*Article* **Molecular Dynamics Simulations of Xe Behaviors at the Grain Boundary in UO2**

**Yaping Xia 1, Zhen Wang 2,\*, Li Wang 3, Yangchun Chen 1, Zhixiao Liu 3, Qingqing Wang 2, Lu Wu <sup>2</sup> and Huiqiu Deng 1,\***


**Abstract:** In this study, we investigated the behavior of xenon (Xe) bubbles in uranium dioxide (UO2) grain boundaries using molecular dynamics simulations and compared it to that in the UO2 bulk. The results show that the formation energy of Xe clusters at the Σ5 grain boundaries (GBs) is much lower than in the bulk. The diffusion activation energy of a single interstitial Xe atom at the GBs was approximately 1 eV lower than that in the bulk. Furthermore, the nucleation and growth of Xe bubbles in the Σ5 GBs at 1000 and 2000 K were simulated. The volume and pressure of bubbles with different numbers of Xe atoms were simulated. The bubble pressure dropped with increasing temperature at low Xe concentrations, whereas the volume increased. The radial distribution function was computed to explore the configuration evolution of Xe bubbles. The bubble structures in the GB and bulk material at the same temperature were also compared. Xe atoms were more regular in the bulk, whereas multiple Xe atoms formed a planar structure at the GBs.

**Keywords:** UO2; grain boundary; Xe bubble; molecular dynamics
