Development of Protective Coatings to Reduce Hydrogen and Tritium Permeation

Publisher Website
Google Scholar
Abstract
An important demand with respect to the operability of a nuclear process heat system, such as the prototype plant for nuclear process heat, is the complete retention of tritium. A significant contribution to the solution of this problem is expected by a drastic reduction of the permeation of hydrogen and tritium through the heat exchanger walls. The most promising way to prevent this permeation appears to be to coat the parts concerned, which are made of high-temperature alloys, with oxide layers. Through preoxidation under well-defined conditions, it should be possible to obtain oxide layers that promise a lasting inhibition of the hydrogen and tritium permeation under process conditions. The process used to obtain permeation-resistant oxide layers on the high-temperature alloys in question—in particular on Hastelloy-X—is characterized by the application of a low oxidation potential, so that Cr2O3 layers will form. Steam at low pressure in argon with and without the addition of hydrogen is used as the oxidizing agent. Furthermore, the formation of dense Cr2O3 layers is conditional on a suitable pretreatment. The best layers, with respect to the inhibition of permeation and to stability in the steam reforming process gas, were obtained by preoxidizing at 1273 K under special thermocycling conditions. They reduced the permeation by a factor of over 2000, which increased to over 3000 under the effects of a process gas exposure. Chemical vapor deposition Al2O3 coatings were tested to see if they would be suitable as alternatives. High inhibiting factors (over 1000) were obtained with Al2O3 coatings deposited on preoxidized substrates.