Reduction of Uranium Trioxide (UO3) to Uranium Dioxide (UO2) for Ceramic Nuclear Fuel

This work investigates the effects of temperature and process time on the thermal reduction of uranium(VI) trioxide (UO3) to uranium(IV) dioxide (UO2) in a hydrogen atmosphere in the production of powdered precursors of ceramic nuclear fuel. The optimal temperature (500°C) and exposure time (180 min) to achieve the target phase composition and uranium dioxide stoichiometric ratio were determined by X-ray powder diffraction (XRD). Scanning electron microscopy (SEM) and XRD showed that long exposure times do not increase grain or secondary agglomerate sizes (DXRD = 13.4–16.1 nm). X-ray photoelectron spectroscopy (XPS) confirmed the achievement of the target stoichiometry and showed 82–83% uranium reduction efficiency. The uranium dioxide produced under the optimized conditions is suitable for manufacturing ceramic nuclear fuel with superior mechanical properties via spark plasma sintering technology.