Atomistic simulation of xenon bubble re-solution at dislocations versus in bulk UO2 due to thermal spike

Abstract

The re-solution rate of xenon (Xe) bubbles in irradiated uranium dioxide (UO₂) is a critical parameter related to fission gas bubble evolution and fission gas release. Molecular dynamics (MD) simulations have been used to understand the effect of spatial location near a dislocation, in addition to gas density and temperature, on the re-solution for nanometric Xe bubbles induced by thermal spikes at a ½<110>{100} edge dislocation or a ½<110> screw dislocation, as well in bulk UO₂. As well, these MD simulations also investigate the effect of bubble shape on re-solution at the edge dislocation and our results show that the re-solution for a bubble at the dislocation has a weak dependence on the spike track direction and the bubble shape. Interestingly, the average value of re-solution from a Xe bubble located near a dislocation is close to that observed in bulk UO₂. Xe re-solution in the UO₂ matrix is dependent on gas density and temperature, in addition to bubble size. A pressurized bubble has a stronger resistance to thermal spikes than equilibrium bubbles with a similar size. As well, re-solution evidently increases with increasing temperature from 800 to 1500 K. We propose an improved exponentially saturating function to predict re-solution as a function of gas density, bubble size and temperature based on the MD simulation results obtained for Xe bubble re-solution due to thermal spikes in UO₂.