What any device called a reactor does. May be called "a meltdown", "destabilizing", "going critical", or something more fanciful. The failure of an actual nuclear reactor will often be described with the actual term "meltdown", but it will not resemble any meltdown known to science. The resulting explosion will be suspiciously similar to that of an atom bomb, or at least large enough to blow the vehicle/facility in question to pieces. Alternately, if the main result is a release of radiation, it will be described by a huge red circle on a map. The size and danger level of the circle may suggest even more death than an atom bomb would cause.