Nuclear and radiation accidents and incidents

This article is about nuclear and radiation accidents in general. For a list of military nuclear accidents, see List of military nuclear accidents. For a list of civilian nuclear accidents, see List of civilian nuclear accidents. For a discussion of the controversy over nuclear power, see Nuclear debate (disambiguation).

See also: Lists of nuclear disasters and radioactive incidents

Pathways from airborne radioactive contamination to man

A nuclear and radiation accident is usually defined as a loss of control of radioactive material with the potential to cause radiation poisoning. The likelihood and potential impact of such accidents has been a topic of debate practically since the first nuclear reactors were constructed. It has also been a key factor in public concern about nuclear facilities. Many technical measures to reduce the risk of accidents or (should one occur) to minimize the amount of radioactivity released to the environment have been adopted. Despite the use of such measures, "there have been many accidents with varying impacts as well near misses and incidents".

Nuclear accidents (often defined by the International Atomic Energy Agency's International Nuclear Event Scale) are much larger in magnitude of effects than a typical radiation accident. The prime example of a "major nuclear accident" is one in which a reactor core is damaged and large amounts of radiation are released, such as in the Chernobyl Disaster in 1986. In the period to 2007, sixty-three accidents have occurred at nuclear power plants. Twenty-nine of these have occurred since Chernobyl, and 71 percent of all nuclear accidents (45 out of 63) occurred in the United States.

Serious radiation accidents include the radiotherapy accident in Costa Rica, radiotherapy accident in Zaragoza, radiation accident in Morocco, Goiania accident, radiation accident in Mexico City, radiotherapy unit accident in Thailand, and the Mayapuri radiological accident.

The web page at the International Atomic Energy Agency, which deals with recent accidents is [15].

Nuclear power plant accidents

The abandoned city of Prypiat, Ukraine, following the Chernobyl disaster. The Chernobyl nuclear power plant is in the background.

The worst nuclear accident to date was the Chernobyl disaster which occurred in 1986 in Ukraine. That accident killed 56 people directly, and caused an estimated 4,000 additional cases of fatal cancer, as well as damaging almost $7 billion of property. Radioactive fallout from the accident concentrated over or near Belarus, Ukraine and Russia and at least 350,000 people were forcibly resettled away from these areas.

Sixty-three accidents have occurred at nuclear power plants. Twenty-nine of these have occurred since the 1986 Chernobyl disaster, and 71 percent of all nuclear accidents (45 out of 63) occurred in the United States. There have been comparatively few fatalities associated with nuclear power plant accidents, but there has often been significant property damage.

Nuclear power plant accidents
with multiple fatalities and/or more than US$100 million in property damage, 1952-2010

Date	Location	Description	Fatalities	Cost (in millions 2006 $)	INES level
October 8, 1957	Windscale, UK	Windscale fire ignites plutonium piles, contaminating surrounding dairy farms	33	US$78	5
January 3, 1961	Idaho Falls, Idaho, US	Explosion at National Reactor Testing Station	3	$US22
February 22, 1977	Jaslovske Bohunice, Czechoslovakia	Severe corrosion of reactor and release of radioactivity into the plant area, necessitating total decommission	0	US$1,700
March 28, 1979	Middletown, Pennsylvania, US	Loss of coolant and partial core meltdown, see Three Mile Island accident and Three Mile Island accident health effects	0	US$2,400	5
September 15, 1984	Athens, Alabama, US	Safety violations, operator error, and design problems force six year outage at Browns Ferry Unit 2	0	US$110
March 9, 1985	Athens, Alabama, US	Instrumentation systems malfunction during startup, which led to suspension of operations at all three Browns Ferry Units	0	US$1,830
April 11, 1986	Plymouth, Massachusetts, US	Recurring equipment problems force emergency shutdown of Boston Edison’s Pilgrim Nuclear Power Plant	0	US$1,001
April 26, 1986	Kiev, Ukraine	Steam explosion and meltdown (see Chernobyl disaster) necessitating the evacuation of 300,000 people from Kiev and dispersing radioactive material across Europe (see Chernobyl disaster effects)	4,056	US$6,700	7
May 4, 1986	Hamm-Uentrop, Germany	Experimental reactor releases excessive radiation to four square kilometers surrounding the facility	0	US$267
March 31, 1987	Delta, Pennsylvania, US	Peach Bottom units 2 and 3 shutdown due to cooling malfunctions and unexplained equipment problems	0	US$400
December 19, 1987	Lycoming, New York, US	Malfunctions force Niagara Mohawk Power Corporation to shut down Nine Mile Point Unit 1	0	US$150
March 17, 1989	Lusby, Maryland, US	Inspections at Calvert Cliff Units 1 and 2 reveal cracks at pressurized heater sleeves, forcing extended shutdowns	0	US$120
November 24, 1989	Greifswald, East Germany	Electrical error causes fire in the main trough that destroys control lines and five main coolant pumps	0	UD$443
February 20, 1996	Waterford, Connecticut, US	Leaking valve forces shutdown Millstone Nuclear Power Plant Units 1 and 2, multiple equipment failures found	0	US$254
September 2, 1996	Crystal River, Florida, US	Balance-of-plant equipment malfunction forces shutdown and extensive repairs at Crystal River Unit 3	0	US$384
September 30, 1999	Ibaraki Prefecture, Japan	Workers at the Tokaimura uranium processing facility try to save time by mixing uranium in buckets, killing two and injuring 1200	2	US$54	4
February 16, 2002	Oak Harbor, Ohio, US	Severe corrosion of control rod forces 24-month outage of Davis-Besse reactor	0	US$143
August 9, 2004	Fukui Prefecture, Japan	Steam explosion at Mihama Nuclear Power Plant kills 5 workers and injures dozens more	5	US$9	1
February 1, 2010	Montpelier, Vermont, US	Deteriorating underground pipes from the Vermont Yankee Nuclear Power Plant leak radioactive tritium into groundwater supplies	0	US$700

To compare the historical safety record of civilian nuclear energy with the historical record of other forms of electrical generation, Ball, Roberts, and Simpson, the IAEA, and the Paul Scherrer Institut found in separate studies that during the period from 1970 - 1992, there were just 39 on-the-job deaths of nuclear power plant workers worldwide, while during the same time period, there were 6,400 on-the-job deaths of coal power plant workers, 1,200 on-the-job deaths of natural gas power plant workers and members of the general public caused by natural gas power plants, and 4,000 deaths of members of the general public caused by hydroelectric power plants. In particular, coal power plants are estimated to kill 24,000 Americans per year, due to lung disease as well as causing 40,000 heart attacks per year in the United States. According to Scientific American, the average coal power plant emits more than 100 times as much radiation per year than a comparatively sized nuclear power plant does, in the form of toxic coal waste known as fly ash.

Radiation accidents

Serious radiation accidents include:

• 29 September 1957 – Mayak nuclear waste storage tank explosion at Chelyabinsk. Two hundred plus fatalities and this figure is a conservative estimate; 270,000 people were exposed to dangerous radiation levels. Over thirty small communities had been removed from Soviet maps between 1958 and 1991.
• July 4, 1961 – Soviet submarine K-19 accident. Eight fatalities and more than 30 people were over-exposed to radiation.
• 1962 – Radiation accident in Mexico City, four fatalities.
• 1979 - Church Rock Uranium Mill Spill in New Mexico, USA.
• March 1984 – Radiation accident in Morocco, eight fatalities. 　
• August 10, 1985 – Soviet submarine K-431 accident. Ten fatalities and 49 other people suffered radiation injuries.
• September 13, 1987 – Goiania accident. Four fatalities and 249 other people received serious radiation contamination.
• December 1990 – Radiotherapy accident in Zaragoza. Eleven fatalities and 27 other patients were injured.
• 6 April 1993 - accident at the Tomsk-7 Reprocessing Complex, when a tank exploded while being cleaned with nitric acid. The explosion released a cloud of radioactive gas. (INES level 4).
• 1996 – Radiotherapy accident in Costa Rica. Thirteen fatalities and 114 other patients received an overdose of radiation.
• February 2000 - Three deaths and ten injuries resulted in Samut Prakarn when a radiation-therapy unit was dismantled.
• April 2010 - Mayapuri radiological accident, India, one fatality.

Accident types

Loss of coolant accident

Main article: Loss of coolant

See also: Nuclear meltdown and Design Basis Accident

Criticality accidents

A criticality accident (also sometimes referred to as an "excursion" or "power excursion") occurs when a nuclear chain reaction is accidentally allowed to occur in fissile material, such as enriched uranium or plutonium. The Chernobyl accident is an example of a criticality accident. This accident destroyed a reactor at the plant and left a large geographic area uninhabitable. In a smaller scale accident at Sarov a technician working with highly enriched uranium was irradiated while preparing an experiment involving a sphere of fissile material. The Sarov accident is interesting because the system remained critical for many days before it could be stopped, though safely located in a shielded experimental hall. This is an example of a limited scope accident where only a few people can be harmed, while no release of radioactivity into the environment occurred. A criticality accident with limited off site release of both radiation (gamma and neutron) and a very small release of radioactivity occurred at Tokaimura in 1999 during the production of enriched uranium fuel . Two workers died, a third was permanently injured, and 350 citizens were exposed to radiation.

Decay heat

Decay heat accidents are where the heat generated by the radioactive decay causes harm. In a large nuclear reactor, a loss of coolant accident can damage the core: for example, at Three Mile Island a recently shutdown (SCRAMed) PWR reactor was left for a length of time without cooling water. As a result the nuclear fuel was damaged, and the core partially melted. The removal of the decay heat is a significant reactor safety concern, especially shortly after shutdown. Failure to remove decay heat may cause the reactor core temperature to rise to dangerous levels and has caused nuclear accidents. The heat removal is usually achieved through several redundant and diverse systems, and the heat is often dissipated to an 'ultimate heat sink' which has a large capacity and requires no active power, though this method is typically used after decay heat has reduced to a very small value. However, the main cause of release of radioactivity in the Three Mile Island accident was a Pilot-operated relief valve on the primary loop which stuck in the open position. This caused the overflow tank into which it drained to rupture and release large amounts of radioactive cooling water into the containment building.

Transport

Transport accidents can cause a release of radioactivity resulting in contamination or shielding to be damaged resulting in direct irradiation. In Cochabamba a defective gamma radiography set was transported in a passenger bus as cargo. The gamma source was outside the shielding, and it irradiated some bus passengers.

In the United Kingdom, it was revealed in a court case that in March 2002 a radiotherapy source was transported from Leeds to Sellafield with defective shielding. The shielding had a gap on the underside. It is thought that no human has been seriously harmed by the escaping radiation.

Equipment failure

Equipment failure is one possible type of accident, recently at Białystok in Poland the electronics associated with a particle accelerator used for the treatment of cancer suffered a malfunction . This then led to the overexposure of at least one patient. While the initial failure was the simple failure of a semiconductor diode, it set in motion a series of events which led to a radiation injury.

A related cause of accidents is failure of control software, as in the cases involving the Therac-25 medical radiotherapy equipment: the elimination of a hardware safety interlock in a new design model exposed a previously undetected bug in the control software, which could lead to patients receiving massive overdoses under a specific set of conditions.

Human error

A sketch used by doctors to determine the amount of radiation to which each person had been exposed during the Slotin excursion.

An assessment conducted by the Commissariat a` l’E´ nergie Atomique (CEA) in France concluded that no amount of technical innovation can eliminate the risk of human-induced errors associated with the operation of nuclear power plants. Two types of mistakes were deemed most serious: errors committed during field operations, such as maintenance and testing, that can cause an accident; and human errors made during small accidents that cascade to complete failure.

In 1946 Canadian Manhattan Project physicist Louis Slotin performed a risky experiment known as "tickling the dragon's tail" which involved two hemispheres of neutron-reflective beryllium being brought together around a plutonium core to bring it to criticality. Against operating procedures, the hemispheres were separated only by a screwdriver. The screwdriver slipped and set off a chain reaction criticality accident filling the room with harmful radiation and a flash of blue light (caused by excited, ionized air particles returning to their unexcited states). Slotin reflexively separated the hemispheres in reaction to the heat flash and blue light, preventing further irradiation of several co-workers present in the room. However Slotin absorbed a lethal dose of the radiation and died nine days afterwards.

Lost source

Lost source accidents, also referred to as an orphan source are incidents in which a radioactive source is lost, stolen or abandoned. The source then might cause harm to humans. For example, see the event in Lilo where sources were left behind by the Soviet army. Another case occurred at Yanango where a radiography source was lost, also at Samut Prakarn a cobalt-60 teletherapy source was lost and at Gilan in Iran a radiography source harmed a welder. The best known example of this type of event is the Goiânia accident which occurred in Brazil.

The International Atomic Energy Agency has provided guides for scrap metal collectors on what a sealed source might look like. The scrap metal industry is the one where lost sources are most likely to be found.

Others

Some accidents defy classification. These accidents happen when the unexpected occurs with a radioactive source. For instance if a bird were to grab a radioactive source containing radium from a window sill and then fly away with it, return to its nest and then die shortly afterwards from direct irradiation then a minor radiation accident would have occurred. As the hypothetical act of placing the source on a window sill by a human permitted the bird access to the source, it is unclear how such an event should be classified, as a lost source event or a something else. Radium lost and found describes a tale of a pig walking about with a radium source inside; this was a radium source lost from a hospital. There are also accidents which are "normal" industrial accidents that involve radioactive material. For instance a runaway reaction at Tomsk involving red oil caused radioactive material to be spread around the site.

For a list of many of the most important accidents see the International Atomic Energy Agency site.

Analyses of nuclear power plant accidents

The Nuclear Regulatory Commission (NRC) now requires each nuclear power plant in the U.S. to have a probabilistic risk assessment (PRA) performed upon it. The two types of such plants in the US (as of 2007) are boiling water reactors and pressurized water reactors, and a study based on two early such PRAs was done (NUREG-1150) and released to the public. However, those early PRAs made unrealistically conservative assumptions, and the NRC is now generating a new study: SOARCA.

Nuclear Regulatory Commission

Nuclear Regulatory Commission Headquarters and Regional staff members typically participate in four full-scale and emergency response exercises each year, selected from among the list of full-scale Federal Emergency Management Agency (FEMA)-graded exercises required of nuclear facilities. Regional staff members and selected Headquarters staff also participate in post-plume, ingestion phase response exercises. On-scene participants include the NRC licensee, and State, county, and local emergency response agencies. This allows for Federal interagency participation that will provide increased preparedness during the potential for an event at an operating nuclear reactor.

The US Nuclear Regulatory Commission, (NRC) collects reports of incidents occurring at regulated facilities. The agency currently uses a 4 level taxonomy to classify reported incidents:

• Notification of Unusual Event
• Alert
• Site Area Emergency
• General Emergency

Not all reportable events constitute accidents. Incidents which threaten the normal operation or security of a facility may be reportable but not result in any release of radioactivity.

The US Department of Energy uses a similar classification system for events occurring at fuel cycle plants and facilities owned by the US government which are therefore regulated by the DOE instead of the NRC.

NRC Alerts

• Indian Point Unit 2, Buchanan, New York, 15-Feb-2000.

NRC Site Area Emergencies

• LaSalle County Nuclear Generating Station Unit 1, Seneca, Illinois, 20-Feb-2006.
• Honeywell International, Metropolis, Illinois, 22-Dec-2003.
• Idaho National Engineering & Environmental Laboratory, Idaho Falls, Idaho, 27-Jul-2000 and 17-Sep-2000.
• Idaho National Engineering & Environmental Laboratory, Idaho Falls, Idaho, 12-Jul-1999.
• Nuclear Fuel Services, Erwin, Tennessee, 2-Apr-1996.
• Nine Mile Point Unit 2, Oswego, New York, 13-Aug-1991.
• Vogtle Electric Generating Plant Unit 1, Burke County, Georgia, 20-Mar-1990.
• Davis-Besse, Oak Harbor, Ohio, 09-Jun-1985. Originally declared as an "Unusual Event" but upgraded by NRC findings.
• Ginna, Ontario, New York, 25-Jan-1982.

NRC General Emergencies

• Three Mile Island Unit 2, 28-Mar-1979.

See also

• Background radiation
• Chernobyl compared to other radioactivity releases
• Chernobyl disaster effects
• Common mode failure
• Duke Power Co. v. Carolina Environmental Study Group
• Fuel element failure
• Goiânia accident
• Radioactive scrap metal
• Orphan source
• International Nuclear Events Scale
• Ionizing radiation (for a table of radiation exposures)
• List of Chernobyl-related articles
• List of crimes involving radioactive substances
• List of disasters
• List of dam failures
• List of oil spills
• List of nuclear reactors
• Lists of nuclear disasters and radioactive incidents
• Nuclear debate
• Radiation
• Radioactive contamination
• Radiation poisoning
• Radioactive waste
• United States military nuclear incident terminology
• World Association of Nuclear Operators (WANO)

External links

• U.S. Nuclear Accidents (lutins.org) most comprehensive online list of incidents involving U.S. nuclear facilities and vessels, 1950–present
• US Nuclear Regulatory Commission (NRC) website with search function and electronic public reading room
• International Atomic Energy Agency website with extensive online library
• Canada's Nuclear Safety Commission (CNSC)
• Chernobyl Children's Project International
• Concerned Citizens for Nuclear Safety Detailed articles on nuclear watchdog activities in the US
• World Nuclear Association: Radiation Doses Background on ionizing radiation and doses
• Canadian Centre for Occupational Health & Safety More information on radiation units and doses.
• Radiological Incidents Database Extensive, well-referenced list of radiological incidents
• A Review of Criticality Accidents
• Nuclear Files.org List of nuclear accidents
• Annotated bibliography of military and civilian nuclear accidents from the Alsos Digital Library
• Critical Hour: Three Mile Island, The Nuclear Legacy, And National Security. Albert J. Fritsch, Arthur H. Purcell, and Mary Byrd Davis (2005).Updated edition, June 2006
• Annotated bibliography on civilian and Military accidents from the Alsos Digital Library for Nuclear Issues