Heat rejection with mechanical pumped cooling loop for lunar surface nuclear reactor power system

The fission heat in a lunar surface nuclear reactor power system transported to the Stirling engine could not be fully converted into electrical power and the exhaust heat was released to the heat rejection system. Based on the technology feasibility, a mechanical pumped cooling loop was proposed for heat rejection system, composed mainly of mechanical pumps, cooling loops and radiator plates. A heat rejection model with the convective and radiative heat transfer was developed. The convective heat transfer coefficient was larger than the radiative heat transfer coefficient by two orders of magnitude and the radiative heat transfer was the primary step controlling the heat rejection process. The radiator size and mass of the heat rejection system were calculated by the model and they were greatly affected by the cooling temperature. Increasing cooling temperature could reduce the required radiator size and mass of the heat rejection system, since higher cooling temperature could increase the heat rejection driving force. Considering the thermal efficiency of the nuclear power system, the reasonable cooling temperature would be in the range of 480 K-520 K, with the lowest specific mass of the lunar surface nuclear power system being 66 kg/kWe achieved in this range.