The permeation of tritium through 316L stainless steel with multiple coatings

TiN + TiC + TiN and TiN + TiC + SiO2 films were deposited on the surface of 316L austenitic stainless steel by means of physical vapor deposition (PVD ). The thickness of the films was about 2-3 mum. The film is compact, oxida tion-resistant, and has good adherence with the substrate below 500 degrees C. Tritium gas permeation of 316L with multiple films was examined, and it was found that the tritium permeability in 316L with a TiN + TIC + TiN film was 4-5 orders of magnitude lower, and in 316L with a TiN + TiC + SiO2 fil m was 4-6 orders of magnitude lower than that in 316L with a Pd film at abo ut 200-500 degreesC. At about 600 degreesC, the permeability of 316L with t he multiple coating was 3-4 orders of magnitude lower than that in 316L wit h a Pd film. The result shows that the tritium permeation barrier is formed by multiple coating above 300 degreesC, and it is stable below 500 degrees C. However, the barrier is partly destroyed at about 600 degreesC because o f oxidation; although this results in degradation of the barrier, it still plays a positive role. These films may be useful as coatings for the first wall, tritium blanket, and heat exchanger in fusion reactors for tritium pe rmeation resistance. (C) 2000 Elsevier Science B.V. All rights reserved.