Characterization of oxide scales formed on Alloy 82 in nominal PWR primary water at 340 degrees C and in hydrogenated steam at 400 degrees C

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nominal PWR primary water at 340 degrees C and in hydrogenated steam at 400 degrees C

C. Duhamel, M. Sennour, F. Georgi, C. Guerre, E. Chaumun, J. Crepin, E.

Heripre, I. de Curieres

To cite this version:

C. Duhamel, M. Sennour, F. Georgi, C. Guerre, E. Chaumun, et al.. Characterization of oxide scales formed on Alloy 82 in nominal PWR primary water at 340 degrees C and in hydrogenated steam at 400 degrees C. USNRC 2015 Meeting – International Cooperative Group for Environmentally Assisted Cracking, May 2015, Ann Harbor, United States. �cea-02500813�

Characterization of oxide scales formed on Alloy 82 in nominal PWR primary water at 340°C and in

hydrogenated steam at 400 ° C

C. Duhamel

, M. Sennour

, F. Georgi

, C. Guerre

, E. Chaumun

, J. Crépin

, E. Héripré

, I. de Curières

1

MINES ParisTech, PSL Research University, Centre des Matériaux, Evry, France

2

MINES ParisTech, PSL Research University, CEMEF, Evry, France

3

CEA, DEN, DPC, SCCME, LECA, Gif-sur-Yvette, France

4

Ecole Polytechnique, Laboratoire de Mécanique des Solides, Palaiseau, France

5

IRSN, Fontenay-aux-Roses, France

SCC of Alloy 82

1. Representativeness of SCC tests in hydrogenated steam

2. Description of the oxide scale formed on Alloy 82

• Effect of weld (composition and/or welding process)

• Effect of thermal treatment

Initiation tests performed in hydrogenated steam at 400°C

• SCC initiation is difficult in Alloy 82  test acceleration

• Previous results on Alloy 600 show that :

• Stress corrosion cracks exhibit similar features

• Trend between heats is respected

• Same activation energy for initiation

Hydrogenated steam 400°C

Primary water 360°C vs

Materials and oxidation conditions

C Si Mn P S Cu Mo Ni Cr Co Nb Ti Fe

RCC-M <0.1 <0.5 2.5/3.5 <0.03 <0.015 <0.5 - >67 18/22 <0.1 2/3 <0.75 <3 Weld A 0.025 0.07 2.57 0.004 <0.001 <0.01 - 71.7 19.12 0.04 2.41 0.1 3.07 Weld B 0.014 0.17 2.88 0.002 0.017 <0.01 0.05 72.9 18.15 0.01 2.83 <0.01 2.3

S

L T

304L 304L

A82

20 mm

Weld A B

Welding process Gas tungsten arc welding (GTAW) Flux core arc welding (FCAW) Metallurgical state As-welded Thermally-treated

7h - 600°C

As-welded

H

• 400°C

• P

= 200 bar, P(H

) = 800 mbar

• 1500h / 2500h

P

• 340°C

• [H

] = 37 mL / kg H

O

• 1500h / 2500h

Oxidation tests performed on coupons with 1 µm mirror finish in stainless steel autoclaves.

Oxidation in hydrogenated steam at 400 ° C

Weld A B

Welding process Gas tungsten arc welding (GTAW) Flux core arc welding (FCAW) Metallurgical state As-welded Thermally-treated

7h - 600°C

As-welded

Oxidation duration (h) 2500 1500/2500 2500

SEM observations Weld A – AW – 2500h

1 µm 2µm

Duplex structure:

• Discontinuous outer layer with pyramidal and platelet-like crystallites

• Continuous inner layer

Oxide penetrations (depth < 500 nm)

XPS depth profiles Weld A – AW – 2500h

Ni Cr Fe O Mn Nb

oxide alloy

XPS spectra: Ni 2p _3/2

Marchetti et al. (2015)

• Shape and binding energies consistent with NiFe

O

• Ni(OH)

cannot be excluded

Binding Energy (eV)

850 870 860

Ni 2p_3/2

855.8 eV

861.6 eV

Intensity (arbitrary units)

Weld A – AW – 2500h

Before sputtering

XPS spectra: Cr 2p _3/2

Marchetti et al. (2015)

• Before sputtering: hard to distinguish NiCr

O

from Cr

O

• Cr with the oxidation state +III is detected for the longest sputtering time

575 570 580

Binding Energy (eV)

Intensity (arbitrary units)

Cr 2p_3/2

576.9 eV

Before sputtering 120 nm

574.7 eV

Cr⁰ Cr³⁺

Weld A – AW – 2500h

XPS spectra: Fe 2p

Binding Energy (eV) 720 710

740 730

Fe 2p 2p_3/2

2p_1/2

Intensity (arbitrary units) 711.2 eV 〜710 eV

0 s 10 s

30 s

• Before sputtering:

consistent with NiFe

Cr

O

or Fe

Cr

O

• Slight shift towards lower energies:

• Fe/Cr  in NiFe

Cr

O

?

• Fe (III)  Fe (II)?

Biesinger et al. (2011)

〜 711 eV

Weld A – AW – 2500h

XPS depth profiles Weld A – AW – 2500h

oxide alloy

NiFe

Cr

O

NiFe

Cr

O

or Cr

O

Ni Cr Fe O Mn Nb Oxygen still detected

probably associated with Cr

XPS depth profiles

Ni Cr Fe O Mn Nb

Weld A – AW – 2500h Weld A – TT – 2500h

Open symbols: AW Plain symbols: TT

Similar results for all the samples

TEM analyses

Weld A – AW – 2500h

100 nm

MnS particles

EDX Line scan

outer cristallites

Inner layer

80

60

40

20

Oxide Alloy

at. %

Ni Cr Fe O Mn

Nb

Alloy:

Fluctuation of composition Strong localized Cr depletion Outer layer:

Ni- and Fe-rich cristallite Inner layer:

Cr-rich

Small amounts of Mn

STEM-HAADF

TEM analyses

14

Weld A – AW – 2500h

100 nm

MnS particles

outer cristallites

Inner layer

Outer layer:

NiFe

O

/ NiFe

Cr

O

NiFe2O4

5 nm _{5 n m}

Ni(Fe,Cr)2O4

Cr2O3

Alloy

(a) (b)

(c)

NiCr2O4

NiFe2O4

5 nm _{5 n m}

Ni(Fe,Cr)2O4

Cr2O3

Alloy

(a) (b)

(c)

NiCr2O4

STEM-HAADF

TEM analyses

Weld A – AW – 2500h

100 nm

MnS particles

outer cristallites

Inner layer

Inner layer:

- NiCr

O

- Cr

O

NiFe2O4

5 nm _{5 n m}

Ni(Fe,Cr)2O4

Cr2O3

(a) (b)

(c)

NiCr2O4

Outer layer:

NiFe

O

/ NiFe

Cr

O

STEM-HAADF

TEM analyses

Weld A – AW – 2500h

100 nm

MnS particles

outer cristallites

Inner layer

Inner layer:

- NiCr

O

- Cr

O

Outer layer:

NiFe

O

/ NiFe

Cr

O

STEM-HAADF

TEM-BF

Alloy:

Recrystallized sub-layer Thickness: 150 – 300 nm

Nanograins: varying composition

Oxide penetration

Oxidation in primary water at 340 ° C

Weld A

Welding process Gas tungsten arc welding (GTAW) Metallurgical state As-welded Thermally-treated

7h - 600°C

Oxidation duration (h) 1500 1500

SEM observations

Discontinuous outer layer with pyramidal crystallites and filaments

2µm

As-welded Heat-treated

Heat-treated sample

50 nm

Weld A – TT – 1500h

NiCr2O4

Alloy

100 nm

NiO (a)

5 nm

NiFe2O4

(b)

(c) (d)

2.45 Å

Filament oxide

Outer layer - NiFe

O

- NiO

- filament

Heat-treated sample

50 nm

Weld A – AW – 1500h

5 nm

NiCr2O4

Alloy

100 nm

NiO (a)

5 nm

NiFe2O4

(b)

(c) (d)

2.45 Å

Filament oxide

Outer layer - NiFe

O

- NiO

Inner layer

- NiCr

O

Heat-treated samples Weld A – TT – 1500h

Oxide penetration

H

-

Recrystallized sub-layer

200 nm

As-welded sample

Penetrative oxidation

100 nm

(a)

(c) (d)

O Cr Fe Ni

(b)

(e) (f)

Primary water – 1500h

Cr oxide

As-welded sample Primary water – 1500h

200 nm A

-

Highly deformed sub-layer

Summary

24

(b)

(a) ^NiFe2O4 (50 – 200 nm)

Ni(Cr,Fe)₂O₄(20 – 50 nm)

MnS

MnS

15 -20 nm

NiCr₂O₄ Cr₂O₃

(c)

NiCr₂O₄ (Ni,Fe)(Cr,Fe)₂O₄

NiO(100 – 200 nm)

NiFe₂O₄

(15 – 40 nm)

CrS CrS

NiCr₂O₄

Penetrative oxidation

15 -20 nm

(Ni,Fe)(Cr,Fe)₂O₄

(b)

(a) Ni(Cr,Fe)₂O₄(20 – 50 nm)

MnS

MnS

15 -20 nm

NiCr₂O₄ Cr₂O₃

(c)

CrS CrS

NiCr₂O₄ (Ni,Fe)(Cr,Fe)₂O₄

NiO(100 – 200 nm)

NiFe₂O₄

(15 – 40 nm)

CrS CrS

NiCr₂O₄

Penetrative oxidation

15 -20 nm

(Ni,Fe)(Cr,Fe)₂O₄

Oxide penetration

H

– 400°C All samples

P

– 340°C As-welded

(b)

(a) ^NiFe2O4 (50 – 200 nm)

Ni(Cr,Fe)₂O₄(20 – 50 nm)

MnS

MnS

15 -20 nm

NiCr₂O₄ Cr₂O₃

(c)

CrS CrS

NiCr₂O₄ (Ni,Fe)(Cr,Fe)₂O₄

NiO(100 – 200 nm)

NiFe₂O₄

(15 – 40 nm)

CrS CrS

NiCr₂O₄

Penetrative oxidation

15 -20 nm

(Ni,Fe)(Cr,Fe)₂O₄

Oxide penetration

Heat-treated

Cr₂O₃

• Similar oxidation kinetics

• Duplex Cr-rich inner layer:

• NiCr

O

in primary water

• Cr

O

in hydrogenated steam

• Oxide penetrations

Conclusions (1/2)

• Environment:

Marchetti et al. (2015)

 Surface oxide layer not strictly identical but consistent with literature data

 Similar oxidation tests performed on 304L SS show a difference in the oxidation kinetics but not in the oxide structure

Cissé et al., JNM (2012)

Conclusions (2/2)

• Alloy microstructure:

• For a given environment, no effect of weld composition, welding process or thermal treatment on the oxidation kinetics and oxide structure

• Different sub-surface states: recrystallized or high density of dislocations

• No effect on the continuous inner layer

• But the morphology of oxide penetration strongly differs Origin of the recrystallized layer?

As-prepared, non oxidized sample

 Machining by EDM + grinding + mirror polish

Thank you for your attention