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
Nuclear reactor safety system actuation of these valves depressurizes the reactor vessel and allows lower pressure coolant injection systems to function, which have very large capacities in comparison to the high pressure systems. Some depressurization systems are automatic in function, while others may require operators to manually activate them. In pressurized water reactors with large dry or ice condenser containments, the valves of the system are called "Pilot operated release valves". LPCI consists of a pump or pumps that inject coolant into the reactor vessel once it has been depressurized. In some nuclear power plants, LPCI is a mode of operation of a residual