HELIUM COOLANT

HELIUM COOLANT

INTERACTION WITH MATERIALS, SPECIFICITIES OF THE HIGH

TEMPERATURES.

PHYSICS AND CHEMISTRY OF THE INTERFACE BETWEEN GAS AND STRUCTURAL MATERIALS

CÉLINE CABET

DÉPARTEMENT DES MATÉRIAUX POUR LE NUCLÉAIRE

1 OCTOBRE 2013

2

GEN IV SYSTEMS OPERATING CONDITIONS

1 OCTOBRE 2013

OUTLINE

Characteristics of the helium coolant

Surface reactivity of Ni-Cr alloys in high temperature helium Catastrophic corrosion of Ni-Cr alloys in HT helium

Oxidation kinetics of Ni-Cr alloys in HT helium

Summary

CHARACTERISTICS OF

THE HELIUM COOLANT

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HELIUM-COOLED REACTORS

Higher efficiency high temperature

Cool He 350-590°C

Hot He 750-950°C

Reactor vessel

Cross Vessel Power

conversion vessel

Reactor is linked to an power conversion system (Brayton cycle) or to a

secondary circuit for

process heat production GFR-HTR common R&D program on structural materials

5

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REQUIREMENTS ON AN INTERMEDIATE HEAT EXCHANGER

Cooling gas He (+impurities) at ~5 MPa He inlet temperature 800-950°C

Target life >20 years

Wall thickness few millimeters

Environmental characteristics

PCHE

PFHE

Determining materials properties

 microstructure stability

 creep and creep-fatigue resistance

 compatibility with coolant

Wrought creep-resistant Ni-Cr alloys

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CHEMISTRY OF THE COOLING HELIUM

In-core HT materials He

O

H

O N

CO

Experience from the operation of former He-cooled reactors

Steady state

(Pa) He

purif

in jecti o n

(1) K. Krompholz et al., Proc. 8th International Congress on Metallic Corrosion, vol. II, Dechema, Frankfurt, 1981, p. 1613 (2) R. Nieder, Gas-Cooled Reactors Today, vol.2, BNES, London, 1982, p. 91

(3) G.E. Wasielewski et al., in Gas-Cooled Reactors with Emphasis on Advanced Systems, vol. I, IAEA, Vienna, 1976, p. 379 (4) N. Sakaba and Y. Hirayama, Proc. GLOBAL 2005, Tsukuba, Japan, 2005, Paper #263

H

O (CH

CO CO

)

H

H

O CO

CO CH

N

2-50 0.1-3 0-5 1-30 0.3-5 0-0.5

Gas mixing panel

Test section

Gas analysers

PRINCIPLE OF CORROSION LOOPS WITH CONTROLLED CHEMISTRY HELIUM

moisture

control

CORINTH

CORROSION LOOP WITH HELIUM CHEMISTRY CONTROL

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9

gas-tight chamber

fatigue bench temperature

control gas

chromato- graph gas control

and analyzers

gas bottles

specimen and induction coil

CONTROLLED ENVIRONMENT FATIGUE

AND CREEP-FATIGUE SYSTEM

SURFACE REACTIVITY OF NI-CR ALLOYS IN IMPUR

HELIUM AT HIGH

TEMPERATURE

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higher temperature intermediate

temperature

<760°C

HIGH TEMPERATURE ALLOYS FOR INTERMEDIATE HEAT EXCHANGERS

carbide-former ss strengthening

 Can chromia be formed under impure helium in a GCR?

corrosion resistance

Alloy C Ni Fe Cr Mo W Co Al

Fe-32Ni-20Cr 0.06-0.1 30-35 base 19-23 0.15-0.6 Ti: 0.15-0.6

Ni-22Cr-9Mo 0.08 base 1.7 21.9 9.3 11.4 1.0 Ti: 0.3; Si:0.1 Mn: 0.1 Ni-22Cr-14W 0.11 base 1.3 22.4 1.3 13.9 0.2 0.3 Mn: 0.5; Si: 0.4

La: 0.016

SURFACE REACTIVITY EXPERIMENTS (CR-RICH ALLOYS)

helium H

CH

CO H

O

10

20 1.9 2.1 0.05

Gas flow rate: 0,68ml/cm

/s

900°C

(1°C/min)

T(°C)

t(h) 25h

980°C

(0.5°C/min)

20h

cooling in pure He

Step 2 Step 1

(Pa)

cooling in pure He

13

SURFACE OXIDE SCALE

FORMATION & DESTRUCTION

Al

O

Cr-rich (with Mn) oxide

900°C, 25h

I

W-rich carbide

Al

O

Mn-rich oxide (with Al, few Cr)

900°C, 25h plus 980°C, 20h

2 µm

2 µm

scale destruction from the inner side

Step 2 Step 1

T>T _A T<T _A

Ni-22Cr-14W,

He /20 H

/2,1 CO /1,9 CH

/0,05 H

O (Pa)

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F. Rouillard et al., Oxid. Met, 68 (2007) 133

14

Production of CO(g)

& scale destruction

5 10 15 20 25 30 35 40

0 200 400 600 800 1000

0 5 10 ⁴ 1 10 ⁵ 1.5 10 ⁵ 2 10 ⁵

P CO (µbar) P CH4 (µbar)

T(°C)

Pression partielle (µbar) Température (°C)

temps (s)

SURFACE REACTIVITY: GAS PHASE ANALYSIS

P(CO)

CO

CH

time (s)

Partial pressure (µbar)

Step 2 Step 1

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| 15

Ni-22Cr-14W,

He /20 H

/2,1 CO /1,9 CH

/0,05 H

O (Pa)

F. Rouillard et al., J. Nucl. Mater., 362 (2007) 248

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Cr CO

C O

Cr _{2 3}  3 _Solution  3  2

REACTIONS ON THE CR-RICH ALLOY SURFACE

Oxide reduction by the carbon in solution ^(1-6)

T>T _A

2 3

2

2 2 3

3 H O  Cr  Cr O  H

Build-up of the Cr-oxide / oxidation by H ₂ O (&CO)

Solution 3

2 O 3 C

Al Al

2 CO

3   

surface

internal

T<T _A

(1) Quadakkers W. J., Werkstof. Korr. 36 (1985) 335 - (2) Christ H.-J. et al., Mater. Sci. Eng. 87 (1987) 161 (3) Warren M. R., H. Temp. Technol. 4 (1986) 119 - (4) Brenner K.G.E. et al., Nucl. Technol. 66 n°2 (1984) 404 (5) Cabet C. et al. Mater. Sci. Forum 595-598 (2008) 439 - (6) F. Rouillard et al., Oxid. Met., 68 (2007) 133

F. Rouillard et al., Corr. Sci., 51 (2009) 752

16

5 10 15 20 25 30 35 40

0 200 400 600 800 1000

0 5 10 ⁴ 1 10 ⁵ 1.5 10 ⁵ 2 10 ⁵

P CO (µbar) P CH4 (µbar)

T(°C)

Pression partielle (µbar) Température (°C)

temps (s)

SURFACE REACTIVITY: CRITICAL TEMPERATURE T _A

P(CO)

CO

CH

time (s)

Partial pressure (µbar)

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T _A

Cr

O

+ 3C

 3CO + 2Cr CO

temps (s)

Ni-22Cr-14W,

He /20 H

/2,1 CO /1,9 CH

/0, 5 H

O (Pa)

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850 900 950 1000

0 1 2 3 4 5 6

T

in ° C

P(CO) in Pa

Haynes 230 Inconel 617 ref(2) Inconel 617 ref(1) 850

900 950 1000

0 1 2 3 4 5 6

T

in ° C

P(CO) in Pa

Haynes 230 Inconel 617 ref(2) Inconel 617 ref(1)

EFFECT OF THE PARTIAL PRESSURE P(CO)

Ni-22Cr-14W: Rouillard F., Thèse de l’ENSM-SE (2007)

ref(1) Cabet C., Chapovaloff J. et al., J. Nucl. Mater., 375 (2008) p.173 ref(2) Quadakkers W.J., Werkst. Korros., 36 (1985) p.335

Ni-22Cr-14W Ni-22Cr-9Mo ref(1) Ni-22Cr-9Mo ref(2)

3 solution

2 3

A

1

a ( C )

) Cr ( a . ) CO ( ) P T (

K  Cr

O

 3 C



 



3 CO  2 Cr

P(CO) en Pa

18

OXIDE REDUCTION - THERMOCHEMISTRY

Hypothesis 1: T

corresponds to the interfacial condition:

Hypothesis 2: the surface scale is pervious to CO(g) (through micro-channels) Hypothesis 3: the oxide is assumed to be pure chromia

Hypothesis 4: there is a local equilibrium between alloy and carbides

) CO ( P . P

) T ( ) K C (

a

i O i A

gaz 1 2

1

2



i gaz métal

C O

/

CO     1 2

 ) C

( a ) C (

a



) Cr ( M C

C ) Cr (

M

 6

 23

23 6 23 6 3

) M ( a

) C M ( a ).

T ( ) K

C (

a



(1) Gosse S. et al., Mater. Sci. Forum, 595-598 (2008) 975 Rouillard F. et al., Mater. Sci. Forum, 595-598 (2008) 429

Thermocalc® caculation (Calphad method)

2 3 2 2

2

i / O i A

P

) T ( ) K

Cr (

a 

2 3

2

O 2 Cr 3 / 2 O

Cr 



i i

i

) ( Cr ).% Cr

Cr (

a  

in a Transmission Electron Microscope HT mass spectrometry

measurements ⁽¹⁾

19

Cr CO

C O

Cr

 3



 



3  2

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850 900 950 1000

0 1 2 3 4 5 6

TAin °C

P(CO) in Pa

Haynes 230 Inconel 617 ref (1)

Oxide stablity

Oxide reduction

STABILITY OF THE SURFACE CHROMIA VS. P(CO)

 What is the corrosion behavior when the chromia scale is not stable?

Chromia reduction

Chromia stability

data on Alloy 230 from F. Rouillard, PhD thesis (2007)

data on Alloy 617 after W. J. Quadakkers, Werkst. Korros. 36 (1985) 335

Ni-22Cr-14W Ni-22Cr-9Mo

CR-RICH ALLOYS

CORROSION BEHAVIOR IN IMPURE HELIUM AT HIGH

TEMPERATURE

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850 900 950 1000

0 1 2 3 4 5 6

TAin °C

P(CO) in Pa

Haynes 230 Inconel 617 ref (1)

Oxide stablity

Oxide reduction

He / 0.5 CO / 20 H

/

0.05-1.2 H

O (Pa) Chromia reduction

Chromia stability

(NO CH ₄ ) CORROSION IN THE AREA FOR CHROMIA

REDUCTION (1/3)

Ni-22Cr-14W Ni-22Cr-9Mo

Data on Ni-22Cr-14W: Rouillard F., Thèse de l’ENSM-SE (2007)

Data on Ni-22Cr-9Mo: Quadakkers W.J., Werkst. Korros., 36 (1985) 335

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CORROSION IN THE AREA FOR CHROMIA REDUCTION (2/3)

Carbon loss

-0,6 -0,4 -0,2 0,0

0 500 1000

time (h)

carbon loss (mg/cm²)

-0,6 -0,4 -0,2 0,0

0 0,2 0,4 0,6 0,8 1 1,2 1,4

P(H₂O) (Pa)

carbon loss (mg/cm²)

(NO CH ₄ )

Ni-22Cr-14W, 950°C

He /0,5 CO /20 H

/0,05 H

O (Pa)

Ni-22Cr-14W, 250h, 950°C

He /0,5 CO /20 H

/0,05-1,2 H

O (Pa)

C. Cabet et al., J. Eng. Turb. Power 131 (2009) 062902

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CORROSION IN THE AREA FOR CHROMIA REDUCTION (2/3)

full

decarburization (4mm) and recristallisation

(NO CH ₄ )

Ni-22Cr-9Mo, 582h, 1000°C

He /2 CO /19,7 H

/1 CH

/0,2 H

O (Pa)

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H

= 280 H

= 200

CONSEQUENCES OF DECARBURIZATION (1/2)

Decarburization and softening

no gb carbide

Ni-22Cr-14W, 1000h, 950°C 25

He /0.5 CO /20 H

/0.05 H

O (Pa)

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CONSEQUENCES OF DECARBURIZATION (2/2)

Graph and data from Tsuji H., Nakajima H., Kondo T., Proc. specialists' meeting on high-temperature metallic materials for gas-cooled reactors, Cracow, Poland (1988) p.81

area for carburization

area for chromia stability

area for decarburization

Str e s s (MPa )

Decrease in creep life

5 10

2 5 10

Time to rupture (h)

26

Ni-Cr-Fe-Mo (C) 950°C

creep under impur He

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850 900 950 1000

0 1 2 3 4 5 6

T

in ° C

P(CO) in Pa

Haynes 230

Inconel 617 ref (1)

Oxide stablity

Oxide reduction

He / 1.5 CO / 50 H

/

30 CH

/ 0.05 H

O (Pa) Chromia reduction

Chromia stability

CORROSION IN THE AREA FOR CHROMIA REDUCTION (1/3)

(HIGH CH ₄ )

Ni-22Cr-14W Ni-22Cr-9Mo

Data on Ni-22Cr-14W: Rouillard F., Thèse de l’ENSM-SE (2007)

Data on Ni-22Cr-9Mo: Quadakkers W.J., Werkst. Korros., 36 (1985) 335

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CORROSION IN THE AREA FOR CHROMIA REDUCTION (2/3)

0 10 20 30 40

0 200 400 600 800 1000

C ar b o n p ick -u p (mg .cm

)

time (h)

230 #2 230 #3 230 #3

2Pa

30Pa

Carbon deposition

P(CH

)

(HIGH CH ₄ )

Ni-22Cr-14W, 950°C

He /1,5 CO /50 H

/30 CH

/0,05 H

O et He /0,5 CO /20 H

/2 CH

/0,05 H

O (Pa)

C. Cabet et al., J. Eng. Turb. Power 131 (2009) 062902

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Cr ₃ C ₂ , Cr ₇ C ₃ , Cr ₂₃ C ₆

no oxide coarse

carbides

(HIGH CH ₄ ) CORROSION IN THE AREA FOR CHROMIA

REDUCTION (3/3)

Surface and bulk carburization

Ni-22Cr-14W, 240h, 950°C

He / 1,5 CO/ 50 H

/30 CH

/0,05 H

O (Pa)

C. Cabet et al., J. Nucl. Mater., 392 (2009) 235

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200 250 300 350 400 450 500 550 600

0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6

x (mm)

Hv

240h 1000h

as received

CONSEQUENCES OF CARBURIZATION (1/2)

Hardening

Ni-22Cr-14W, 950°C

He / 1,5 CO/ 50 H

/30 CH

/0,05 H

O (Pa)

30

 Corrosion pre-treatment:

specimens were

carburized, oxidized, or decarburized for ~500hrs

 RT tensile testing:

carburized alloy exhibits reduced ductility

CONSEQUENCES OF CARBURIZATION (2/2)

carburized

Embrittlement

25°C, 5.10

s

standard tensile specimen Φ6mm

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Ni-22Cr-9Mo, ~500h, 950°C, impure He ³¹

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32

CORROSION UNDER REDUCING HELIUM

If P(CO) is inadequate, the surface Cr-oxide can be reduced by the carbon in solution

and catastrophic corrosion occurs

decarburization and reduction of creep life carburization and embrittlement

He impurity levels can be specified for supporting the formation of the surface Cr-oxide ( in terms of a minimum P(CO) to be

controlled ! )

The helium chemistry must be controlled to allow for alloy

oxidation and the corrosion lifetime will be determined by the

oxidation rate

CORROSION KINETICS OF CR-RICH ALLOYS IN

OXIDIZING HELIUM AT

HIGH TEMPERATURE

850 900 950 1000

0 1 2 3 4 5 6

TAin °C

P(CO) in Pa

Haynes 230 Inconel 617 ref (1)

Oxide stablity

Oxide reduction

CORROSION IN THE AREA FOR CHROMIA STABILITY

He / 5 CO / 20 H

/ 2 CH

/ 0.15 H

O (Pa)

Chromia reduction

Chromia stability

 What is the oxidation rate when the chromia scale is stable?

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Ni-22Cr-14W Ni-22Cr-9Mo

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MICROSTRUCTURE OF OXIDIZED ALLOYS (1/2)

secondary carbides Cr, Mo, Ni

internal oxide Al, O carbide-depleted

zone

external oxide Cr, Ti, O

Ni-22Cr-9Mo, 527h, 950°C He /5 CO /19,7 H

/0,4 H

O (Pa)

35

1 OCTOBRE 2013

external oxide

MICROSTRUCTURE OF OXIDIZED ALLOYS (2/2)

Al, O + pores

carbides Cr, Mo, Ni metal

inclusion

internal oxide Al, O

carbide depleted zone Cr, Ti, O

Ni-22Cr-9Mo, 5000h, 950°C, He /5 CO /20 H

/2 CH

/0,2 H

O (Pa)

Ni-22Cr-9Mo (Al: 1,0%) Ni-22Cr-9Mo (Al: 1,3%)

C. Cabet et al., J. Energ. Power Eng. 5 (2011) 942

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OXIDATION KINETICS

0.0 0.5 1.0 1.5 2.0 2.5

0 1000 2000 3000 4000 5000

D m ( m g /c m

)

Time (h)

617 #1 617 #2

Global parabolic mass gain

Ni-22Cr-9Mo, 950°C, He /5 CO /20 H

/2 CH

/0,2 H

O (Pa)

37

cast 1 cast 2

EFFECT THE WATER VAPOR PARTIAL PRESSURE

0 0.5 1 1.5 2

0 200 400 600

mass gain (mg.cm-2 )

time (hrs)

4µbar H

O

0.5µbar H

O air

Ni-22Cr-9Mo, 950°C, He /5 CO /20 H

/H

O (Pa)

Role of P(H20) has been investigated in:

S. Guillou et al.,

Oxid. Met., 76 (2011) 193

0.05Pa H

O

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CHANGE IN THE MICROSTRUCTURE

-140 -120 -100 -80 -60 -40 -20 0 20

0 1000 2000 3000 4000 5000

dimension (µm)

Time (h)

Global parabolic evolution

external oxide thickness

internal oxidation depth

carbide-depletion depth

C. Cabet et al., Nucl Eng. Des, 251 (2012) 139

Ni-22Cr-9Mo, 950°C, He /5 CO /20 H

/2 CH

/0,2 H

O (Pa)

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EXTRAPOLATION OF THE PARABOLIC EVOLUTION

Parabolic rate constant Ni-22Cr-9Mo (cast 2) Mass gain (mg².cm

.h

) 0,00090 Carbon pick-up (mg².cm

.h

) 0,000010 External oxide thickness (µm².h

) ~0,019 Internal oxidation depth (µm².h

) ~0,34 Carbide-depletion depth (µm².h

) ~3,1

Ni-22Cr-9Mo (cast 2)

Mass gain ~10 mg.cm

Carbon pick-up 0,4 mg.cm

External oxide ~50 µm Internal oxidation up to ~240 µm Carbide-depletion up to ~740 µm

in-service target:

20 years

C. Cabet et al., Nucl Eng. Des, 251 (2012) 139

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POSSIBLE CONSEQUENECS OF THE LONG TERM OXIDATION

initial

oxidized Ni-22Cr-9Mo

Surface scale ~50 µm

Internal oxidation up to ~240 µm Carbidedepletion up to ~740 µm

Load bearing section

initial

Internal oxidation

oxidized

couche de surface zone décarburée

Kinetic law validity

850 900 950 1000

0 1 2 3 4 5 6

TAin °C

P(CO) in Pa

Haynes 230 Inconel 617 ref (1) Oxide stablity

Oxide reduction

Oxide reduction

Intergranular

oxide 41

Ni-22Cr-14W Ni-22Cr-9Mo

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42

Several damaging mode are interacting

ENVIRONEMENT EFFECT ON SERVICE PROPERTIES

fatigue cracks oxidation in

He

creep damage

aging

SUMMARY

INTERACTION BETWEEN HELIUM COOLANT AND

STRUCTURAL MATERIALS – EXAMPLE OF NI-CR

ALLOYS

1 OCTOBRE 2013

SUMMARY ON CORROSION PROCESSES IN HELIUM COOLANT (CR-RICH ALLOYS)

Cr )

g ( CO C

O

Cr

 3



 



3  2

850 900 950 1000

0 10 20 30 40 50 60

P(CO) in µbar TA in °C

Haynes 230

Inconel 617 [Quadakkers]

Oxide stablity Oxide reduction

Chromia reduction

Oxide surface scale Carburization Decarburization

with CH ₄

No CH ₄

Embrittlement  creep life ! Need for lifetime prediction !

! unacceptable in service !

Chromia stability

Ni-22Cr-14W Ni-22Cr-9Mo

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45

SUMMARY ON OXIDATION RATE IN HELIUM COOLANT (CR-RICH ALLOYS)

20 years

Ni-22Cr-9Mo

Surface oxide ~50 µm

Internal oxidation ~240 µm Carbide depletion ~740 µm

In controlled chemistry helium, Cr-rich alloys comply with a globally parabolic oxidation

The oxidation rate depends on:

Material chemistry (%Cr, minor elements) Impurity content ( P(H

), P(H

O) )

Temperature

At 950°C, oxidation rate is high for the intermediate heat exchanger application

-140 -120 -100 -80 -60 -40 -20 0 20

0 1000 2000 3000 4000 5000

dimension (µm)

Time (h)

external oxide thickness

internal oxidation depth carbide-depletion depth

Céline Cabet

Département des Matériaux pour le Nucléaire

Ackowledgements

Brigitte Duprey, Fanny Balbaud, Fabien Rouillard, Clara Desgranges

Richard Wright, Laura Carroll,

Sébastien Guillou, Arnaud Monnier, Pamela Lett,

Florent Thieblemenont, Aurélie Thomazic, Lucille

Lemort, Morgane Lemiller, Raphael Madland