Thermal expansion and degradation of uranium mononitride under high-temperature oxidative conditions

The chemical and physical properties of advanced nuclear fuels, particularly in the moderately high temperature regime relevant for fuel storage, remain largely understudied. In this work, we combine in situ high-temperature (high-T) experiments with ab initio molecular dynamics (AIMD) simulations to investigate the behavior of UN under thermally oxidizing conditions. The phase composition and the coefficient of thermal expansion (CTE) were determined by in situ high-T X-ray diffraction (XRD) and Raman spectroscopy. UO2 was identified as the only major intermediate phase, while minor α-U2(N,O)3+x phases detected in the bulk and β-U2N3 on UN surface. A significantly higher CTE was observed under oxidizing conditions (12.3 × 10-6 at 500 K). AIMD simulations, supported by in situ XRD and Raman spectroscopy, attribute this increase to UN lattice distortion, rather than to oxygen diffusion.

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Publication Details

Journal
npj Materials Degradation
Published
2025-12-12
DOI
https://doi.org/10.1038/s41529-025-00708-1
Citations
1
Primary Topic
Nuclear Materials and Properties
Type
article
Field-Weighted Citation Impact
0.52

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article

Thermal expansion and degradation of uranium mononitride under high-temperature oxidative conditions

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Thermal expansion and degradation of uranium mononitride under high-temperature oxidative conditions

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article en
1 citations

Abstract

The chemical and physical properties of advanced nuclear fuels, particularly in the moderately high temperature regime relevant for fuel storage, remain largely understudied. In this work, we combine in situ high-temperature (high-T) experiments with ab initio molecular dynamics (AIMD) simulations to investigate the behavior of UN under thermally oxidizing conditions. The phase composition and the coefficient of thermal expansion (CTE) were determined by in situ high-T X-ray diffraction (XRD) and Raman spectroscopy. UO2 was identified as the only major intermediate phase, while minor α-U2(N,O)3+x phases detected in the bulk and β-U2N3 on UN surface. A significantly higher CTE was observed under oxidizing conditions (12.3 × 10-6 at 500 K). AIMD simulations, supported by in situ XRD and Raman spectroscopy, attribute this increase to UN lattice distortion, rather than to oxygen diffusion.

npj Materials DegradationVol. 9(1)
Los Alamos National Laboratory (US), North Carolina State University (US), Idaho National Laboratory (US), Arizona State University (US), Washington State University (US)
U.S. Nuclear Regulatory Commission
Openalex Percentile: Top 29%
Nuclear Materials and Properties
0.52
DOIOpen Access PDFOpenAlex
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