24P085-P
Retention and Desorption of Deuterium in Heavily Irradiated W
重照射損傷を受けたタングステンの水素同位体保持・放出特性
Shiori NAITOU1, Naoki FUTAGAMI1, Shouji MIYAMOTO2, Tomonori TOKUNAGA1,Hideo WATANABE3, Naoaki YOSHIDA3
1
内藤梓小里 ，二神直樹 1，宮本正二 2, 徳永知倫 1，渡辺英雄 3, 吉田直亮 3
1

IGSES Kyushu Univ., 2NSK Co. Ltd., 3RIAM Kyushu Univ.
九大総理工1、日本精工2、九大応力研3
6-1, Kasugakoen, Kasuga-City, Fukuoka 816-8580, Japan
〒816-8580 福岡県春日市春日公園6-1

In this study behavior of implanted deuterium in tungsten samples with different type of defects wereexamined. In case of tungsten irradiated by energetic heavy ions, it was identified that not only vacancies
and dislocations but also fine vacancy clusters such as nano-voids and small complex, act as strong
trapping site of deuterium by comparing the microstructure and TDS spectrum.

1. Introduction
Plasma facing materials in a fusion reactor alarge number of lattice defects are formed by theheavy irradiation of fast neutrons. On the otherhand, hydrogen isotopes from the plasma
penetrate into the material through the surface
and are trapped by the radiation induced defects.
Estimation of tritium inventory in the plasma
facing material in fusion reactors is very
important from the standpoint of safety. In orderto estimate the amount of the retained tritium,
nature of the accumulated defects and theirinteraction with hydrogen isotopes must beunderstand well.
Tungsten is a potential candidate of plasma
facing materials for protecting heavy heat load andparticle loads. In this work, therefore, several kindsof tungsten samples with different treatments suchas heating, plastic deformation and heavy ion
irradiation are prepared. By comparing the behaviorof implanted deuterium and microstructure in thesesamples, interaction of hydrogen isotopes with thedefects were examined.
2. Experimental procedures
In this study, tungsten sheets manufactured by
Nilaco Co. (99.95% purity, 0.1 mm-thick) wereused as a sample. After cutting into a size of 5 × 10mm from the sheet, mechanical polishing,annealing (if necessary) and electro-polishing werecarried out successively.
Some samples were annealed for 30 min attemperatures from 1173 K to 1323 K. They wereirradiatedatroomtemperaturewith
0.2keV-deuterium ions to 1x1021ions/m2 and TDS
experiments
wereperformed
successively.
Microstructure was also observed by TEM to look
for the responsible defects for trapping ofdeuterium.
Some of the recrystallized samples wereirradiated at room temperature with 2.4 MeVcopper ions. After the irradiation, TEM observation
and TDS experiment were also carried out.
3. Results and Discussions
TDS spectra of D2 from the annealed samples
and mechanically deformed samples are shown in
Fig.1. Desorption from the as received sample issimilar to that of 1173K/30min-sample. Remarkable
desorption peaks at around 330-420K (peak A) and420-560K (peak B) become smaller by increasing
the annealing temperature. Desorption from there-crystallized samples is very small and desorption
at the peak B almost vanished. Fig.2 shows TDS
spectrum of DH from the annealed samples. It is
worth to note that a new peak around 600-900K(peak C) appear in addition to peak A and Peak B.
After heavy ion irradiation up to 0.01dpa,
0.1dpa and 1dpa at room temperature, TDS
experiments were performed. As shown in Fig.3,large peaks A, B and C appeared.
In case of copper ion irradiation, dense defects
are accumulated above 0.1dpa. Fig.4 shows
micrograph of the pre-thinned tungsten irradiatedup to 1dpa. As can be seen in the micrograph, notonly dislocation loops but also dense nano-voids areformed. It is considered that very dense single
vacancies and their small complex are also
accumulated in the sample in addition to theobservable defects. Formation of fine vacancy
clusters and nano-voids even at low temperatures
where vacancies can not migrate thermally is very
important from the standpoint of tritium inventory.
In case of irradiation with high energy heavy ionsand neutrons, in which cascade collisions occur
often, fine vacancy clusters are formed even at low

fluence and at low temperature.
Mechanically deformed tungsten has also
desorption peak C at 850 K, because the vacancies
and their fine clusters are formed by the crossing of
dislocations under the plastic deformation. To
diminish the strong trapping of hydrogen isotope atpeak C, the mechanically deformed tungsten should
be annealed well above 1223 K.
From the experimental results of TDS and TEM
we assign the trapping site of each desorption peaks
as followings:
Peak A (330~420K) : In addition to adsorption at
the surface, single vacancies and their very fineclusters act as trapping for D.
Peak B (420~560K) : Kinks of dislocations is oneof the candidate of the corresponding trapping sites.
Peak C (660~900K) : Very fine vacancy complex
and nano-voids for D2. Trapping energy wasestimated to be 1.8eV in the previous work.

Fig.1 Thermal desorption of D2 from the annealed
samples.

Fig.2 Thermal desorption of DH from the annealed
samples.

Fig.3 Thermal desorption of D2 from the Cu ion
irradiated samples.

Fig.4 Nano-voids and dislocation loops formed bycopper ion irradiation