XPS study of external α-radiolytic oxidation of UO2 in the presence of argon or hydrogen

UO2\ua0pellets exposed to 1.85 MBq and 3.30 MBq Am-241 sources with a 30 μm separation in solution were studied under Ar and H2\ua0atmospheres. The 1.85 MBq Am-241 source was shown to have a too low radiolytic production to cause any measurable change in UO2\ua0surface oxidation state. However, a significant oxidation was observed after exposure to the 3.30 MBq source under Ar atmosphere through the production of U(V), as seen from the U4f7/2-peak deconvolution and valence band peak analysis. The H2\ua0atmosphere was shown to suppress the oxidation of the UO2\ua0pellet surface as well as the dissolution in both Milli-Q and NaHCO3\ua0solutions. The dissolved uranium concentration was reduced by a factor 10 under H2\ua0atmosphere as compared to the Ar atmosphere experiments