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 safety in the United States designs: The proposed AP1000 has a maximum core damage frequency of per plant per year. The European Pressurized Reactor (EPR) has a maximum core damage frequency of per plant per year. According to the Nuclear Regulatory Commission, 20 states in the USA have requested stocks of potassium iodide which the NRC suggests should be available for those living within of a nuclear power plant in the unlikely event of a severe accident. Radioactive iodine (radioiodine) is one of the products that can be released in a serious nuclear power plant accident. Potassium iodide (KI) is a non radioactive form of