Three-dimensional phase-field simulation of intergranular bubble evolution in UO2 during irradiation

Abstract

In this study, a three-dimensional phase-field model was developed to investigate the evolution of intergranular bubbles during irradiation. The model considered several grain structures and multiple fission gas bubbles, with the microstructure evolution being governed by improved dynamic equations. Verification of the phase-field model showed good agreement with the theory in describing the properties of grain boundary (GB). The study examined the dependency of bubble percolation on bubble shape, fission rate, and average grain size. The simulation results revealed that the changes in these three factors have significant effects on the shape of GB bubbles, the percolation rate, and the connectivity threshold of GB bubbles. The bubble connection threshold was obtained from the curve of triple junction coverage versus grain boundary coverage. The results indicate that the connectivity threshold increases with the higher fission rate and lager average grain size. This investigation into bubble percolation during irradiation provides valuable insights for further study on fission gas release in UO2 fuel within nuclear reactors.