Nuclear Meltdown

the china syndrome

A nuclear meltdown is an informal term for a severe nuclear reactor accident that results in core damage from overheating. The term is not officially defined by the International Atomic Energy Agency. Meltdown conditions can be created when system failures lead to temperatures and heat generation that exceed cooling capacity to the extent that the nuclear fuel assemblies overheat and melt, either partially or completely.

A meltdown is considered very serious because of the potential that highly intense radioactive materials with long half-lives and lethal threat could be released into the environment. The effects of a nuclear meltdown depend on the safety features designed into a reactor. A modern reactor is designed both to make a meltdown unlikely, and to contain one should it occur.

In a modern reactor, a nuclear meltdown, whether partial or total, should be contained inside the reactor’s containment structure. Thus (assuming that no other major disasters occur) while the meltdown will severely damage the reactor itself, possibly contaminating the whole structure with highly radioactive material, a meltdown alone should not lead to significant radiation release or danger to the public.

In practice, however, a nuclear meltdown is often part of a larger chain of disasters (although there have been so few meltdowns in the history of nuclear power that there is not a large pool of statistical information from which to draw a credible conclusion as to what ‘often’ happens in such circumstances). For example, in the Chernobyl accident, by the time the core melted, there had already been a large steam explosion and graphite fire and major release of radioactive contamination (as with almost all Soviet reactors, there was no containment structure at Chernobyl).

A number of Soviet Navy nuclear submarines experienced nuclear meltdowns, including K-27, K-140, and K-431. The only large-scale nuclear meltdowns at civilian nuclear power plants were at the Lucens reactor, Switzerland, in 1969; the Three Mile Island accident in Pennsylvania, U.S.A., in 1979; the Chernobyl disaster at Chernobyl Nuclear Power Plant, Ukraine, USSR, in 1986; and the Fukushima I nuclear accidents at Fukushima Nuclear Power Plant, Japan, in 2011.

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