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Revision as of 04:18, 29 December 2002 by Kwertii (talk | contribs)(diff) ← Previous revision | Latest revision (diff) | Newer revision → (diff)A nuclear meltdown occurs when fission in the core of a nuclear reactor becomes uncontrollable.
Reasons for this may include mechanical failure of the control rods, loss of pressure or circulation in the core coolant system, operator error, or any combination of these factors. The net result of all of them is that the core temperature rapidly rises tremendously, melting fuel rods and control rods until eventually it becomes hot enough to melt through its containment vessel. The pressure in the core may build up and cause a large explosion which spews highly radioactive material in all directions.
The only known large scale nuclear meltdown in history was at Chernobyl, Ukraine, in 1986, though there have been many near misses, such as the partial meltdown at Three Mile Island, Pennsylvania in 1979 and a number of incidents on nuclear submarines.