List of civilian nuclear accidents

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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. Military accidents are listed at List of military nuclear accidents. Civil radiation accidents not involving fissile material are listed at List of civilian radiation 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. Notably severe: there must be well-attested and substantial health damage, property damage or contamination; if an International Nuclear Event Scale (INES) level is available, of at least two.
  2. Nuclear aspect: the damage must be related directly to nuclear operations or materials; the event should involve fissile material or a reactor, not merely (for example) having occurred at the site of a nuclear power plant.
  3. Primarily civilian: the nuclear operation/material must be principally for non-military purposes.


  • 12 December 1952 — INES Level 5[1] - Chalk River, Ontario, 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 NRX reactor. The operators purged the reactor's heavy water moderator, and the reaction stopped in under 30 seconds. A subsequent cover gas system failure led to hydrogen explosions, which severely damaged the reactor core. The fission products from approximately 30 kg (66 lb) of uranium were released through the reactor stack. Contaminated light-water coolant leaked from the damaged coolant circuit into the reactor building; some 4,000 m3 (140,000 cu ft) were pumped via pipeline to a disposal area to avoid contamination of the Ottawa River. Subsequent monitoring of surrounding water sources revealed no contamination. After the incident, approximately 1202 people were involved in the two-year-long cleanup.[2] No immediate fatalities or injuries resulted from the incident; a 1982 follow-up study of exposed workers showed no long-term health effects, though Atomic Energy of Canada Limited (AECL) dosimetry files were lost in a 1956 fire. Future U.S. President Jimmy Carter, an engineer and then a lieutenant in the U.S. Navy, was among the cleanup crew.[3]
  • 24 May 1958 — INES Level needed - Chalk River, Ontario, 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. Approximately 679 people were employed in the clean-up.[4][5] A corporal named Bjarnie Hannibal Paulson who was at the cleanup did not die from his exposure, but developed unusual skin cancers. Paulson had to testify at many hearings before he was awarded compensation for his radiation injuries.[6]
  • 25 October 1958 - INES Level needed - Vinča, Serbia (then Yugoslavia) - Criticality excursion, irradiation of personnel
    • During a subcritical counting experiment, a power buildup went undetected at the Vinca Nuclear Institute's zero-power natural uranium heavy water-moderated research reactor.[7] 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.[8] Six scientists received radiation doses of 2–4 sieverts (200–400 rem) [9] (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 IAEA.[10]


  • A core melt accident occurred at the Westinghouse Waltz Mill test reactor. From what information remains of the event, one fuel element melted, resulting in the disposition of 2 million gallons of contaminated water generated during the accident. At least a portion of the water was retained on site in lagoons, a condition which eventually led to detectable 90Sr in groundwater plus contaminated soil. The site is currently undergoing cleanup.
  • An error by a worker at a United Nuclear Corporation fuel facility led to an accidental criticality. Robert Peabody, believing he was using a diluted uranium solution, accidentally put concentrated solution into an agitation tank containing sodium carbonate. Peabody was exposed to 100 Gy (10,000 rad) of radiation and died two days later. Ninety minutes after the criticality, a plant manager and another administrator returned to the building and were exposed to 1 Gy (100 rad), but suffered no ill effects.[13][14]
  • 5 October 1966 — INES Level needed - Monroe, Michigan, United States - Partial meltdown
  • A sodium cooling system malfunction caused a partial meltdown at the Enrico Fermi demonstration nuclear breeder reactor (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.[15]
  • Winter 1966-1967 (date unknown) – INES Level needed – location unknown – loss of coolant accident
    • The Soviet icebreaker Lenin, the USSR’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 Sea, along with 60% of the fuel elements packed in a separate container. The reactors were replaced with two new ones, and the ship reentered 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 station. Contamination was confined to the reactor core. The core was repaired and restarted in 1969, operating until the plant's shutdown in 2004.[16][17]
  • 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.[18][19]
  • Defueling and partial dismantling occurred from 1969 to 1973. In 1988, the lowest caverns were filled with concrete, and a regulatory permit was issued in December 1990. Currently, the archives of the Canton of Vaud are located in the caverns.[20]


  • A fire in a cable duct after a short circuit disabled the electrical power supply for all feedwater and emergency core cooling pumps. A power supply was improvised by the operating personnel after several hours.
  • 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 affected reactor was decommissioned following this accident.[21]


  • A brief power excursion in Reactor A2 led to a rupture of fuel bundles and a minor 80 GBq (2,200 mCi) release of nuclear materials at the Saint-Laurent Nuclear Power Plant. The reactor was repaired and continued operation until its decommissioning in 1992.[25]
  • March 1981 — INES Level 2 - Tsuruga, Japan - Radioactive materials released into Sea of Japan; overexposure of workers
  • 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 20 Gy of gamma and 17 Gy of neutron radiation which killed him two days later. Another 17 people outside of the reactor room absorbed doses ranging from 350 mGy to less than 10 mGy.[27] pg103[28]
  • Spherical fuel pebbles became lodged in the pipe used to deliver fuel elements to the reactor at an experimental 300-megawatt THTR-300 HTGR. Attempts by an operator to dislodge the fuel pebble damaged the pipe, releasing activated coolant gas which was detectable up to two kilometers from the reactor.[30]


  • 6 April 1993 — INES Level 4 - Tomsk, Russia - Explosion
  • A pressure buildup led to an explosive mechanical failure in a 34 m3 (1,200 cu ft) 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, 8,757 kg (19,306 lb) uranium, 449 g (15.8 oz) plutonium 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 (160 mCi) of Pu 239 and 30 TBq (810 Ci) of other radionuclides into the environment. The contamination plume extended 28 km (17 mi) NE of building 201, 20 km (12 mi) 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 20 mSv/yr).[31][32][33]
  • 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 Plant. The Hokuriku Electric Power Company who owned the reactor did not report this incident and falsified records, covering it up until March, 2007.[35]
  • Inadequately trained part-time workers prepared a uranyl nitrate solution containing about 16.6 kg (37 lb) of uranium, which exceeded the critical mass, into a precipitation tank at a uranium reprocessing facility in Tokai-mura northeast of Tokyo, Japan. 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.[36][37][38][39]


  • 10 April 2003 — INES Level 3 - Paks, Hungary - Fuel damaged
  • Partially spent fuel rods undergoing cleaning in a tank of heavy water ruptured and spilled fuel pellets at Paks Nuclear Power Plant. 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 131I.[40]
  • 20 t (20 long tons; 22 short tons) of uranium and 160 kg (350 lb) of plutonium dissolved in 83 kl (2,900 cu ft) of nitric acid leaked 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.[41][42]
  • November 2005 — INES Level needed - Braidwood, Illinois, United States - Nuclear material leak
  • 35 l (7.7 imp gal; 9.2 US gal) 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. A required public hearing on the licensing of the plant was not held due to the absence of public notification.[45][46][47][48]


  • After the 2011 Tōhoku earthquake and tsunami of March 11, the emergency power supply of the Fukushima-Daiichi nuclear power plant failed. This was followed by deliberate releases of radioactive gas from reactors 1 and 2 to relieve pressure.
  • On March 12, triggered by falling water levels and exposed fuel rods, a hydrogen explosion occurred at reactor 1, resulting in the collapse of the concrete outer structure.[53][54][55][56][57] Although the reactor containment itself was confirmed to be intact,[58][59][60] the hourly radiation from the plant reached 1.015 Sv (101.5 rem) - an amount equivalent to that allowable for ordinary people in one year.[61][62]
  • Residents of the Fukushima area were advised to stay inside, close doors and windows, turn off air conditioning, and to cover their mouths with masks, towels or handkerchiefs as well as not to drink tap water.[63] By the evening of March 12, the exclusion zone had been extended to 20 kilometres (12 mi) around the plant[64] and 70,000 to 80,000 people had been evacuated from homes in northern Japan.[65]
  • On March 14, a second, hydrogen explosion (nearly identical to the first explosion in Unit 1) occurred in the reactor building for Unit 3, with similar effects.[66]
  • On March 15, a third explosion occurs in the “pressure suppression room” of Unit 2[67] and is initially said not to have breached the reactor’s inner steel containment vessel,[68] but later reports indicated that the explosion damaged the steel containment structure of Unit 2 and much larger releases of radiation were expected than previously.[67]
  • On March 15, a fourth explosion damages the 4th floor area above the reactor and spent fuel pool of the Unit 4 reactor.[69] Contrary to the TEPCO press release, aerial photos show that most of the outer building was actually destroyed. The fuel rods (both new and spent fuel) of reactor Unit 4, stored in the now exposed spent fuel pool, were reportedly exposed to air – this would have risked the melting of the nuclear fuel. However, later research found the fuel rods been covered by water all the time.[70][71]
  • On 16 March TEPCO estimated that 70% of the fuel in Unit 1 had melted, and 33% in Unit 2, further suspecting that Unit 3's core might also be damaged.[72] In November 2011 TEPCO released the report of the Modular Accident Analysis Program (MAAP).[73] The report showed that the reactor pressure vessel (RPV) in Unit 1 (commonly known as the reactor core) had been damaged during the disaster, and that significant amounts of fuel had fallen into the bottom of the primary containment vessel (PCV) – the erosion of the concrete of the PCV by the molten fuel immediately after the disaster was estimated to have been stopped in approx. 0.7 metres (2 ft 4 in) depth, with the thickness of the containment being 7.6 metres (25 ft). Gas sampling done before the report detected no signs of an ongoing reaction of the fuel with the concrete of the PCV and all the fuel in Unit 1 was estimated to be "well cooled down, including the fuel dropped on the bottom of the reactor". MAAP further showed that fuel in Unit 2 and Unit 3 had melted, however less than Unit 1, and fuel was presumed to be still in the RPV, with no significant amounts of fuel fallen to the bottom of the PCV. The report further suggested that "there is a range in the evaluation results" from "most fuel in the RPV (some fuel in PCV)" in Unit 2 and Unit 3, to "all fuel in the RPV (none fuel fallen to the PCV)". For Unit 2 and Unit 3 it was estimated that the "fuel is cooled sufficiently". The larger damage in Unit 1 was according to the report due to long time that cooling water was no injected in Unit 1, letting much more decay heat accumulate – for about 1 day there was no water injection for Unit 1, while Unit 2 and Unit 3 had only a quarter of a day without water injection. As of December 2013, it was reported that TEPCO estimated for Unit 1 that "the decay heat must have decreased enough, the molten fuel can be assumed to remain in PCV (Primary container vessel)".[74]

See also


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  2. "The NRX Incident" by Peter Jedicke
  3. "The Canadian Nuclear FAQ - Section D: Safety and Liability".<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  4. "Reactor Accidents at Chalk River:The Human Fallout" by Dr. Gordon Edwards
  5. "What are the details of the accident at Chalk River's NRU reactor in 1958?" by Dr. Jeremy Whitlock
  6. "The Canadian Coalition for Nuclear Responsibility" letter by Dr. Gordon Edwards
  7. [1]
  8. [2]
  9. [3]
  10. [4]
  11. Rockwell International Corporation, Energy Systems Group. "Sodium Reactor Experiment Decommissioning Final Report" (PDF). ESG-DOE-13403. Retrieved 21 May 2014.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  12. [5]
  14. McLaughlin et al. pages 33-34
  15. [6]
  16. [7]
  17. [8]
  18. [9]
  19. [10]
  20. "Interface between Operator, Regulatory Body and Public" at
  21. [11]
  22. [12]
  23. [13]
  24. [14]
  25. [15]
  26. [16]
  27. [17]
  28. [18]
  29. (memoires of vice chief engineer of operation Anatoly Dyatlov, in Russian)
  30. [Begründung zur atomrechtlichen Anordnung vom 3. Juni 1986 des Ministers für Wirtschaft, Mittelstand und Technologie, declaration given in the Landtag (parliament) of the state Northrhine-Westphalia on 4th June 1986]
  31. [19]
  32. [20]
  33. Timeline: Nuclear plant accidents
  35. Japanese utility to shut reactor after admitting accident cover-up
  36. Tokaimura Criticality Accident
  37. Tokaimura Criticality Accident Nuclear Issues Briefing Paper #52
  38. Chronology and Press Reports of the Tokaimura Criticality
  39. Timeline: Nuclear plant accidents
  40. Incremented radioactivity of the heat carrier during refueling outage at a time of fuel cleaning | Nuclear power in Europe
  41. Huge radioactive leak closes Thorp nuclear plant
  42. British Nuclear Group releases report on Sellafield leak
  43. Exelon Braidwood Nuclear Facility Update on Tritium Releases and Groundwater Impacts
  45. Federal Register: May 4, 2007 (Volume 72, Number 86)
  46. Secrecy Shrouds Accident at Nuclear Plant
  47. More revelations about Nuclear Fuel Services, Inc.
  48. Erwin nuke problems known
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  60. Explosion at Fukushima I reactor 1; 4 injured, 3 irradiated (Japanese)
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  67. 67.0 67.1 Hiroko Tabuchi, Keith Bradsher, Matt Wald (March 14, 2011). "Japan Faces Prospect of Nuclear Catastrophe as Workers Leave Plant". The New York Times. <templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
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  70. Hiroko Tabuchi, Keith Bradsher,David E. Sanger Matthew L. Wald (March 15, 2011). "Fire and Damage at Japanese Plant Raise Risk of Nuclear Disaster". The New York Times. <templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  72. Fukushima Timeline
  73. The Evaluation Status of Reactor Core Damage at Fukushima Daiichi Nuclear Power Station Units 1 to 3 November 30, 2011 Tokyo Electric Power Company
  74. Most of fuel NOT remaining in reactor1 core / Tepco “but molten fuel is stopped in the concrete base”

External links

es:Anexo:Accidentes nucleares civiles