Deviations from the parabolic kinetics during oxidation of zirconium alloysof zirconium alloysMartin Steinbrück, Mirco Große Karlsruhe Institute of Technology, Institute for Applied Materials, Germany17th I t ti l S i Zi i i th N l I d t 03 07 02 2013 H d b d I di
Institute for Applied Materials IAM-AWP & Program NUKLEAR
17th International Symposium on Zirconium in the Nuclear Industry, 03.‐07.02.2013, Hyderabad, India
KIT – University of the State of Baden‐Wuerttemberg and National Research Center of the Helmholtz Association www.kit.edu
Motivation
Oxidation of zirconium alloy claddings during severe accidents causes degradation of cladding and loss of
PWRfueldegradation of cladding and loss of
barrier effect as well as production of hydrogen and heat
ueelement
Oxidation kinetics and corresponding hydrogen source term have to be known for appropriate accident management measuresmeasures
At KIT extensive investigations on oxidation of zirconium alloys in various atmospheres have been performed in the framework of the QUENCH program including integral bundle tests and small‐
l t ff t i t
Institute for Applied Materials2 Martin Steinbrück ASTM Zr in Nucl. Ind. 2013
scale separate‐effects experiments
ExperimentalMost tests were conducted in a NETZSCH STA409 coupled with steam injector and mass
TG
spectrometer; some in horizontal tube furnace with air lock
Typical temperature range: yp p g600‐1600°C
Zr alloys: Zry‐4 Zry‐2 Duplex DX‐D4 M5® INRROZry 4, Zry 2, Duplex DX D4, M5 , E110, ZirloTM
Atmospheres: t i it
INRRO
steam, oxygen, air, nitrogen, mixtures of these
Mostly isothermal tests, some
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transient experiments
Martin Steinbrück ASTM Zr in Nucl. Ind. 2013
Oxidation in steam (oxygen)
Most LOCA and SFD codes use parabolic oxidation correlations, (i.e. n=1/2 in )
Zr(O)n
m tkSm /
ZrO2
Zr(O)precipitatesT>1500°C
-Zr(O) ZrO2
prior -Zr -Zr(O)
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1200 °C, quench 1600 °C, quench
Oxidation in steam (oxygen)
Deviations from parabolic kinetics at temperatures <1100°C
2,6 700 °C
2,0
2,2
2,4 Zry-4 Duplex Zirlo M5
1,4
1,6
1,8
g(m
/S)
5 E110
0,8
1,0
1,2
,
lg
1 2 3 4 50,4
0,6
0,8
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lg(Time/s)
Oxidation in steam (oxygen)
Deviations from parabolic kinetics at temperatures <1100°C
2,6 700 °CSub parabolic (cubic)
2,0
2,2
2,4 Zry-4 Duplex Zirlo M5
Sub-parabolic (cubic) kinetics
1,4
1,6
1,8
g(m
/S)
5 E110
0,8
1,0
1,2
,
lg
1 2 3 4 50,4
0,6
0,8
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lg(Time/s)
Oxidation in steam (oxygen)
Deviations from parabolic kinetics at temperatures <1100°C
2,6 700 °CSub parabolic (cubic)
2,0
2,2
2,4 Zry-4 Duplex Zirlo M5
Sub-parabolic (cubic) kinetics
n=1
1,4
1,6
1,8
g(m
/S)
5 E110
n=1/2
1/3
0,8
1,0
1,2
,
lg n=1/3
1 2 3 4 50,4
0,6
0,8
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lg(Time/s)
Oxidation in steam (oxygen)
Deviations from parabolic kinetics at temperatures <1100°C
2,6 700 °CSub parabolic (cubic)
2,0
2,2
2,4 Zry-4 Duplex Zirlo M5
Sub-parabolic (cubic) kinetics
T iti f ( b )
n=1
1,4
1,6
1,8
g(m
/S)
5 E110 Transition from (sub-)
parabolic to linear kinetics after critical time / oxide thickness
n=1/2
1/3
0,8
1,0
1,2
,
lg time / oxide thickness due to breakaway
n=1/3
1 2 3 4 50,4
0,6
0,8
Institute for Applied Materials8 Martin Steinbrück ASTM Zr in Nucl. Ind. 2013
lg(Time/s)
Oxidation in steam (oxygen)
Deviations from parabolic kinetics at temperatures <1100°C
2,6 700 °CSub parabolic (cubic)
2,0
2,2
2,4 Zry-4 Duplex Zirlo M5
Sub-parabolic (cubic) kinetics
T iti f ( b )
n=1
1,4
1,6
1,8
g(m
/S)
5 E110 Transition from (sub-)
parabolic to linear kinetics after critical time / oxide thickness
n=1/2
1/3
0,8
1,0
1,2
,
lg time / oxide thickness due to breakaway
Si il ki ti f ll
n=1/3
1 2 3 4 50,4
0,6
0,8 Similar kinetics of all alloys before transition, but strongly varying behavior at and after
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lg(Time/s) behavior at and after transition
Breakaway oxidation
Loss of protective properties of oxide scale due to its mechanical failure.
Breakaway is caused by phase transformation
E110
Breakaway is caused by phase transformation from meta‐stable tetragonal to monoclinic oxide and corresponding change in density up to ca. 1050°C.
Critical times and oxide thicknesses for breakaway strongly depend on type of alloy and boundary conditions
24 h, 900 °C
(ca. 30 min at 1000°C and 8 h at 600°C).
During breakaway significant amounts of hydrogen can be absorbed (>40 at.%, 7000
Zry-4
wppm) due to local enrichment of H2 in pores and cracks near the metal/oxide interface (“hydrogen pump”).
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3 h, 1000 °C
Transition times (h) and corresponding critical oxide scale thickness (µm) during oxidation in steam(µ ) g
T, °C Zircaloy‐4 Duplex‐D4 ZirloTM M5® E110600 8.2 (7) 7.7 (3) 6.3 (8) nt nt700 2.2 (9) 2.2 (9) 1.4 (9) nt 13 (21)700 2.2 (9) 2.2 (9) 1.4 (9) nt 13 (21)800 7.4 (41) 7.3 (35) 5.2 (32) nt 0.9 (12)900 1.3 (40) 1.4 (38) 2.1 (40) nt 0.8 (24)1000 0.6 (89) 0.9 (105) 0.6 (76) nt 0.6 (48)≥1100 t t t t t
2.5
3.0
Zry-4
2.5
3.0
M5
≥1100 nt nt nt nt nt
1.5
2.0
lg(
m/S
)
1.5
2.0
lg(
m/S
)
0.0
0.5
1.0
1/3
1/2n=1
0 0
0.5
1.0
1/3
1/2n=1
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2 3 4 5
lg(Time/s)2 3 4 5
0.0
lg(Time/s)
Correlation of H absorption and oxide morphology
30
40
10
20
x H, a
t.% Zry‐4
0
10
D
Zry4
070080090010001100
M5
E110
Zirlo
Duplex
T, °C M5
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6007 M5C M5
Correlation of H absorption and oxide morphologyIn‐situ NR of H uptake during oxidation of Zry‐4 at 1000°C in steam
1400
1600
In situ NR of H uptake during oxidation of Zry 4 at 1000 C in steam
30
40
1000
1200
1400
m
10
20
x H, a
t.% Zry‐4
600
800
1000
H, w
ppm
0
10
D
Zry4200
400
600c H
070080090010001100
M5
E110
Zirlo
Duplex
T, °C M50 3600 7200 10800 14400 18000
0
200
id ti ti
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6007 M5C M5oxidation time, s
Oxidation in atmospheres containing nitrogen
Air ingress reactor core, spent fuel pond, or transportation cask
Nitrogen in BWR containments (inertization) and ECCS
Late phase after RPV failure
Residual fuel
Breach in the primary circuit
Residual fuel
Breach in the primary circuit
Late phase after RPV failureLate phase after RPV failure
Residual fuel
Breach in the primary circuit
Residual fuel
Breach in the primary circuit
Late phase after RPV failure
Nitrogen in BWR containments (inertization) and ECCS pressurizers
Prototypically following steam oxidation and mixed with steam
Residual fuel elements
RPV rupture
Residual fuel elements
RPV rupture
Residual fuel elements
RPV rupture
Residual fuel elements
RPV rupture
Mid loop operationMid loop operation
with steam
Consequences:
Open RPV lidOpen RPV lidOpen RPV lidOpen RPV lidOpen RPV lidOpen RPV lidOpen RPV lidOpen RPV lidOpen RPV lid
Significant heat release causing temperature runaway from lower temperatures than in steam
Strong degradation of cladding causing early loss of barrier effect
Spent fuel storage pool accidentSpent fuel storage pool accident
barrier effect
High oxygen activity influencing FP chemistry and transport
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Oxidation of Zr alloys in N2, O2 and air
25 ~ Linear oxidation kinetics1200 °C
20
25
Parabolic oxidation kinetics
Linear oxidation kinetics1200 °C
10
15
m
, %
0
5
Nitrogen Parabolic reaction kinetics0 200 400 600 800 1000
Time, s
Oxidation rate in air is much higher than in oxygen or steam
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g yg
Martin Steinbrück ASTM Zr in Nucl. Ind. 2013
Oxidation of Zr alloys in N2, O2 and air1 h
25 1200 °C
1 h
20
25 1200 °C
1.5 h
10
15
m
, %
0
5
Nitrogen 3 h
0 200 400 600 800 1000
Time, s
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Consequences of air ingress for cladding
1 hour at 1200°C in steam 1 hour at 1200°C in air
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Loss of barrier effect of cladding
Mechanism of air oxidation
1
Diffusion of air through imperfections in the oxide scale to the metal/oxide
2
scale to the metal/oxide interface
Consumption of oxygen
3
Remaining nitrogen reacts with zirconium and forms ZrN
4
1 initially formed dense oxide ZrO
ZrN is re‐oxidized by fresh air with progressing reaction associated with a volume
1 – initially formed dense oxide ZrO2
2 – porous oxide after oxidation of ZrN3 – ZrO2 / ZrN mixture4 Z (O)
increase by 48%
Formation of porous and non‐t ti id l
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4 – -Zr(O)protective oxide scales
Reaction of ZrOx with nitrogen
12
14
1200°C
10
12
6
8
m, %
Oxygen load: 0% (-Zr)0 7% ( Z (O))
2
40.7% (-Zr(O)) 5.7% (-Zr(O)) 33.1% (substoich. ox.) 35% (stoichiometr. ox.)
0 1000 2000 3000 40000
Time, s
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Influence of pre‐oxidation (PO) in steam on subsequent reaction in air and nitrogen
Protective effect of
Example: Zry-4, 1200°C
linear parabolic
Protective effect of PO on subsequent oxidation in air as long as oxide scale
15 min air PO + 50 min air
gis intact
Accelerating effect of PO on
parabolic linear
175 min N2 PO + 27 min N2
subsequent reaction in nitrogen
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2 2
Oxidation of Zr alloys in various atmospheres51200°C
20
25 Air H2O O2
PO + Air -Zr + N2
5
4
51200°C
10
15
2
PO + N2
N2
m, %
Air3
4
4
5
10
0 200 400 600 8000
Time, s
12
1 2 3
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Oxidation of Zr alloys in various atmospheres
Reaction of Zr 4 in Kinetic rate la Relati e reaction rate a*Reaction of Zry‐4 in Kinetic rate law Relative reaction rate, a.u.
N2 parabolic 1
N after pre oxidation in O linear 10N2 after pre‐oxidation in O2 linear 10
N2 with oxygen‐stabilized ‐Zr(O) linear 70
O2 H2O parabolic 100O2, H2O parabolic 100
Air after pre‐oxidation in O2 parabolic 100
Air linear 150Air linear 150
* at 1200°C
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Oxidation in mixed steam‐air atmospheres
Zry‐4, 1 hour at 1200°C
0.1 H2O0.9 air
0.3 H2O0.7 air
0.7 H2O0.3 air
H2O
Increasing degradation with raising content of air in the mixture
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Oxidation in mixed atmospheres
1 hour at 1000 °C in steam 1 hour at 1000 °C in 50/50 steam/N2
Strong effect of nitrogen on oxidation and degradation
Nitrogen acts like a catalyst (NOT like an inert gas)
Enhanced hydrogen source term by oxidation in mixtures
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y g ycontaining nitrogen
Conclusions
The usually applied parabolic oxidation kinetics are, strictly speaking, only valid at temperatures above 1000°C and for fast transients (with fast passing of the breakaway region).( p g y g )
Sub‐parabolic kinetics is observed at temperatures below 1000°C.
Breakaway has to be taken into account for slow transients and long duration scenarios at medium temperatures (600‐1000°C).
Nitrogen is not an inert gas under the conditions of a nuclear accident. It accelerates oxidation and causes rather linear kinetics.
Computer codes simulating severe accident scenarios should take into account non‐parabolic oxidation kinetics. Various activities are ongoing worldwide
Institute for Applied Materials25 Martin Steinbrück ASTM Zr in Nucl. Ind. 2013
activities are ongoing worldwide.
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