Study on the Dynamic Characteristics of the Supercritical CO2 Recompression Brayton Cycle for a Lead-Bismuth Generator Set

Abstract Lead-cooled fast reactor (LFR) is one type of Gen-IV nuclear reactor with great development potential. The supercritical CO2 (sCO2) Brayton cycle power generation system has the advantages of compact equipment, high efficiency, and great flexibility. Its cycle characteristics are highly consistent with the application requirements of high efficiency, flexibility, and safety of LFR, and it is regarded as the ideal power cycle of LFR. As one of the difficulties of LFR-sCO2 cycle power system, the study on dynamic characteristics and the control strategies of the whole system is relatively scarce. This work takes a MW-scale LFR-sCO2 system as the research object. The dynamic model and the simulation program were established, and the dynamic characteristics of the system were studied. The results show that the increase in rotational speed can quickly raise the mass flow rate and net power, and the surge margin of the compressor also increases significantly, but the net efficiency decreases. The reduction in flow rate or temperature of lead-bismuth eutectic can effectively reduce the heat load of IHX and net power of the system, but the heat power change rate of the system is much faster with the change of mass flow rate. The variation trends of the key parameters with the mass flow rate and temperature of circulating cooling water are basically similar. The split ratio has a significant impact on the compressor surge margin (SMmc and SMrc). With a 5% increase in α, SMmc decreases from 59.89% to 55.87%, while SMrc increases from 46.61% to 56.23%. To avoid the occurrence of compressor surge, it is necessary to pay attention to the change of surge margin caused by the change of α during the variable load operation of the system.