Surface Effects on Tritium Diffusion in Materials in a Radiation Environment

Tritium transport and distribution in a material are controlled by chemical potential gradients, thermal gradients, and cross-coupling to impurities and defects. Surfaces influence tritium diffusion by acting as sources and sinks for defects and impurities. Surface films restrict tritium transfer between the solid and surrounding fluids. Radiation directly affects boundary processes such as dissociation or adsorption, may erode a surface film or the surface itself, and introduces defects and impurities into the solid by radiation damage, transmutation, or ion implantation, thereby modifying tritium transport within the solid and its transfer across external interfaces. There have been no definitive investigations of these effects, but their practical significance has been demonstrated in tritium release or absorption studies with stainless steel, Zircaloy, niobium, and other materials.