24P112-P
Tritium Retention to the First Wall of JT-60U
JT-60U第一壁炭素材タイルへのトリチウム蓄積	 
Ayumu Adachi1, Masafumi Yoshida1, Toshiharu Takeishi1, Tetsuo Tanabe1, Takao Hayashi2,
Tomohide Nakano2, Masakatsu Fukumoto2, Jyunichi Yagyuu2, Yasuhiko Miyo2,
Kei Masaki2, Kiyoshi Itami2

足立歩1,	  吉田雅史1,	  竹石敏治1,	  田辺哲朗1, 林孝夫2、仲野友英2、福本正勝2、柳生純一2、三代康彦2、正木圭2、伊丹潔2
1Kyushu University, Kasuga Fukuoka 816-8580, Japan2

九州大学 〒816-8580	  福岡県春日市春日公園 6-1
Japan Atomic Energy Agency, Mukouyama 801-1, Naka-shi, Ibaraki-ken 311-0193, Japan
日本原子力研究開発機構 〒311-0193	  茨城県那珂市向山 801-1

Tritium inventory in some of the graphite tiles used as the first wall of JT-60U was measured by a full combustion
method. The result showed that the amount of retained T increased with increasing the exposed discharge period of thetiles. Tritium retention rate was determined to be ~13 % of the total tritium production rate determined by the neutron
production rate. It was confirmed that these retained tritium were part of the energetic tritium produced by DD
reaction without being replaced by H during HH discharges.

1. Introduction
Selecting materials for vacuum vessel component
is one of the key issues in the development offusion energy.
Because of its excellent
performance under high heat load, carbon is one of
the candidates for plasma-facing wall, and it has
been widely used in most of the major tokamak
fusion reactor.
However recent studies haveshown that carbon tends to retain and store tritium.
Understanding of the process of tritium
accumulation in carbon tiles is urgently required forthe management of tritium fueling and safety. In
this study, the tritium inventory in graphite tiles
used as the first wall of JT-60U was measured by
the full combustion method and the tritium
retention rate to the first wall in respect of the total
T production rate by DD reactions during
discharges was evaluated.
2. Experimental
2.1 Sample tiles(bulk plates). The plates were crushed into 12
mesh fragments to make it easier to combust andput into quartz tube.
Analyzed tiles were located at the equatorial
position of the first wall in JT-60U indicated inFig.1. The tiles were exposed to DD discharges
with different times as shown in Table 1 during
operation years of 1991 to 2003.
Table 1 Sample’s position & DD discharge time

Surface tiles were numbered in order of DD
discharge time length. In JT-60U, HH discharges
were performed after DD discharge campaign fortritium removal.
2.2 Experimental apparatus and operation

Fig.1 Samples from JT-60U
Sample plates of 10x10x1 mm were cut from afirst wall tile including its surface (surface plates)
or from inside around 2 mm and 20 mm in depth

Fig. 2 Experimental apparatus

Fig.2 is a schematic diagram of experimental
apparatus used in the full combustion experiment.
All of the tritium contained in crushed samples wasreleased by heating them up to 1273 K with anelectric furnace. Humid argon gas with additional
oxygen (10000 ppmH2 + 50000 ppmO2) was used
as a purging gas and its flow rate was fixed to 0.2
L/min. Released tritium were transferred to acopper oxide bed at 623 K to convert HT to thetritiated water HTO, and collected in dual purewater bubblers. The amount of tritium collected in
the bubblers was measured with a liquid
scintillation counter. In all cases, the tritium
concentration in the second bubbler was less than
1 % of the first bubbler.
3. Results and Discussion

Fig.3 Tritium inventory of each examined sample
Fig.3 shows the tritium inventory of eachexamined sample plate. The tritium inventory
varied from ∼1011 to ∼1013 T atoms/cm2 for thesurface plates and ~1010 T atoms/cm2 for the bulkplates. The horizontal line in Fig.3 shows thebackground level, which is the tritium activity ofpure water in the bubbler. Since bulk plates retained
no more than background level of tritium, only theT retained in the surface plates were taken into
account for the estimation of T inventory. From theresults of the surface plates, it is clear that retained
tritium increased with increasing the exposed DD
discharge time of the tiles.
Under the assumption of toroidal and poloidal
symmetry, the overall tritium inventory for whole
first wall of JT-60U (50 m2) was estimated for
different discharge times. In Fig.4, the overall
tritium inventories for whole first wall of JT-60U
are plotted against the amount of tritium producedby DD reactions during the respective discharge
times.

Fig.4 Comparison of the estimated overall tritiumin inventory for whole first wall with the amount oftritium produced during the respective discharge
times of the analyzed tiles
The gradient of the line in the figure shows about
13% of T produced by DD reactions in plasma wasretained in the first wall. This value agrees withthe previous evaluation given by a tritium imaging
plate technique [1]. All these confirms that thepart of energetic tritium produced by DD reaction
were directly implanted within a few µm from theeroded plasma facing surface and retained therewithout being replaced by H during HH discharges
performed after each DD discharge campaign.
4. Conclusion
Tritium retention in first wall graphite tiles
exposed to different discharge times was measured
by the full combustion method. Integrating thetritium retention of each tile with the total surface
area of first wall, the tritium inventory for whole
first wall was evaluated. Comparing the tritium
inventory estimated from each tile with the amountof tritium produced during respective discharge
time of each tile, it was found that about 13 % of
the total tritium produced was retained in the firstwall. The present results confirm that the part ofenergetic tritium produced by DD reaction wereimplanted into plasma facing surface and retained
there without being replaced by H during HH
discharges.
References[1] M. Yoshida, et al. Fusion Science and Technology,
in press