Investigating the Corrosion Behaviour of Zircaloy-4 …...25 A presentation by Wood. Accelerated...
Transcript of Investigating the Corrosion Behaviour of Zircaloy-4 …...25 A presentation by Wood. Accelerated...
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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
7 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
Zircaloy-4 sheet
specimens pre-filmed in
500 °C air to form
relatively thick oxide films
in a timely manner
Testing Conditions
8 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
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
9 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
10 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
Pre-stressed Oxides
11 A presentation by Wood.
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
15 A presentation by Wood.
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
16 A presentation by Wood.
Within thick oxides (>20 µm),
boiling is required for
accelerated corrosion to occur
Coolant chem. 2 ppm LiOH
Autoclave temp. 250 °C
Results – influence of chemistry
17 A presentation by Wood.
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
Coolant chem. 2 ppm LiOH
Autoclave temp. 250 °C
Results – influence of stress
18 A presentation by Wood.
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
Coolant chem. 2 ppm LiOH
Autoclave temp. 250 °C
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
20 A presentation by Wood.
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
21 A presentation by Wood.
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
Discussion – Hypothesised Mechanism
22 A presentation by Wood.
Effect of Stress Effect of Boiling
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
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
Discussion – Hypothesised Mechanism
23 A presentation by Wood.
Effect of Stress Effect of Boiling Effect of LiOH
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
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
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
24 A presentation by Wood.
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
25 A presentation by Wood.
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
Discussion – Hypothesised Mechanism
26 A presentation by Wood.
Effect of Stress Effect of Boiling Effect of LiOH
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
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
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?
27 A presentation by Wood.
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
33 A presentation by Wood.
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
34 A presentation by Wood.
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?
36 A presentation by Wood.
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
Small amount of acceleration
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?
37 A presentation by Wood.
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
Small amount of acceleration
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?
38 A presentation by Wood.
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
40 A presentation by Wood.