Melting behavior of americium-doped uranium dioxide

Uranium-americium mixed oxides are considered as potential blankets for americium transmutation in fast neutron reactors. Their thermophysical properties and notably their melting behavior have not been properly assessed although required in order to evaluate the safety of these compounds under irradiation. In this study, we measured via laser heating the melting points under inert atmosphere (Ar) of U1 xAmxO2±δ samples with Am/(U+Am) contents equal to 10, 15 and 20 mol.%. The experimental atmosphere was chosen in order to maintain, as much as possible throughout the heating/cooling cycles, the oxygen-to-metal ratio, initially set very close to 2.00. Structural characterizations of the samples carried out before and after melting confirm that this goal was satisfactorily attained. The obtained melting/solidification temperatures, measured here for the first time, indicate that under the current experimental conditions and as far as the investigated AmO2 contents, the solidus line of the UO2-AmO2 system follows with very good approximation the ideal solution behavior. Accordingly, the observed liquidus formation temperature decreases from 3130 ± 20 K for pure UO2 to 3051 ± 30 K for U0.8Am0.2O2±δ.