Abstract: The application of high burnup fuel in commercial nuclear reactors is primarily driven by compelling economic imperatives. In the competitive landscape of nuclear power generation, increasing fuel burnup can significantly extend the operational cycle of reactor cores, reduce the frequency of refueling outages, and minimize the volume of spent nuclear fuel requiring long-term storage and disposal. These benefits collectively translate into substantial cost savings for nuclear power plants, enhancing their economic viability and competitiveness relative to other energy sources. However, as fuel burnup levels rise continuously, the fuel assemblies, particularly the uranium dioxide fuel pellets, undergo progressive performance degradation due to prolonged exposure to intense neutron irradiation, high temperatures, and mechanical stresses within the reactor core. This degradation manifests in various forms, with fuel pellet fragmentation and axial relocation emerging as two of the most critical issues that compromise fuel integrity. Fuel pellet axial relocation exerts multiple adverse effects on reactor safety, especially concerning accident prevention and mitigation. A key consequence is the formation of localized hotspots in the ballooned regions of the fuel cladding. When fragmented fuel pellets migrate axially and accumulate in specific areas of the cladding, they disrupt the uniform heat transfer between the fuel and the coolant. This uneven heat distribution leads to localized overheating of the cladding, which not only accelerates cladding corrosion and creep but also elevates the risk of cladding rupture under accident conditions such as loss-of-coolant accidents (LOCAs) or reactivity-initiated accidents (RIAs). Such a scenario would severely undermine the reactor’s safety barriers and trigger radioactive material release, posing significant threats to both the environment and public health. To address this critical technical challenge, in this study, an axial relocation model was developed for high burnup fuel pellets based on the LOCUST code, a specialized tool widely utilized for fuel performance analysis in nuclear engineering applications. The development process was guided by fundamental theories of fuel mechanics, heat transfer, and irradiation-induced material behavior, ensuring the model’s ability to capture the complex physical mechanisms underlying pellet relocation. Subsequently, rigorous verification of the model was conducted by comparing its predictions against analytical solutions derived from established theoretical frameworks. This verification step confirmed the model’s accuracy in replicating key physical phenomena under idealized conditions. To further enhance the model’s credibility and practical applicability, comprehensive validation was performed using data from the FR2 reactor test, which are renowned for providing high-quality, well-documented datasets on fuel performance under various operating conditions. The comparison between the simulation results generated by the LOCUST code’s axial relocation model and the experimental data demonstrated excellent agreement across multiple key parameters, including pellet relocation distance, cladding temperature distribution, and hotspot characteristics. These verification and validation results collectively indicate that the axial relocation model developed in this study exhibits robust predictive capabilities, making it a valuable tool for assessing the safety of high burnup fuel in commercial nuclear reactors and supporting the optimal design and operation of next-generation nuclear fuel systems.