International Workshop on

“Influence of atomic displacement rate, neutron spectrum and irradiation temperature

on radiation-induced ageing of power reactor components”,

October 4, 2005, Ulyanovsk, Russia

M. Hasegawa1 ） , Y. Nagai1), T. Toyama1),

Zheng Tang1), Y. Nishiyama2), M. Suzuki2),

T. Ohkubo4) and K. Hono4)

1) Tohoku University, Japan

hasegawa@imr.tohoku.ac.jp

2) Japan Atomic Energy Research Institute (JAERI), Japan

3) National Institute for Materials Science (NIMS), Japan

Effects of irradiation flux on embrittlement mechanisms on reactor pressure vessel steel:

Cu nano-precipitates and defects studied by positron annihilation and 3 dimensional atom probe

Outline

RPV Surveillance Test Specimens

1) Introd. to Positron Annihilation (PA*))

2) Flux EeffctsCalder Hall Reactor vs JMTR

(PA & 3D-AP**))

* ) Positron Annihilation (PA)**) 3 Dimensional Atom Probe (3D-AP)

e+

2

1

0.511 MeV

0.511 MeV

1.27 MeV0

22Na

(a) Injection and thermalization, (b) Diffusion, (c) Trapping, (d) Annihilation.

(a)

(b)

(c)

(d)

Cu Fe

e+ annihilates with a Cu electron

e+: Self-Searching Probe22Na

Cu Nano-Precipitates

Cu Nanovoid

Cu-V Complex

1

2

Positron Quantum Dot StatePositron Density

Cu5Cu1

Cu59

Diameter ~ 1 nm

Embedded ParticlesEmbedded Particles

- Cu Precipitates in Dilute Fe-Cu Alloys -- Cu Precipitates in Dilute Fe-Cu Alloys -

Positron Density DistributionsPositron Density Distributions

Fe

Cu

Super-Cell:1024 atom sites

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

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

Fe

Cu

CDB CDB Ratio Spectra

γ1 γ2

Ge detector

Coincidence Doppler Broadening : CDB

e+e-

22

01LcpcmE

22

02LcpcmE

pL : Electron Momentum along the Emitted γ–ray

Ge detector

Normalize to Pure Fe

0 10 20 30 40

0.5

1

1.5

2

pL [10-3 m0c]R

atio

to

Pu

re F

e

Pure Cu

Pure Fe As-irrad.

0 10 20 30 40

102

103

104

105

106

Pure Fe Pure Cu Pure Fe As-irrad.

pL [10-3 m0c]

Cou

nts

Low High Low High

Low Momentum Region : Vacancy type defects

High Momentum Region : Cu Nano-Precipitates

Cu 3d10

Electrons

0 10 20 30 400.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Rat

io t

o pu

re F

e

PL [10-3m0c]

Fe-0.3wt%Cu

pure Cu

As irradiated

τ1 = 165ps : ~ monovacancies(V1)τ2 = 405ps (51%) nanovoids (~V30)

Vacancy & nanovoid covered with Cu atoms

0 10 20 30 400.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Rat

io t

o pu

re C

uPL [10-3m0c]

pure Fe

As irradiated

Fe-0.3wt%Cu

Fe-0.3wt%Cu: CDB Ratio Curves neutron-irrad.: 8.3×1018n/cm2, 100C

Cu 3d Peak

Almost Flat

Vac. Type Defects Vac. Type Defects

No Fe Valley

Pure Fe

Pure Cu

As-Irrad.As-Irrad.

Normalized to Fe Normalized to Cu

0 10 20 30 40 50 60

100

200

300

400 V51

V59

V27

V15

V9

V5

V2 ([100])

V2 ([111])

V1

Bulk

Pos

itron

Life

time

(ps)

Number of Vacancies

0

2

4

6

8

B

indi

ng E

nerg

y (e

V)

Positron Lifetime and Binding Energy in Vacancy Clusters in Fe

V2 [111] V2 [100]

V9V5

V15

Positron Lifetime

Positron Binding Energy

Neutron Flux Effects on the Embrittlement Mechanisms ?

Neutron Flux (n/cm2/s)

101210111010109108

MTRBWR·PWR

Calder Hall-Type Reactor

10141013

Em

brit

tlem

ent

脆化

量

照射量の平方Fluence

Total

Matrix Defects

Cu Nano Precipitates

Soneda (2003)

Embrittlement Mechanisms: Fluence Evolution

C Si Mn P S Ni Cr Cu Mo Al N

0.10 0.23 1.1 0.014 0.015 0.17 0.0960.14-0.19

0.054 0.027 0.006

Post-Weld Heat Treatment : 600ºC, 4h.

C-Mn base Ferritic Steel wt.%

CHR Surveillance JMTR*

Flux (n/cm2-s) 4.2×108 2.2×1012

Fluence (n/cm2) 2.7×1017 2.2×1018

Irradiation Period 20 years 7 days

Irradiation Temperature (ºC) 240 224*Japan Materials Testing Reactor

Low flux High flux

Irradiation Conditions

Calder Hall Reactor (CHR) in Tokai*, Japan: Surveillance Test Specimen

* In –Service (1966 – 1998)

CHRSurveillance

4.2x108n/cm2·s

JMTR3.6x1012n/cm2·s

Irradiated at 240ºC

Strengthening by IrradiationCHR vs. JMTR

0.5 0.55 0.6

0.004

0.006

0.008

0.01

0.012

Low Momentum Fraction

Hig

h M

omen

tum

Fra

ctio

n

CDB (Low, High) Momentum Correlation

Thermal Ageing:Cu Nano Precipitates

Vacancy-Type Defects

Pure Cu

Pure Fe

Unirrad.

Pure Fe irrad.

JMTR

aged at 300ºC, 70,000h

CHR Surveillance

aged at 400ºC, 70,000h

0

100

200

Posi

tron

Lif

etim

e [p

s]

0

20

40

60

80

100

I 2 [

%]

Positron Lifetime

CHR Surveillance

JMTR

Unirrad.

300ºC, 70,000h

400ºC, 70,000h

V1

bulk Fe

V1τ2

τav

τ1

I2

10nm

10n

m

30nm

Cu

Mn

Ni

Si

CHR Surveillance

10nm

10n

m

30nm

JMTR

3D-AP Mapping : As-irrad.

200 300 400 500 600 700

100

120

140

160

Hv

Unirrad.

surveillance JMTR

As-irrad.

Annealing Temperature [°C]

Isochronal Annealing: CDB & Hardness200~700ºC, 30 min.

Vickers Microhardness

0.9 1 1.1 1.20.5

1

1.5

2

Low Momentum Fraction

Hig

h M

omen

tum

Fra

ctio

n

As-irrad.

300°C

400°C

As-irrad.

400°C

Surveillance JMTR

500°C

500°C

Pure Fe

Pure Cu

Unirrad.

300°C

600°C

600°C

650°C

Pure Fe（ As-irrad.）

CDB Low/High Momentum Correlation

Recovery of Vacancy-Type Defects

Recovery of Cu Nano- Precipitates

0.9 1 1.1 1.20.5

1

1.5

2

Low Momentum Fraction

Hig

h M

omen

tum

Fra

ctio

n

As-irrad.

300°C

400°C

As-irrad.

400°C

Surveillance JMTR

500°C

500°C

Pure Fe

Pure Cu

Unirrad.

300°C

600°C

600°C

650°C

CHR SurveillanceJMTR

0.9 1 1.1 1.20.5

1

1.5

2

Low Momentum Fraction

Hig

h M

omen

tum

Fra

ctio

n

As-irrad.

300°C

400°C

As-irrad.

400°C

Surveillance JMTR

500°C

500°C

Pure Fe

Pure Cu

Unirrad.

300°C

600°C

600°C

650°C

CHR SurveillanceJMTR

3D-AP Mapping : Annealed at 450ºC for 0.5h

10nm

10n

m

30nm

Cu

Mn

Ni

Si

CHR Surveillance

10nm

10n

m

30nm

JMTR

As-irradiated State

CHR-Surveillance : Cu nano-precipitates

JMTR : Almost no Cu precipitates but vacancy-type defects

Post-Irradiation Annealing

CHR-Surveillance : The Cu nano-precipitates anneal out and Hv recovers at 650ºC.

JMTR : The vacancy-type defects recover at 450ºC. The Cu precipitation is not significant.

CHR-Surveillance : Low Flux JMTR : High Flux

Positron Annihilation and 3D-AP Analysis for RPV SteelsSummary : CHR vs. JMTR

Marked Flux Effects Low flux irradiation in CHR :

Strengthning is caused by enhanced Cu precipitation at very low doses.

High flux irradiation in JMTR : Almost the same strengthening is due to matrix defects but not to Cu precipitates.

LEAP 　 in Hasegawa Lab. (Oarai Center)（ Local Electrode Atom Probe: LEAP 　 By IMAGO ）

Specimen

Local Electrode

Position SensitiveDetector

High Field Region

Conventional Atom Probe(Energy-Compensating Type)

LEAP Atom Probe

10x10x60 nm

3x105 Atoms, 6 hours

60x60x170 nm

2x107 Atoms, 1hour

Cu Precipitates: Fe-1.0wt%Cu Aged at 475C for 10h