China has recently promised to reach carbon neutral before 2060. To achieve this ambitious goal, it is necessary to substantially increase the electricity production from clean sources, such as renewable power and nuclear power, to replace the previous share of coal power generation. Most of the nuclear reactors currently in operation in China are pressurized water reactors (PWR). The nuclear steam supply system (NSSS) in PWR is a complex nonlinear system. The steam bypass system ensures the steam generator’s cooling capacity in accident conditions and is essential for safe and efficient plant operation. Because of the broad transport delay and non-linearity in the steam bypass control system, it is difficult for the currently widely used proportional-integral-derivative (PID) control to obtain satisfactory control effects. Therefore, it is necessary and meaningful to design a suitable steam bypass control system for NSSS.

The investigation of the steam bypass system is performed by MATLAB & Simulink for a large-scale PWR. The nonlinear model is developed by applying the mass and energy conservation equations of fluids and the critical flow correction. The state-space multivariable models are derived by linearizing the nonlinear model at different operation points. Open-loop simulation experiments have been carried out to study the steam bypass system’s dynamic, and the state-space model simulation results are validated by comparing with the results from the nonlinear model. The open-loop results show that the overall system has a considerable transport delay. Thus, a linear active disturbance rejection controller (LADRC) is designed for the steam bypass system. This research assumes that the model and the amount of delay are nearly unknown; however, the proposed controller still performs better than the existing Ziegler-Nichols (Z-N) tuned PID controller. The LADRC has a shorter settling time than the PID controller; the control system can satisfy the design purposes.

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