128 A Tribute to Rodney C. Ewing: Celebrating a Half-Century of Transformative Contributions to Geoscience, Mineralogy, and Material Science

Honoring Prof. Rodney C. Ewing (1946–2024), this session celebrates over 50 years of groundbreaking contributions to mineralogy, geoscience, and materials science, from atomic-scale processes to field-scale applications.

Monday, 20 October 2025
1:30 PM - 5:30 PM
HBGCC, 217A

Long-Term Aging of UO2 in Oxidizing Environments

Paper number: 128-5
Program: Technical Sessions
Time: 2:40 PM – 2:55 PM

Authors

Abstract

Uraninite (UO2) is the most abundant uranium ore mineral, the product of proposed bioremediation strategies for uranium-contaminated soils and aquifers, and its synthetic analog is the primary constituent of most nuclear fuels. Understanding oxidative corrosion is essential in all of these settings. During early stages of oxidation, UO2 incorporates interstitial oxygen up to a stoichiometry of UO2.25 without disruption of the uranium lattice, but the structural details of the process are the subject of ongoing debate. In 2015 we published the atomic-scale structure of the oxygen diffusion profile that forms below the (111) surface during the first weeks of oxidation under dry O2 gas as determined by crystal truncation rod (CTR) X-ray scattering, X-ray photoelectron spectroscopy, and density functional theory (DFT) [1].  Oxygen interstitials order into a nanoscale superlattice with three-layer periodicity. In the decade since, we have examined analogous behavior of the (001) [2] and (110) surfaces.  We have further investigated the corrosion of all three surfaces following oxidation reactions exceeding two years.  We find complex diffusion profiles under all three, with tantalizing evidence suggesting a common structure may form, driven by the long-range influence of the uranium f-electrons. Diffusion kinetics appear linked not only to the oxidation of uranium, but also to possible screening by structural oxygen. 

[1] Stubbs, J.E., Chaka, A.M., Ilton, E.S., Biwer, C.A., Engelhard, M.H., Bargar, J.R., Eng, P.J. (2015) UO2 Oxidative Corrosion by Nonclassical Diffusion. Phys. Rev. Lett. 114, 246103.

[2] Stubbs, J.E., Biwer, C.A., Chaka, A.M., Ilton, E.S., Du, Y., Bargar, J.R., Eng, P.J. (2017) Oxidative Corrosion of the UO2 (001) Surface by Nonclassical Diffusion. Langmuir 33, 13189-13196.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-413283

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