Research on Dynamic Characteristics of PWR Nuclear Power Unit under Variable Power Loads Based on APROS

A dynamic model of the million kilowatt PWR unit including the main equipment of the primary and secondary circuits was built based on the modular modeling method by using the simulation software APROS. The steady-state and dynamic processes were simulated and verified. The dynamic characteristics of the main parameters of the system under the different rates of linear load shedding and different step load shedding were studied. The results show that when the step load reduction is less than or equal to 2% full power (FP), the average temperature (T_avg) fluctuation in the primary circuit is small, which cannot cause the action of control bar; when the step load reduction is greater than 2%FP and less than or equal to 5%FP, the T_avg fluctuation causes the control bar to act but quickly returns to the temperature dead zone. Eventually, the stabilized T_avg ended up higher than the initial temperature. In the process of linear load change, the maximum pressure change of the pressurizer can reach 0.3 MPa. Since the specific volume of coolant is positively related to the temperature, the changing trend of the pressurizer water level is consistent with that of the average temperature of the loop. The purpose of this study is to provide theoretical reference for the flexible operation of PWR nuclear power plant.