Effect of Primary Water Zinc Injection on PWSCC in Ni-Based RCS Components

Effect of Primary Water
Zinc Injection on PWSCC in
Ni-Based RCS Components
Peter Andresen
GE Global Research
May 30, 2007
MRP/PWROG Mitigation Briefing to NRC RES
History and Status of Zinc Injection
• BWRs started adding zinc for radiation field control in 1986
• Farley 2 was the first US PWR plant to inject zinc in 1994
• By Dec 2006, 39 PWR units world-wide were injecting zinc,
including 18 International units
• Of the 21 US PWRs, 5 are injecting with the prime objective
of PWSCC mitigation (≥15 ppb zinc), and the remainder for
radiation field control, using lower zinc injection levels
• A further 10 PWRs have indicated definite plans to
implement zinc within the next year or two
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2
Plants Injecting Zinc
Number of Units Injecting Zinc by Year
45
40
35
Number of Units
30
25
20
15
10
5
0
1994
1995
1996
1997
New US Units
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1998
1999
2000
New International Units
3
2001
2002
2003
2004
2005
Cumulative Units Injecting Zinc
2006
Overall Correlation of Dose Rate to Zinc Exposure
Positive Benefit with Zinc
Cumulative Dose Rate Reduction Based on Zinc Exposure
1.2
Cumulative Dose Rate Reduction Fraction
1
Alloy 600 & 690 Plants w/Natural Zinc
y = -0.1052Ln(x) + 1.2676
2
R = 0.6643
0.8
0.6
0.4
Alloy 800 Plants w/Depleted Zinc
y = -0.1437Ln(x) + 1.3895
2
R = 0.6322
0.2
Alloy 600 & 690 w/Depleted Zinc
y = -0.0777Ln(x) + 1.053
2
R = 0.5386
0
0
200
400
600
800
1000
1200
1400
1600
1800
Cumulative Zinc Exposure, ppb-months
Alloy 800 w/Depleted Zinc
Log Alloy 800 Plants w/Depleted Zinc
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Alloy 600 & 690 w/Depleted Zinc
Log Alloy 600 & 690 w/Depleted Zinc
4
Alloy 600 & 690 w/Natural Zinc
Log Alloy 600 & 690 w/Natural Zinc
2000
Field SG Data Evaluation:
PWSCC Zn Mitigation
• Five units injecting zinc primarily for PWSCC mitigation
(15-40 ppb)
• Farley 1 and 2, Diablo Canyon 1 and 2, and
Beaver Valley 1
• Steam Generator data analyzed for PWSCC indications:
– Numbers of cumulative PWSCC indications
¾ Rate of increase in PWSCC observations (2 to 10X reduction)
– Voltage growth rate data
¾ Growth rate measurements (20% to 60% reduction)
• Comparisons performed of the results for periods of
operation with and without zinc
– Quantify the Benefit!
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5
Example of Smallest Zn Benefit Observed
31% Decrease in Weibull Slope
(It would take 1.9 times as long to go from 1% to 10% tubes affected)
Weibull Fit (Least Squares)
90%
63%
50%
20%
Cumulative Percentage of Tubes Failed
No zinc
Intermittant zinc
addition between
green and red
lines.(see Table 2-1
for details)
10%
5 ppb zinc
Pre-zinc slope
b = 1.64
5%
2%
100% RPC Exam
1%
Shot-peened
0.5%
0.2%
100% +Pt® Exams
Commence
to = 0.00 EFPY
0.1%
0.05%
Partial RPC Exam
b = 1.13
0.02%
Theta = 856 EFPY
0.01%
1
2
3
4
5
6
8
10
Service Time (EFPY)
20
30
40
50
60
80
100
Sequoyah 2 (5 ppb zinc) has experienced a 31% decrease in Weibull Slope
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Example of Largest Zn Benefit Observed
79% Decrease in Weibull Slope
(It would take 9.6 times as long to go from 0.8% to 10% tubes affected)
Weibull Fit (Least Squares)
No zinc
90%
63%
50%
Intermittant zinc
addition between
green and red
lines.(see Table 2-1
for details)
Cumulative Percentage of Tubes Failed
20%
10%
35 ppb zinc
5%
Pre-zinc slope
b = 4.35
2%
1%
100% +Pt Exams
Commence
0.5%
0.2%
to = 0.00 EFPY
0.1%
100% RPC Exam
0.05%
b = 0.90
0.02%
Theta = 3.49E+03 EFPY
0.01%
1
2
3
4
5
6
8
10
20
30
40
50
60
80
100
Service Time (EDY @ 607°F)
Beaver Valley 1 (35 ppb zinc) has experienced a 79% decrease in Weibull Slope
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Fuel Materials Compatibility (Fuel)
Zinc, by itself, is not expected to negatively affect fuel
cladding integrity.
– Early autoclave and in-reactor tests showed no impact.
– Cladding corrosion measurements have shown zinc to
have little or no impact on clad performance.
• Assessments by vendors have determined that zinc does
not interact with or exacerbate the degradation of leaking
rod failure locations caused by other mechanisms.
• Zinc was shown to have no negative effect on other fuel
component materials during early autoclave testing,
• FRP and vendors are expanding the fuel surveillance
database as higher duty plants inject zinc.
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Fuel Materials Compatibility (Fuel)
Experience:
• Fuel surveillances at Farley, Diablo Canyon and Palisades
have shown zinc to be relatively benign at low duty units.
• In 2002, FRP sponsored detailed crud scrapes at Diablo
Canyon-1 following Cycle 11 on the two highest-powered
assemblies in-core for later comparison with higher duty fuels
– Surveillance performed for background information.
• Crud scrapes and cladding corrosion measurements at
Callaway (first high-duty plant to add zinc) following
Cycles 13 (2004) and 14 (2005) showed no accelerated
cladding corrosion.
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Fuel Materials Compatibility (Fuel)
• Vandellos II (Spain) demonstration in progress. Vandellos
bounds most PWRs in U.S. with respect to fuel duty.
–
–
–
–
Baseline oxide measurements taken during Refuel 14 (spring 2005)
Zinc injection commenced half-way into Cycle 15 (June 2006)
Refuel 15 planned May 2007 (oxide measurements & crud scrapes
Refuel 16 planned fall 2008 (oxide measurements & crud scrapes)
• Expansion of the database to other high-duty units is being
pursued.
• FRP-sponsored autoclave experiments are underway to
define the limits under which zinc can be added.
– This includes heated single-rod tests under bounding heat flux and
sub-cooled nucleate boiling conditions and includes tests at high
zinc concentrations and various levels of contaminants (e.g. silica)
known to negatively affect crud deposits.
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Zinc Mitigation of PWSCC Initiation and Growth
The inhibitive effect of zinc on PWSCC initiation is well
documented
• Decrease in SG degradation rate (indications) by 2 to 10X
• Farley 2 head experience
However:
• Reduced crack growth benefit of zinc shown for A600 SG
tubes does not necessarily transfer to thick-wall RCS
components and to A82/182 welds
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11
Mitigation of PWSCC in RCS
A600/182/82 by Zinc Injection
• MRP/PWROG objective is to supplement confirmed radiation
field control benefit from zinc injection with demonstrated
reduction in rate of PWSCC initiation and growth in thick-wall
RCS components to:
•
•
Avoid or delay component repair/replacement by retarding PWSCC
initiation and growth of shallow (undetected) cracks
Obtain inspection relief for susceptible RCS locations by
demonstrating reduction in initiation and growth of existing cracks
• Parallel efforts underway by FRP and Chemistry to assure:
•
•
Recommended levels do not effect fuel performance and cladding
integrity
Orderly dissemination to utilities via Zn application guidelines
• Investigating synergistic PWSCC benefit of zinc and elevated H2
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12
Zn: Penetration to Crack Tip
Limited benefit of Zn in
BWRs related to high
corrosion potential, which
drives Zn2+ from crack.
But at low potential, Zn
diffuses slowly and is initially
“consumed” by incorporation
into crack oxides.
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13
GE Tests on SS at 20 ppb Zn
NobleChem + 20 ppb Zn2+
Longer-term Effects of Zn on SCC
0.5
11.6
C237 - 0.5TCT of 316L / 20%RA
Start 25 ksi√in, 2 ppm O2, Pure Water
0.1
0.3
11.2
11.1
1.62x10-7 mm/s
Outlet conductivity
Begin ZnO Injection at 1232 h.
11.3
Begin 6.18% H 2 in Ar at 679 h.
Crack length (mm)
0.1
0
-0.1
-0.2
-0.3
CT potential
-0.4
0.08
Crack Length Increment (mm)
0.2
2.9x10-8 mm/s
11.4
-7
da/dt =1.62x10 mm/s
Conductivity, μS/cm or Potential, Vshe
8.3x10-9 mm/s
11.5
C237 - 0.5TCT of 316L / 20%RA
Start 25 ksi√in, 2 ppm O2, Pure Water
2 ppm O2 Addition
0.4
6.18% H2 in Ar Addition
Initial Zn2+ Addition Period
-8
da/dt = 1.1x10 mm/s
-8
da/dt = 2.91x10 mm/s
0.06
0.04
0.02
11
2+
Steady State Zn Addition
-9
da/dt = 8.3x10 mm/s
-0.5
Pt potential
10.9
200
-0.6
700
1200
1700
2200
2700
0
0
Test Time (hours)
100
200
300
400
500
600
Test Time (hours)
700
Injection of Zn+2 at low potentials may mitigate cracking
in highly irradiated materials. Zn is currently injected at
5 – 7 ppb into reactor feed water for radiation control
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14
800
900
1000
Effects of Zn on SCC Growth Rate
Test
Li, ppm
B, ppm
pH300C (1)
Zn, ppb
Duration
hours
1
2.2
600
7.2
0 → 30
5000
2
2.2
600
7.2
0 → 10 →
30 → 0
6500
3
0.3
1200
6.9
0 → 30 → 0
5000
500 hrs for SCC transitioning + 1500 hrs per test segment
Each test uses two 1TCT specimens; 325C, 30 cc/kg H2
Spike Zn for several weeks to saturate system and crack
Testing focused on Ni-metal stability = high H2
Testing now underway on Alloy 182 weld metal
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15
30 ppb Zn Effect
Spiked to 150 ppb Zn injected for six weeks
SCC#3 - c272 - Alloy 600, CRDM Tube, 93510
11.45
0.4
11.3
11.25
To ~150 ppb Zn as
acetate @ 1420h
11.35
To Constant K @ 913h
Crack length, mm
11.4
-8
5 x 10
mm/s
0
-0.2
1.8 x 10-8
mm/s
-0.4
-0.6
3.1 x 10-8
mm/s
c272 - 0.5TCT of A600 CRDM, 325C
25 ksi√in, 20 cc/kg H2, 600 B / 2.2 Li
11.2
Pt potential
11.15
1000
0.2
1400
1800
Conductivity, μS/cm or Potential, Vshe
To ~50 ppb Zn as
acetate @ 2429h
Outlet conductivity ÷100
-0.8
CT potential
2200
2600
-1
3000
Test Time, hours
Specimens run at 325C, 600 B / 2.2 Li, 30 cc/kg H2
then 150 ppb Zn injected for six weeks.
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Test #2: 30 ppb Zn Effect
Spiked to 150 ppb Zn injected for six weeks
0.4
11.52
Outlet conductivity ÷100
0.2
11.5
-9
11.44
40 ppb @ 5698h
1.7 x 10-8
mm/s
60 ppb @ 5531h
Zn reduced to
100 ppb @ 5478h
Crack length without
Ref.Probe
Start Zn injection
150 ppb @ 4328h
11.46
To constant K
@ 3033h
Crack length, mm
0
11.48
-0.2
-0.4
-0.6
c292 - 0.5TCT of A600 CRDM, 325C
15 ksi√in, 18 cc/kg H2, 600 B / 2.2 Li
11.42
-0.8
Pt potential CT potential
11.4
3300
3800
4300
4800
5300
-1
5800
Test Time, hours
325C, 600 B / 2.2 Li, 18 cc/kg H2
Used 15 ksi√in so growth rates are lower
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Conductivity, S/cm or Potential, Vshe
3 x 10 mm/s
Test #2: 30 ppb Zn Effect
Spiked to 150 ppb Zn injected for six weeks
11.5
0.4
Outlet conductivity ÷100
0.2
c293 - 0.5TCT of A600 CRDM, 325C
15 ksi√in, 18 cc/kg H2, 600 B / 2.2 Li
6 x 10-9 mm/s
Crack length without
Ref.Probe
11.4
40 ppb @ 5698h
-0.4
-0.6
-0.8
Pt potential
11.38
3300
60 ppb @ 5531h
11.42
Zn reduced to
100 ppb @ 5478h
1.7 x 10-8
mm/s
-0.2
Start Zn injection
150 ppb @ 4328h
11.44
To constant K
@ 3033h
Crack length, mm
0
11.46
3800
4300
CT potential
4800
5300
-1
5800
Test Time, hours
325C, 600 B / 2.2 Li, 18 cc/kg H2
Used 15 ksi√in so growth rates are lower
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Conductivity, μS/cm or Potential, Vshe
11.48
Test #1: Zn Maps in Crack
Microprobe (WDS) very roughness/orientation sensitive
Zn fracture surface
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Test #2: Zn Maps in Crack
Auger Electron Spectroscopy in IG Area Near Fatigue Precrack
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20
Test #2: Zn Maps in Crack
Auger Electron Spectroscopy in IG Area Near Crack Tip
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Test #3: 30 ppb Zn Effect
~50 ppb Zn for ~10 weeks – no effect observed yet
SCC#4 - c315 - Alloy 600, CRDM Tube, 93510
SCC#4 - c316 - Alloy 600, CRDM Tube, 93510
11.23
0.4
11.28
0.4
Outlet conductivity ÷100
Outlet conductivity ÷100
11.24
-0.2
-0.4
11.23
11.22
c315 - 0.5TCT of A600 CRDM, 325C
15 ksi√in, 18 cc/kg H2, 600B/2.2Li
6.6 x 10-9
mm/s
Pt potential
4000
4500
5000
11.19
-0.2
-0.4
5 x 10-9
mm/s
c316 - 0.5TCT of A600 CRDM, 325C
15 ksi√in, 18 cc/kg H2, 600 B / 2.2 Li
Pt potential
11.17
3000
5500
Test Time, hours
4000
4500
325C, 600 B / 2.2 Li, 18 cc/kg H2
At 15 ksi√in growth rates are lower
22
CT potential
-1
3500
Test Time, hours
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-0.6
-0.8
CT potential
-1
3500
11.2
0
11.18
-0.8
11.21
11.2
3000
-0.6
11.21
Zn fluctuates during stabilization
period - analysis takes ~1 week
5000
5500
Conductivity, μS/cm or Potential, Vshe
11.25
0
0.2
11.22
Crack length, mm
Crack length, mm
11.26
Zn fluctuates during stabilization
period - analysis takes ~1 week
Conductivity, μS/cm or Potential, Vshe
To 50 ppb Zn @ 3994h
0.2
To 50 ppb Zn @ 3994h
11.27
Conclusions on Zn Effects
Summary and Interpretation of Zn Results:
• Some benefit may occur at high Zn levels (150 ppb)
• Limited evidence of benefit at 30+ ppb Zn, 25 ksi√in
• Stronger evidence of benefit at 30+ ppb Zn, 15 ksi√in
• Follow-up, corroborative experiments essential
• Uncertain theoretical benefit of Zn in NiO structure
– known benefit is from Zn incorporation into spinel
• Testing underway focuses on Alloy 182
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23
A600 PWSCC Summary of
Test Results and Ongoing Work
Field and test data shows zinc inhibits PWSCC initiation in Alloy
600/82/182; recently-initiated PWROG project will provide confirmation.
Task-by-task results over the next few years.
Some initial tests indicate zinc can reduce growth rate of undetected
(shallow-low stress intensity) cracks in thick A600 components,
confirmatory tests underway. Results in 2008.
A600 tests to date have not shown zinc can reduce growth rate of deep
cracks in high stress areas (high stress intensity cracks). It appears that
crack-tip in a fast-growing crack out-runs zinc species that deposit on
crack flanks rather than on the tip. Further testing is underway. Results
expected in 2008.
Ongoing testing will address crack growth in A182 material.
Future MRP work will include evaluation of synergistic effects of elevated
hydrogen and zinc.
SCC tests require thousand hours; results are slow to come.
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Present Schedule for Deliverable on Chemical
Mitigation
• Technical basis document to be provided to NRC in 2008
– Zinc
– Hydrogen
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25