A semi-empirical model for the air oxidation kinetics of UO2

UO 2 is readily oxidized to U 3 O 8 at a high temperature, and this reaction has received considerable attention in the field of nuclear fuel cycles. A voloxidation process which makes use of the characteristics of a UO 2 oxidation has been developed to treat the spent fuels produced by irradiation of UO 2 . In this work, semi-empirical kinetic models to describe the sigmoidal behavior of a UO 2 oxidation were selected and compared in order to obtain a kinetic expression with different temperatures. Two basic approaches of a nucleation-and-growth model and an autocatalytic reaction model were adequate enough to describe the S-shaped oxidation behavior, and an equation to correlate the model parameters with the temperature was introduced. The calculation results of the two models satisfy the experimental data for UO 2 spheres and the activation energy of a reaction rate constant was evaluated. The models were also adopted as a surface reaction time term for a UO 2 pellet.