Nuclear meltdown - Wikipedia, the free encyclopedia
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
or by the U.S. Nuclear Regulatory Commission
However, it has been defined to mean the accidental melting of the core of a nuclear reactor,
and is in common usage a reference to the core's either complete or partial collapse. "Core melt accident" and "partial core melt" are the analogous technical terms, though the severity of these nuclear accidents can vary in the extreme.
A meltdown occurs when a severe failure of a nuclear power plant system prevents proper cooling of the reactor core, 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.
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.