Stress Corrosion Cracking (SCC):M d l f C k O i AModels for Crack Opening Area

Tae Ahn and Jack GwoU S NRCU.S. NRC

For Waste Container Corrosion WorkshopWaste Container Corrosion Workshop

June 16, 2011

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Disclaimer

The 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 any licensing action that may beaddressed or of the acceptability of any licensing action that may be under consideration at the NRC.

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Outline

• Models:- Base assumptions- Disruptive seismic casep- Nominal case- Data and SOAR results in disposal system

• Other Applications:- Marine SCC of stainless steel- Cladding failureg

• Summary and Future Work

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Crack Network from SCC

• Maximum crack density (SNL, 2007)

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Stress Analysis with Crack Network

• Dimensions of the plate and setup for the analysis (left)• Longitudinal stress distribution along center with 2 inch spacing between cracks (right)

(Structural Integrity Associates 2002) 1 in = 2 54 cm; 1 ksi = 6 9 MPa(Structural Integrity Associates, 2002), 1 in 2.54 cm; 1 ksi 6.9 MPa

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Model for Estimate of Maximum Crack Opening Area

• Stress Based Model for Stress Corrosion Cracking (SCC) under Seismic Conditions

- Impact stress is imposed on the canister, forming deformed area and crack formation (SNL, 2007a; SNL, 2007b). The crack area density per unit deformed area is expressed by

δ C /Eδ = C σ/E

δ: crack areal density (m2/m2)σ: applied stress (MPa)E: Young’s modulus (MPa)C: geometric constant

- Each crack area is the crack length times crack width, which is proportional to the square of canister thickness; and the number of cracks is inversely proportional to the square of the canister thickness.

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Model for Estimate of Maximum Crack Opening Area (continued)

- The model is conservative, because a maximum geometric number of cracks wasconsidered based on the numerical analysis that the crack spacing cannot be shorter than the canister thickness (Structural Integrity Associates, 2002).shorter than the canister thickness (Structural Integrity Associates, 2002).

- Under nominal conditions, the deformed area can be determined by weld area and residual weld stress is applied.

Ratio of Stress and Young’s Modulus for Various Metals (used in Gwo, et al, 2011), 1 MPa = 0.145 ksi

YS (MPa) E (MPa) x 10-3 YS/E (mean) ( ) ( ) ( )x 103

Stainless Steel 170 - 310 193-207 1.2

Carbon Steel 207 207 1.0

C 70 310 108 117 1 7Copper 70-310 108-117 1.7

Zircaloy 241 99 2.4

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Model for Estimate of Maximum Crack Opening Area (continued)

- The results of the numerical analysis of crack spacing was not critical to Young’s modulus and Poisson’s ratio, and the tested stress was arbitrary in the range of 207 MPa (30.0 ksi) (Structural Integrity Associates, 2002).

- The residual weld stress of candidate alloys is a maximum of (402 – 670) MPa (60 -100 ksi) (not mitigated) (EPRI, 2005).

- The Heat Affected Zone (HAZ) in weld area is in a range of (0.6 – 1.8) mm(0.024 – 0.071 in) (EPRI, 2005). Metal Handbook (ASM International,1994) present analogue data on weld and HAZ in the range of (2x103 to 4x104) cm2 per (2-3)x105

cm2 [3.1x102 to 6.2x103) cm2 per (3.1 – 4.7)x104 in2 ].cm [3.1x10 to 6.2x10 ) cm per (3.1 4.7)x10 in ].

- In the nominal case, the flaw size distribution will be also used to assess the stressintensity factor associated with each flaw in the weld. If the density of cracks that can grow is more than that from the uniform density of cracks described above thecan grow is more than that from the uniform density of cracks described above, themaximum uniform density will be used.

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Release Estimate through Opening Area in Aqueous Environment

History of mean waste package mechanically damaged area by seismicity in a repository with (dashed lines) and without (solid lines) backfill (Gwo, et al., 2011)

Mean release rates of radionuclides away from the boundary of the near field into far field for the seismic ground motion test case (solid lines) and the baseline test case (dashed lines) (Gwo, et al., 2011)(dashed lines) (Gwo, et al., 2011)

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Marine Stress Corrosion Cracking of Stainless Steel: Japan Program

(Shirai, et al., 2011a,b; Tani, et al., 2010)

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Marine Stress Corrosion Cracking of Stainless Steel: Japan Program (Continued)

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Hydride Cracking in Cladding Materials

Circumferential HydridesCladding

• Circumferential hydrides can be reoriented radially under appropriate temperature andstress decreasing fract re to ghness and fract re strength (Ch ng 2004)stress, decreasing fracture toughness and fracture strength (Chung, 2004).

• Flaws on the inner or outer surface may draw hydrogen by diffusion, that may lead tocrack propagation. It may happen in high burnup spent nuclear fuel (Chung, 2004).

• The area opening by cracks could be similar to stress corrosion cracking, unless longitudinal unzipping occurs by the stress imposed by the corrosion products ofcladding materials or the matrix of spent nuclear fuel.

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Summary

• SOAR model for disruptive event was well accepted (e.g., IHLRWMC paper, Gwo, et al., 2011).

• Furthered in rationalizing base assumptions on the model with materials properties, extending tothe nominal casethe nominal case

• Gap analysis results are potentially applicable for various types of candidate metals and disposal systems. They include carbon steel, stainless steel, copper, titanium, and nickel-based alloys, in mild, near neutral pH, reducing environment, salt environment, and alkaline environment.

• Exchanged effectively with related projects such as storage canister corrosion and cladding failure of spent nuclear fuel

• Started to establish data base from the limited availability• Started to establish data base from the limited availability

• Started communications with international communities (e.g., JAEA, Japan)

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Future Plan

• Assess rigorously base assumptions for various materials properties.

• Assess more realistic cases (e.g., crack density)

• Collect more data from industry experience for various materials

Sh k l d ith k t i t l ddi f t l f l th l t d• Share knowledge with work on storage canister, cladding of spent nuclear fuel, or other related projects, for mutual benefits

• Conduct international exchange (CRIEPI, JNES, JAEA of Japan, EC ITU, and Manchester, UK)

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References

ASM International (The Materials Information Society), ASM Handbook, Volume 2. Properties and Selection: Nonferrous Alloys and Special-Purpose Materials, 1990.

Chung, H. “Understanding Hydride- and Hydrogen-Related Processes in High-Burnup Cladding in Spent-Fuel-Storage and Accident Situations Proceedings of 2004 International Meeting on LWR FuelSpent-Fuel-Storage and Accident Situations, Proceedings of 2004 International Meeting on LWR Fuel Performance, Orlando, Florida, September 19-22, Paper No. 1064, 2004.

Electric Power Research Institute (EPRI), “Effects of Marine Environments on Stress Corrosion Cracking of Austenitic Stainless Steels,” EPRI 1011820, 2005 [available at http://www.epri.com].

Gwo, J., T. Ahn, and X. He, “Modeling Disruptive Events Using the β-SOAR Model: Levels of β-SOARModel Flexibility in Applications and Initial Insights,” Proceedings of 2011 International Radioactive Waste Management Conference (IHLRWMC), Albuquerque, New Mexico, April 10–14, pp 867 874 2011pp. 867–874, 2011.

Sandia National Laboratories (SNL), “Stress Corrosion Cracking of Waste Package Outer Barrier andDrip Shield Materials,” ANL-EBS-MD-000005 REV 04 ERD 2, 2007a.

SNL, “Seismic Consequence Abstraction,” MDL-WIS-PA-000003 REV 03 ERD 1, 2007b.

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References (continued)

Shirai, K., M. Wataru and T. Saegusa, “Long-Term Containment Performance test of Metal Cask,” Proceedings of 2011 International Radioactive Waste Management Conference (IHLRWMC), Albuquerque, New Mexico, April 10–14, Paper No. 3332, 2011a.

Shirai K J Tani T Arai M Wataru H Takeda and T Saegusa “SCC Evaluation of Multi-PurposeShirai, K., J. Tani, T. Arai, M. Wataru, H. Takeda, and T. Saegusa, SCC Evaluation of Multi-PurposeCanister,” Proceedings of 2011 International Radioactive Waste Management Conference (IHLRWMC), Albuquerque, New Mexico, April 10–14, Paper No. 3333, 2011b.

Structural Integrity Associates, “Structural Integrity Associates Support of Waste Package Design Year 2001,“ License Support Network (LSN), DEN001314737, 2002.

Tani, J., K. Shirai, M. Wataru and T. Saegusa, “Stress Corrosion Cracking of Stainless Steel Canister of Concrete Cask,” International Seminar on Interim Storage of Spent Fuel (ISSF) 2010, Central Research Institute for Electric Power Industry Tokyo Japan 2010Central Research Institute for Electric Power Industry, Tokyo, Japan, 2010.

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