Barium Silicate Glass/Inconel X-750 Interaction

Abstract

Water reactor safety programs at the Idaho National Engineering Laboratory have required the development of specialized instrumentation. An example is the electrical conductivity-sensitive liquid level transducer developed for use in pressurized-water reactors (PWRs) in which the operation of the sensing probe (Fig. 1) relies upon the passage of current through the water between the center pin of the electrode and its shell such that when water is present the resulting voltage is low, and conversely, when water is absent the voltage is high.¹ The transducer’s ceramic seal is a hot-pressed glass ceramic with the following composition (mole percent): SiO₂ — 55, BaO — 25, TiO₂ — 5.5, CaO — 5.5, As₂O₅ — 3, Bi₂O₃ — 2, A1₂O₃ — 2, and CeO₂ — 1; its metal housing is Inconel X-750. The ceramic material provides an essential dielectric barrier between the center pin and the outer housing. The operation of the probe as well as the integrity of the PWR environment requires a hermetically-bonded seal between the ceramic and the metal. However, during testing, an increasing number of probe assemblies failed owing to poor glass-to-metal seals as well as void formation within the ceramic. Therefore, a program was initiated to characterize the metallic surface with respect to pre-oxidation treatment and determine optimum conditions for wetting and bonding of the metal by the glass to obtain baseline data relevant to production of acceptable transducer seals.

Work supported by U. S. Department of Energy, under DOE Contract No. DE-AC07-76ID01570.