Development of Chloride- Induced Stress Corrosion …€¦ · • 1999 St. Lucie Type 304 stainless steel ECCS suction piping ... review process and additional ... Criteria define

© 2016 Electric Power Research Institute, Inc. All rights reserved.

Shannon Chu

Senior Technical Leader

International Light Water Reactor Materials

Reliability Conference and Exhibition

August 2-4, 2016

Development of Chloride-

Induced Stress Corrosion

Cracking (CISCC) Aging

Management Guidelines

5-19-2016

2© 2016 Electric Power Research Institute, Inc. All rights reserved.

Chloride-Induced Stress Corrosion Cracking (CISCC) of stainless steel reactor components has occurred when three elements are all present:

– Tensile stress

– Susceptible Material

– Corrosive Environment

Surface contamination by atmospheric chlorides

Sufficient humidity (deliquescence)

EPRI has a multi-year project to

– Evaluate susceptibility to CISCC for welded stainless steel used fuel canisters

– Develop related aging management guidelines

– Evaluate the consequences of through-wall CISCC in used fuel canisters

CISCC

Tensile

StressSusceptible

Material

Corrosive

Environment

SCC


EPRI and NRC modeled WRS, reasonable agreement in results

Sufficient stress in canister welds to support CISCC, through wall tensile stress is present

Tensile Stress - Welding Residual Stress


Susceptible Material – SS 304 and 316

Type 304 Specimens Deposited With 1 g/m2 Salt

Held at 52 °C [136 °F] for 8 Months (NUREG/CR-7170)

CISCC of Stainless Steels Operating Experience (Not Complete List)

• 1999 St. Lucie Type 304 stainless steel ECCS suction piping

• 2001 Koberg (South Africa) 304L stainless steel tanks

• 2005 Turkey Point 304 stainless steel spent fuel pool cooling line

• 2009 SONGS Type 304 stainless steel piping (3 separate locations)

(NRC Information Notice 2012-20)

Type 316L Specimen

Treated with Salt Fog and

Held At 43 °C [109 °F] for 32

Weeks (NUREG/CR-7030)


• Chloride sources include breaking ocean waves, cooling tower drift, road salt; no established lower bound threshold chloride areal surface concentration for CISCC

• Canister surface temperatures that are about 30°C [ 86 °F] above ambient or lower may lead to aqueous conditions due to deliquescence at high local humidities

• CISCC propagation rates increase with higher temperature

• Fastest propagation would tend to occur on surfaces that are just cool enough to sustain deliquescent brine

Corrosive Environment (?)

Stress Corrosion

Cracking

Deliquescence of

Chloride


2015 2016 2017 2018 and beyond

EPRI Reports

CISCC Susceptibility Assessment Criteria

Aging Management

Guidelines

Canister Mitigation and Repair Technology

Field Data Compilation and Assessment

Flaw Growth & Flaw Tolerance

Assessment

CISCC Test Programs and Model Development

Collaborative Research and Development Efforts

Voluntary Surface Sampling and Environmental Monitoring

Nondestructive Examination Techniques & Delivery Systems

Chloride-Induced Stress Corrosion Cracking R&D

NEI Guidance for Operations-Based Aging Management for Dry Cask Storage, Rev. 1

Visual Examinations of Canister Surfaces

ASME Task Group on Inservice Inspection of Spent Fuel Storage & Transportation Containments

Canister Breach Risk and Consequence Assessment

Confinement Breach Consequence Analysis


CISCC Initiation & Growth Testing, Modeling

Testing results generally not considered representative of field conditions

– Cold work, stress/strain higher than expected in order to accelerate testing

– Humidity/Cl deposition (field concentrations unknown, complex behavior of

brines on surfaces)

Some continuing CISCC initiation and growth testing, very limited scope

Developing consensus on testing approach remains challenging

– Scale and scope of need much greater than available resources

– Sandia National Laboratories, Evaluation of the Frequencies for Canister

Inspections for SCC (February 2, 2016)

Identifies significant limitations of existing flaw growth models and

associated experimental crack growth data

Outlines significant differences among currently proposed flaw growth

models, including EPRI’s flaw growth model


Voluntary Surface Sampling and Environmental Monitoring

Past efforts collected surface samples from canisters at 3 sites, many challenges

to evaluating the data, did find very small amounts of chloride present

Two volunteer sites are continuing with projects to collect samples from surrogate

stainless steel surfaces, one site also using wet candle and filter methods to

monitor environmental chlorides

Chloride aerosol concentration is measured by dozens of EPA sites across the

U.S.


Field Data Compilation and Assessment

CISCC aging management approach will require consideration of new data and

results as they become available

Operating Experience and Inspection Results

– ISFSI Aging Management INPO Database (AMID)

Environmental Monitoring, Laboratory Testing Results and Other Research

– EPRI Extended Storage Collaboration Program (ESCP)


Canister Breach Risk and Consequence Assessment

NRC Public Meeting: Discussion of risk-informing framework for spent fuel

storage certification and licensing activities held April 28, 2016

Expect continued collaboration of NRC, EPRI, NEI, and cask vendors via

Regulatory Issue Resolution Protocol (RIRP)

EPRI has current project to evaluate available risk information (PRAs, dose

assessments, failure mode analyses) and define scope of additional work needed

for consequence analysis that is specific to through-wall CISCC of one or more

dry storage canisters


ASME Boiler Pressure Vessel Section XI Task Group on

In-service Inspection of Spent Fuel Storage and

Transportation Containments

Task group was formed at the request of the Nuclear Regulatory Commission

Developing the final recommendations for canister inspection scope, methods,

frequency, and acceptance criteria

EPRI participating and intending our aging management guidance to be a

significant resource

Targeting 2019 for a final code case with recommendations


Canister Mitigation and Repair Technology

Evaluating technologies applied to operating components for relevance to

canisters

Interested in uniquely applicable technologies (cleaning)

CRIEPI has specifically considered application of peening for dry storage

canisters

Challenges

– Competitive/proprietary issues among cask vendors

– Surface of canisters already in service is exposed to environment but is not

readily physically accessible


NDE and Delivery System Development

Dry Canister Storage System Inspection and Robotic Delivery System Development

– A prototype robotic delivery system has been developed that is capable of entering vertical dry storage cask designs. Future design iterations are planned to enter horizontal cask designs.

– The robotic system has been successfully deployed into two empty cask systems with an NDE payload.

– NDE inspection development has shown significant potential to identify defects in canisters.

EPRI NDE and delivery system demonstrations in 2016

– McGuire May 16

– Maine Yankee July 11

EPRI mockups available for testing NDE technologies

Vendor development of visual and UT inspection capabilities is also proceeding, coordinating efforts via ESCP subcommittee


Format, Content, and Implementation Guidance for Dry

Cask Storage Operations-Based Aging Management (NEI

14-03 Rev. 1)

Introduces “tollgates” and “learning aging management”

Tollgates obligate the licensee to perform periodic assessments of the aggregate

state of knowledge of aging-related operational experience, research, monitoring,

and inspections to ascertain the ability of dry cask storage structures, systems

and components (SSCs) to continue performing their intended safety functions

throughout the period of extended operation

NRC endorsement requested, review process and additional information

exchange is on-going


EPRI Susceptibility Assessment Criteria

Criteria define site conditions and canister parameters associated with earlier potential for CISCC initiation and growth based on literature review, failure modes and effects analysis, and flaw growth and tolerance assessment

Criteria allow ranking of canisters to set priorities for inspection and other aging management efforts in order to direct resources to sites where CISCC is more likely to occur, limited guidance on use of ranking criteria to identify canisters that are considered “bounding”

ISFSI Susceptibility Ranking

– Proximity to chloride source and local absolute humidity are key variables

Canister Susceptibility Ranking

– Intended to identify canister(s) to be inspected at a given site and to guide scope expansion if needed

– Geometry (horizontal or vertical) affects locations of maximum chloride deposition and locations of minimum temperature, canisters with different geometries are ranked separately

– Canister material, storage duration, and current canister power are key variables


EPRI CISCC Aging Management Guidance

Consider risk-informed and learning approaches

Use Susceptibility Assessment Criteria in setting recommended inspection scope

and expansion criteria

Provide criteria for timing of initial inspection (20 years + delay)

Provide inspection acceptance criteria

Include details of confinement integrity assessment as an appendix

– This assessment compares the relative probability of through-wall CISCC for

various inspection regimes and parameters to a “no-inspection” case

Discuss mitigation and repair in an appendix

Significant reference/resource for ASME Task Group on ISI of Canisters

Continued effort to support ASME Task Group and provide implementation

training after publication


Together…Shaping the Future of Electricity

Documents

Development of Chloride- Induced Stress Corrosion …€¦ · • 1999 St. Lucie Type 304 stainless steel ECCS suction piping ... review process and additional ... Criteria define