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AREVA NP GmbH - Technical Center NTCMF-G, Elisabeth Keim / IAEA Workshop on Structural Integrity, 23-26 June 2009AREVA NP All rights are reserved, see liability notice. 1

AREVA NP GmbH - Technical Center NTCMF-G, Elisabeth Keim / IAEA Workshop on Structural Integrity, 23-26 June 2009AREVA NP All rights are reserved, see liability notice. 2

RPV Irradiation Surveillance Programs

Elisabeth Keim, Hieronymus Hein

AREVA NP GmbHTechnical Center

IAEA Workshop on Structural Integrity

The reproduction, transmission or use of this document or its contents is not permitted without express written authority. Offenders will be liable for damages. All rights, including rights created

by patent grant or registration of a utility model or design, are reserved.

3AREVA NP All rights are reserved, see liability notice.AREVA NP GmbH - Technical Center NTCMF-G, Elisabeth Keim / IAEA Workshop on Structural Integrity, 23-26 June 2009

Contents

Introduction

RPV Ageing Mechanisms

RPV Irradiation Surveillance

RPV Surveillance Requirements According to KTA

KTA 3203

Technical Requirements

Examination of Microstructure

Specific Issues

Long Term Operation

Countermeasures

Outlook


RPV Safety AssessmentRequirement: brittle fracture has to be excluded according to present state of the art

Introduction

∆T

Temperature (°C)

Load Path

MaterialS

tress

in

tens

ity,

Frac

ture

toug

hnes

sM

Pa

√m

a

K = σ ⋅ √ π aσ


RPV Beltline Region is Exposed to a Neutron Spectrum



Impact of Irradiation by Fast Neutrons (E >1MeV) on the Microstructure in the RPV Beltline Region


Core

Axial Neutron Fluence

150

0

150

100 10-1

cm

ϕrel

Matrix damage

Cu-Rich Precipitates (CRP) with Ni, Mn, Si, …

P segregation on grain boundary


Main parameters for RPV irradiation embrittlement


Core

Axial Neutron Fluence

150

0

150

100 10-1

cm

ϕrel

Material and it’s chemical composition

Irradiation temperature

Neutron flux

Energy spectrum of the neutrons

Irradiation time

Neutron fluence


Thermal Ageing of RPV MaterialsFor western RPV steels with Cu≤0.25% thermal ageing is not observed for T≤325°C for long operating times

Some significance in Magnox type reactors (UK) in C-Mn RPV steels with 360 °C exposure temperature

Other Influencing Factors

Hydrogen: no effect under operating conditions (embrittlement of ferritic RPV material by hydrogen no more detectable at 250°C )

Gamma irradiation: not significant at LWR operating temperatures due to strong annealing effects► No indications of γ-irradiation effect on change of material

properties of ferritic RPV materials under operating conditions► If any γ effect would exist it is limited on the surface of inner RPV

wall because the attenuation for γ is higher than for neutrons



Neutron Irradiation as Most Important Ageing Mechanism


Neutron fluence distribution in a RPV (German Convoy PWR)


Impact of Neutron Fluence ( >1017 n/cm2) on the RPV Material Properties



Management of RPV Irradiation Behavior


Irradiation Surveillance Programs

Monitoring material changesdepending on neutron fluence

RPV Integrity AssessmentFracture mechanics based PTS analysis p-T curves, in-service pressure tests

Assessment

Core Loading ManagementLow leakage

RPV Neutron ShieldingDummy assembliesInternals replacement

Thermal AnnealingRecovery heat treatment

Countermeasures


ObjectiveStrength and toughness properties of materials in the RPV core beltline region as a function of neutron irradiation by accelerated irradiation specimen capsules

Transfer functionsNeutron fluence Φ in n/cm2 for E > 1 MeV (0,5 MeV for VVER reactors) used for RPV irradiation surveillance

FMD (Freely Migrating Defects) and DPA (Displacement Per Atom; based on gamma, neutrons or both) are also often used for research purposes

Neutron DPA also used as damage function for comparing neutron radiation damage in two different nuclear reactors (e.g MTR and LWR) for proving the transferability of results



Safety Standards Germany: KTA 3203 “Surveillance of the Irradiation Behaviour of Reactor Pressure Vessel Materials of LWR Facilities”

US: ASTM E-185 “Standard Practice for Design of Surveillance Programs for Light-Water Moderated Nuclear Power Reactor Vessels”

France: RCC-M 2000, Z G 3430 Irradiation Effects


BM : base metalWM: weld metalAF: assessment fluence


Use of Surveillance Results for RPV Safety AssessmentReference temperature RT for KIc lower bound curveRTNDT concept based on Charpy shift: RTNDTj=RTNDT+∆T41

Master Curve approach based on direct fracture toughness measurement: RTT0


Initial condition: adjusted by RTNDT

0

20

40

60

80

100

120

-150 -100 -50 0 50Temperature[°C]

Cha

rpye

nerg

y [J]

∆T41

0

50

100

150

200

-150 -100 -50 0 50Temperature[°C]

Frac

ture

toug

hnes

s-1

/2]

ASME KIC Curve

Plant spec. KIC - curve

irradiated: adjusted byRTNDTj = RTNDT + ∆T41

∆T41

[MPa

*m

Plant spec. A V -T - curve


Scope of RPV Irradiation Surveillance ProgramsProject managementManufacture of specimens, fluence detectors, temperature monitors, and capsulesInsertion and take out of capsules, transportation servicesRadiochemical examinations and testing in the „Hot Cells“ laboratoryNeutron fluence calculations for specimens and RPVEvaluation of the results and RPV safety assessment according to regulatory requirements



BasicsGeneral Safety Criterion: Requirement for "Reactor-coolant pressure boundary" that dangerous leakage, rapidly propagating cracks and brittle fracture have to be excluded in accordance with the state of science and technology.

KTA safety standard 3203 defines provisions to be made to meet these requirements within their scope of application (RPV irradiation surveillance).

For primary circuit components the requirements of the aforementioned criteria are defined to comprise the following KTA safety standards:

KTA 3201.1 Materials and Product Forms,KTA 3201.2 Design and Analysis,KTA 3201.3 Manufacture,KTA 3201.4 Inservice Inspections and Operational Monitoring.



ScopeKTA safety standard 3203 defines requirements to be met regarding the monitoring of reactor pressure vessel (RPV) materials behavior under the effects of neutron irradiationa) performance and evaluation of irradiation surveillance programs,b) determination of neutron fluence,c) determination of the irradiation temperature,d) retention of specimens,e) documentation.Bestimmung der Neutronenfluenz,

RPV monitoring by irradiation surveillance program to determine the strength and toughness properties of base and weld materials in the core beltline region of the RPV

as a function of defined neutron irradiation

by means of accelerated irradiation specimen capsules

KTA 3203


Purpose of the irradiation surveillance programto experimentally verify the tensile and fracture toughness properties of the RPV material at assessment fluence (neutron fluence used in the assessment against brittle fracture)

to determine the location of the fracture toughness curve eithera) indirectly according to the RTNDT concept by comparing test results

obtained from accelerated-irradiation specimens and unirradiated specimens, or

b) to the fracture toughness concept by examining irradiated fracture toughness specimens (e.g. by determination of the reference temperature T0 to ASTM E 1921-97).

Necessity of irradiation surveillance programNeutron fluence ≥ 1⋅1017 cm-2 (E > 1 MeV)

KTA 3203


Result of the irradiation programAdjusted reference temperature RTNDTj , the limit value RTlimit shall be verified to cover RTNDTj as a result of an irradiation program

RTNDTj shall be taken for the proof of safety against brittle fracture

KTA 3203


RTlimit - German surveillance data

KTA 3203


RTlimit - German, French and US surveillance data

KTA 3203

R. BARTSCH1, R. LANGER2, G. NAGEL: NEW GERMAN KTA RULE 3203 FOR IRRADIATION SURVEILLANCE, EVALUATION AND APPLICATION IN THE SAFETY ANALYSIS OF RPVFontevraud 2002


SpecimensOriginal materials corresponding to those materials which are used in the RPV beltline region with respect to the manufacturing processSpecimens for the unirradiated set and the set to be irradiated shall be taken as near as possible to each otherBase material

Take out at ¼ T (at a depth of at least one quarter of the quenched and tempered wall thickness, but not more than 80 mm below the cylinder inner surface)T-L transverse (axial) specimens (with a longitudinal axis either transverse to the main direction of forming or parallel to the rotational axis of symmetry)Charpy-V and fracture mechanics specimens: notch axis shall be perpendicular to the plane of transverse and longitudinal directions or perpendicular to the cylindrical surface

Weld metal Charpy-V and fracture mechanics specimens: transverse specimens with notch axis perpendicular to the direction of welding and weld surface

Tensile specimens as parallel to welding direction

KTA 3203

Rissfortschritts-richtung

Schweiß-richtung

Wurzel


Number of test specimens

KTA 3203

≤ 1⋅1019 cm-2 (E > 1 MeV)

> 1⋅1019 cm-2 (E > 1 MeV)


Temperature monitors

Determination of highest temperature of irradiation specimens entire exposition time with measurement uncertainty of10 K

KTA 3203


Neutron detectorsWithin each set of irradiation specimens, 3 similar detectors for neutron fluence determination shall be inserted at respective locations, irradiated and evaluated

KTA 3203


Insertion, withdrawal, testing

Specimens, neutron detectors and temperature monitors in leak-tight capsules

Insertion at the earliest upon completion of hot trial operation, withdrawal during planned shutdowns, e.g. during refueling

Testing within one year after withdrawal

Testing and evaluations in certified test laboratories

KTA 3203


Irradiation6.1(3): Special evaluations for considering the neutron flux density are not required for RPV materials meeting the requirements of section B 5.1

B 5.1: Range of application of the RTlimit curve

Materials fabrication and heat treatment shall be adapted accordingly (ensured by the specified strength and toughness values in accordance with KTA 3201.1 and KTA 3201.3) and shall be evidenced during acceptance testing

Cu ≤ 0.15 %, Ni ≤ 1.1 % (1.1 % < Ni ≤ 1.7 %: RTLimit-curve applicable to 6•1018 cm-2, E > 1 MeV)

275 °C < Tirr < 300 °C

Lead factor = 1.5 to 12 (usually < 3)

The irradiation temperature shall normally not exceed the temperature of the ferritic RPV inner wall by more than 5 K

KTA 3203


Neutron fluenceDetermination of the complete neutron spectrum and neutron fluence (E > 1 MeV) for the specimen location and the RPV inner wall at the location of maximum flux density

The calculation based on an analytical program according to the neutron transport theory

The calculation of the neutron fluence shall be compared with the evaluation of the detector results

KTA 3203


Mechanical testsTensile test: yield strength ReH or proof stress Rp0.2, tensile strength Rm, elongation at fracture A5 as well as percentage elongation before reduction Ag and reduction of area Z at room temperature, at 150 °C and at the temperature corresponding to the long-term irradiation

Charpy-V test: complete absorbed energy-versus-temperature curves including lateral expansion and ductile fracture percentage, with the curves beginning at the lower shelf, characterized by a ductile percentage < 5% of the fracture area,up to the temperature corresponding to the long-term irradiation

Transition temperature shift from average (best-fit) curves at absorbed energy of 41 J (∆T41)

Adjusted reference temperature RTNDTj = RTNDT + ∆T41

KTA 3203

0

20

40

60

80

100

120

-150 -100 -50 0 50

Temperature [°C]

Cha

rpy

ener

gy[J

]

∆ T 41


RTNDTj at assessment fluence

The adjusted reference temperature RTNDTj shall be compared to the RTlimit

*) value of the respective reactor

Where values are available from two irradiated specimen sets, interpolation or extrapolation may be applied to obtain the assessment fluence; each suitable function is permitted (preferably the exponential function RTNDTj = A • Φn)

Extrapolation is not permitted if values from only one irradiated specimen set are available

Otherwise no requirement to apply trend curves for RTNDTj

KTA 3203

*) The limit value of the reference temperature (RTlimit) is the highest adjusted reference temperature on which the proof of equivalent safety margin against brittle fracture is based.


It shall be verified thatRTNDTj ≤ RTGrenz

Upper-shelf energy characterized by a ductile percentage > 95% of the fracture area does not exceed a value of absorbed energy of 68 J(single value)

Specimen retentionAll tested and untested specimens as well as the reserve material shall be retained

DocumentationShall permit complete traceability of the specimen history from fabrication to specimen evaluation and testing upon irradiation

KTA 3203


Complete Infrastructure

Materials Engineering and Testing, Plant Life ManagementRadiochemistry, Analytical Chemistry, Radiation Metrology, Hot CellsNeutron Physics



Radiochemical LaboratoryRadiochemistryChemical AnalysisRadiation MetrologyRadiation ProtectionHot Cells

Hot CellsMaterial TestingMetallographic ExaminationsManufacture of SpecimensTransport Container



High Resolution Techniques

Not mandatory for RPV irradiation surveillance, however very useful for understanding of embrittlement mechanisms

Most important methods

Transmission Electron Microscopy (TEM)

Scanning Auger Electron Spectroscopy (AES)

Field Emission Gun Scanning Transmission Electron Microscopy (FEGSTEM)

Small Angle Neutron Scattering (SANS)

Positron Annihilation Spectroscopy (PAS)

Atom Probe Tomography (APT)



Transmission Electron Microscopy TEM

High resolution, however to a lesser extent

Used for identification of matrix defects

Scanning Auger Electron Spectroscopy AES

Auger electrons are emitted from the first few atom layers at the specimen surface.

Used for chemical analysis of segregations to grain boundaries (P)



FEGSTEM

Scanning Electron Microscope, where electron beam focused on specimen surface

Imaging of surface and chemical analysis



Small Angle Neutron Scattering SANS

Size and distribution of radiation induces clusters (e.g. Cu enriched clusters)

Peak radius, volume fraction and number density of clusters



Positron Annihilation Spectroscopy PAS

Size of vacancy related defects by measurement of positron life time during interaction with electrons


Electron

2 Annihilation quanta


Atom Probe Tomography APT

Chemical composition and location of clusters by detection of ablated atoms

Needle shaped specimens of 1 mm x 1 mm x 15 mm



Longitudinal (L-T) vs. transverse (T-L) specimens

Specimen orientation in surveillance programs of older plants is longitudinal to the main working direction

However, up-to-date standards require transverse orientation because material toughness is lower in transverse direction

Specific Issues


Longitudinal (L-T) vs. transverse (T-L) specimens

T41 of T-L somewhat higher than for L-T (and USE lower)

Irradiation induced shift ∆T41 is independent of specimen orientation

Lower bound proposal of USNRC Standard Review plan to substitute 65 % of L-T USE if no T-L USE values are available

See also: Leitz, C., Klausnitzer, E.N., and Hofmann, G., „Influence of Specimen Orientation on the Upper Shelf Energy and Transition Temperature Shift of Reactor VessemSteel Base Metal“, ASTM STP 1170, 1993

If L-T data are available but T-L data are required testing of reconstituted compound specimens is a proven approach

Specific Issues


Specific Issues

Manufacture of CCA and SE(B) by reconstitution


Flux effects - Status

Some flux effects (usually higher DBTT shift at lower flux) observed in some Western LWR and in VVER, in particular for Cu rich RPV steels, however the issue is very complex and needs further clarification

Flux effects (if any) have to be taken into account for transferability of surveillance specimens and MTR results to RPVwall

EPRI workshop on Dose Rate Effects in Reactor Pressure Vessel Materials, Olympic Valley, California, November 12 – 14, 2001

Workshop “Trend Curve Development for Surveillance Data with insight on Flux Effects at High Fluence: Damage Mechanisms and Modeling”, Mol, Belgium, SCK-CEN, November 19-21, 2008

Specific Issues


German flux effect data

Neutron flux range 2E10 - 5E12 cm-2s-1 (E > 1MeV)

Neutron fluence range 2E18 - 1E20 cm-2 (E > 1MeV), mainly beyond EoL (32 EFPY)

No evidence for a neutron flux effect on material properties (∆T41)

Well designed materials: no indication of flux impact on ∆T41

High Cu materials: no indication of flux impact on ∆T41(potential discussion for one data point only with 4.7E12 cm-2s-1, flux impact on microstructure needs further investigation)

High Ni materials: no indication of flux impact on ∆T41

Confirmation of German Safety Standard KTA 3203 where no flux rate effect has to be considered

Specific Issues


German flux effect dataWell designed material BM 174 (22NiMoCr3-7, 0.1 % Cu)

Specific Issues

0

50

100

150

200

0,0E+00 5,0E+19 1,0E+20 1,5E+20

Neutron Fluence [cm-2] (E > 1 MeV)

∆T 4

1 [K]

BM 174, surv. program, f =7.2E10 cm-2 sec-1

BM 174, inner irr. position, f =3.1E12 cm-2sec-1

BM 174, VAK, f =2.5E12 cm-2sec-1

• PWR vs. MTR (VAK): no flux effect


0

50

100

150

200

0,0E+00 1,0E+19 2,0E+19 3,0E+19 4,0E+19

Fluence Φ [cm-2] (E > 1 MeV)

∆T 4

1, ∆

RT N

DT [

K]

P390 WM PWR f=2.1E11 cm-2 s-1

P390 WM VAK f=2.3 - 2.6E12 cm-2 s-1

P390 RegGuide 1-99 Rev 2 Pos 2

German flux effect dataHigh Cu material P390 WM NiCrMo1/LW320 (0.27 % Cu)

Specific Issues



0

50

100

150

200

0,0E+00 1,0E+19 2,0E+19 3,0E+19 4,0E+19

Neutron Fluence [cm-2] (E > 1 MeV)

∆T 41

[K]

WM 186 D, KWO, Cu = 0.22% f =6.1E10 cm-2 sec-1

WM 186 D, VAK, Cu = 0.22% f =2.1E12 cm-2 sec-1

WM 186 A, VAK, Cu = 0.14% f =2.6E12 cm-2 sec-1

WM 186 B, VAK, Cu = 0.30% f =2.6E12 cm-2 sec-1

WM 186 C, VAK, Cu = 0.42% f =2.6E12 cm-2 sec-1

German flux effect dataHigh Cu materials SAW 186 (= P370 WM, 0.14 … 0.42 % Cu)

Specific Issues

SANS results of P370 material show flux effect on microstructure but not on mechanical properties!

Bergner, A Ulbricht, H Hein and M Kammel:Flux dependence of cluster formation in neutron irradiated weld materialJ. Phys.: Condens. Matter 20 (2008) 104262 (6pp)

Flux ratio = 34


0

50

100

150

0,0E+00 1,0E+19 2,0E+19 3,0E+19 4,0E+19

Fluence Φ [cm-2] (E > 1 MeV)

∆T4

1, ∆

RTN

DT [K

]

P16 PWR f=2.0E10 cm-2 s-1

P16 (CARISMA) VAK f=1.1-3E12 cm-2 s-1

WM RegGuide 1-99 Rev 2 Pos 2

German flux effect dataHigh Ni material P16 WM (1.7 % Ni)

Specific Issues



EoL Neutron fluences (32 FPY) - Situation in Germany

Long Term Operation

2,8E19 1,3E19 1E19 3E18

KWO KKS GKN 1

Pre-Convoy,Convoy

n/cm2 (E>1MeV)


Objective

Increasing age of the existing NPPs and envisaged lifetime extensions up to an EOL of 80 years

Need for an improved understanding and prediction of RPV irradiation embrittlement effects under long term operation (LTO)

Irradiation effects caused by high neutron fluences such as the possible formation of Late Blooming Phases and as yet other unknown defects must be considered adequately in safety assessments

In this context the availability of microstructural data is also essential for the understanding of the involved mechanisms

Long Term Operation


High fluence and/or long irradiation

Specific focus on long term effects (Late Blooming Phases, neutron flux)

High Ni welds with high DBTT shift

Long Term Operation


Late Blooming Phases (LBP)

Possible significant increase of irradiation embrittlement at high fluences

LBP formation favored if

Low or no Cu content

High Ni and Mn

Low irradiation temperature

High fluence(>>1E19 n/cm2, E>1MeV)

Long Term Operation


Countermeasures

Core Loading ManagementLow leakage

RPV Neutron ShieldingDummy assembliesInternals replacement

Thermal AnnealingRecovery heat treatment


Core Loading Management (low leakage)

Neutron Fluence E > 1 MeV at the Inner RPV Surface of a PWR

Countermeasures

1.57E+19

6.59E+18

7.89E+18

1.14E+19

9.11E+18

1.24E+19

0.0E+00

1.0E+18

2.0E+18

3.0E+18

4.0E+18

5.0E+18

6.0E+18

7.0E+18

8.0E+18

9.0E+18

1.0E+19

1.1E+19

1.2E+19

1.3E+19

1.4E+19

1.5E+19

1.6E+19

1.7E+19

0 5 10 15 20 25 30 35

Full Power Years

Flue

nce

in 1

/cm

²

EO

C 2

319

.70

VLJ

with steel elements

without steel elements

EO

C 7

6.15

VLJ

EO

C 1

19.

41 V

LJ

EO

C 1

512

.94

VLJ

EO

L32

VLJ

insertion of absorber rods

beginning of low leakagecore loading


RPV Neutron Shielding Use of dummy or shielding assemblies at the core edge in the azimuthal region of the fluence maximum

fuel assemblies with high burn up and inserted absorber rods (AgInCd)

modified fuel assemblies with steel rods instead of fuel pellets

special steel elements

Countermeasures


US NRC Regulations

Countermeasures

RPV Anneals Worldwide

Fifteen “dry” anneals on VVER-440 RPV, 1987 – 1995

Loviisa-1 (VVER-440) RPV successfully ”dry” annealed in 1996

Two “wet” anneals: U.S. Army SM-1A vessel in Alaska in 1967 and the BR3 vessel in Belgium in 1984

Annealing Rule in 10 CFR Part 50.66

Regulatory Guide 1.162 on Annealing Program requirements and reporting

Annealing Rule and Regulatory Guide 1.162 contain reference to NUREG/CR-6327)

William L. Server: Annealing Activities in the U.S. - A Brief OverviewApril 15, 2002 – ATHENA Meeting


Countermeasures

Examples for Annealing of VVER 440 Welds (low Ni, some Cu)


Countermeasures

Annealing Measures in GermanySuccessful qualification by Siemens/KWU in the late 80ies but realization was not necessary

Annealing at 450 °C for 2…7 days


439 units worldwide (129 units of > 30 years)

Outlook


RPV surveillance and safety assessment is an essential part of PLIM/PLEX worldwide

Long term irradiation induced ageingRPV hardly replaceable

60 operational years are on the agenda

Design life of 60 years for Generations III, III+ (EPR), IVLife Time Extension activities for Generation II

USA: extended license life renewals of many NPPs

Europe: Switzerland, The Netherlands, France, Spain, Sweden, …

Additional surveillance capsules have been inserted in some RPV in The Netherlands, Switzerland and Germany

Outlook

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