THE FORMATION OF TRITIUM PERMEATION BARRIERS BY CVD

The effectiveness as permeation barriers of the following CVD coatings have been investigated: TiC (1 to 2 mum in thickness); a bi-layer of TiN on TiC (3 mum total thickness) and CVD Al2O3 on a TiN/TiC bi-layer. The substrate materials were TZM (a Mo alloy) and 316L stainless steel in the form of discs of diameter 48 mm and thickness 0.1 or 1 mm. Permeation measurements were performed in the temperature range 515-742 K using deuterium at pressures in the range 1-50 kPa. CVD layers were shown to form reasonably effective permeation barriers. At a temperature of 673 K TiC is around 6000 times less permeable to deuterium than 316L stainless steel.