Investigating the Corrosion Behaviour of Zircaloy-4 …...25 A presentation by Wood. Accelerated...

woodplc.com

Investigating the Corrosion

Behaviour of Zircaloy-4 in LiOH

under a Thermal Gradient and

Two Phase Flow Regime.

Helen Hulme1, Alexandra Panteli1, Felicity Baxter1,

Mhairi Gass1, Aidan Cole-Baker1, Paul Binks1, Mark

Fenwick1, Michael Waters1, James Smith2

• Part one – influence of two phase flow

– Introduction

– Testing procedure

– Results

– Discussion

• Part two – relationship between [LiOH] & Temp.

– Introduction - Literature data

– Testing procedure

– Results & Discussion

• Summary & Industrial Context

Outline

Part one – influence of two phase flow on

corrosion of Zircaloy-4 in LiOH

3

Objective: To understand the influence of two-phase flow (subcooled nucleate boiling) within thick oxide films under a thermal gradient on the corrosion properties of zirconium alloys in LiOH chemistry.

– Is there potential to cause a localised increase in LiOH concentration in cracks / pores, as a result of boiling in thick oxide films, leading to accelerated corrosion?

– What is the critical LiOH concentration required to cause accelerated corrosion?

– Could this be detrimental to the use of LiOH without boric acid additions, eg. For SMR design considerations?

Introduction

Heating block

Specimen

enclosedNo specimenWater flow

Testing Conditions

5

Testing under a thermal gradient was

performed in Wood’s “heat flux rig”

• Recirculating autoclave loop

• Pressurised system

• Single coolant temperature

• Variable flow across

specimen

• ΔT across specimen (<90 °C)

Testing Conditions

6 A presentation by Wood.

Test

Parameters

Initial Oxide

Thickness (µm)Water Chemistry Thermal Gradient Pre-Stressed Boiling

10

LiOH Yes No No

2 LiOH Yes No Yes

3

< 20

NH4OH Yes No Yes

4 LiOH Yes No No

5 LiOH Yes No Yes

6 LiOH No No No

7

> 20

LiOH Yes No No

8 NH4OH Yes No No

9 NH4OH Yes No Yes

10 NH4OH No No No

11 LiOH Yes No Yes

12 LiOH Yes Yes Yes

Testing Conditions


Test

Parameters

Initial Oxide


10

LiOH Yes No No

2 LiOH Yes No Yes

3

< 20

NH4OH Yes No Yes

4 LiOH Yes No No

5 LiOH Yes No Yes

6 LiOH No No No

7

> 20

LiOH Yes No No

8 NH4OH Yes No No

9 NH4OH Yes No Yes

10 NH4OH No No No

11 LiOH Yes No Yes

12 LiOH Yes Yes Yes

Zircaloy-4 sheet

specimens pre-filmed in

500 °C air to form

relatively thick oxide films

in a timely manner

Testing Conditions


Test

Parameters

Initial Oxide


10

LiOH Yes No No

2 LiOH Yes No Yes

3

< 20

NH4OH Yes No Yes

4 LiOH Yes No No

5 LiOH Yes No Yes

6 LiOH No No No

7

> 20

LiOH Yes No No

8 NH4OH Yes No No

9 NH4OH Yes No Yes

10 NH4OH No No No

11 LiOH Yes No Yes

12 LiOH Yes Yes Yes

Corieu et al, 1962 Corrosion

behaviour of Zircaloy-4 in

NH4OH similar to water (i.e. no

accelerated corrosion even in

extreme concentrations).

Using NH4OH removes any

effect of pH

Testing Conditions


Test

Parameters

Initial Oxide


10

LiOH Yes No No

2 LiOH Yes No Yes

3

< 20

NH4OH Yes No Yes

4 LiOH Yes No No

5 LiOH Yes No Yes

6 LiOH No No No

7

> 20

LiOH Yes No No

8 NH4OH Yes No No

9 NH4OH Yes No Yes

10 NH4OH No No No

11 LiOH Yes No Yes

12 LiOH Yes Yes Yes

Pre-stressed Oxides


Pre-filmed Oxide

Zircaloy Specimen

Attach to heater

block and Heat-up

Pre-filmed Oxide

Zircaloy Specimen

Steel Heater Block

• Standard specimens are pre-filmed unrestrained.

• Test set-up induces a stress on the Zircaloy specimen upon heating.

• To reduce this, specimen is pre-filmed attached to the heater block, conditioning it to

the test environment

Results

12

Results – influence of oxide thickness


Thick Oxides (>20 µm)

required for accelerated

corrosion to occur

Thick = >20 µm

Thin = <20 µm

Coolant chem. 2 ppm LiOH

Autoclave temp. 250 °C

Results – influence of boiling


Within thick oxides (>20 µm),

boiling is required for

accelerated corrosion to occur



Results – influence of chemistry


For thick oxides (>20 µm) under

boiling conditions, LiOH is required

for accelerated corrosion to occur.

Accelerated corrosion is not

observed in the presence of NH4OH



Results – influence of stress


For thick oxides (>20 µm) under

boiling conditions in LiOH, stress in

the oxide is required for

accelerated corrosion to occur.

Accelerated corrosion is not

observed if the oxide is formed in a

pre-stressed condition



19

Discussion

• For accelerated corrosion to be observed during testing, the following criteria must be met:

– Thick >20 µm oxide film

– Sub-cooled boiling

– LiOH chemistry

– Stress

Discussion – key observations


Key observations:

• Results from pre-filmed specimens under non-boiling conditions do not show

accelerated corrosion, indicating this is not a memory effect.

• Comparable test conditions using NH4OH do not show accelerated corrosion,

demonstrating that LiOH does have an effect.

Discussion – Hypothesised Mechanism


Effect of Stress

Stress causes the pores

& cracks present in the

oxide to open and

create a more

accessible pathway for

the coolant to

penetrate nearer the

metal / oxide interface

Effect of Boiling Effect of LiOH



Effect of Stress Effect of Boiling



oxide to open and

create a more


the coolant to



Boiling within the cracks &

pores that have limited

accessibility to the coolant

causes localised

concentration of LiOH

solution to levels above that

of the bulk coolant. SIMS

analysis agrees with this

occuring



Effect of Stress Effect of Boiling Effect of LiOH



oxide to open and

create a more


the coolant to






causes localised





observation

Similar observations were

seen by Jeong et al. 1999,

following accelerated

corrosion under a 70 ppm

LiOH, 350 °C isothermal

autoclave environment

Effect of boiling: SIMS results


Accelerated Accelerated

Non-acceleratedNon-accelerated

Where accelerated corrosion

was observed (as a result of

boiling), lithium was leachable

from cracks and pores

indicating local accumulation

of lithium in these regions.

All data from oxides >20 µm

Effect of boiling: SIMS results


Accelerated Accelerated

Non-acceleratedNon-accelerated

Leachable lithium content was

measured using ICP-OES.

This equates to a lithium

concentration of 25 ppm within

the entire oxide film.

Calculations estimate the metal /

oxide interface temperature,

under conditions for boiling,

would be ~315 °C

This is significantly lower than

that expected for accelerated

corrosion

ICPOES - Inductively Coupled Plasma Optical

Emission Spectroscopy



Effect of Stress Effect of Boiling Effect of LiOH



oxide to open and

create a more


the coolant to






causes localised





occurring

Billot et al. proposed that

at high levels, lithium

becomes incorporated

into the oxide film on

pore walls forming

Li2ZrO3 within pores,

which dissolves, further

developing the porous

network.

Billot et al suggest an additional impact of oxide thickness, whereby the dimensions of the pores become sufficient to support rapid transport of lithium to the metal / oxide interface when the oxide thickness exceeds approximately 20 µm. Our data is consistent with this.

• Criteria for accelerated corrosion:

– Thick >20 µm oxide film

– Sub-cooled boiling

– LiOH chemistry

– Stress

The above conditions cause LiOH to concentrate to a critical level

resulting in accelerated corrosion.

Q. What level of LiOH is required for accelerated corrosion to occur?

What does this mean for industry?


Part two – investigating the relationship

between critical [LiOH] and temperature

28

Introduction - Understanding from Literature

29

Data taken from Murgatroyd et al., Pecheur et al., Ramasubramanian et al., Bramwell et al., Jeong et al. and McDonald et al.

Grey lines indicate bounding conditions for acceleration based on these data.

All data are taken from post-transition (i.e. beyond 2 µm) corrosion rates of Zircaloy.

Testing Conditions

30

Specimen

ID

Steam Pre-Film

(Demin, 400

°C)

Aqueous Pre-film

(2 ppm LiOH, 350

°C)

Cal

cula

ted

tim

e at

tem

p.

acco

rdin

g to

Hill

ner

(day

s)

Test ConditionsEx

po

sure

(day

s)

Oxi

de

thic

knes

s (µ

m)

Exp

osu

re

(day

s)

Oxi

de

thic

knes

s (µ

m)

[LiO

H]

(pp

m)

Tem

per

atu

re

(°C

)

AC1 56 2.40 10 3.15 2282 350

AC2 56 3.03 10 3.57 259

AC3 56 2.78 10 3.39 24660 350

AC4 56 2.47 10 3.25 236

AC5 56 2.46 10 3.25 236110 350

AC6 56 2.96 10 3.50 254

AC7 56 2.81 10 3.41 482250 330

AC8 56 2.37 10 3.09 436

Pre-film in steam to

obtain post-

transition corrosion

films in reasonable

timeframe.

Additional pre-film

in water to remove

any memory effects

from steam

environment

Oxide thickness’ time

estimated using Hillner

1977 corrosion equations

Testing Conditions

31

Test

Condition

Temp.

(°C)

[LiOH]

(ppm)

Exposure in

LiOH (days)

1 350 2 215

2 350 60 177

3 350 110 120

4 330 250 76

Results

32

Results


No acceleration – cyclic

corrosion observed

Accelerated corrosion seen after an incubation period

(oxide growth of ~2 µm)Despite almost double

[LiOH], similar incubation

period and accelerated

corrosion rate

Results


No accelerated

corrosion observed

for 250 ppm LiOH,

330 °C; however, not

yet achieved 2 µm

oxide in this

environment

35

Summary

Summary - What does all this information tell us?


1

10

100

1000

10000

100000

573 583 593 603 613 623 633 643 653

Lith

ium

Co

nce

ntr

atio

n (p

pm

)

Temperature (K)

Not accelerated

Accelerated

Small amount of acceleration

Our data

1

10

100

1000

10000

100000

573 583 593 603 613 623 633 643 653

Lit

hiu

m C

on

ce

ntr

ati

on

(p

pm

)

Temperature (K)

Not accelerated

Accelerated


Our data

1

10

100

1000

10000

100000

300 310 320 330 340 350 360 370 380

Lith

ium

Co

nce

ntr

atio

n (

pp

m)

Temperature (°C)

Accelerated

Accelerated (slower rate)

Not accelerated

Isothermal - Accelerated

Isothermal - Not accelerated

Thermal Gradient

Literature data

Test data

Thre

sho

ld r

edu

ctio

n

due

to s

tres

sLi

enh

ance

men

t d

ue

to b

oili

ng

Eq. 1

Temperature (K)

𝐿𝑖 = 8 x 1015 𝑒−0.095.𝑇Equation 1:

LiOH has been shown to affect the

corrosion behaviour of thick >20 µm

oxide under boiling and stress conditions.

This is thought to be due to

accumulation of LiOH in cracks and pores

as a result of boiling which increases the

concentration of LiOH locally.

Stress impacts this mechanism; data

suggests this is by lowering the critical

[LiOH] required for accelerated corrosion to

occur from 800 ppm to 25 ppm @ 315 °C

?

- boiling

Summary - What does all this information tell us?


1

10

100

1000

10000

100000

573 583 593 603 613 623 633 643 653

Lith

ium

Co

nce

ntr

atio

n (p

pm

)

Temperature (K)

Not accelerated

Accelerated


Our data

1

10

100

1000

10000

100000

573 583 593 603 613 623 633 643 653

Lit

hiu

m C

on

ce

ntr

ati

on

(p

pm

)

Temperature (K)

Not accelerated

Accelerated


Our data

1

10

100

1000

10000

100000

300 310 320 330 340 350 360 370 380

Lith

ium

Co

nce

ntr

atio

n (

pp

m)

Temperature (°C)

Accelerated

Accelerated (slower rate)

Not accelerated

Isothermal - Accelerated

Isothermal - Not accelerated

Thermal Gradient

Literature data

Test data

Thre

sho

ld r

edu

ctio

n

due

to s

tres

sLi

enh

ance

men

t d

ue

to b

oili

ng

Eq. 1

Temperature (K)

Further studies have investigated the

relationship between [LiOH] and

temperature. Data obtained to date has

allowed us to reduce the threshold band

for the critical [LiOH] – temperature

relationship than that produced from

literature alone.

Key point to note is that this relates to

the temperature of the metal / oxide

interface, not the coolant!

𝐿𝑖 = 8 x 1015 𝑒−0.095.𝑇Equation 1:

- boiling

?

• Data here suggest that the use of 2 ppm LiOH may not have an adverse effect on corrosion

where oxide films < 20 µm because the temperature of the metal / oxide interface would not

be significantly higher than the coolant, therefore an extremely high level of LiOH would be

required to cause accelerated corrosion

– This argument assumes the absence of stress, which appears to lower the critical lithium

concentration required for accelerated corrosion at a given temperature.

• Key considerations for the use of LiOH in the absence of boric acid (e.g. For future SMR

applications) include:

– Could sub-cooled nucleate boiling influence corrosion later in life when films are

thickest?

– How does the metal / oxide interface temperature change during the core lifetime?

Does the oxide film experience changes in stress during corrosion?

– Read-across to other zirconium alloys?

– Effect of irradiation on this mechanism?

Summary - What does this mean for Industry?


woodplc.com

• Coriou, H., Grall, L., Meunier, J., Pelras, M., Willermoz, H., Corrosion du Zircaloys dans Divers Milieux Alcalins a Haute Temperature, Journal

of Nuclear Materials, 7(3), 1962: 320-327.

• Kandlikar, S.G., Heat Transfer Characteristics in Partial Boiling, Fully Developed Boiling, and Significant Void Flow Regions of Subcooled

Flow Boiling, Journal of Heat Transfer, 120 (2), (1998) 395 – 401.

• Abram, T.J., Modelling the Waterside Corrosion of PWR Fuel Rods, IAEA Technical committee Meeting on Water Reactor Fuel Element

Modelling at High Burnup, Windermere 1994, IAEA-TECDOC-957, p329.

• Kingery, W.D., Francl, J., Coble, R.L., & Vasilos, T., Thermal Conductivity: X, Data for Several Pure Oxide Materials Corrected to Zero

Porosity, Journal of the American Chemical Society, 37 (2), 1954, p107-111.

• Jeong, Y.H., Kim, K.H., Baek, J.H., Cation Incorporation into Zirconium Oxide in LiOH, NaOH, and KOH Solutions, Journal of Nuclear

Materials, 275 (2) 1999, pp 171-177.

• Murgatroyd R.A., Winton, J., Hydriding of Zircaloy-2 in Lithium Hydroxide Solutions, Journal of Nuclear Materials, 23 (1967) pp 249 –

256.

• Pecheur, D, Godlewski, J., Peybernes, J., Fayette, L., Noe, M.M Frichet, A., & Kerrec, O., Contribution to the Understanding of the Water

Chemistry on the Oxidation Kinetics of Zircaloy-4 Cladding, 12th Zirconium in the Nuclear Industry Symposium, 2000, STP 1354, pp 793.

• Ramasubramanian, N., Precoanin, N., Ling, V.C., Lithium Uptake and the Accelerated Corrosion of Zirconium Alloys, 8th Zirconium in the

Nuclear Industry Symposium, 1989, STP 1023, pp 187.

• Bramwell, I.L, Parsons, P.D., Tice, D.R, Corrosion of Zircaloy-4 PWR Fuel Cladding in Lithiated and Borated Water Environments, 9th

Zirconium in the Nuclear Industry Symposium, 1991, STP 1132, pp 628.

• McDonald, S.G., Sabol, G.P., & Sheppard, K.D., Effect of Lithium hydroxide on the Corrosion Behavior of Zircaloy-4, 6th Zirconium in the

Nuclear Industry, 1984, STP 824, p519.

• Hillner E., Corrosion of Zirconium Base Alloys – An Overview, Zirconium in the Nuclear Industry, ASTM STP 633, A.L. Lowe and G.W. Parry

(1977) pp 211 – 235

References


Investigating the Corrosion Behaviour of Zircaloy-4 …...25 A presentation by Wood. Accelerated...

Documents

Transcript of Investigating the Corrosion Behaviour of Zircaloy-4 …...25 A presentation by Wood. Accelerated...