Dynamic modeling and validation of the 5 MW small modular supercritical CO2 Brayton-Cycle reactor system

Small nuclear reactor system (SMR) has good development prospect in energy supply because of its flexible arrangement, wide application, and low cost. Among many small nuclear reactor systems, the Brayton cycle reactor system with supercritical CO2 (SCO2) as a working medium stands out. It has the advantages of high conversion efficiency, simple design, compact structure, high inherent safety, and is suitable for almost all nuclear power systems, especially small modular reactors (SMR). However, due to the unique thermophysical properties of SCO2, the transient operation characteristics of the system and the coupling effect between the main equipment are not precise. In this study, a dynamic model of the 5 MW modular SCO2 Brayton cycle reactor system was established, and the system's dynamic operation characteristics and off-design control strategy were evaluated. Firstly, the steady-state simulation of the system is carried out to verify the physical model of the main equipment. Secondly, the typical transient operating conditions such as the reactor power fluctuation, reactor reactivity insertion, cooling water flow rate and temperature fluctuation, and loss of the external load are calculated. The dynamic characteristics of the system and the coupling effect between the main equipment are analyzed. The simulation results show that the control system is with good control effect and regulation ability under the condition of the reactor control rod ejection accident. The system is quite sensitive to the change of the cooling water temperature and flow rate. When the external load is lost, the turbine bypass control method can quickly match the system output power and keep the rotor speed reasonably. The dynamic modeling of the system is beneficial for the analysis of the operation characteristics and control effect of the system under variable conditions. It can provide the basis for the design, evaluation, and control strategy formulation of the system.