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

• The system analysis program for the 5 MW Small Modular Supercritical CO 2 Brayton-Cycle Reactor System is established and validated. • When the reactor power decreases, the power decrease percentage of the regenerator is the largest and the heat transfer may deteriorate. • At the case of the reactor rod ejection accident, the reactor system is with the good ability of the negative feedback regulation and certain self-stability. • When the temperature of cooling water only increases by 1 °C, the system output power can reduce about 10%. Ensuring the sufficient cooling capacity of the cooler is significant. • The compressor is more sensitive to the input parameter disturbance caused by the reactor and cooler. 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 CO 2 (SCO 2) 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 SCO 2 , 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 SCO 2 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. [ABSTRACT FROM AUTHOR]