esign and Optimization of He-Xe Brayton cycles system for MW-level space nuclear reactor application

Space reactor has a good future in sea, land, air and space by virtue of its small size, applicability and high efficiency, and the combination of high temperature gas-cooled reactor and Brayton cycle is more suitable for exploration missions at the megawatt power level. A space gas-cooled reactor with a thermal power of 3 MW is used as a research object, and the design and optimization of this research object is carried out using EBSILON simulation software. The efficiency comparison between direct and indirect Brayton cycle is carried out under different conditions, the direct Brayton cycle was found to be 1.4%-2.8% more efficient than the indirect Brayton cycle and occupies less space. The efficiencies of four configurations of the Brayton cycle are compared. When the compressor inlet temperature is 400 K, the recompression efficiency is lower, and the efficiency of both the interstage-cooled cycle and the simple reheat cycle is higher than 30% when the turbine inlet temperature reaches 1400K. When the compressor inlet temperature is 350K, the simple reheat cycle can achieve 29.6% efficiency at a turbine inlet temperature of 1200K. When the compressor inlet temperature is 300K, the efficiency of all four cycle structures is higher than 20%. And when the turbine inlet temperature is higher than 1150K, the efficiency of all four structures is higher than 30%. The optimal pressure ratios are different for the different configurations, with 2.2 and 3.5 for the simple reheat cycle and the interstage-cooled cycle, respectively. And the optimal pressure ratio for the recompression cycle is also related to its diversion ratio, the recompression cycle efficiencies are 0.417 and 0.141 when the splitting ratios are 0 and 0.4, respectively. In actual operation, the pressure loss of the system is unavoidable. It is found that the efficiency reduction caused by the high pressure relative loss is 1.7% higher than the reduction caused by the low pressure relative loss. The exergy analysis method was also used to verify that the recompression cycle efficiency was lower than the simple reheat cycle efficiency. The losses in both are concentrated in the cooler and reactor, with the cooler and reactor losses of the recompression cycle together accounting for 79.6% of the total losses. Finally, the simple reheat cycle was taken as the optimal structure, and a space reactor system with a thermal power of 3 MW and an electrical power of 1 MW is successfully designed.