Heterogeneous nucleation of fission gas bubbles and gas migration in uranium dioxide

Abstract

The number and size of fission gas bubbles precipitated in irradiated uranium dioxide are calculated from a theory based on a balance between nucleation of bubbles at vacancy clusters produced by fission fragments and the agglomeration of bubbles by random motion. The distribution of bubble sizes is determined by gas atom capture, bubble agglomeration and irradiation re-solution. Irradiation re-solution exceeds gas atom capture for large bubbles and causes the larger bubbles formed by agglomeration to shrink. The effect of the precipitated gas bubbles on gas migration is considered, and it is shovrm that the bubble diffusion coefficient is likely to be larger than the trap-release diffusion coefficient. The predictions are compared with other theories of bubble nucleation, and with experimental observation.