Study on water level control system of natural circulation steam generator

The natural circulation U-tube steam generator (UTSG) plays an important role in the operation and safety of pressurized water reactor (PWR) nuclear power plants (NPPs). It is very difficult to control the water level of UTSG during the operation of PWR. Therefore, it is necessary to study its dynamic characteristics. Based on the mass, energy and momentum conservation equations, the nonlinear model (NM) and transfer function model (TM) of UTSG are obtained through mechanism derivation. By introducing typical disturbance into the TM, the changing trend of transient response conforms to the physical law, and the dynamic characteristics are obtained based on the transient results. Based on time domain and frequency domain analysis, the water level control system (WLCS) of UTSG is designed, including the control scheme and controller parameters. The simulation results show that the performance of the WLCS is better than the traditional one. The WLCS not only solves the problem of poor linearity of the feedwater regulating valve (FRV), but also solves the problem of controller redesigning after the FRV replacing. The control system can be switched automatically at 15% power level.