Institute for Applied Materials IAM-AWP & Program …...Institute for Applied Materials IAM-AWP &...

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

Institute for Applied Materials3

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)


1200 °C, quench 1600 °C, quench


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


lg(Time/s)



2,6 700 °CSub parabolic (cubic)

2,0

2,2


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


lg(Time/s)




2,0

2,2



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


lg(Time/s)




2,0

2,2



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


lg(Time/s)




2,0

2,2



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


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”).


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


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


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


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


Late phase after RPV failureLate phase after RPV failure

Residual fuel


Residual fuel


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


RPV rupture


RPV rupture


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


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

Institute for Applied Materials15

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


Consequences of air ingress for cladding

1 hour at 1200°C in steam 1 hour at 1200°C in air

L f b i ff t f l ddiInstitute for Applied Materials17 Martin Steinbrück ASTM Zr in Nucl. Ind. 2013

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


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


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


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


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


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


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


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


activities are ongoing worldwide.

Institute for Applied Materials IAM-AWP & Program …...Institute for Applied Materials IAM-AWP &...

Documents

Transcript of Institute for Applied Materials IAM-AWP & Program …...Institute for Applied Materials IAM-AWP &...