Abstract
Thin films of UO2, U2O5, and UO3 were prepared in situ and exposed to reactive gas plasmas of O2, H2 and H2O vapour produced with an ECR plasma source (electron cyclotron resonance) under UHV conditions. The plasma constituents were analysed using a residual gas analyser mass spectrometer. For comparison, the thin films were also exposed to the plasma precursor gases under comparable conditions. Surface analysis was conducted using X-Ray and ultraviolet photoelectron spectroscopy before and after exposure, by measuring the U 4f, O 1s core levels and the valence band region. The evolution of the peaks was monitored as a function of temperature and time of exposure. After interacting with water plasma at 400 °C, the surface of UO2 was oxidized to a higher oxidation state compared to when starting with U2O5 while the UO3 film displayed weak surface reduction. When exposed to water plasma at ambient temperature, the outermost surface layer is composed of hexavalent uranium in all three cases.
Highlights
The major route for matrix dissolution of uranium oxide based spent nuclear fuel and the subsequent release of radionuclides in a geological repository, is radiation-induced oxidation.[1]
Thin films of UO2, U2O5, and UO3 were prepared in situ and exposed to reactive gas plasmas of O2, H2 and H2O vapour produced with an ECR plasma source under UHV conditions
Electrochemical studies have indicated that catalytic decomposition of H2O2 on UO2 requires the presence of uranium in higher oxidation state than +IV16 and recent studies of H2O2-induced leaching of UO2 have shown that the redox reactivity of UO2 decreases with H2O2 exposure and that this trend is accompanied by a change in the uranium oxidation state even under conditions where dissolution of U(VI) is favoured.[17,18]
Summary
The major route for matrix dissolution of uranium oxide based spent nuclear fuel and the subsequent release of radionuclides in a geological repository, is radiation-induced oxidation.[1]. Three different types of uranium oxide thin films UO2, U2O5 and UO3 were exposed to water plasma at 400 °C for 10 and 30 minutes.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
