Diapositive 1

Report
ODS steels – part II :
corrosion resistance in high temperature
helium and in liquid sodium
Jean Louis Courouau
Laure Martinelli
Fanny Balbaud-Célérier
Fabien Rouillard
Sébastien Guillou
Paméla Lett
Florent Thiéblememont
Aurélie Thomazic
Lucille Lemort
Céline Cabet
CEA, DEN, DPC, SCCME, Laboratoire d’Etude de la Corrosion Non Aqueuse
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MATGENIV.2 – 02-06-2009 – TR 1
Corrosion resistance of ODS in HT helium
• VHTR and GFR: materials et environment
• Corrosion loops
• Surface reactivity in impure helium
• HT corrosion in impure helium
• Area for chromia stability
• Area for chromia reduction: carburization
• Area for chromia reduction: decarburization
• Data on ODS corrosion behaviour
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MATGENIV.2 – 02-06-2009 – TR 2
Gas-cooled reactors:
Materials and environment
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MATGENIV.2 – 02-06-2009 – TR 3
Motivations for HT gas cooled reactors
Share of each energy source in the world energy demand
Coal 25%
Oil 35%
Biomass 10%
Nuclear 6%
Hydro 2%
Other
renew ables 1%
Natural Gas 21%
To increase the share of nuclear
energy, one option is to work on
increasing the share of nuclear in
electricity production but most
importantly to promote the
increased use of electricity and
nuclear heat in transport and
industry
Le VHTR is the only GEN IV
system able to provide in the near
term process heat above 600°C
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MATGENIV.2 – 02-06-2009 – TR 4
HT processes
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MATGENIV.2 – 02-06-2009 – TR 5
Massive hydrogen production
HIGH TEMPERATURE
ELECTROLYSIS
I/S or HYBRIDE CYCLE
e-
eH2 O
air
H2
O2-
O2
H2
O2-
O2
H2
cathode
anode
(ZrO2)0.91(Y2O3)0.09
Materials
compatibility
DEN/DANS/DPC/SCCME
NEED FOR MORE EFFICIENT
YIELD 35%  >50% ?
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MATGENIV.2 – 02-06-2009 – TR 6
Cogeneration
grid
η = 33-48%
eη = 99%
HTE, I/S cycle, desalination
H2
η = 35-50%
T°C
Industrial
processes
< 900°C
η = 99%
HTR/GFR
H2O
< 650°C
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MATGENIV.2 – 02-06-2009 – TR 7
Gas-cooled reactor systems
Fast Reactors: (SFR and) GFR
with a closed fuel cycle
V-HTR for H2 production in
interaction with the ANTARES project
2035-2040
2020-2025
Cross
Duct
Reactor
vessel
PCV with IHX
HTR-GFR common R&D programs on structural materials
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MATGENIV.2 – 02-06-2009 – TR 8
VHTR design
Reactor Vessel
Power: ~600 MWth
Outlet temperature ~850°C
Prismatic block type
Main Circulator
He outlet
850-950°C
IHX
electricity
Max. Fuel Temperature
Operating : 1300°C
Accidental : 1600°C
process heat
He inlet
390-490°C
H2 production
Cross Vessel
Shutdown Cooling
Circulator
Reactor Building
Plate IHX modules
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IHX Vessel
MATGENIV.2 – 02-06-2009 – TR 9
Environment and requirements on IHX materials
PCHE
IHX main characteristics
Primary coolant
He (+impurities) at 50-70 bar
He inlet temperature 850-950°C
PFHE
Expected lifetime
100 000 hours
Wall thickness
few millimetres
Component integrity
Courtesy of Heatrics
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strength at high and low temperature
 creep resistance
 compatibility with coolant
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MATGENIV.2 – 02-06-2009 – TR 10
HT Metallic Materials for circuit and IHX
Data from the
60-80’s (1-3)
Type Alloy 800
Inconel 617 (Co, Mo)
Hastelloy X (Mo)
Haynes 230® (W, Mo)
up to 760°C
highest creep properties
higher corrosion resistance
possible creep and oxidation resistance
wrought creep resistant Ni alloys (20-22wt.% Cr)
protection against oxidation by a chromia scale
Ni
C
Cr
Mn
Inconel 617
base 0.06 22.3
Hastelloy X
base 0.06 21.6 0.5
Ti
Si
Al
Fe
Mo
0.4
0.1
1.3
1.1
8.7
0.2
18.3 8.8
W
Co
11.7
0.5
0.9
Haynes 230® base 0.10 21.8 0.5
0.4 0.3 1.4 1.3 14.2 0.2
Not or not fully qualified in ASME code (nuclear applications)
(1)
(2)
(3)
Nickel H., Schubert F., Schuster H., Gas-cooled reactors today vol.2, BNES, London (1982) 173-178
Kondo T., Proc. IAEA specialists' meeting, Vienna, Austria (1981)
Rittenhouse P.L. et al., High-Temperature Gas-Cooled Reactor Techn. Dev. Prog. – ORNL
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GFR design
Reactor Vessel
Pin fuel
Plate fuel
Core
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MATGENIV.2 – 02-06-2009 – TR 12
Environment and requirements on GFR core materials
Cladding main characteristics
Max. temperature
850-950°C
High neutron dose
200 dpa
Primary coolant
He (+impurities) at 50 bar
Expected lifetime
2 to 5 years
SiC/SiC composite but
gas-tightness
mechanical strength (LT)
radiation stability (?)
F/M ODS steel but
Max temp 800°C
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Component integrity
 LT and HT mechanical strength
radation stability
 corrosion resistance
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MATGENIV.2 – 02-06-2009 – TR 13
VHTR normal atmosphere
injection
O2 H2O N2
(CO2)
H2O (CH4
CO CO2)
He
Graphite
HT
He
Steady state
H2
H2O
CO2
20-500
1-30
0-50 10-300 3-50 0-50 (µbar)
Oxygen and water vapor oxidize
graphite
(1)
(2)
(3)
(4)
CH4
N2
Experience from the operation of
former He-cooled reactors (1)
purif
 Compatibility with graphite
and C/C composites
CO
 Compatibility with structural
metallic materials
Impurities interact with
metals at HT (2-4)
surface scale growth
carburization
decarburization
Graham L.W. et al., Gas-cooled reactors with emphasis on advanced systems vol.I. IAEA, Vienna (1976) 319
Brenner K.G.E., L.W. Graham, Nuclear Technology, 66 n°2 (1984) 404
J. Christ, U. Künecke, K. Meyer, H. G. Sockel, Mater. Sci. Eng. A 87 (1987) 161
W. J. Quadakkers, H. Schuster, Werkstoffe und Korrosion 36 (1985) 141
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Corrosion loops
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MATGENIV.2 – 02-06-2009 – TR 15
HT corrosion test: to control the He chemistry
Gas mixing
panel
Test section
Gas
analysers
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moisture
control
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MATGENIV.2 – 02-06-2009 – TR 16
HT corrosion test: to control the He chemistry
CORINTH
CORrosion of INnovative materials in high Temperature Helium
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MATGENIV.2 – 02-06-2009 – TR 17
Thermobalance with humidity control for TGA
• Continuously monitoring of the sample mass variations
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MATGENIV.2 – 02-06-2009 – TR 18
Surface reactivity of
chromia-forming alloys
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MATGENIV.2 – 02-06-2009 – TR 19
Surface reactivity: experimental
H2
CH4
CO
H 2O
200µbar
19µbar
49µbar
1.6 µbar
Ptot = 1 atm
Gas flow rate: 0.68ml/cm2/s
T(°C)
Step 2
Step 1
980°C,
900°C,
(0.5°C/min)
(1°C/min)
20h
cooling
in pure He
25h
Chromia-forming Alloy 230
t(h)
Rouillard F., Cabet C. et al. Oxid Met 68 (2007) 133
after W. J. Quadakkers, Werkstoffe und Korrosion 36 (1985) 335
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Oxide scale formation & destruction
Step 1
Step 2
T<TA
T>TA
2 µm
2 µm
Mn-rich oxide
(with Al, few Cr)
Cr-rich (with
Mn) oxide
Iary W-rich
carbide
Al2O3
Al2O3
900°C, 25h plus 980°C, 20h
900°C, 25h
scale destruction
from the inner side
Haynes 230, He /200 H2 /21 CO /
19 CH4 /0.5 H2O (µbar)
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Surface reactivity: gas phase analysis
Step 2
Step 1
40
1000
Production of CO(g)
& scale destruction
35
T(°C)
800
P
P
25
CO
(µbar)
CH4
600
(µbar)
CO
P(CO)inlet
20
400
Température (°C)
(µbar)
Partial pressure
partielle (µbar)
Pression
30
CH4
15
200
10
5
0
0
5 10
4
1 10
5
1.5 10
5
2 10
5
Haynes 230®
He /200 H2 /21 CO /
19 CH4 /0.5 H2O (µbar)
time (s)
temps
(s)
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Surface reactions
Oxidation by H2O (&CO)
T<TA
3H2O  2Cr  Cr2O3  3H2
surface
3CO  2Al  Al2O3  3CSolution
internal
Cr-oxide reduction by carbon(1-5)
T>TA
Cr2O3  3CSolution  3CO  2Cr
(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., Girardin G. et al. Mat Sci Forum 595-598 (2008) 439
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Surface reactivity: critical temperature TA
40
1000
TA
Cr2O3 + 3[C]  3CO + 2Cr
35
T(°C)
800
CO
P
P
25
CO
(µbar)
CH4
600
(µbar)
P(CO)inlet
20
400
Température (°C)
(µbar)
Partial pressure
partielle (µbar)
Pression
30
CH4
15
200
10
5
0
0
5 10
4
1 10
5
1.5 10
5
time (s)
temps
(s)
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2 10
5
Haynes 230®
He /200 H2 /21 CO /
19 CH4 /0.5 H2O (µbar)
MATGENIV.2 – 02-06-2009 – TR 24
Stability of the surface chromia vs. P(CO)
1000
Cr2O3  3CSolution  3CO  2Cr
Chromia
reduction
Oxide
reduction
TA in °C
950
Oxide stablity stability
Chromia
900
Haynes 230
Inconel 617 [Quadakkers]
850
0
10
20
30
40
50
60
P(CO) in µbar
Corrosion behaviour in both domains ?
from Rouillard F., Cabet C. et al. Oxid Met 68 (2007) 133
data on Inconel 617 after W. J. Quadakkers, Werkstoffe und Korrosion 36 (1985) 335
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Corrosion behaviour
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MATGENIV.2 – 02-06-2009 – TR 26
Corrosion test in the area for chromia stability
1000
reduction
Oxide
Chromia
reduction
TA in °C
950
He / 50 CO / 200 H2 /
20 CH4 / 1.5 H2O (µbar)
Oxide stablity
Chromia stability
900
Haynes 230
Inconel 617 [Quadakkers]
850
0
10
20
30
40
50
60
P(CO) in µbar
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MATGENIV.2 – 02-06-2009 – TR 27
Corrosion test in the area for chromia stability
Medium term test
growth of a Cr-rich surface
oxide scale
no in-depth change in the
microstructure
Cr2O3 +
(Cr,Mn) spinel
retain the creep properties
Al2O3
Lifetime on the long run ?
 long term stability ?
 oxidation kinetics
[effect of alloy, T, P(O2),
P(H2O)…] ?
Haynes 230® 800 hrs, 950°C
He /50 CO/ 200 H2 /20 CH4 /1.5 H2O (µbar)
 effect of surface changes ?
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MATGENIV.2 – 02-06-2009 – TR 28
Corrosion test in the area for chromia reduction
(with CH4)
1000
He / 5 CO / 200 H2 /
20 CH4 / 0.5 H2O (µbar)
Chromia
reduction
Oxide reduction
TA in °C
950
Oxide stablity stability
Chromia
900
Haynes 230
Inconel 617 [Quadakkers]
850
0
10
20
30
40
50
60
P(CO) in µbar
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MATGENIV.2 – 02-06-2009 – TR 29
Corrosion test in the area for chromia reduction
(with CH4)
Surface and bulk carburization
no surface
scale
Al2O3
Cr-rich
carbides
20 µm
C(500hrs) =
+0.08wt.%
Haynes 230® 500 hrs, 950°C
He /5 CO/ 200 H2 /20 CH4 /0.5 H2O (µbar)
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MATGENIV.2 – 02-06-2009 – TR 30
Corrosion test in the area for chromia reduction
(high CH4)
1000
He / 15 CO / 500 H2 /
300 CH4 / 0.5 H2O (µbar)
Chromia
reduction
Oxide reduction
TA in °C
950
Oxide stablity
Chromia stability
900
Haynes 230
Inconel 617 [Quadakkers]
850
0
10
20
30
40
50
60
P(CO) in µbar
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MATGENIV.2 – 02-06-2009 – TR 31
Corrosion test in the area for chromia instability
(high CH4)
Massive carburization and hardening
600
240h
550
1000h
No surface
scale
500
Hv
450
Cr-rich
carbides
400
350
300
as received
250
~300 µm
200
0
0,2
0,4
0,6
0,8
1
1,2
1,4
x (mm)
Haynes 230® 240 hrs, 950°C
He /15 CO/ 500 H2 /300 CH4 /0.5 H2O (µbar)
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1,6
C(500hrs) =
+1.69wt.%
MATGENIV.2 – 02-06-2009 – TR 32
Consequences of carburization
% Strain vs Stress (MPa)
900
850
800
750
Courtesy of R. Wright, INL
700
RT Tensile Curves of Alloy 617 at 900°C
650
carburized
oxidized
600
Stress (Mpa)
550
500
IN617-7
450
400
IN617-2
350
•
Carburized Alloy 617 specimens
exhibit nil ductility at room
temperature
300
250
200
150
•
Oxidized Alloy 617 exhibits 26%
reduction in area at room
temperature
100
50
0
0
5
10
15
20
25
% Strain
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MATGENIV.2 – 02-06-2009 – TR 33
30
Corrosion test in the area for chromia reduction
(no CH4)
1000
He / 5 CO / 200 H2 /
/ 0.5 H2O (µbar)
Chromia
reduction
Oxide reduction
TA in °C
950
Oxide stablity
Chromia
stability
900
Haynes 230
Inconel 617 [Quadakkers]
850
0
10
20
30
40
50
60
P(CO) in µbar
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MATGENIV.2 – 02-06-2009 – TR 34
Corrosion test in the area for chromia reduction
Decarburization and softening
No surface
HV =scale
200
(no CH4)
no IIary
carbides at
gb
Al2O3
Dissolution
of carbides
HV = 280
20 µm
C(500hrs) = -0.04wt.%
Haynes 230, 950°C, 1000 hrs
Haynes
950°C,
hrs CH /0.5 H O (µbar)
He230,
/15 CO/
500250
H2 /300
4
2
He /15 CO/ 500 H2 /300 CH4 /0.5 H2O (µbar)
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MATGENIV.2 – 02-06-2009 – TR 35
Creep rupture properties in ‘decarburizing’ He
Decrease in creep life
Hastelloy XR
950°C
Stress (MPa)
area for
carburization
area for
decarburization
area for chromia
stability
Tsuji H., Nakajima H., Kondo T., Proc. specialists' meeting on high-temperature metallic materials for gascooled reactors, 81-90. Cracow, Poland. (1988)
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MATGENIV.2 – 02-06-2009 – TR 36
Summary on corrosion phenomena
1000
TTA
Cr2O3  3CSolution 
3CO(g)  2Cr
Chromia Oxide
reduction
reduction
TA in °C
950
Chromia stability
Oxide stablity
900
Haynes 230
Inconel 617 [Quadakkers]
850
with CH4
Carburization
Embrittlement
0
10
20
without
CH4
30
50
60
P(CO) in µbar
oxide surface scale
Decarburization
 creep life
! unacceptable in service !
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few effect on tensile
and creep prop
! Chemistry control !
MATGENIV.2 – 02-06-2009 – TR 37
Data on ODS
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MATGENIV.2 – 02-06-2009 – TR 38
Corrosion test in the area for ‘oxidation’
1000
reduction
Oxide
Chromia
reduction
TA in °C
950
He / 50 CO / 200 H2 /
20 CH4 / 1.5 H2O (µbar)
Oxide stablity
Chromia stability
900
Haynes 230
Inconel 617 [Quadakkers]
850
0
10
20
30
40
50
60
P(CO) in µbar
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MATGENIV.2 – 02-06-2009 – TR 39
Corrosion test on PM1000 in ‘oxidation’ domain
PM1000
1027 hrs,
950°C
20 µm
XRD: Cr2O3 + mixed Ti-Cr oxide
-
Inconel 617,
813 hrs, 950°C
impure He
Cr2O3
doped in Ti
with TiO2
on top
Ti depleted
zone
Bulk
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Mass gains in oxidation regime
1,2
1
m (mg/cm²)
0,8
0,6
Hastelloy X
0,4
MA957
12YWT
PM1000
PM1000/air
PM2000
PM2000/air
Hastelloy X
0,2
ODS
0
0
200
400
600
800
1000
1200
Temps (heures)
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MATGENIV.2 – 02-06-2009 – TR 41
Literature data on test of ODS in ‘oxidation’ domain
10µm
MA956 and other alloys after 1000 h at 1000°C
Suzuki T. et al., JAERI-Research--95-088 (1996)
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MATGENIV.2 – 02-06-2009 – TR 42
Corrosion test in the area for ‘carburisation’
1000
He / 5 CO / 200 H2 /
20 CH4 / 0.5 H2O (µbar)
TA in °C
950
Chromia
reduction
Oxide reduction
carburisation
Oxide stablity stability
Chromia
900
Haynes 230
Inconel 617 [Quadakkers]
850
0
10
20
30
40
50
60
P(CO) in µbar
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MATGENIV.2 – 02-06-2009 – TR 43
Corrosion test in the ‘carburizing’ domain
alumina
PM1000
240 hrs, 950°C
Cr-rich
Ti-rich
particles
Heavy carburization
10 µm
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MATGENIV.2 – 02-06-2009 – TR 44
Corrosion test in the area for decarburisation
1000
He / 5 CO / 200 H2 /
/ 0.5 H2O (µbar)
Chromia
reduction
Oxide reduction
decarburisation
TA in °C
950
Oxide stablity
Chromia
stability
900
Haynes 230
Inconel 617 [Quadakkers]
850
0
10
20
30
40
50
60
P(CO) in µbar
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MATGENIV.2 – 02-06-2009 – TR 45
Corrosion test in the ‘decarburizing’ domain
PM1000
1000 hrs, 950°C
20 µm
Mixed Cr-Ti
oxide
Ti depleted
zone
10 µm
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MATGENIV.2 – 02-06-2009 – TR 46
Corrosion test in the ‘decarburizing’ domain
Global carbon
percentage
after test at
950°C
Hast X
PM1000
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MATGENIV.2 – 02-06-2009 – TR 47
Summary
ODS steels and Ni-based ODS alloys
= promising materials for circuit and GFR
cladding
to operate at higher temperatures and up to
higher doses
– HT strength
– Radiation stability
– Oxidation resistance… effect of RE
(but carburization resistance and embrittlement ?)
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MATGENIV.2 – 02-06-2009 – TR 48
Corrosion resistance of ODS steels in liquid Na
SFR and cladding material
Corrosion loops
Corrosion of austenitic steels:
results, models and question marks
Data on corrosion of ferritic (ODS) steels
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MATGENIV.2 – 02-06-2009 – TR 49
SFR and cladding
material
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MATGENIV.2 – 02-06-2009 – TR 50
Fuel subassembly
Superphénix
(1200MWe)
Wrapper tube
Cladding tube
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MATGENIV.2 – 02-06-2009 – TR 51
Materials and conditions in advanced SFR
Element
Material
Core
Cladding A
15/15-25Ti ;
F 13-18Cr ODS
WT : F/M 9-12 Cr
Cold primary
structures
A 316 LN
Hot primary
structures and
components
A 316LN
F/M 9-12 Cr
Secondary
structures and
SG
A 316 LN
F/M 9-12 Cr
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Wall
thin
Thick
Nominal
operation
400-700°C
8-10 m/s
[O] < 5 ppm
Lifetime
850°C few hrs
>2y
[O] = 15 ppm / 100 h
400 - 450°C
few m/s
[O] < 5 ppm
60y
thin
thick
550 -650°C
few m/s
[O] < 5 ppm
10 y
and 60y
thin
thick
300-650°C
few m/s
[O] < 5 ppm
10 y
and 60y
thick
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Transient
500°C( ?) few hrs,
[O] = 15 ppm / 100 h
850°C few hrs
[O] = 15 ppm / 100 h
Reaction sodium/water
(NaOH/Na)
[O] = 200 ppm / 2000 h
MATGENIV.2 – 02-06-2009 – TR 52
Cladding: martensitic or ferritic ODS steel
Martensitic : 9-12Cr
- Isotropic (mechanical properties)
- Easier to manufacture
- (Possibly) lower irradiation embrittlement
- T < 800- 850°C
Ferritic : 14-18Cr
- More stable oxide films on surface
- fuel cladding chemical interaction
- reprocessing of the spend fuel (nitric acid dissolution)
- (Possibly) better corrosion resistance
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MATGENIV.2 – 02-06-2009 – TR 53
Advanced SFR (Gen IV)
• Economics
– Life time extension
– Higher temperature (efficient energy conversion)
• Innovative design
– simplification, integrated or loop concept,
maintenance, alternative heat carrier fluid etc
• Further enhanced safety (vacuum, water, fire)
– alternative secondary and heat carrier fluid
• Reduction of waste and recycling
– fuel (+MA)
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• New materials (creep
and swelling resistant)
• More demanding
conditions
– Temperature
– lifetime
– transitory
MATGENIV.2 – 02-06-2009 – TR 54
Objectives
• Experience gained from former SFR:
metallic materials are (highly) compatible with liquid sodium
•
However: new materials in more severe conditions
 Understanding of the metal/sodium interaction
– Mass loss
– Change in the alloy composition
– Change in the alloy microstructure
change in the
component properties
 Determination of corrosion kinetics:
Corrosion rate as a function of time + influence of parameters
– Component lifetime
– Need for sodium chemical control
– Circuit contamination source
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input data for design
engineers
MATGENIV.2 – 02-06-2009 – TR 55
Corrosion loops
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MATGENIV.2 – 02-06-2009 – TR 56
Forced convection loop
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MATGENIV.2 – 02-06-2009 – TR 57
Small device with rotating cylinder
LIBS
A
B
Motor
Loop
Purification
Cylindrical
sample
• Na = 3- 4 l per module
• T up to 750 °C
DEN/DANS/DPC/SCCME
Cold trap +
EM pump
• v = 3-12 m/s (3000-15000 tr/min)
• [O] = 0.7 à 38 ppm
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MATGENIV.2 – 02-06-2009 – TR 58
Austenitic steels
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MATGENIV.2 – 02-06-2009 – TR 59
Corrosion features
• Dissolution and mass transfer
– Dissolution of metals (Cr, Ni, Mn)  mass loss in hot part
– Mass transfer with precipitation to cold zone
dissolution
transport by
convection
precipitation
• Exchange of interstitial
elements (C, N)
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MATGENIV.2 – 02-06-2009 – TR 60
Corrosion morphology
• Surface cleaning
• Preferential dissolution of
alloying elements: Ni, Cr,
Mn (T>570°C)
• Formation of a ferrite layer
and dissolution (T>590°C);
depletion of Cr, Ni in the
adjacent austenite
+ precipitation of other
phases
GDOES analysis of
Baque – 1978 – Accore 14244
the surface of
austenitic steel
X8 16Cr13NiMoVNb
ferrite
after 5000h in Na
(5m/s) at 700°C with depleted
austenite
Sound
5.5ppm O2 Na
austenite
grain
boundary
• Steady state corrosion:
constant thickness of ferrite
and depleted austenite
Borgstedt H. U. and Mathews C. K. in Applied chemistry of
the alkali metals, New-York, Plenum Press (1987)
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MATGENIV.2 – 02-06-2009 – TR 61
Influence of Na velocity
• Effect of velocity on the rate of metal loss for various stainless
steels and conditions
• V<3 m/s, Rcorr  when V 
• V>3 m/s, Rcorr constant
• V >12 m/s corrosionerosion and cavitation
[Weeks, 1973]
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MATGENIV.2 – 02-06-2009 – TR 62
Influence of temperature
• The corrosion rate
of steels depends on
temperature following
an Arrhenius law :
Rcorr= A. exp(-Ea/RT)
• Corrosion rate also
depends on the oxygen
content
Kolster et al. (1984)
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MATGENIV.2 – 02-06-2009 – TR 63
Role of oxygen
• Change in the corrosion rate
 change in the corrosion
mechanism
• Critical oxygen level: 2-10ppm
Kolster et al.( 1984)
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MATGENIV.2 – 02-06-2009 – TR 64
Role of oxygen
• Effect of O on the Cr (and Fe?) solubility
via NaCrO2, thus on mass transfer
• Ni dissolves directly
Sodium
[O]
Bulk steel
Cr
NaCrO2
Na-Fe-O
Fe
Ni
Diffusion layer
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[Ni]
Recession
depth
MATGENIV.2 – 02-06-2009 – TR 65
Reactivity of interstitial elements: carburization
Concentration profile of carbon in
austenitic steel 15-15 Ti B after
exposure to ‘carburizing’ sodium
(5 m/s) for 5000 h at 700°C
• Deposition of carbon by
sodium and inward diffusion
– Change in the mean carbon
content
– Carburization from the
surface to ~100µm deep
• Some cladding tubes failed in
the Rapsodie experimental
reactor due to carburization
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MATGENIV.2 – 02-06-2009 – TR 66
Reactivity of interstitial elements
• Deposition/removal of carbon doesn’t
influence the mass transfer BUT
Sodium
Bulk steel
Cr23C6
Diffusion
layer
DEN/DANS/DPC/SCCME
– It may produce
carburization (high Cr content) /
decarburization (low Cr content)
– That may impact the mechanical
properties
embrittlement / loss of HT strength if the
affected thickness becomes significant
[C]
Recession
depth
– It occurs if the coolant sodium is polluted
(hydrocarbon) or if a transfer is possible
with an other material (carbon activity)
• Nitrogen transfer may produce
denitridation (virtualy zero solubility in sodium)
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MATGENIV.2 – 02-06-2009 – TR 67
Modeling of the corrosion rate
• What we have:
experimental models
R=f(T, V)
– that are only valid for austenitic steels
– that are only valid in a given temperature range
– that do not consider interstitial
 What we need: a mechanistic model
– Based on elementary mechanisms
– Input = physical-chemical data
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MATGENIV.2 – 02-06-2009 – TR 68
Dissolution mechanism: elementary process

V
JDiff
Jconv
Fes=Fediss SJdiss=n(Fed)/t
Jdiss



J T  J Dif  J Conv

JT
Cb(x)
kd
FesFediss
kpr

J diss C
w(x)
x

J diss :
Solubility limit(T)
Jdiss=kd Fe/MFe-kprCw
Eq: kdFe/MFe=kprSFe
Jdiss=kpr(SFe-Cw)
Precipitation rate(T)
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MATGENIV.2 – 02-06-2009 – TR 69
Dissolution mechanism: elementary process
CFe Diffusion

J Dif
Cw



J T  J Dif  J Conv
Convection

JT
Cb(x)

J diss C
w(x)

C()=Cb
J
 Conv
y
In the boundary layer (first Fick’s Law):


CFe DFe 
JT  
µFe  C FeV µFe=µ°+RTLnCFe
RT
Mass transfer coefficient
C Fe
C w  Cb
 DFe
 K (Cw  Cb )
JTy   DFe
y

depends on hydraulic diameter, viscosity, flow rate, DFe
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MATGENIV.2 – 02-06-2009 – TR 70
x
Dissolution mechanism: elementary process
Steady state: CFe is not time dependent  no matter accumulation

 J  Cst


J Diff  J diss K(Cw-Cb)=kpr(SFe-Cw)
Cw=(kprSFe-KCb)/(kpr+K)
The metal loss rate is then: n(Fe)/t=SJdiss
 Fe hFe
M Fe t

Kk pr
(S Fe  Cb )
K  k pr
Inputs: K(V,viscosity,DFe), kpr, SFe Outputs: hFe/t
F. Balbaud-Celerier, F. Barbier, J. Nucl. Mater. 289 (2001) 227
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MATGENIV.2 – 02-06-2009 – TR 71
Closed system: mass transfer
• Mechanistic model (local model: material/medium level):
dissolution mechanisms gives h=f(t), Rcorr=h/t
 steel life time in the hot part of the system
dissolution
Transport by
convection
precipitation
• Mass transfer model (global model: system level)
Input data are the outputs of the mechanistic model (Rcorr= h/t).
Output data are the corrosion rate as a function of the position in the
system Rcorr(x)
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MATGENIV.2 – 02-06-2009 – TR 72
Mass transfer mechanism
• Dissolution/precipitation:
Iron flux and iron concentration are calculated all along the system
• Use of the second Fick’s law to
Cb(x=0,t0)=S(T)
determine Cb(x) all along the system:
z
y

J
anisothermal
system
n
  (inlet fluxes  outlet fluxes )
t
 
 

  Cdv   J .dS   .Jdv
 t v  BL S   v  
x
(
  
.J  .(J diss / prec , J Diff )  CM .V  V .CM


Cb (r , x, t )  
 V .Cb (r , x, t )  . DCb (r , x, t )
t
)
=0
Incompressible
fluid
• Inputs of the mass transfer model = outputs of the mechanistic model:
J diss / prec  Cst (T , x)(S (T )  Cb (T , x))
• Balance equation at steady state


 J diss / prec .dS  0
syst
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numerical
solution
analytical
solution
MATGENIV.2 – 02-06-2009 – TR 73
Austenitic steels : summary
Borgstedt H. U., JNM 317 (2003) 160
• Corrosion is slow in pure sodium
• But it depends on material, T, V, [C]…
and [O]
Sodium
[O]
Bulk steel
Cr
Fe
NaCrO2
Na-Fe-O
• Preferential dissolution of elements
induces
– mass loss
– microstructure changes
Ni
Cr23C6
Diffusion
layer
[Ni]
[C]
Recession
depth
• Mass transfer occurs between hot
zones and cold zones
• Interstitials can dissolve/deposit with
(de)carburization
 Need for a mechanistic model
r  Sh(Re, Sc).D.d H (a( s )  a(l ) )
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MATGENIV.2 – 02-06-2009 – TR 74
Data on ferritic (ODS)
steels
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MATGENIV.2 – 02-06-2009 – TR 75
Ferritic steels
• Corrosion morphology
– Lower mass loss
– No depletion of alloying element
– But deeper change in the
microstructure:
• recrystallization (x10)
• Internal oxidation (if [O] >20-40 pm,
transitory)
• Parameters : material, T, V, [C], [O]
• Low Cr ferritic steels suffer from
decarburization (role of Cr, V, Nb, Ti, HT)
EM12: 9%Cr
• Mechanisms should basically be the
same
Balbaud F. et al., ICAPP’09
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MATGENIV.2 – 02-06-2009 – TR 76
ODS steels
• Very few data
• Mechanism should
basically be the same
• Smaller mass loss?
• Higher carburisation?
Approximated concentration profiles of C, N
and O for MA957 (14%Cr) and 11%Cr-1%Mo
ODS steels after exposure to Na (4m/s) at
675°C for 3000h
[Yoshida et al., 2004]
[Suzuki et al., 1988]
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MATGENIV.2 – 02-06-2009 – TR 77
Thank you for your kind
attention 
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MATGENIV.2 – 02-06-2009 – TR 78
Sodium reactivity with water / air
• In air at ambiant
temperature
• Sodium fire
• Excess water
Na + H2O = NaOH + ½ H2
+ Heat (145 kJ/mol)
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MATGENIV.2 – 02-06-2009 – TR 79
Creep stress to rupture (MPa)
Creep rupture properties in ‘oxidizing’ helium
850°C
100
No significant
effect of the
oxidizing VHTR He
950°C
617 - Bar - 850 and 950°C - vacuum
617 - Cold rolled plate - 850°C - RCG He
617 - Cold rolled plate - 850°C - He 5.5
230 - Bar - 950°C - vacuum
Alloys 617 & 230
850° & 950°C
230 - Hot rolled plate - 850°C - vaccum
230 - Cold rolled plate - 850°C - RCG He
230- Cold rolled plate - 850°C - He 5.5
10
10
DEN/DANS/DPC/SCCME
100
Time (hours) 1 000
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10 000
MATGENIV.2 – 02-06-2009 – TR 80

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