Optimization of thermodynamic performance and mass evaluation for MW-class space nuclear reactor coupled with noble gas binary mixtures Brayton cycle

Abstract

Space exploration technology is an important indicator of society's technological level. A space reactor coupled with a Brayton cycle is preferable for megawatt-scale space power systems. Noble gas binary mixtures have high chemical stability, heat transfer performance, and compressibility, making them the principal choice of working fluid for the space reactor Brayton cycle, which is also the key factor affecting the thermodynamic performance and mass of the system. This study developed thermodynamic performance and mass evaluation models for the space nuclear Brayton cycle and discovered the inherent relationship between system thermodynamic performance and mass. The effects of noble gas binary mixtures on system performance and mass were investigated. The results indicated that the elevated molar mass of noble gas binary mixtures reduced the aerodynamic load and mass of the turbomachines and increased the mass of the recuperator. There are optimal values of the total mass, specific mass of the system, and working fluid composition. Helium-xenon mixture is the optimal working fluid because it can achieve the highest thermodynamic efficiency and lowest mass. Furthermore, the optimal scheme of the helium-xenon Brayton cycle for a space nuclear power system was obtained by multi-objective optimization. Its power generation efficiency, specific mass, and helium molar fraction in the helium-xenon working fluid are 29.04%, 5.65 t∙MW−1 and 77.5%, respectively. This study provides a reference for the design and optimization of space nuclear power systems.