Simulation study of frequency control characteristics of a generation III + nuclear power plant

Abstract

The AP1000, as an advanced Generation III + pressurized water reactor (PWR) nuclear power plant (NPP), is designed to have better transient response capability, higher security and economy compared with the traditional Generation II PWR NPPs. This is partly due to the implementation of the advanced Mechanical Shim (MSHIM) core control strategy that eliminates the need for boron concentration adjustments during load follow operations. Since the world’s first AP1000 NPP is still under construction, there is no actual operating experience and data. This paper studies the dynamic responses and control characteristics of the AP1000 NPP during frequency control transients by modeling and simulation. First, a complete set of nonlinear mathematical models for the AP1000 NPP, including those of the nuclear steam supply system (NSSS) and balance of plant (BOP) system, was established. The S-function modules for these mathematical models and the modules of corresponding control systems were developed in MATLAB/Simulink. Then, by coupling all the modules according to the “reactor-following-turbine” operation mode, a full-scope, dynamic simulation platform of the AP1000 NPP was developed. After validation of the platform against the best-estimate analysis code CENTS developed by the Westinghouse under two typical 10% of full power (FP) step load change transients, it was used for the dynamic simulation and study of frequency control characteristics of the AP1000 NPP. Typical frequency control transients with ± 3%FP step load changes in power grid were simulated. Dynamic responses of key parameters of the NSSS and BOP system were presented and studied to assess and evaluate the load follow capability, economy and safety of the AP1000 NPP during these transients. Moreover, the impact of key primary frequency control parameters on the dynamic response characteristics of the AP1000 NPP and the control effect of system frequency was also studied, and the recommended values of the frequency deadband and bias coefficient have been given for the world’s first AP1000 NPP under construction in Sanmen, Zhejiang province of China. The simulation and analysis results in the present study contribute to the digestion and absorption of the frequency control characteristics of the AP1000 and can also offer certain guidance for the engineering practice.