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

MoD‐PMI 2019 NIFS, 2019/June/18‐20 Deuterium trapping at irradiation‐induced defects in tungsten studied by positron annihilation spectroscopy T. Toyama 1) , K. Ami 2) , K. Inoue 1) , Y. Nagai 1) , K. Sato 3) , Q. Xu 3) , Y. Hatano 2) 1) Tohoku Univ. 2) Toyama Univ. 3) Kyoto Univ. 1/21

Japan Atomic Energy Agency, Oarai Site Sendai Pacific Ocean JOYO Oarai Tokyo NIFS 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: 2 H + 3 H  4 He + n Materials will be irradiated with plasma 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 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. 4/21

Why does hydrogen retention increase after irradiation? Exposure to hydrogen gas Non‐irrad. W Irrad. W Non‐irrad. W Irrad. W hydrogen Hydrogen retention is almost zero Hydrogen trapping at due to the very low solubility of irradiation‐induced defects is hydrogen in W suggested. (D/W~10 ‐12 @300 ℃ ). In this study, we show hydrogen trapping at irradiation‐ induced defects by using positron annihilation spectroscopy. 5/21

Why does hydrogen retention increase after irradiation? Very low solubility limit in bulk H 2 （in vacuum） Strong trapping at vacancy is K. Ohsawa et al., Phys. Rev. B suggested. 85 (2012) 094102. 6/21

Purpose of this study To observe deuterium trapping at vacancy clusters by positron annihilation spectroscopy. Tungsten Deuterium Vacancy cluster 7/21

Pure tungsten (4N) φ6 × 0.5 mm disk  900 ℃ × 1h  1300 ℃ × 0.5h (re‐crystallization) Heat treatment process Neutron irradiation HFIR @ORNL In D 2 gas atmosphere (~ 0.1 MPa) 8x10 20 n/cm 2 (~0.3 dpa) or In vacuum (~10 ‐4 Pa ） ~300 ℃ × 48 days 300 ℃ × 100 h Diffusion length of deuterium in bulk : ~0.3 mm 5 Specimens Annealing in Neutron Annealing in Annealing in D 2 irradiation vacuum D 2 As‐prepared ‐ ‐ ‐ ‐ ✔ As‐prepared  Annealed in D 2 ‐ ‐ ‐ ✔ As‐irrad. ‐ ‐ ‐ ✔ ✔ Irrad.  Annealed in vacuum ‐ ✔ ✔ Irrad.  Annealed in D 2 ‐ 8/21

Positron annihilation spectroscopy electron positron  2  1 E 1 = mc 2 = 511 keV E 2 = mc 2 = 511 keV 10/21

Positron annihilation spectroscopy; samples and source Identical samples. ~10x10x0.5mm. Positron source. 22 NaCl are sealed by Kapton film. 22 NaCl (2‐3mm in diameter) ~ 10mm 11/21

Positron annihilation spectroscopy; detectors Positron source sandwiched by 2 samples. 12/21

Positron annihilation spectroscopy; lifetime Calculated positron lifetime in Tungsten Calculated Positron lifetime (ps) e + T . Troev et al., Nucl. Inst. Meth. Phys. Res. B. 267 (2009) 535. Potential e + ‐1 Positron lifetime, τ = � dr 𝑜 �������� 𝑠 𝑜 �������� 𝑠 𝑕�𝑠� 13/21

Positron lifetime Intensity of  2 [%] 60 40 Calculated positron lifetime value in 20 vacancy cluster in tungsten 真空焼鈍では、 0 T. Troev et al., 500 陽電⼦寿命に Nucl. Inst. Meth. Phys. Res. B. 267 (2009) 535. 変化無し 450 τ 2 V 37 V 17 Positron lifetime [ps] 400 V 13 D 2 焼鈍では、 τ ave , τ 2 , τ 1 が 350 τ ave 短くなった 300 τ 1 250 200 150 寿命計算値︓ T. Troev et al., Nucl. 100 bulk Inst. Meth. Phys. Res. B. 267 0 (2009) 535. 照射 照射 →D 2 焼鈍 As‐prepared As‐prepared As‐Irrad. RC1 RC2 CN1 CN2 CN3 → 真空焼鈍 →Annealed in D 2 14/21

Positron lifetime Intensity of  2 [%] 60 40 20 0 No change 500 after annealing in vacuum 450 τ 2 V 37 V 17 Positron lifetime [ps] 400 V 13 Decrease of 350 τ ave , τ 2 , τ 1 after τ ave V 9 annealing in D 2 300 τ 1 V 4 250 200 V 1 150 Bulk 100 0 As‐prepared As‐prepared As‐Irrad. Irrad. Irrad. RC1 RC2 RCN1 RCN2 RCN3 →Annealed →Annealed →Annealed in D 2 in vacuum in D 2 15/21

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 effect p Z : momentum of e ‐ ‐e + pair cp cp   2  2  Z Z E m c E m c  2  1 e - e + 1 0 2 0 2 2 ( m 0 c 2 = 511 keV ) 511 Hz > 511 Hz < 511 Hz 10 6 Momentum distribution : Tungsten 10 5 Identical to element. 10 4 Copper Counts  Chemical environment 10 3 at e + trapping sites is obtained. 10 2 511 keV 10 1 10 0 480 490 500 510 520 530 540 γ-ray energy (keV) 17/21

Coincidence Doppler broadening measurement 1.3 Low momentum 1.2 RCN1 RCN2 1.1 Ratio to bulk tungsten RCN3 1.0 High momentum 0.9 0.8 Irrad. 0.7 → Annealed in D 2 As-Irrad. 0.6 0.5 Irrad. 0.4 → Annealed in vacuum 0.3 0 5 10 15 20 25 30 35 Momentum [x10 ‐3 m 0 c ] D1 18/21

Correlation of Low‐ & High‐ momentum As‐prepared 0.010 As‐prepared → Annealed in D 2 High momentum component 0.009 0.008 0.007 Irrad. →Annealed As‐Irrad. in D 2 0.006 Irrad. →Annealed in vacuum 0.58 0.60 0.62 0.64 Low momentum component 19/21

Correlation of Low‐ & High‐ momentum As‐prepared 0.010 As‐prepared → Annealed in D 2 High momentum component Electron‐irradiation: As‐Irrad. 8.5 MeV, ~100 ℃ , ~1x10 ‐3 dpa 0.009 Irrad. →Annealed in vacuum 0.008 Irrad. →Annealed in D 2 0.007 Irrad. →Annealed As‐Irrad. in D 2 0.006 Irrad. →Annealed in vacuum 0.58 0.60 0.62 0.64 Low momentum component 20/21

Summary Pure tungsten was neutron‐irradiated (~300 ℃ × 48 days), then annealed in vacuum or deuterium gas (300 ℃ × 100 h ） Annealed in D 2 gas As‐Irrad. Annealed in vacuum No change of Deuterium is inside vacancy cluster vacancy cluster Deuterium trapping at irradiation‐induced defects was successfully observed. T . Toyama et al., J. Nucl. Mater., 499 (2018) 464. 21/21