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A nuclear meltdown (core meltdown, core melt accident, meltdown or partial core melt [2]) is a severe nuclear reactor accident that results in core damage from overheating. The term nuclear meltdown is not officially defined by the International Atomic Energy Agency [3] or by the United States Nuclear Regulatory Commission. [4]
The 1979 Three Mile Island accident in Pennsylvania was caused by a series of failures in secondary systems at the reactor, which allowed radioactive steam to escape and resulted in the partial core meltdown of one of two reactors at the site, making it the most significant accident in U.S. history.
The world's first nuclear reactor meltdown was the NRX reactor at Chalk River Laboratories, Ontario, Canada in 1952. [22] The worst nuclear accident to date is the Chernobyl disaster which occurred in 1986 in the Ukrainian SSR, now Ukraine. The accident killed approximately 30 people directly [23] and damaged approximately $7 billion of property.
Erosion of the 150-millimetre-thick (5.9 in) carbon steel reactor head at Davis-Besse Nuclear Power Plant, in Oak Harbor, Ohio, USA, in 2002, caused by a persistent leak of borated water The Hanford Site, in Benton County, Washington, USA, represents two-thirds of America's high-level radioactive waste by volume.
Soviet submarine K-19 reactor accident 1961, July 4 More than 30 people were over-exposed to radiation when the starboard reactor cooling system failed and the reactor temp rose uncontrollably. Emergency repairs ordered by the captain successfully cooled the reactor and avoided meltdown, but exposed the workers to high levels of radiation. [17] 8
However, following the event, the number of reactors under construction in the U.S. declined from 1980 to 1998, with increasing construction costs and delayed completion dates for some reactors. [105] Many similar Babcock & Wilcox reactors on order were canceled. In total, 52 U.S. nuclear reactors were canceled between 1980 and 1984. [106]
Globally, there have been at least 99 (civilian and military) recorded nuclear reactor accidents from 1952 to 2009 (defined as incidents that either resulted in the loss of human life or more than US$50,000 of property damage, the amount the US federal government uses to define major energy accidents that must be reported), totaling US$20.5 billion in property damages.
On March 28, Three Mile Island Nuclear Generating Station's Unit 2 reactor experiences a partial core meltdown, in Pennsylvania, US. It is the worst nuclear accident in US history based on radioactive material released. [124] It is classed as a Level 5 nuclear accident out of seven on the International Nuclear Event Scale. [125] [126]