Thermomechanical analysis of UO2 fuel rods with SiC_f/SiC composite cladding under normal and accident conditions

To assess the mechanical response and structural integrity of fuel cladding under high-temperature conditions, a two-dimensional axisymmetric finite-element model of a UO 2 –SiC composite cladding system was developed. The model incorporates key fuel performance mechanisms including irradiation swelling, high-temperature creep, and fission gas release. Applicability was verified by mesh-independence studies and comparison with published data. Simulations covered steady-state operation with linear heat rates from 18 to 26 kW/m and LOCA scenarios with coolant injection delays of 50–90 s. At the upper bound steady state (26 kW/m), fission gas release produced a nonlinear rise in plenum pressure up to 32 MPa, which became the dominant contributor to cladding hoop stress. Under LOCA conditions, peak stress strongly depends on coolant injection timing; however, effective cooling within a 100 s window limited peak stress below 100 MPa, indicating a manageable failure risk. Weibull-based failure analysis yields probabilities below 1.2×10 -5 for steady-state operation at the maximum linear heat rate of 26 kW/m, and below 9.5×10 -12 for accident scenarios initiated from a steady-state power of 18 kW/m. These results demonstrate the model’s utility as a practical tool for evaluating the mechanical behavior of advanced cladding systems under both normal operation and accident scenarios.