The dual role of aluminum on xenon behavior in U3Si2/Al dispersion fuel: a combined DFT and experimental study

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Abstract
U3Si2 is a promising accident-tolerant fuel, and its use in dispersion fuel form with an aluminum (Al) matrix is widely deployed in test and research reactors. However, in such U3Si2/Al dispersion fuels, managing fission gases, particularly xenon (Xe), remains a critical challenge for long-term stability, and the role of the Al matrix in mediating Xe behavior is still poorly understood. This study combines first-principles calculations and experimental validation to elucidate the atomic-scale interactions between Xe and Al in U3Si2. We reveal that Xe exhibits intrinsically low solubility and negligible interstitial clustering in the pristine U3Si2, attributable to its large atomic size and the pervasive covalent Si–Si network. Interestingly, Al plays a dual role. It enhances Xe diffusion by reducing its effective atomic size via charge transfer, while simultaneously suppressing bubble nucleation in the irradiated region by pre-occupying vacancy sites. Although Xe diffusion is enhanced within Al-rich regions, the overall migration through fuel particles remains limited, consistent with the swelling resistance observed in U3Si2. These findings provide a theoretical basis for predicting Xe behavior in U3Si2/Al dispersion fuel systems and reveal key mechanisms for designing swelling-resistant nuclear fuels.

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