THERMODYNAMIC MODELING OF THE O-U-ZR SYSTEM

To increase the basic knowledge of key phenomena which occur during th e molten cerium-concrete interaction (MCCI) resulting from the event o f a severe accident in a nuclear power plant, we are developing a ther modynamic database for the cerium (TDBCR) including the main materials involved. The first step of the accident is the core degradation, res ulting 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) an d isopleth sections of particular interest. The extent of the O-U liqu id miscibility gap into the ternary system is especially discussed. (C ) 1998 Elsevier Science B.V. All rights reserved.