The influence of calcium ions on the development of acidity in corrosion product deposits on SIMFUEL, UO2

In order to clarify the influence of groundwater constituents on the formation of corrosion products and secondary phase deposits on corroding/dissolving nuclear fuel surfaces under waste disposal conditions we have investigated the influence of Ca2+, present as CaCl2. The influence of calcium ions on the anodic dissolution of SIMFUEL (doped uranium dioxide) has been characterized over the potential range 0–500 mV (vs. SCE). Through the use of X-ray photoelectron spectroscopy (XPS) the surface composition over this potential range has been determined. Ca2+ was found not to influence the conversion of UIVO2 to U1-2xIVU2xVO2+x, but to suppress the subsequent formation of a UVI surface species which lead to the formation of a hydrated deposit, UO3 · yH2O. The adsorption of Ca2+ on the UO2 surface is believed to inhibit fuel dissolution either via inhibiting the stabilization of the cation precursor (UO2(OH)2)ads or by blocking the O2− anion transfer reaction from the fuel surface.