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. Hasegawa 1 ）, Y. Nagai 1), T. Toyama 1), Zheng Tang 1), Y. Nishiyama 2), M. Suzuki 2), T. Ohkubo 4) and K. Hono 4) 1) Tohoku University, Japan 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 Eeffcts Calder Hall Reactor vs JMTR (PA & 3D-AP** ) ) * ) Positron Annihilation (PA) **) 3 Dimensional Atom Probe (3D-AP)

e+e+ 22 1 MeV 1.27 MeV 00 22 Na (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 Probe 22 Na Cu Nano-Precipitates Cu Nanovoid Cu-V Complex 11 22 Positron Quantum Dot State Positron Density

Cu 5 Cu 1 Cu 59 Diameter ~ 1 nm Embedded Particles - Cu Precipitates in Dilute Fe-Cu Alloys - Positron 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 Cu 59 in Fe matrix. The isodensity value is 0.5% of the maximum. Fe Cu

CDB CDB Ratio Spectra γ1γ1 γ2γ2 Ge detector Coincidence Doppler Broadening : CDB e+e+ e-e- p L : Electron Momentum along the Emitted γ–ray Ge detector Normalize to Pure Fe Low High LowHigh Low Momentum Region : Vacancy type defects High Momentum Region : Cu Nano-Precipitates Cu 3d 10 Electrons

τ 1 = 165ps : ~ monovacancies(V 1 ) τ 2 = 405ps (51%) nanovoids (~V 30 ) Vacancy & nanovoid covered with Cu atoms Fe-0.3wt%Cu: CDB Ratio Curves neutron-irrad.: 8.3×10 18 n/cm 2, 100C Cu 3d Peak Almost Flat Vac. Type Defects No Fe Valley Pure Fe Pure Cu As-Irrad. Normalized to Fe Normalized to Cu

Positron Lifetime and Binding Energy in Vacancy Clusters in Fe V 2 [111] V 2 [100] V9V9 V5V5 V 15 Positron Lifetime Positron Binding Energy

Neutron Flux Effects on the Embrittlement Mechanisms ? Neutron Flux (n/cm 2 /s) MTR BWR·PWR Calder Hall-Type Reactor Embrittlement Total Matrix Defects Cu Nano Precipitates Soneda (2003) Embrittlement Mechanisms: Fluence Evolution

CSiMnPSNiCrCuMoAlN Post-Weld Heat Treatment : 600ºC, 4h. C-Mn base Ferritic Steel wt.% CHR SurveillanceJMTR * Flux (n/cm 2 -s) 4.2× ×10 12 Fluence (n/cm 2 ) 2.7× ×10 18 Irradiation Period 20 years7 days Irradiation Temperature (ºC) *Japan Materials Testing Reactor Low flux High flux Irradiation Conditions Calder Hall Reactor (CHR) in Tokai *, Japan: Surveillance Test Specimen * In –Service (1966 – 1998)

CHR Surveillance 4.2x10 8 n/cm 2 ·s JMTR 3.6x10 12 n/cm 2 ·s Irradiated at 240ºC Strengthening by Irradiation CHR vs. JMTR

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 Positron Lifetime CHR Surveillance JMTR Unirrad. 300ºC, 70,000h 400ºC, 70,000h V1V1 bulk Fe V1V1 τ2τ2 τ av τ1τ1 I2I2

10nm 30nm Cu Mn Ni Si CHR Surveillance 10nm 30nm JMTR 3D-AP Mapping : As-irrad.

Isochronal Annealing: CDB & Hardness 200~700ºC, 30 min. Vickers Microhardness Pure Fe （ As-irrad. ） CDB Low/High Momentum Correlation Recovery of Vacancy-Type Defects Recovery of Cu Nano- Precipitates CHR Surveillance JMTR CHR Surveillance JMTR

3D-AP Mapping : Annealed at 450ºC for 0.5h 10nm 30nm Cu Mn Ni Si CHR Surveillance 10nm 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 Steels Summary : 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 Sensitive Detector High Field Region

Conventional Atom Probe (Energy-Compensating Type) LEAP Atom Probe 10x10x60 nm 3x10 5 Atoms, 6 hours 60x60x170 nm 2x10 7 Atoms, 1hour Cu Precipitates: Fe-1.0wt%Cu Aged at 475C for 10h