Plasma and Fusion Research

Volume 15, 1405062 (2020)

Regular Articles

Tritium Balance in Large Helical Device during and after the First Deuterium Plasma Experiment Campaign
Masahiro TANAKA1), Hiromi KATO, Naoyuki SUZUKI, Suguru MASUZAKI1), Miyuki YAJIMA, Miki NAKADA and Chie IWATA
National Institutes of Natural Sciences, National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
1)
The Graduate University for Advanced Studies, SOKENDAI, Toki, Gifu 509-5292, Japan
(Received 3 February 2020 / Accepted 2 July 2020 / Published 19 August 2020)

Abstract

The Large Helical Device (LHD) started the deuterium plasma experiment on March 7, 2017. Approximately 6.4 GBq of tritium was produced in the first deuterium plasma experiment campaign and were utilized as tracers for the investigation of release behavior and the balance of tritium in the LHD vacuum vessel. To determine the tritium balance in LHD, the tritium release from the vacuum vessel was continually observed during the plasma experiment period and the vacuum vessel maintenance activities. The tritium exhaust rate was approximately 32.8% at the end of the plasma experiment. After the plasma experiment, the vacuum vessel was ventilated by room air for the maintenance activity and the tritium release from the in-vessel components was observed. The tritium release rate gradually decreased and became constant after four-month in spite of water vapor concentration. It is suggested that the tritium release mechanism from the vacuum vessel is a diffusion-limited process from the bulk. The tritium release amount during the maintenance activity for one year was approximately 5.0%. Considering the decrease of tritium decay for 1.5 years, tritium inventory in LHD was estimated to be approximately 3.66 GBq (57.2%) at the end of maintenance activity.

Keywords

Large Helical Device, deuterium plasma experiment, vacuum vessel ventilation, tritium inventory, tritium balance, tritium release behavior

DOI: 10.1585/pfr.15.1405062

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