Extensive investigation of the mechanical properties of a Chooz A internal component

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Extensive investigation of the mechanical properties of a

Chooz A internal component

J. Hure, B. Tanguy, C. Ritter, A. Courcelle, S. Bourganel, A. Galia, F. Sefta

To cite this version:

J. Hure, B. Tanguy, C. Ritter, A. Courcelle, S. Bourganel, et al.. Extensive investigation of the

mechanical properties of a Chooz A internal component. Fontevraud 9 - Contribution of Materials

Investigations and Operating Experience to Light Water NPPs’ Safety, Performance and Reliability,

Sep 2018, Avignon, France. �cea-02338720�

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Extensive investigation of the mechanical properties

a Section for Research on Irradiated Materials, CEA Saclay

J. Hurea_{, B. Tanguy}a_{, C. Ritter}a_{, A. Courcelle}a

Fontevraud 9, September 17th - 20th, Avignon, France

of a Chooz A internal component

S. Bourganelb_{, A. Galia}b_{, F. Sefta}c

b Service d'Etude des Réacteurs et de Mathématiques Appliquées, CEA Saclay c EDF Lab

(3)

Background

Internal Structures of Pressurized Water Reactors (PWR's)

SA304(L) for baﬄe plates CW316 for bolts

308 for welds

(Allen et al., 2010)

Evolution of mechanical properties with irradiation

Increase of yield stress

300 series Austenitic stainless steels :

Decrease of strain-hardening capability Decrease of fracture toughness

As a consequence of nanoscale irradiation defects

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Background

3/17

Evolution of yield stress with irradiation

200 400 600 800 1000

304L-1 (A) SA, Bor-60 at 320ºC, 330ºC

304L-1 (A) SA, Samara at 300ºC, 330ºC 304L-1 (A) SA, Samara at 300ºC, 380ºC 304L-1 (A) SA, Bor-60 +Samara, 330ºC 304L-1 (CB) SA, Bor-60 at 320ºC, 330ºC 304-3 (FD) SA, Bor-60 at 320ºC, 330ºC 304 (EH or J 7) SA, Bor-60 at 320ºC, 330ºC 304-J 3 (EH) 10%CW, Bor-60 at 320ºC, 330ºC 347-2 (EC) SA, Bor-60 at 320ºC, 330ºC 304 Decom. PWR at 288-315ºC, 320ºC 304 Oskarshamn 1/2 at 280ºC, 270-290ºC 304L Oskarshamn 1/2 at 280ºC, 288-295ºC 304L Barseback 1 at 288ºC, 288ºC 347 Point Beach 2, 320ºC 304 BWR at 288ºC, 288ºC 304 Chooz A at 288ºC, 320ºC 304 BWR at 288ºC, 300ºC 304 BWR at 288ºC, 300ºC 304L BWR at 288ºC, 300ºC Y ie ld S tr en gt h (M P a)

Neutron Dose (dpa)

Type 304, 304L, & 347 SS MRP Curve (a) 0 20 40 60 80 100 300 400 500 600 700 800 900 1000 1100 316-1 (B) 15%CW, Bor-60 at 320ºC, 330ºC 316-1 (B) 15%CW, Samara at 300ºC, 330ºC 316-1 (B) 15%CW, Samara at 300ºC, 380ºC 316-1 (B) 15%CW, BOR-60 + Samara, 330ºC 316-2 (DB=J 6) 15%CW, BOR-60 at 320ºC, 330ºC 316-3 (DA) 11%CW, BOR-60 at 320ºC, 330ºC 316-4 (DC) CW, BOR-60 at 320ºC, 330ºC 316-L1 (EA) CW, BOR-60 at 320ºC, 330ºC 316-L2 (EB) CW, BOR-60 at 320ºC, 330ºC 316-H1 (J 5) CW, BOR-60 at 320ºC, 330ºC 316-1 (C) SA, BOR-60 at 320ºC, 330ºC 316 CW Farley 1 at 303-357ºC, 320ºC 316 CW Ringhals 2 at 290ºC, 320ºC 316CW PWR at 310-335ºC, 290-340ºC 316CW PWR at 290-310ºC, 290-340ºC Y ie ld S tr en gt h (M P a)

Neutron Dose (dpa)

Type 316 Cold Worked SS MRP Curve

(a)

0 20 40 60 80 100

(Chopra & Rao, 2011)

Well documented for doses up to 100dpa: Saturation for doses higher than ~20dpa

Consistent results between LWR and Fast reactors irradiation conditions Higher saturation for CW316 compared to SA304

(5)

Background

Evolution of fracture toughness with irradiation

(Chopra & Rao, 2011)

Saturation for doses higher than ~20dpa

Consistent trends between LWR and Fast reactors irradiation conditions But large variability

Limited data from LWRs retrieved materials at high doses

0 100 200 300 400 500 600 0 5 10 15 20 25 304 J APEIC (CT) 304 J APEIC (BB) 304 J APEIC (SR) 304 MRP-160 316CW/347 MRP-79 304 MRP-79 304L MRP-79 E308L MRP-79 304L/316L (Ehrnsten 2006) 304/316L NUREG/CR-6960 304/304L HAZ NUREG/CR-6960 CF-8M Aged NUREG/CR-6960 304 Sensi NUREG/CR-6960 304/304L L-T (Demma 2007) 304/304L T-L (Demma 2007) 304 (Fyfitch 2009) JIc (k J/ m 2)

Neutron Exposure (dpa) Austenitic SSs Irradiated in LWRs Tested at 250-320ºC 835 kJ /m2

Closed Symbols: BWR Water Open Symbols: Air

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Background

4/17

Evolution of fracture toughness with irradiation

(Hojna, 2017)

Saturation for doses higher than ~20dpa

Consistent trends between LWR and Fast reactors irradiation conditions But large variability

Limited data from LWRs retrieved materials at high doses Similar fracture mechanisms ?

Main objective of this study

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Material

Decommisionned PWR Chooz A reactor (operating between 1967 and 1991)

304 austenitic stainless steel

Characterization of sub-blocks in blocks A, C, H Retrieved baﬄe separating fuel assemblies

Diﬀerent irradiation temperatures (~300°C / ~330°C) Diﬀerent irradiation doses (between ~1 and ~30 dpa)

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Evaluation of irradiation doses

6/17

Sampling of material

Measurements of

Available data not suﬃcient for a purely numerical estimation of dpa

Coupled Experimental / Numerical strategy

at well-deﬁned locations along the blocks

Residual 59_{Co and}60_{Co activity}

TRIPOLI-4 Monte-Carlo transport code JEFF 3.1.1 Nuclear DataBase

DARWIN/PEPIN2 evolution code

Simplifying assumptions Calibration

DPA, neutron spectrum

(9)

Evaluation of irradiation doses

Unknowns

Initial 59_Co

Norm of the neutron spectrum

Predicted Residual 59_Co Predicted Activity 60_Co Simulation Measured Residual 59_Co Measured Activity 60_Co Comparison Optimization DPA

Results: Dose estimation (at block locations)

Older estimations

(used in previous studies)

(10)

Tensile and fracture toughness specimens machining

8/17

Machining of samples (CEA Saclay Hot Cells)

Electric Discharge Machining Conventional Milling

Available samples

10 ﬂat tensile specimens (one homothetic x2)

7 Compact Tension (CT12.5) fracture toughness specimens

Mechanical tests performed at CEA Saclay Hot Cells

(11)

Plastic behavior of porous materials

Macroscopic yield criterion for porous material (spherical voids)

Shear Hydrostatic pressure

Gurson-Tvergaard-Needleman (GTN) criterion (1977, 1981, 1984)

Reduced yield stress as increases

Plastic ﬂow ?

Tensile properties

Conventional tensile curves (330°C)

Signiﬁcant local ductility, followed by shear band failure

Overall saturation of mechanical properties for doses higher than 16dpa Yield stress ~850MPa

Ultimate tensile strength stress ~900MPa No significant effect of tensile sample geometry (Unexpected ?) effect of irradiation temperature

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12/29

Plastic ﬂow under hydrostatic pressure

Rice & Tracey law (1969)

Plastic ﬂow under shear

Material incompressibility

Material incompressibility Void growth

No void growth, but ...

11/29

Hydrostatic pressure

Gurson-Tvergaard-Needleman (GTN) criterion (1977, 1981, 1984) Stress triaxiality

Reduced yield stress as increases Plastic ﬂow ?

Tensile properties

10/17

Conventional tensile curves (20°C)

Stable neck propagation (along the gage length) during the stress plateau

Reproducible stress-strain curves at 18dpa: Stress plateau and re-hardening

Yield stress ~1000MPa

Ultimate tensile strength stress ~1100MPa

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Tensile properties : Comparison with literature data

Consistent with previously published data

High doses values higher than MRP2004 curve at ~300°C

Saturation value for MRP curve based on Fast Reactor data Similar observations for ultimate tensile strength

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Some extensions of early models (1969 - ...)

Strain-hardening

Coalescence modeling

Competition between void softening and matrix hardening

Phenomenological law for the evolution of porosity in the coalescence regime Homogenization in the coalescence regime

New dimensionless parameters:

(Gurson, 1977)

(Thomason, 1985)

(Tvergaard & Needleman, 1984)

Fracture toughness properties

Methodology

Precracking in fatigue at 20°C

Interrupted tests at 330°C (for a given ) Final fracture at 20°C

Post-mortem measurements of : Initial crack length

Crack propagation

Typical results (at a given dose)

Very reproducible Load - Opening loading curves

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Some extensions of early models (1969 - ...) Plastic behavior of porous materials Plastic behavior of porous materials

Fracture toughness properties : Comparison with literature data

Fast Reactor Irradiation

New data lead to for dose > 16dpa

within the scatter of previous results (at lower doses) for LWR conditions consistent with the saturation value from Fast reactors data

Signiﬁcantly above the MRP bounding line

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Some extensions of early models (1969 - ...)

14/29

12/29

11/29

Fracture Mechanisms

14/17

At 20°C (on tensile samples)

Fracture surfaces almost fully intergranular

Related to martensitic transformation during straining ? Local zones of ductile fracture through void growth to coalescence

Similar observations for fracture surfaces at 20°C on CT specimens In addition : fatigue crack is also mostly intergranular

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Some extensions of early models (1969 - ...) Plastic behavior of porous materials Plastic behavior of porous materials Fracture Mechanisms

At 330°C (on tensile samples)

Fracture surfaces fully transgranular with dimples

Two dimple size populations : ~10microns and ~1 microns Elongated dimples: failure in a shear band

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At 330°C (on fracture toughness samples)

Three main features on fracture surfaces

Presence of stringers with MnS inclusions

Micron-scale classical ductile fracture (transgranular dimples) Planar facets with ridges and nanoscale dimples

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At 330°C (on fracture toughness samples)

3 main features on fracture surfaces

Presence of stringers with MnS inclusions

Micron-scale classical ductile fracture (transgranular dimples) Planar facets with ridges and nanoscale dimples

(20)

Some extensions of early models (1969 - ...) Plastic behavior of porous materials Plastic behavior of porous materials Conclusions and open questions

Investigation of the mechanical properties of a Chooz A internal component Tensile properties consistent with previous data

Void growth to coalescence fracture mechanisms at 330°C Intergranular failure at 20°C

Fracture properties supplement existing data for LWR conditions

Void growth to coalescence fracture mechanisms at 330°C Still signiﬁcant at 20dpa/330°C:

Similar to Fast reactors data showing Channel fracture

Nano-scale dimples on planar inter/trans (?) facets: Mechanism ?

Mechanism and modelling of intergranular fracture Open questions