Improvement of the Reactor Control System in AP1000

Abstract

AP1000 is a two-loop pressurized water reactor (PWR) developed by Westinghouse, which uses the forces of nature and simplicity of design to enhance plant safety and reduce construction costs. Compared to traditional reactor control strategies, the AP1000 adopts an advanced Mechanical Shim (MSHIM) core control strategy, which controls the reactivity and the axial power distribution without the need of boron adjusting. The main control signal of MSHIM is the difference of average core coolant temperature and reference temperature obtained from turbine load. In order to improve the response speed, a mismatch signal obtained by the difference of the nuclear power and target power is introduced as the auxiliary control signal. However, this auxiliary signal may cause the control rod acting too fast, also, the power mismatch channel noise is not suitable as a differential lead control channel. To solve this problem, we remove the nuclear power signal channel, and use the average coolant temperature error as the only control signal. Furthermore, a P controller is added for adjusting the control signal to increase the response speed and reduce the steady error. The proposed method was verified by dynamic performance simulation and compared to the original control system. The calculation results show that the modified power control system could not only simplifies the control logic but also enhances the control performance. And, the proposed method satisfies the needs of reactor core power control and power distribution control. The conclusions have reference value for the engineering practice.