Thermodynamic modelling of advanced oxide and carbide nuclear fuels: Description of the U-Pu-O-C systems

► A thermodynamic modelling of the U-Pu-O-C system is derived using the CALPHAD method. ► The calculated phase diagrams of all the sub-systems and the thermodynamic properties of all the phases are described and found in good agreement with the experimental data. ► The variation of the oxygen potential in oxide fuels versus oxygen to metal ratio is explained by the change of the cation oxidation states and the formation of oxygen vacancies and interstitials.