Determination of gaseous fission product behavior near the cerium dioxide Σ3(111)/[11¯0] tilt grain boundary via first-principles study

Xi, Jianqi; Liu, Bin; Xu, Haixuan; Zhang, Yanwen; Weber, William J.

doi:10.1016/j.jnucmat.2017.11.046

Title: Determination of gaseous fission product behavior near the cerium dioxide $Σ 3 (111)/[1 \bar{1} 0]$ tilt grain boundary via first-principles study

Journal Article · 01 December 2017 · Journal of Nuclear Materials

DOI: https://doi.org/10.1016/j.jnucmat.2017.11.046 · OSTI ID:1422557

Xi, Jianqi ^[1]; Liu, Bin ^[2]; Xu, Haixuan ^[1];

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Univ. of Tennessee, Knoxville, TN (United States). Department of Materials Science and Engineering
Shanghai University (China). School of Materials Science and Engineering
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division; Univ. of Tennessee, Knoxville, TN (United States). Department of Materials Science and Engineering
Univ. of Tennessee, Knoxville, TN (United States). Department of Materials Science and Engineering; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division

We present that grain boundaries (GBs) are the most abundant structural defects in nanostructured nuclear fuels and play an important role in determining fission product behavior, which further affects the performance of nuclear fuels. In this work, cerium dioxide (CeO₂) is used as a surrogate material for mixed oxide fuels to understand gaseous fission product behavior, specifically Xe. First-principles calculations are employed to comprehensively study the behavior of Xe and trap sites for Xe near the $Σ 3 (111)/[1 \bar{1} 0]$ grain boundary in CeO₂, which will provide guidance on overall trends for Xe stability and diffusion at grain boundaries vs in the bulk. Significant segregation behavior of trap sites, regardless of charge states, is observed near the GB. This is mainly ascribed to the local atomic structure near the GB, which results in weaker bond strength and more negative segregation energies. For Xe, however, the segregation profile near the GB is different. Our calculations show that, as the size of trap sites increases, the segregation propensity of Xe is reduced. In addition, under hyper-stoichiometric conditions, the solubility of Xe trapped at the GB is significantly higher than that in the bulk, suggesting higher Xe concentration than that in the bulk. The results of this work demonstrate that the diffusion mechanism of Xe in CeO₂ is comparable to that in UO₂. The diffusion activation energies of Xe atoms in the Σ3GB are lower than that in the bulk CeO₂. Lastly, these results suggest that the diffusivity of Xe atoms is higher along the GB than that in the bulk, which enhances the aggregation of Xe atoms near the GB.