Corium (nuclear reactor) from the pre-meltdown reactor or be due to spontaneous fission of reactor-created actinides. In the absence of adequate cooling, the materials inside of the reactor vessel overheat and deform as they undergo thermal expansion, and the reactor structure fails once the temperature reaches the melting point of its structural materials. The corium melt then accumulates at the bottom of the reactor vessel. In the case of adequate cooling of the corium melt, the melt can solidify and the spread of damage is limited to the reactor itself. However, corium may melt through the reactor vessel and flow out or be
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 The Châtillon site was superseded for later nuclear research by a new site at Saclay.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