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<p>(U<sub>1 − <i>x</i></sub>,Th<sub><i>x</i></sub>)O<sub>2</sub>, commonly known as the ThO<sub>2</sub>-based MOX, is a promising nuclear fuel candidate for various advanced reactors. A thorough understanding of its high-temperature creep behavior is demanding for assessing its fuel performance and predicting its service lifetime under normal operating and extreme accidental conditions. By utilizing the molecular dynamics simulations, we investigate the creep mechanisms and their transitions of nanocrystalline (U<sub>1 − <i>x</i></sub>,Th<sub><i>x</i></sub>)O<sub>2</sub> MOX affected by thorium contents, grain sizes, temperatures and stresses. We find that at lower temperatures and stresses, Coble creep is the dominant creep mechanism in nanocrystalline (U<sub>1 − <i>x</i></sub>,Th<sub><i>x</i></sub>)O<sub>2</sub>, which is rate-limited by cation diffusion along grain boundaries. Beyond a critical stress, significant grain boundary sliding activates, causing a transition from the Coble creep to Lifshitz sliding-dominated creep. As temperature approaches the superionic transition temperature of nanocrystalline (U<sub>1 − <i>x</i></sub>,Th<sub><i>x</i></sub>)O<sub>2</sub>, the pre-melting of its anionic sublattice leads to a marked enhancement in ionic diffusivity. Such enhancement in cationic diffusivity enables the cation to diffuse in lattice, thereby leading to a transition from Coble creep to Nabarro-Herring creep. The findings of this work not only provide valuable insights into the high-temperature creep behaviors of ThO<sub>2</sub>-based MOX fuels under extreme conditions but also shed light on the future design of fluorite-type fuels with tailored creep performance.</p>

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Superionic Transition-Induced Diffusional Creep Behavior Transitions in Nanocrystalline (U1 − x, Thx)O2 Nuclear Fuels

  • 期刊论文

  • 发表日期：

    2026年1月16日

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  • Fengnian Zhuang,
  • Gaosheng Yan,
  • Hong Chen,
  • Yi Zhang,
  • Wenshan Yu,
  • Minglong Xu,
  • Shengping Shen

摘要

(U1 − x,Thx)O2, commonly known as the ThO2-based MOX, is a promising nuclear fuel candidate for various advanced reactors. A thorough understanding of its high-temperature creep behavior is demanding for assessing its fuel performance and predicting its service lifetime under normal operating and extreme accidental conditions. By utilizing the molecular dynamics simulations, we investigate the creep mechanisms and their transitions of nanocrystalline (U1 − x,Thx)O2 MOX affected by thorium contents, grain sizes, temperatures and stresses. We find that at lower temperatures and stresses, Coble creep is the dominant creep mechanism in nanocrystalline (U1 − x,Thx)O2, which is rate-limited by cation diffusion along grain boundaries. Beyond a critical stress, significant grain boundary sliding activates, causing a transition from the Coble creep to Lifshitz sliding-dominated creep. As temperature approaches the superionic transition temperature of nanocrystalline (U1 − x,Thx)O2, the pre-melting of its anionic sublattice leads to a marked enhancement in ionic diffusivity. Such enhancement in cationic diffusivity enables the cation to diffuse in lattice, thereby leading to a transition from Coble creep to Nabarro-Herring creep. The findings of this work not only provide valuable insights into the high-temperature creep behaviors of ThO2-based MOX fuels under extreme conditions but also shed light on the future design of fluorite-type fuels with tailored creep performance.