Thermodynamic of the chemical interactions

The development of accident-tolerant fuel cladding (ATF) is one way of improving the safety of light water reactors. Among the most promising avenues of research, the chromium-coated zirconium alloy (M5) is being carefully evaluated under extreme conditions. The CALPHAD optimization method has established itself as a powerful tool for the prediction of phase equilibria and thermochemical properties for all types of materials, including the most complex. Nevertheless, a credible thermodynamic optimization of a multi-element system requires the fine determination of the properties of the subsystems such as the precise knowledge of the crystallographic parameters of the phases, their thermodynamic quantities and the characteristics of the transformations which will be used as input data and validation points of the modeling. The thermodynamic description of a complex system thus requires a complementary approach between experimenters and modelers. The group of competences constituted by the UCCS of Lille (elaboration and crystallographic and microstructural characterizations), the IM2NP of Marseille (differential thermal and calorimetric analyses), the PC2A of Lille and the IRSN (theoretical modelling and CALPHAD) proposes to study the chemical equilibria at high temperatures within the Cr-O-Zr or even Cr-O-U system. Once these data have been established, they will provide initial elements for defining the criteria for the rupture of ATF fuel elements in an accident situation.