Conceptual Design of a 100-kWe Space Nuclear Reactor Power System with High-Power AMTEC

Abstract

Alkali Metal Thermal‐to‐Electric Conversion (AMTEC), although currently at a Technology Readiness Level‐3 (TRL‐3), has an excellent potential for use in Space Nuclear Reactor Power (SNRP) systems for NASA’s deep‐space exploration missions. In addition to operating at a conversion efficiency > 20%, representing the highest fraction (> 60%) of Carnot efficiency of all other static and dynamic conversion technology options, the relatively high heat rejection radiator temperature (650–700 K) reduces the size and mass of the radiator and of the SNRP system. A high‐power AMTEC unit design has been developed and optimized for operating at reactor exit temperatures ⩽ 1180 K and radiator temperature ⩽ 680 K. Depending on the reactor exit temperature, the nominal electrical power of the AMTEC unit, measuring 594 mm × 410 mm × 115 mm and weighting 44.3 kg, could be as high as 5.6 kWe, with a margin of ⩾ 5% for an additional load‐following increase. A conceptual design of a 100 kWe SNRP system with these high‐power AMTEC units is developed and presented in this paper. The total mass of major subsystems, including the converters, nuclear reactor, shadow radiation shield, and radiator, is calculated and compared with that for the SP‐100. Despite the large specific mass of the AMTEC units compared to the SiGe thermoelectrics in the SP‐100 system, the lower masses of the reactor, radiation shield, and radiator make the present AMTEC‐SNRP system > 26% lighter, for the same electrical power. An optimized AMTEC‐SNRP system could potentially operate at a specific power > 30 We/kg (or specific mass < 33 kg/kWe), use non‐refractory structures of super‐steel alloys with well‐know properties, relatively low density, low Ductile‐To‐Brittle (DTB) transition temperatures, and good compatibility with space and planetary environments containing CO2 and oxygen. The radiator area for the baseline 100 kWe AMTEC SNRP system is < 27 m2, which, together with operating the potassium heat pipes in the radiator sonic limited shortly after a reactor shutdown, would extensively prolong the cool‐down time of the reactor from several days to many months, before freezing the sodium in the reactor’s heat pipes (371 K).