Influence of nonmetallic elements on the compatibility of structural materials with liquid alkali metals

Abstract

Liquid alkali metals such as sodium and lithium are being considered as heat-transfer media in liquid-metal cooled fast-breeder reactors and a tritium-breeding blanket in fusion reactor, concepts, respectively. In these applications, the interaction(s) of nonmetallic impurity elements in the liquid alkali metals, such as oxygen, carbon, nitrogen, and hydrogen, with structural materials is of concern. This paper discusses purification methods for control of nonmetallic impurity elements in liquid sodium and lithium, and the limitations of the various methods. Interactions between structural metals and nonmetallic elements in liquid alkali metals are analyzed in terms of equilibrium distribution coefficients and the concentrations of nonmetallic elements in liquid alkali metals that are sufficient for compound formation with the structural metals. A number of experimental observations that describe various types of interactions are presented, and major differences in material behavior in liquid sodium and lithium environments are identified.