Plasma and Fusion Research

Volume 14, 1405125 (2019)

Regular Articles

Effect of Re-Deposition Layers in Plasma-Facing Wall on Tritium Retention and Tritium Depth Profile
Masao MATSUYAMA, Hideki ZUSHI1), Kazutoshi TOKUNAGA1), Arseniy KUZMIN2) and Kazuaki HANADA1)
Hydrogen Isotope Research Center, Organization for Promotion of Research, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan
1)
Rearch Institute for Applied Mechanics, Kyushu University, 6-1 Kasuga-Koen, Kasuga, Fukuoka 816-8580, Japan
2)
National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
(Received 25 October 2018 / Accepted 4 June 2019 / Published 11 July 2019)

Abstract

Effect of the re-deposition layers formed on plasma-exposed stainless steel type 316L (SS316L) in QUEST on the retention and depth profile of tritium has been studied by both methods of tritium exposure experiments and numerical analyses of X-ray spectra observed by the β-ray-induced X-ray spectrometry (BIXS). Both samples of plasma-exposed and non-exposed SS316L were exposed to tritium gas under given temperature, time and pressure conditions. Surface of the former sample was covered with re-deposition layers after exposing to the plasma experiments. After tritium exposure, X-ray spectra induced by β-rays emitted from tritium atoms retained in the surface layers and/or dissolved into the bulk were measured using an ultra-low energy X-ray detector consisting of pure Ge semiconductor, and numerical analysis of the observed spectrum was conducted to estimate a tritium depth profile in the sample. As a result, it was found that the amount of tritium in surface layers of the plasma-exposed sample was about five times larger than that of the non-exposed sample, and the tritium depth profile for the plasma-exposed sample was about half depth in comparison with that for the non-exposed sample although the degassing temperature and tritium exposure conditions were the same for both samples. It was suggested, therefore, that the re-deposition layers played a role of diffusion barrier of tritium atoms formed on the sample surface.

Keywords

tritium retention, tritium depth profile, re-deposition layers, β-ray-induced X-ray spectrum, numerical analysis

DOI: 10.1585/pfr.14.1405125

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