Effect of water vapor on tritium decontamination of stainless steel 316

To establish efficient decontamination methods for tritium-contaminated stainless steels, the desorption of tritium was studied for SS-316 in dry and wet argon gas carriers at different temperatures. The specimen was exposed to tritium at 523 K for 3 hours. The tritium inventory was in a range from 2 to 12 MBq. The desorption at elevated temperatures was measured by using a liquid scintillation counter. In addition, the tritium depth profiles in the specimen were evaluated by beta-ray induced X-ray spectrometry. It was found that the decontamination efficiency was enhanced by the presence of moisture. This effect was ascribed to the isotope exchange reaction on the surface. The depth profile measurements revealed the presence of tritium-rich subsurface layer and the bulk with lower tritium concentration. The majority of tritium was, however, found in the bulk, indicating that extraction of bulk tritium is essential for the decontamination of SS-316 exposed to tritium at high temperatures.