tomeltdown
A meltdown is one of the major nuclear reactor accidents, also called a core meltdown. Abnormal temperature rise in the core due to failure of the cooling system, causing the nuclear fuel to melt. Meltdown is the state in which most of the fuel melts and accumulates at the bottom of the pressure vessel, and melt-through is the state in which the bottom of the pressure vessel melts due to the high temperature and the fuel penetrates through the bottom of the vessel.