Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH...

Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft

M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 1

Oxidation of Zircaloy in prototypic air-steam mixturesOxidation of Zircaloy in prototypic air-steam mixtures

M. Steinbrück, P. Severloh, U. Stegmaier, T. ZieglerInstitute for Materials Research IInstitute for Materials Research I

Forschungszentrum Karlsruhe Forschungszentrum Karlsruhe Postfach 3640, 76021 Karlsruhe, GermanyPostfach 3640, 76021 Karlsruhe, Germany



Motivation

Scenarios for air ingress: Residual fuel

elements

Breach in the primary circuit

RPV rupture

Open RPV lid

1) Late phase after failure of RPV 2) Mid loop operation 3)…

Consequences: • Strong exothermal reaction (RHair >> RHsteam)

• Less cooling effect

• Detrimental effect of nitrogen on oxide scales

• Higher oxygen activity in the core

Temperature escalation

Degradation

Oxidation of fuel

FP release and transport

What are prototypical atmospheres?

1) First steam, then air (sequential)

2) Mixed air-steam atmospheres

For both no data are available so far



Motivation

0 200 400 600 800 10000

5

10

15

20

25

m,

%

Time, s

Oxygen Parabolic oxidation kinetics

1200 °C



Motivation

0 200 400 600 800 10000

5

10

15

20

25

m,

%

Time, s

Oxygen

Nitrogen

Parabolic oxidation kinetics

Parabolic oxidation kinetics

1200 °C



Motivation

0 200 400 600 800 10000

5

10

15

20

25

m,

%

Time, s

Oxygen

Nitrogen

AirParabolic oxidation kinetics

Parabolic reaction kinetics

~ Linear oxidation kinetics1200 °C

Oxidation rate in air is much higher than in oxygen or steam



Oxidation of Zircaloy-4 in mixed air-steam atmospheres



BOX Rig for oxidation experiments under controlled atmosphere

H 2 A r H O2 M ixer

Ar

W ater s torage

C on tro lledevapora to r

m ixer

Control center

Furnace

L iqu id flow con tro lle r

Mass spectrometer

Com puter system

Sam ple

Gas supply system

T C

H O2

Air

G as flow con tro lle rs

CEM



BOX Rig for oxidation experiments under controlled atmosphere

Furnace

ControlledEvaporatorMixer

Controllerfor gas and water

Heated pipe to MS

Massspectrometer

Air lock



BOX Rig: Sample holder with Zry-4 cladding segment

ZrO2 rod

Zry-4 claddingsegment

Heatedflange



Test matrix

• 1 hour or 10 min, isotherm

• 3 temperatures:

800, 900, 1000, 1100, 1200, 1300, 1400, 1500 °C

• 9 compositions:

air/steam mixtures with 0, 2.7, 5, 10, 30, 50, 70, 90, 100 vol.% air

81 tests



Test conduct and MS results of the series at 1500 °C

Input rates:

Rates measured by MS:

0 2000 4000 6000 8000 10000 12000 140000

20

40

60

80

100

600

800

1000

1200

1400

1600

Te

mp

era

ture

, °C

Flo

w r

ate

, l/h

an

d g

/h

Time, s

Ar, ln/h Steam, g/h Air, ln/h Temp.

0 2000 4000 6000 8000 10000 12000 140000

20

40

60

80

100

0

5

10

15

Ra

te (

MS

), l/

h a

nd

g/h

Time, s

Steam, g/h N

2, l/h

O2, l/h

H2, l/h

H2 r

ate

(M

S),

l/h



Metallographic post-test appearance of specimens after 1 hour isothermal oxidation at 800 °C

Air 0.9 air / 0.1 H2O 0.7 air / 0.3 H2O 0.5 air / 0.5 H2O 0.3 air / 0.7 H2O

0.1 air / 0.9 H2O 0.05 air / 0.95 H2O 0.03 air / 0.97 H2O H2O

800 °C1 h





900 °C1 h






1000 °C1 h




1300 °C10 min



Metallographic post-test appearance of specimens after 10 min isothermal oxidation at 1300 °C



1300 °C, 10 min, 0.3 air/ 0.7 H2O

Metallographic post-test appearance of specimens after 10 min isothermal oxidation at 1300 °C in 30% air + 70% steam



10

min

in a

ir

1200°C 1300°C

1400°C1500°C

Metallographic post-test appearance of specimens after 10 min isothermal oxidation various temperatures in air



10

min

in s

team

1200°C 1300°C

1400°C1500°C

Metallographic post-test appearance of specimens after 10 min isothermal oxidation various temperatures in steam



Oxidation of Zircaloy-4 in mixed air-steam atmospheres

0 20 40 60 80 100

1

2

3

10

20

30 800 °C 900 °C 1000 °C 1100 °C 1200 °C

m,

%

Air, Vol.%

0 20 40 60 80 1000

5

10

15

20

25

30

35 1200 °C 1300 °C 1400 °C 1500 °C

m,

%

Air, Vol.%

• First influence of air in mixtures on oxidation behaviour at 900 °C (locally)

• Increasing degradation of oxide scale with temperature and air concentration (local → layer)

• Reversal at 1500 °C: almost no impairment of the oxide scales by air

1 h 10 min



Sequential oxidation of Zircaloy-4 first in oxygen and then air or nitrogen



Test rig with thermal balance and mass spectrometer

TG m easuring head

Y O plate2 3

Al O plate2 3

Zry-4specimen

TC

M ass spectrom eter

Gas in letA r/O , N , a ir2 2

Therm obalance

Vacuum system

C apillary

Analyticalbalance

H igh-tem peraturefurnace

Specim en



Comparison between oxidation in O2, N2, and air

0 1000 2000 3000 4000 50000

5

10

15

20

25

30

35

m,

%

Time, s

1100 °C: Ox. in O

2

Pre-ox. in O2, ox. in air

Pre-ox. in O2, react. in N

2

Ox. in air React. in N

2

1000 °C: Pre-ox. in O

2, ox. in air

Oxidation in air is not the sum of the reaction in oxygen and nitrogen!



0 1000 2000 3000 4000 50000

5

10

15

20

25

30

35

m,

%

Time, s

1100 °C: Ox. in O

2



2


2


2, ox. in air

Pre-oxidation in oxygen suppresses the influence of nitrogen during subsequent oxidation in air

Comparison between oxidation in O2, N2, and air: Influence of pre-oxidation



0 1000 2000 3000 4000 50000

5

10

15

20

25

30

35

m,

%

Time, s

1100 °C: Ox. in O

2



2


2


2, ox. in air

Pre-oxidation in oxygen causes an increase of the reaction rate in nitrogen

Comparison between oxidation in O2, N2, and air: Influence of pre-oxidation



0 1000 2000 3000 4000 50000

5

10

15

20

25

30

35

m,

%

Time, s

1100 °C: Ox. in O

2



2


2


2, ox. in air

Significant higher oxidation rates at 1000 °C in comparison to 1100 °C!

Comparison between oxidation in O2, N2, and air: Influence of breakaway at 1000 °C



0 1000 2000 3000 4000 50000

5

10

15

20

25

30

35

m,

%

Time, s

1100 °C: Ox. in O

2



2


2


2, ox. in air

Comparison between oxidation in O2, N2, and air: Post-test appearance of specimens



1100 °C, air1100 °C, O2 1100 °C, N2

1100 °C, PO, air 1100 °C, PO, N2

Comparison between oxidation in O2, N2, and air: Metallographic PT examination

With pre-oxidation (PO)



0 500 1000 1500 20000

5

10

15

20

25

air PO: 5 µm, air PO: 20 µm, air PO: 150 µm, air O

2

m,

%

Time, s

Little pre-oxidation in oxygen (steam) causes a significant reduction of the detrimental effect of subsequent oxidation in air

Isothermal tests at 1200 °C in air in dependence on the degree of pre-oxidation



0 500 1000 1500 20000.00

0.01

0.02

0.03

0.04

0.05

d(

m)/

dt,

%/s

Time, s

air PO: 5 µm, air PO: 20 µm, air PO: 150 µm, air O

2

Oxidation rates in oxygen and in air after significant pre-oxidation are almost identical

Isothermal tests in air at 1200 °C in dependence on the degree of pre-oxidation



1200 °CNo PO

Air

1200 °C3 s PO in O2

Air

1200 °C10 min PO in O2

Air

1200 °C10 s PO in O2

Air

Isothermal tests in air in dependence on the degree of pre-oxidation: Post-test metallography



Reaction rates in nitrogen are higher after pre-oxidation in oxygen, but seem to be independent on the degree of pre-oxidation

0 500 1000 1500 20000.00

0.01

0.02

0.03

d(

m)/

dt,

%/s

Time, s

N2

PO: 5 µm, N2

PO: 20 µm, N2

PO: 150 µm, N2

mit Voroxidationohne Voroxidation

Isothermal tests in nitrogen at 1200 °C in dependence on the degree of pre-oxidation

With pre-oxidationWithout pre-oxidation



1200 °CNo PO

N2

1200 °C3 s PO in O2

N2

1200 °C10 min PO in O2

N2

1200 °C10 s PO in O2

N2

Isothermal tests in nitrogen at 1200 °C in dependence on the degree of pre-oxidation



Oxidation of zirconium without pre-oxidation in:

Oxygen: parabolic kinetics

Nitrogen: parabolic kinetics (very slow)

Air: linear kinetics (very fast, nitride formation at metal/oxide phase boundary)

Oxidation of zirconium with pre-oxidation in:

Nitrogen: linear kinetics, nitride formation at external oxide surface

Air: parabolic kinetics like in oxygen (as long as oxide scale is dense)

Nitride formation only in the absence of oxygen and in the presence of oxide!

Sequential oxidation of Zircaloy-4 in oxygen and air/nitrogen



Future work

• Experiments on sequential oxidation in various atmospheres at 800, 1000, 1200, and 1400 °C; test of new specimens avoiding external+internal oxidation (diploma thesis)

• Kinetic tests on the oxidation of Zircaloy in mixed air-steam atmospheres

• Tests on oxidation of pre-existing external nitride scales in steam

• Further experiments necessary for model development

Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH...

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Transcript of Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH...