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
Zoé (reactor) 60 aluminum-cased vertical rods containing three tons of uranium oxide pellets, controlled by cadmium rods. The heavy water was purchased from Norsk Hydro. A cooling system was added after the reactor had operated for a time, allowing it to run at a heat release rate of 200 kilowatts. The name Zoé was an acronym, from Zéro de puissance" (zero power, that is, very little capacity to produce electricity, which made it easier and faster to build); Oxyde d'uranium" (uranium oxide), "Eau lourde" (heavy water). The Châtillon site was superseded for later nuclear research by a new site at Saclay. The