Characterization of Surface Barrier Effect upon Tritium Permeation Through Stainless Steel with Auger Electron Spectroscopy

The surface barrier effect on tritium permeation through SUS-316 stainless steel was characterized with Auger electron spectroscopy for the surfaces which had been confirmed to have different barriers from our previous study. The surface which was prepared by heat treatment at 1273K for 1 hr in vacuum(10⁻⁴ Pa) was not contaminated with oxygen and carbon but covered uniformly with a large amount of sulfur. The surface exposed to air at room temperature after the vacuum annealing was covered with duplex oxide layers: the top layer consisted of iron oxide and the inner layer consisted of chromium, iron and nickel oxides. The iron oxide in the top layer was easily reduced with hydrogen gas at elevated temperatures but inner oxide layer was not completely reduced under the present conditions. These results were correlated to the surface barrier effect on tritium permeation based on our previous experimental results concerning the dissolution rate of gaseous tritium into stainless steel.