meltdown

noun

1. the melting of a significant portion of a nuclear-reactor core due to inadequate cooling of the fuel elements, a condition that could lead to the escape of radiation.
2. a quickly developing breakdown or collapse: a bond-market meltdown; the meltdown of a marriage.
3. Informal. a sudden loss of control over one’s feelings or behavior: My toddler had a meltdown when I tried to leave the house.

noun

1. (in a nuclear reactor) the melting of the fuel rods as a result of a defect in the cooling system, with the possible escape of radiation into the environment
2. informal a sudden disastrous failure with potential for widespread harm, as a stock-exchange crash
3. informal the process or state of irreversible breakdown or declinethe community is slowly going into meltdown

n.by 1937 in the ice-cream industry; by 1956 in reference to a nuclear reactor, from verbal phrase, from melt (v.) + down (adv.). Metaphoric extension since 1979.

1. Severe overheating of a nuclear reactor core, resulting in melting of the core and escape of radiation.

The most serious accident that can occur at a nuclear reactor. In a meltdown, the radioactive material in the reactor becomes very hot, melting some or all of the fuel in the reactor. A meltdown may or may not be followed by the release of radioactive material to the environment. A partial meltdown, with very little external radiation, occurred at Three Mile Island (see also Three Mile Island) in 1979; a complete meltdown happened at Chernobyl in 1986.