Nuclear safety and security called a nuclear meltdown. After shutting down, for some time the reactor still needs external energy to power its cooling systems. Normally this energy is provided by the power grid to which that plant is connected, or by emergency diesel generators. Failure to provide power for the cooling systems, as happened in Fukushima I, can cause serious accidents. Nuclear safety rules in the United States "do not adequately weigh the risk of a single event that would knock out electricity from the grid and from emergency generators, as a quake and tsunami recently did in Japan", Nuclear Regulatory Commission officials
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 The Châtillon site was superseded for later nuclear research by a new site at Saclay.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