27pB03
イオン照射損傷を与えたタングステン中の水素同位体交換
Hydrogen isotope exchange in ion-damaged tungsten
狩川拓也1,Heun Tae Lee1,大塚裕介1,上田良夫1,高木郁二2,福本正勝3,井上多加志3,谷口正樹3,坂本慶司3
KARIKAWA Takuya1, LEE Heun Tae1, OHTSUKA Yusuke1, UEDA Yoshio1, TAKAGI Ikuji2,
FUKUMOTO Masakatsu3, INOUE Takashi3, TANIGUCHI Masaki3, SAKAMOTO Keishi31

大阪大学大学院工学研究科, 2京都大学大学院工学研究科, 3日本原子力研究開発機構
Graduate School of Engineering, Osaka University, 1Graduate School of Engineering, Kyoto University,3Japan Atomic Energy Agency

1

2. Experimental
Two types of hydrogen isotope exchangeexperiments with 700keV ion-damaged W werecarried out. Firstly, ion-damaged specimens irradiatedby deuterium (D) are irradiated by hydrogen (H) at
473 K (Type-1 experiment). The fluences were
1.5×1024 D/m2 and 1.0×1023 to 1.5×1024 H/m2.
Secondly, similar damaged specimens irradiated by D
at 473 K were annealed at 573 K to desorb D atrelatively low energy trap sites (~1.4 eV) [2] before H
irradiation at 473 K (Type-2 experiment). The purpose
is to investigate the effect of the isotope exchangeagainst the strongly trapped D (~2.0 eV) [2]. D depth
profile was observed up to 1.5 µm by D(3He,p)4He
nuclear reaction by using a Van de Graaff generator inKyoto University. The energy of 3He was 1.7 MeV.

3. Results
Type-1 experiment showed that more than 76% oftrapped D up to the depth of 1.5 µm was removed by
H irradiation (Fig. 1). The release rate of D atoms was
the highest in near surface region (within 0-0.5 µm).
In this region, reduction in D retention took placeinstantaneously after H irradiation, which indicatesmobile H atoms diffused to this region within the143D only
+1.0×1023 H/m2
+5.0×1023 H/m2
+1.5×1024 H/m2121026

Tungsten is one candidate for plasma facing
materials (PFMs) in ITER and is planned for future
fusion reactors. PFMs are simultaneously exposed
to fuel particles and 14MeV neutrons generated by
DT reactions. The radiation damage produced by
the neutrons will increase tritium retention intungsten (W) due to production of hydrogen isotope
trap sites [1]. Increased tritium retention will impactsafety and operational limits of ITER and future
fusion reactors. Therefore, it is important to assess
the trap characteristics produced in tungsten anddevelop the way to remove tritium trapped in thesesites. It is known that annealing is one way toremove tritium. In this study, however, we study theeffect of isotope exchange because it could takeplace at lower temperatures than annealing
temperatures.

fluence of 1023 H/m2. The D retention near the surface(0-0.5 µm) was reduced by two orders of magnitude inthe H fluence of 1.5 × 1024 H/m2 (corresponding to 1.5× 104 sec). Therefore, isotope exchange is very
effective to remove T atoms trapped in this depth
region. At deeper regions, reduction in D retention
also took place, but is slower than that of top surface
region.
D concentration(10 D/m )1. Introduction

864
20
0.0

0.5

1.0

1.5

depth(µm)

Fig. 1 D depth profile after H irradiation (Type-1experiment) 1.5 × 1024 D/m2 + 0~1.5 × 1024 H/m2

Type-2 experiment also showed H fluence
dependence for removal efficiency of strongly trapped
D. For 1.0 × 1023 H/m2 irradiation, the amount ofretained D was not clearly decreased at all regions.
For the fluences of 5.0 × 1023 H/m2 and 1.5 × 1024
H/m2, the amount of trapped D atoms was reduced up
to the depth of 1.0 µm. For the fluence of 1.5 × 1024
H/m2, about 66% of initial D was desorbed up to thedepth of 1.5 µm. From these experiments, our data
showed the removal efficiency sharply decreases withdepth, which suggests that isotope exchange would
not be useful within a reasonable time for the removalof T accumulated at neutron induced trap sites in deep
regions. This is a remaining issue for the T removal by
the isotope exchange process.

References[1] O.V. Ogorodnikova, et al., Journal of Nuclear
Materials, 415 (2011) 5661-5666.
[2] K. Tsukatani, et al., Fusion Science andTechnology, 60(4), 1543-1547 (Nov.2011).