9th International Workshop on Hydrogen Isotopes in Fusion Reactor MaterialsSalamanca, Spain, June 2 - 3, 2008

1

Simulation experiments Simulation experiments on neutron damage of on neutron damage of tungsten tungsten

M. Fukumoto, H. Kashiwagi, Y. Ohtsuka, Y. Ueda　　　 Graduate School of Engineering, Osaka University

M. Taniguchi, T. Inoue, K. Sakamoto, J. Yagyu, T. Arai　　　 Japan Atomic Energy Agency

I. Takagi 　　　 Graduate School of Engineering, Kyoto University

T. Kawamura, N. Yoshida　　　 Interdisciplinary Graduate School of Engineering Sciences, Kyushu University

2 Purpose of this study & Outline of this talkPurpose of this study & Outline of this talk

Purpose of this study Investigation of hydrogen isotope behavior in damaged W

Outline of this talk Blister formation

Effects of radiation damage on blister formation Deuterium retention

D concentration in damaged W Effects of annealing on D retention TDS profiles as a function of fluence Preliminary TMAP7 simulation

3 Experimental sequenceExperimental sequence

W samples Hot rolled and stress relived Mirror-polished less than 0.01 m

roughness

1. Damage Creation Ion energy: 300 and 700 keV H-

Pulse duration: 1 s every 60 s (~1000 shots) Temperature: below 473 K (to avoid recovery of defects)

2. H-C irradiation Ion energy: 1.0 keV

(include H+, H2+, and H3

+)

Fluence: 7.5 x 1024 H+/m2

Carbon: ~0.8 % Temperature: 473 K

3. SEM observation

2. D implantation Ion energy: 1.0 keV

(include D+, D2+, and D3

+)

Fluence: 0.5 x 1024 ~ 8.0 x 1024 D+/m2

Temperature: 473 K

3. SIMS/NRA measurements NRA was used for absolute calibration

4. TDS measurements 1 K/s, R.T. ~ 1100 K

Blister formationD depth distributionD desorption

1.5. Annealing 673 K, 1 h 1173 K, 1 h

4 Effects of radiation damage on blister formationEffects of radiation damage on blister formation

The number of blisters was decreased with increasing radiation damage The blisters with diameter of 20m or

less was decreased

（ a ） 0dpa

（ b ） 0.3dpa

（ c ） 3.5dpa

20m

100

101

102

103

104

Num

ber of

Blis

ters

(m

m-2

)

1 10 100Blister Size (m)

0 dpa

0.3 dpa

3.5 dpa

20m

20m

Fluence: 7.5 x 1024 H+/m2

Temp.: 473 K Carbon: ~0.8 %

5 Mechanism of blister formationMechanism of blister formation

trapped at grain boundaries→blister formation

Undamaged W 700keV H- damaged W

decrease of H trapped at grain boundaries

dam

age

d z

one

~1

.5

m

H was not accumulate at the grain boundaries within radiation damage Small blisters (<20 m) were decreased

Large blisters were formed since radiation damage was not produced

6 D distribution as a function of fluence (D distribution as a function of fluence (473 K473 K))

D conc. near surface was saturated at ~5.0x1023 D+/m2

D conc.: ~0.9x1027 D/m3

Trap density 0.014 traps/W

Production rate 0.014 traps/W·dpa

Similar to 800 MeV p damage* ~0.01 traps/W·dpa

D conc. at ~1.0 µm was not saturated up to 8.0x1024 D+/m2

* B.M. Oliver et al., J. Nucl. Mater. 307-31

1 (2002) 1418.

Fluence: 0.5 ~ 8.0 x 1024 D+/m2

Temp.: 473 K Damage: ~4.8 dpa

5

4

3

2

1

0

Dis

plac

emen

t (d

pa)

2.52.01.51.00.50.0Depth (m)

1.0

0.8

0.6

0.4

0.2

0.0

D C

once

ntra

tion

(x10

27 D

/m3 )

Displacement

5.0 x 1023 D+/ m2

2.0 x 1024 D+/ m2

5.0 x 1024 D+/ m2

8.0 x 1024 D+/ m2

7 Effects of 673 K annealing on D trappingEffects of 673 K annealing on D trapping

D concentration was decreased by annealing at 673 K for 1 h. Change of surface density

0.8x1027 => 0.6x1027 D/m2

~20 % reduction

Most of self-interstitials could b

e eliminated*. Vacancy type defects are still r

emained.

* M. J. Attard et al., Phys. Rev. Lett., 19, (1967) 73.

Fluence: 5.0 x 1024 D+/m2

Temp.: 473 K Damage: ~4.9 dpa

5

4

3

2

1

0

Dis

plac

emen

t (d

pa)

2.52.01.51.00.50.0Depth (m)

1.0

0.8

0.6

0.4

0.2

0.0

D C

once

ntra

tion

(x10

27 D

/m3 ) Displacement

Unannealed

Annealed at 673 K for 1 h

8 Effects of 1173 K annealing on D trappingEffects of 1173 K annealing on D trapping

D conc. was also decreased by annealing at 1173K for 1h. Change of surface density

0.9x1027 => 0.2x1027 D+/m2

~80 % reduction (near surface)

Single vacancies could be annealed by this heat treatment* Voids formation could be still t

ake place**

* D. Jeannotte et al., Phys. Rev. Lett., 19, (1967) 232.

** H. Eleveld et al., J.N.M., 212-215, (1994) 1421.

Fluence: 5.0 x 1023 D+/m2

Temp.: 473 K Damage: ~4.4 dpa

5

4

3

2

1

0

Dis

plac

emen

t (d

pa)

2.52.01.51.00.50.0Depth (m)

1.0

0.8

0.6

0.4

0.2

0.0

D C

once

ntra

tion

(x10

27 D

/m3 ) Displacement

Unannealed

Annealed at 1173 K for 1 h

9 TDS spectra of two samplesTDS spectra of two samples

Fitted by Gaussian functions. Peak 1: ~770 K Peak 2: ~860 K Peak 3: ~920 K

Fluence: 5.0 x 1024 D+/m2

Temp.: 473 K

3.0

2.5

2.0

1.5

1.0

0.5

0.0

D2

Rel

ease

Rat

e (x

1018

D2/

m2 s)

11001000900800700600500Temperature (K)

TDS Profile Total Fit

Peak 1 ( 770 K)～

Peak 2 ( 860 K)～

Peak 3 ( 920 K)～

Undamaged W ~4.8 dpa damaged W

3.0

2.5

2.0

1.5

1.0

0.5

0.0

D2

Rel

ease

Rat

e (x

1018

D2/

m2 s)

11001000900800700600500Temperature (K)

TDS Profile Total Fit

Peak 1 ( 770 K)～

Peak 2 ( 860 K)～

Damaged W has much higher D desorption

10 Fluence dependence of each peakFluence dependence of each peak

Damaged samples Peak 1 (~770 K)

one order of magnitude higher than undamaged sample

increased with fluence Peak 2 (~860 K)

same as undamaged sample

constant with fluence Peak 3 (~920 K)

only damaged samples increased with fluence

D was trapped at the vacancies (Peak 1) and voids (Peak 3)

Fluence: 0.5 ~ 8.0 x 1024 D+/m2

Temp.: 473 K Damage: ~4.8 dpa

1.0

0.8

0.6

0.4

0.2

0.0

Ret

aine

d D

eute

rium

(x1

021 D

/m2 )

1086420Incident Fluence (x1024 D+/ m2s)

Peak 1 (Damaged W)

Peak 2 (Damaged W)

Peak 3 (Damaged W)

Peak 1 (Undamaged W) Peak 2 (Undamaged W)

11 D distribution as a function of fluence (D distribution as a function of fluence (673 K673 K))

In the case of 673 K implantation, trapping and annealing of damage were simultaneously took place

Radiation damage around ~1.1 m could be annealed during implantation

Fluence: 0.5 ~ 5.0 x 1024 D+/m2

Temp.: 673 K Damage: ~3.2 dpa

4

3

2

1

0

Dis

plac

emen

t (d

pa)

2.52.01.51.00.50.0Depth (m)

1.0

0.8

0.6

0.4

0.2

0.0

D C

once

ntra

tion

(x10

27 D

/m3 ) Displacement

5.0 x 1023 D+/ m3

2.0 x 1024 D+/ m3

5.0 x 1024 D+/ m3

12 D distribution simulated by TMAP7D distribution simulated by TMAP7

Simulation conditions Trap energy: 1.34eV(vacancies)*

2.1eV (voids)* Diffusion coeff.: Fraunfelder’s Trapping rate: De-trapping rate: Distribution: TRIM-88 Trap density:

0.014 traps/W·dpa

Other conditions: same as exp.

D trapping proceeds from surface trapping sites

All trap sites were filled less than 6.0 x 1022 D+/m2

Much lower than exp. results (8.0 x 1024 D+/m2)

TMAP7 results did not agree with exp. results

*M. Poon et al., JNM, 374 (2008) 390.

2sD

4.0

3.0

2.0

1.0

0.0

(a) 1.34 eV traps

7.5x1021

D+/ m

2s

1.5x1022

D+/ m

2s

3.0x1022

D+/ m

2s

4.0

3.0

2.0

1.0

0.01.41.21.00.80.60.40.20.0

Depth (m)

(b) 2.1 eV traps

4.5x1022

D+/ m

2s

6.0x1022

D+/ m

2s

D C

once

ntra

tion

(x10

27 D

/m3 )

kT

Etexp0

13 ConclusionConclusion

Blister Formation Hydrogen isotopes were not accumulate at the grain boundaries within

damaged zone

Deuterium depth profiles D conc. near surface was saturated at the fluence of 5.0 x 1023 D+/m2

D conc. near surface was 0.9 x 1027 D/m3

Damage production rate was similar to 800 MeV p irradiated W D conc. at ~1.0 m was increased but not saturated up to the fluece of

8.0 x 1024 D+/m2

Preliminary TMAP7 simulation did not reproduce exp. Results

TDS measurements D was trapped at the vacancies and voids produced with high-energy i

on irradiation

14 Experimental sequenceExperimental sequence

1. Damage Creation Ion energy: 300 and 700 keV H-

Pulse duration: 1 s every 60 s (~1000 shots) Temperature: below 473 K (to avoid recovery of defects)

2. H-C irradiation Ion energy: 1.0 keV

(include H+, H2+, and H3

+)

Fluence: 7.5 x 1024 H+/m2

Carbon: ~0.8 % Temperature: 473 K

3. SEM observation

W samples Hot rolled and stress relived 99.99 at% Mirror-polished less than 0.01 m roughness

2. D implantation Ion energy: 1.0 keV

(include D+, D2+, and D3

+)

Fluence: 0.5 x 1024 ~ 8.0 x 1024 D+/m2

Temperature: 473 K

3. SIMS/NRA measurements NRA was used for absolute calibration

4. TDS measurements 1 K/s, R.T. ~ 1100 K

15 Outline of this talkOutline of this talk

Background and Purpose of this study

Experimental sequence

Experimental results Blister formation

Effect of radiation damage on blister formation Deuterium retention

D concentration in damaged W Effects of annealing on D retention TDS profiles as a function of incident fluence Preliminary TMAP7 simulation

Conclusion

16 Background and Purpose of this studyBackground and Purpose of this study

Background of this study In ITER, W is a candidate PFM for diverter region

Extensive studies have been made for “undamaged” W In DT fusion phase, fast neutrons are generated

W is simultaneously irradiated by hydrogen isotopes and neutrons

Interaction between radiation-induced defects and hydrogen isotope in W materials is very important

Trapping, release, and diffusion in damaged W are not clear

Purpose of this study Investigation of surface morphology and deuterium behavior in

damaged W Blistering, D depth distribution and desorption characteristics

17

4mBlister GapRedeposition layer of W

sputtered by FIB Surface

10m

Fabrication and measurementwere made by FIB (30 keV Ga)

A blister with diameter of 25 m had a blister gap at 5 m in depth.

A large blister with diameter of approximately 100 m had a blister gap at 10 m in depth.

A.A. Haasz et al.: The effect of ion damage on deuterium trapping in tungsten, J. Nucl Mat., 266-269, pp.520-525(1999).

5 m

10 m

Relationship between blister diameterRelationship between blister diameterand depth of blister gapsand depth of blister gaps

25m

100m

18

12

10

8

6

4

2

0

Dep

th o

f Blis

ter G

aps

(m

)120100806040200

Diameter of Blisters (m)

700keV H-

300keV H-

0dpa 300keV, 3.7dpa

ブリスタの直径と亀裂深さの関係ブリスタの直径と亀裂深さの関係

~ 1.5 m

~ 5.5 m0dpa

300keV,700keV H- による照射損傷で、深さ 1.5m 付近の亀裂が減少 300keV H-: 損傷の範囲より深い 700keV H-: 損傷の範囲内

300keV, 3.7dpa

照射損傷により減少するブリスタ直径

照射損傷でも減少しないブリスタ直

径

~ 1.0 m

19 Effect of damaged zone on blister formationEffect of damaged zone on blister formation

The blisters less than 20 m in diameter were decreased with an increase in damaged zone 300keV H- ： decrease of small blisters was low 700keV H- ： small blisters were suppressed

（ a ） 0dpa

（ b ） 300 keV, 3.7 dpa

（ c ） 700 keV, 3.5dpa

100

101

102

103

104

Num

ber of

Blis

ters

(m

m-2

)

1 10 100Blister Size (m)

0 dpa

damaged by300 keV H-

damaged by700 keV H-

20m

20m

20m

Fluence: 7.5 x 1024 H+/m2

Temp.: 473 K Carbon: ~0.8 %