High-vacuum tight, liquid sodium resistant joint between ThO2 ceramic and metal

A high-vacuum tight joint between thoria ceramic and metal has been developed for manufacturing liquid sodium oxygen meters; an oxide glass being chosen as sealing material. Taking into account both thermodynamic and kinetic aspects of the highest possible liquid sodium resistance, a borate glass has been synthesized that proved to be well-suited for the intended purpose. Supposed processes of the interaction between sodium and the solder glass are discussed. Unlike previous solutions, the joining technique described has some practical advantage. Glass-sealed liquid sodium oxygen meters have been employed under industrial conditions in liquid metal reactor cooling circuits for periods of up to 14000 h. (orig.)