1. PPC-10
Smolenice Castle, Slovakia
Sept , 2011
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 , Japan
2Japan Atomic Energy Agency, Tokai, Ibaraki , Japan
3Institute for Materials Research, Tohoku University, Sendai, Miyagi , Japan

2. 2) Fe-Cu Model Alloys: Cu Nano-Clusters (Precipitates)
Outline
1) Backｇround
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 Materials
Mechnisms: Nanostructural Features
Irradiation Embrittlement & Hardening
1st & 2nd Generation A533B
Post Irradiation Annealing (PIA) Experiments

3. Origin of irradiation-induced embrittlement
Nuclear Reactor Pressure Vessel (RPV) Steel
Origin of irradiation-induced embrittlement
1) Solute Nano-Clusters
2) Matrix Defects
(vacancy-type defects,
dislocation loops, ···)
dislocation
Grain boundary
3) P Segregation at Grain Boundary

4. Laser-Assisted Local Electrode Atom Probe
Position sensitive ion detector Z Y X
Local electrode
Laser
Vtotal
Needle sample
Vextraction
～100nm
Time of Flight Mass 4
Energy-compensated type (with “Reflectron”) 4 4

5. Cu Nano-Particles in Fe
Positron Quantum-Dot Confinement
in a Precipitate of 59 Cu Atoms
LEAP 3D-Atom Probe
2x107 Atoms, 1hour
e+　Self-Searching:
Cu Nano-Particles　in Fe
1nm
Density isosurface of a quantum-dot confined positron
in a Cu59 in Fe matrix. The isodensity value is 0.5%
of the maximum.
60x60x170 nm

6. 2a) Cu Nano-Precipitates (Clusters) : Size 2D-ACAR: Momentum Smearing
Z. Tang et al.:
J. Phys.: Condens. Matter 20 (2008) ,
Size-dependent momentum smearing effect
of positron annihilation radiation
in embedded nano Cu clusters

7. 2b) Cu Nano-Precipitates (Clusters) : Number Density AMOC: Time Evolution of HMCF (W-Parameter)
　　 Trapping Model
A. Inoue et al.: Phys. Rev. B83 (2011)

8. Fe-0.88at.%Cu: Thermal Aging @550˚C
CDB Ratio Curve
3D-AP 2h
30nm
10nm
0.1h
0.2h
2h: Complete e+ Quantum-Dot Confinement
Fig.1

9. Time Evolution of CDB HMCF (W-Parameter)
Pure Cu
Pure Fe

10. Positron Age-Momentum Correlation (AMOC)
Using digital oscilloscope：Time resolution ~170ps
Number density estimated by positron annihilation
Time dependent
HMCF　（W-parameter)
Positron trapping rate
Number density
Number Density (×1017 cm-3)
3D-AP e+
Aging Time (h)
　　　Size
Diameter (nm)
0.1
0.2 2
0.9
1.1
2.5
0.15
1.2
1.9
0.61
1.4
1.8
In this talk, firstly, I would like to briefly explain why we employ positron annihilation for elemental analysis rather than other technique,
and introduce the site which positron probes. For defect scientists, positron is a tool of vacancy-type defects. But, not only the vacancy-type defects
but also other sites, such as positron affinitive embedded clusters, polar groups in polymers, and so on, are also positron trapping sites.
In this talk, I would like to concentrate on “positron affinitive embedded clusters in materials”.
As examples, I introduce Cu clusters in Fe and solute clusters, so called GP zone, in Al.
And I would like to comment two points on CDB data analysis and their interpretation from my personal experience.
Finally, I show the competition between positron annihilation and other techniques in the study of embedded clusters.

11. 3) RPV Steel: Surveillance Test Specimen Materials 1St & 2nd Generation A533B
Irradiation –Induced Embrittlement (Hardening) Mechanisms Post Irradiation Annealing (PIA) Experiments
PIA: 1st Gen A533B
Kuramoto et al.: Submitted to J. Nucl. Mater.
Fluence Dependence
Takeuchi et al. : J. Nucl. Mater. 402 (2010) 93.

12. Reactor Pressure Vessel (RPV) Steel: A533B
Chemical Composition
wt.%
A533B C Si Mn P S Ni Cr Cu Mo
1st. Gen.
0.19
0.30
1.30
0.015
0.010
0.68
0.17
0.16
0.53
2nd. Gen.
1.43
0.004
0.001
0.65
0.13
0.04
0.50
Purified: Cu, P, S
JMTR Irradiation
Fluence: 3.9x1019n/cm2 (0.061dpa)
Flux: 1.8x1013n/cm2・sec
Temperature: 2902C

13. Annealing Temperature [ ℃ ] Average Positron Lifetime [ps] V
Annealing Behavior of Average Positron Lifetime
1st. Gen.(0.16Cu) & 2nd. Gen.(0.04Cu) A533B, 3.9×1019 n/cm2
200
300
400
500
600
100
120
140
160
180
Annealing Temperature [ ℃ ]
Average
Positron Lifetime [ps] V 1
Unirrad. (1st. Gen.)
Fe bulk
Unirrad. (2nd. Gen.)
st.
Gen. (0.16Cu) 2
nd.
Gen. (0.04Cu)
As-irrad.

14. CDB HMCF-LMCF Correlations
1st. Gen. (0.16Cu) & 2nd. Gen. (0.04Cu) A533B, 3.9×1019 n/cm2
450 °C
400 °C
300 °C
As-irrad.
(1st. Gen. )
550 °C
Unirrad.
(1st. Gen. )
600 °C
600 °C
As-irrad.
(2nd. Gen. )
Unirrad.
(2nd. Gen. )
450 °C
300 °C

15. Neutron Irradiation: 8.3×1018n/cm2 (1.2×10-2dpa, ~100ºC)
Fe-Cu Model Alloys ( 0.3wt.%Cu, 0.05wt.%Cu )
0.5
0.55
0.6
0.65
0.004
0.006
0.008
0.01
0.012
0.014
LMCF
HMCF
Pure Cu
500
0.3Cu
500
0.05Cu
As-irrad.
Pure Fe
Unirrad.
Unirrad.
As-irrad.

16. Atom Maps of the Solutes: Annealing Behavior (As-irrad.~400℃)
1st. Gen. (0.16Cu) A533B, 3.9×1019 n/cm2
As-irrad.
350 °C
400 °C Cu Si Mn P Ni
10nm

17. Atom Maps of the Solutes: Annealing Behavior (As-irrad.~350 ℃)
2nd. Gen. (0.04Cu) A533B, 3.9×1019 n/cm2
As-irrad.
300 ℃
350 ℃ Si Mn Ni P Cu
10nm

18. Average Chemical Compositions of Solute Clusters
3.9×1019 n/cm2
1st. Gen. (0.16Cu) A533B
2nd. Gen. (0.04Cu) A533B Cu Mn Si
Composition [%] Ni
Composition [%] Fe
Annealing Temperature [°C]
Annealing Temperature [°C]

19. Radius of Gyration (rg), Number Density (Nd) & Volume Fraction (Vf)
A533B, 3.9×1019 n/cm2 rg
Radius of Gyration
1st. Gen. (0.16Cu)
CuMnSiNi Clusters
1st. Gen.
2nd. Gen. (0.04Cu)
MnSiNi Clusters Nd
Number Density
2nd. Gen.
Hardening
Russell-Brown
Model Vf
Volume Fraction

20. Annealing Behavior of Irradiation Hardening (∆Hv)
1st. Gen. (0.16Cu) A533B, 3.9×1019 n/cm2
e+ : Vac-Defects
3D-AP: CuMnSiNi Clusters
As-irrad.

21. Av 3.9×1019n/cm2 LMCF HMCF Hv 1st. Gen. (0.16Cu) 2nd. Gen. (0.04Cu)
As-irrad.
Annealing Temperature [°C]

22. 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
Quantative !!