Three-dimensional phase-field modeling of fission gas resolution effect on nano-sized bubble formation in uranium-based fuel

Uranium-based fuels are widely used in nuclear reactors, where fission gas atoms interact with irradiation-induced vacancies, leading to bubble formation during irradiation. While gas atoms are typically trapped in gas-vacancy clusters, the release of these atoms plays a pivotal role in the early-stage growth of bubbles. In this study, the phase-field (PF) method is utilized to simulate bubble formation, considering gas resolution under varying damage rates and fission densities in both single-crystal and bicrystal models. The results reveal that gas atoms resolved from bubbles via heterogeneous resolution significantly affect the growth of individual bubbles. In contrast, the formation of intergranular bubble is minimally affected by gas resolution due to the high diffusivity of resolved atoms in the grain boundary region, which facilitates their reabsorption into the bubbles. These findings contribute to a deeper understanding of the role of fission gas resolution in the formation of nano-sized bubbles.