2.2.3. Nucleation of Xe/Kr Cluster in UO2-Containing Point Defects

MD simulation was performed to simulate the nucleation process of Xe bubbles. Five systems with sizes of 10 *a*<sup>0</sup> × 10 *a*<sup>0</sup> × 10 *a*<sup>0</sup> (*a*<sup>0</sup> is the lattice constant of UO2 fluorite structure at the temperature of 2500 K) were studied, which are mainly perfect bulk without defects, with 1% vacancies concentration, with 2% vacancies concentration, with 1% interstitial concentration, and with 2% interstitial concentration. Then, 2% and 5% concentration of Xe/Kr atoms were added to the different systems, and the Xe/Kr atoms were randomly and uniformly located at octahedral interstitial sites. The specific simulation process is as follows.

After static relaxation of the initial system relaxation of the above configuration with a high temperature, the temperature was raised to 2500 K to accelerate the diffusion of Xe/Kr atoms. Then, the simulation was conducted in the NVT ensemble for 20 ns. Finally, the obtained configuration was subjected to static relaxation to ensure a stable configuration.

#### **3. Results and Discussion**
