Effect of Niobium on Sintering Process of Gamma Phase Uranium Alloys Fuel Pellets

Abstract As a candidate material for metallic fuel, U-Mo metal fuel pellets are the most promising. U-Mo and U-Mo-Nb alloy pellets with a certain porosity were successfully prepared by the process of hydrogenation/dehydrogenation—compression molding—argon liquid-phase sintering. In order to study the effect of Nb addition on γ phase uranium alloy fuel pellets, microstructure and thermophysical properties of the samples were investigated using scanning electron microscope (SEM), in situ synchrotron X-ray diffraction (XRD), and differential scanning calorimeter (DSC) measurements. Results showed that with the increase of Nb content in the pellets from the nonadd to micro-adding, Nb can facilitate the diffusion of Mo into the U matrix, resulting in the formation of a metastable γ-U phase. Meanwhile, during the same liquid phase sintering process of U-Mo fuel pellets, with the increase of Nb content, the number of secondary phases in U-Mo fuel pellets gradually decreased, while the size and number of voids of the secondary phases decreased. The specific heat capacity and thermal diffusivity of porous γ phase uranium alloys fuel pellets with different density were measured and thermal conductivity from 100 °C to 600 °C were calculated according to the experiment results. It is suggested that the thermal conductivity will increase with the density of pellets increasing.