Kinetic studies of NO₂ oxidation of uranium oxides by in situ XRD and neutron diffraction

An innovative voloxidation process employing NO₂ as the oxidant has been proposed and demonstrated. A fundamental understanding of the phase transition of U₃O₈ to UO₃ in the presence of NO₂ at elevated temperatures is needed to further optimize this advanced voloxidation process. Neutron and X-ray diffraction data were collected at the SNS's Powgen instrument and at the HTML, respectively, to determine the atom positions and unit cell of the ε-UO₃ produced from the reaction of U₃O₈ with NO₂. Real-time monitoring of the reaction is also being performed using in situ XRD. Reactions are conducted at a variety of temperatures using a customized XRD stage. Results show increasing reaction rate with temperature within the reference range. The data are refined and used to generate reaction curves with the goal of developing a model for the phase transition reaction in combination with thermodynamic models of the NO_x system.