EDF AGEING MANAGEMENT: R&D MATERIALS · PDF filesurface defect FMA is conducted for ... Gas...

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)


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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.


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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.


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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


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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],


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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).


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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


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THERMAL AGEING OF LOW ALLOY STEELS (1/2)


� 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.


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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


� 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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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


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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.


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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


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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)


Removed elbow aged about

200,000 h at 323°C

J-∆a tests at 320°C

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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


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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)


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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)


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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)


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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.


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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%)


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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


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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 ..).


Thank you for your

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