Nuclear and radiation accidents and incidents involving HEU or plutonium trafficking: A nuclear meltdown is a severe nuclear reactor accident that results in reactor core damage from overheating. It has been defined as the accidental melting of the core of a nuclear reactor, and refers to the core's either complete or partial collapse. A core melt accident occurs when the heat generated by a nuclear reactor exceeds the heat removed by the cooling systems to the point where at least one nuclear fuel element exceeds its melting point. This differs from a fuel element failure, which is not caused by high temperatures. A meltdown may be
Natural nuclear fission reactor Natural nuclear fission reactor A natural nuclear fission reactor is a uranium deposit where self-sustaining nuclear chain reactions have occurred. This can be examined by analysis of isotope ratios. The existence of this phenomenon was discovered in 1972 at Oklo in Gabon by French physicist Francis Perrin. The conditions under which a natural nuclear reactor could exist had been predicted in 1956 by Paul Kazuo Kuroda. The conditions found were very similar to what was predicted. Oklo is the only known location for this in the world and consists of 16 sites at which self-sustaining nuclear fission reactions are thought