Noble-Gas Binary Mixtures for Closed-Brayton-Cycle Space Reactor Power Systems

Abstract

The advantages and limitations of pure helium and noble-gas binary mixtures as working fluids for space nuclear reactor power systems with closed Brayton cycles are examined. Helium has the best transport properties, but its small molecular weight increases the aerodynamic loading of the impeller blades. The binary mixture of He-Xe with a molecular weight of 40 g/mol is the recommended working fluid because it has the same heat transfer coefficient as helium, but results in a significant reduction in the aerodynamic loading (10% of that with helium) and hence, in the size and mass of the turbomachines and the power system. The performance parameters of a power system with no single-point failure in reactor cooling, three independent closed-Brayton-cycle loops, and He-Xe binary-mixture working fluid (40 g/mol) are presented and compared with those reported for similar systems.