Application of SPS in the fabrication of UN and (U,Th)N pellets from microspheres

Journal article, 2020

In this study, the process involved in the fabrication of a potential accident tolerant fuel is described. Homogeneous uranium nitride microspheres doped with different thorium content were successfully manufactured using an internal gelation process followed by carbothermic reduction, and nitridation. Elemental analysis of the materials showed low carbon and oxygen content, the two major impurities found in the products of carbothermic reduction. Uranium nitride microspheres were pressed and sintered using spark plasma sintering (SPS) to produce pellets with variable density. Final density can be tailored by choosing the sintering temperature, pressure and time. Density values of 77–98% of theoretical density (%TD) were found. As expected, higher temperatures and pressures resulted in a denser material. Furthermore, a direct correlation between the onset sintering temperature and thorium content in the materials was observed. The change of onset temperature has been related to an increment in the activation energy for self-diffusion due to the substitution of uranium atoms by thorium in the crystal structure.