Effects of Irradiation Damage and Helium to Hydrogen Permeation Barrier Ceramics Coating

Tritium permeation through structural materials in a fusion reactor is a critical issue from the viewpoints of radiological safety and fuel loss. As a solution, fabrication of tritium permeation barrier coatings has been investigated for several decades. In recent years, several irradiation tests have been conducted for the ceramic coatings in order to understand irradiation effects on their characteristics and functions. However, there are few experimental reports on multiirradiation tests of neutrons and alpha particles produced by nuclear reactions and radioactive decay of tritium. In this study, yttrium oxide coatings were fabricated by radio frequency magnetron sputtering, and their microstructures and deuterium permeation behaviors were investigated after nickel ion irradiation and helium implantation tests simulating irradiation damage by neutrons and alpha particles. The irradiated samples showed the formation of voids and an amorphous layer. In the deuterium permeation tests, all the samples showed almost the same permeation flux at less than 400 oC. A decrease in the flux due to grain growth and/or crystallization was confirmed at higher than 450 oC. The fluxes of the irradiated samples decreased at higher temperatures than unirradiated samples, suggesting that the voids prevented structural change. The microstructure and deuterium behavior of the Ni-He-sequential-irradiated sample was similar to the those of Ni-irradiated sample. Therefore, in the case that He implantation conducted after heavy ion irradiation, He might have little effects on the characteristics and functions of the coatings. Keyword: tritium, permeation, ceramics, ion irradiation