Analysis of the Impact of Helium-Xenon Mixture Ratio on the Dynamic Characteristics of the Brayton Cycle Systems

To address the issue of deviation from the design value of the working fluid mixture ratio due to leakage or uneven charging during the operation of a space gas-cooled reactor coupled with a helium-xenon Brayton cycle system, which in turn affects the safety and stability of the system, this study establishes a dynamic model of the space gas-cooled reactor-coupled helium-xenon Brayton cycle system based on the Simulink platform. This model includes the reactor core, turbine, compressor, regenerator, cooler, and radiator. By setting different molar masses of the helium-xenon mixed working fluid (50±5) g/mol, the model simulates the dynamic response characteristics of key parameters of the cycle system under external reactive step disturbances. The results show that when the working fluid's molar mass deviates to 45 g/mol, the system’s cycle efficiency decreases by 1.4%, the average convective heat transfer coefficient within the reactor increases by 12.9%, and the system's response time is shortened by 6.8% compared to the designed mixture ratio under reactive steps. Conversely, when the working fluid's molar mass deviates to 55 g/mol, the cycle efficiency increases by 0.78%, the average convective heat transfer coefficient within the reactor decreases by 16.8%, and the system's response time is extended by 4.9%. The findings can provide references for the safe operation and control strategies of space nuclear power systems.