Safety Evaluation Review of Topical Report for PWSCC ... · – for Alloy 82/182 DMWs, a...

© 2015 Electric Power Research Institute, Inc. All rights reserved.

Materials Reliability Program (MRP)

NRC Public Meeting - Rockville, MD

January 21, 2015

Safety Evaluation Review of Topical

Report for PWSCC Mitigation by Peening

(MRP-335, Revision 1)

2© 2015 Electric Power Research Institute, Inc. All rights reserved.

Introduction and Purpose

Richard Clemens - Wolf Creek


Purpose

Present Industry’s positions that:

The technical basis already in the topical report and references is sufficient

for SE

• Additional confirmatory testing is not needed to support SE

Will be performed under Appendix B process controls

• Min/max essential variables not needed for standardization

• Performance criteria approach combined with 10 CFR 50 Appendix B

Criterion IX are appropriate and follow ASME Code Case precedent

SE desired mid-2015 to support industry application in 2016

• Originally scheduled to be completed by April 2015


Basis for conclusion that the technical basis

for efficacy is sufficient for SE

Glenn White - Dominion Engineering, Inc.


Sufficiency of Existing Technical Basis

Data and Research

Operating Experience

Nuclear Risk and Leakage Risk Met Conservatively


Sufficiency of Existing Technical BasisData and Research

Extensive vendor testing of peening effectiveness, including

– Stress measurements of mockups

– Corrosion tests including in simulated primary water

• With and without pre-existing flaws

– Long-term sustainability testing

• Thermal stress relaxation

• Load cycling

Independent confirmatory testing sponsored by EPRI

– Stress measurements

– Long-term sustainability testing


Sufficiency of Existing Technical BasisData and Research - Testing Documented in MRP-267R1 Demonstrating Peening Effectiveness

Performance criteria are applied to assess peening mitigation:– The residual stress in the surface region following peening is compressive to a

specified depth

– The total stress (residual plus operating) is within limits to prevent PWSCC

initiation in service

– The full area of material considered susceptible is effectively mitigated

– Analyses and testing confirm the resistance to PWSCC initiation on the treated

surface

– Analyses and testing demonstrate that the specified stress condition is maintained

for the remaining component operating life


Stress measurements by XRD with progressive electropolishing and strain gauge adjustment

The measured samples represented a wide range of initial residual stress conditions prior to

peening

Flat plate samples of nickel-based alloys (Alloy 600, Alloy 132, Alloy 182) and stainless steels

(304 and 316L) were peened with ULP, ALP, or WJP

– Plate and welded plate samples

– Residual stress was compressive to a depth of at least 1.0 mm

Mock ups of BMNs were constructed of Alloy 600/82/182 and the BMN ID, OD, and J-groove

weld were peened with ULP or WJP

– Residual stress was compressive to a depth of at least 1.0-1.5 mm in most cases

– For WJP of the inner surface of BMNs, the residual stress was compressive to a depth of

about 0.5 mm

Sufficiency of Existing Technical BasisData and Research - Residual Stress Measurement


Sufficiency of Existing Technical BasisData and Research - SCC Testing

Testing was performed by the LP and WJP vendors, as well as by an independent

lab (AREVA) sponsored by EPRI

Various samples with no pre-existing flaws were tested in various corrosive

environments

– SCC was detected in unpeened samples but not peened samples

Various pre-cracked coupons were peened and subjected to various SCC

environments

– Shallow cracks located in the compressive stress zone were effectively mitigated

– Cracks significantly deeper than the compressive zone tended to grow at a rate

similar to that for unpeened samples

WJP was applied to temper-colored, pre-cracked coupons

– No growth of the pre-existing cracks due to the WJP application itself was

observed


Sufficiency of Existing Technical BasisData and Research - SCC Testing Mitigation of Growth of Pre-Existing Cracks (Data provided by MHI)

Alloy 600/316SS Weld Plate Samples Treated by WJP

USP


Sufficiency of Existing Technical Basis Data and Research - Thermal Exposure and Load Cycling Testing (NRI) - Independent Testing Sponsored by EPRI

Evaluated the stress relaxation of a peening-induced compressive stress layer at and close to

the sample surface under the influence of load cycling and operating temperature

Samples manufactured at NRI from Alloy 600 plate material supplied by EPRI

Samples subject to different peening procedures by different vendors, with one set tested in

as-manufactured condition

Tested in an autoclave loop filled with simulated PWR water at 300°C for different numbers of

cycles

– Each cycle consists of a slow ramp-up to three fourths of yield strength, 10 day holding

period, and slow ramp-down to a load of zero


Sufficiency of Existing Technical BasisData and Research - Corrosion Testing (AREVA) - Independent Testing Sponsored by EPRI

Alloy 182 weld deposits on Alloy 600

specimens were used to make U-bends

U-bends were treated with WJP, ULP, or ALP

U-bends were exposed to simulated PWR

water at 360°C for 3000 hours over two

phases of experimentation

U-bends treated with ULP, ALP, or WJP did

not have any cracks detected following PWR

water exposure

Spring Loaded U-Bend

ULP, WJP, and ALP are effective for mitigating PWSCC in heavily cold worked weld metal


Sufficiency of Existing Technical BasisOperating Experience

Over a decade of implementation in BWRs and PWRs for mitigating PWSCC in Alloy 600/82/182/132

– Water Jet Peening

– Laser Peening

Extensive additional PWR experience with other peening methods

– Abrasive water jet (AWJ) peening

– Shot peening of steam generator tubing

– Pressurizer heater sheaths

– Alloy 718 fuel assembly screws

Applied in other industries for safety critical components, asset

management, and material performance improvement


Sufficiency of Existing Technical BasisOperating Experience - Peening Mitigation in Japanese PWRs and BWRs

Japanese PWRs (starting in 2001)

– At least 23 out of 24 PWR units have applied WJP or ULP to BMNs and/or RV inlet/outlet

nozzle DMWs

– WJP and ULP have also been applied to RV safety injection nozzles

– Ultrasonic Shot Peening (USP) has been applied to

Steam generator inlet or outlet nozzles at more than 10 PWRs

9 replacement RV heads with Alloy 690 nozzles

Japanese BWRs (starting in 1999)

– WJP and ULP have extensively been applied to core shrouds and bottom head

penetrations (i.e., CRD stud tubes)

– Applying to new ABWR units during the fabrication and construction phases


Sufficiency of Existing Technical BasisNuclear Risk and Leakage Risk Met Conservatively

Deterministic and probabilistic analyses were used to determine

appropriate inspection requirements for Alloy 82/182 piping butt welds

and RPVHPNs mitigated by peening

Deterministic analyses assess the effect of peening on crack growth as

a function of time for various crack types at different locations

Probabilistic analyses assess the effect of peening on the probability of

pressure boundary leakage or rupture assuming reduced frequency of

inspection– Component loading including effect of peening on residual stress field

– PWSCC crack initiation

– PWSCC crack growth

– Simulation of various inspections including UT, ET, and direct visual exam (VE)

Main probabilistic cases do not take any credit for ET exams


Sufficiency of Existing Technical BasisNuclear Risk and Leakage Risk Met Conservatively - Conclusions

Deterministic analysis shows that peening eliminates or slows

growth for cracks that are sufficiently shallow

Probabilistic analyses show that peening mitigation with the

recommended inspection requirements and intervals results in:– for Alloy 82/182 DMWs, a probability of leakage that is greatly reduced compared to that for no

mitigation and standard intervals, demonstrating a much reduced probability of a flaw reaching its

critical size

– for RPVHPNs, an acceptably low nozzle ejection frequency (per the approach of MRP-105), and

also a nozzle ejection frequency that is close to that calculated for no mitigation and standard

intervals (i.e., risk neutral)

Probabilistic analyses include significant conservatisms such

that benefits of peening tend to be under predicted

No safety issues associated with peening


ASME Code and Standards

Richard Gimple - Wolf Creek



Performance Based Standard vs Prescriptive Standard:

– A performance based standard focuses on desired characteristics

of the final product, service or activity rather than requirements for

the processes to produce it

Performance criteria specify the objectives that when met assure

the final outcome is sufficient

Appropriate for activities where proprietary information is involved

Encourages innovation and allows adaptation to improvements

and alternative processes/techniques

– Initially identified for the appropriate approach in N-770 for MSIP



Code Case N-770-4 integrated peening mitigation performance criteria

appropriate for reduced inspection requirements

Performance criteria approach similar to that taken for MSIP was used

Japanese experience, Japanese JANTI VIP-03 and presentations by

representatives of MHI and Hitachi provided International input for ASME

Technical basis provided through MRP-267 and MRP-335 and PVP papers

Peening performance criteria and pre- and post-peening examinations

evaluated and approved through the consensus process

Approved by the ASME Code as Code Case N-770-4 on May 7, 2014

Significant International experience and review in Japan by JANTI

Strong fully vetted technical basis by EPRI and PVP

Take-away from ASME process: significant technical basis with over 10 years of application

experience, ASME determined this is not a Repair/Replacement activity requiring codification of the

process, performance criteria is the appropriate approach for proprietary peening techniques



Draft Code Case N-729-5 highlights:

– Maintains the performance criteria approach used in Code Case N-770-4

– Utilizes the same technical basis for the process with additional analysis

specific to the impact of the RVH penetration inspection

– Adjusts performance criteria where needed to account for different

configurations of RVH penetrations

Same approach as ASME Code as Code Case N-770-4

Strong technical basis (same as CC N-770-4)

Location specific analysis of peening application on inspection requirements to ensure no

increase in safety risk relative to the current inspections of unmitigated penetrations

Take-away: significant Industry support, strong technical basis, an improved safety (risk of

failure) position, not an ASME Repair/Replacement activity


Implementation Guidance for Consistency

Jeff Wilson - Exelon


Peening Process – Development to Implementation

COMPRESSIVE

DEPTH

COVERAGE

AREA

IMPLEMENT PEENING UNDER

SPECIAL PROCESS CONTROLS

(10 CFR 50 APPENDIX B

CRITERION IX)

---

QUALITY RECORDS VALIDATE

PROCESS WITHIN ESSENTIAL

VARIABLE LIMITS

---

LICENSEE REVIEWS /

APPROVES PEENING

EFFECTIVENESS

---

PROCESS / RESULTS SUBJECT

TO NRC INSPECTION

DEVELOP PEENING TECHNICAL

BASIS

---

ESTABLISH PROCESS

SPECIFIC ESSENTIAL

VARIABLES

---

CONFIRM "PERFORMANCE

CRITERIA" MET (i.e. PROCESS

EFFECTIVE)

---

DEVELOP SPECIAL PROCESS

CONTROLS / PROCEDURES

(10 CFR 50 APPENDIX B

CRITERION IX)

---

LICENSEE REVIEWS /

APPROVES PROCESS

PROCESS

DEVELOPMENT /

VALIDATION

INFIELD PROCESS

IMPLEMENTATION

PERFORMANCE CRITERIA

COMPRESSIVE

STRESS


Implementation Guidance for ConsistencyPeening Process Control

Peening vendors will be required to meet stress magnitude and depth

requirements, and peening coverage requirements

Peening vendors will be required to establish and provide essential

variables and associated ranges of acceptable application-specific values

– Part of the controlled special process procedures submitted for licensee pre-

implementation approval

– Will ensure that specified stress and coverage requirements are met

– Essential variables will be unique to the peening technology offered and specific

to each vendor and type of component being peened

Control by the peening vendor of the essential variables particular to the

peening technology utilized and the satisfaction of the performance

criteria result in a robust mitigation process


Implementation Guidance for ConsistencyPeening Process Control

Evaluation of peening application to RCS pressure boundary locations under 10 CFR 50.59

found:

No analysis or procedure identified in the Safety Analysis Report is expected to be adversely

affected

No accident condition or scenario in Safety Analysis Report is expected to be adversely

affected

• If anything, loss of pressure boundary conditions or scenarios are in a better safety

position following the application of peening.

Control of the Peening Process is not a safety issue and should be treated consistent with other

maintenance and repair activities at the Site under 10 CFR 50 Criterion IX. Control of Special

Processes

Other activities typically performed under this criterion are Freeze Sealing, Welding,

Soldering, Leak Stop Injection of Gasketed Joints to name a few


Implementation Guidance for ConsistencyKey Peening Process Control Variables

Water Jet Peening

Nozzle Diameter

Jet stand-off distance and nozzle offset in ID

applications

Water flow rate

Application time

Impingement angle

Stationary nozzle time

Water level and water temperature

Laser Peening

Laser type

Pulse energy

Pulse repetition rate

Pulse duration

Laser spot footprint dimensions

Pulse layer count

• These lists of key variables are for WJP and LP processes that participated in EPRI’s R&D program

• Other, new or optimized surface stress improvement processes will have other key process control variables

• Essential variables are usually only a subset of the of the key process variables

• Performance criteria such as those in ASME Code are appropriate, sufficient and follow precedent for defining

the generic “end state” requirements that a surface stress process must achieve (e.g., depth, coverage, stress)


Implementation Guidance for ConsistencyPerformance Parameters

Component

ASME

Code Case

Surface Stress

Magnitude

Nominal Compressive

Residual Stress Depth Coverage Zone

Peened

Alloy 82/182

DMWs

N-770-4

Appendix I

Residual stress plus

nominal operating stress

on peened surface shall

be compressive

at least

0.04 in. (1.0 mm)

Entire wetted surface of

PWSCC susceptible

material including the

weld, butter, and base

material, as applicable

Peened

RPVHPNs

Draft

N-729-5

Appendix II

Residual stress plus

nominal operating stress

on peened surface shall

not exceed +10 ksi

Nozzle ID: at least

0.01 in. (0.25 mm)

Nozzle OD/weld: at

least 0.04 in. (1.0 mm)

Wetted surface of

attachment weld, butter,

and nozzle base

material (OD and ID)

that is susceptible to

PWSCC


Process Implementation

Gary Poling - AREVA

Note: Slides #28-33 are an EXAMPLE. Requirements are plant, process

and geometry specific. Processes other than AREVA’s will have different

essential variables and approaches for process qualification.

Application of UHP Cavitation Peening

Implementation as a Controlled Special Process Under an Appendix B Program

EXAMPLE

January 21, 2015

p.29

UHP Cavitation PeeningSpecial Process

Both qualification and implementation will be performed in

accordance with the AREVA Inc Quality Assurance Program

(QAP) for special processes

Complies with Criterion IX of 10 CFR 50, Appendix B, Control

of Special Processes and Requirement 9, Control of

Processes, of ASME NQA-1

p.30

UHP Cavitation PeeningQualification

The peening process effectiveness shall be demonstrated on

full scale representative mockups at the nominal, max and min

ranges of essential variables used for site implementation

Full scale nozzle mockups include material and geometry

constraints

X-ray diffraction will be used to determine the residual stress

on peened full scale representative mockups

Confirm the desired peening coverage has been achieved

Confirm the desired depth of compression has been achieved

A qualification report will be provided to the utility that

documents how all requirements are met for the Topical

Report / Relief Request / ASME Code

Essential Variable Range for Qualification Mockups and

Site Implementation are the same

p.31

UHP Cavitation PeeningEssential Variables

Nozzle

Water pressure

Standoff distance

Position

Velocity

Backpressure

Application specific

Essential Variables are Controlled and Monitored

p.32

UHP Cavitation PeeningImplementation

Essential variables are controlled/monitored to

ensure acceptable results are achieved

The tooling control system will record the value

of each essential variable

The electronic data will be reviewed/verified

post-process

Will be part of the archived record

The operator will have a real-time display of all

essential variables

If an essential variable gets outside of qualified

limits the operator is immediately alerted

Noise alarm

Flashing light

In – Process Verification / Post – Process Verification

p.33

UHP Cavitation PeeningSummary

The UHP Cavitation Peening process will be qualified and

implemented in accordance with the AREVA Inc., Quality

Assurance Program for special processes as approved by

the licensee

Essential variables will be ‘bounded’ during process

qualification on representative full scale nozzle mockups

Essential variables will be controlled/monitored during

implementation

Both in-process and post-process verification will be used to

confirm the desired results are achieved

A final report will be provided to the utility that documents

how all requirements were met


Exelon Application of Appendix B

Jack Feimster - Exelon


Exelon Application of Appendix B

Specification – Specify to meet the technical requirements of

MRP-335, ASME Code Case N-729-5, ASME Section XI and

Exelon implementation of Appendix B Criterion IX Special

Processes

Procurement – Contract will be Safety Related ensuring the

use of Vendor’s 10CFR50 Appendix B program

Oversight – Exelon will use contractor oversight procedure for

Safety Related work

Controls and Management – Vendor to manage critical

parameters and supply data that demonstrates compliance to

the specification


Topical Report Review Process:

Schedule

Paul Crooker - EPRI


NRC Schedule Evolution for MRP-335R1 Topical Report SE

Timeline

MRP submitted the topical report for review in February 2013

Fee exemption approved in April 2013

Acceptance Review started in August 2013

Acceptance Review completed in November 2013

In June 2014 Confirmatory Research was added on the SE

critical path delaying the SE by about 3 years

RAIs Issued

– Draft – June 30, 2014

– Final – September 2014

A public meeting was held on September 9, 2014, that

covered many issues including; confirmatory research, RAIs,

vendor meetings, performance parameters, inspection

requirements, and 50.59 implementation requirements

MRP submitted written RAI responses on October 10, 2014

Begin Acceptance Review – August 5

Acceptance Review or Denial Letter – Nov 15, 2013

RAI’s issues to EPRI – Apr 4, 2014

RAI responses back from EPRI – Jun 30, 2014

Draft SE issued to EPRI – Nov 21, 2014

Draft SE comments / draft update to TR – Jan 2, 2015

Final SE issued to EPRI – Apr 24, 2015

Final TR-A from EPRI – Jul 20, 2015

Final validation letter to EPRI – Aug 25, 2015

(~1 year between Issuing RAIs and Issuing Final SE)

NRC’s Schedule at Start of Acceptance Review in August 2013

September 2014 – EPRI to submit responses to NRC RAIs

NRC to review supplemental information

November 2014 – Follow up or new RAIs to EPRI

Summer 2017 – Draft SE for MRP-335 (~3 year delay)

NRC’s Schedule at Public Meeting in September 2014


Conclusions and Next Steps

William Sims - Entergy


Conclusions

It is the Industry’s position that:

The technical basis already in the topical report and references is sufficient for SE

Additional confirmatory testing is not needed to support SE

Will be performed under Appendix B process controls

Min/max essential variables not needed for standardization

Performance criteria approach combined with 10 CFR 50 Appendix B Criterion IX are appropriate and follow ASME Code Case precedent

It is impractical and inappropriate for NRC to specify acceptable ranges of essential process variables for each process

Vendor visits are encouraged for NRC staff

SE needed by mid-2015

Implementation begins in 2016


Next Steps

Close Open Actions

– NRC to establish a process and date when they will provide

requirements for inspection relief (due by end of 2014)

– NRC to provide updated schedule for SE (due by end of 2014)

– Schedule for peening vendor meetings

– Status and expedite review and response on RAIs

NRC feedback and response to Industry conclusions of

today’s public meeting


Closing

Richard Clemens - Wolf Creek


Closing Remarks

PWSCC is time sensitive

– Peening should be encouraged for asset protection, regulatory

schedule delays discourage timely, proactive mitigation

Industry made decisions based on the NRC’s August 2013

schedule

The current NRC schedule will force lead plant projects in

2016/17 to mitigate without knowing the NRC’s requirements


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