A steam rupture occurs within a nuclear power plant (such as pressurized water reactors and boiling water reactors) when the temperature of the reactor reaches a certain level too quickly. This results in pockets of steam to form within the coolant piping which causes hotspots. These soon burst causing (sometimes radioactive) steam to leak into the reactor or plant. As seen in Chernobyl, this can cause major parts of the reactor to explode under pressure, and generally wreck the place.