Tritium retention on stainless steel surface exposed to plasmas in LHD

Abstract

Tritium retention of samples exposed to plasmas in the Large Helical Device (LHD) during each campaign in 12th, 13th and 14th cycles has been studied. Small sample plates made of stainless steel type 316L were fixed in advance at four different walls in LHD: location of a sample plate was 1.5U, 5.5U, 6.5L and 9.5L. After plasma exposure in each cycle, these samples were exposed to tritium gas at a temperature of 300 or 623 K. Retention behavior of tritium in surface layers of each sample was mainly examined using β-ray-induced X-ray spectrometry (BIXS) and X-ray photoelectron spectroscopy (XPS). The energy spectra observed by BIXS and XPS showed the depositions of boron, carbon, titanium, chromium, iron, nickel and molybdenum with oxygen. Tritium retention of the samples exposed to plasma increased than that of a bare SS316L sample, although it was largely different in the location of a sample. When the samples were exposed to tritium gas at 300 K, the order of magnitude of tritium retention was as follows: 9.5»5.5U>6.5L>1.5U for 12th cycle, 6.5L>9.5>1.5U>5.5U for 13th cycle, and 6.5L>1.5U~5.5U>9.5L for 14th cycle. © 2012 The Japan Society of Plasma Science and Nuclear Fusion Research.