Advanced Water Level Control For The Steam Generator In Pressurized Nuclear Power Plant

Steam generator is the key equipment of heat exchange in nuclear power plants. The water level of steam generator has direct impact on the quality of outlet steam and the safety of system. Thus, it is vital and necessary to maintain the water level within its limits for safety.In this paper, the structure and the water level control principle of U-tube steam generator (UTSG) in Pressurized Water Reactor (PWR) are introduced, and the steady state and dynamic characteristic of the water level model is discussed. Based on the general mathematical model of water level control system, different control methods are presented, such as fuzzy control, fuzzy PID as well as MPC with feed-forward compensation. MATLAB is used for the digital simulation of the water level control system of steam generator. After calculation and analysis of the performance of the water level control systems, the two kinds of different control systems are designed and compared.The simulation results demonstrate that if the first method is selected, compared with fuzzy PID, the fuzzy control system is robust and less vibrative, however, it has longer response time and larger overshoot. Therefore, the fuzzy control system is more suitable for the water level control at high load, while the fuzzy PID control system is preferable at low load. As an alternative, the MPC water level control system has better performance compared with the multi-variable PID water level control system. Besides, MPC can explicitly handle constraints systematically during the design and implementation of the controller, resulting in a relaxation of the safety margins and as a consequence, a reduction of the frequency of reactor trips.Thus, according to the different control requirements and objectives, proper control strategy should be used to design the water level control system of steam generator to guarantee the safe operation of the nuclear power plant.From a practical point of view, PID three parameters water level control system is widely used; fuzzy control has been practically applied in some subsystems of nuclear power plant in France, Belgium and Japan; as the theoretical study and the simulation develop, MPC will be promising in the operation of nuclear power plant.