On the change in UO2 redox reactivity as a function of H2O2 exposure

Abstract

To assess the long-term leaching behaviour of UO₂, the main constituent of spent nuclear fuel, the oxidative dissolution of UO₂ pellets was studied at high H₂O₂ exposures ranging from 0.33 mol m⁻² to 1.36 mol m⁻². The experiments were performed in aqueous media containing 10 mM HCO₃⁻ where the pellets were exposed to H₂O₂ three consecutive times. The results indicate that the dissolution yield (amount of dissolved uranium per consumed H₂O₂) at high H₂O₂ exposures is significantly lower compared to previous studies of both pellets and powders and decreases for each H₂O₂ addition for a given pellet. This implies a change in redox reactivity, which is attributed to irreversible alteration of the pellet surface. Surface characterization after the exposure to H₂O₂, by SEM, XRD and Raman spectroscopy shows, that the surface of all pellets is significantly oxidized.