Tritium permeation barriers for fusion technology

A review of the effectiveness as permeation barriers of several coatings deposited on materials of interest for fusion technology is presented. The coating materials studied were Al2O3, TiC and a bilayer of TiC/TiN deposited by pack cementation, chemical vapour deposition (CVD) and vacuum plasma spraying (VPS). Also, the effectiveness of direct oxide growth on the surface of the substrate is discussed. The results were obtained either with or without the layer being in contact with the eutectic breeder lithium compound Pb-17Li. The studies were performed in the temperature range 515-742K using deuterium at pressures in the range 1-50kPa. The minimum obtained reduction in permeation was one order of magnitude for Al2O3, TiC and TiC/TiN deposited by CVD on AISI 316L, and the maximum was three orders of magnitude obtained for an aluminium layer deposited by VPS on MANET. (orig.)