Multiphysics Coupling Simulation and Output Characteristics Analysis of Thermionic Space Reactor TOPAZ-II

Thermionic reactors, with proven success in space applications and superior power scalability, present a promising technological solution for space nuclear power systems. To investigate the operational characteristics of thermionic space reactors, a system analysis code is developed for the TOPAZ-II reactor. This code enables coupled nuclear-thermal-hydraulic-electrical calculations. Full-power steady-state verification and multi-power benchmarking are performed. The start-up process of the reactor is simulated and compared. The effects of different boundary conditions on system-level steady-state output characteristics are analyzed. The results indicate that the full-power steady-state calculation error of the developed code is less than 2.5%. A comparison between the multi-power steady-state calculations and the measurements of the V-71 unit demonstrates good consistency. The system responses during the start-up transient process agree well with the referenced values. When the single-boundary variation intervals of cesium vapor pressure, nuclear power, and load resistance are (0.76 torr, 2 torr), (115 kW, 135 kW), and (0.068 Ω, 0.141 Ω) respectively, the system can achieve more efficient output electrical power than that in the reference steady-state. These findings provide valuable insights for improving the operational strategies of thermionic space reactors, and the system analysis code could serve as a theoretical tool for safety analysis.