This is a comprehensive study of two mechanisms of fission gas bubble re-solution in UO2 by molecular dynamics (MD) simulations: homogeneous re-solution and heterogeneous re-solution. For the homogeneous mechanism, a hybrid approach is employed whereby Monte Carlo (MC) simulations are used to obtain the full recoil energy spectrum of fission gas atoms, and MD simulations are used to build an extensive library of fission gas atom re-solution events. This library is used for calculating a recoil spectrum averaged displacement distribution of fission gas atoms around bubbles. The results show that past estimates of the homogeneous re-solution parameter are very inaccurate. For a better understanding of heterogeneous re-solution, sputtering and the re-solution of Xenon fission gas bubbles due to electronic energy deposition of fission fragments is investigated using MD simulations. First, a two-temperature model (TTM) coupling the electronic (e-) and phonon (p-) system is employed to determine the temperature profile along the tracks of fission fragments. The e-p coupling constant within the model is determined by comparing the sputtering yields deduced from the MD simulations with those obtained experimentally. Next, fission fragments tracks are simulated in a UO2 sample containing one Xenon bubble. At high (dE/dx)e bubbles are partially re-dissolved, however, for ions with electronic stopping power lower than 34 keV/nm, bubble re-solution is not observed. Thus, bubble re-solution due to the electronic stopping of fission fragments in UO2 is likely to be insignificant compared to homogeneous re-solution.
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