Behaviour of tritium in plasma-sprayed tungsten coating on steel exposed to tritium plasma

In order to understand the role of a plasma-sprayed tungsten (W) coating on tritium (T) permeation in a W-coated ferritic/martensitic steel (F82H), we have examined depth profiles of T in the coating and the substrate using the tritium imaging plate technique after T loading by a dc glow-discharged plasma at 453 and 573 K for 2 h. Tritium loaded by plasma exposure was distributed uniformly in the whole coating, while T penetrated to the substrate by diffusion. The former is caused by T diffusion through open pores and/or along grain boundaries followed by adsorption on grain surfaces and dissolution in the grains. The main role of the W coating on T permeation is to reduce the incoming flux at the coating/substrate interface owing to pore diffusion in the coating and the effective area for T dissolution in the substrate.