High Power AMTEC Converters for Deep-Space Nuclear Reactor Power Systems

Abstract

A high electrical power, Alkali Metal Thermal‐To‐Electric Conversion (AMTEC) unit design is developed, and performance estimates as functions of the beta″‐alumina solid electrolyte (BASE) temperature (or anode vapor pressure), condenser temperature, and the type of the working fluid (sodium or potassium) are calculated and discussed. The Na and K‐AMTEC units, measuring 410 mm × 594 mm × 115 mm in outside dimensions, are identical except for the type of the BASE and working fluid. The peak efficiency of the Na‐AMTEC at a BASE temperature of 1123 K is 29.2%, decreasing to 26.8% at a BASE temperature of 1073 K. The corresponding specific powers of the Na‐AMTEC unit are 76 and 54 We/kg, respectively. For nominal operation at 85% of peak electrical power at BASE temperatures of 1123 K and 1073 K, the conversion efficiency of the Na‐AMTEC decreases to 26.7% and 24.5%, respectively, but the corresponding specific powers increase significantly to 125 and 91 We/kg, respectively. The Na‐AMTEC nominally generates 4.0 and 5.6 kWe when operating at BASE temperatures of 1073 K and 1123 K, respectively. When operating at the same anode vapor pressure of 76.8 kPa, the BASE temperature in the K‐AMTEC is only 1002 K, versus 1123 K for the Na‐AMTEC, generating only 2.0 kWe at a specific electrical power of 45 We/kg. In addition to the lower specific power, the specific radiator area for the K‐AMTEC is significantly larger than for the Na‐AMTEC because of the lower conversion efficiency (∼ 22.5%). The Na‐AMTEC operates at higher conversion efficiency and higher electrical power than the K‐AMTEC for condenser temperatures ⩾ 620 K.