34 ciscc susceptibility and cgr testing sindelar srnl sti-2017-00323
1. Spent Fuel and Waste Science and Technology
CISCC Susceptibility and CGR
Testing
Robert L. Sindelar,
J.T. Carter, A.J. Duncan, P.-S. Lam,
K.E. Metzger, B.L. Garcia-Diaz, K.N. Hair
Savannah River National Laboratory
NFWST Annual Meeting
May 24, 2017
SRNL-STI-2017-00323
2. Spent Fuel and
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CISCC
from an Initial Dry Salt/Dust Mixture
Chloride-induced stress corrosion cracking can occur from
an initial dry salt/dust mixture deposited on stainless steel
and that has deliquesced to form a brine/electrolyte.
Occurrence not certain:
– Formation of “free brine” in a mixture is extremely difficult
– Contact of mixture with brine against stainless steel to cause
pitting/cracking is extremely difficult
Applications to canister ISI
– Where are the examination regions?
– What are we looking for with a remote VT examination?
– How to disposition indications?
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3
Welding Residual Stress - Driving Force*
for Stress Corrosion Cracking
*With a chloride brine, WRS are sufficient to cause SCC.
Quantification of Influence of sensitization on pitting/cracking TBD
Sandia Mockup Canister:
OD= 67.25 in = 1708.15mm; Wall Thickness= 16 mm (0.63 in.)
Double-V, 15-16 in/min, 30V/400A; Heat input= 45 kJ/in
Figure 5 Residual Stress Contour Map parallel to a Circumferential Weld
through the Wall Thickness of the Sandia Mockup Canister [8]
(Courtesy of Sandia National Laboratories)
Figure 6 Residual Stress Contour Map parallel to a Longitudinal Weld
through the Wall Thickness of the Sandia Mockup Canister [8]
(Courtesy of Sandia National Laboratories)
Figure 7 Definition of a Part-though-wall Surface Crack
[from P.-S. Lam, et.al., PVP2017-66055]
Figure 9 Stress Intensity Factor at the Surface Point (f= 0°)
of an Axial Semi-elliptical Crack under Canister Welding Residual Stress
Figure 10 Stress Intensity Factor at the deepest Point (f= 90°)
of an Axial Semi-elliptical Crack under Canister Welding Residual Stress
4. Spent Fuel and
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SRNL CISCC Tests – Teardrop and
BLCT Specimens
Instrumented Bolt
BLCT Specimen
Teardrop Coupon
Salt mixture
Cradle
4
Test Environments*:
#1 CaCl2/KCl/NaCl + CeO2 @ 50% RH & 50°C
#2 Sea Salt + Sand/Kaolin/Feldspar @ 50% RH & 50°C
#3 Sea Salt + Sand/Kaolin/Feldspar @ 30% RH & 50°C
May 24, 2017 CISCC Susceptibility and CGR Testing
*Absolute humidity of ~30 g/m3 is
bounding in nature. At 50% RH & 50°C,
AH=42 g/m3. Salt/dust mixture selected
from observations (Bryan)
5. Spent Fuel and
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Salt Mixtures and T/RH
Conditions for 5 Month Duration
5May 24, 2017 CISCC Susceptibility and CGR Testing
Test
Environmental
conditions
Simulated Dust Crack Length A/W
Stress Intensity
(ksi-in^1/2)
#1 50 ºC and 50% RH† 98% CeO2
0.8% NaCl 0.552 29.1
0.8% KCl
0.4% CaCl2
#2 50 ºC and 50% RH†
50% Washed Sand*
(-200 mesh) 0.588 27.8
12.5% Kaolin
12.5% Feldspar
25% Artificial Sea Salt$
#3 50 ºC and 30% RH‡
50% Washed Sand*
(-200 mesh) 0.488 23.7
12.5% Kaolin
12.5% Feldspar
25% Artificial Sea Salt$
* Secondary compounds of sea sand besides SiO2 can be Zircon, Ilmenite and Rutile
† Achieved using ASTM E104 saturated aqueous solution of NaBr
‡ Achieved using ASTM E104 saturated aqueous solution of MgCl2
$ Composition and form as specified by ASTM D1142
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May 24, 2017 CISCC Susceptibility and CGR Testing 7
Photographs Before and
After Cleaning
35 mm before & after cleaning
Corrosion area is ~0.25-0.28 cm2
top to bottom: 0.58 cm
right to left: 0.61 cm
6% of the surface area is pitted as
shown in this image
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VT-3 and VT-1 Images using Videoscope
8
VT-3:
VT-1:
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Surface Height (Area 2)
(mm)
9
LCM Imaging Locations
10. Spent Fuel and
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Linear
Profiles
A
B
A
B
Teardrop Sample Area 1
Magnification
: 50X
92 mm
< 78 mm
85 mm
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11. Spent Fuel and
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Surface Magnification: 10X, Cross-Section
Magnification 50X– Area 2
Surface (Laser + Optical)
Cross-Section (Laser +
Optical)
A
D
B
C 500 um
11
Cross -
Section
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12
100 um
100 um
Interconnected Cracking Below Surface
• Smallest pits in terms of diameter and pit
depth and yet produced networks of
“long” cracks below the surface
13. Spent Fuel and
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11.4 um13.9um 11.4 um 7.0 um
127.9 um
70.3um
118.7 um
20.4 um
14.5 um
189.8 um
A
24.4 um
250.0 um
54.8 um
12.2 umB
5.7um 4.5um
210.2 um
103.8um
D
C
100 um
100 um
Pitting and Cracking Depth (Preliminary Results)
13
Avg. Crack
Rate:0.36
mm/year
14. Spent Fuel and
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May 24, 2017 CISCC Susceptibility and CGR Testing 14
Additional Teardrop Specimens -
Photographs Before Cleaning
25% Sea Salt, 75%CeO2
Exposure: 3 Months, 50°C, 50%RH
25% Sea Salt, 75% Sea Dust 100% Sea Salt
15. Spent Fuel and
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15
May 24, 2017 CISCC Susceptibility and CGR Testing
Tear drop-shaped
sample
Adherent
salt/dust layer
Bolt-loaded sample
Fatigue fractured bolt-loaded sample
BLCT Results with Companion
Teardrop
Fatigued
Region
Heat
Tint
Salt/Dust Mix
98 wt% CeO2
0.8 wt% NaCl
0.8 wt% KCl
0.4 wt% CaCl2
5 month exposure
50°C
RH= 50%
16. Spent Fuel and
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Summary
16
- Inspect weld regions at conditions where dust and salt collect and salt deliquesces
- Flaws perpendicular to the canister welds are under high, pure tension loading
- There are visual indications (brown spots) of corrosion (pitting)
- Appears challenging (not possible?) to observe cracking with videoscope
- No apparent correlation of pit size and cracking incidence (e.g. “small” pits may be
associated with “long” cracks)
- Teardrop specimen test results show CGRs on order of 0.5 mm/year
Path forward:
- Compile library of surface photographs/micrographs for visual appearance of
pitting/cracking under relevant conditions and compare to cross-section micrographs
- Evaluate influence of sensitization
CISCC Susceptibility and CGR TestingMay 24, 2017
17. Spent Fuel and
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ASME Code Case for Canister ISI –
Lack of Consensus
Initial inspection parameters
– Number of canisters, canister selection
– Frequency of inspection and canister rotation protocol
Use of visual examination methods (VT-1, VT-3) to
classify potential degradation
Use of the “major/minor/insignificant” corrosion
metric to initiate volumetric (e.g. UT) examination
– Volumetric methods to characterize (size) a flaw within the
constraints of canister system do not exist at present
Flaw disposition method
May 24, 2017 CISCC Susceptibility and CGR Testing 17
