sticky relay contacts and generally poor construction in the Soviet-built reactor.


  • April 6, 1993 — INES Level 4 - Tomskmarker, Russia - Explosion
*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 at the Tomsk-7 Siberian Chemical Enterprise plutonium reprocessing facility. 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 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. 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).

*Operators attempting to insert one control rod during an inspection neglected procedure and instead withdrew three causing a 15 minute uncontrolled sustained reaction at the number 1 reactor of Shika Nuclear Power Plantmarker. The Hokuriku Electric Company who owned the reactor did not report this incident and falsified records, covering it up until March, 2007.

  • September 30, 1999 — INES Level 4 - Ibaraki Prefecturemarker, Japan - Accidental criticality
*Workers put uranyl nitrate solution containing about 16.6 kg of uranium, which exceeded the critical mass, into a precipitation tank at a uranium reprocessing facility in Tokai-muramarker northeast of Tokyo, Japanmarker. 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. 116 other workers received lesser doses of 1 mSv or greater though not in excess of the allowable limit.


  • April 10, 2003 — INES Level 3 - Paksmarker, Hungary - Fuel damaged
*Partially spent fuel rods undergoing cleaning in a tank of heavy water ruptured and spilled fuel pellets at Paks Nuclear Power Plantmarker. It is suspected that inadequate cooling of the rods during the cleaning process combined with a sudden influx of cold water thermally shocked fuel rods causing them to split. Boric acid was added to the tank to prevent the loose fuel pellets from achieving criticality. Ammonia and hydrazine were also added to absorb iodine-131. ,

*Twenty metric tons of uranium and 160 kilograms of plutonium dissolved in 83,000 litres of nitric acid leaked over several months from a cracked pipe into a stainless steel sump chamber at the Thorp nuclear fuel reprocessing plantmarker. The partially processed spent fuel was drained into holding tanks outside the plant. .

  • November 2005 — INES Level needed - Braidwood, Illinoismarker, United States - Nuclear material leak
*Tritium contamination of groundwater was discovered at Exelon's Braidwood stationmarker. Groundwater off site remains within safe drinking standards though the NRC is requiring the plant to correct any problems related to the release.

  • March 6, 2006 — INES Level needed - Erwin, Tennesseemarker, United States - Nuclear material leak
*Thirty-five liters of a highly enriched uranium solution leaked during transfer into a lab at Nuclear Fuel Services Erwin Plant. The incident caused a seven-month shutdown and a required public hearing on the licensing of the plant.

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