Effect of cooling schemes on performance of MW-class space nuclear closed Brayton cycle

Abstract

The space-closed Brayton cycle (SBC) system is compact, lightweight, and boasts stable operation, making it an ideal energy conversion technology for high-power space reactors. To ensure safe and reliable operation of the system, a small fraction of the working fluid, a helium and xenon (He–Xe) mixture, is used to cool bearings and generators and then rejoins the mainstream. This cooling inevitably affects the cycle performance. In this study, four different cooling schemes for bearings and generators were formulated for SBC and the effect of bleeding gas on the performance of key components and cycles analyzed. Experimental results indicated that an increase in the bleeding ratio led to temperature pinch points of the recuperator and reduced the heat absorption of the reactor in the first three schemes. Consequently, the cycle efficiency of Schemes (1) and (2) increased. Conversely, in Schemes (3) and (4), the output work of the turbine decreased and the power of the fan increased, which decreased the power generation and cycle efficiency of these two schemes. Subsequently, the four cooling schemes were optimized and compared under the temperature pinch point limitation of the recuperator. The results showed that Scheme (1) had the highest efficiency of power generation because the cooling gas recovered the heat losses of the bearings and generator, and the inlet temperature of the turbine was the highest. The power generation efficiency of Scheme (4) was the lowest. This investigation provides a reference for future cooling designs of the SBC.