Modelling the growth and evolution of statistically significant populations of intergranular fission gas bubbles by IPM

The time-evolution of an intergranular bubble population is considered using the Included Phase Model (IPM). The model considers the generation and coupled transport of vacancies and gas atoms driven by interfacial energy, elasticity, and internal energy in a framework that admits complex interface morphology. The model predicts overpressure, bubble growth, coarsening, and coalescence leading to the formation of interconnected high-aspect-ratio bubbles on the grain face. The computational efficiency of this model is leveraged to simulate sets of 250 bubbles over time, which compare well with the CAGR-UOX-SWELL SEM measurements and the established SIFGRS model. Analysis of the simulation results highlights the importance of the bubble density as an indicator of bubble structure formed by coalescence and suggests that the two-point autocorrelation function captures the formation of an interconnected network which could improve release thresholds.