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EDF AGEING MANAGEMENT:
R&D MATERIALS
PROGRAMMES
J-P MASSOUD, L. GRISY, EDF SEPTEN
P. LE DELLIOU, S. SAILLET, P. TODESCHINI, EDF R&D
4th PLIM Conference
LYON, October 2017
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SUMMARY
EDF Ageing Management: R&D Materials Programmes | PLIM Lyon - October 2017
1. FRENCH NUCLEAR FLEET SPECIFIC CONTEXT
2. MATERIAL AGEING PROGRAMME
3. FOCUS ON THERMAL AGEING OF METALLIC COMPONENTS
� - LOW ALLOY STEELS
- - CAST STAINLESS STEELS
- - AUSTENITIC STAINLESS STEELS WELDS
- - DISSIMILAR METAL WELDS
- - CARBON STEELS
4. CONCLUSIONS
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FRENCH NUCLEAR FLEET SPECIFIC CONTEXT
� The EDF lifetime management policy for LTO (Long Term Operation) of the NPPs is
based on three main principles:
� Regulatory context characterized by 10-year PSR (Periodic Safety Reviews) including
continuous safety improvement;
� Adequate maintenance policy associated with in-service inspections, and performance
improvement to increase operational capacities and availability of the units, in
compliance with safety requirements;
� Ageing and obsolescence management process for main NPP safety related
components to cope with ageing degradation mechanisms, including operating
experience feedback.
� LTO is supported by R&D programmes such as:
� 1/3 scaled PWR containment building : Vercors Programme [companion paper N°076]
� Metallic Materials Ageing Programmes (primary and secondary circuits components)
EDF Ageing Management: R&D Materials Programmes | PLIM Lyon - October 2017
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MATERIALS AGEING PROGRAMME
� The major objectives of the Metallic Materials Programme are:
� To ensure that all the pertinent ageing mechanisms are evaluated (including
potential mechanisms),
� Increase the knowledge in the areas and technical fields when required,
� Avoid unfavorable extrapolations due to a lack of data,
� Acquire needed data for equivalent 60 years ageing to check they remain
within the design and safety criteria.
EDF Ageing Management: R&D Materials Programmes | PLIM Lyon - October 2017
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MATERIALS AGEING PROGRAMME: METHOD
� Programmes systematically conducted:
� for all areas sensitive to ageing or degradation mechanisms
� on representative materials (archive, or sampled materials, or removed components, or dedicated
mock-upsG).
� Ageing is performed:
� in lab furnaces up to 100 000 or 200 000 hours (for thermal ageing evaluation),
� in “Test Reactor” or Power Reactors (for irradiation damage evaluation),
� in loops or autoclaves (for corrosion simulations).
� Materials are tested after (up to) equivalent 60 years ageing times,
� Measured properties:
� Mechanical data (toughness, tensile properties, fatigue...),
� SCC (Stress Corrosion Cracking) data: initiation and propagation, etc.
EDF Ageing Management: R&D Materials Programmes | PLIM Lyon - October 2017
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MATERIALS AGEING PROGRAMME:
Programmes and actions on primary and secondary circuits components underway
include (1/3):
� Reactor pressure vessel (RPV):
� Irradiation ageing of the core zone (∆RTNDT), [companion paper 052]
� Austenitic stainless steel cladding toughness,
� Thermal ageing of low alloy steels (base metals, welds, Heat Affected Zones),
� PWSCC (initiation and propagation) of nickel based components,
� RPV internals:
� Bolts: irradiation embrittlement, irradiation creep, Irradiation Assisted Stress Corrosion
Cracking (IASCC),
� Core barrel, baffles and formers: irradiation embrittlement, potential swellingG
EDF Ageing Management: R&D Materials Programmes | PLIM Lyon - October 2017
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MATERIALS AGEING PROGRAMME
Programmes and actions on primary and secondary circuits components underway
include (2/3):
� Primary loop:
� Cast Austenitic Stainless Steel (CASS) components (elbows, pump casing, valves....): long
term thermal ageing,
� Homogeneous austenitic stainless steels welds and stainless steel dissimilar metal welds
(DMW): potential thermal ageing,
� SCC: austenitic stainless steel in slightly polluted environment or cold worked,
� Austenitic and cast duplex stainless steel: fatigue behaviour (mainly initiation) including
environmental effects [companion paper in this conference, n°039],
EDF Ageing Management: R&D Materials Programmes | PLIM Lyon - October 2017
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MATERIALS AGEING PROGRAMME
Programmes and actions on primary and secondary circuits components underway
include (3/3):
� Pressurizer:
� Thermal ageing (345 °C) of low alloy steel pressure boundary components (base metal,
welds and heat affected zones),
� Homogeneous austenitic stainless steels welds of the surge line: thermal ageing,
� Secondary side:
� Thermal ageing of carbon steels.
� Flow assisted corrosion (FAC).
EDF Ageing Management: R&D Materials Programmes | PLIM Lyon - October 2017
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MATERIALS AGEING PROGRAM:
FOCUS ON THERMAL AGEING
� All ferritic (or martensitic) steels potentially susceptible to various forms of thermal
ageing in the temperature range 300-350°C,
� Potentially affected components:
� LAS: mainly PZR (due to high service temperature ~ 350°C),
� Cast Duplex Stainless Steels: primary circuit tubes, elbows, pump casing, fittings,
valvesG. (due to their ferrite content)
� Primary Circuit Austenitic Welds (due to their ferrite content),
� C-Steels of secondary side (thermal ageing + strain ageing).
� Martensitic Stainless Steels Components: stems, bolting, pump impellersG
EDF Ageing Management: R&D Materials Programmes | PLIM Lyon - October 2017
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THERMAL AGEING OF LOW ALLOY STEELS (1/2)
EDF Ageing Management: R&D Materials Programmes | PLIM Lyon - October 2017
� PWR RPV, SG and PZR steels are designed to have a low susceptibility to thermal
ageing at service temperatures (~290 to 350°C)
� low Phosphorus %, Mo addition, low CuGlimited hardness, bainitic microstructure,
� NPP components may operate for very long times, up to ~500 000 h (~60 years)
� Knowledge of physical mechanisms suggests that small ageing effects might be possible for such
durations and service temperatures. Phosphorus Segregation at Grain Boundaries
� Potential evolutions of mechanical properties have to be taken into account in the
integrity assessement of the components
� RCC-M (design and manufacturing) and RSE-M (maintenance) codes give DBTT shifts predictions
due to thermal ageing
� An experimental program has been undertaken to validate these predictions with
relatively long ageing times (30 000 h) at 300 and 350°C and representative
microstructures
� Base and weld metals, cladding HAZ: coarse and fine grain structures
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THERMAL AGEING OF LOW ALLOY STEELS (2/2)
MAIN RESULTS:
� For base and weld metals, measured embrittlements are
consistent with predictions (RCC-M, RSE-M codes).
� HAZ embrittlements are more marked but lower than
predictions.
� HAZ Coarse grain structure does not evidence a much
higher susceptibility to ageing than the rest of the HAZ.
� Code predictions are in all cases conservative.
� Complementary investigations on decommissioned
components useful to quantify this conservatism.
EDF Ageing Management: R&D Materials Programmes | PLIM Lyon - October 2017
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THERMAL AGEING OF CAST DUPLEX COMPONENTS (1/6)
� Some components of the primary loops of EDF PWRs are made of
static cast duplex SS: elbows, pump casings, branch connections
� Duplex SS (CF8M and CF3 type) may age at relatively low temperatures,
in the temperature range of PWRs service conditions
EDF Ageing Management: R&D Materials Programmes | PLIM Lyon - October 2017
� This embrittlement, associated with the presence of casting defects, may increase the
risk of failure
� In a context of life extension, it is important to assess the safety margins to crack
initiation and to crack propagation instability
� No prediction of aged materials properties in the codes: need of specific programmes
� A very long term experimental programme has been undertaken to develop materials
properties predictions
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THERMAL AGEING OF CAST DUPLEX COMPONENTS (2/6)
EXPERIMENTAL R&D PROGRAMME:
� Thermal Ageing Phenomenon:
� Duplex SS composed of two phases: ferrite (≈10 to 30% volume) + austenite
� Micro-structural evolution of the ferritic phase
� Relevant parameters: ferrite content, w%Cr, w%Si, w%Mo (and w% Ni)
� Laboratory Ageing Programme
� Acceptance blocks coming from in-service elbows + R&D products
� Aging between 285°C and 400°C – times up to 200,000 h (25 years!)
� Charpy impact tests and Fracture toughness tests on CT specimens at 20°C and 320°C
� Tensile tests, hardness measurementsG
EDF Ageing Management: R&D Materials Programmes | PLIM Lyon - October 2017
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THERMAL AGEING OF CAST DUPLEX COMPONENTS (3/6)
MAIN RESULTS:
� Ageing kinetics / Charpy KCU or KV (RT and 320°C) as a function of
equivalent ageing time at 325°C (or 290°C) for more than 50 different
materials
� Correlation Tearing Resistance / Charpy Toughness
� Prediction formulae of Charpy impact energy and Fracture Toughness of
aged cast materials vs initial properties, ferrite content, % Cr, Mo and Si,
ageing time and temperatureF
� On site ageing monitoring techniques developed to confirm the predictions.
EDF Ageing Management: R&D Materials Programmes | PLIM Lyon - October 2017
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THERMAL AGEING OF CAST DUPLEX COMPONENTS (4/6)
ON-SITE MONITORING OF COMPONENTS AGEING
� Non destructive measurements
� Thermo-Electric Power (TEP)
� Small Angle Neutron Scattering (SANS)
� Chemical composition (Cr, Mo, Ni) using portable X-ray fluorescence
spectrometry
� Ferrite content
� Microhardness measurementsG
� Direct measurements of ductile tearing resistance
� Miniature CT specimens (CT10-5)
� Boat samples cut by edm process
EDF Ageing Management: R&D Materials Programmes | PLIM Lyon - October 2017
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THERMAL AGEING OF CAST DUPLEX COMPONENTS (5/6)
LABORATORY STUDY OF REMOVED ELBOWS
� Some elbows are removed during SGs replacement
� These elbows are studied in-depth:
� Metallurgical studies
� Chemical analysis
� Mechanical characterization (hardness, tensile tests, Charpy
impact tests, toughness tests on CT specimens)
� Additional aging treatments
� At 325°C or 350°C
� To reach aging time equivalent to (or beyond) EOL (325,000 h or
500,000 h)
EDF Ageing Management: R&D Materials Programmes | PLIM Lyon - October 2017
Removed elbow aged about
200,000 h at 323°C
J-∆a tests at 320°C
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THERMAL AGEING OF CAST DUPLEX COMPONENTS (6/6)
CAST DUPLEX METHODOLOGY (SUMMARY):
� Formulae were developed to predict Charpy impact energy and Fracture Toughness
of aged CF8M, CF3 cast components
� The characterization of numerous shrinkage cavities enabled to define an envelope
surface defect
� FMA is conducted for each type of elbow with the envelope surface defect, taking
into account the margin coefficients of the French RSE-M Code
� Large tests and their detailed analysis contributed to the validation of the integrity
assessment of the CASS elbows
� On-site monitoring of components is also performed to assess the toughness
prediction and to follow the most severe manufacturing defects
EDF Ageing Management: R&D Materials Programmes | PLIM Lyon - October 2017
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THERMAL AGEING OF AUSTENITIC STAINLESS STEELS
WELDS (1/2)
� Austenitic stainless steels welds may age at PWR in the temperature range of
PWRs service conditions
� Same ageing as cast duplex stainless steels involving ferrite content (although lower
ferrite content: up to 10%)
� Toughness and tearing resistance (J0.2 and J1mm) data on aged SS welds codified
in French RSE-M (minimum values)
� An experimental program has been undertaken to confirm these data for the
different types of existing stainless steels welds:
� Manual Metal Arc (MMA)
� Gas Tungsten Arc Welding (GTAW)
� Electroslag Welding (ESW)
EDF Ageing Management: R&D Materials Programmes | PLIM Lyon - October 2017
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THERMAL AGEING OF AUSTENITIC STAINLESS STEELS
WELDS (2/2) � R&D Programme on representative full-scale mockups (thickness 80 mm and 30
mm, ferrite content around 10%)
� Submerged Arc Weld (SAW) mock-up 76 mm thick, 316L filler metal, 316L base metal
� Submerged Arc Weld (SAW) mock-up 40 mm thick, 316L filler metal, 316L base metal
� Orbital TIG Weld (GTAW) mock-up 73 mm thick, 316L filler metal, 316L base metal
� Long ageing times (up to 30 000 h at 400°C on representative welds)
� Kinetics of Charpy-Toughness data and Tearing Resistance (J0.2 -J1mm) data.
� Main results:
� Low sensitivity to thermal aging,
� Confirm the codified (French RSE-M) data (minimum)
EDF Ageing Management: R&D Materials Programmes | PLIM Lyon - October 2017
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THERMAL AGEING OF STAINLESS STEEL DMW (1/2)
� Dissimilar Metal Welds are located between the ferritic low alloy steel heavy section
components and the austenitic stainless steel piping systems.
� DMW have a specific dilution area between ferritic base metal and SS weld metal,
� Behaviour and potential ageing of these dilution zones (and HAZ ferritic side)
� Few Toughness and Tearing Resistance (J0.2 and J1mm) existing data
� An experimental program has been undertaken to complement these data
� R&D Programme on representative full-scale mockups (thickness 80 mm and 30 mm)
with dilution area similar to those existing on actual components
� Manual Metal Arc (MMA) :16MND5 LAS / 309L-308L stainless steel buttering
� Gas Tungsten Arc Welding (GTAW): 16MND5 LAS / 309L-308L stainless steel buttering
� Long ageing times (up to 30 000 h at 400°C)
EDF Ageing Management: R&D Materials Programmes | PLIM Lyon - October 2017
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THERMAL AGEING OF STAINLESS STEEL DMW (2/2)
R&D PROGRAMME MAIN RESULTS:
� Charpy and CT fracture toughness at both, the ferritic side (in the Heat Affected
Zone) and the stainless steel buttering side of the fusion line were performed
� Ageing degree rather small, both in the HAZ and in the weld metal near the fusion
line (after 10 000 hours / 400°C)
� On-going aging treatments up to 30 000 hours / 400°C.
EDF Ageing Management: R&D Materials Programmes | PLIM Lyon - October 2017
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THERMAL AGEING OF CARBON STEELS (1/2)
� Toughness and Tearing Resistance (J0.2 and J1mm mini values) data on Carbon-
Manganese steels (base metal and welds) are codified in French RSE-M code
� Potential evolutions of mechanical properties due to thermal ageing have to be taken
into account in the integrity assessment of the components
� DBTT shifts due to thermal ageing + strain ageing = 15°C, for « killed » steels (%Al / %N
> 2) or stress-relieved welds
� An experimental R&D program has been undertaken to confirm the tearing resistance
data and DBTT shift due to thermal + strain ageing
� Characterization of a removed carbon manganese steel elbow (with high sulphur content)
� Thermal + strain ageing programme on a removed carbon manganese steel elbow and on
representative plates (with high Phosphorus content: up to 0.034%)
EDF Ageing Management: R&D Materials Programmes | PLIM Lyon - October 2017
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THERMAL AGEING OF CARBON STEELS (2/2)
R&D PROGRAMME MAIN RESULTS:
� Confirmation of the codified (RSE-M) tearing resistance data (minimum values):
� J0,2 > 92 kJ/m2 at T< 100°C,
� J0,2 > 55 kJ/m2 at T> 200°C
� Low sensitivity of carbon manganese steel to thermal aging
� less than 15°C even for high P content
� and for severe ageing: 30 000 h at 400°C
� Low strain ageing effect
EDF Ageing Management: R&D Materials Programmes | PLIM Lyon - October 2017
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CONCLUSIONS
� The Materials programmes are almost completed (RPV and internals
irradiation, thermal ageing of CASS, martensitic stainless steels, welds ...).
� Data are collected in databases and compared with codified values, and, where
applicable, predictive formulae are proposed.
� A few programmes are still in progress (long term thermal ageing of austenitic
welds and dissimilar metal welds, fatigue, swelling, IASCC, SCC ..).
EDF Ageing Management: R&D Materials Programmes | PLIM Lyon - October 2017