Sensitivity Analysis of Rod Ejection Accident Based on PWR MOX/UO₂ Benchmark

To better understand the rod ejection accident(REA) process in pressurized water reactors(PWRs) containing MOX fuel, and to investigate the main influencing parameters and their influence laws on key evaluation parameters such as core relative power peak after rod ejection, this paper takes the PWR MOX/UO₂ transient benchmark core as the research object. The newly pin-by-pin wise transient neutronics/thermal-hydraulic(N-TH) coupling code CORCA-SPₙ, based on the SPₙ method and developed by the Nuclear Power Institute of China(NPIC), was employed to conduct sensitivity analysis for the zero-power rod ejection case in Part IV of the benchmark. A total of 39 rod ejection conditions were simulated, covering 10 key parameters including rod ejection speed. The results show that: 1) Delayed neutron fraction, rod ejection speed, boron concentration, core inlet temperature, and transient time step size have significant influences on the core relative power peak, reactivity peak, super-prompt critical duration, average core coolant temperature, and average core fuel temperature during the zero-power rod ejection transient, and they are identified as key parameters affecting the rod ejection results. 2) The top four parameters affecting the core relative power peak and reactivity peak are ranked as: delayed neutron fraction, boron concentration, core inlet temperature, and rod ejection speed. 3) Neutron velocity, gap heat transfer coefficient, fuel Doppler temperature weighting coefficient, and core inlet mass flow rate show no obvious influence on the reactivity peak during the rod ejection transient.