U₃Si₂ is regarded as a highly promising accident-tolerant fuel because of its high uranium density, high thermal conductivity, and favorable thermophysical properties. Under irradiation, however, the accumulation, migration, and aggregation of fission-gas atoms, particularly Xe, can induce bubble formation, fuel swelling, and performance degradation. In this work, first-principles calculations based on density functional theory with the Hubbard correction (DFT+U) were performed to systematically investigate the dissolution, cluster formation, and diffusion behaviors of Xe in U₃Si₂, as well as the effect of local Al doping on these processes. The results show that Xe has large positive dissolution energies at interstitial sites, indicating an extremely low interstitial solubility in U₃Si₂. Among the interstitial configurations considered, only the Int1 site can stably accommodate a Xe atom, whereas Xe atoms at the other interstitial sites are unstable after structural relaxation. In contrast, Xe is more favorably incorporated into vacancy defects because of the larger local free volume provided by vacancies. The calculated binding energies of Xe-Xe pairs at neighboring interstitial sites are negative, indicating that Xe does not spontaneously form stable diatomic clusters through an interstitial clustering mechanism in U₃Si₂. Migration-barrier calculations further reveal a clear mechanistic difference in Xe diffusion. Interstitial diffusion involves relatively high migration barriers and pronounced anisotropy, whereas vacancy-assisted diffusion exhibits much lower barriers, indicating that vacancy-assisted migration is the dominant diffusion mechanism for Xe in U₃Si₂. The introduction of Al further modifies the local behavior of Xe. Al doping lowers the dissolution energy of Xe at both interstitial and vacancy-related sites, reduces the local lattice distortion induced by Xe incorporation, and changes the Xe-Xe interaction at neighboring interstitial sites from repulsive to attractive. In addition, Al doping significantly decreases the migration barriers of representative interstitial and vacancy-assisted diffusion pathways, although it does not change the dominant role of the vacancy-assisted diffusion mechanism. These results indicate that local Al doping can promote the dissolution, cluster formation, and diffusion of Xe in U₃Si₂, and may therefore accelerate the subsequent evolution of fission-gas behavior. This work clarifies the atomic-scale evolution characteristics of Xe in U₃Si₂ and reveals the potentially unfavorable effect of Al doping on the resistance of U₃Si₂ to fission-gas-induced swelling. The present results provide a theoretical basis for understanding fission-gas behavior in U₃Si₂-based fuels and for optimizing their performance as accident-tolerant nuclear fuels.