Thermodynamic Performance Analysis of Megawatts Portable Nuclear Power System Based on Regenerative Brayton Cycle

Nuclear energy is a challenging and ambitious choice for space power system in contrast to solar and chemical fuel. It is able to realize high power and long operating time simultaneously to meet the need of potential applications. Aiming at the thermodynamic performances of the regenerative Brayton cycle with two-stage compression, the paper is objective to get a set of reasonable and competitive operating parameters for the design of the space nuclear power system. Thermodynamic process calculation is applied to analyze the relations of cycle efficiency and influence factors including compression ratio, gas temperature at cold side and hot side, recuperator efficiency, system pressure. The mass estimate model is established to calculate total mass and specific mass of the system with the variation of such design parameters. The calculating results using MATLAB code show that the optimal compression ratio of single compressor varies between 1.2 and 2 along with the other parameters. Either decreasing the cold side temperature or increasing the hot side temperature contributes to enhance the cycle efficiency to about 50%. When the recuperator efficiency changes from 60% to 98%, an ideal heat exchange efficiency, the efficiency corresponding to the optimal compression ratio increase from 35.8% to 52%. But the total mass will also rise from 9.1 tons to 29 tons. It is concluded that the system with cold side and hot side temperature of 450 K and 1300 K, recuperation efficiency of 80% is capable to obtain the maximum cycle efficiency of 36% and the system mass of 10.2 tons. Supposing a space nuclear power system with thermal power of 5 MW, the specific mass is only 5.8 kg/kWe, which indicates obvious technical and economic advantages.