Migration and aggregation of fission products and their impacts on physical properties in UO2: Deep potential molecular dynamics simulations

ZH Chen and YF Hong and JK Deng and ZB Gao and RH Chen and R Tang and HX Xiao and XD Ding and J Sun, PHYSICAL REVIEW MATERIALS, 9, 083601 (2025).

DOI: 10.1103/f3kx-84sy

Fission products (FP) are inevitable byproducts of nuclear fission in the fuel during reactor operation. The migration and aggregation of FP in uranium dioxide (UO2)-based nuclear fuels play a crucial role in determining fuel performance and safety throughout the nuclear fuel cycle. However, accurately characterizing the atomic diffusion and early cluster formation of FP remains challenging in experiments. To address this issue, we employed self-developed deep potential (DP) models for UO2-Xe and UO2-I systems to perform molecular dynamics (MD) simulations. These simulations investigate the effects of Xe and I migration and aggregation on the mechanical properties and thermal conductivity of UO2 fuel. First, the accuracy of the DP models was verified. Next, the diffusion coefficients and cluster formation behavior of Xe and I in UO2 were analyzed, revealing three distinct temperature-dependent diffusion mechanisms. Furthermore, the MD simulation results demonstrate that the incorporation of FP significantly reduces the mechanical properties and thermal conductivity of UO2. Interestingly, the aggregation of FP into clusters mitigates these reductions, improving both mechanical properties and thermal conductivity. Notably, the recovery of mechanical properties through Xe aggregation is quite limited, primarily due to the formation of larger Xe clusters. In contrast, Xe aggregation leads to a more substantial improvement in thermal conductivity compared to I aggregation, attributed to reduced phonon scattering resulting from the fewer residual dispersed Xe atoms in the UO2 matrix. These insights are critical for improving reactor safety and extending operational lifespans through a better understanding of the migration and aggregation of FP.

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