Vaporization of Core Materials in Postulated Severe Light Water Reactor Accidents

The vaporization of core materials other than fission products during a postulated severe light water reactor accident is treated by chemical thermodynamics. The core materials considered were (a) the control rod materials, silver, cadmium, and indium; (b) the structural materials, iron, chromium, nickel, and manganese; (c) cladding material, zirconium and tin; and (d) the fuel, uranium oxide. Thermodynamic data employed for the solid and gaseous elements and oxides were based on measurements, while the data for the gaseous hydroxides were generally based on estimates from literature. Thermodynamic criteria were derived to determine whether the metallic element or the solid oxide was the stable condensed phase for the accident environmental conditions. Equations for the partial pressures for all gaseous species were also derived. The relevant environmental conditions were provided by the pressurized water reactor and boiling water reactor heat-up thermal-hydraulic codes. The volatilities of the core materials were found to decrease roughly in the following order: cadmium, indium, tin, iron, silver, manganese, nickel, chromium, uranium, and zirconium. Cadmium and indium would provide the largest mass of core material that can be transported out of the core.