Exploring cluster formation in uranium oxidation using high resolution X-ray spectroscopy at elevated temperatures

doi:10.1038/s43246-025-00795-2

Exploring cluster formation in uranium oxidation using high resolution X-ray spectroscopy at elevated temperatures

2025-04-17

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Kristina O. Kvashnina *

DOI：10.1038/s43246-025-00795-2

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Uranium dioxide (UO2) is a complex material with significant relevance to nuclear energy, materials science, and fundamental research. Understanding its high-temperature behavior is crucial for developing new uranium-based materials and improving nuclear fuel efficiency in nuclear reactors. Here we study the evolution of uranium state during the oxidation of UO2 in air at temperatures up to 550 degrees C using the in situ X-ray absorption spectroscopy in high energy resolution fluorescence detection mode at the U M4 edge, combined with electronic structure calculations. Our data reveal a complex sequence of events occurring over minutes and hours at elevated temperatures, including changes in the electronic and local structure, 5f electron occupancy, the formation of U cuboctahedral clusters, and the creation of U4O9 and U3O7 mixed U oxide phases. These findings highlight the fundamental role of clustering processes and pentavalent uranium in both the oxidation process and the stabilization of uranium materials.

Keywords:

CHARGE-DISTRIBUTION

CRYSTALLINE-STRUCTURE

OXYGEN DIFFUSION

DEFECT STRUCTURE

LOCAL-STRUCTURE

UO2

DIOXIDE

OXIDES

SCATTERING

LATTICE

Exploring cluster formation in uranium oxidation using high resolution X-ray spectroscopy at elevated temperatures

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