During a nuclear meltdown, the core of the reactor becomes extremely hot, reaching temperatures of around 1400-1450°C, which is the melting point of steel. This leads to the formation of corium, a mixture of molten fuel and structural materials. As the corium accumulates at the bottom of the pressure vessel, which may contain superheated steam, it can melt through the vessel and fall into a water pool. This interaction can trigger a significant steam explosion, especially if the water mass is substantial, resulting in the potential release of radioactive fission products outside the containment area. However, if the pressure vessel is filled with water, or if the fuel remains submerged, the risk of a catastrophic explosion decreases, and the scenario may result in less violent boiling rather than an explosive reaction. Understanding these dynamics is crucial, especially in light of recent events in Japan.
