Anodic reactions occurring on simulated spent nuclear fuel (SIMFUEL) in hydrogen peroxide solutions containing bicarbonate/carbonate – The effect of fission products

Abstract

The anodic behaviour of simulated spent nuclear fuel (SIMFUEL) was studied in NaCl solutions containing H2O2 and various concentration of HCO3−/CO32− using electrochemical, surface and solution analytical techniques. The two main anodic reactions are the oxidative dissolution of UO2 and H2O2 oxidation. The relative importance of both reactions is controlled by the presence or absence of noble metal (ε) particles dispersed throughout the UO2 matrix, the applied potential and the HCO3−/CO32− concentration. Both reactions are suppressed by the formation of UVI surface films. When the formation of these films is prevented at higher HCO3−/CO32− concentrations, both reactions occur readily on the sublayer of UIV1-2xUV2xO2+x. When present, noble metal (ε) particles support H2O2 oxidation over the full potential range. At low potentials the peroxycarbonate (HCO4−) species formed is rapidly oxidized on the particles. At high potentials H2O2 can be directly oxidized on the noble metal particles rendered catalytic by pre-oxidation (e.g., Pd to PdII).