Mechanical shim mode analysis for large-scale advanced pressurized water reactor

The mechanical shim (MSHIM) operation mode and the load following technology of the large-scale passive advanced PWR core use the relevant design of the AP1000 nuclear power plant as reference, but differ from it due to its higher power and unique control rod loading pattern. Therefore, it is extremely necessary to analyze the applicability of evaluation code for the MSHIM operation mode, the performance of the MSHIM load following operation mode, the characteristics of the start-up and restart processes based on the design of large-scale passive advanced PWR. In this paper, the applicability of MSHIM operation mode for the AP1000 calculation code to the large-scale passive advanced PWR is firstly evaluated based on the analysis of the methodology for the PWR's MSHIM operation mode and the analysis of the difference between AP1000 and the large-scale passive advanced PWR. Secondly, the typical 100%-70%-100% and 100%-70%-100% load following operation modes of both the initial and the equilibrium cycles are calculated and analyzed based on the neutronics modeling of the large-scale passive advanced PWR core. In addition, the operation capability of the initial start-up and restart processes in MSHIM mode of the initial and equilibrium cycles are simulated and analyzed quantitatively. The numerical results show that MSHIM mode has the certain ability for load following in both initial and equilibrium cycles without adjusting the boron concentration, but for start and restart conditions it is required to adjust the concentration of boron. (authors)