IAEA Coordinated Research Projects on Irradiated Reactor Pressure Vessel Structural

IntegrityW. L. Server, ATI Consulting

R. K. Nanstad, ORNLPresented at Second International Symposium on Nuclear Power Plant Life Management, Shanghai,

China, October 2007

IAEA History on RPV Steels• IAEA has supported neutron radiation effects on RPV steels since the mid 1960s – Consultants’ meetings– Specialists’ meetings– Conferences– Coordinated research projects (CRPs)

• In 1972, 25 countries operated water cooled type reactors – Individual studies on the basic phenomenon of radiation hardening

and embrittlement were being conducted– Laboratories applied different test conditions using different steels

and varying test samples to assess radiation embrittlement• It was the intent of IAEA to develop a correlative comparison to test the uniformity of international results through CRPs

RPV Integrity after Irradiation

Irradiation damage challenge

Coreweld

Testing

Model

Matrix damage

• CRP 4 : Assuring Structural Integrity of RPV (1995-2002) : 24 Organizations from 19 Member States • CRP 4 : Assuring Structural Integrity of RPV (1995-2002) : 24 Organizations from 19 Member States

• CRP 3 : Optimizing RPV Surveillance Programmes and Analyses (1983-2001) 24 Organizations from 18 Member States• CRP 3 : Optimizing RPV Surveillance Programmes and Analyses (1983-2001) 24 Organizations from 18 Member States

• CRP 2 : Analysis of the Behavior of RPV Steels under Neutron Irradiation (1977-1986) : 10 Organizations from 9 Member States • CRP 2 : Analysis of the Behavior of RPV Steels under Neutron Irradiation (1977-1986) : 10 Organizations from 9 Member States

• CRP 1 : Irradiation Embrittlement of RPV Steels (1971-1975): 9 Organizations from 8 Member States• CRP 1 : Irradiation Embrittlement of RPV Steels (1971-1975): 9 Organizations from 8 Member States

IAEA CRPson RPV Structural Integrity

• CRP 5 : Surveillance Programme Results Application to RPV Integrity Assessment (1999-2003) : 24 Organizations from 15 Member States

• CRP 5 : Surveillance Programme Results Application to RPV Integrity Assessment (1999-2003) : 24 Organizations from 15 Member States

IAEA CRPson RPV Structural Integrity

• CRP 6 : Mechanism of Ni Effect on Radiation Embrittlement of RPVMaterials (1999-2003), 11 Organizations from 10 Member States• CRP 6 : Mechanism of Ni Effect on Radiation Embrittlement of RPVMaterials (1999-2003), 11 Organizations from 10 Member States

• CRP 7 : Evaluation of Radiation Damage on WWER-440 RPV Materials using IAEA Database (2001-2004), 8 Organizations from 7 Member States

• CRP 7 : Evaluation of Radiation Damage on WWER-440 RPV Materials using IAEA Database (2001-2004), 8 Organizations from 7 Member States• CRP 8 : Master Curve Approach to Monitor Fracture Toughness of

RPV (2004-2008), 15 Organizations from 11 Member States• CRP 8 : Master Curve Approach to Monitor Fracture Toughness of RPV (2004-2008), 15 Organizations from 11 Member States• CRP 9 : Review and Benchmark of Calculation Methods for

Structural Integrity Assessment of RPVs during PTS (2005-2008), 10 Organizations from 10 Member States

• CRP 9 : Review and Benchmark of Calculation Methods for Structural Integrity Assessment of RPVs during PTS (2005-2008), 10 Organizations from 10 Member States

More than 120 research organizations from 20 countries since 1971

CRP 1: Irradiation Embrittlement of Pressure Vessel Steels

• Duration : 1971 to 1975• Reference steel ASTM A-533 Grade B Class 1 (HSST Plate 03) provided by USA• Main goals :

– Establish standardized approaches for direct inter-comparison of mechanical properties and neutron fluence/ spectra data after irradiation in nine different reactors– To compare the embrittlement sensitivity of national steels with that of the HSST Plate 03 reference steel

• Documented in IAEA-176 (1975)• One key outcome was confirmation that specific residual elements, namely copper and phosphorus, enhance irradiation embrittlement of RPV steels –provided basis for next CRP

CRP 2: Analysis of Irradiation Behavior of Advanced RPV Steels

• Duration: 1977 to 1986• Purpose:

– To undertake a comparative study of the irradiation embrittlement behavior of improved (advanced) steels produced in France, Germany, and Japan– To demonstrate that careful specification of the steel for RPV can eliminate the problem of potential failure including that caused by neutron embrittlement

• Same organizations as in CRP-1• Documented in Technical Report Series 265 (1986)• Advanced RPV steels have adequate toughness extending to years beyond original license life• Improvements in neutron dosimetry methods and application of fracture toughness were achieved

CRP 3: Optimizing RPV Surveillance Programs and Analyses

• Duration : 1983 to 2001• 16 base and 6 weld materials were irradiated and tested to assess synergistic effects of copper, nickel, and phosphorus for older and advanced RPV steels• Main objectives:

– Establish guidelines for surveillance testing that could be used internationally– Optimize measurement of fracture resistance– Establish correlative methods– Identify mechanisms of radiation embrittlement

• Reference material (JRQ: ASTM A 533B-1 plate, specially fabricated in Japan to show relatively large shifts) was procured for this and future programs –IAEA-TECDOC-1230 (2001)

JRQ Reference Material

6JRQ 12

1.1 1.2 1.3 1.4

2.1 2.2 2.32.42.5

3.1 3.2 3.3 3.4

4.1 4.2 4.3 4.4

5.1 5.2 5.3 5.4

6.1 6.2 6.36.4

7.1 7.2 7.3 7.4

63,5 63,5 63,5242

�38

1010

1010

1010

4.5

6.5

6JRQ 12

1.1 1.2 1.3 1.4

2.1 2.2 2.32.42.5

3.1 3.2 3.3 3.4

4.1 4.2 4.3 4.4

5.1 5.2 5.3 5.4

6.1 6.2 6.36.4

7.1 7.2 7.3 7.4

63,5 63,5 63,5242

�38

1010

1010

1010

4.5

6.5

• Large 25 ton steel plate manufactured by Kawasaki Steel

• Cutting diagram of test pieces 1 m X 1 m

• Test blocks supplied to participants for:–Chemical composition–Tensile properties– Impact properties–Fracture properties

• Comparatively homogeneous and still is being used as reference steel

CRP 4: Assuring Structural Integrityof RPV

• Duration: 1995 to 2002• Collected a large amount of experimental data

– To check the Master Curve (MC) fracture toughness approach using JRQ, as well as other national steels

– To verify the application of Master Curve using small precracked Charpy size specimens

• Conclusions :– MC approach can be applied to wide set of national RPV LWR steels including WWER RPV materials

– Demonstrated that small size precracked Charpy specimens can be used for determination of valid values of fracture toughness for RPV ferritic steels in the transition temperature region

– Established basis for conducting CRP-5

Master Curve Approach

-200 -150 -100 -50 0 500

50

100

150

200

250

300

M = 30

5 %

95 %

JRQ T-L σY = 490 MPa B = 10 mm 50-175 mm

CLEAVAGEDUCTILE

T0 = -71 oC

B0 = 25 mm

K JC [

MPa√

m]

T [oC]

T0

)](019.0exp[7030 0TTKJc −⋅⋅+=

CRP 5: Surveillance Program Application to RPV Integrity

• Duration : 1999 to 2003• Goals:

– Develop a large database of fracture toughness data using the MC methodology for both precracked Charpy size and 1T-CT specimens – IAEA-TECDOC-1435 (2005)

– Develop international guidelines for measuring and applying Master Curve fracture toughness results for RPV integrity assessment – IAEA Technical Report Series 429 (2005)

• Key outcomes were recommendation to ASTM Standard E 1921 to acknowledge bias between specimen types and effects of loading rate within “valid” static rate testing range

Guidelines for Implementation of Master Curve Methodology (TRS 429)

Section 3

Section 8

Section 7

Section 6

Section 5

Section 4Type and number of SMfracture mechanicsspecimens

Test using ASTM E1921 toobtain To and σTo (andother fracture parameters)

Obtain best estimate of Tofor SMAdjust for small number,combination or type,censoring, or abnormal data

Best estimate of To for RPVMaterial Bias adjustment or otherconstraint adjustmentRatio or other material heatadjustment, plus non-homogeneity (σΗΤ) (includingthrough-thickness)

Use ∆Τo vs ∆T41J (∆Tk)correlation; need σcorr,σ∆ and σiNo

Yes

Is SM irradiated?

Application-defined flawsize, flaw type, and stressstate

Deterministic Application

Use ASME CodeCurves and RTTo(Code Case N-629)Use Master Curvewith x% lowerbound

Other approachesconsidering shapechange, etc...

Perform Analysis

Probabilistic Application

Use best estimate To asfunction of φt, Master Curvestatistical distribution, andother uncertainties

Fluence funciton to allowprojection (σφt) andattenuation

Margin based on uncertainties,define Y and x (if necessary)

Master Curve Comparisonfor 6JRQ Test Results

0

50

100

150

200

250

300

350

-75 -50 -25 0 25 50 75T-T0 in °C

K Jc(1

T) in

MPa

m0.5

ARG BRA BULNRI VIT FINFZR IWM HUNJAP KOR ROMPRO KUR ESPUSE USI USO

KJc(med) 1T

KJc(0.05)1

KJc(0.01)1T

Charpy size SE(B) specimens, 1/4-T and 3/4-T

0

50

100

150

200

250

300

350

-75 -50 -25 0 25 50 75T-T0 in °C

K Jc(1

T) in

MPa

m0.5

NRI VITFZR IWMROM PROUSO

KJc(med) 1T

KJc(0.05)1TKJc(0.01)1T

1T-CT specimens 1/4-T and 3/4-T

T0 for PCC = -66oC T0 for 1T-CT = -54oCBias = -12oC

CRP 6: Effects of Nickel on Irradiation Embrittlement of RPV Steels

• Duration: 1999 to 2003• Focus on effect of higher Ni content in WWER-1000 steels and compared with other RPV steels• Irradiations/testing were conducted for WWER-1000 base metal (1.2% Ni) and weld (1.7% Ni) provided by RRC Kurchatov Institute

– Higher radiation sensitivity of high nickel weld metal was seen as compared with lower Ni base metal– Weld metal shifts exceeded Russian Guide at higher than current life fluence levels

• High Mn content leads to much greater irradiation-induced embrittlement than low Mn content as supported by results from WWER-1000 and PWR national steels (up to 3.5% Ni)• Documented in IAEA-TECDOC-1441 (2005)

Irradiated Test Results for WWER-1000 Base and Weld Metals

0

20

40

60

80

100

120

140

160

0 2 4 6 8 10 12 14 16 18

Fluence, x 1019 n/cm2 (E > 0.5 MeV)

∆ T41

J, o

C (as

adjus

ted)

Base Metal (Ni = 1.2 mass%)Weld Metal (Ni = 1.7 mass%)

Trend for 1.2 mass% NiTrend for 1.7 mass% Ni

1.2% Ni

1.7% Ni

Atom Probe Tomography Showing Copper-Enriched Precipitates

Ni associates with Cu in precipitates, as well as Mn and P (and possibly Si), in irradiated U.S. weld metal with high bulk Cu and Ni contents

Cu Ni Mn Si P 10 nm

Atom Probe Results for Low Cu WWER-1000 Weld Show Clustering

Ultrafine Mn-, Ni-and Si-enriched precipitates at low dose; not Cu-enriched

CRP 7: Prediction of Radiation Embrittlement of WWER-440 RPVs• Duration: 2001 to 2004• Analysis of embrittlement surveillance data in IAEA database developed for WWER-440 RPV steels

• Evaluation of predictive formulae depending on material chemical composition, neutron fluence, and neutron flux

• Development of guidelines, including methodology for evaluation of surveillance data, for prediction of radiation embrittlement –including use of Master Curve data

• Documented in IAEA-TECDOC-1442 (2005)

Comparison of Experimental Data with Predictions for WWER-440 Steels

Metal Formula Standard Deviation

Weld Metal

∆T = [884×P + 51.3×Cu]Φ0.29

= 800×(1.11×P + 0.064×Cu) Φ0.29

22.6°C

Base Metal

∆T = 8.37×Φ0.43

21.7°C

CRP 8: Master Curve Approach to Monitor Fracture Toughness of RPVs• Duration: 2004 to 2008• Three key topic areas:

– Test specimen bias, constraint, and geometry effects• Effect of constraint between different surveillance-type

specimens and application to the RPV – data collection• Finite element round robin exercises underway

– Effects of loading rate, including impact loading conditions• JRQ data generated and other RPV steel data compiled• Round robin exercise for instrumented impact testing

completed – used proposed European standard for testing– Changes in Master Curve shape for highly embrittled

RPV materials or limitations on use of Master Curve (i.e., IGF or other fracture mode)

CRP 9: Review and Benchmark Calculation for PTS

• Duration: 2005 to 2008• Perform series of deterministic benchmark RPV integrity calculations for typical PTS regimes, varying critical parameters, in order to quantify effects for both WWER and PWR 3-loop RPVs

• Based on sensitivity of various parameters studied, vessel integrity assessments will be consolidated into IAEA Good Practice Handbook for RPV Integrity Evaluations for PTS

• Portions of Good Practice Handbook and key recommendations for PTS calculations also will be included in a separate IAEA Technical ReportSeries on PTS

Challenges Still Remain• IAEA has contributed significantly to dissemination of knowledge regarding RPV structural integrity though nine CRPs, sponsored meetings, and associated publications• Other advances in technology exist that still need further integration; eg.:

– Elastic-plastic fracture mechanics using even smaller test specimens– Large databases of surveillance data from various types of reactors to assess uncertainties associated with predictive embrittlement correlations/models– Enhanced microstructural tools, such as atom probe tomography and SANS, for obtaining better understanding of radiation damage mechanisms– Computational sciences that provide ability to rapidly perform modeling studies, such as molecular dynamics

Key Issues Relative to PLiM andLonger Operating Life

• Always a need for proper surveillance programs – surprises still can happen

• Need for adequate irradiated fracture toughness data at doses indicative of 50-60-70-80+ years of operation– Resolution of any dose rate effects in this dose-dose rate regime

– Definition of any new embrittlement mechanisms operating at high doses

• Post-irradiation heat treatments and consequences similar to temper embrittlement in HAZ or other susceptible region

Next Steps in RPV Integrity

Design Operation

Neutron Embrittlement

Structural Integrity

Anticipated transientsTemperatureStresses

Actual transientsTemperatureStresses

Beltline materials Neutron dose rate/doseMaterial PropertiesAny defects (PSI)

Surveillance programMeasured dose rate/doseProperty changesMonitoring ISI

Material Needs Still Exist•Fracture toughness data at high doses indicative of longer RPV operating time•Use of data for developing predictive models and/or mitigative measures–Mechanistic understanding–Microstructure characterization