Energy Conversion Options for Advanced Radioisotope Power Systems

Static and dynamic energy conversion technologies for Advanced Radioisotope Power Systems (ARPSs) are reviewed and their impact on the system’s total mass and specific electrical power and the amount of ²³⁸PuO₂ fuel needed for the heat source are assessed and compared. Conversion technologies considered are Segmented and cascaded Thermoelectric, Alkali‐Metal Thermal‐to‐Electric Conversion, and Free Piston Stirling Engines (FPSEs) and, for comparison, SiGe thermoelectric. Estimates for a 100 We ARPS indicate that when using SiGe thermoelectric, operating between 1273 K and 573 K, 8 General Purpose Heat Source (GPHS) modules would be required and the system’s specific power is ∼ 4.6 We/kg. Using STE converters, operating between 973 K and 373 K, 5 GPHS modules are required and the ARPS’s specific power is ∼ 7.28 We/kg. The next generation STE converters that could operate between 1273 K and 573 K, for a projected system efficiency of 13.8%, decrease the number of GPHS modules needed to 4 and increase the system’s specific power to ∼ 9.9 We/kg. With cascaded SiGe‐STE converters, operating between 1273 K and 373 K, the system’s efficiency could be as much as 16%, requiring only 3 GPHS modules, for an estimated specific power of 10.7 We/kg. This specific power is more than twice that for SOA RTG. With the current version 1.0 of FPSEs, the 100 We ARPS needs only two GPHS modules, but its specific power (4.1 we/kg) is slightly lower than that of SOA RTG (4.6 We/kg). Future introduction of versions 1.1 and 2.0 engines, with slightly higher conversion efficiency and significantly lower mass, could increase the system’s specific power to ∼ 7.5 We/kg, using the same number of GPHS modules as version 1.0 engines. With Na‐AMTEC and K‐AMTEC, the 100 We ARPS needs 3 and 4 GPHS modules, respectively, for an estimated specific power of 5.3 and 5.8 We/kg, respectively.