Abstract
UO2 pellets 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 atmospheres. The 1.85 MBq Am-241 source was shown to have a too low radiolytic production to cause any measurable change in UO2 surface 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 atmosphere was shown to suppress the oxidation of the UO2 pellet surface as well as the dissolution in both Milli-Q and NaHCO3 solutions. The dissolved uranium concentration was reduced by a factor 10 under H2 atmosphere as compared to the Ar atmosphere experiments.
Highlights
The release of radiotoxic species from a final geological nuclear waste repository is governed by the oxidative dissolution of the UO2-matrix in the case of a canister failure
Two UO2-pellets were exposed to the 3.30 MBq Am-241 source in a 10 mM NaHCO3-solution under Ar and H2 atmospheres respectively for ~45 days
In the later stages of the experiment there were significantly lower amounts of uranium released under H2 atmosphere, showing that H2 had an inhibiting effect on the oxidative dissolution of uranium in the presence of carbonate
Summary
The release of radiotoxic species from a final geological nuclear waste repository is governed by the oxidative dissolution of the UO2-matrix in the case of a canister failure. H2 has been shown in several studies to protect the UO2-surface of used fuel from oxidation, the mechanism is not fully understood [9]
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