Corrosion behaviour of Al based tritium permeation barriers in flowing Pb–17Li

Tritium permeation barriers on low-activation steels are required in fusion technology in order to reduce the tritium permeation rate through the structural material into the cooling water system. Al–Fe layers with alumina on top can fulfil the required reduction rate. Three techniques were selected to produce such a multi-layered coating system: chemical vapour deposition (CVD) by CEA, hot-dip aluminising (HDA) by FZK and vacuum plasma spraying (VPS) by JRC Ispra. A sufficient corrosion resistance against Pb–17Li attack is also required for the coating. Therefore, the corrosion behaviour of these three coatings on ferritic–martensitic steels was studied in the PICOLO loop of FZK in flowing Pb–17Li at 480 °C up to 10 000 h. Corrosion effects could not be found on HDA and VPS coated specimens even up to the longest time of exposure. The total thickness of the two-layered system remained unchanged at around 130 μm for all examined HDA and VPS specimens. In contrast to this, corrosion effects could be inspected on CVD coated specimens.