deuterium trapping at irradiation‐induced defects in...

Deuterium trapping at irradiation‐induced defects in tungsten studied by positron

annihilation spectroscopy

T. Toyama1), K. Ami2), K. Inoue1), Y. Nagai1), K. Sato3), Q. Xu3), Y. Hatano2)

MoD‐PMI 2019NIFS, 2019/June/18‐20

1) Tohoku Univ. 2)Toyama Univ.3)Kyoto Univ.

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Tokyo

Oarai

NIFS

Sendai

JMTR

JOYOPacific Ocean

Lake Natsumi

Japan Atomic Energy Agency, Oarai Site

HTTR⇒

International Research Center for Nuclear Materials Science, IMR, Tohoku University

2/21

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

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

Fusion reaction: 2H + 3H 4He + n

Materials will be irradiated with plasma and neutron. Severe condition for materials.

ITER

3/21

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.

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In this study, we show hydrogen trapping at irradiation‐induced defects by using positron annihilation spectroscopy.

Why does hydrogen retention increase after irradiation?

Exposure to hydrogen gas

Non‐irrad. W

Hydrogen retention is almost zero due to the very low solubility of hydrogen in W(D/W~10‐12 @300℃).

Hydrogen trapping at irradiation‐induced defects is suggested.

Irrad. W

hydrogen

Non‐irrad. W Irrad. W

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

Very low solubility limit in bulk

Strong trapping at vacancy is suggested.

H2 （in vacuum）

Why does hydrogen retention increase after irradiation?

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To observe deuterium trapping at vacancy clusters by positron annihilation spectroscopy.

Purpose of this study

TungstenDeuterium

Vacancy cluster

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Neutron irradiation

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

HFIR @ORNL8x1020 n/cm2 (~0.3 dpa)~300 ℃ × 48 days

Heat treatment process

In D2 gas atmosphere (~ 0.1 MPa) orIn vacuum (~10‐4 Pa）300 ℃ × 100 h

Annealing in D2

Neutron irradiation

Annealing in vacuum

Annealing in D2

As‐prepared ‐ ‐ ‐ ‐

As‐prepared Annealed in D2 ✔ ‐ ‐ ‐

As‐irrad. ‐ ✔ ‐ ‐

Irrad. Annealed in vacuum ✔ ✔ ‐

Irrad. Annealed in D2 ✔ ‐ ✔

Diffusion length of deuterium in bulk : ~0.3 mm

5 Specimens

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21

positron

E1 = mc2 = 511 keV E2 = mc2 = 511 keV

electron

Positron annihilation spectroscopy

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Positron source. 22NaCl are sealed by Kapton film.

22NaCl (2‐3mm in diameter)

~ 10mm

Identical samples. ~10x10x0.5mm.

Positron annihilation spectroscopy; samples and source

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Positron source sandwiched by 2 samples.

Positron annihilation spectroscopy; detectors

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e+

e+Potential

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

Calculated

Positron

lifetim

e (ps)

Positron lifetime, τ = dr 𝑛 𝑟 𝑛 𝑟 𝑔 𝑟‐1

Calculated positron lifetime in Tungsten

Positron annihilation spectroscopy; lifetime

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RC1

RC2

CN1

CN2

CN3

0100

150

200

250

300

350

400

450

500

Posi

tron

life

time

[ps] V13

V17

V37

0

20

40

60

Inte

nsity

of

2 [%

]

As‐prepared As‐prepared→Annealed in D2

As‐Irrad.

τave

τ1

τ2

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

真空焼鈍では、陽電⼦寿命に変化無し

照射→真空焼鈍

照射→D2焼鈍

D2焼鈍では、τave , τ2, τ1が短くなった


Calculated positron lifetime value in vacancy cluster in tungsten

bulk

Positron lifetime

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RC1

RC2

RCN1

RCN2

RCN3

0100

150

200

250

300

350

400

450

500

Posi

tron

life

time

[ps]

Bulk

V1

V4

V9

V13

V17

V37

0

20

40

60

Inte

nsity

of

2 [%

]

No change after annealing in vacuum

Decrease of τave , τ2, τ1 after annealing in D2

τave

τ1

τ2

As‐prepared As‐prepared→Annealed in D2

As‐Irrad. Irrad. →Annealed in vacuum

Irrad. →Annealed in D2

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

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480 490 500 510 520 530 540100

101

102

103

104

105

106

Measurement of momentum of e‐‐e+ pair by Doppler effect

e- e+

pZ : momentum of e‐‐e+ pair

2122

01ZcpcmE

22

02ZcpcmE

511 Hz

> 511 Hz < 511 Hz

Coun

ts

γ-ray energy (keV)

511 keV

( m0c2 = 511 keV )

Copper

TungstenMomentum distribution : Identical to element.

Chemical environment at e+ trapping sites is obtained.

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0 5 10 15 20 25 30 350.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3 RCN1 RCN2 RCN3

D1

Ratio

to bulk tung

sten

Momentum [x10‐3 m0c]

Irrad. → Annealed in vacuum

As-Irrad.

Irrad. → Annealed in D2

Low momentum

High momentum

Coincidence Doppler broadening measurement

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0.58 0.60 0.62 0.64

0.006

0.007

0.008

0.009

0.010

Low momentum component

High

mom

entu

m c

ompo

nent

As‐preparedAs‐prepared → Annealed in D2

As‐Irrad.

Irrad. →Annealed in vacuum


Correlation of Low‐ & High‐ momentum

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0.58 0.60 0.62 0.64

0.006

0.007

0.008

0.009

0.010

As‐Irrad. Electron‐irradiation: 8.5 MeV, ~100℃ , ~1x10‐3 dpa

As‐preparedAs‐prepared → Annealed in D2

As‐Irrad.





Low momentum component

High

mom

entu

m c

ompo

nent

Correlation of Low‐ & High‐ momentum

20/21

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

Deuterium trapping at irradiation‐induced defects was successfully observed.

As‐Irrad. Annealed in vacuum

No change of vacancy cluster

Deuterium is inside vacancy cluster

Annealed in D2 gas

Summary

T. Toyama et al., J. Nucl. Mater., 499 (2018) 464.

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deuterium trapping at irradiation‐induced defects in...

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