Development of anti-permeation and corrosion barrier coatings for the WCLL breeding blanket of the European DEMO

Tritium permeation from breeder material to the Water Coolant System (WCS) in Water Cooled Lithium Lead (WCLL) Breeding Blanket (BB) is one of the technological issues to be solved in the design of the European DEMO. Since the tritium extraction from the Water Coolant System is more challenging and expensive than the extraction from the eutectic alloy PbLi, it is mandatory to use of a protective coating on the blanket wall to minimize the permeation rate. Moreover, a protective coating can prevent the corrosion of EUROFER steel by the action of PbLi. alumina-based coatings are considered as reference for barriers thanks to their good chemical compatibility with the PbLi alloy and their capability to reduce permeation. Three coating technologies were selected in the frame of the EUROfusion project: electrochemical ECX (chemical deposition) process, Pulsed Laser Deposition (PLD) and Atomic Layer Deposition (ALD) coating. The coatings were developed and optimized in order to satisfy the design requirements of good mechanical compatibility with steels, strong adhesion, corrosion compatibility in PbLi at relevant BB design conditions and a Permeation Reduction Factor at least of 200 under neutron irradiation. The present paper aims to describe the status of the technologies and the main results obtained. The final objectives of the R&D activities are to demonstrate the applicability of the coating to WCLL BB and therefore the scale-up of the technologies from laboratory scale to the BB scale.