Transient characteristics and adjustment ranges of key parameters in supercritical CO2 direct-cooled microreactor system with simplified control strategies

The combination of supercritical carbon dioxide (SCO₂) Brayton cycle and microreactor is a promising technology. SCO₂ direct-cooled microreactor system takes advantages of compact system design and high efficiency, which can be applied in various scenes. Although the design SCO₂ Brayton cycle system is already compact, the control rods in reactor core still results in relatively large design size of the reactor. Considering relatively high negative temperature coefficient of reactor core and fast response characteristics of SCO₂ Brayton cycle, simplified control strategies are proposed in this paper to reduce the number of control rods in the reactor, thus decreasing the diameter of the reactor. Aimed towards the design of SCO₂ cooled floating nuclear power plant (SCFNP),the simplified control strategies are proposed. Then, adjustment ranges of system key parameters with different control strategies are simulated, and comparisons between them in various aspects are performed. According to the results, inventory control, shaft speed control and bypass valve control are proved to be able to adjust reactor power effectively instead of control rods. When applied shaft speed control and bypass valve control, system maximum temperature obviously exceeds the design temperature, which is about 12% and 20% respectively. What's more, inventory control and shaft speed control take about six times longer than bypass control to stabilized the system parameters. Besides, advantages and disadvantages are concluded of the three different control strategies, which can be used as reference of the control system design for SCO₂ direct-cooled microreactor system.