Study on hydrogen absorption in Zr powder used for tritium confinement in a production system of tritium for fusion reactors with a high-temperature gas-cooled reactor

A tritium production method using a high-temperature gas-cooled reactor loaded with lithium compound particles has been proposed for steadily starting up and stably operating a fusion reactor. In order to confine the produced tritium, small lithium-compound particles are considered to be coated by ceramic materials. The present authors have proposed adding zirconium fine particles into the inside of the ceramic coating to improve tritium confinement performance. In this work, powdered zirconium was exposed to hydrogen or deuterium gas in a closed volume at elevated temperatures and absorption rate constant and Sieverts' constant were evaluated by the pressure drop by absorption. After the experiments, it was found that the powdered zirconium sample became a lump by a sintering effect. By referring literature data for α-zirconium and its oxide, the observed absorption rate was speculated to include the influence of sintering and oxide layer. The obtained Sieverts’ constants were slightly smaller than literature data. By taking into account the observed hydrogen absorption behavior in powdered zirconium, tritium leak from alumina-coated lithium-compound particles containing zirconium fine particles was roughly estimated in some conditions. Tritium permeation rate can be reduced by adding zirconium but the leak suppression effect is limited.