Dynamic simulation and study of Mechanical Shim (MSHIM) core control strategy for AP1000 reactor

Abstract

The advanced Mechanical Shim (MSHIM) core control strategy is implemented in the AP1000 reactor by a digital rod control system. This control system comprises of two separate rod controllers that automatically control the core reactivity and axial power distribution using the gray and black M control banks and the axial offset (AO) control bank respectively. It has been demonstrated that the MSHIM control system can provide superior reactor control capabilities via automatic rod control only, which needs it to take more burdens than many other traditional core control systems during load change transients. This paper presents the dynamic simulation, and the parameter sensitivity analysis and optimization of the MSHIM control system for AP1000 reactor. A nodal core model is used to describe the dynamic behavior of the reactor core first. Then the nodal model and the original and revised MSHIM strategies are implemented in the AP1000 reactor to develop a fast simulation program in MATLAB/SIMULINK. Based on the simulation program, the MSHIM load follow and load regulation operations are simulated, the results of which demonstrate that the core reactivity and axial power distribution can be well-controlled via automatic rod control only. To show the effects of key factors on the control system behavior, the MSHIM load follow simulations with different control parameter values are performed. According to the simulation results and subsequent quantitative analysis, the mechanisms by which the key factors affect the control system behavior are illustrated and the optimum numerical ranges of these parameters are obtained. These results can be used for the preliminary parameter selection and sensitivity analysis of the MSHIM control system to achieve stable reactor control during power maneuvers.