Geochemistry of the Cigar Lake uranium deposit: XPS studies

Samples of uranium ore from the Cigar Lake deposit in northern Saskatchewan, Canada, were analyzed using XPS. High-resolution spectra were recorded for the strongest bands of the major elements (U 4 f , C 1 s, O 1 s, Pb 4 f, S 2 p, Cu 2 p, Fe 2p, and the valence region (0-20 eV)) to obtain chemical state information for these samples. In general, the U-VI/U-IV ratio was very low, i.e., much less than 0.5, the threshold for the oxidative dissolution of UO2. The low values of the UVVI/U-IV ratio observed for samples from the Cigar Lake deposit indicate thermodynamic stability of the uranium ore in the reduced aqueous environment. Similarities between the disposal vault envisaged in the Canadian Nuclear Fuel Waste Management Program and the Cigar Lake deposit suggest that, if geochemical conditions in the vault were to be similar to those in the deposit, the longterm dissolution of UO2 fuel would be very minimal.