A model for fission-gas-bubble behavior in amorphous uranium silicide compounds

A model for the behavior of fission gas in irradiated amorphous materials is developed. The model proposes that gas bubble nucleation occurs within shear bands initiated around free volume regions. Small gas–atom clusters that form within these regions are susceptible to dissolution by forces generated by the plastic flow of material around the cluster. The bubble coarsening process depends on the materials viscosity and on irradiation-induced re-solution. The bubble distribution eventually reaches a point where larger bubbles from the tail of the evolving lognormal size distribution begin to contact the more numerous nanometer-sized bubbles from the peak region. This condition defines the knee in the swelling curve. The fission density at which the knee occurs is a function of fission rate. Calculations for the behavior of the knee, swelling, and the fraction of gas in bubbles in irradiated U3Si2 intermetallic compounds are compared to measured quantities.