The integration of thorium into uranium dioxide (UO₂) fuel presents a promising strategy to enhance fuel cycle sustainability, reduce long-term radiotoxicity, and improve proliferation resistance in nuclear reactors. This study investigates the neutronic performance of a mixed oxide fuel composed of UO₂ and thorium dioxide (ThO₂) in the context of Small Modular Reactors (SMRs), focusing on both a single fuel rod and a complete fuel assembly configuration. The SCALE simulation suite was employed to model and analyze key neutronic parameters, including effective multiplication factor (k-eff), neutron flux distribution, and isotopic evolution over burnup. The analysis explores various UO₂/ThO₂ ratios, with special attention to the moderation properties, resonance absorption behavior, and the production of fissile ²³³U from thorium. In the single-rod model, the addition of ThO₂ slightly reduces initial reactivity but leads to favorable breeding characteristics due to the generation of ²³³U, which contributes to sustained fission over time. In the full assembly configuration, moderation effects and inter-rod neutron interactions further influence the reactivity trends and spatial flux profiles. Results demonstrate that mixed UO₂/ThO₂ fuel exhibits competitive neutronic behavior when compared to conventional UO₂ fuel, with notable advantages in terms of fissile regeneration and longer fuel cycle potential. Moreover, the thorium content contributes to flattening the power distribution across the assembly, which may reduce localized thermal stresses and improve fuel utilization. These findings highlight the feasibility of incorporating thorium into SMR fuel designs and encourage further investigation into thermo-mechanical performance and reprocessing implications. The study supports the development of advanced fuel cycles aligned with the goals of next-generation reactor technologies.