Neutron scattering structure studies of materialsloaded by high neutron fluence in NPI ŘežPavol Mikula, Petr Lukáš, P. Strunz, J. Šaroun, Miroslav Vrána

Nuclear Physics Institute AS CR v.v.i., 250 68 Řež, Czech RepublicResearch Centre Řež, Ltd., 250 68 Řež, Czech Republic

mean reactor power 10 MW

thermal flux in the core 1x1018 ns-1m-2

beam tube 1 1013 ns-1m-2

fuel enrichment 36% 235U

tank type

light water moderated and cooled

Reactor LVR 15, NRI Řež p.l.c.

Neutron diffraction laboratoryBNCT

HR-SANS

test diffractometer neutron depth

profiling

powder diffractometer

HK9

HK8

HK6 HK3

HK2

HK4

powder diffractometer

strain diffractometer

strain scanner

10 2 m

C0 + C3H3BO3

Residual strain/stress measurement

Plane-wave diffractionIn diffraction neutron is considered as a (matter) waveAtoms/nuclei are scattering centres Scattered waves interfereBragg condition provides the angles where interference maxima can be foundStress in the material brings about the change of the position of atoms in the crystalline lattice – deformation, strain ∆dhkl/dhkl

Position of the interference maxima are sensitive to the value of the lattice spacing => strain component perpendicular to the lattice planes is measured

λ – neutron wavelength, θ – Bragg angle, dhkl – lattice spacing

Q

PSD

Monochromator Neutron beam from source

Gauge volume

Beam defining optics for the incident beam

and shielding

Beam defining optics for the

diffracted beam and shielding

Specimen

Q

2θ

Beam stop

Conventional neutron strain scanner

Diffraction profileseen by PSD at someBragg angle θB

Irradiated part of thepolycrystalline material

Strains are of the order of 10-3 – 10-4, high angular resolution is required

θB

beam shutter

positionsensitive detectorsample

Neutron strain scanner• high-resolution ∆d/d≈2x10-3

• neutron flux 106 n s-1cm-2

• gauge volume 1-300 mm3

• two-wavelength sandwichmonochromator

• linear position-sensitive detector• x,y,z linear stage• two-circle goniometer

88 90 920.0

0.4

0.8

2θ / deg

100% α 32.6% α + 67.4% γ

α 2111.65A

rel. in

tensit

y

2θ / deg96 98 100

0.0

0.4

0.8

1.2 32.8% γ + 67.2% α 100% γ

γ 2002.7A

γ 3111.65A

Sandwich monochromatorSi111(2.7A) & Si220(1.65A)Si111(2.7A) & Ge311(1.45A)

SPN-100 high-resolution diffractometer

monochromator

Slits

sample

PSD detector

αM αS

αM,S beam divergence, LM distance monochromator-specimen, RM monochromator bending radius, θM,,SBragg angle - monochromator, specimen

−

−= 1

sin12

MM

M

M

SMS R

Ltgtg

θθθαα

−

=S

MM

MM

tgtg

LRθθθ

21sin

αs=0 ⇒

Neutron diffraction optics using bent perfect Neutron diffraction optics using bent perfect Si/GeSi/Ge single crystalssingle crystals

Focusing condition for qFocusing condition for quasiparalleluasiparallel beambeam

High resolution instrumentation

Neutron diffraction stress/strain determination

♦ elastic strains only♦ one component of the elastic strain

tensor only is obtained in a single measurement♦ strains can be converted to stresses

using appropriate elastic moduli♦ determined selectively only from

grains which are suitably oriented with respect to the scattering vector♦ averaged strain values over those

grains

Characteristics

dhkl - lattice spacing, θhkl - diffraction angle, εhkl -lattice strain, λ - neutron wavelength

hklhkl

hkl

hkl

hklhklhkl d

dd

dd θθε ∆−=∆=−

= hklcot ,0,0

,0

Bragg law 2dsinθ=λ

Lattice strain

Macrostrain scanning (from the peak shift)

dhkl - lattice spacing, θhkl - diffraction angle, εhkl - lattice strain

hklhkl

hkl

hkl

hklhklhkl d

dd

dd θθε ∆−=∆=−

= hklcot ,0,0

,0 hklhklhkl

hkl

hkl

hklhklhkl cot

dd

ddd

θθε ∆−=∆=−

= ,0,0

,0

Elastic strains only One component of the elastic strain tensor only is obtained in a single measurement Strains can be converted to stresses using appropriate elastic modules Determined selectively only from grains which are suitably oriented with respect

to the scattering vector Averaged strain values over those grains

Strain - stress conversion

Experimental quantity – strain tensor component

Engineer’s task – strain tensor component

hklijε

ijσ

Theory of elasticity ∑=αβ

αβαβσε,ijij S

∑=αβ

αβαβεσ,ijij C

αβ,ijS

αβ,ijC

Elastic compliance constants

Elastic constants

[ ])()1()1)(21( zyxx

xE

εενεννν

σ ++−+−

=Principal components

Ex − diffraction Young modulus, ν − Poisson ratio

Neutron diffraction stress/strain determination

Theory of elasticity

Experimental quantity - strain tensor component

[ ])()1()1)(21( zyxx

xE

εενεννν

σ ++−+−

=

∑=αβ

αβαβεσ,ijij C

∑=αβ

αβαβσε,ijij S

hklijε

Engineer’s task - stress tensor ijσ

Hook’s law αβ,ijS elastic compliance constants

elastic constantsαβ,ijC

Principal components

Ex diffraction Young modulus, ν Poisson ratio

Three different components of the strain tensor should be measured.

x y

z

x

yz

x

yz

scanning direction

scanning direction

scann

ing di

rectio

nin c id e n t b e a m

in c id e n t b e a m

in c id e n t b e a m

scatte

ring v

ector

scattering vector

scattering vector

d if f r acted b eamd if f r acted b eam

d if f r acted b eam

Xcomponent

Zcomponent

Ycomponent

αM αS

Sample

Monochromator

Slits

PSD detector

Incident beam

Diffracted beamFocusing beam

−

=S

MM

MM

2tgθtgθ1sinθ

LRαs= 0

αM,S -beam divergence, LM - distance monochromator-sample, RM - monochromator bending radius, θM,S - Bragg angle at the monochromator/specimen

High-resolution strain scanningRay opticsBragg diffraction optics using bent perfect Si-crystal

PSD

Monochromator Neutron beam from source

Gauge volume

Beam defining optics for the incident beam

and shielding

Beam defining optics for the

diffracted beam and shielding

Specimen

Q

2θ

Beam stop

Neutron strain scanner I

Neutron strain scanner• high-resolution ∆d/d≈2x10-3

• neutron flux 106 n s-1cm-2

• gauge volume 1-300 mm3

• two-wavelength sandwich monochromator

• linear position-sensitive detector

• x,y,z linear stage• two-circle goniometer

Sample environment

Weld deposited passPlate: 15Ch2MFA, 7 mm thicknesswelding material Inconel 52, (steel usedfor construction of reactor vessels)

Gauge volume2x2x10 mm3

Lattice strains

400 450 500 550 6000

50

100

150

200

250

300

350

position -15 mm position 0 mm

Reflection (110)

Inten

sity /

1 80

0 s

Channel number

-20 -15 -10 -5 0 5 10 15 20 25 30-1,0

-0,5

0,0

0,5

1,0

1,5

2,0

2,5

3,0

ε / 1

0-3

mm

7 mm thick steel plate with a weld deposited pass

εx εz εy

-20 -15 -10 -5 0 5 10 15 20 25-1,0

-0,5

0,0

0,5

1,0

1,5

2,0

2,5

3,0

ε / 1

0-3

mm

7 mm thick steel plate with a weld deposited pass

εx εz εy

Sample I Sample II

-

-1

0

1

2

3

4

-4 -2 0 2 4 6 8 10x / mm

y / m

m

initial

1 2 3 4

56

A diagram displaying the course of the welding.

10

x

30075

150

3

z

y

Schematic sketch of the welded plate specimen, used system of coordinates

and localization of the measuring points

Optimization of the welding technologies(high-strength ferritic steel WELDOX700)

Location ofmeasurements

150 mmTest weld

150 mm

2 mm3 mm10 mm

Three components of the residual stress scanned along the line perpendicular to the weld point

The usefulness of the neutron diffraction technique was demonstrated on the study of possible modification of the residual stress distribution in the vicinity of the single pass weld by weld-metal chemical composition. All three stress components sx, sy and sz were measured after releasing the test specimens from the test frame i.e. after removing the external restraint.

Sample 1C Si Mn Cr Ni Mo0.100 - 1.85 0.42 1.94 0.39Sample 2C Si Mn Cr Ni Mo0.102 - 0.76 0.27 3.94 0.24Chemical composition of the weld metal labeled as OK 75.78 (weight %)

Sample 1-40 -30 -20 -10 0 10 20

-200

0

200

400

600

800 x component Y component z component

Stre

ss /

MPa

x / mm-3 0 -2 0 -1 0 0 1 0 2 0 3 0

-2 0 0

0

2 0 0

4 0 0

6 0 0

8 0 0

Stre

ss /

MPa

x / m m

x co m p one n t y co m p one n t z co m p on en t

Sample 2The result of the residual stress scans

C Si Mn P S Cr Ni Mo0.144 0.314 1.004 0.006 0.0013 0.372 0.057 0.019V Ti Cu Al Nb B N Ca0.047 0.015 0.016 0.043 0.020 0.0015 0.005 0.0024Chemical composition of the WELDOX700 steel (weight %).

Neutron diffraction technique was applied on stress scanning on two samples with the weld carried out by two different electrodes of different Ni content

NPIResidual strain mapping: Austenite protection welded on a ferrite

AusteniteAusteniteFerriteFerrite

5 mm5 mm15 mm15 mm

Scanning pointsScanning points

110, 111 110, 111 -- reflection planesreflection planes

-5 0 5 10 15 20-4

-2

0

2

4

6

8

110 tangential 110 radial 111 tangential 111 radial

∆d /

d x

10-4

mm

Radial componentRadial component

Tangential componentTangential component

Horizontally focusing monochromator

Monochromator shielding

Deformation machine

SamplePosition sensitive detector

NPI - TKSN-400 Strain/Stress Diffractometer

TKSN-400 Strain/Stress Diffractometer

Tensile force

Tensile force

1V, 1500A

Neutron diffraction profile intensity phase volume fraction position strain/stress width/shape microstrain

Termo-mechanical loading

Special deformation rig for tension/compression loading

Thermocouples Resistant heating system Water cooling system

Tension-compression rig

( ) [ ]( )ξξ LGVRdd hkl ⊗⊗=Ω/ΣModeling in reciprocal space

( )

⟩⟨−−

−

−

2

02/12

0

22

21~

hkl

hkl

ddexpG πε

πξξ ( ) ( ) ( )220 221~

effhkl DdL

+−−

πξξ

⟨ε2⟩1/2 root-mean-square microstrainDeff effective dimension of coherently

diffracting blocks

Gaussian Lorentzian

Analysis of diffraction lineprofiles

Indirect deconvolution method

Diffraction-line broadening

Observed profile Fexp(2θ)=[Finst⊗Fspec](2θ)Finst(2θ) = [Fwavelengtht⊗Faberration](2θ)

Specimen broadened profile Fspec

Size effect (Schrerrer, 1918)

θθβλcos)2(

KD =

Strain effect (Stokes&Wilson, 1944)“apparent strain”

Deconvolution Stokes method (Fourier transform) )()()(

exp

nFnFnF inst

spec=

Two-step indirect deconvolution method

e=β(2θ)cotgθ

Energy-Dispersive Neutron-Transmission Diffraction

2dhkl sin Θ hkl = λ Θ hkl = 90ο λ =2dhkl

Diffraction edge I(λ) modulation

Instrumental resolution ∆d/d=5.7x10-4

200 250 300 350

0.00

0.05

0.10

0.15Standard sample1 mm slit

Amplitud

e

Channel number

Sample thickness dependence of Ao

200 220 240 260 280 300 320 340-0.05

0.00

0.05

0.10

0.15

0.20

0.25

Standard sample2 mm slit

Amplitud

e

Channel number

FWHM=5.7x10-4 rad

FWHM=12.5x10-4 rad

200 250 300 350-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5 Fe(321) t=12 mm t=24 mm t=36 mm

Amplitud

e

Channel number

225 250 275 300 325-0,05

0,00

0,05

0,10

0,15

0,20

Deriv

ative

Channel number

ARMCO standard

Ampli

tude

Channel number

250 300-0,02

-0,01

0,00

ARMCO standard

EDNTD examplesBragg diffraction edge of a 8 mm thick sample

Energy-Dispersive Neutron-Transmission Diffraction

1.5201.5221.5241.5261.5281.5301.5320.280.300.320.340.360.38

prestrain 10%tra

nsmiss

ion

wavelength (Å)

1.5201.5221.5241.5261.5281.5301.5320.320.340.360.380.40 prestrain 0%

trans

miss

ion

wavelength (Å)

1.5201.5221.5241.5261.5281.5301.5320.280.300.320.340.36 prestrain 2%

trans

miss

ion

wavelength (Å)

1.5201.5221.5241.5261.5281.5301.5320.280.300.320.340.360.38

prestrain 5%

trans

miss

ion

wavelength (Å)

low-carbon steel 0.22% C, 0.64% Mn, 0.41% Si, 0.035% P, 0.04% S (in wt.%) Fe (321) diffraction edges

Comparison of the EDNTD and BDAA techniques

0 5 10 15 200.000.250.500.751.001.251.50

diffraction edge diffraction profile

micro

strain

< ε2 >1

/2 (1

0-3)

prestrain (%)

46.4 46.8 47.2 47.6 48.0

0

2

4

6

8

10

12int

ensity

/ rel

units

2θ / deg

5% strain

1% strain

110 reflection

Residual stresses in highly radioactive materials

Residual stresses in highly radioactive materials

Motivation...

reactor construction materials radiation damage - material degradation during

service monitoring of residual stress level with operation

time and neutron fluence component integrity assessment, support of

operation prolongation

Dedicated shielding container

neutron beam n e ut ro

n be a m

specimen

shieldingshutter,collimator

linear stage

linear stagesteppingmotor

easy specimen installationin the hot cells

remote control of beamshutters and collimators

specimen positioning

dedicated facility - shielding box, beam shutters, specimen manipulators

Residual stresses in radioactive reactor components

First testing experiment

CT specimens from the steelA347 weld joint irradiated in experimental

reactor LWR-15 to 6.2 1020 n/cm-2

tested inside the in-pile reactor water-loop BWR-2 final fractured by fatigue at room

temperature in air total specimen activity of 11 GBq

weld metal

x z ybase metal

fusionline

fracturesurface

notch

First testing experiment

0 10 20 30 40-300

-200

-100

0

100

200

300

400

µ strain

(a) active CT

x / mm0 10 20 30 40

-300

-200

-100

0

100

200

300

400

µ strain

x / mm

(b) reference CT

Scan of the residual strain component perpendicular to the fracture surface in the active specimen (a) and the reference specimen (b).Tensile residual strains of the same amplitude of ε ~3 10-4 located in the vicinity of the crack tip. Localization of the strain maximum is slightly different - irregular propagation of the crack tip

Residual stresses in highly radioactive materials

Conclusions

All functions of the new experimental container have been proved

good shielding capacity mechanical functions in the hot cells easy and safe opening and closing the container installation of the specimen into the specimen holder

by using a mechanical manipulator remote control of specimen positioning and beam shutters

Small-angle neutron scatteringmethod and its applications

SANS instrumentation

i n c i d e n t b e a m

specimen

2-d PSD detector

Collimator system – pin hole geometry

SANS instrumentationCollimator type SANScamera, slit geometry

Double bent crystalHigh-resolution SANScamera

Ultra high resolutionBonse-Hart SANS camera

SANS instrumentation

SANS technique size rangeCollimator instruments 1 nm .. 100 nmDC diffractometers with bent crystals 10 nm .. 1 µmDC diffractometers with perfect crystals (Bonse-Hart) 1 µm .. 10 µm

Developed experimentaltechnique

Advanced data evaluationmethod & software− multiple scattering− Non-linear data fitting

of a single model tomultiple data sets

-0.005 0.000 0.005 0.010

-0.005

0.000

0.005

0.010-0.005 0.000 0.005 0.010

-0.005

0.000

0.005

0.010

Q y (Å-1 )

Qx (Å-1)

14

56

2.2E2

8.9E2

3.5E3

-0.005 0.000 0.005 0.010

-0.005

0.000

0.005

0.010-0.005 0.000 0.005 0.010

-0.005

0.000

0.005

0.010

[111]

Q y (Å-1 )

Qx (Å-1)

Example of data taken by a neutron diffractometer and by a pin-hole instrument

Example: Study of porosity in plasma-sprayed ceramics

1 10 1000.010.1

110

1001000

10000 z=5 mm

z=2.5 mm

empty beam

T=1730 oC

z dΣ

/dθ

Qx [ µm-1]

Bonse-Hart Collimator instruments0.01 0.1 1

0

20

40

60

80

100

120

140

0.1 10

5

10

15

as sprayed 1300 oC 1520 oC 1730 oC

D(R)

[10-2

µm-1]

R [µm]

SANS data for various resolutions and sample thickness fitted to a single model.

Size distribution of pores in plasma-sprayed Al2O3

• High creep resistance• High-temperature applications (turbines)• Microstructure:

– two-phases: γ-phase matrix strengthened by γ’ precipitates or other phases

– Precipitate size: nm-µm, depending on heat treatment

– heat treatment: to optimize microstructure

• Characteristics of γ’ and/or other strenghtening phases essential formechanical properties

Ni-base superalloys

Composition: e.g. Cr 8.0, Co 4.0, Mo 0.5, Al 5.7, W 9.0, Ti 0.7, Ta 5.7, Ni balance; in wt%

Ex-situ samples DT706, SANS

0.010.1

1

10

100

azimuthal average

Qx (Å-1)

dΣ/dΩ

(cm

-1sr-1

)

B DA-1 C B ST C B MST C B MST-1 C

0 500 10000.0001

0.001

0.01

size (Å)

volum

e dist

ributi

on (

dimen

sionle

ss)

volume distribution B DA-1 B ST B MST B MST-1

Model: dense spheres (γ’) with log-normal size distribution, large inhomogeneities, incl. η(Q-4 scattering)

STDAMST MST-1

DT706

• Electron microscopy: uncertain about existence of precipitates in DA• Cooling/heating rate important (not only the hold temperature and time)• We can model well the data => in-situ behavior can be well assessed

0 500 1000 1500 2000 2500 30000

500

1000

1500

2000

2500

3000

DA-1

0.540 -- 0.600 0.480 -- 0.540 0.420 -- 0.480 0.360 -- 0.420 0.300 -- 0.360 0.240 -- 0.300 0.180 -- 0.240 0.120 -- 0.180 0.060 -- 0.120 0 -- 0.060

y (Å)

x (Å)0 2000 4000 6000 80000

2000

4000

6000

8000

ST

0.900 -- 1.00 0.800 -- 0.900 0.700 -- 0.800 0.600 -- 0.700 0.500 -- 0.600 0.400 -- 0.500 0.300 -- 0.400 0.200 -- 0.300 0.100 -- 0.200 0 -- 0.100

y (Å)

x (Å)0 2000 4000 6000 80000

2000

4000

6000

8000

MST

0.900 -- 1.00 0.800 -- 0.900 0.700 -- 0.800 0.600 -- 0.700 0.500 -- 0.600 0.400 -- 0.500 0.300 -- 0.400 0.200 -- 0.300 0.100 -- 0.200 0 -- 0.100

y (Å)

x (Å)0 2000 4000 6000 80000

2000

4000

6000

8000

MST-1

0.900 -- 1.00 0.800 -- 0.900 0.700 -- 0.800 0.600 -- 0.700 0.500 -- 0.600 0.400 -- 0.500 0.300 -- 0.400 0.200 -- 0.300 0.100 -- 0.200 0 -- 0.100

y (Å)

x (Å)

Volume fraction 5% 20% 13% 24%

In-situ SANS (HTF furnace)

00:00 12:00 24:00 36:00 48:00 60:00 72:00 84:00-1000500

600

700

800900

1000

1100

1200

0.5 K/min4 K/min20 K/min

temperature

Temp

eratur

e (°C

)

Aim: Cooling rate (from solution treatment temperature) influence on precipitate microstructure

Scattering curves (SDD=5m, λ=4.55Å and SDD=6m, λ=19.6Å)

• Carbides scattering: present even at solution treatment temperature 1080°C• 20 K/min: visible precipitation starts only during the 835°C hold, not before• 4 K/min: precipitation starts at 852°C• 0.5 K/min: Precipitates (majority of volume) created already before holding,

– starting at 890°C - most probably ηprecipitation

– accelerated at 865°C – γ‘ precipitation start.

1E-3 0.01 0.10.01

0.1

1

10

100

1000

DT70620 K/min

Q-4

azimuthalaverage

Q (Å-1)

dΣ/dΩ

(cm

-1sr-1

)measured, fit

1080°C 835°C, 1 min 835°C, 4 min 835°C, 23 min 835°C, 52 min 835°C, 1 h 26 min 835°C, 2 h 06 min 835°C, 3 h 28 min 835°C, 4 h 06 min 835°C, 9 h 32 min 835°C, 10 h 11 min room temperature after

1E-3 0.01 0.10.01

0.1

1

10

100

1000Q-4

DT7064 K/min

azimuthal average

Q (Å-1)

dΣ/dΩ

(cm

-1sr-1

)

measured, fit 1080°C 847°C 835°C, 1 min 835°C, 4 min 835°C, 38 min 835°C, 1 h 17 min 835°C, 8 h 45 min 835°C, 9 h 25 min room temperature after

1E-3 0.01 0.10.01

0.1

1

10

100

1000

Q-4

DT7060.5 K/min

azimuthal average

Q (Å-1)

dΣ/dΩ

(cm

-1sr-1

)

measured, fit 1080°C 857°C 847°C 835°C, 35 min 835°C, 1 h 14 min 835°C, 5 h 17 min 835°C, 6 h 36 min room temperature after

Size (γ‘)

00:00 04:00 08:00 12:00 16:00 20:00 24:00 28:0040050060070080090010001100120013001400

Temp

eratur

e (K) Temperature

00:00 04:00 08:00 12:00 16:00 20:00 24:00 28:000

200

400

600

800

1000

1200

1400size - γ '

Time (hours)

size (

Å)

after coolling rate 0.5 K/min after coolling rate 2.3 K/min after coolling rate 4 K/min after coolling rate 20 K/min

0.0 0.3 0.6 0.9 1.2 1.50.0

0.3

0.6

0.9

1.2

1.5

y (µm

)

x (µm)0.0 0.3 0.6 0.9 1.2 1.5

x (µm)

Model: η and γ’

Outcome

• Evolution of size and volume fraction for various cooling rates

• Microstructure can be tuned (γ’ size, distance) using the results of in situ SANS

• Cooling rate has to be properly chosen and accurately controlled during the heat treatment

• An indication of growth of η on expense of γ’ on holding after slower cooling.

Radiation induced embrittlement in reactor pressure vessel steels

APT observation Nano-sized aggregates of solute atom are formed as a result of diffusion processes in crystal lattice damaged by neutron irradiation. Small-angle neutron scattering(SANS) permits to measure mean size and volume fraction of these aggregates.Additional information on chemical composition of the aggregates is obtained from the ratio of magnetic and nuclear scattering cross-sections

SANS model

ferromagnetic matrix

Ldet = 4 m Ldet = 1.1 m

Measured (greyscale) and fitted (lines) scattering patterns from irradiated A533B steel (C1)

The SANS measurements were carried out at the BENSC-V4 instrument of the HMI Berlin

detector distances: 1.1 m and 4 m neutron wavelength: 0.6 nm horizontal magnetic field: 1.1 T

-3 -2 -1 0 1 2 3-3

-2

-1

0

1

2

3

Qx [nm-1] Q y

[nm-1 ]

-0.6 -0.3 0.0 0.3 0.6

-0.6

-0.3

0.0

0.3

0.6

Qx [nm-1]

Q y [n

m-1 ]

SANS experiments on RPV steels

Volume fraction is evaluated from the magnetic component modulated by ~ sin(α)2.

Mα

Q

10 1000.0

0.5

1.0

1.5

base

1.12 1024 m-2, 1y 5.89 1024 m-2, 5y 9.96 1024 m-2, 10y 1.411024 m-2, 5y, 475oC/165h 295oC / 10 y

D M(R

) [µm

-1]

R [Å]

Size distributions after subtraction of reference (unirradiated) sample (steel 15Kh2MFA).

10 1000.0

0.5

1.0

1.5

weld

1.22 1024 m-2, 1y 2.20 1024 m-2, 2y 5.26 1024 m-2, 5y 4.78 1024 m-2, 5y, 475oC/165h 295oC / 5 y

D M(R

) [µm

-1]

R [Å]

SANS experiments on RPV steels

Radiation-induced precipitates are recognized as a peak at R~ 0.1 nm