Thermodynamic modelling of the O-U-Zr system

To increase the basic knowledge of key phenomena which occur during the molten corium-concrete interaction (MCCI) resulting from the event of a severe accident in a nuclear power plant, we are developing a thermodynamic database for the corium (TDBCR) including the main materials involved. The first step of the accident is the core degradation, resulting from the interaction of the fuel (UO2) with the zircaloy (98 wt% Zr). That is why the thermodynamic modelling of the fundamental O-U-Zr system is performed from a critical assessment of all the available experimental information. Optimized Gibbs energy parameters are given, and comparison between calculated and experimental equilibrium phase diagrams or thermodynamic properties is presented both for binary sub-systems and the ternary one, by means of isothermal (up to 3300 K) sections of particular interest. The extent of the O-U liquid miscibility gap into the ternary system is especially discussed. (orig.)