Defect cluster and nonequilibrium gas bubble associated growth in irradiated UMo fuels – A cluster dynamics and phase field model

Irradiation examination shows that gas bubble swelling kinetics are much faster after irradiation-induced recrystallization than that prior to recrystallization in U-10 wt% Mo alloy (UMo) fuels. These kinetics imply that gas bubbles in coarse grains and small recrystallized grains have different growth behavior. For the first time, researchers developed a phase-field model of gas bubble evolution integrating microstructure-dependent cluster dynamics to study the gas bubble swelling behavior in the recrystallization zone of UMo fuels. Generation, diffusion, reaction, sink, emission, and clustering of vacancies and interstitials are described by the cluster dynamics model while a phase-field model is used to describe the evolution of nonequilibrium gas bubbles including nucleation and growth. With the coupled model, the effect of defect generation rate, clustering rate, interstitial emission, and sink rates on grain boundaries on the gas bubble evolution are systematically simulated. A set of model parameters (defect generation rate, clustering rate, interstitial emission, and sink rates) is determined by comparing measured and simulated gas bubble swelling kinetics. The results demonstrate that interstitial clustering is one of the important physical mechanisms that results in fast gas bubble swelling kinetics in the recrystallization zone. The developed model can also be extended to study the associated growth of defect and second-phase precipitates often observed in irradiated materials.