Low pressure tritium interaction with Inconel 625 and AISI 316 L stainless steel surfaces: an evaluation of the recombination and adsorption constants

The surface constants for the recombination (σk2) and adsorption (σk1) of tritium in Inconel 625 and austenitic stainless steel AISI 316 L were determined from the measurement of tritium permeation through engineering components (bellows) typical of those used on large fusion devices which will operate with tritium. Experimental permeation measurements were performed over the temperature range 450–620 K and an interpretation of the data was attempted based on a surface-limited tritium release model. At the tritium partial pressure of 0.1 Pa present in a machine such as JET, the flow of tritium is strongly influenced by surface reactions. Furthermore, it is often assumed that oxide layers, acting as permeation barriers, are present on such components. However, for effectiveness, such barriers must be intact and this may not necessarily be the case for engineering components in which mechanical stresses can lead to oxide cracking. The recombination (σk2) and adsorption (σk1) constants of tritium were estimated for both stationary and continually flexing bellows.