View your list of saved words. (You can log in using Facebook.)
Occurrence in which a huge amount of thermal energy and radiation is released as a result of an uncontrolled chain reaction in a nuclear power reactor. The chain reaction that occurs in the reactor's core must be carefully regulated by control rods, which absorb neutrons, and a moderator, which reduces their energy. If the core becomes too hot, it can melt, releasing large amounts of radiation. See alsoChernobyl accident.
This entry comes from Encyclopædia Britannica Concise. For the full entry on meltdown, visit Britannica.com.