Abstract: This study aims to establish a numerical simulation method for analyzing the chemical interaction (FCCI, fuel-cladding chemical interaction) between UO₂ fuel and HT9 ferritic-martensitic stainless steel cladding, providing a theoretical tool for evaluating the service performance of fast reactor fuel elements. Based on the fuel performance analysis program MOOSE (multiphysics object-oriented simulation environment)-BEEs, this research incorporated models for FCCI behavior, cladding damage induced by FCCI, and a barrier layer shielding model. The model was validated by comparing it with experimental data from the DFR (Downley Fast Reactor) and BN600 (Beloyarsk BN600 Nuclear Plant) reactors, as well as other empirical correlations. Using the MFF3 (mechanistic fuel failure) experimental conditions, corrosion depth was systematically calculated, the effects of temperature and contact stress on corrosion depth were analyzed, and the impact of cladding damage on stress distribution was investigated in the study. The results indicate that the corrosion depth predicted by the proposed model aligns well with the DFR model in terms of trends, with a maximum error of less than 30% compared to BN600 experimental data. Compared to other empirical correlations, the model’s predictions cover most experimental data points and show good agreement with the HEDL2 model recommended by the BISON program. This demonstrates the high applicability and predictive accuracy of the proposed cladding corrosion model. The analysis reveals that FCCI reactions intensify significantly with increasing temperature and burnup, leading to a notable increase in cladding corrosion depth. This finding underscores the importance of temperature and burnup in fast reactor fuel design and operation to mitigate FCCI reactions and extend fuel element service life. Furthermore, the presence of contact stress significantly exacerbates FCCI reactions, causing a sharp increase in corrosion depth. As corrosion depth increases, the cladding thickness gradually decreases, reducing its load-bearing capacity and making previously stress-resistant areas more vulnerable. This change significantly affects the axial stress distribution in the cladding, potentially leading to stress redistribution and structural failure in certain regions. Therefore, fuel element design must fully consider the impact of contact stress on FCCI reactions to ensure the mechanical performance and structural integrity of the cladding. The influence of the barrier layer on cladding performance is primarily reflected in corrosion inhibition and mechanical properties. As nitriding time increases, the barrier layer’s inhibitory effect on FCCI becomes significantly stronger, with corrosion depth becoming almost negligible after 80 hours of nitriding. However, although the barrier layer significantly reduces corrosion depth, corrosion-induced cladding damage may lead to relaxation of contact between the cladding and the fuel, causing contact stress to increase with nitriding time. This phenomenon indicates that while the barrier layer effectively inhibits corrosion, it may also negatively affect the cladding’s mechanical properties. In conclusion, the model established in this study not only accurately predicts cladding corrosion depth but also provides a scientific basis for the design and performance analysis of fast reactor fuel elements. By comprehensively considering the effects of temperature, burnup, and contact stress, the proposed analytical method offers theoretical support for optimizing fuel element design and provides effective strategies for extending the service life and enhancing the safety of fast reactor fuel. Future research can further refine the model by incorporating additional factors, aiming to provide a more comprehensive and precise tool for the design and optimization of fast reactor fuel in practical applications.