Design of closed Brayton cycle power generation system for megawatt-scale space nuclear reactor

With advancements in aerospace technology, nuclear fission reactors have become essential for space power systems. However, the harsh space environment, complex structures, and varied choices of materials and working fluids pose significant design challenges. To facilitate the realization of high-power space nuclear propulsion systems, this paper proposes a universal research framework consisting of six modules: control, material properties, structural design, thermodynamic models, individual component/coupled system analysis, and feedback adjustment. A closed Brayton cycle is employed, using a He-Xe mixed gas as the working fluid, and the inputs are categorized into static and dynamic parameters. Corresponding models are developed with Python, Refprop, and simulation software, coupled into a model of space nuclear reactor closed Brayton cycle power generation system (SNRCBC). The steady-state simulations for individual components are calibrated, an eight-stage startup scheme is proposed, and transient simulations of the startup process are conducted, verifying the accuracy and correctness of both individual component models and the coupled system model. Finally, simulations are performed under four operating conditions: variable reactivity, variable shaft speed, variable working fluid flow, and variable load. The simulation results show that under steady-state conditions, the reactor core output power reaches 3.248 MW, the generated power is 1.072 MW, and the thermoelectric conversion efficiency is 33.03%. In the transient simulation under varying operating conditions, the system model demonstrates good self-regulation capabilities. This work provides valuable insights for the conceptual design of space nuclear reactor power generation systems.