Transient characteristics of supercritical carbon dioxide Brayton cycle system with or without control strategy under accident conditions

Supercritical carbon dioxide (SCO2) Brayton cycle reactor system is a popular type of small modular reactor system. It has many benefits, such as high thermal efficiency, system structure simply and compact. So it can be widely used in various scenarios. In this study, establish the SCO2 Brayton cycle system model which have multiple control models based on Modelica language. Transient conditions with and without control strategies were simulated for reactivity introduction accidents and external load loss accidents, among which the control strategies were bypass control, rotor speed control and throttle control respectively. The response characteristics of system variables in different accidents without control or under different control strategies are compared and analyzed. Then, the control effect of different control strategies is judged by the change amplitude of system parameters. Results display that the rotor speed control and throttle control can reduce the variation amplitude of system parameters in both accidents, rotor speed control can reduce the variation amplitude of representative parameters by more than 50 %, the control effect is better. Bypass control can reduce the amplitude of changes of most system variable in reactivity introduction accidents, the variation amplitude of partial parameters decreased by 7.69 %-34.17 %. But it can not play the role of reducing the changes of system variable in external load loss accidents. Therefore, the control effect of bypass control should be judged according to the actual situation. The research results can a provide reference for the study about formulation and selection of control strategies for SCO2 Brayton cycle systems.