Compatibility of Materials with Alkali Metals for Space Nuclear Power Systems

Abstract

The alkali metals lithium, potassium, and cesium are of principal interest as heat transfer and working fluids in high-performance space-nuclear reactors employing single-and multiloop Rankine cycle conversion. The compatibility of these alkali metals with structural alloys has been investigated for more than a decade in both laboratory- and engineering-scale tests. It is demonstrated that reliable engineering systems involving potassium and cesium can be constructed and operated at 2000°F with first-generation niobium-base alloys like Nb-1% Zr and at 2200°F with advanced niobium-base alloys. Niobium-base alloys can be used at higher temperatures in lithium systems. Tantalum-base alloys appear to be satisfactory for potassium or cesium to at least 2200°F and probably a few hundred degrees higher with lithium. Very advanced systems designed for temperatures of 2500°F and higher probably will require a new group of alloys; tungsten-base alloys appear to be strong candidates for these applications.