Abstract
In the helium-cooled lead-lithium (HCLL) design concept for blanket structures of a future fusion power plant, the eutectic Pb-15.7Li alloy is used as a liquid tritium breeder and is in direct contact with the structural material, e.g., ferritic-martensitic steels. Compatibility tests showed that a high corrosion attack appears and that the dissolved steel elements like Fe and Cr form precipitates, with a high risk of system blockages. Therefore, coatings as corrosion barriers are required for a reliable plant operation. Because of safety reasons, a distinct permeation reduction of the tritium, produced in the Pb-Li alloy by nuclear reactions, into the environment has to be limited, too. Previous developments already showed that Al-based coatings can perform very well as anti-corrosion and tritium permeation (T-permeation) reduction barriers in a PbLi environment. However, industrially relevant coating technologies for fusion application are still missing and/or cannot fulfil low activation criteria. Electrochemical deposition processes are highly flexible and used widely for the production of functional coatings, e.g., for corrosion protection. Nevertheless, because of its unique electrochemistry, Al cannot be deposited from water-based systems. Therefore, the development of two different Al coating processes from nonaqueous systems was initiated and proofed by the successful generation of protective and reproducible scales after heat treatment.
