Design and optimization analysis of a 100 kW-level heat rejection system for space nuclear power systems

The space nuclear power system is an ideal energy source for deep space exploration missions. The heat rejection system performs the critical function of dissipating the residual heat. This study develops and optimizes a 100 kW-level heat rejection system based on modular heat pipe radiators, aiming to achieve high heat rejection with minimal mass. A complete thermophysical model was constructed to analyze the coupled behavior of coolant loops, heat pipes, and radiation fins. Unlike previous studies that primarily focus on steady-state geometry, the novelty of this work lies in its comprehensive evaluation of the system under both steady and extreme fault conditions. Simulation results verify the system's strong thermal stability and self-compensating capability when subjected to coolant loss or single-pipe failure. When the radiator group with the highest heat rejection rate fails, the total heat rejection remains above 97.7%. Water was identified as the preferred coolant due to its lower mass and superior heat transfer characteristics compared with sodium–potassium(Na-K) alloy. Through parametric optimization of the radiator configuration, the system's specific heat rejection increased by nearly 50% without compromising safety margins. These improvements significantly enhance the efficiency, reliability, and deployment feasibility of space nuclear power systems. The proposed design provides a technical foundation for nuclear-powered spacecraft requiring lightweight, fault-tolerant, and high-efficiency thermal control solutions.