Thermal hydraulic design and mass optimization of a 100-kWe S-CO2 cooled Mars-surface fission reactor system

Fission reactor with electrical power of 100 kW to megawatt is a promising power option for upcoming deep space exploration. To reduce the number of space launches and the costs, it is necessary to design an energy supply system coupling fission reactor with energy conversion system of high efficiency and compactness. The combination of gas-cooled fast reactor and supercritical carbon dioxide (S-CO2) Brayton cycle has the advantages of simple system layout, compact structure and high thermal efficiency. This paper aims to carry out researches on the thermal hydraulic design and mass optimization of 100kWe reactor system for Mars-surface application. An analysis code which includes thermodynamic models for different components in the system, as well as mass evaluation models for radiator, recuperator and reactor, is developed and validated to provide an analysis tool. An S-CO2 Brayton cycle directly cooled reactor system is proposed, which applies Tube-In-Duct fuel assembly to make up the core and heat pipe radiator as heat rejection system. The thermal hydraulic evaluation of the reactor core, thermodynamic performance evaluation as well as overall mass evaluation of the whole system are carried out to achieve an optimized 100kWe fission reactor system for Mars surface with minimum mass. The optimal design has an operating pressure of 16 MPa, core outlet temperature of 600 degrees C, radiator panel area of 120 m2 and an overall mass of 1862.98 kg considering the reactor and key components of Brayton cycle. S-CO2 Brayton cycle directly cooled reactor system has a comparable specific mass as He-Xe cooled reactor with lower operating temperature, which is beneficial for material selection and provides another option for space reactor development.