Deuterium trapping at irradiationinduced defects in tungsten studied - - PowerPoint PPT Presentation

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 2019 NIFS, 2019/June/18‐20

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

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Tokyo Oarai NIFS Sendai

JMTR JOYO Pacific Ocean Lake Natsumi Japan Atomic Energy Agency, Oarai Site HTTR ⇒

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

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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

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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.

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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 Tungsten Deuterium Vacancy cluster

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Neutron irradiation

Pure tungsten (4N) φ6×0.5 mm disk  900 ℃×1h  1300 ℃×0.5h (re‐crystallization) HFIR @ORNL 8x1020 n/cm2 (~0.3 dpa) ~300 ℃ × 48 days

Heat treatment process

In D2 gas atmosphere (~ 0.1 MPa)

• r

In 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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2 1

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 lifetime (ps)

Positron lifetime, τ = dr 𝑜 𝑠 𝑜 𝑠 𝑕𝑠

‐1

Calculated positron lifetime in Tungsten

Positron annihilation spectroscopy; lifetime

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RC1 RC2 CN1 CN2 CN3

100 150 200 250 300 350 400 450 500

Positron lifetime [ps]

V13 V17 V37

20 40 60

Intensity 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

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

Calculated positron lifetime value in vacancy cluster in tungsten

bulk

Positron lifetime

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RC1 RC2 RCN1 RCN2 RCN3

100 150 200 250 300 350 400 450 500

Positron lifetime [ps]

Bulk V1 V4 V9 V13 V17 V37

20 40 60

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

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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480 490 500 510 520 530 540 100 101 102 103 104 105 106

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

e- e+

pZ : momentum of e‐‐e+ pair

2 1

2

2 1 Z

cp c m E   2

2 2 Z

cp c m E  

511 Hz > 511 Hz < 511 Hz

Counts γ-ray energy (keV)

511 keV

( m0c2 = 511 keV )

Copper Tungsten Momentum distribution : Identical to element.  Chemical environment at e+ trapping sites is

• btained.

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5 10 15 20 25 30 35 0.3 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 tungsten 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 momentum component As‐prepared As‐prepared → Annealed in D2 As‐Irrad.

• Irrad. →Annealed

in vacuum

• Irrad. →Annealed

in D2

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

• Irrad. →Annealed

in vacuum

• Irrad. →Annealed

in D2

• Irrad. →Annealed in D2
• Irrad. →Annealed in vacuum

Low momentum component High momentum component

Correlation of Low‐ & High‐ momentum

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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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