*Article* **Effect of Radiation Defects on Thermo–Mechanical Properties of UO2 Investigated by Molecular Dynamics Method**

**Ziqiang Wang 1,2, Miaosen Yu 2, Chen Yang 1, Xuehao Long 2, Ning Gao 2,3,\*, Zhongwen Yao 4,\*, Limin Dong <sup>5</sup> and Xuelin Wang <sup>2</sup>**


**Abstract:** Nuclear fuel performance is deteriorated due to radiation defects. Therefore, to investigate the effect of irradiation-induced defects on nuclear fuel properties is essential. In this work, the influence of radiation defects on the thermo-mechanical properties of UO2 within 600–1500 K has been studied using the molecular dynamics method. Two types of point defects have been investigated in the present work: Frenkel pairs and antisites with concentrations of 0 to 5%. The results indicate that these point defects reduce the thermal expansion coefficient (α) at all studied temperatures. The elastic modulus at finite temperatures decreases linearly with the increase in concentration of Frenkel defects and antisites. The extent of reduction (*R*) in elastic modulus due to two different defects follows the trend *R*<sup>f</sup> > *R*<sup>a</sup> for all studied defect concentrations. All these results indicate that Frenkel pairs and antisite defects could degrade the performance of UO2 and should be seriously considered for estimation of radiation damage in nuclear fuels used in nuclear reactors.

**Keywords:** uranium dioxide; Frenkel pairs; antisites; molecular dynamics; elastic modulus; thermal expansion
