The nuclear power plant design strategy for preventing accidents and mitigating their potential effects is “defense in depth”— if something fails, there is a back-up system to limit the harm done, if that system should also fail there is another back-up system for it, etc., etc.
Of course it is possible that each system in this series of back-ups might fail one after the other, but the probability for that is exceedingly small. The Media often publicize a failure of some particular system in some plant, implying that it was a close call” on disaster; they completely miss the point of defense in depth which easily takes care of such failures.
Even in the Three Mile Island accident where at least two equipment failures were severely compounded by human errors, two lines of defense were still not breached— essentially all of the radioactivity remained sealed in the thick steel reactor vessel, and that vessel was sealed inside the heavily reinforced concrete and steel lined “containment” building which was never even challenged. It was clearly not a close call on disaster to the surrounding population. The Soviet Chernobyl reactor, built on a much less safe design concept, did not have such a containment structure; if it did, that disaster would have been averted.
Risks from reactor accidents are estimated by the rapidly developing science of “probabilistic risk analysis” (PRA). A PRA must be done separately for each power plant (at a cost of $5 million) but we give typical results here: A fuel melt-down might be expected once in 20,000 years of reactor operation.
In 2 out of 3 melt-downs there would be no deaths, in 1 out of 5 there would be over 1000 deaths, and in 1 out of 100,000 there would be 50,000 deaths. The average for all meltdowns would be 400 deaths. Since air pollution from coal burning is estimated to be causing 10,000 deaths per year, there would have to be 25 melt-downs each year for nuclear power to be as dangerous as coal burning.
Of course deaths from coal burning air pollution are not noticeable, but the same is true for the cancer deaths from reactor accidents. In the worst accident considered, expected once in 100,000 melt-downs (once in 2 billion years of reactor operation), the cancer deaths would be among 10 million people, increasing their cancer risk typically from 20% (the current U.S. average) to 20.5%. This is much less than the geographical variation— 22% in New England to 17% in the Rocky Mountain states.
Very high radiation doses can destroy body functions and lead to death within 60 days, but such “noticeable” deaths would be expected in only 2% of reactor melt-down accidents; there would be over 100 in 0.2% of meltdowns, and 3500 in 1 out of 100,000 melt-downs. To date, the largest number of noticeable deaths from coal burning was in an air pollution incident (London, 1952) where there were 3500 extra deaths in one week. Of course the nuclear accidents are hypothetical and there are many much worse hypothetical accidents in other electricity generation technologies; e.g., there are hydroelectric dams in California whose sudden failure could cause 200,000 deaths.
December 1952 - Chalk River Experimental Reactor, Canada
World’s first major nuclear reactor disaster. Power surge and partial loss of coolant leads to core damage – an extensive cleanup effort is required
September 1957 – Chelyabinsk, Soviet Union (INES Level 6)
Over 200 people die when the Mayak nuclear waste storage tank explodes.
About 270,000 people are exposed to dangerous radiation levels.
October 1957 – Windscale Nuclear Reactor, England
Radiation is released when the graphite core of the reactor catches fire.
The accident kills 33 people.
July 1959 –Santa Susana Field Laboratory, CA, United States
Significant amounts of radioactive gases are released when a power excursion causes severe overheating of the reactor core which melts one third of the nuclear fuel.
April 1960 - Test Reactor at Waltz Mills, United States Radioactivity is release when fuel elements melt. January 1961 - Idaho Falls, United States Explosion in the reactor kills three people.
1962 – Mexico City
Four people die from overexposure to radiation.
July 1964 – Charlestown, RI, United States
One person is killed and two other people are exposed to 100rad (1Gy) due to a workplace mistake.
January 1965 - Savannah River Reprocessing Plant, United States 6.5 kg plutonium sludge is released.
Winter 1966-1967 – Lenin, USSR
A major accident (possibly a meltdown) kills (a rumored) 30 crew people.
The three reactors are later removed and dumped into the Tsivolko Fjord on the Kara Sea.
November 1967 - Grenoble Nuclear Power Plant, France
Radioactive materials are accidentally released.
October 1968 - La Hague Reprocessing Plant, France
Radioactive material is leaked.
January 1969 – (Experimental nuclear reactor), Switzerland
Technical failure causes the release of radioactive water
April 1973 - Hanford Nuclear Weapons Complex, United States
Thousands of cubic meters of radioactive waste are accidentally released.
September 1973 - Sellafield Reprocessing Plant, United Kingdom
35 workers are contaminated following a technical failure
January 1974 - Leningrad Nuclear Power Plant, USSR
February 1974: Leningrad Nuclear Power Plant, USSR
Three people killed in an explosion and radiation leak
September 1974 - Los Alamos Nuclear Weapons Laboratory, United States
Release of radioactive water
January 1975 - Mihama Nuclear Power Plant, Japan
Release of radioactivity
January 1976 - Bohunice Nuclear Power Plant, Slovakia
Two workers are killed by radioactive carbon dioxide
February 1976 - Bohunice Nuclear Power Plant, Slovakia
January 1978 - Colorado Reactor, United States
Radioactive helium is released.
June 1978 - Brunsbuettel Nuclear Power Plant, Germany
Release of two tons of radioactive steam
December 1978 - Beloyarsk Nuclear Power Plant, USSR
Eight workers are irradiated in a fire and loss of reactor control.
March 1979 - Three Mile Island Nuclear Powerplant, PA, United States (INES 5)
Plant suffers a partial core meltdown and radioactive material is released.
April 1979 - Tokaimura Nuclear Complex, Japan
Two workers suffer radioactive contamination
March 1980 – Saint-Laurent Nuclear Power Plant, France (INES Level 4)
Brief power excursion in Reactor A2 leads to a rupture of fuel bundles and a release (8 x 1010 Bq) of nuclear materials.
September 1980 - La Hague Reprocessing Plant, France
Pump failure causes accidental release of radioactive water
January 1981 - La Hague Reprocessing Plant, France
March 1981 – Tsuruga Nuclear Power Plant, Japan (INES Level 2)
More than 100 workers are exposed to 155 millirems (1.55 mSv) / day radiation which exceeds the Japan Atomic Power Company’s limit of 1 mSv / day.
Radioactive materials are released into the Sea of Japan.
October 1981 - Sellafield Reprocessing Plant, United Kingdom
300-times the normal discharge level of Iodine-131 is released.
January 1982 - R.E. Ginna Nuclear Power Plant, United States
Steam generator ruptures
February 1982 - Salem Nuclear Power Plant, United States
100 cubic metres of radioactive water is released.
September 1983 - Buenos Aires, Argentina. (INES Level 4)
Operational error leads to death when operator absorbs 2000 rad (20 Gy) of gamma and 1700 rad (17 Gy) of neutron radiation.
Another 17 people outside of the reactor room absorb doses ranging from 35 rad (0.35 Gy) to less than 1 rad (0.01 Gy).
October 1983 - Blayas Nuclear Power Plant, France
Technical failure and human error cause accident
November 1983 - Sellafield Reprocessing Plant, United Kingdom
Plant discharges highly radioactive wastes directly into the sea
June 1985 - Balakovo Nuclear Power Plant, USSR
Explosion and steam leakage kill 14 workers.
October 1985 - Hinkley Point Nuclear Power Station, United Kingdom
Accidental radioactive release into the sea
February 1986 - Trawsfynydd Nuclear Power Plant, United Kingdom
Release of 13 tonnes of radioactive carbon dioxide
February 1986 - Sellafield Reprocessing Plant, United Kingdom Three workers suffer radioactive contamination
April 1986 – Chernobyl Nuclear Reactor, USSR
Meltdown and fire occur lead to the release of massive quantities of radioactive material.
56 people die directly from the meltdown and an additional (estimated) 4,000 deaths are attributed to results from excessive radiation.
December 1986 - Surry Nuclear Power Plant, United States
Explosion kills four people.
September 1987 – Goiania, Brazil
A stolen radiotherapy source leads to the deaths of four people and the radioactive contamination of 245 other people. Of the contaminated people, 20 showed signs of radiation sickness and required treatment.
December 1987 - Biblis Nuclear Power Plant, Germany
December 1987 - Atucha Nuclear Power Plant, Argentina
Accidental release of 50 tonnes of water
December 1988 - Burghfield Atomic Weapons Establishment, United Kingdom
January 1989 - Savannah River Reprocessing Plant, United States
Eight workers are contaminated
January 1990 - Gravelines Nuclear Power Plant, France
Pump fails during a shut-down
February 1990 - Point Lepreau, Canada
Eight employees receive radiation exposure
June 1990 - Fessenheim Nuclear Power Plant, France
Five cubic meters of radioactive water are spilled during refueling
December 1990 - Blayais Nuclear Power Plant, France
Two workers are irradiated during refueling
December 1990 - Leningrad Nuclear Power Plant, USSR
Radiation is leaked
February 1991 - Fukui Nuclear Power Plant, Japan
Release of radioactivity
February 1991 - Mihama Nuclear Power Plant, Japan
Rupture of steam generator pipe causes release of radioactivity
September 1991 - Kozloduy Nuclear Power Plant, Bulgaria
November 1991 - Oconee Nuclear Power Plant, United States
Leak of 190,000 litres of water from cooling system, reactor shut-down
December 1991 - Kolskaya Nuclear Power Plant, USSR
January 1992 - Kola Nuclear Power Plant, USSR
Radioactive leak, reactor shut-down
January 1992 - Balakovo Nuclear Power Plant, USSR
Technical failure in shut-down system
January 1992 - Darlington Nuclear Power Plant, Canada
Leak causes a shut-down
March 1992 - Leningrad Nuclear Power Plant, USSR
Incident with radiation leakage, shut-down of reactor
July 1992 - Ignalina Nuclear Power Plant, Lithuania
Leakage of radiation due to breakdown of cooling system
September 1992 - Kola Nuclear Power Plant, USSR
Leakage of radioactive water
December 1992 - Beloyarsk Nuclear Power Plant, USSR
Radioactive water leakage
January 1993 - Kozloduy Nuclear Power Plant, Bulgaria
Leak releases radioactive steam
January 1993 - Perry Nuclear Power Plant, United States
Radioactive release from leaking fuel rods
January 1993 – Paluel, France
Technical failure at causes subcooling accident
February 1993 - Darlington Nuclear Power Plant, Canada
Spillage of 18,000 litres of heavy water
February 1993 - Fukushima Nuclear Power Plant, Japan
High pressure steam accident kills one worker and injures two others
April 1993 – Tomsk-7 Siberian Chemical Enterprise, Russia (INES Level 4)
Pressure buildup leads to an explosion. Approximately 6 GBq of Pu 239 and 30 TBq of various other radionuclides are released into the environment.
160 on-site workers and almost 2,000 cleanup workers are exposed to total doses of up to 50 mSv (the threshold limit for radiation workers is 100 mSv per 5 years).
December 1995 - Monju Fast Breeder Reactor, Japan
Fire due to leakage of sodium coolant. Japanese nuclear industry attempts to cover up full extent of accident, reactor shut-down
January 1996 - Dimitrovgrad Nuclear Research Centre, Russia
Leakage of radiation due to human error and technical failure
March 1997 – Tokaimura, Japan
At least 35 workers are contaminated with minor radiation after a fire and explosion occurs at a reprocessing plant.
September 30, 1999 – Ibaraki Prefecture / Tokai-mura, Japan (INES Level 4)
Criticality at a uranium reprocessing facility exposes 116 workers to radiation doses of 1 mSv or greater. Three workers are exposed to (neutron) radiation doses in excess of allowable limits. Two workers die.
August 2004 – Mihama Nuclear Power Plant
Four people die when hot water and steam leak from a broken pipe.
March 11–20, 2011 – Fukushima I Nuclear Power Plant, Japan (INES Level 7) Partial meltdowns in multiple reactors leads to fires, explosions, and the release of substantial amounts of hazardous nuclear materials into the environment. Two people die.