Pierre-Yves Chevalier

A thermodynamic evaluation of four Si-M (M = Mo, Ta, Ti, W) binary systems☆

Abstract The different solution phases and stoichiometric compounds of the Si-Mo, Si-Ta, Si-Ti and Si-W systems have been analysed in terms of thermodynamic models based on selected values of the pure elements. For each system, a set of self consistent parameters has been obtained by using the optimisation procedure developped by Lukas et al [1]. Phase diagrams and characteristic thermodynamic functions have been calculated and compared with the corresponding experimental values using the THERMODATA software.

Progress in the thermodynamic modelling of the O–U binary system

Abstract The fuel of civil nuclear plants, UO 2 , melts at 3120 K. During an hypothetical severe accident, urania, submitted to high temperatures and various oxygen potentials, presents a wide non-stoichiometry range: the melting temperature of UO 2± x , related to oxygen potential, decreases in all cases. In this scenario, urania could react with other materials, firstly zircaloy, and the melting temperature of (U, Zr)O 2± x still decreases. That is why the critical assessment of the O–U binary system including the non-stoichiometry range of urania, is a major step to a correct thermodynamic modelling of multicomponent systems for nuclear safety. The very numerous experimental information has been compiled and analysed. The associate model was used for the liquid phase, and a sublattice model for UO 2± x ; U 4 O 9− y , U 3 O 8 and UO 3 were treated as stoichiometric. Phase diagram and thermodynamic properties have been calculated from the optimised Gibbs energy parameters. The calculated consistency with the experimental ones is quite satisfactory.

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) and isopleth sections of particular interest. The extent of the O–U liquid miscibility gap into the ternary system is especially discussed.

A Thermodynamic evaluation of the Bi-In System

Abstract The different solution phases and intermetallic compounds of the Bi-In system have been analysed in terms of thermodynamic models based on selected values for the pure elements. A set of self-consistent parameters has been obtained by using the optimization procedure developped by Lukas et al. |1|. Phase diagram and caracteristic thermodynamic functions have been calculated and compared with the corresponding experimental values using the THERMODATA software.

A thermodynamic evaluation of the Mn-Si system

Abstract Available experimental information concerning thermodynamic properties as well as phase equilibria has been compiled and used for the assessment of new self-consistent parameters for all phases in the Mn-Si system, by means of the well-known Lukas et al. s program. Phase diagram and characteristic thermodynamic functions have been calculated and compared with the experimental values, leading to a very satisfactory agreement. Thermodynamic models and pure elements data are consistent with the S.G.T.E (Scientific Groupe Thermodata Europe) recommendations. Thus, the assessed parameters may be incorporated in specialized solution databases.

Thermodynamic modelling of the N–U system

Abstract Thermodynamic properties constitute part of our general knowledge about physical and chemical properties of nuclear materials, as the solid substance UN 1− x (fcc_B1). This is why the thermodynamic modelling of the N–U binary system is performed here from a critical assessment of most of the available experimental information, with one of the most commonly used optimization procedure. Optimized Gibbs energy parameters are given, and a comparison between the calculated and experimental equilibrium phase diagram or thermodynamic properties is presented.