ELECTROCHEMICAL AND SURFACE ANALYSIS OF HYDROGEN EFFECTS ON URANIUM DIOXIDE

摘要

Electrochemical and X-ray photoelectron spectroscopic (XPS) techniques were used to investigate the effect of hydrogen on the aqueous corrosion of SIMFUEL (UO_(2)) electrodes with different degrees of simulated burn-up under nuclear waste disposal conditions. Corrosion potential measurements (E_(CORR)) showed that as fuel burn-up increased, E_(CORR) in 5percent H_(2)/95percent Ar decreased. XPS, performed after E_(CORR) measurements, showed the surface film composition as a function of the purge gas used (Ar or 5percent H_(2)/95percent Ar). The uranium (4f_(7/2)) peak was resolved into contributions from U~(IV), U~(V), and U~(VI). When purged with H_(2), the film composition is mainly U~(IV), meaning very little oxidation to U~(V) and/or U~(VI) has occurred. This suppression of oxidation can be attributed to the presence of epsilon-particles in the SIMFUEL since experiments on SIMFUEL samples with no epsilon-particles showed a lower percentage of U~(IV) and higher percentages of U~(V) and U~(VI), due to more extensive surface oxidation. Consistent with this observation, E_(CORR) on the SIMFUEL containing no epsilon-particles was 150 mV more positive than values recorded on the SIMFUEL with epsilon-particles.