Examples of nuclear accidents and incidents classified on the INES scale See glossary pages 33 to 36 Level 7 1986 – Chernobyl (Ukraine) Further to a series of human errors as well as design faults, reactor 4 suffered core meltdown followed by an explosion which caused the release of nuclear fuel into the atmosphere. The contamination spread across the whole of Europe. Details p. 16 2011 – Fukushima-Daiichi (Japan) This accident was the consequence of a tsunami caused by an earthquake of magnitude 9 on the Richter scale, resulting in the total loss of the electrical power supplies and the nuclear reactor cooling systems, and substantial radioactive releases into the environment. Details p. 26 Level 6 1957 – Kyshtym (Russia – former USSR) The explosion of a tank of liquid nuclear waste released a radioactive cloud which contaminated an entire region around Kychtym, covering 800 km2. More than 200 people died, 10,000 people were evacuated and 470,000 were exposed to radiation. Level 5 1957 – Windscale, renamed Sellafield (United Kingdom) The graphite core of reactor 1 ignited during a routine annealing operation, and fission products – essentially iodine-131 – were released into the atmosphere. No evacuation was required, but the competent authorities took measures such as prohibiting the consumption of locally produced foodstuffs. 1979 – Three Mile Island (United States) Further to an accidental chain of events, the core of unit 2 reactor of the Three Mile Island NPP (TMI-2) suffered partial meltdown, leading to the release of a small amount of radioactivity into the environment. Details p. 12 Level 4 1959 – Santa Susana (United States) The experimental sodium reactor at the Santa Susana Field Laboratory near Simi Valley in California suffered partial core meltdown. 1969 – Saint-Laurent-des-Eaux (Loir-et-Cher département(*), France) Forty-seven kilograms of uranium dioxide began to melt in GCR 1 during a fuel loading operation. Details p. 8 1969 – Lucens (Switzerland) The rupture of a pressure tube caused a pulse of current and the reactor (a small experimental device built in a rocky cavern) exploded. The reactor was totally destroyed. The core underwent partial meltdown. The majority of the radioactive substances were contained within the cavern. 1971 – Monticello NPP (United States) A water tank overflowed, releasing 190 m3 of contaminated water into the Mississippi River. Radioactive matter subsequently entered into the water intake system of the city of Saint-Paul (Minnesota). 1980 – Saint-Laurent-des-Eaux NPP (Loir-et-Cher département(*), France) Reactor core meltdown occurred on GCR 2. A piece of sheet metal obstructed part of the cooling system. The temperature rose sharply, causing 20 kg of uranium to melt and leading to emergency shutdown of the reactor. The accident severely damaged the facility. Details p. 8 1993 – Tomsk-7 (Russia) A chain reaction occurred in the Tomsk-7 waste reprocessing plant, causing a large explosion and a significant release of radioactive material into the atmosphere. 1999 – Tokaimura (Japan) Further to a handling error, an abnormally large quantity of uranium (16.6 kg), very much greater than the safety value of 2.3 kg) was introduced into a settling tank, causing a criticality reaction. This accident killed two workmen. 2000 – Indian Point (United States) Reactor 2 of the Indian Point NPP released a small quantity of radioactive steam. This was caused by a steam generator malfunction. Level 3 1981 – La Hague (Manche département(*), France) A fire broke out in a non-confined radioactive waste storage silo in the reprocessing plant. * Administrative region headed by a Prefect. 6 • Les cahiers Histoire de l’ASN • November 2023
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