Westinghouse Non-Proprietary Class 3 © 2016 Westinghouse Electric Company LLC. All Rights Reserved.
1
Andrew Ruminski
Westinghouse Electric Company
Materials Center of Excellence
Churchill
Review of reactor containment building
corrosion events and prediction corrosion rates
2
Westinghouse Non-Proprietary Class 3 © 2016 Westinghouse Electric Company LLC. All Rights Reserved.
Operating Experience
• Non-uniform, through-wall, corrosion at interface between
containment liner steel & concrete
• Several incidents worldwide1-3
– Brunswick Unit 2 - 1999
– Anna Unit 2 - 1999
– D.C. Cook Unit 2 - 1999
– Beaver Valley Unit 1 - 2009 and 2013
– Ringhals Unit 2 - 2006
– Various French plants
1) Sandia National Laboratory Report SAND2010-8718, “Nuclear Containment
Steel Liner Corrosion Workshop: Final Summary and Recommendations
Report,” July 2011.
2) V. Shah and C. Hookman, “Long-term aging of light water reactor concrete
containments,” Nuclear Engineering & Design, Vol. 185 (1998), pp. 51-81
3) P. Effsing, “Containment Leakages – Ringhals Unit 2,” PWROG-MSC
Hollywood, Florida, April 2015.
3
Westinghouse Non-Proprietary Class 3 © 2016 Westinghouse Electric Company LLC. All Rights Reserved.
Through-Wall Corrosion Incidents
• Incidents associated with organic foreign material
– Embedded gloves, brushes, and / or lumber
– Source of chlorides, sulfates & organic acids
• Ringhals Unit 2 attributed to pitting corrosion & MIC
Average Penetration Rates (mmpy)
North Anna 2 0.41
D. C. Cook 2 0.38
Beaver Valley Unit 1 0.25
Passivity perturbed
4
Westinghouse Non-Proprietary Class 3 © 2016 Westinghouse Electric Company LLC. All Rights Reserved.
Conditions of Through-wall Corrosion
• Measurable sulfates, fluorides, & chlorides at interface
• Black corrosion deposits (magnetite) at concrete interface
• Formation of magnetite due to low oxygen & chlorides3-6
• Sulfur bearing specimens & yellow deposits on plant side– Possible evidence of MIC
• pH from swipe ~ 6 – Non-passivating
– Conducive to SRB-MIC 7
3) R. Javaherdashti, Microbiologically Influenced Corrosion: An Engineering
Insight, Springer-Verlag, London (2008).
4) F. R. Pérez et al.,“Effect of Chloride Concentration, Immersion Time and Steel
Composition on the Spinel Phase Formation”, Materials Chemistry and Physics,
117, 214-223, (2009).
5) C. T. Lee et al., “An In Situ Raman-Electrochemical Investigation of Carbon
Steel Corrosion in Na2CO3 / NaHCO3, Na2SO4 and NaCl Solutions”, Journal of
the Electrochemical Society, 153 (2), B33-B41, (2006).
6) C. A. Barrero et al., “On Magnetite Formation as a Corrosion Product of Steel”,
Proceedings of the International Conference on the Applications of the
Mössbauer Effect, September 2-7 2001, Oxford.
7) R. Javaherdashti, Microbiologically Influenced Corrosion: An Engineering
Insight, Springer-Verlag, London (2008).
5
Westinghouse Non-Proprietary Class 3 © 2016 Westinghouse Electric Company LLC. All Rights Reserved.
Liner / Concrete Interface
EDS Data from Thick Black Oxide (Magnetite)
Spectrum
C
(w %)
O
(w %)
Si
(w %)
Ca
(w %)
Mn
(w %)
Fe
(w %)
1 2.6 30.6 0.1 0.1 1.2 65.4
Black
Oxide
Swipe:
pH ~6
SO4-2 0.8 µg / cm2
F- 0.2 µg / cm2
Cl- 0.1 µg / cm2
6
Westinghouse Non-Proprietary Class 3 © 2016 Westinghouse Electric Company LLC. All Rights Reserved.
Plant Side, Leaking from Hole
Yellow
Deposit
EDS Data from Yellow Deposit
Spectra
C
(w %)
O
(w %)
Cr
(w %)
Si
(w %)
S
(w %)
Ti
(w %)
Mn
(w %)
Fe
(w %)
Cu
(w %)
Zn
(w %)
1 13.3 37.0 0.2 0.2 1.6 0.1 0.2 46.7 - 0.7
2 2.5 5.3 - 0.2 1.3 0.8 0.5 88.3 - 1.2
3 12.4 38.1 - 0.1 0.4 - - 48.2 - 0.7
4 14.5 42.7 1.1 1.0 1.6 0.2 0.6 37.0 0.9 0.4
5 18.4 29.6 - 0.3 0.9 0.6 0.2 48.9 - 1.1
6 77.2 22.8 - - - - - - - -
Sulfur bearing
Possible MIC byproduct
7
Westinghouse Non-Proprietary Class 3 © 2016 Westinghouse Electric Company LLC. All Rights Reserved.
Published Data
• General corrosion rates of steels near ambient 6-9
– Less severe than liner plate rates observed in NPP
• Atmospheric conditions ~ 0.025 mm per year (mpy)
• Passivating high pH environment (~ 12.5) in concrete 1-2
– Corrosion rates in concrete 5 to 10 lower
6) ASM Handbook of Corrosion Data, edited by B. D. Craig, First Edition, p. 160.
7) M. Raphael and R. Shalon, “Influence of Climate on Corrosion of Reinforcement,” Proceedings International RILEM Symposium, Vol. 1, 1971, pp.
177-196.
8) E. Escalante and S. Ito, “Measuring the Rate of Corrosion of Steel in Concrete,” Corrosion Rates of Steel in Concrete, ASTM STP 1065, N. Berke
et al. editors, pp. 86-102.
9) C. Locke and A. Siman, “Electrochemistry of Reinforcing Steel in Salt Contaminated Concrete,” Corrosion of Reinforcing Steel in Concrete, ASTM
STP 713, D. Tonini and J. Gaidis editors, pp. 3-16.
8
Westinghouse Non-Proprietary Class 3 © 2016 Westinghouse Electric Company LLC. All Rights Reserved.
Summary of Published Ambient Corrosion Rates
Corrosion Rates for Structural Carbon SteelExposure Conditions mmpy Ref
Atmospheric, 1st Several Years 0.025 6
Atmospheric, Past Several Years 0.013 6
Encased in concrete, no salt 0.003 7
Encased in concrete, exposed salt 0.013 8
Encased in concrete,1.0% NaCl 0.14 9
Observed NPP Liner Corrosion ~3x greater
9
Westinghouse Non-Proprietary Class 3 © 2016 Westinghouse Electric Company LLC. All Rights Reserved.
Thermal Effects
• Corrosion data assumed to be 25oC (77oF)
• Operating temperature of NPP liner <49oC (<120oF)
• Activation energy of 36 800 J / mole 10
• Rate approximately 3 times greater than “ambient”
10) Jäggi et al., Corrosion of Reinforcement in Concrete, Chapter 7, “Macrocell Corrosion of Steel in Concrete – Experiments and Numerical
Modelling,” 2007, pp. 75-88.
10
Westinghouse Non-Proprietary Class 3 © 2016 Westinghouse Electric Company LLC. All Rights Reserved.
Breakdown of Corrosion Immunity – Acid
• Reduction in pH
– Carbon dioxide from the atmosphere
• Eventually Reduce the pH to approximately 8.3
– Organic debris embedded in the concrete
– Acids from MIC (pH as low as 4)
11
Westinghouse Non-Proprietary Class 3 © 2016 Westinghouse Electric Company LLC. All Rights Reserved.
Breakdown of Corrosion Immunity – Chlorides
• Cl- ion to OH- ratio greater than 0.3
• Passivating film on steel is penetrated
– Corrosion initiated
• Iron ion precipitation/hydrolysis reaction reduces pH
– Chloride and acidic attacks synergistic
• Corrosion rate with chlorides 50 times greater passivated
12
Westinghouse Non-Proprietary Class 3 © 2016 Westinghouse Electric Company LLC. All Rights Reserved.
Effect of Moisture
• Oxygen & electrical conductivity of concrete impact
corrosion
• Both low oxygen solubility & diffusivity low in water
saturated concrete
– Worst case corrosion with intermittent wetting
– Intermittent wetting also intensifies contamination
13
Westinghouse Non-Proprietary Class 3 © 2016 Westinghouse Electric Company LLC. All Rights Reserved.
Predicted Corrosion Rate
14
Westinghouse Non-Proprietary Class 3 © 2016 Westinghouse Electric Company LLC. All Rights Reserved.
Time to Penetrate Containment Liner
15
Westinghouse Non-Proprietary Class 3 © 2016 Westinghouse Electric Company LLC. All Rights Reserved.
Summary
• Steel in Containment Concrete – Passivated with corrosion rate (~0.01 mmpy)– Active corrosion rate with carbonation (~0.08 mmpy)– Corrosion rate with contamination (~0.44 mmpy)
• 10 mm liner penetration– >1000 years with passivation– >100 years with active corrosion (non contamination)
• Penetration incidents associated with contamination – Chlorides, organic acids, MIC – Up to 0.4 mmpy– >25 year to penetrate liners