*Article* **Effects of Point Defects on the Stable Occupation, Diffusion and Nucleation of Xe and Kr in UO2**

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


**Abstract:** 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.

**Keywords:** UO2; Xe; Kr; occupation; diffusion; nucleation; molecular dynamics
