Preparation of Chromium doped uranium nitride via Sol-Gel and Carbothermic reduction

Uranium nitride (UN) has been proposed as an accident tolerant fuel due to its enhanced thermal properties compared to the standard UO2. However, due to its low oxidation resistance, its implementation in water cooled reactors has not been allowed. A method to improve the corrosion resistance involves doping with oxide scale forming elements such as aluminum or chromium. In this work, UN microspheres were produced by an internal gelation method followed by carbothermic reduction and nitridation. Chromium was added as dopant in the solution to produce a homogenous mixture with uranium. The ternary phase (U2CrN3) was observed for the first time in Cr-doped UN microspheres produced via sol-gel and carbothermic reduction. Materials with and without the ternary phase were produced, and a mechanism of reaction was proposed. Chromium precipitations were also observed on the surface of the microspheres produced, indicating low solubility of Cr compounds in the UN matrix. ICP-MS and XRF measurements showed that Cr content is reduced after heating treatments, probably due to evaporation. Additionally, these results showed that Cr in the ternary phase is completely soluble in aqua regia, unlike the Cr in the material without the ternary phase.