Oxidation of UO2 by radiolytic oxidants

The kinetics of UO ₂ oxidation by H ₂O ₂ has been studied using aqueous suspensions of UO ₂-powder. The second order rate constant for the reaction between H ₂O ₂ and UO ₂ has been determined to 8 × 10 ⁻⁷ m/min (based on the surface to solution volume ratio) in the absence of carbonate. By studying the reaction between UO ₂ and other oxidants, it is possible to draw conclusions concerning the mechanism. The logarithm of the second order rate constant, ln k, for UO ₂ oxidation appears to be linearly related to the one-electron reduction potential, E ⁰, of the oxidant. This indicates that the rate limiting step in the oxidation of UO ₂ is one-electron transfer. A Fenton like mechanism is plausible for the reaction between UO ₂ and H ₂O ₂. The diffusion controlled rate constant in this particular system is approximately 10 ³ m/min, and therefore the reactions with OH ^{} and CO ₃ ⁻ are estimated to be diffusion controlled.