S1-6
中性子照射タングステンにおけるトリチウムリテンションと透過
Tritium retention and permeation for neutron-damaged W大矢恭久1)、波多野雄治2)、片山一成3)、山内有二4)、信太祐二4)、大塚哲平5)、近田拓未1)、原正憲2)、大宅諒6)、上田良夫6)、外山健7)、島田雅8)、Dean Buchenauer9), Chase Taylor8),
Bob Pawelko8), Brad Merrill8), Lee Cadwallader8), Rob Kolasinski9), David Donovan10)
Yasuhisa Oya1), Yuji Hatano2), Kazunari Katayama3), Yuji Yamauchi4), Yuji Nobuta4),
Teppei Otsuka5), Takumi Chikada1), Masanori Hara2), Makoto Ohya6), Yoshio Ueda6),Takeshi Toyama7), Masashi Shimada8), Dean Buchenauer9), Chase Taylor8), Bob Pawelko8),
Brad Merrill8), Lee Cadwallader8), Rob Kolasinski9), David Donovan10)
1)2)静大、 富山大、3)九大、4)北大、5)近大、6)阪大、7)東北大、8)INL、9)SNL、10)テネシー大1)
Shizuoka Univ., 2)Univ. Toyama, 3)Kyushu Univ., 14Hokkaido Univ., 5)Kindai Univ.,
6)
Osaka Univ., 7)Tohoku Univ., 8)INL, 9)SNL, 10)Univ. Tennessee

Results and discussion
Fig. 1 shows the D retention behavior for 0.01 dpa
and 0.1 dpa Fe ion damaged W with D ion fluence of
1.0 × 1022 D+ m-2 at room temperature. The TDS
spectra clearly showed that major D desorption
temperature was shifted to 850 K for the higher
damaged sample (0.1 dpa), although large D
desorption peak for 0.01 dpa is observed at 670 K. It
indicates that the major trapping site of hydrogenisotope is changed from vacancies to voids bydamage accumulation. For the initial evaluation of2.0

Fe2 + irradiated W with D2+ implantation
0.01 dpa [4]0.1 dpa [4]Neutron damaged W with D plasma
0 dpa
0.1 dpa

1.2
1.0

1.5
0.81.00.60.4

0.5
0.2
0.0400600

8001000

Desorption rate / 1018 D2 m -2 s-1

Experimental
Disks of stress-relieved W were irradiated using
several different methods. As a surrogate for neutron
damage, a subset of the samples was irradiated by 6
MeV Fe2+ at room temperature in TIARA, QST. A
second set of W specimens were exposed to 6.4 MeV
Fe3+ at higher temperature in DuET, Kyoto
University up to 1.0 dpa. All sets of samples wereexposed to 1 keV D2+ ions up to a fluence of 1.0 ×1022 D m-2 at room temperature. In addition, Rabbit
irradiation at ORNL was also done with the higher
damage concentration of 0.1 dpa and these samples
were transferred to INL to perform D plasma
exposure using TPE device with the temperature of673 K with D ion flux of 7.2 × 1021 D m-2s-1 up to thefluence of 5.2 × 1025 D m-2. Thereafter, thermal
desorption spectroscopy (TDS) was applied with theheating rate of 0.5 K s-1 up to 1173 K. The defectconcentration and formation of voids were evaluatedby positron annihilation spectroscopy (PAS). To
complement these results, TEM images of the ion
damaged W were also acquired to evaluate thedistribution of dislocation loops and voids for Fedamaged W.

Desorption rate / 1017 D2 m -2 s-1

Introduction
Elucidation of tritium dynamics is one of the key
issues for sustainable D-T fusion. Tungsten will beexposed to high fluxes of tritium (T) accompaniedwith various energetic particles. Therefore, T
retention and its trapping states will be dramaticallychanged by the accumulation of ion and neutroninduced damage and recovery by heating.
In our previous Japan–US collaboration program,
TITAN project, has demonstrated the n-irradiation
effect on hydrogen isotope retention in W, where theD retention for 0.025 displacements per atom (dpa)
is significantly larger than that for undamaged W.
For the design of tritium recycling, hydrogen isotope
including tritium permeation study is also mandatory.
These facts motivate us to perform extensivehydrogen isotope retention experiments in damaged
W under the framework of Japan/US joint project,PHENIX.

0.01200

Temperature / KFig. 1 D2 TDS spectra for Fe2+ damaged W with D2+implantation （D2+ fluence： 1 × 1022 D m-2 at roomtemperature）and 0.1 dpa neutron damaged W with Dplasma exposure (D fluence: ~ 5 × 1025 D m-2 at 673 K) .

-1-1

Permeability / mol m s Pa-0.5

Zakharov et al.
un-dameged W
Fe2+ irradiated W (0.1 dpa)

-11

10-1210-1310-14

10

0.8

0.9

1.0

1.1-1

1000 / T / K

Fig. 2 D permeability for 0.1 dpa Fe2+ irradiated W.

neutron irradiation effect, small W single crystal
specimen with the size of 4 mm × 4 mm, which ispicked up from tab of tensile specimen (0.1 dpa
neutron irradiation at 673 K), is used. Fig. 1 also
shows D2 TDS spectra for 0.1-dpa-neutron-damaged
W and un-damaged W with TPE D plasma exposure.
It is clear that the D retention is clearly enhanced by
the neutron irradiation and the desorption
temperature is shifted toward higher temperatureside. Comparing to D ion irradiation, the TDS
spectrum is broadened and extended toward higher
temperature side, leading that D was migrated intoW bulk region due to damage introduction
throughout the sample by neutron irradiation and D
migration by high temperature and high flux
irradiation.
In order to elucidate how D diffuses throughdamaged W, D permeability through Fe2+ damaged
specimen were measured. We hypothesize thattrapping of D by defects affects the number ofavailable D diffusion pathways through the lattice.
This would be manifested by a reduction in D
permeability for damaged W, which we confirmed
experimentally as shown in Fig. 2. Furthermore, by
heating above 1100 K, D permeability wascompletely consistent with that for undamaged W,
suggesting that irradiation-induced defects had beenrecovered. It can be said that the nature of the defects
is critical, and their stability will strongly influence
D permeability. We observed no experimental
conditions that led to the enhancement of D
permeability due to damage introduction.
Furthermore, we note that thermal annealing isquite important to determine the recovery conditionof irradiation damage and two sets of experiments
were performed. Consider Fig. 3, which shows D2
TDS spectra for 0.1 dpa Fe2+ damaged W. Here we
examine the effect of heating both during theirradiation process and afterward; temperatures of573 K and 1173 K are considered. A clear reduction

Fig. 3 Comparison of D2 TDS spectra for damaged W withhigh temperature irradiation and that with annealing after
room temperature irradiation.

of D desorption at ~ 800 K due to higher temperatureirradiation was found in comparison with postannealed W at the same temperature, which also
causes the desorption peak to shift to lower
temperature at 573 K and 873 K. In particular, postmortem PAS results showed that the recovery ofvoids was remarkable at 873 K and the trap density
was clearly small. These results show that dynamic
recovery of defects is enhanced by higher
temperature irradiation, and the formation ofvacancies reduces the D trapping energy.
SummaryThis paper presents recent results, including ananalysis of D retention by various methods over arange of defect concentrations. The accumulation ofdefects resulted in the formation of stable trappingsites which, based on our TDS results, are consistentwith voids. We propose that D trapping by defects
reduces the number of available D diffusion
pathways through the lattice, a mechanism that could
lead to a reduction of D permeability. Finally, we
note that dynamic recovery of damages is enhancedby high temperature irradiation.
Acknowledgement
This work was performed under the framework ofJapan-US collaboration program (PHENIX) andsupported by Kyoto University (ZE-28A-17),
Institute for Applied Mechanics, Kyushu University
and University of Toyama collaboration program(NIFS16KUHR035). The Fe ion irradiation was
done in the framework of collaborative research
program at The University of Tokyo.