On the system UO2-CeO2

The investigations of the system UO2-Ce O2 by X-rays at high temperatures in a controlled atmosphere allows to trace the ternary diagram U-Ce-O between ambient temperature and 1000sup(o)C. The oxide reduction for Ce/U + Ce >= 20 at% with coexistence of the two fcc phases at ambient temperature. The disappearance of this biphase domain increases with the CeU + Ce ratio. It is at T = 260sup(o)C for 70% of Ce. The existence of a large monophase domain below this temperature allows to predict the structure of impurities in this system (essentially the oxygen vacancies). The experimental limit of the reduction, which tends to the composition O/Ce = 1.714, is much smaller than the one observed by Markin et. al. For the Ce/U + Ce > 0.50 contents the existence of a phase of the type M2O3 is observed in equilibrium with the phase of the type MO2sub(-)sub(x). (orig.)