Today's Word of the Day means...
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 in 1979; a complete meltdown happened at Chernobyl in 1986.
A disaster: They are facing a credibility meltdown/The Glenn campaign has achieved almost total meltdown
[1970s+; fr the nuclear power-plant disaster in which the core of radioactive material melts down into the earth below, the term found by 1963]