Review of reactor containment building corrosion events and prediction corrosion rates

Transcription

1 Review of reactor containment building corrosion events and prediction corrosion rates Andrew Ruminski Westinghouse Electric Company Materials Center of Excellence Churchill 1

2 Operating Experience Non-uniform, through-wall, corrosion at interface between containment liner steel & concrete Several incidents worldwide 1-3 Brunswick Unit Anna Unit D.C. Cook Unit Beaver Valley Unit and 2013 Ringhals Unit Various French plants 1) Sandia National Laboratory Report SAND , Nuclear Containment Steel Liner Corrosion Workshop: Final Summary and Recommendations Report, July ) V. Shah and C. Hookman, Long-term aging of light water reactor concrete containments, Nuclear Engineering & Design, Vol. 185 (1998), pp ) P. Effsing, Containment Leakages Ringhals Unit 2, PWROG-MSC Hollywood, Florida, April

3 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 D. C. Cook Beaver Valley Unit Passivity perturbed

4 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 & chlorides 3-6 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, , (2009). 5) C. T. Lee et al., An In Situ Raman-Electrochemical Investigation of Carbon Steel Corrosion in Na 2 CO 3 / NaHCO 3, Na 2 SO 4 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 , Oxford. 7) R. Javaherdashti, Microbiologically Influenced Corrosion: An Engineering Insight, Springer-Verlag, London (2008). 4

5 Liner / Concrete Interface Swipe: ph ~6 SO µg / cm 2 F µg / cm 2 Cl µg / cm 2 Black Oxide EDS Data from Thick Black Oxide (Magnetite) Spectrum C (w %) O (w %) Si (w %) Ca (w %) Mn (w %) Fe (w %)

6 Plant Side, Leaking from Hole Yellow Deposit Sulfur bearing Possible MIC byproduct EDS Data from Yellow Deposit C O Cr Si S Ti Mn Fe Cu Zn Spectra (w %) (w %) (w %) (w %) (w %) (w %) (w %) (w %) (w %) (w %)

7 Published Data General corrosion rates of steels near ambient 6-9 Less severe than liner plate rates observed in NPP Atmospheric conditions ~ 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 ) M. Raphael and R. Shalon, Influence of Climate on Corrosion of Reinforcement, Proceedings International RILEM Symposium, Vol. 1, 1971, pp ) 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 ) 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

8 Summary of Published Ambient Corrosion Rates Corrosion Rates for Structural Carbon Steel Exposure Conditions mmpy Ref Atmospheric, 1 st Several Years Atmospheric, Past Several Years Encased in concrete, no salt Encased in concrete, exposed salt Encased in concrete,1.0% NaCl Observed NPP Liner Corrosion ~3x greater 8

9 Thermal Effects Corrosion data assumed to be 25 o C (77 o F) Operating temperature of NPP liner <49 o C (<120 o F) Activation energy of 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

10 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) 10

11 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 11

12 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 12

13 Predicted Corrosion Rate 13

14 Time to Penetrate Containment Liner 14

15 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 15