Approach to a Phenomenological Description of Hydrogen and Tritium Permeation Through Steels, and the Action of Oxide Scales to Reduce Permeation.

摘要

Experiments are presented investigating the action of corrosion scales on several steels against hydrogen and tritium permeation. We are interested in such model experiments to learn how to prevent tritium permeation from the primary circuit of an HTR to the secondary side. The same problem might be of some importance in later fusion reactor technology. Our corrosion scales were formed in a temperature range between 500 exp 0 C and 950 exp 0 C under varying steam hydrogen mixtures. Thickness of the scales was up to several mu m. By adequate choice of the 'process' parameters we succeeded to produce oxid scales with relativ high reduction factors for hydrogen permeation as compared with the permeation through the blank metal surfaces. Such scales also show a linear correlation between hydrogen pressure and permeation and an increased activation energy for permeation as compared to that of the blank metal. Our observations cast doubt on elder theories trying to explain the action of oxide films. We try here to apply a formalism presented first by Ash and Barrer to describe our findings. According to our experiments we believe that oxide scales formed under the conditions prevailing here act rather as a 'dissociationbarrier' than as a 'diffusionbarrier'. (ERA citation 08:032026)