Knowra Nuclear meltdown Nuclear meltdown A severe nuclear reactor accident in which overheating melts some or all of the reactor core. It can damage barriers that contain radioactive material, but does not by itself imply a nuclear explosion.
Decay heat : Heat produced by radioactive decay of fission products and other unstable nuclei after a reactor shuts down. It continues heating the core after fission stops, so shutdown alone cannot prevent melting.
Three Mile Island accident : The 1979 Pennsylvania reactor accident in which a partial core meltdown occurred at Three Mile Island Unit 2. It demonstrated that substantial core melting can occur while most radioactive material remains contained.
Radioactive contamination : The presence of radioactive substances in places or materials where they are unwanted. A meltdown can disperse radioactive material into air, water, soil, and buildings.
Nuclear explosion : An explosion driven by an extremely rapid nuclear chain reaction that releases energy through fission or fusion. A reactor-core meltdown is a heat-driven accident, not a nuclear detonation.
Corium : A mixture of molten nuclear fuel, cladding, structural materials, and concrete formed during a severe reactor accident. Its composition and movement determine where melted core material collects and what barriers it attacks.
Reactor coolant : A fluid that removes heat from a nuclear reactor core and transfers it to a power-conversion system or heat sink. Loss or inadequate flow of coolant can let fuel temperatures rise toward melting.
Chernobyl disaster : The 1986 accident at Chernobyl Unit 4, where a power surge and explosions destroyed the reactor and released radioactive material. The accident included extensive fuel melting, but its graphite fire and absent containment shaped the releases.
Nuclear accident emergency response : Actions taken to protect people and limit damage during and after a nuclear facility accident. Authorities may use evacuation, sheltering, monitoring, and other measures as releases evolve.
Nuclear reactor scram : The rapid shutdown of a nuclear reactor by inserting control rods or otherwise stopping the chain reaction. A scram stops sustained fission but leaves decay heat that still requires cooling.
Severe accident management : Strategies and procedures for preventing or mitigating major reactor damage after safety systems fail. Operators must choose actions under uncertain conditions once core damage begins.
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