Nuclear meltdown

:"Meltdown" redirects here. For the music festival of the same name, see Meltdown (festival).

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A nuclear meltdown occurs when the core of a nuclear reactor melts, and is generally considered a serious nuclear accident. The reactor core may melt through the floor of the reactor chamber and drop down. It continues down until it melts enough surrounding material that it is diluted and cooled to a temperature no longer hot enough to melt through the material underneath, or until it hits groundwater. Note that a thermonuclear explosion does not happen in a nuclear meltdown, although a steam explosion may occur, if it hits water.

Related Topics:
Nuclear reactor - Nuclear accident - Thermonuclear explosion

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As the geometry and presence of water is crucial to maintaining the chain-reaction, the molten core cannot form an uncontrolled critical mass (a recriticality). However, the molten reactor core will continue generating enough heat through radioactive decay ('decay heat') to maintain or even increase its temperature. One possibility is that a large steam explosion occurs when the molten mass encounters water (in the lower plenum or in the reactor cavity) after melting.

Related Topics:
Critical mass - Decay heat

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