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Positron annihilation study of neutron-irradiated nuclear reactor pressure vessel (RPV) steels

and their model alloys

Y. Nagai1, A. Kuramoto1, T. Toyama1, T. Takeuchi2, M. Hasegawa3

1The Oarai Center, Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313, Japan

2Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan3Institute for Materials Research, Tohoku University, Sendai, Miyagi 980-8577, Japan

hasegawa@imr.tohoku.ac.jp

PPC-10 Smolenice Castle, Slovakia

Sept. 5 - 9, 2011

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Outline

1) Back ｇ round

2) Fe-Cu Model Alloys: Cu Nano-Clusters (Precipitates) a) Size: 2D-ACAR Momentum Smearing

b) Number Density: AMOC

3) RPV Steel: Surveillance Test Specimen MaterialsMechnisms: Nanostructural Features

Irradiation Embrittlement & Hardening1st & 2nd Generation A533B

Post Irradiation Annealing (PIA) Experiments

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Origin of irradiation-induced embrittlement

Nuclear Reactor Pressure Vessel (RPV) Steel

dislocation

1) Solute Nano-Clusters

3) P Segregation at Grain Boundary

Grain boundary

2) Matrix Defects (vacancy-type defects, dislocation loops, ···)

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Local electrode Laser

Vtotal

Vextraction

Position sensitive ion detector

Time of Flight Mass～

100nm

ZY

X

Needle sample

Laser-Assisted Local Electrode Atom Probe

4Energy-compensated type (with “Reflectron”)

5

LEAP 3D-Atom Probe

60x60x170 nm

2x107 Atoms, 1houre+ 　 Self-Searching:

Cu Nano-Particles 　 in Fe

Positron Quantum-Dot Confinement in a Precipitate of 59 Cu Atoms

Density isosurface of a quantum-dot confined positron in a Cu59 in Fe matrix. The isodensity value is 0.5% of the maximum.

1nm

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2a) Cu Nano-Precipitates (Clusters) : Size

2D-ACAR: Momentum Smearing

Z. Tang et al.:J. Phys.: Condens. Matter 20 (2008) 445203,

Size-dependent momentum smearing effect of positron annihilation radiation

in embedded nano Cu clusters

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2b) Cu Nano-Precipitates (Clusters) : Number Density

AMOC: Time Evolution of HMCF (W-Parameter) 　　 Trapping Model

A. Inoue et al.: Phys. Rev. B83 (2011) 115459

Fig.1

0 10 20 30 40

1

1.5

2

Ratio

to P

ure F

e

pL [10-3 m0c]

Pure Cu 0.1h 0.2h 2h

2h

30nm

10nm

0.1h

0.2h

Fe-0.88at.%Cu: Thermal Aging @550˚C

CDB Ratio Curve 3D-AP

2h: Complete e+ Quantum-Dot Confinement

0 0.2 0.4 0.6 0.8 10.08

0.1

0.12

0.14

0.16

0.18

pure Fe pure Cu 0.1h 0.2h 2h

Time [ns]

W-p

aram

eter

Time Evolution of CDB HMCF (W-Parameter)

Pure Fe

Pure Cu

Positron Age-Momentum Correlation (AMOC)

Using digital oscilloscope ： Time resolution ~170ps

Number Density (×1017 cm-3)3D-AP e+

Aging Time (h) 　　　 SizeDiameter (nm)

0.10.22

0.91.12.5

0.151.21.9

0.611.41.8

Number density estimated by positron annihilation

Time dependent HMCF 　（ W-parameter)

Positron trapping rate

Number density

3) RPV Steel: Surveillance Test Specimen Materials

1St & 2nd Generation A533B

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PIA: 1st Gen A533B Kuramoto et al.: Submitted to J. Nucl. Mater.

Fluence Dependence Takeuchi et al. : J. Nucl. Mater. 402 (2010) 93.

Irradiation –Induced Embrittlement (Hardening) Mechanisms

Post Irradiation Annealing (PIA) Experiments

wt.% Chemical Composition

A533B C Si MnP S NiCrCu Mo1st. Gen. 0.19 0.30 1.300.015 0.010 0.680.170.16 0.53

2nd. Gen. 0.19 0.19 1.430.004 0.001 0.650.130.04 0.50

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Reactor Pressure Vessel (RPV) Steel: A533B

JMTR Irradiation

Fluence: 3.9x1019n/cm2 (0.061dpa)Flux: 1.8x1013n/cm2 ・ sec

Temperature: 2902C

Purified: Cu, P, S

Annealing Behavior of Average Positron Lifetime 1st. Gen.(0.16Cu) & 2nd. Gen.(0.04Cu) A533B, 3.9×1019 n/cm2

As-irrad.

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200 300 400 500 600100

120

140

160

180

Annealing Temperature [℃ ]

Ave

rage

Pos

itron

Life

time

[ps] V1

Unirrad. (1st. Gen.)

Fe bulk

Unirrad. (2nd. Gen.)

1st.Gen. (0.16Cu)2nd.Gen. (0.04Cu)

1 1.02 1.04 1.06

1

1.2

1.4

1.6H

igh

Mom

entu

m C

ompo

nent

Fra

ctio

n

Low Momentum Component Fraction

Pure Fe

Pure Cu

Pure Fe as-irrad.

1st.Gen. (0.16Cu)2nd.Gen. (0.04Cu)

CDB HMCF-LMCF Correlations 1st. Gen. (0.16Cu) & 2nd. Gen. (0.04Cu) A533B, 3.9×1019 n/cm2

As-irrad. (1st. Gen. )

400 °C

450 °C

600 °C

300 °C

300 °C

As-irrad.(2nd. Gen. )

600 °C

Unirrad.(1st. Gen. )

550 °C

Unirrad.(2nd. Gen. ) 450 °C

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0.5 0.55 0.6 0.650.004

0.006

0.008

0.01

0.012

0.014

LMCF

HMCF

As-irrad.

As-irrad.

Unirrad.

500Pure Cu

Pure Fe

500

Unirrad.

Neutron Irradiation: 8.3×1018n/cm2 (1.2×10-2dpa, ~100ºC)Fe-Cu Model Alloys ( 0.3wt.%Cu, 0.05wt.%Cu )

0.3Cu

0.05Cu

As-irrad. 350 °C 400 °C

10nm

Si

Mn

P

Ni

Cu

Atom Maps of the Solutes: Annealing Behavior (As-irrad.~400℃)1st. Gen. (0.16Cu) A533B, 3.9×1019 n/cm2

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Atom Maps of the Solutes: Annealing Behavior (As-irrad.~350 ℃)2nd. Gen. (0.04Cu) A533B, 3.9×1019 n/cm2

300 ℃ 350 ℃As-irrad.

Si

Mn

P

Ni

Cu10nm

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As-ir-

rad.

350 400 450 50075

80

85

90

95

100

Annealing Temperature [°C]

Com

posi

tion

[%]

Com

posi

tion

[%]

Average Chemical Compositions of Solute Clusters3.9×1019 n/cm2

Annealing Temperature [°C]As-irrad. 300 350 400

75

80

85

90

95

100

Cu,Mn,Si,NiothersFe,

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1st. Gen. (0.16Cu) A533B 2nd. Gen. (0.04Cu) A533B

Cu

Mn

SiNi

Fe

200 300 400 500 6000

1

2

Rad

ius

of G

yrat

ion

[nm

]

200 300 400 500 60002468

10

Num

ber D

ensi

ty[1

023/m

3 ]

200 300 400 500 60002468

10

Vol

ume

Frac

tion

[×10

-3]

Annealing Temperature [℃]

Radius of Gyration (rg), Number Density (Nd) & Volume Fraction (Vf)A533B, 3.9×1019 n/cm2

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rg

Nd

Vf

Radius of Gyration

Number Density

Volume Fraction

1st. Gen.

2nd. Gen.

1st. Gen. (0.16Cu)

CuMnSiNi Clusters

2nd. Gen. (0.04Cu)

MnSiNi Clusters

Hardening

Russell-Brown Model

200 300 400 500 600

0

20

40

60

80Δ

Hv

Annealing Temperature [℃]

ExperimentalEstimated Hardening from SCs

Annealing Behavior of Irradiation Hardening (∆Hv)1st. Gen. (0.16Cu) A533B, 3.9×1019 n/cm2

As-irrad.20

e+ : Vac-Defects

3D-AP: CuMnSiNi Clusters

0.8

1

1.2

1.4

Hig

h M

omen

tum

C

ompo

nent

Fra

ctio

n

Unirrad. (1st., 0.16Cu)Pure Fe

Unirrad. (2nd., 0.04Cu)

200 300 400 500 6000

20

40

60

80

ΔH

v

100

120

140

160

180

Ave

rage

P

ositr

on L

ifetim

e [p

s]

Unirrad. (1st., 0.16Cu)

Fe Bulk

V1

Unirrad. (2nd., 0.04Cu)

1st., 0.16Cu2nd., 0.04Cu

1

1.02

1.04

1.06

Low

Mom

entu

m

Com

pone

nt F

ract

ion

Unirrad. (1st., 0.16Cu)

Pure Fe

Unirrad. (2nd, 0.04Cu)

As-irrad.Annealing Temperature [°C]

1st. Gen. (0.16Cu)2nd. Gen. (0.04Cu)3.9×1019n/cm2

Av

LMCF

HMCF

Hv

What & How Positron Annihilation Can Say on RPV-Embrittlement Mechnisms ?

Unique Nano-Features 1) Cu-Rich Nano-Clusters Evolution, Recovery: Clear-Cut Info. Size, Number Density: Not Easy 2) Vacancy-Related Defects

Correlation: Mech. Properties Integration: Other Methods, such as 3D-AP, SANS,TEM

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Quantative !!