ML24107B036

The U.S. Nuclear Regulatory Commission Sponsored Projects on Chloride-Induced Stress Corrosion Cracking

ML24107B036
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Issue date:	05/31/2024
From:	Darrell Dunn NRC/NMSS/DFM/MSB
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Download: ML24107B036 (1)

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NRC Sponsored Projects on Chloride-Induced Stress Corrosion Cracking Darrell Dunn NRC/NMSS/DFM/MSB

Outline

• Completed projects - inspection and mitigation

• Current projects - Chloride-induced stress corrosion cracking (CISCC) risk assessment o CISCC growth rate testing o Probabilistic assessment of CISCC

• Guidance development o New Regulatory Guide for ASME Section XI code cases applicable to 10 CFR Part 72 licensees and certificate of compliance holders

• Public outreach o CISCC consequence analysis NEI UFMC May 2024 2

CISCC Testing Observations

• Faster crack growth rates in magnesium chloride compared to sodium chloride

• CISCC growth rates dependent on

• temperature

• stress intensity

• relative humidity

• chloride concentration

• nitrate to chloride ratio Nitrate is an effective inhibitor for CISCC PNNL-32455 PNNL-Recommended CISCC Growth Rate Evaluation Test Plan for the NRC Update #1, January 2022 NEI UFMC May 2024 3

Probabilistic Assessment of CISCC SAND2024-01093, Assessing Uncertainty in Modeling Stress Corrosion Cracking January 2024

• Compared crack growth rate (CGR) models typically used in CISCC

• Evaluated 3 parameters o Limiting relative humidity for corrosion initiation (RHL) o Salt deposition rate (DD),

o threshold crack tip stress intensity factor (Kth)

DD > Kth > RHL NEI UFMC May 2024 4

ASME N-860

• Applies only to welded austenitic stainless steel canisters

• Assumes that chloride-induced stress corrosion cracking (CISCC) is the most credible and bounding degradation mechanism

• Uses EPRI-3002005371, Susceptibility Assessment Criteria for CISCC of Welded Stainless Steel Canisters for Dry Cask Storage Systems, to set initial inspection population

• CISCC ranking: ZISFSI = Clstarting + Cladj + AHadj

• High rank site: ZISFSI 8

• Low rank site: ZISFSI 7

• Inspection interval can be increased from 10 to 20 years for low rank sites with no indications CISCC NEI UFMC May 2024 5

Locations and ZISFSI Values 71 operating ISFSI sites with 3755 welded austenitic stainless steel DSS in use as of December 2023 ZISFSI = Clstarting + Cladj + AHadj EPRI-3002005371 ZISFSI ISFSI sites (estimated)

DSSs (estimated) 1-3 60 3,148 4-7 6

295 8-10 5

312 NEI UFMC May 2024 6

Risk Assessment for ZISFSI 3 Sites

• Atmospheric CISCC has occurred at locations that are less than 1 km from a marine shoreline (NRC Information Notice 201220, ML12319A440)

• ZISFSI 7

• Composition of salt deposits at ISFSI sites with ZISFSI 3 are not expected promote CISCC

• Assuming CISCC could occur, CISCC propagation ZISFSI 3 sites would proceed slowly SAND202306366J, Considerations for Realistic Atmospheric Environments: An Application to Corrosion Testing, R. M.

Katona, A. W. Knight, M. Maguire, C. R. Bryan, and R. F. Schaller.

NEI UFMC May 2024 7

New Regulatory Guide 3.78 Regulatory Guide (RG) 3.78, Acceptable ASME Section XI Inservice Inspection Code Cases for 10 CFR Part 72

• RG 3.78 will be published for public comment as Draft Guide (DG) 3058

• Future acceptable ASME Section XI Code Cases applicable to 10 CFR Part 72 Licensees and Certificate of Compliance holders

• Will include ASME Code Case N860, Inspection Requirements and Evaluation Standards for Spent Nuclear Fuel Storage and Transportation Containment SystemsSection XI, Div. 1;Section XI, Div. 2.

• DG3058 includes alternative inspection intervals of up to 40 years for ZISFSI 3 sites NEI UFMC May 2024 8

Consequence Analysis for CISCC Initial assessment

• Risk assessment for accidents are bounding for CISCC consequences

• Site boundary doses are below regulatory limits Current effort

• GoldSim Monte Carlo simulation software model under development

• Conduct simulations to understand the importance of input parameters GoldSim CISCC consequence analysis model user interface NEI UFMC May 2024 9

Reports

• PNNL24412 Rev. 1: Nondestructive Examination Guidance for Dry Storage Casks, September 2016, ML16228A081

• PNNL28427: Evaluation of Nondestructive Examination Responses from Chloride-Induced Stress Corrosion Cracks, September 2019, ML19255B838

• PNNL28643: Dry Storage System Test Facility for Evaluating Canister Inspection Technologies, September 2019, ML19269B757

• PNNL29774: PNNL-Recommended CISCC Measurement Test Plan for the NRC, April 2020, ML20084K352

• PNNL30001: Inspection Technology Demonstration on Dry Storage System Test Facility Flaw Sizing Demonstration, September 2020, ML20275A004

• PNNL28643: Assessment of Cold Spray Technology for Nuclear Power Applications, March 2021, ML21263A107

• PNNL32455: PNNL-Recommended CISCC Growth Rate Evaluation Test Plan for the NRC Update #1, January 2022

• SAND202401093: Assessing Uncertainty in Modeling Stress Corrosion Cracking January 2024

• PNNL35667: CISCC Testing of 300 Series Stainless Steels Test Results From Concentrated Salts, October 2023 NEI UFMC May 2024 10

NRC Sponsored Projects on Chloride-Induced Stress Corrosion Cracking Darrell Dunn NRC/NMSS/DFM/MSB