Classical molecular dynamics simulations are used to investigate the fission gas Xe behavior in a U-Mo alloy fuel matrix.The embedded atom method potential proposed by Smiova et al.is used to describe the U-Mo-Xe system.The results show that the initial configuration of interstitial Xe atoms in U-Mo alloys is very instable and has a strong tendency to get together and to form a Xe bubble by ejecting the adjacent U atoms and Mo atoms from their former normal lattice sites.The pressure in Xe bubbles is initially quite high and then drops with increasing Xe concentration obviously.The matrix swelling of U-Mo alloys associated with the Xe bubble growth follows approximately a linear relationship with the ratio of Xe to U at low Xe concentration while the rate of swelling increases rapidly at high Xe concentration.The simulation results are in good agreement with the experimental data.The recovery of the damaged structure in the U-Mo alloys matrix is also investigated.It is shown that a damaged structure cannot be recovered completely after a system is relaxed for a long time while still having lots of defects.