Hydrogen isotope retention in the first wall tiles of JT-60U

Yoshida, Masafumi; Tanabe, Tetsuo*; Sugiyama, Kazuyoshi*; Hayashi, Takao; Masaki, Kei; Yagyu, Junichi; Sato, Masayasu

We have investigated hydrogen isotopes retention in the graphite outboard first wall tiles of JT-60U by means of TDS, SIMS and SEM. The SEM examination confirms that these tiles are mostly eroded. Differently from graphite divertor tiles, in which H retention was dominated owing to HH discharges preformed after DD discharges to remove tritium, deuterium is dominated in hydrogen isotopes retention of the first wall tiles and penetrates deeper from the surface. This is attributed to injection of high energy D and difficulty of isotopical replacement owing to their lower temperature. Although the total retention of the hydrogen isotopes in the unit area of the first wall region normalized by discharge duration is not large, the integrated amount over the whole surface could be appreciably large. This type of hydrogen retention could be also possible for the metallic wall.