Lead-Bismuth Eutectic Cooled Fast Reactor (LBEFR) uses low melting point and high boiling point lead-bismuth as the coolant, and is one of the most promising Generation IV nuclear systems. However, fuel rods in LBEFR have to be subjected to more severe operation conditions compared with Light Water Reactor (LWR) fuels, such as harder neutron spectrum, higher temperature, and enhanced coolant corrosiveness, resulting in distinct evolution processes of fuel behavior. In this study, with full consideration of geometry and material design characteristics, models on distinct phenomena of LBEFR fuels, such as fuel constituent migration, pellet restructuring, cladding corrosion, have been developed and implanted into the program FROBA initially developed for LWR fuel analysis. The capability of the upgraded FROBA for LBEFR fuel performance analysis was preliminarily verified with several benchmark cases. Subsequently, a fuel behavior simulation was conducted for MOX-T91 fuel in a compact LBEFR under long-term normal operation and a power ramp following the normal operation. Compared with traditional LWR fuels, the LBEFR fuel operated at significantly higher temperatures, triggering substantially more fission gas release. To accommodate the large volume of released fission gases and suppress internal pressure rise, LBEFR fuel requires a large plenum design. Benefiting from the coolant outlet temperature controlled around 500 °C, the corrosion of T91 cladding was limited, resulting in a minimal oxide layer thickness that poses no significant threat to cladding structural integrity. However, at high burnup stages, the T91 cladding exhibited pronounced irradiation swelling specifically within the critical temperature range of 420 ± 40 °C. To ensure cladding deformation remains within acceptable limits, T91 should avoid operation within this swelling-sensitive temperature range. Power ramp sensitivity analysis reveals that elevated fuel temperatures drive fuel restructuring-induced central void formation, significantly influencing the thermo-mechanical response. In specific, the central void formation could reduce fuel center temperatures and alleviate contact pressure during pellet-cladding mechanical interaction. These findings provide valuable insights crucial for the design and optimization of LBEFR fuels.
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