Nuclear chain reaction between being slightly subcritical and slightly delayed-supercritical, but must always remain below prompt-critical. It is impossible for a nuclear power plant to undergo a nuclear chain reaction that results in an explosion of power comparable with a nuclear weapon, but even low-powered explosions due to uncontrolled chain reactions, that would be considered "fizzles" in a bomb, may still cause considerable damage and meltdown in a reactor. For example, the Chernobyl disaster involved a runaway chain reaction but the result was a low-powered steam explosion from the relatively small release of heat, as compared with a bomb. However, the reactor complex
Nuclear power of the fission reactor power-level, principally the nuclear engineering reliance on a negative Void coefficient of reactivity, a form of Passive nuclear safety. The chain reaction can also be manually stopped completely by inserting control rods into the reactor core. While again depending on the reactor design, a mixture of both passive and active Nuclear reactor safety systems, the most well known being the Essential service coolant system, operate to remove decay heat. Alongside this, a number of further Defense in depth (nuclear engineering) principles are relied upon, such as physical containment barriers. Some serious nuclear and radiation accidents have