Thermodynamic analysis and multi-objective optimization of a hybrid He-Xe Brayton-AMTEC nuclear cogeneration system for lunar base

A helium-xenon closed Brayton cycle combined heat and power system is proposed for a lunar base. The system integrates an alkali metal thermoelectric converter with lithium fluoride thermal energy storage. The AMTEC taps reactor heat above the turbine material limit and converts it directly into electricity, while its waste heat preheats the compressed working fluid, forming a hybrid dynamic-static conversion architecture. On the heating side, waste heat recovered from the main loop meets the baseline thermal demand, and a 20 GJ LiF two-tank storage unit supplies additional heat during the lunar night. Thermodynamic, mass, and economic models are built to evaluate system. A contribution analysis indicates that adding the AMTEC raises the electrical efficiency by 2.07 percentage points. A 720-h transient simulation shows that the heating supply remains fully reliable throughout the lunar night, with the state of charge of the TES never falling below 53%. Response surface methodology identifies the pressure ratio and the reactor temperature as the dominant design parameters and reveals a clear AMTEC temperature threshold behavior. Multi-objective optimization with a non-dominated sorting whale algorithm produces a Pareto front that balances electrical efficiency, CHP efficiency, and LCOE. The recommended design attains a CHP efficiency of 80.75%, an electrical efficiency of 32.42%, and an LCOE of 0.0491 $/kWh, which represents a 7.44-percentage-point improvement in CHP efficiency over the baseline.