Gamma-ray irradiation effect on deuterium retention in reduced activation ferritic/martensitic steel and ceramic coatings

Tritium permeation and retention are serious problems in D-T fusion reactors from the viewpoint of fuel efficiency and radiological safety. Functional ceramic coatings have been intensively studied for the development of tritium permeation barriers for several decades, while reports about tritium retention in the ceramic coatings are scarce. Moreover, irradiation may affect tritium retention in fusion materials, which is important to precisely evaluate tritium inventory in the reactor. In this study, the gamma-ray irradiation effect on deuterium retention in reduced activation ferritic/martensitic steel and three kinds of ceramic coatings were investigated through deuterium exposure, gamma-ray irradiation using cobalt-60 gamma-ray sources and deuterium depth profile measurements. The amount of deuterium retention in yttrium oxide, silicon carbide, and zirconium oxide coatings decreased after the irradiation in the dose rate of 2.43 Gy s⁻¹, while no clear change in the retention was observed at the lower dose rate. From these results, the gamma-irradiation effect on deuterium retention would have a threshold dose rate. Diffusion and desorption of deuterium would be accelerated by excitation of deuterium via energy transfer from electrons generated by Compton scattering.