| AVS 63rd International Symposium & Exhibition | |
| Actinides and Rare Earths Focus Topic | Tuesday Sessions |
| Session AC-TuP |
| Session: | Chemistry and Physics of the Actinides and Rare Earths Poster Session |
| Presenter: | Scott Donald, Lawrence Livermore National Laboratory |
| Authors: | S. Donald, Lawrence Livermore National Laboratory M. Davisson, Lawrence Livermore National Laboratory Z. Dai, Lawrence Livermore National Laboratory A.J. Nelson, Lawrence Livermore National Laboratory |
| Correspondent: | Click to Email |
The evolution in vacuum of UO2 powder samples, previously aged under a controlled environment composed of 20% O2 and relative humidity varying from 34% to 98%, was studied using core level x-ray photoelectron spectroscopy. Upon exposure to ultra-high vacuum, the U 4f peak position was found to shift to a lower binding energy with time, consistent with a decrease in the overall oxidation state of the uranium. No samples were found to reduce fully to stoichiometric UO2 under vacuum; those exhibiting the greatest decay with time asymptotically approached a mean uranium valence of +4.5, analogous to U4O9, within 14 days. The reaction rate was found to be variable with the initial mean uranium valence, with more oxidized samples reducing more quickly. Scanning electron microscopy images of the aged powders showed corresponding structural variation and enhanced surface cracking, both of which may serve to facilitate the reduction process.
The work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.