Exergy Analysis of Kilopower Nuclear Reactor Systems for Lunar Power Applications

Extended human exploration of the Moon requires power and in situ resource utilization (ISRU) capabilities to sustain human life. Meeting this need entails a complex systems integration task that needs physics-based models to support decision making. Exergy analysis includes the effects of both the first and second law of thermodynamics, accounting for irreversible processes and quantifying the useful work that can be extracted from a system. It therefore provides a tool for assessing the performance of diverse systems with consistent metrics that facilitate systems integration. Lunar power and ISRU systems are examples of such complex systems. An exergy-based analysis of the Kilopower Reactor Using Stirling Technology (KRUSTY) power generation system is conducted to assess overall KRUSTY performance. KRUSTY, a part of the Kilopower project, is a nuclear fission and Stirling converter power generation system intended for use in space, with the primary focus on generating power for a lunar base. Daytime exergy efficiency for the KRUSTY system is generally higher than nighttime efficiency due to coupling with the lunar surface temperature. The presented results show that the KRUSTY integrated system efficiency is greater than alternate photovoltaic-based power generation schemes for lunar exploration in most use cases analyzed. This improved performance is due to reduced surface area and radiative forcing of the KRUSTY system during daytime operation. Results also indicate higher exergy efficiency at colder ambient temperatures, allowing transient power draw cases to be created which maximize exergy efficiency by biasing towards nighttime operation.