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Understanding Long-Term Corrosion of Alloy 22 Container in the Potential Yucca Mountain

Repository for High-Level Nuclear Waste Disposal

T. Ahn,1 H. Jung,2 X. He2 and O. Pensado2

1U.S. Nuclear Regulatory Commission, Washington, D.C. 20555-0001, U.S.A.2Center for Nuclear Waste Regulatory Analyses, San Antonio, TX 78238-5166,

U.S.A.

Third International Workshop on Long-term Prediction of Corrosion Damage in Nuclear Waste Systems

May 14 – 18, 2007The Pennsylvania State University (with OECD),

State College, PA 16802, U.S.A.

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Disclaimer

The U.S. Nuclear Regulatory Commission (NRC) staff views expressed herein are preliminary and do not constitute a final judgment or determination of the matters addressed or of the acceptability of a license application for a geological repository at Yucca Mountain. The paper describes work performed by the Center for Nuclear Waste Regulatory Analyses (CNWRA) for the NRC under contract number NRC-02-02-012. The activities reported here were performed on behalf of the NRC office of Nuclear Material Safety and Safeguards, Division of High Level Waste Repository Safety.

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Outline

• Purpose

• Persistence of Passive Film- Anodic Sulfur Segregation- Conformance of Chromium Oxide- Other Potential Concerns

• Susceptibility and Propagation of Crevice Corrosion- Quantity and Chemistry of Groundwater- Induction Time- Limited Susceptibility and Restricted Area of

Propagation

• Summary

• References

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Purpose

• Prepare for reviewing any U.S. Department of Energy’s license application for a potential Yucca Mountain repository

• The outer container of a waste package at a potential Yucca Mountain repository may be constructed of Alloy 22, a corrosion resistant Ni-22Cr-13Mo-3W-4Fe alloy

• Present factors potentially relevant to Alloy 22 corrosion in a potential Yucca Mountain repository environments

• Obtain feedback from the expert peer group

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Anodic Sulfur Segregation –Issues

Mechanism of the breakdown of the passive film induced by enrichment of sulfur at the metal-passive film interface (Marcus, 1995)(Reprinted from “Sulfur-Assisted Corrosion Mechanisms and the Role of Alloyed elements” by P. Marcus in Corrosion Mechanisms in Theory and Practice edited by P. Marcus and J. Oudar, Marcel Dekker, Copyright (1995), with permission from Marcel Dekker)

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Anodic Sulfur Segregation –Observations and Postulates

• Change of general corrosion rates within the data uncertainty range (Jones et al., 2005)

• Approximately 900 years to form a mono-layer of the sulfur at interface (Marcus, 2001)

• Enhancement of general corrosion rate (Marcus, 1995)

• Formation of soluble sulfur molybdenum compound (Marcus and Moscatelli, 1989)

• Protective film formation with chromium (Marcus and Grimal, 1990)

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Anodic Sulfur Segregation –Sulfur Dissolution Kinetics

The first figure is for Ni-2a/o Mo (100) with pre-sorbed sulfur (initial coverage 43 ng/cm2) and polarized in the active region at 320 mV/SHE in 0.05 M H2SO4 (Marcus and Moscatelli, 1989); the second figure is for sulfur coverage on Fe-17Cr-12.6Ni (100) and Fe-17Cr-14.5Ni-2.3Mo (100) alloys in 0.05 M H2SO4 at the corrosion potential (Elbiache and Marcus, 1992). 1 ng/cm2 = 1.42 x 10-11 lb/in2.

• (First) Reprinted from “The Electrochemical Society, Inc. [1989]. All rights reserved. Except as provided under U.S. copyright law, this work may not be reproduced, resold, distributed, or modified without the express permission of The Electrochemical Society (ECS). The archival version of this work was published in “The Role of Alloyed Molybdenum in the Dissolution and the Passivation of Nickel-Molybdenum Alloys in the Presence of Adsorbed Sulfur” by P. Marcus and M. Moscatelli in J. Electrochemical Soc., Vol. 136, No. 6, 1989

• (Second) Reprinted from Publication “The Role of Molybdenum in the Dissolution and the Passivation of Stainless Steels with Adsorbed Sulfur” by A. Elbiache and P. Marcus, Corrosion Science, Vol. 33, No. 2. P. 262 - 269, Copyright (1992), with permission from Elsevier

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Anodic Sulfur Segregation –Sulfur Dissolution Kinetics (Continued)

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Anodic Sulfur Segregation –Model Analysis (Ahn and Pan, 2006; Passarelli et al., 2005)

Penetration Depth =

∑ [CRp * Ctp + CRf * Ctf]

CRp : slow passive corrosionrate

Ctp : slow passive corrosion time

CRf : fast enhancedcorrosion rate

Ctf : fast enhanced corrosion time

0.1

1

10

0.001 0.01 0.1 1 10

Sulfur-enhanced Corrosion Time (Year)

Pe

ne

tra

tio

n D

ep

th o

f W

as

te

Pa

ck

ag

e (

cm

)

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Anodic Sulfur Segregation –Case Study

• Case 1 – segregation time of 18 years at 10-5 cm/year [3.9x 10-6

inch/year], sulfur dissolution with molybdenum

• Case 2 – slow sulfur dissolution (still fast compared to segregation time), down to 0.15 or 0.02 sulfur coverage

* Both cases do not seem to result in noticeable corrosion penetration

* Data from Smailos (1993) and Fang and Staehle (1999) –continuous sulfur supply

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Anodic Sulfur Segregation –Case Study (Continued)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

n

θ

13% Mo (Alloy 22)

2% Mo

θ: fractional sulfur coverage; n: atomic plane number under corrosion

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Conformance of Chromium Oxide –Observations and Postulates

• Chromium barrier oxide

• Point defect model (PDM, Macdonald et al., 2004; Chao et al. andLin et al., 1981; Urquidi-Macdonald and Macdonald, 1987)

• Long-term postulates – finite thickness of passive film (Urquidi-Macdonald and Macdonald, 2003), and minimal effects of potential void formation (Pensado et al., 2002)

• Natural analogue studies of nickel-iron meteorites (Sridhar and Cragnolino, 2002)

• Decrease of general corrosion rates with time under deliquescence conditions up to 180 °C [356 °F] (Yang et al., 2007)

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Conformance of Chromium Oxide –Issues

• Observation of low chromium content in passive film –

(1) Lawrence Livermore National Laboratory, Long Term Corrosion Test Facility (LTCTF) (Bechtel SAIC Company, 2003)

(2) CNWRA tests in 4 M NaCl simulated groundwater of pH = 7.5 at 95 °C [203 °F] for two years (Dunn et al., 2005)

• Silica deposits

(1) LTCTF and CNWRA tests(2) analogue studies of Josephinite – Andradite, a ferric silicate

with a composition of Ca3Fe2(SiO4)3

(Sridhar and Cragnolino, 2002)

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Other Potential Concerns

• Chromium depletion in metal near to the passive film in LTCTF and CNWRA tests - no apparent effects in corrosion rates

• Selective sorption of chemical species in accumulated corrosion products (Dzombak and Morel, 1990) – not observed in LTCTF

• Development of large cathodic surface area – insulator and limited cathodic capacity (Kelly et al., 2006)

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Crevice Corrosion –Quantity and Chemistry of Groundwater

• Low volumes of water dripping

• A small probability for unfavorable water chemistry,

producing limited opportunities to induce crevice

corrosion (Pensado, 2006)

• Only small fraction of containers may be subject to crevice

corrosion

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Crevice Corrosion –Induction Times

• Pits propagate in the crevice during crevice corrosion

- Pit induction times (Lin et al., 1981; Urquidi-Macdonald and Macdonald, 1987)

- very sensitive to ΔV (pitting potential – applied potential); the frequency decreased drastically with time

• Crevice corrosion induction times increased with potential decrease

- repassivation potential as an asymptotic potential - nucleation process (Okada, 1984)

• Times for forming critical chemistry in crevice are short (Combrade, 2001; Walton et al., 1996)

• The laboratory data could be used for the long-term prediction of localized corrosion

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Crevice Corrosion –Limited Susceptibility and Restricted Area of Propagation

• Crevice area – tight area of buckled drip shield and container under applied stress by rock falls, 0.01 – 0.1 area opening fraction of total waste package surface area

• Weld area – more susceptible for crevice corrosion, ~ 0.01 area opening fraction of total waste package area

• Pit area in the crevice – crevice corrosion propagation was limited to some deep sites, after initial transient period; 10 – 100 μm [3.9x(10-4 – 10-3) inch] size; 0.01 – 0.1 area opening fraction of total waste package area (He and Dunn, 2005)

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Crevice Corrosion –Current Transients

• Crevice Corrosion of Alloy 22in 5 M NaCl Solutions at 95 °C

• Propagation Limited to Some Deep Pits

He and Dunn (2005)

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Summary

• Long-term passivity may be persistent for Alloy 22 under potential Yucca Mountain repository conditions.

• The alloy’s molybdenum content may allow the possibility of the segregated sulfur to quickly dissolve and the alloy to repassivate quickly.

• The point defect model offers insights for long-term conformance of chromium oxide passive film, whereas silica deposits may havehelped protect the intact metal surface.

• Data and models in literature suggest that the induction times for crevice corrosion are within the laboratory test time of days.

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Summary (Continued)

• The potential Yucca Mountain repository may have low volumes of groundwater and a small probability for unfavorable water chemistry, producing limited opportunities to induce crevice corrosion.

• If crevice corrosion were to occur, the opening area could be restricted by effects of metal fabrication, limited crevice area and pit formation in the crevice.

• A performance assessment of the total system suggests that radionuclide releases appear sensitive to the opening surface area of the waste package.

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References

• T. Ahn and Y.-M. Pan, Summary of NRC Work and Waste Package Corrosion Risk Insights, NWTRB Workshop on Localized Corrosion of Alloy 22 in Yucca Mountain Environments, Las Vegas, NV, September 25 - 26, 2006, NRC ADAMS ML062640338, 2006

• ASTM International, Standard Practice for Prediction of the Long-Term Behavior of Materials, Including Waste Forms, Used in Engineered Barrier Systems (EBS) for Geological Disposal of High-Level Radioactive Waste, ASTM Designation: C 1174 – 04, West Conshohocken, PA

• Bechtel SAIC Company, Technical Basis Document No. 6: Waste Package and Drip Shield Corrosion, Revision 6, Las Vegas, NV, 2003

• C. Y. Chao, L. F. Lin and D. D. Macdonald, A Point Defect Model for Anodic Passive Films, I. Film Growth Kinetics, J. Electrochemical Society, Vol.128, p. 1187 - 1194, 1981

• P. Combrade, The Crevice Corrosion of Metallic Materials, MC TC R 01-1190, FRAMATOME ANP, 2001

• D. S. Dunn, O. Pensado, Y.-M. Pan, R. T. Pabalan, L. Yang, X. He, and K. T. Chiang, Passive and Localized Corrosion of Alloy 22 Modeling and Experiments, CNWRA 2005-02, Center for Nuclear Waste Regulatory Analyses, San Antonio, TX, 2005

• D. A. Dzombak and F. M. M. Morel, Surface Complexation Modeling - Hydrous Ferric Oxide, John Wiley & Sons, New York, 1990

• A. Elbiache and P. Marcus, The Role of Molybdenum in the Dissolution and the Passivation of Stainless Steels with Adsorbed Sulphur, Corrosion Science, Vol. 33, No. 2, pp. 261 - 269, 1992

• Z. Fang and R. W. Staehle, Effect of the Valence of Sulfur on Passivation of Alloy 600, 690, and 800 at 25 ̊C and 95 ̊C, CORROSION, Vol.55, No.4, p.355 - 379, 1999

• X. He and D. S. Dunn, Crevice Corrosion Penetration Rates of Alloy 22 in Chloride-Containing Waters - Progress Report, CNWRA 2006 - 001, Center for Nuclear Waste Regulatory Analyses, San Antonio, TX, 2005

• R. H. Jones, D. R. Baer, C. F. Windisch Jr., R. B. Rebak, Corrosion Enhanced Enrichment of Sulfur and Implications for Alloy 22, UCRL-CONF-217194, Lawrence Livermore National Laboratory, Livermore, CA, Corrosion/2006 Conference and Exposition, San Diego, CA, 2005

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References (Continued)

• R. G. Kelly, A. Agrawal, F. Cui, X. Shan, U. Landau and J. Payer, Consideration of the Role of the Cathode Region in Localized Corrosion, Proceedings of the 11th International High-Level Radioactive Waste Management Conference, Las Vegas, NV, American Nuclear Society, LaGrange Park, IL, 2006

• L. F. Lin, C. Y. Chao and D. D. Macdonald, A Point Defect Model for Anodic Passive Films, II. Chemical Breakdown and Pit Initiation, J. Electrochemical Society, Vol.128, p. 1194 - 1198, 1981

• D. D. Macdonald, A. Sun, N. Priyantha and P. Jayaweera, An Electrochemical Study of Alloy 22 in NaCl Brine at Elevated Temperature: II.

Reaction Mechanism Analysis, Journal of Electroanalytical Chemistry, 572, p.421-431, 2004.

• P. Marcus, Long Term Extrapolation of Passive Behavior, Proceedings from an International Workshop on Long-Term Extrapolation of Passive Behavior, p. 55 - 60, Nuclear Waste Technical Review Board Meeting, Arlington, VA, July 19 - 20, 2001

• P. Marcus, Sulfur-Assisted Corrosion Mechanisms and the Role of Alloyed Elements, Chapter 8, pp. 239 - 263, in Corrosion Mechanisms in Theory and Practice, by P. Marcus and J. Oudar, Marcel Dekker, Inc., 1995

• P. Marcus and J. M. Grimal, The Antagonistic Roles of Chromium and Sulfur in the Passivation of Ni-Cr-Fe Alloys Studies by XPS and Radiochemical Techniques, Corrosion Science, Vol. 31, pp. 377 - 382, 1990

• P. Marcus and M. Moscatelli, The Role of Alloyed Molybdenum in the Dissolution and the Passivation of Nickel-Molybdenum Alloys in the Presence of Adsorbed Sulfur, J. Electrochem. Soc., Vol. 136, No. 6, pp. 1634 - 1637, 1989

• S. Mohanty, T. J. McCartin and D. W. Esh, Total-system Performance Assessment (TPA) Version 4.0 Code: Module Description and User’s Guide, Center for Nuclear Waste Regulatory Analyses, San Antonio, TX, 2002

• T. Okada, Halide Nuclei Theory of Pit Initiation in Passive Metals, J. Electrochemical Society, Vol. 131, p. 241 - 247, 1984

• A. Passarelli, D. Dunn, O. Pensado, T. Bloomer and T. Ahn, Risk Assessment of Uniform and Localized Corrosion of Alloy 22, Met. and Mat. Trans. A, Vol. 36A, pp. 1121 - 1127, 2005

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References (Continued)

• O. Pensado, Corrosion Model to Support Total System Performance Assessments, NWTRB Workshop on Localized Corrosion of Alloy 22 in Yucca Mountain Environments, Las Vegas, NV, September 25-26, 2006, NRC ADAMS ML062640354, 2006

• O. Pensado, D. S. Dunn, G. A. Cragnolino, and V. Jain, Passive Dissolution of Container Materials - Modeling and Experiments, CNWRA 2003-01, Center for Nuclear Waste Regulatory Analyses, San Antonio, Texas, 2002

• E. Smailos, Corrosion of High-Level Waste Packaging Materials in Disposal Relevant Brines, Nuclear Technology, Vol.104, p.343-350, 1993

• N. Sridhar and G. Cragnolino, Evaluation of Analogs for the Performance Assessment of High-Level Waste Container Materials, CNWRA 2002-02, Center for Nuclear Waste Regulatory Analyses, San Antonio, TX, 2002

• M. Urquidi-Macdonald and D. D. Macdonald, Transients in the Growth of Passive Films on High Level Nuclear Waste Canisters, in European Federation of Corrosion Publications, No. 36, Prediction of Long Term Corrosion Behavior in Nuclear Waste Systems, ed. by D. Feron and D. D. Macdonald, pp. 165 - 178, 2003

• M. Urquidi-Macdonald and D. D. Macdonald, Theoretical Distribution Functions for the Breakdown of Passive Films, J. Electrochemical Society, Vol. 134, P. 41, 1987

• U. S. Nuclear Regulatory Commission, Yucca Mountain Review Plan, NUREG-1804, Revision 2, Washington, D. C., 2003

• J. C. Walton, G. Cragnolino and S. K. Kalandros, A Numerical Model of Crevice Corrosion for Passive and Active Metals, CorrosionScience, Vol. 38, p. 1-18, 1996

• L. Yang, D. Dunn, G. Cragnolino, X. He, Y.-M. Pan, A. Csontos and T. Ahn, Corrosion Behavior of Alloy 22 in Concentrated Nitrate and Chloride Salt Environments at Elevated Temperatures, NACE CORROSION 2007 CONFERENCE & EXPO, Paper No. 07580, NACE International, Houston, TX, 2007