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.

Xe and Kr gases produced during the use of uranium dioxide (UO₂)-fuelled reactors can easily form bubbles, resulting in fuel swelling or performance degradation. Therefore, it is important to understand the influence of point defects on the behaviour of Xe and Kr gases in UO₂. In this work, the effects of point defects on the behavioural characteristics of Xe/Kr clusters in UO₂ have been systematically studied using molecular dynamics. The results show that Xe and Kr clusters occupy vacancies as nucleation points by squeezing U atoms out of the lattice, and the existence of vacancies makes the clusters more stable. The diffusion of interstitial Xe/Kr atoms and clusters in UO₂ is also investigated. It is found that the activation energy is ~2 eV and that the diffusion of the interstitial atoms is very difficult. Xe and Kr bubbles form at high temperatures. The more interstitial Xe/Kr atoms or vacancies in the system, the easier the clusters form.

To ensure the safety and efficient operation of nuclear reactors, it is imperative to understand the effects of various dopants (Ti, Th, and Zr) on the solubility of the fission product Xe in UO₂. In this study, Hubbard corrected density functional theory (DFT + U) and occupation matrix control were used to investigate the bulk and defect properties of UO₂. The results show that the UO₂-Ti system is more favorable for Xe dissolution in vacancies, whereas the UO₂-Th system has little effect on the dissolution of Xe atoms. Th, Zr, and Ti inhibit the aggregation of Xe clusters, and Ti is the least favorable for the nucleation and growth of Xe clusters.