A new spatially resolved model for defects and fission gas bubbles interaction at the mesoscale

Fission gases (Xe, Kr) produced during irradiation in nuclear fuel have very low solubility in the matrix, and precipitate into bubbles. These bubbles interact with point defects of the fuel (vacancies, self-interstitials, etc.) causing significant microstructural evolution which may eventually affect the overall performance of the fuel. Spatially resolved models have been developed to predict and model the microstructural changes at the mesoscale. We present a new model, which focuses on the interaction between point defects and xenon gas bubbles in UO₂. This model overcomes the limitation of the existing cluster dynamics models as it can account for spatialization, as well as the limitation of the spatially resolved phase-field models as it can also account for very small defect clusters. Modeling of the phenomena of coalescence of two bubbles in a vacancy supersaturation and the vanishing of a small bubble in the presence of a larger bubble (Ostwald ripening) prove the credibility of the new model. 2-D analysis of the movement and growth of bubbles in a vacancy concentration gradient is presented and it simulates the physical behaviour with good agreement. (authors)