The effect of pH on the anodic dissolution of SIMFUEL (UO2)

The dissolution mechanism of anodically oxidized SIMFUEL (doped uranium dioxide) has been determined as a function of pH over the range 0–13. Cyclic voltammetry was used to determine the changes in surface reactivity of UO2 in acidic, neutral and alkaline solutions. The UO2 specimens were also anodically oxidized for 1 h at various applied potentials and subsequently analyzed using X-ray photoelectron spectroscopy (XPS). Under acidic conditions, a surface-adsorbed hydrolyzed UV is formed and converted to UVI prior to dissolution. At pH 13, XPS shows a thicker and highly porous hydroxylated surface layer, containing UV and UVI species. This is consistent with thermodynamic expectations. The relatively low UVI content of the surface at E ⩾ 200 mV (vs SCE) suggests that the influence of UVI surface species on the kinetics of the overall dissolution process is minor compared to neutral and acidic conditions.