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<p>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. UO<sub>2</sub> was identified as the only major intermediate phase, while minor α-U<sub>2</sub>(N,O)<sub>3+x</sub> phases detected in the bulk and β-U<sub>2</sub>N<sub>3</sub> on UN surface. A significantly higher CTE was observed under oxidizing conditions (12.3 × 10<sup>-6</sup> 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.</p><p></p>

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

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年12月12日

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  • Natalie S. Yaw,
  • Sam Karcher,
  • Mohamed AbdulHameed,
  • Emma C. Kindall,
  • Arjen van Veelen,
  • Malin C. Dixon Wilkins,
  • Bryn Merrill,
  • Hongwu Xu,
  • Joshua T. White,
  • Benjamin Beeler,
  • John S. McCloy,
  • Xiaofeng Guo

摘要

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.