MoD‐PMI 2019
NIFS, 2019/June/18‐20

Deuterium trapping at irradiation‐induced
defects in tungsten studied by positronannihilation spectroscopy
T. Toyama1), K. Ami2), K. Inoue1), Y. Nagai1),
K. Sato3), Q. Xu3), Y. Hatano2)
1) Tohoku Univ.
2)Toyama Univ.
3)Kyoto Univ.

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Japan Atomic Energy Agency, Oarai Site

Sendai

Pacific Ocean
JOYOOarai
NIFS

Tokyo
Lake Natsumi

JMTR

HTTR ⇒International Research Center
for Nuclear Materials Science, IMR,Tohoku University
2/21

ITER

http://www.rist.or.jp/atomica/dic/dic_detail.php?Dic_Key=2543

Fusion reaction:
2H + 3H  4He + nMaterials will be irradiated withplasma and neutron.
 Severe condition for materials.

Tungsten : the first candidate as the plasma‐facing material.
 High melting point Low sputter rate
 Low activation

 Low solubility of hydrogen isotopes:
important for reducing tritium retention
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Present issue :After irradiation, hydrogen retention in tungsten increases.
Thermal Desorption Spectrometry of Non‐irradiated/Irradiated tungsten
exposed to deuterium plasma

Increase of deuterium retention

Y. Hatano et al., J. Nucl. Mater., 438 (2013) S114‐S119.
4/21

Why does hydrogen retention increase after irradiation?
Exposure to hydrogen gas
Non‐irrad. W

Non‐irrad. W

Irrad. W

Irrad. W

hydrogenHydrogen retention is almost zerodue to the very low solubility ofhydrogen in W
(D/W~10‐12 @300℃).

Hydrogen trapping at
irradiation‐induced defects issuggested.

In this study, we show hydrogen trapping at irradiation‐induced defects by using positron annihilation spectroscopy.
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Why does hydrogen retention increase after irradiation?
Very low solubility limit in bulk

H2 （in vacuum）

K. Ohsawa et al., Phys. Rev. B
85 (2012) 094102.

Strong trapping at vacancy issuggested.
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Purpose of this study
To observe deuterium trapping at vacancy
clusters by positron annihilation spectroscopy.

Tungsten
Deuterium
Vacancy cluster

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Pure tungsten (4N)
φ6×0.5 mm disk  900 ℃×1h  1300 ℃×0.5h (re‐crystallization)
Neutron irradiation

Heat treatment process

HFIR @ORNL
8x1020 n/cm2 (~0.3 dpa)
~300 ℃ × 48 days

In D2 gas atmosphere (~ 0.1 MPa)
orIn vacuum (~10‐4 Pa）
300 ℃ × 100 hDiffusion length of deuterium in bulk : ~0.3 mm

5 Specimens
Annealing inD2

Neutronirradiation

Annealing in Annealing invacuum
D2

As‐prepared‐‐‐‐As‐prepared  Annealed in D2✔

‐‐‐

As‐irrad.

‐✔

‐‐Irrad.  Annealed in vacuum✔

✔

‐Irrad.  Annealed in D2

✔

‐

✔
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Positron annihilation spectroscopy

electron positron1
E1 = mc2 = 511 keV

2
E2 = mc2 = 511 keV

10/21

Positron annihilation spectroscopy; samples and source

Identicalsamples.
~10x10x0.5mm.

Positron source.
22NaCl are sealedby Kapton film.
22NaCl (2‐3mm indiameter)~ 10mm11/21

Positron annihilation spectroscopy; detectors

Positron source
sandwiched by 2samples.

12/21

Positron annihilation spectroscopy; lifetimee+Calculated Positron lifetime (ps)Calculated positron lifetime in Tungsten

T. Troev et al., Nucl. Inst. Meth.
Phys. Res. B. 267 (2009) 535.

Potential
e+‐1

Positron lifetime, τ =dr 𝑛𝑟 𝑛𝑟 𝑔 𝑟
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60400500450

τ237V17V13400350

τave300

D2焼鈍では、τave , τ2, τ1が短くなったτ1250200
1501000

寿命計算値︓T. Troev et al., Nucl.
Inst. Meth. Phys. Res. B. 267(2009) 535.

bulk
照射→D2焼鈍

CN3照射
→真空焼鈍

CN2RC2As‐prepared As‐prepared
As‐Irrad.
→Annealed in D2

RC1

Positron lifetime [ps]Calculated positron lifetime value invacancy cluster in tungsten
T. Troev et al., 真空焼鈍では、
Nucl. Inst. Meth.
Phys. Res. B. 267 (2009) 535.
陽電⼦寿命に変化無しV20CN1Intensity of 2 [%]Positron lifetime

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6040
200500τ2V37V17V13400
350
300250τaveV9τ1V4200

No changeafter annealing
in vacuum
Decrease ofτave , τ2, τ1 afterannealing in D2

V1150

Bulk

100
0Irrad.
→Annealedin D2

RCN3Irrad.
→Annealedin vacuum

RCN2

RC2

As‐prepared As‐prepared
As‐Irrad.
→Annealed in D2

RC1

Positron lifetime [ps]

450

RCN1

Intensity of 2 [%]Positron lifetime

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Decrease of positron lifetime :due to deuterium trapping at vacancy clusters?
Hydrogen trapping effect on positron
lifetime in vacancy clusters in tungsten

T. Troev et al., Nucl. Inst. Meth. Phys. Res. B. 267 (2009) 535.

16/21

Measurement of momentum of e‐‐e+ pair by Doppler effectcp Z
E1  m0 c 
22pZ : momentum of e‐‐e+ paircpE 2  m0 c 2  Z2
2e- e+1( m0c2 = 511 keV )511 Hz> 511 Hz< 511 Hz

106
10104

CountsMomentum distribution :Identical to element.

Tungsten

5Copper Chemical environment
at e+ trapping sites isobtained.

310102511 keV

101
100
480

490

500

510

520

γ-ray energy (keV)

530

540
17/21Coincidence Doppler broadening measurement

Ratio to bulk tungsten

1.3

Low momentum

1.2

RCN1

1.1

RCN3

RCN2

1.0
High momentum

0.9
0.8

Irrad.
→ Annealed in D2

0.7
As-Irrad.

0.6
0.5

Irrad.
→ Annealed in vacuum

0.4
0.3

05

101520253035

Momentum [x10‐3 m0c]
D1

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Correlation of Low‐ & High‐ momentum

High momentum component

0.010

As‐prepared
As‐prepared → Annealed in D2

0.009

0.008

0.007

Irrad. →Annealed
in D2

As‐Irrad.

0.006

Irrad. →Annealedin vacuum
0.58

0.60

0.62

Low momentum component

0.64
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Correlation of Low‐ & High‐ momentum

High momentum component

0.010

As‐prepared
As‐prepared → Annealed in D2
Electron‐irradiation:
8.5 MeV, ~100℃ , ~1x10‐3 dpa

As‐Irrad.

0.009

Irrad. →Annealed in vacuum
0.008

Irrad. →Annealed in D2
0.007

Irrad. →Annealed
in D2

As‐Irrad.

0.006

Irrad. →Annealedin vacuum
0.58

0.60

0.62

Low momentum component

0.64
20/21

Summary
Pure tungsten was neutron‐irradiated (~300 ℃ × 48 days), then annealedin vacuum or deuterium gas (300 ℃ × 100 h）

As‐Irrad.

Annealed in vacuum

No change ofvacancy cluster

Annealed in D2 gas

Deuterium is insidevacancy cluster

Deuterium trapping at irradiation‐induced defects
was successfully observed.
T. Toyama et al., J. Nucl. Mater., 499 (2018) 464.
21/21