Daily Load-Follow Operation in APR1400 Without Soluble Boron Adjustment Using the Mode-K+

In this study, the feasibility of performing daily load-follow operation (DLFO) in a pressurized water reactor without soluble boron adjustment was investigated to mitigate issues related to reactivity control and radioactive waste generation. The APR1400 reactor’s initial cycle configuration was simulated under various burnup conditions. Results indicated that the partial strength control element assembly (PSCEA), which uses Inconel as a neutron absorber, should be modified to enhance its reactivity worth. Inconel’s weak absorption capability led to deep insertion of regulating banks during power reduction to counteract negative temperature feedback and increase in xenon concentration. Instead of altering the PSCEA’s physical design, stronger neutron absorbers such as hafnium, Ag-In-Cd (AIC), B₄C, and manganese were evaluated as potential replacements. B₄C demonstrated the highest total reactivity worth, whereas manganese performed the weakest. Both hafnium and AIC showed similar and successful axial shape index (ASI) control at the beginning of cycle, middle of cycle, and end of cycle. Hafnium’s superior material properties, including its higher melting point, corrosion resistance, and density, make it a more suitable replacement for Inconel in the PSCEA. By modifying the PSCEA material, DLFO without soluble boron concentration adjustment was successfully achieved in the standard APR1400 initial cycle and the Low-Enriched Uranium Plus (LEU+) loaded APR1400 core with much higher fuel burnup. The analysis was performed using the KANT in-house three-dimensional diffusion nodal code, with cross sections generated using the Serpent Monte Carlo code.