shadow corrosion-induced bow of zircaloy-2 channels · 2010-06-10 · 4 shadow corrosion-induced...
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16th Int. Symposium on Zirconium in the NuclearIndustry, May 13, 2010, Chengdu, China
Shadow Corrosion-InducedBow Of Zircaloy-2 Channels
S. T. Mahmood, P. E. Cantonwine, Y.P. Lin, D. C. CrawfordGlobal Nuclear Fuel
E. V. Mader, K. EdsingerElectric Power Research Institute
2
Outline
Background
Poolside data
Hotcell data
Discussion
Conclusions
3
Channels in a BWR and Potential forControl Blade Interference
• BWR fuel assemblies located insidechannel boxes.
• Four assemblies in each control cellwith a control blade (CB).
• CB-channel interference possible ifchannel deformation is excessive.
• Channel deformation from bulge andbow.
• Channel bow occurs due to lengthdifferential from:
– Neutron fluence gradient– Hydrogen differential from
shadow corrosion on CB side
4
Shadow Corrosion-Induced Channel Bow• Shadow Corrosion: enhanced in-reactor
corrosion on Zr-alloy when placed in closeproximity to a dissimilar metal.
• Extent of shadow corrosion depends on gapdistance.
• Enhanced corrosion on channel face exposedto stainless steel CB casing.
• Higher corrosion associated with higherhydrogen concentration.
• Higher hydrogen concentration results in largervolume increase.
• Channel bow from length differential acrosschannel.
•
90 in
90 in
90 in
))(( tHPUBow Dµ
5
Objective of Present Work• Previous work based on 3-cycle channels
(Proc. Int. LWRFP Meeting, San Francisco, 2007)– ~1500 – 2100 days– ~37 – 48 GWd/MTU
• Shadow bow correlated with hydrogen differential
• Main open issue– Kinetics of corrosion and hydriding– CB exposure early, channel bow late in life
• Present work– Broader exposure range by including 1-cycle and 4-cycle channels– Improved understanding of general and shadow corrosion and hydriding
from metallography and hydrogen measurements– Examine distance effect§ CB-channel interference depends on gap between channel and CB§ Relative gap for S-lattice = 0.74, C-lattice = 0.83 and D-lattice = 1.0
6
Terminology
Shadow Bow:Measured – predicted bow from fluence gradientBlade-side:Channel face adjacent to the control blade(sides 3 and 4).Non-blade-side:Channel face away from the control blade(sides 1 and 2).
ECBE:Effective Control Blade Exposure is theproduct of the control blade insertionlength (inches) and insertion time (days)for each insertion applied, weighted bytime of application, and summed.
0
20
40
60
80
100
120
140
160
0 500 1000 1500 2000 2500 3000
Residence time (days)
Inse
rtio
n D
ista
nce
(in)
Bundle 1: ECBE = 17795 inch-days
Bundle 2: ECBE = 712 inch-days
4.1 mm
ECBE712 in-day
ECBE~18,000in-day
Similar CB insertion, but verydifferent ECBE due to weighting
A B C D E F G H J
12
3
45
6
7
8
9
Side 4
Side1
Side3
Side 2
10
K
ControlBlade
7
Channel Bow Measurements
Bow measurements biased high (towards CB).
S-lattice plants tend to develop higher bow at lower exposure.
-500
-400
-300
-200
-100
0
100
200
300
400
500
20 25 30 35 40 45 50 55Exposure (GWd/MTU)
Mea
sure
d B
ow (m
il)S-Lattice ECBE > 10000 inch-daysD-lattice ECBE > 10000 inch-days
+- 2 Sigma Uncertaintyin Measured Bow Datawhen only FluenceGradient-Induced Bow isactive (I.e, ECBE ~ 0)
12.7 mm
-12.7 mm
Zircaloy-2 channels
S- and D-Lattice plants
Comparison of ECBE >10000 inch-days with noearly-life control
8
Lattice Type and Channel Thickness Effects
Shadow bow decrease with increasing gap.
Shadow bow increase with decreasing channel thickness.
Relative gap
S-lattice = 0.74C-lattice = 0.83D-lattice = 1.0
-100
-50
0
50
100
150
200
250
300
350
120T S-Lattice 120T C-Lattice 100T C-Lattice 100T D-Lattice
Channel Type
Mea
n Sh
adow
Bow
(mil)
8.9 mm
S vs. C C vs. D120 vs. 100
Channel Thickness
120T ~ 20% thickerthan 100T
9
Exposure Dependency of Shadow Bow
Shadow corrosion condition (CB insertion) generally occur early in life, butlarge shadow bow develop late in life. WHY?Did shadow oxide build up fast early in life and hydrogen pickup later, ordid oxide build up and hydrogen pickup both develop with exposure?
S-lattice
120T channels
ECBE > 20000 in-days
0
50
100
150
200
250
300
350
400
20.0 25.0 30.0 35.0 40.0 45.0 50.0
Exposure (GWd/MTU)
Shad
ow B
ow (m
il)
10.2 mm
10
Characteristics of Retrieved Coupons
11 channels, 2 sides, 4 elevationsPlants: 4Cycles: 1 to 4 two-year cycles Residence time: 680 – 2400 daysExposure: ~20 – 48 GWd/MTU ECBE: 0 – 34,000 inch-daysMeasured bow: up to ~370 mils (9.6 mm)
20 55 90 120
2 X X X X4 X X X X2 X X X X4 X X X X2 X X X X4 X X X X2 X X X X4 X X X X2 X X X X4 X X X X2 X4 X2 X X X X4 X X X X2 X X X X4 X X X X2 X X X X4 X X X X1 X X X X3 X X X X1 X X X X3 X X X X
D
LatticeType
S
S
C
679
2401
2401
1486
1882
1882
2079
ResidenceTime(days)
1486
1486
1486
24.6
376.2
3
3
27112
271122079
Zircaloy-2
Zircaloy-2
48.1
48.1
A
C7
8
B5
3
323
28
4
4
17795
712
1 34105 22
D10
11
Zircaloy-2
Zircaloy-2
43.9
42.9
A 9 Zircaloy-2 19.7S
10721
21916
16216
14025
Zircaloy-2
3
3
39.7
36.5
39.6
40.7
3
3
314
6 -30
Zircaloy-2
Zircaloy-2
48.2
47.9
3
3 0
Coupon Elevations (in)
1 61
2 119
ChannelSide
Zircaloy-2
Zircaloy-2
ECBE(in-days)
8133
292
4 336
PlantChannel
IDMax. Avg.Bow (mils)
ChannelMaterial
Exposure(GWd/MTU)
No. ofCycles
Zircaloy-2A B C D E F G H J
12
3
4
5
6
7
8
9
Side 4
Side1
Side3
Side 2
11
0
20
40
60
Oxi
de T
hick
ness
(mic
rons
)
1 2 3 4 5 6 7 8 9 10 11 20
5590 12
0
Channel ID
Elevation(in)
Blade
Outer surfaceBlade side
Oxide Thickness Overview
Outer surface on CB side has thickest oxide.
0102030405060
Oxi
de T
hick
ness
(mic
rons
)
1 2 3 4 5 6 7 8 9 10 11 20
5590 12
0
Channel ID
Elevation(in)
Outer surfaceNon-blade side
0102030405060
Oxi
de T
hick
ness
(mic
rons
)
1 2 3 4 5 6 7 8 9 10 11 20
5590 12
0
Channel ID
Elevation(in)
Blade
Inner surfaceBlade side
0102030405060
Oxi
de T
hick
ness
(mic
rons
)
1 2 3 4 5 6 7 8 9 10 11 20
5590 12
0
Channel ID
Elevation(in)
Control Blade
Inner surfaceNon-blade side
90 in Side 1 Side 3
Zircaloy-2
Outer Surface
Inner Surface
50 mm
12
4-Cycle Channel (~18000 in-day ECBE, D-lattice plant)
• Oxide thickness on blade side similar to other high bow 3-cycle channels.
• High hydrogen contents, especially on blade side.
• Lower ECBE 4-cycle channel had less blade side corrosion and hydrogen.
A B C D E F G H J
1234
56
7
8
9
Side 4
Side1
Side3
Side 2
55 in
90 in Side 1
277 ppm
196 ppm
33 mm total
29 mm total
250 mm250 mmSide 3
629 ppm
672 ppm
60 mm total
61 mm totaloxide
250 mm250 mm
13
Single-Cycle Channel (~34000 in-day ECBE, S-lattice plant)
• Very high ECBE from plant with small inter-channel gap.
• Difference in oxide and hydrogen between blade and non-blade sides.
• Blade side oxide and hydrogen much less than in 3- and 4-cycle channels.
120 in
90 in
Side 2
13 ppm
11 ppm
Side 4
49 ppm
48 ppm
14 mm total21 mm total
28 mm total 12 mm total
250 mm250 mm250 mm250 mm
14
Hydriding Kinetics
• H concentration increases with number of cycles.• H concentration higher on blade side.• HPU (%) increase with number of cycles.• Similar HPU (%) on blade/non-blade side of multi-cycle channelsbut higher on blade side of 1-cycle channel.
CB
Sid
e, M
etal
Non
-CB
Sid
e, M
etal
CB
Sid
e, O
xide
Non
-CB
Sid
e, O
xide 9
12
34
1110
0
50
100
150
200
250
300
350
400
Hyd
roge
n C
once
ntra
tion
(ppm
)
Channel ID
1 Cycle
4 Cycles3 Cycles
9 1 7 8 2 4 3 5 11 10Non-CB Side
CB Side
0
10
20
30
40
50
60
Hyd
roge
n Pi
ck U
p (%
)
Channel ID
4 Cycles
3 Cycles
1 Cycle
15
Measured vs. Estimated Total Channel Bow
usingtheoreticalcorrelation
usingexperimentalcorrelation
usingtheoreticalcorrelation
usingexperimentalcorrelation
1 74 56 2 76 58 612 190 144 56 246 200 1193 295 225 8 303 233 2924 376 286 19 395 305 336
B 5 346 263 3 349 266 3147 -139 -106 146 7 40 258 291 221 149 440 370 376
A 9 48 37 -10 38 27 2210 436 332 96 532 428 32311 98 75 -1 97 74 28
Total Estimated Bow(mils)
EstimatedBow due toIrradiation
Growth(mils)
MeasuredBow (mils)Ch ID
A
D
C
Estimated Bow due to HDifferential (mils)
Plant
0
100
200
300
400
500
600
0 100 200 300 400 500 600
Measured Bow (mils)
Tota
l Est
imat
ed B
ow (m
ils)
0.25% lin. changeper 1000 ppm H
0.33% lin. changeper 1000 ppm H
• Linear correlation between measured and estimated channel bow.
• Further validation of bow due to length increase from hydride precipitation.
• 0.25% better fit than theoretical 0.33% linear change per 1000 ppm H.
16
ECBE Effect on Corrosion
• ECBE correlations for multiple-cycle channels.
• Oxide thickness increase with ECBE if shadow corrosion was present.
• Both channel exposure and ECBE affect blade side oxide thickness.
05
101520253035404550
0 5000 10000 15000 20000 25000 30000 35000
ECBE (in-days)
Out
er S
urfa
ce O
xide
Thi
ckne
ss(m
icro
ns)
Non-CB sideCB side
Channel 9Single Cycle
Exhibitedshadowcorrosion
4C
4C
4C: 4-cycle channels
17
Shadow and General Corrosion Kinetics
• Blade vs. non-blade side differential in oxide thickness setup after 1st cycleexposure to CB.
• Shadow oxide on blade side with significant ECBE grow at a different ratethan non-shadow oxide.
• Zry-2 develop thinner oxide than Zry-4.
05
101520253035404550
10 15 20 25 30 35 40 45 50
Channel Exposure (GWd/MTU)
Out
er S
urfa
ce O
xide
Thi
ckne
ss(m
icro
ns)
Non-CB sideCB side
Zircaloy-4
))(( tHPUBow Dµ
18
Hydrogen Pickup Kinetics
0
10
20
30
40
50
60
70
500 1000 1500 2000 2500
Channel Residence Time (days)
Hydr
ogen
Pic
ku U
p (%
) Non-CB sideCB side
Zircaloy-4
• Higher HPU% on blade side of 1-cycle channel with shadow corrosion.
• HPU% differential between blade and non-blade side diminishes withtime/exposure.
• Zry-4 shows low HPU% compared with Zry-2.
9 1 7 8 2 4 3 5 11 10Non-CB Side
CB Side
0
10
20
30
40
50
60
Hyd
roge
n Pi
ck U
p (%
)
Channel ID
4 Cycles
3 Cycles
1 Cycle
9 1 7 8 2 4 3 5 11 10Non-CB Side
CB Side
0
10
20
30
40
50
60
Hyd
roge
n Pi
ck U
p (%
)
Channel ID
4 Cycles
3 Cycles
1 Cycle
9 1 7 8 2 4 3 5 11 10Non-CB Side
CB Side
0
10
20
30
40
50
60
Hyd
roge
n Pi
ck U
p (%
)
Channel ID
4 Cycles
3 Cycles
1 Cycle
))(( tHPUBow Dµ
19
Hydriding Kinetics
0
50
100
150
200250
300
350
400
450
10 15 20 25 30 35 40 45 50
Channel Exposure (GWd/MTU)Hy
drog
en C
once
ntra
tion
(ppm
)
Non-CB sideCB side
Zircaloy-4
• Blade vs. non-blade side differential in hydrogen setup after 1st cycleexposure to CB.
• Hydrogen on blade side with significant ECBE accumulate at a differentrate than non-shadow oxide, driven by corrosion kinetics.
• Zry-2 develop more hydrogen than Zry-4.
0
100
200
300
400
500
600
0 100 200 300 400 500 600
Measured Bow (mils)
Tota
l Est
imat
ed B
ow (m
ils)
0.25% lin.change per1000 ppm H
0.33% lin.change per1000 ppm H
))(( tHPUBow Dµ
20
Discussion
Large H differential causing bow is the combined result of increasing oxidedifferential and increasing HPU.
Nature of oxide is an important part of shadow corrosion mechanism.
Different shadow corrosion kinetics (after removal of shadow condition)implies a permanent change to the oxide.
HPU for Zry-2 increases with exposure; however, similarity in HPU for agiven multi-cycle channel (affected or not by shadow corrosion) impliessignificance of metallurgical condition affected by exposure/time.
Dissolution of Zr(Fe,Cr)2 and Zr2(Fe,Ni) are the key microstructuralchanges. Zry-4 without Zr2(Fe,Ni) does not develop high HPU.Incorporation of dissolved Ni into barrier oxide layer may be a factor forhigh HPU for Zry-2.
21
Summary and Conclusion - 1Shadow bow observations• Shadow bow develop at high exposure but conditions for shadow
corrosion occurred early in life.• Shadow corrosion-induced bow greatest in plants with the smallest
channel-to-blade gap.
Shadow Bow Correlation• Correlates with hydrogen differential (based on S-, C- and D-lattices
plants and 1- to 4-cycle channels).• Linear dimensional change of 0.25% per 1000 ppm hydrogen, less than
expected from theoretical isotropic considerations.
22
Summary and Conclusion - 2Kinetics of corrosion and hydriding• Different for the channel side with shadow corrosion vs. the side
unaffected by shadow corrosion.• Small differential in oxide thickness and hydrogen content established
after low exposure• Differentials increase with exposure/time, driven by higher rate of
corrosion on channel side affected by shadow corrosion• HPU% following initial shadow corrosion is higher• HPU% increases with exposure/time; little effect due to shadow corrosion• Zry-4 shows low HPU% to high exposure
Implication• HPU% variation with time and fluence likely associated with dissolution of
SPPs• Release of Ni from the dissolution of Zr2(Fe,Ni) SPPs may be the key to
high HPU% in Zry-2
16th Int. Symposium on Zirconium in the NuclearIndustry, May 9-13, 2010, Chengdu, China
Shadow Corrosion-InducedBow Of Zircaloy-2 Channels
S. T. Mahmood, P. E. Cantonwine, Y.P. Lin, D. C. CrawfordGlobal Nuclear Fuel
E. V. Mader, K. EdsingerElectric Power Research Institute
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