The influence of silicate on the development of acidity in corrosion product deposits on SIMFUEL (UO2)

The influence of silicate on the formation of corrosion products and secondary phase deposits on corroding/dissolving nuclear fuel surfaces under waste disposal conditions were investigated. SIMFUEL (doped uranium dioxide) has been characterized over the potential range 100–500 mV (vs. SCE). Through the use of X-ray photoelectron spectroscopy (XPS) the surface composition over this potential range has been determined. The presence of silicate was found to have little influence on the oxidation of UO2 to produce the oxidized surface layer U1-2xIVU2xVO2+x. However, depending on its concentration it could suppress the conversion reaction U1-2xIVU2xVO2+x→UO3·yH2O for potentials ⩽250 mV (vs. SCE). This suppression appears due to the adsorption of silicate on the fuel surface. The accumulation of a hydrated UVI silicate on the fuel surface occurs when UVI is formed at higher anodic potentials, leading to a suppression of anodic dissolution. The UO22+ formed in, and subsequently transported out of, the acidified sites accumulates on the outer fuel surface as a hydrated UVI silicate.