Effect of oxygen-to-metal ratio on properties of corium prepared from UO2 and zircaloy-2

The UO2 and zircaloy system has been studied in severe accident research because these materials form most of a molten corium. In addition, during core meltdown, it is expected that water vapor and hydrogen which is produced in the H2O–zircaloy reaction fill the reactor core space. In this study, simulated corium specimens were prepared considering the ambient atmosphere in an accident, and adjustment of the oxygen-to-metal (O/M) ratio. Phase observations by XRD and EPMA and measurement of thermal conductivity were then done on the specimens. It was confirmed that the prepared O/M ratio had hardly any effect on melting temperature although UO2+x has obvious dependency on the O/M ratio. Thermal conductivity of the molten specimens showed little dependency on the O/M ratio and temperature. It appeared that the thermal conductivity had already been significantly decreased by the solution of U and Zr. Microstructure information as lattice constant and phase segregation was obtained by XRD and EPMA observation.These properties will be basic data for the development of conditioning techniques for an actual corium.