Optimization of Dissolved Hydrogen in Primary Water to Mitigate PWSCC in Ni-Based

Optimization of Dissolved
Hydrogen in Primary Water to
Mitigate PWSCC in Ni-Based
RCS Components
Peter Andresen
GE Global Research
May 30, 2007
MRP/PWROG Briefing to NRC RES
MRP Chemical Mitigation of PWSCC:
Background and Objectives
• PWR primary water chemistry is known to have a limited effect on
the initiation of PWSCC in Alloy 600.
• However, it must be assumed that cracks (some below NDE-limit)
have already initiated in many thick-walled components.
• Thus the need for reliable data on crack growth rate (CGR) effects.
– Can advantage be taken of moving to higher hydrogen levels
to mitigate PWSCC (and extend inspection intervals)?
• Strong theoretical basis, supported in particular by extensive test data
from the NR program, to recommend moving to higher hydrogen levels
in PWR primary water to obtain some mitigation of PWSCC for Ni-base
alloys used in thick-wall components.
• Goal is to develop data to optimize the primary water chemistry
guidelines to achieve some PWSCC mitigation. The potential mitigation
benefit is enormous because it would apply to almost all of the RCS.
© 2007 Electric Power Research Institute, Inc. All rights reserved.
2
PWSCC Mitigation by Elevated H2
• MRP test program at (GE-GRC) has now been running for over
2 years. Need for very long duration tests has resulted in a limited
number of data.
• Results to date on elevated hydrogen are encouraging but not
conclusive. Testing to continue at least until 2008.
• The April 2006 meeting of the MRP Expert Panel on PWSCC was
devoted mainly to consideration of chemical mitigation where
Naval Reactors data on this subject was made available.
• This presentation will focus on the prospects for PWSCC mitigation
by means of optimizing H2 levels in primary water.
© 2007 Electric Power Research Institute, Inc. All rights reserved.
3
Experimental Strategy
• Crack growth rate measurements techniques with thorough
transition from fatigue to SCC.
• Use susceptible heat of A600, ~120,000 hrs testing
(CRDM heat 93510 from Framatome).
• Two 0.5T CT specimens tested in series.
• Moderate stress intensity factor, K = 25 ksi√in
• Test in 325C water with a range of Zn, B/Li & H2
• Use B/Li-equilibrated demineralizer to maintain high water
purity and good H2 control.
• Use ZrO2 / Cu2O and Pt reference electrodes.
© 2007 Electric Power Research Institute, Inc. All rights reserved.
4
Alloy 600 CRDM Housing
Heat 93510 received from Framatome
Considered various orientations; used orientation at right,
which is the C-L orientation
© 2007 Electric Power Research Institute, Inc. All rights reserved.
5
Ni Alloy Crack Growth Rate vs H2
Proximity of Ni/NiO and
H2/H2O is
very important
for Ni alloys
H
2 /H
2O
Proximity depends on
H2 & temperature but
not on pH
Fe
2O
3
↑H2
Fe
3O
4
Fe
↑pH
Low H2 unwise because of radiolysis in core
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6
B/Li Effects at Constant pH
B = 1100 → 3200 → 1100 → 60 pH300C = 6.9
Li = 2 → 7 → 2 → 0.3 pH325C = 7.25
SCC#2 - c283 - Alloy 600, CRDM Tube, 93510
11.44
pH325C constant at ~7.25
Pt potential
11.14
1200
-0.4
-0.6
c283 - 0.5TCT of A600 CRDM, 325C
25 ksi√in, 30 cc/kg H2, Varying B/Li
11.19
-0.2
SCC#3 - c316 - Alloy 600, CRDM Tube, 93510
11.195
Outlet conductivity ÷100
11.19
2200
4.6 x 10-9
mm/s
11.185
-0.8
CT potential
2700
0.2
Pure Water
-1
1700
0.4
3200
Test Time, hours
11.18
11.175
-0.2
-0.4
11.17
11.165
4.9 x 10
mm/s
c316 - 0.5TCT of A600 CRDM, 325C
15 ksi√in, 18 cc/kg H2, 600 B / 2.2 Li
-9
2200
2400
2600
2800
3000
3200
Test Time, hours
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7
-0.6
-0.8
Pt potential
11.16
2000
0
3400
CT potential
3600
3800
-1
4000
Conductivity, ηS/cm or Potential, Vshe
3.5 x 10-8
mm/s
0
Crack length, mm
11.24
To 60 ppm B,
0.3 ppm Li @ 3315h
0.2
Conductivity, μS/cm or Potential, Vshe
0.4
To 600 ppm B,
2.2 ppm Li @ 2325h
To 1100 ppm B,
2 ppm Li @ 2675h
To 3200 ppm B,
7 ppm Li @ 1880h
11.29
Pure water → 600B / 2.2Li
pH325C = 5.86 → 7.53
0.6
To Constant
K @ 2011h
To 1100 ppm B,
2 ppm Li
11.34
To Constant K
@ 1201h
Crack length, mm
11.39
0.8
Conductivity x0.01
Effect of Corrosion Potential &
Cold Work of SS & Ni Alloys
Lower H2
↑ Yield strength ↑ growth rate at low potential
Crack Growth Rate (mils/day)
X-750
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
-100
HTH, 360oC,
Higher H2
K=49 MPa√m
Max
Full width
at half max
-50
0
50
100
EcPNi/NiO-EcP (mV)
Screened Round Robin data
- highest quality data
- corrected corr. potential
- growth rates corrected
to 30 MPa√m
14.2
μin/h
0.5
2000 ppb O2
Ann. 304SS
200 ppb O2
0.25
1.E-07
-0.1
0.0
42.5
28.3
14.2
μin/h
GE PLEDGE
Predictions
30 MPa√m
Sens SS
0.5
0.3
0.4
Corrosion Potential, Vshe
Sensitized SS
© 2007 Electric Power Research Institute, Inc. All rights reserved.
1.E-09
-0.6
-0.5
-0.4
-0.3
←42000
ppb O2
14.2
÷in/h
Cold work data cut
Higher rates from:
* Alloy 182
0.25
0.1
0.1
0.06 ÷S/cm
Alloy 182
H2 peak
0.06 μS/cm
0.2
←2000
1.E-07
1.E-08
CW
-0.2
-0.1
0.0
0.1
0.2
0.3
Corrosion Potential, Vshe
Cold worked SS/600
8
42.5
28.3
SS PLEDGE
Predictions
* Normal YS
0.06 ÷S/cm
BWRVIP Mean
30 MPa√m
GE PLEDGE Predictions for Unsensitized
Stainless Steel (upper curve for 20% CW)
0.1
← 200
Includes:
* All alloys tested
* All heat treatments
* No cold work data
* Medium screening
←H2 O2→
2000 ppb O2
Ann. 304SS
200 ppb O2
0.25
0.06 μS/cm
Industry Mean
30 MPa√m
-0.2
CW A600
CW A600
0.06 μS/cm
-0.3
← 500 ppb O2
←2000 ppb O2
316L (A14128, square )
304L (Grand Gulf, circle )
non-sensitized SS
50%RA 140 C (black )
10%RA 140C (grey )
0.1
-0.4
Circles = constant load
Triangles = "gentle" cyclic
SO4 & Cl data in pink
1.E-06
1.E-08
1.E-08
-0.5
Sens 304 SS Round Robin (open)
Crack Growth Rate, mm/s
42.5
1.E-07
1.E-09
-0.6
Alloy 182, Alloy 600 & St.Steel
30 MPa√m, 288C Water
1.E-06
28.3
GE PLEDGE
Predictions
30 MPa√m
Sensitized 304 Stainless Steel
30 MPa√m, 288C Water
0.06-0.4 μS/cm, 0-25 ppb SO4
SKI Round Robin Data
filled triangle = constant load
open squares = "gentle" cyclic
Crack Growth Rate, mm/s
Crack Growth Rate, mm/s
1.E-06
←2000 ppb O2
filled triangle = constant load
open squares = "gentle" cyclic
← 200 ppb O2
← 500 ppb O2
Sensitized 304 Stainless Steel
30 MPa√m, 288C Water
0.06-0.4 μS/cm, 0-25 ppb SO4
1.E-05
← 200 ppb O2
1.E-05
1.E-05
0.4
1.E-09
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1
Corrosion Potential, Vshe
Ni alloys
0.2
0.3
0.4
Very High Growth Rate in B/Li + O2
28.3
28
27.9
27.8
6 x 10-8 mm/s
-0.1
3.5 x 10-6
mm/s
-0.2
-0.3
-0.4
27.7
CT Corrosion Potential
-0.5
27.6
2.5 x 10-8 mm/s
-0.6
27.5
2200
Potential, Vshe or Conductivity, μS/cm
30/21 ks√in,
0.01 Hz + 900 s hold
pH288C ~ 6.79
0
To 95 ppb H2 @2354h
Crack length, mm
28.1
c85 - 1T CT of Sens. SS - AJ9139
95 ppb H2, 1200 ppm B, 2.2 ppm Li, 288C
To 200 ppb O2 @2279h
28.2
0.1
-0.7
2250
2300
2350
2400
2450
Time, hours
Thus, high growth rates occur as oxidants shift the crack chemistry –
and can overwhelm B/Li buffering
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9
CGR Peak at Ni/NiO Phase Boundary
A 3-8X peak in growth rate
occurs at Ni/NiO boundary
fH2 = f(Temp)
PWR
Crack Growth Rate (mils/day)
X-750 HTH, 360oC, K=49 MPa√m
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
-100
CANDU
Max
Full width
at half max
Higher H2 →
-50
0
50
100
EcPNi/NiO-EcP (mV)
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Role of H2 and B/Li/pH Water Chemistry
1.E-05
← 200
Circles = constant load
Triangles = "gentle" cyclic
SO4 & Cl data in pink
Connection between BWR & PWR
leverages data & understanding.
←42000
Sens 304 SS Round Robin (open)
←2000
ppb O2
Alloy 182, Alloy 600 & St.Steel
30 MPa√m, 288C Water
Crack Growth Rate, mm/s
1.E-06
Includes:
* All alloys tested
* All heat treatments
* No cold work data
* Medium screening
Extensive PWR data – applicable
because B/Li/pH is not important
in deaerated water.
42.5
28.3
1.E-07
14.2
μin/h
There is a ~8X peak vs. H2 for
Alloy 82/182 weld metal that is
relevant to BWRs.
Cold work data cut
Higher rates from:
* Alloy 182
1.E-08
0.25
0.1
0.06 μS/cm
Alloy 182
H2 peak
SS PLEDGE
Predictions
* Normal YS
Thermal activation also important.
0.06 μS/cm
BWRVIP Mean
30 MPa√m
1.E-09
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
Corrosion Potential, Vshe
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11
Role of H2 Also Relevant to BWRs
9.E-07
6.E-07
5.E-07
4.E-07
Moderate H 2 BWRs
7.E-07
CGR, mm/s
Based on BWR (274C)
Alloy 82 (8.1X peak vs. H2
ECP offset = 10.5, λ = 20.2)
NobleChem BWRs
8.E-07
3.E-07
2.E-07
1.E-07
0.E+00
10
100
1000
10000
H2 Level, ppb
Peak growth rate occurs at much lower H2 at 274C of BWR materials
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12
Crack Growth Rate (mils/day)
Ni Alloy Crack Growth Rate vs. H2
X-750 HTH, 360oC, K=49 MPa√m
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
-100
For alloy 600:
• height ≈ 2.5 – 3X
• ½ width ≈ 50 mV
(≈ 8X Δ in H2)
Max
Full width
at half max`
-50
0
50
100
EcPNi/NiO-EcP (mV)
KAPL data: consistent benefit of ↑H2 288 – 360 °C
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Ni Alloy Crack Growth Rate vs. H2
SCC Growth Rate / Minimum SCC Growth Rate
Alloy 600, Deaerated Water
3.0
Nickel Oxide
Nickel Metal
2.5
“Background” CGR
at low or high H2 is
likely a bit lower –
this could
markedly increase
the peak height
2.0
1.5
1.0
?
?
0.5
0.0
-100
K = 60 ksi√in, 338°C
K = 25 ksi√in, 338°C
K = 60 ksi√in, 316°C
-50
0
50
100
EcPNi/NiO - EcP (mV)
KAPL data: consistent benefit of ↑H2 vs. temperature & K
Hard to conclude that the peak is not actually at Ni/NiO
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Ni Alloy Crack Growth Rate vs. H2
0.5
Nickel Oxide
Nickel Metal
0.4
0.2
0.15
0.3
0.1
0.2
0.05
0.1
0
-100
-50
0
50
0
100
EcP Ni/NiO-EcP (mV)
KAPL data: CGR different, but peak vs. H2
is similar for different temperatures and K
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15
Crack Growth Rate K=25
(mils/day)
Crack Growth Rate K=60
(mils/day)
Alloy 600, 338°C, K=66 and 27 MPa√m
Alloy 82 Weld Metal Crack Growth Rate vs. H2
Hard to conclude that the peak is not actually at Ni/NiO
© 2007 Electric Power Research Institute, Inc. All rights reserved.
16
Modeling H2 Effects on CGR
8
Typical range of applicability of
Morton fomulation, often
limited when the Morton model
drops below 1.0, which is by
definition the background CGR
7
5
4
3
SCC Growth Rate / Minimum SCC Growth Rate
Relative CGR
6
2
Modified equation
1
Morton formulation
0
0.1
1
10
100
Log H 2, cc/kg
KAPL model modified
to →1 rather than →0
and fit data better
X-750 HTH, Deaerated Water, 360°C
6
5
4
1000
3
2
1
0
-100
-50
0
EcPNi/NiO - EcP (mV)
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17
50
100
Modeling H2 Effects on CGR
8
Typical range of applicability of
Morton fomulation, often
limited when the Morton model
drops below 1.0, which is by
definition the background CGR
7
Relative CGR
6
5
Ni/NiO Phase Boundary
= 10(0.0111*T(°C) – 2.59) cc/kg H2
4
3
2
Modified equation
1
Morton formulation
0
0.1
1
10
100
1000
Log H 2, cc/kg
⎛
⎡ ΔECP + ECP
⎜
OS
VP = ( P − 1) exp ⎜ − 0.5 ⎢
⎢ λ + (0.46 )1 P
⎜
⎣
⎝
⎤
⎥
⎥
⎦
2⎞
⎟
⎟ +1
⎟
⎠
ECPos = offset of CGR peak from Ni/NiO
phase boundary (see Morton)
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18
VP = velocity vs. peak (e.g., 1-8)
P = height of peak (e.g., 3-8X)
λ = width of peak (see Morton)
= 20.2 (A82) or 35.6 (A600)
ΔECP = H2 value vs. peak H2
=29.58 (T+273.3)/298.2 *
log (H2/H2-Peak)
Modeling H2 Effects on CGR
8
Typical range of applicability of
Morton fomulation, often
limited when the Morton model
drops below 1.0, which is by
definition the background CGR
7
Relative CGR
6
5
Morton Formulation
⎛
⎡ ΔECP + ECPOS
VP = P exp ⎜ − 0.5 ⎢
⎜
λ
⎣
⎝
4
3
2
⎤ ⎞⎟
⎥ ⎟
⎦
⎠
2
Modified equation
Morton parameters from
1
Morton formulation
0
0.1
1
10
100
1000
Log H 2, cc/kg
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19
Attanasio & Morton, Proc. 11th Int. Conf. on
Environmental Degradation of Materials, 2003.)
Alloy 600 Crack Growth Rate vs. H2
Corrosion Potential, mVshe
-700
-750
-800
-850
-900
9
Change in CGR for
various step changes in H2
Peak in Growth Rate = 8X
as Expected for Alloy 82/182
8
Arbitrary Growth Rate
7
Schematic Plot of Effect of
H2 on Crack Growth Rate
6
NiO Ni
Phase Stability
5
For 325C where potential ↓
by 59.35 mV per 10X ↑ in H2
& 118.7 mV per unit ↑ in pH
4
H2 change
10 → 20:
20 → 40:
40 → 80:
20 → 80:
20 → 200:
10 → 200:
600 82/182
1.24X 1.34X
1.61X 2.17X
1.38X 2.11X
2.23X 4.58X
2.42X 5.93X
2.99X 7.97X
50 mV Full Width
Half Max
3
2
Peak in Growth Rate = 3X
as Expected for Alloy 600
1
0
0
1
10
100
H2 Fugacity, cc/kg
Schematic of change in growth rate vs. H2
for Alloy 600 & Alloys 82/182
© 2007 Electric Power Research Institute, Inc. All rights reserved.
20
1000
H2 Effects on SCC Growth Rates
SCC#3c - c261 - Alloy 600, CRDM Tube, 93510
SCC#3c - c262 - Alloy 600, CRDM Tube, 93510
-0.85
CT potential
11.45
11.18
2.3 x 10-8
mm/s
4.4 x 10-8
mm/s
11.13
11.08
1000
-0.87
-0.88
-0.87
11.3
11.25
5.3 x 10-8
mm/s
11.2
-0.88
-0.89
-0.89
11.15
c261 - 0.5TCT of A600 CRDM, 325C
25 ksi√in, 20 cc/kg H2, 600 B / 2.2 Li
-0.9
1500
-0.86
3.4 x 10-8
mm/s
3.4 x 10-8
mm/s
11.35
To Constant K
@ 1040h
11.23
4.6 x 10-8
mm/s
Pt potential
11.4
Crack length, mm
11.28
-0.86
Conductivity, μS/cm or Potential, V she
11.33
To Constant K
@ 1040h
Crack length, mm
11.38
3 x 10-8
mm/s
To 80 cc/kg
H2 @ 2697h
Pt potential
To 40 cc/kg
H2 @ 1857h
11.43
To 80 cc/kg
H2 @ 2697h
CT potential
To 40 cc/kg
H2 @ 1857h
-0.85
2000
2500
3000
11.1
1000
3500
Test Time, hours
c262 - 0.5TCT of A600 CRDM, 325C
25 ksi√in, 20 cc/kg H2, 600 B / 2.2 Li
-0.9
1500
2000
2500
3000
Test Time, hours
Thermodynamic response in ECP to changes in H2
2X change in H2 = 17.9 mV at 325C
Alloy 600 CRDM, 325C, 600 B / 2.2 Li, 20 cc/kg H2
© 2007 Electric Power Research Institute, Inc. All rights reserved.
21
3500
Conductivity, μS/cm or Potential, V she
11.48
H2 Effects on SCC Growth Rates
SCC#2a - c261 - Alloy 600, CRDM Tube, 93510
SCC#2b - c261 - Alloy 600, CRDM Tube, 93510
11.24
11.44
2.3 x 10-8
mm/s
Outlet conductivity ÷100
0.4
0.4
11.42
Outlet conductivity ÷100
11.22
-0.6
c261 - 0.5TCT of A600 CRDM, 325C
25 ksi√in, 20 cc/kg H2, 600 B / 2.2 Li
11.14
11.32
11.3
To 40 cc/kg
H2 @ 1857h
To 80 cc/kg
H2 @ 2697h
11.34
3 x 10-8
mm/s
0
-0.2
-0.4
4.6 x 10-8
mm/s
-0.6
c261 - 0.5TCT of A600 CRDM, 325C
25 ksi√in, 20 cc/kg H2, 600 B / 2.2 Li
11.28
-0.8
-0.8
11.26
Pt potential
11.12
1300
CT potential
Pt potential
11.24
2100
-1
1400
1500
1600
1700
1800
1900
2000
2300
2500
2700
CT potential
2900
3100
3300
Test Time, hours
Test Time, hours
Response immediately after H2 change, but then ↑ in CGR
Alloy 600 CRDM, 325C, 600 B / 2.2 Li, 20 cc/kg H2
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22
-1
3500
Conductivity, μS/cm or Potential, V she
-0.4
11.36
0.2
To Constant K
@ 1040h
11.16
-0.2
11.38
Crack length, mm
11.18
4.4 x 10-8
mm/s
0
11.4
Conductivity, μS/cm or Potential, V she
Change from 20 to
40 cc/kg H2 @ 1857h
11.2
To Constant K
@ 1040h
Crack length, mm
0.2
H2 Effects – Short Term
4.0
Expected Response
CT#1 Short Term Response
CT#2 Short Term Response
3.5
Ratio of Growth Rate
Stronger short term
For 2.5X Peak @ 13 cc/kg H2
50 mV Full-Width, Half-Max
3.0
effect is likely related
2.5
to dcpd “shorting”
2.0
when moving farther
into Ni-metal stability
1.5
as H2 ↑
1.0
0.5
1
2
3
4
5
6
7
8
Specific H2 Change Made During Test
Expected & short-term observations of ratio in crack growth
rate for specific changes in H2, e.g., 20 to 40 cc/kg
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23
H2 Effects – Long Term
3.0
Expected Response
CT#1 Long Term Response
CT#2 Long Term Response
Ratio of Growth Rate
2.5
For 2.5X Peak @ 13 cc/kg H2
50 mV Full-Width, Half-Max
2.0
Long-term effect is
more representative
1.5
of actual effect of H2
1.0
0.5
1
2
3
4
5
6
7
8
Specific H2 Change Made During Test
Expected & long-term observations of ratio in crack growth
rate for specific changes in H2 – average overall agreement is 10%
© 2007 Electric Power Research Institute, Inc. All rights reserved.
24
H2 Effects on SCC Growth Rates (35 cc/kg reference)
Alloy 600
Baseline=
35 cc/kg
Alloy 82/182
Alloy 600 (3X Peak Height, λ = 35.6, ECPOS = 0)
Alloy 182/82 (8X Peak Height, λ = 20.2, ECPOS = 0)
Temp, °C
290 °C
310 °C
325 °C
343 °C
290 °C
310 °C
325 °C
343 °C
H2 at Ni/NiO
4.3 cc/kg
7.1 cc/kg
10.4 cc/kg
16.5 cc/kg
4.3 cc/kg
7.1 cc/kg
10.4 cc/kg
16.5 cc/kg
35 → 100
1.30
1.53
1.69
1.76
1.14
1.62
2.52
3.94
35 → 80
1.27
1.44
1.55
1.56
1.14
1.59
2.36
3.22
35 → 50
1.14
1.20
1.22
1.19
1.10
1.37
1.63
1.66
35 → 10
0.54
0.58
0.68
0.91
0.24
0.23
0.33
0.76
35 → 3
0.47
0.69
1.02
1.67
0.16
0.37
1.04
3.63
35 → 1
0.72
1.21
1.74
2.41
0.54
1.37
2.55
4.84
50 → 100
1.14
1.27
1.39
1.47
1.03
1.18
1.54
2.37
50 → 80
1.11
1.20
1.27
1.31
1.03
1.16
1.45
1.93
Predicted effects for specific changes in H2 at various temperatures
Based on CGR peak at Ni/NiO phase boundary with
peak height and width as specified by Morton et al.
© 2007 Electric Power Research Institute, Inc. All rights reserved.
25
H2 Effects on SCC Growth Rates (30 cc/kg reference)
Alloy 600
Baseline=
30 cc/kg
Alloy 82/182
Alloy 600 (3X Peak Height, λ = 35.6, ECPOS = 0)
Alloy 182/82 (8X Peak Height, λ = 20.2, ECPOS = 0)
Temp, °C
290 °C
310 °C
325 °C
343 °C
290 °C
310 °C
325 °C
343 °C
H2 at Ni/NiO
4.3 cc/kg
7.1 cc/kg
10.4 cc/kg
16.5 cc/kg
4.3 cc/kg
7.1 cc/kg
10.4 cc/kg
16.5 cc/kg
30 → 100
1.40
1.66
1.84
1.87
1.25
1.97
3.17
4.71
30 → 80
1.36
1.57
1.68
1.66
1.24
1.94
2.97
3.84
30 → 50
1.22
1.31
1.33
1.27
1.21
1.67
2.05
1.99
30 → 10
0.58
0.63
0.74
0.97
0.27
0.27
0.41
0.91
30 → 3
0.50
0.75
1.10
1.77
0.17
0.44
1.31
4.34
30 → 1
0.77
1.31
1.88
2.56
0.59
1.67
3.20
5.79
50 → 100
1.14
1.27
1.39
1.47
1.03
1.18
1.54
2.37
50 → 80
1.11
1.20
1.27
1.31
1.03
1.16
1.45
1.93
Predicted effects for specific changes in H2 at various temperatures
Based on CGR peak at Ni/NiO phase boundary with
peak height and width as specified by Morton et al.
© 2007 Electric Power Research Institute, Inc. All rights reserved.
26
H2 Effects on SCC Growth Rates
8.E-07
7.E-07
Based on 343C, a current
H2 level of 35 cc/kg and
Alloy 82 (8X peak vs. H2
6.E-07
4.E-07
Current H 2 Level
3.E-07
2.E-07
1.E-07
6
0.E+00
10
100
New H2 Level, cc/kg
Growth Rate and
Factor-of-Improvement
at 343C
1000
5
Based on 343C, a current
H2 level of 35 cc/kg and
Alloy 82 (8X peak vs. H 2
ECP offset = 0, λ = 20.2)
4
Current H 2 Level
1
Factor of Improvement
CGR, mm/s
ECP offset = 0, λ = 20.2)
5.E-07
3
2
1
0
1
10
100
New H2 Level, cc/kg
© 2007 Electric Power Research Institute, Inc. All rights reserved.
27
1000
Effect of H2 or ECP Offset on CG Rate
8.E-07
343C CGR based on a current
H2 level of 35 cc/kg and
Alloy 82 (8X peak vs. H2
λ = 20.2)
7.E-07
Offset ΔECP
=10.5
5.E-07
=0
4.E-07
3.E-07
Current H 2 Level
2.E-07
1.E-07
6
0.E+00
Based on 343C, a current
H 2 level of 35 cc/kg and
5
10
100
New H2 Level, cc/kg
ECP offset from Ni/NiO not
justified: Alloy 82 = +10 mV
and Alloy 600 = -10 mV
1000
4
ECP Offset
Alloy 82 (8X peak vs. H 2
λ = 20.2)
=0
Current H 2 Level
1
Factor of Improvement
CGR, mm/s
6.E-07
3
2
1
=10.5
0
1
10
100
New H2 Level, cc/kg
© 2007 Electric Power Research Institute, Inc. All rights reserved.
28
1000
H2 Effects on SCC Growth Rates
8.E-07
6.E-07
343C
35 cc/kg H2 the
same growth rate
5.E-07
4.E-07
325C
3.E-07
2.E-07
(no benefit) occurs at:
Current H 2 Level
CGR, mm/s
If decreasing from
343C CGR based on a current
H2 level of 35 cc/kg and
Alloy 82 (8X peak vs. H2
ECP offset = 0, λ = 20.2)
7.E-07
343 °C = 7.7 cc/kg H2
325 °C = 3.1 cc/kg H2
310 °C = 1.4 cc/kg H2
290C
1.E-07
290 °C = 0.5 cc/kg H2
0.E+00
1
10
100
1000
New H2 Level, cc/kg
Current operating H2 is above peak, so large reduction in H2 is needed to
get benefit – concern for radiolysis below ~2 – 4 cc/kg H2
© 2007 Electric Power Research Institute, Inc. All rights reserved.
29
Conclusions on Modeling H2 Effects
Summary and Interpretation of H2 Theory & Modeling:
• Thermodynamic ECP response for SS & Ni Alloy vs. H2
- true even for H2 < 0.1 cc/kg (9 ppb) in pure water or B/Li.
• H2 effect appears to apply ~identically independent of
temperature, stress intensity factor, B/Li, or heat.
• H2 peak height (peak-to-background) is ~3X for Alloy 600
and ~6 – 8 for 182/82 weld metals & Alloy X750.
The “background” growth rate may be lower, so peak is higher
• Deviations (offsets) from Ni/NiO are probably noise/scatter:
the offset for Alloy 600 = -10 mV; Alloy 82 = +10 mV.
• H2 peak width (e.g., FWHM) seems to vary, but more data are needed
• Factor-of-improvement analyses are complex because they must
account for temperature, historical H2, new H2, material, etc.
© 2007 Electric Power Research Institute, Inc. All rights reserved.
30
Conclusions on Measuring H2 Effects
Summary and Interpretation of H2 Results:
• Observed thermodynamic response to ECP for changes in H2
• Short term CGR response may be related to changes in Ni/NiO
and Ni-Fe-Cr/spinel oxide stabilities on dcpd
• Effects of H2 on CGR of alloy 600 agrees with KAPL data:
• peak to background is only ~2.5 – 3X
• peak at 325C is ~10.4 cc/kg H2
• width of peak at half-max is ~50 mV = 7X change in H2
• a peak height of 5 – 8X is observed for X750 or 82/182
• Mitigation benefit for a given component depends in rather
complex manner on alloy, temperature & current vs. target H2
• Future work will include Alloy 182 (larger effect of H2)
© 2007 Electric Power Research Institute, Inc. All rights reserved.
31
MRP Current Position on Desirability of Raising H2
• Strong theoretical basis, supported in particular by extensive test data
from the NR program, to recommend moving to higher hydrogen levels
in PWR primary water so as to obtain some mitigation of PWSCC for
Ni-base alloys used in thick-wall components.
• Such a change is expected always to have a positive effect in slowing
down crack growth, no matter what exact material or operating
temperature is involved. Some mitigation benefit already being
accrued with the current trend of moving to higher H2.
• Quantifying the predicted benefit of such a change for any particular
component, however, is complex.
• Overall, the benefit of hydrogen optimization will always be greater at
higher temperatures (e.g., in the pressurizer) and for higher-strength
alloys (e.g., weld metals or Alloy X750, rather than Alloy 600).
• Parallel effort on plant safety/operability evaluation for increased
hydrogen is under way; assessment of effect on fuel integrity of higher
hydrogen is planned (next 3 slides)
© 2007 Electric Power Research Institute, Inc. All rights reserved.
32
H2 Optimization: Prioritized List of Issues
Issue
Rank
Elevated hydrogen during operation
Will elevated H2 levels during operation affect the performance of PWR Zr-based alloys? (crud,
subnucleate boiling, fuel, etc.)
High
Will elevated H2 levels during operation result in explosive gas mixtures in containment during a
LOCA and other licensing/safety issues?
High
Can the plant maintain ≥ 50 cc/kg dissolved H2 with the existing VCT and all plant systems?
Medium
Will the increase in total dissolved gases cause operational problems (gas pocket formation)?
Medium
Will the increase in total dissolved H2 on the primary side affect conditions on the secondary side?
Medium
What are the possible consequences of elevated H2 under off-normal conditions (make-up
additions, letdown loss, etc.) that would be counter-productive?
Medium
Will elevated hydrogen levels have an effect on plants using Zn addition?
Medium
Reduced hydrogen during operation
What margin will be required to ensure radiolytic oxygen production does not occur?
High
Under what conditions will low H2 have no benefit or a negative benefit?
High
Hydrogen effects during plant shutdown
LTCP? Is stored hydrogen important? How quickly can H2 be removed prior to shutdown?
• All safety items were given the highest priority ranking
• Other lower priority issues will be addressed in the final report
© 2007 Electric Power Research Institute, Inc. All rights reserved.
33
Medium
FRP: Concerns with Elevated Coolant DH
1.
Possible H2 pickup increase in Zr-based alloys
–
–
–
2.
Elevated DH affects Fe, Ni solubility
–
3.
Hydride rims (layers with [H]>~1000 ppm) at the outer zone of the
cladding wall thickness could increase corrosion
18% volume expansion of Zr upon conversion to the hydride
contributes to in-reactor growth, dimensional stability
Zr-hydrides, ZrH1.6, may further decrease ductility, fracture
toughness of the metal
Anticipate that Fe solubility increases and Ni solubility decreases.
What happens to crud composition and morphology?
• Enhanced corrosion under deposits? AOA?
Possible Ni metal precipitation on cladding, grids, and thimble
tubes during startup
–
Possible pathway for H2 entry from DH into Zr components
© 2007 Electric Power Research Institute, Inc. All rights reserved.
34
FRP: Recommendations for Implementing
Elevated Coolant Hydrogen
Task 1: Perform out-reactor testing of M5 and ZIRLO to screen for
sensitivity of corrosion and H2 pickup at elevated DH. Tests should
include post-transition corrosion oxides, high DH, Zr-4, -2 controls.
Task 2: Assess the impact of DH on corrosion product species in
the coolant and on startup and shutdown procedures.
Task 3: In-reactor loop tests may be considered and can be used
as a second screening. But it is nearly impossible to simulate
commercial PWR system corrosion & crud deposition in loop tests.
Task 4: Pending favorable screening, begin demonstration in
commercial plants using a cautious approach of increasing DH in
steps of ~10 cc/kg and following with fuel surveillance. First
implementation should be in low or medium duty plants. High duty
plants can follow.
© 2007 Electric Power Research Institute, Inc. All rights reserved.
35
Effect of Reduced Hydrogen on PWSCC
• Ongoing MRP test program focuses on increasing H2 fugacity to
obtain lower CGRs, but growth rates are also predicted to
decrease at much lower H2 levels, except for components
operating at the lowest temperatures in the primary circuit.
• Low H2 approach to optimizing H2 levels is being investigated in
Japan and emerging results should be followed closely.
• Radiolysis is a possible concern here, since the increase in
CGR that would result from a significant elevation of ECP is
much larger than benefit from adjusting H2.
© 2007 Electric Power Research Institute, Inc. All rights reserved.
36
Reduced Hydrogen to Mitigate PWSCC
• To reduce crack growth rates to a level comparable to that of
50 cc/kg, hydrogen would have to be reduced to approximately
2.5 cc/kg H2 at 325°C, which does not provide an adequate
operating margin
• Current data indicate that >1-5 cc/kg H2 is required to suppress
radiolysis and avoid oxidizing conditions
• Japan Atomic Power Company (JAPC) has developed a multiyear plan to investigate operation as low as 5 cc/kg H2
• Possible Issues:
– Effect on corrosion product transport and deposition
– Effect on crack growth rates
© 2007 Electric Power Research Institute, Inc. All rights reserved.
37