List of accidents in nuclear facilities

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The list of accidents at nuclear facilities called accidents, based on the International Nuclear Event Scale Rating INES ( english I nternational N uclear and Radiological E vent S cale ) as an accident of level 4 and have been ranked higher. Less serious incidents are described, for example, in the list of reportable incidents in German nuclear facilities or the list of incidents in European nuclear facilities (for nuclear weapon tests, see the list of nuclear weapons tests in the category: nuclear weapons test ).

This list is limited to nuclear facilities; Therefore, it does not include accidents and risks that occurred during the mining and processing of uranium , uranium ore spoil heaps or sedimentation lakes , such as the rupture of a sedimentation lake dam in the USA in 1979 , which released more radioactivity than the one in Three Mile Island disaster included in this list .

INES was introduced by the International Atomic Energy Agency (IAEA) in order to achieve global standardization in the reporting of incidents and accidents and to inform the public about the scope of the radiological effects of such an incident. Since INES was only introduced in the early 1990s, not all previous events are classified on this scale.

The best-known accidents in nuclear facilities are the Chernobyl nuclear disaster of April 26, 1986 and the Fukushima nuclear disaster of March 11, 2011. In addition to these beyond -design-basis accidents, which are also called super-GAU , there are other accidents that lead to significant contamination and thus has resulted in damage to the environment and health.


date place process INES
August 21, 1945 Los Alamos, New Mexico, United States

Harry K. Daghlian Jr. was working on the Omega site of the Los Alamos Nuclear Research Center and promptly generated a supercritical order when he accidentally dropped a tungsten carbide chunk on a roughly 6kg plutonium core. Though he pushed the piece away, the prompt burst gave him a lethal dose of radiation and died on September 15. ( INES : 4)

May 21, 1946 Los Alamos, New Mexico, United States

In the nuclear research center in Los Alamos , the Canadian physicist Louis Slotin experimented in the presence of several scientists with the same plutonium core, which was subsequently referred to as the “ demon core ”, and two hemispherical beryllium shells that served as neutron reflectors . Slotin held the upper hemisphere through a thumb hole and used a screwdriver to lower it in a controlled manner. When it slipped out of the gap, Slotin tore the hemisphere away; However, he received a dose at which he died on May 30th. (INES: 4)

1949 Hanford Site, Washington, United States The Green Run experiment involved the release of a radioactive cloud from the Hanford Site military nuclear complex . Estimates are in the range of several 100 TBq 131 I and even more 133 Xe. During normal operation, several 10 TBq of medium- and long-lived nuclides were released into the Columbia River every day . At that time, there was still insufficient knowledge about the health risk posed by radioactive iodine.


date place process INES
December 12, 1952 Chalk River Laboratories , Chalk River , Canada The first serious reactor accident occurred in the so-called NRX reactor in the Chalk River Laboratories near Ottawa , Canada . During a test of the research reactor, operating errors, misunderstandings between the operator and the operating personnel, incorrect status displays in the control room, incorrect assessments by the operator and hesitant action caused the reactor core to be destroyed in the event of a partial core meltdown . An oxyhydrogen explosion in the reactor core threw the dome of a four-tonne helium gas container 1.2 m high, causing it to get stuck in the structure. The explosion released at least 100  TBq of fission products into the atmosphere . Up to four million liters of radioactively contaminated water with around 400 TBq of long-lasting fission products were pumped from the basement of the reactor containment into a sandy septic tank in order to prevent contamination of the nearby Ottawa River . The damaged reactor core was buried. The future US President Jimmy Carter , then a nuclear technician in the Navy , helped with the several months of clean-up work. The reactor went back into operation two years later. (INES: 5) 5
November 29, 1955 Idaho Falls, Idaho, United States At the National Reactor Testing Station Idaho , the research reactor EBR-I suffered a partial core meltdown . The core of enriched uranium in combination with 2% zirconium melted in tests aimed at rapidly increasing performance because fuel tubes warped. By evaporation of the coolant NaK , the melting fuel was transported into the tubes of the cooling system and the criticality was not reached , whereby the reactor switched itself off. The reactor core was designed to be interchangeable and could be replaced, so people were not harmed. (INES: 4) 4th
September 29, 1957 Kyschtym, Soviet Union

Also known as the Mayak Accident . The local reprocessing plant stored its waste products in large tanks. The radioactive decay of the substances generates heat, which is why these tanks have to be constantly cooled. After the cooling lines of one of these 250 m³ tanks leaked in the course of 1956 and the cooling was therefore switched off, the contents of this tank began to dry out. Triggered by a spark from an internal measuring device, the contained nitrate salts exploded and released large amounts of radioactive substances. Since the contaminated cloud remained close to the ground, the pollution in the area around the Russian Kyshtym was almost double the amount of the Chernobyl accident. Since the contamination was limited to the Urals , measuring devices did not sound an alarm in Europe (see Chernobyl accident), which meant that the accident could be kept secret from the global public for 30 years.

October 7-12, 1957 Windscale and Sellafield, Great Britain

In the Pile No. 1 in wind Scale heated (now Sellafield) technician for the so-called the reactor at, Wigner energy from the as moderator serving graphite to glow. The reactor was one of two air-cooled and graphite-moderated reactors. They were powered by natural uranium and were used to produce plutonium for nuclear weapons . They were cooled by a stream of air created by huge fans. On the morning of October 7, 1957, the reactor was shut down in a controlled manner and the air cooling was switched off. The reactor was then restarted in the lower power range. Technicians noticed a drop in temperature instead of a rise. In order to be able to dissipate the Wigner energy more quickly, the reactor was driven into a non-permitted power range the next day. The technicians, however, made a fallacy: In normal operation, the temperature peaks occurred in completely different places than during annealing. However, there were no measuring sensors at these locations, and so the graphite began to burn there, initially unnoticed. The air filters withstood the fire only for a short time, after which the radioactivity could escape unhindered through the exhaust air chimneys. Blue flames rose from the rear of the reactor. 750 TBq was released into the atmosphere. The fire burned for four days and consumed much of the graphite presenter. The technicians were only able to push some of the nuclear fuel rods out of the burning area of ​​the reactor. So they cut a firebreak by knocking out neighboring sticks. As a final consequence, the reactor was flooded with water. The flooding was extremely dangerous because the high temperature could have split the water into oxyhydrogen. This would have caused an explosion. Fortunately, however, the water smothered the fire. Large amounts of radioactive gases escaped into the atmosphere. These were mainly iodine , krypton and xenon . Milk production in an area of ​​520 km² was banned. Soon after the destruction of reactor 1 by the accident, reactor 2 was also shut down when it was realized that safe dissipation of the Wigner energy was impossible due to the design. The dismantling of the shutdown reactors began in 1993 and should be completed in 2012. The accident was later blamed for dozens of cancer deaths.

December 30, 1958 Los Alamos, New Mexico, United States A criticality accident occurred while extracting a plutonium-containing solution in the Los Alamos Scientific Laboratory in New Mexico. The operator died of acute radiation sickness. After this accident, manipulators were used for good when working with critical masses in the USA . Until then, despite the criticality accidents in the 1940s, manual labor in handling plutonium was widespread. (INES: 4) 4th
July 26, 1959 Simi Valley, California, United States At the Santa Susana Field Laboratory in California , which operated a sodium-cooled fast breeder with 7.5 MW e , a 30 percent core meltdown occurred in this reactor due to a blocked cooling duct . Most of the fission products could be filtered off. However, most of the radioactive gases were released into the environment, making one of the largest 131 iodine releases in nuclear history. The accident was kept secret for a long time. (INES: 4) 5-6
November 20, 1959 Knoxville, Tennessee, United States At the Oak Ridge National Laboratory , Tennessee radiochemical factory , there was a chemical explosion during the decontamination of work facilities. A total of 15 grams of 239 plutonium were released. In the explosion, this caused considerable contamination of the building, the adjacent streets and the facades of adjacent buildings. It is believed that the explosion was triggered by the contact of nitric acid with decontamination fluids containing phenol . A technician forgot to clean a vaporizer with water to free it from decontamination fluids. Areas that could not be decontaminated were marked with a conspicuous warning color or set in concrete. Oak Ridge authorities began using containment when handling radioactive chemical materials. No other employees have been injured since then. 3-4


date place process INES
January 3, 1961 Idaho Falls, Idaho, United States In the National Reactor Testing Station Idaho at 9:01 p.m. during maintenance work, the prototype of a military boiling water reactor, the SL-1 , which was shut down over Christmas, promptly became supercritical for a few milliseconds and released around 6000 times the power during this time the system was designed. Before the reactivity could decrease due to the formation of vapor bubbles (see vapor bubble coefficient ), the fuel elements of the small reactor core made of highly enriched uranium (90%) disassembled. The two meter high water column surrounding the core collided with about 9 meters / sec. against the reactor cover - the water level had been lowered a little for maintenance work - and caused the entire 12 t boiler to jump up almost three meters to the ceiling, which pushed the control rod back in completely. The fire brigade , alerted by temperature sensors on the ceiling, found everything peaceful at first, except for the frightening radiation behind the door to the staircase.

When the three soldiers entrusted with the maintenance work went missing, they went to the working level above the reactor wearing protective suits. One of the three workers had been staked by a shooting sleeve and nailed to the ceiling, two were lying on the floor. One of the two was found alive; however, he succumbed to his head injury two hours after the accident. Even naked, the body, riddled with splinters, shone at five sieverts an hour. There were no other victims. The rescue workers were relieved every minute. 22 of them received radiation doses in the range from 30 to 270 mSv. Only 131 iodine spread beyond the company premises, but did not pose any danger in the desert.

The SL-1 reactor during its recovery

The decontamination of the building lasted from April to November, in which hundreds were involved for a few minutes each; then the pressure vessel was lifted out and taken to a laboratory, where it was remotely disassembled and examined. It was to be clarified how the reactor, which was actually considered to be inherently safe at the time, could have exploded: After the maintenance work at the turn of the year, the central control rod of the reactor should have been connected to its drive. To do this, it would only have had to be raised a little. However, the investigations then revealed that the rod had been pulled far and with great speed. It was known that the + -shaped 'bars' could clamp into their easily deformable aluminum shells. Sabotage, suicide and murder were discussed as alternative hypotheses.

The reactor building was completely dismantled and buried nearby because transporting the highly radioactive material to the landfill 16 miles away was considered an unnecessary risk. As a consequence of this accident - the so far only prompt burst (power excursion) in a US nuclear power plant - reactors were no longer built that could promptly become overcritical by pulling a single control rod completely, and detailed work instructions for operation and maintenance were provided created.

July 24, 1964 Charlestown, Rhode Island, United States In a United Nuclear Corporation nuclear fuel factory in Charlestown , 38-year-old worker Robert Peabody caused an accident with a liquid uranium solution. As a result, Peabody was exposed to a lethal radiation dose of approximately 88 Sieverts. (INES: 4) 4th
1964-1979 Belojarsk, Soviet Union From 1964 to 1979 there was a series of destruction of fuel channels in reactor 1 of the Belojarsk NPP . In each of these accidents, the personnel were exposed to considerable radiation. (INES: 4) 4th
May 7, 1966 Melekess, near Nizhny Novgorod (Gorki), Soviet Union At the Atomic Reactor Research Institute Melekess, a power excursion through fast neutrons took place in an experimental boiling water reactor ( VK reactor ). The operator and the shift supervisor received high doses of radiation (INES: 3–4). 3-4
5th October 1966 Monroe, Michigan, United States A malfunction of the sodium cooling system in the Enrico Fermi demonstration nuclear breeder reactor on the shore of Lake Erie led to a partial meltdown in which no radiation escaped from the containment. The reactor core contained 105 zirconium- lined pins. The accident is attributed to a piece of zirconium blocking a flow regulator in the sodium cooling system. The reactor building was automatically isolated by sensors, no personnel were in the building at this time. Employees managed to shut down the reactor manually. Two of the 105 fuel assemblies melted, but no radiation was measured outside the containment. However, weeks later there were still fears that it would be criticized. The 60 MWe reactor ran at full power again in October 1970. This incident provided the basis for the book We Almost Lost Detroit by John G. Fuller . 4th
January 21, 1969 Lucens, Switzerland When the cooling system of an experimental reactor at the Lucens experimental nuclear power plant (VAKL) in the canton of Vaud failed , there was a partial core meltdown in the reactor (which was constructed in a similar way to the NRX reactor ) . At the beginning of 1968 there was an inspection of the reactor, which produced 8 MW of energy . It was put into operation in April / May, but then switched off again until January of the next year. During this standstill, external water ran into the cooling circuit of the reactor via a defective fan seal. The magnesium fuel rod cladding tubes corroded. When the reactor was put back into operation in January 1969, the corrosion products hindered cooling. The fuel overheated and several fuel rods melted. A whole bundle of fuel rods caught fire and burst the moderator tank. 1100 kg of heavy water (moderator), melted radioactive material and carbon dioxide (coolant) were thrown into the reactor cavern . Since the increased radioactivity was measured a little earlier, the power plant could be evacuated and the cavern isolated. Initially, a dose rate of about one sievert per hour of radioactivity was measured in the Fels cavern, a small amount of which got into the environment through "two very small leaks"; a few days later, the entire gas content of the cavern was released into the environment in a "controlled manner via filters". The radioactive debris could only be cleared from the tunnel system years later. The cavern still contained a lot of radioactive material, but was sealed in such a way that no radiation could initially get into the environment. The clean-up work lasted until May 1973. The rubble was stored in sealed containers on the site until it was transported to the central interim storage facility in Würenlingen ( Zwilag ) in 2003 . 4-5
May 11, 1969 Rocky Flats, Colorado, United States A spontaneous ignition of plutonium occurred in a container with 600 t of flammable material. The fire burned 2 tons of the material and released plutonia. By taking soil samples in the vicinity of the facility, it was found that the area was contaminated with plutonium. Since the operators of the plant refused to initiate investigations, the samples were taken as part of an unofficial investigation. (INES: 4–5) 4-5


date place process INES
1973 Windscale and Sellafield, Great Britain In the reprocessing plant, an exothermic reaction occurred in a basin that had been emptied for repairs when it was refilled with water due to hot radio nuclides on the basin floor . As a result, part of the facility and 35 workers were radioactively contaminated. Due to the internal contamination and apparently also a certain release, this accident was classified as INES 4. 4th
February 6, 1974 Leningrad, Soviet Union The heat exchanger in block 1 of the Leningrad nuclear power plant broke due to the boiling water . Three people died. Highly radioactive water from the primary circuit together with radioactive filter sludge was released into the environment. (INES: 4–5) 4-5
October 1975 Leningrad, Soviet Union In October 1975 the reactor core in Unit 1 of the Leningrad NPP was partially destroyed. The reactor was shut down. The next day the core was cleaned by pumping an emergency reserve of nitrogen through it and blowing it through the exhaust chimney. About 1.5 megacuria (55 PBq) of radioactive substances were released into the environment. (INES: 4–5) 4-5
1977 Belojarsk, Soviet Union In an accident, 50% of the fuel channels in Unit 2 of the Belojarsk NPP, a pressure tube reactor similar to the RBMK, melted. The repair took about a year. The staff was exposed to high levels of radiation. (INES: 5) 5
February 1977 Jaslovské Bohunice, Czechoslovakia An accident occurred in the first Slovak nuclear power plant Bohunice A-1 , which was equipped with a pressure tube reactor : When loading fresh fuel elements, some of them overheated, a fuel element shot out of its pressure tube and shattered on the loading crane above. One worker died, the reactor hall was contaminated (INES: 4). The reactor was shut down after the accident. 4th
December 31, 1978 Belojarsk, Soviet Union In the turbine house of Block 2 of the Belojarsk NPP, a ceiling plate fell on a turbine oil tank and caused a major fire. 8 people suffered high doses of radiation when organizing the reactor emergency cooling. (INES: 3–4) 3-4
March 28, 1979 Three Mile Island, Pennsylvania, United States

At the Three Mile Island nuclear power plant near Harrisburg , failure of machine parts and measurement signals as well as operating errors by the crew led to the failure of the reactor cooling system, which resulted in a partial meltdown (50% of the core) and the release of 90 TBq of radioactive gases. This accident is the most serious to date in a commercial reactor in the United States. It has been rated INES 5 by the IAEA.



date place process INES
1980 Saint-Laurent, France

The partial melting of a few fuel elements led to contamination of the reactor building (INES: 4). The first two reactors built in St. Laurent were graphite-moderated and gas-cooled. The emergency cooling was therefore not carried out with water, but with air drawn in from the factory environment. After repairs, the reactor continued to operate for a while. Today only two pressurized water reactors are still running in St. Laurent.

September 1982 Chernobyl, Soviet Union In Unit 1 of the Chernobyl NPP, a fuel channel in the middle of the reactor was destroyed by mistakes by the staff. A large amount of radioactive substances were distributed over the industrial area of ​​the nuclear power plant and the city of Pripyat . The personnel involved in liquidating the consequences of this accident received high doses of radiation. (INES: 5) (see 1986: Accident of a higher level, in Block 4) 5
1983 Buenos Aires, Argentina By neglecting safety regulations, an operator died while modifying the core of a research reactor. He was only a few meters away and received a lethal radiation dose of around 20  Gy (INES: 4). 4th
August 10, 1985 Vladivostok, Soviet Union A serious accident occurred in the Chazhma Bay near Vladivostok after the fuel element replacement of the nuclear-powered submarine K-31 (K-431) . The next day the reactor core was flooded again with the moderating cooling water and was therefore critical. Nevertheless, the reactor lid and control rods were raised again to repair a leak. A spontaneous chain reaction occurred. The cooling water exploded, hurling the 12-tonne lid and the reactor's innards onto the pier and also damaged the pressure hull of the submarine. Ten people died from a fatal dose of neutrons, and another 29 people received high doses of radiation. The weakly radioactive cloud only reached a few kilometers because the inventory was fresh. (INES: 5) 5
January 6, 1986 Gore, Oklahoma, United States At the Kerr-McGee reprocessing facility in Gore , Oklahoma , a cylinder containing nuclear material broke after being heated improperly. One worker died and 100 had to be hospitalized. 2-4
April 26, 1986 Chernobyl, Soviet Union

In a super-GAU (INES: 7) in Unit 4 of the Chernobyl nuclear power plant in Ukraine , there was a meltdown and, as a result, explosions. Large amounts of radioactivity were released through exposure and fire of the reactor core, the immediate area was heavily contaminated; there were also numerous direct radiation victims among the auxiliary workers. The worst-case scenario was proven by radioactivity measurements and fallout in Sweden and other European countries. A large restricted area was established and the area evacuated. The number of injured people varies considerably depending on the study. The fact that the accident has resulted in unexpectedly few victims so far (according to the IAEA) is partly due to the fact that the violent graphite fire carried large parts of the radioactivity directly and up into the atmosphere and that the wind was blowing largely in the direction of less populated regions before the evacuation of larger cities such as Prypiat .



date place process INES
April 6, 1993 Seversk, Russia At the nuclear facility in Tomsk near Seversk (also known as Tomsk-7 ), large amounts of short-lived radioactive substances were released in the reprocessing facility (mainly used for the production of weapons-grade plutonium). As a result, around 120 square kilometers in the Seversk region were contaminated (INES: 2–4). 2-4
September 30, 1999 Tōkai-mura, Japan

In a fuel element factory in Tōkai-mura ( Japan ), workers filled a preparation tank with 16.6 kg of uranium mixture (instead of the prescribed 2.3 kg). An uncontrolled chain reaction started and radiation escaped. The number of people who received increased doses of radiation is given as 35 to 63. Three workers were exposed to a particularly high dose of up to 17 Sievert . Approx. 300,000 residents were asked not to leave their homes. This accident is officially rated INES 4, but some scientists have rated it as INES 5. Hisashi Ōuchi, a worker who was believed to have been exposed to radiation doses of 16 to 20 Sieverts, died of liver failure on December 21, 1999, at the age of 35. On April 27, 2000, another worker, Masato Shinohara (40), died after a long illness. He was believed to have been exposed to 6 to 10 Sievert radiation.



date place process INES
March 11, 2006 Fleurus , Belgium In an irradiation facility for the manufacture of radiopharmaceutical products at the Institut national des radio-éléments (IRE) , due to a hydraulic failure, a cobalt source was lifted out of a radiation-shielding water basin, although no irradiation process took place and the door to the room was open. Due to the alarm being triggered, an employee entered the room. During his stay of only 20 seconds, he received a radiation dose of around 4.6 Sievert , which can be life-threatening in the medium term (INES 4). (Accidents in purely medical facilities are usually not classified as INES, but the IRE is a nuclear facility). 4th

2011 – today

date place process INES
March 11, 2011 Fukushima, Japan

Due to damage to the power supply and the cooling systems caused by the great Tōhoku earthquake of March 11, 2011 and the subsequent tsunami , overheating occurred in three reactors and two decay basins of the Fukushima-Daiichi nuclear power plant (Fukushima I) Fuel assemblies. Several explosions occurred: in block 1 on March 12th, in block 3 on March 14th and in blocks 2 and 4 on March 15th. In these explosions, the outer building shells of Units 1 and 3 were severely damaged and radioactive material was released. In addition, several fires broke out in Units 3 and 4 and released large amounts of radioactive substances. For temporary cooling, pure water was first pumped into the reactor cores of units 1, 2 and 3, then sea ​​water mixed with boric acid and finally pure water again. Water was also added from the outside to the affected cooling pools.

The Japanese government ordered evacuation measures with a radius of 20 km, which initially affected around 80,000 people; In a radius of 30 km, residents were advised not to go outside (this affected 200,000 people) and to keep windows and doors closed; the USA recommended an evacuation zone of 80 km a few days after the first explosion, about 2 million people would have been affected. A further area up to 30 km to the north-west of the plant was later evacuated due to measured soil contamination .

The events in blocks 1 to 3 were provisionally  assigned to level INES: 5 by the Japanese nuclear regulatory authority (NISA) on March 18, 2011 , but upgraded to the highest possible level INES: 7 on April 12, 2011. The Japanese government had previously put considerable interest from the national and international media, including footage of the explosions in two reactor buildings, as well as a higher classification by foreign institutions.

The power plant operator Tepco finally also conceded so-called “partial core meltdowns” in reactors 1 and 3, and later also in reactor 2.


See also

Portal: Nuclear Energy  - Overview of Wikipedia content on the topic of nuclear energy

Web links

Individual evidence

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This version was added to the selection of informative lists and portals on May 19, 2006 .