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Paul CrookerTechnical Leader, Principal

Materials R&D Tech Exchange MeetingMay 23, 2017

MRP Thermal Fatigue Program Update

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Presentation Content

MRP thermal fatigue program evolutionOperating experience historyMRP responseRecent trending of operating experienceMRP current effortRecent OE inspection challenges and MRP response

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MRP Thermal Fatigue Program Evolution

Original plant designs and inspection programs did not conceive of all potential thermal fatigue vulnerabilities– Thermal stratification– Thermal mixing

PWR OE during the mid 1980s alerted Industry to the need for management of thermal fatigue Industry responded - collaborative research led to a better

understanding of system behaviorMRP strategy focuses on component identification,

inspection and mitigation

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MRP Thermal Fatigue Program Evolution (2)

MRP thermal fatigue management under NEI 03-08 is implemented by:– MRP-146 Cyclic stratification in non-isolable RCS branch lines

(“Needed” item)– MRP-192 Thermal mixing tees in RHR systems

(“Good Practice” item)

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MRP Thermal Fatigue Program Evolution (3)

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Operating Experience History

5 Events leading into NRC Bulletin 88-08– All through-wall (2 US plants)

6 Events subsequent to Bulletin thru 2000 (12 years)– All through-wall (2 US plants)

3 Events after industry guidance thru 2012 (12 years)– All part-wall (2 US plants, cracking discovered during planned MRP-

146/192 program examinations)

10 Events in US between 2013 and 2015 (2 years)– 3 through-wall– 7 part-wall (cracking discovered during planned MRP-146/192

examinations or extent of condition examinations)

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MRP ResponseProgram successful in detecting flaws before leakage occurs

in many instances; however, opportunities for improvement identifiedEPRI Thermal Fatigue Focus Group (TFFG) established to

assess impact of OE and recommend corrective actionsTFFG objectives:

– Publish Interim Guidance to prevent thermal fatigue degradation from exceeding Regulatory limits

– Identify actions for program improvementTFFG process:

– Review each event– Identify specific program failures– Identify potential causes and determine mitigation alternatives– Develop Interim Guidance to detect cracks at an early stage– Identify knowledge gaps and propose specific research to close gaps

& improve program

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MRP Response (2)

TFFG major findings:– Certain screening criteria found suspect – population of susceptible

piping to increase– Need for expansion of MRP-146/192 inspection zones– Newer NDE techniques and procedures are better in detecting

cracking

Interim Guidance issued in May 2015– 2 “Good Practice” requirements– 8 “Needed” requirements

EDF and Japanese thermal fatigue program benchmarking effort initiated and completed (MRP-408/409)Additional NDE mock-ups created to aid in examiner training

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MRP Response (3)

Maintain plant staff expertise– EPRI Fatigue Management Handbook updated (MRP-235)– Fatigue management training conducted and recorded

MRP-146 Revision 2 published in September 2016 incorporating Interim GuidanceMRP-192 Revision 3 under development and to be

published in 2017 incorporating Interim Guidance

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Recent Trending of Operating Experience

7 Events in US between 2016 and 2017 (1 year)– One through-wall– 5 part-wall (cracking discovered during planned MRP-146

examinations or extent of condition examinations)– 1 part-wall (detected via planned Section XI examinations)

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Recent Trending of Operating Experience (2)Date Reactor

SupplierComponent Flaw Depth Method of

DetectionMarch 2016

W Drain Line 58% Part-wall Extent of Condition*

March 2016

W Charging Line 44% Part-wall MRP-146 Inspection

May 2016

W RHR Suction Line

24% Part-wall Section XIProgram

February 2017

W Safety Injection Line

Through-wall N/A

March 2017

W Safety Injection Line

21% Part-wall MRP-146 Inspection

April2017

W RHR Suction Line

14% Part-wall Extent of Condition*

May 2017

W Safety Injection Line

Part-wall in socket weld

MRP-146 Inspection

* Inspection methods consistent with MRP-146 inspection guidance.

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MRP Current Effort

All 7 events reveal a potential need for modified guidance– Drain line was screened out based on MRP-146 generic guidance,

OE was not expected– One crack location was not considered likely due to line size and

geometry, discovered during a one-time inspection– RHR suction lines were screened out as to run fully hot, OE was not

expected– Possible new source of in-leakage identified from SI system cross-

flow– Flaws detected outside of MRP-146 inspection zone

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MRP Current Effort (2)

TFFG is carefully reviewing each event to fully understand root causes and then make a determination if program changes are necessary Instrumentation for temperature, vibration and/or strain

monitoring has been employed at 3 sites– Data has been very valuable in understanding loading conditions

contributing to crack initiation and fatigue crack growth– Data being reviewed by the TFFG to further understand the thermal

fatigue mechanisms and component susceptibility

Publication of Interim Guidance, if necessary, expected later this year

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MRP Current Effort (3)

Overall, the MRP Thermal Fatigue Program has proven successful in detecting flaws before leakage occurs or when cracking presents a challenge to existing structural marginsThrough the continued engagement of the MRP and the

TFFG, improvements in existing thermal fatigue programmatic guidance will be evaluated and implemented as necessary

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Recent OE Inspection Challenges

Newly Identified Cracking Morphologies– RCS High Pressure Injection Nozzle cracking (3-inch OD)Axial cracks on the nozzle side without craze cracking Examination from the nozzle side may be difficult due to geometry

– NDE Challenge: single-side examination for axial crack detection

– RCS Drain cracking (2-inch OD)Weld cracks initiating in the heat-affected zone then propagating

into the weld– NDE challenge: difficult to detect the crack tip inside the weld– NDE challenge: weld complexity may trigger false calls

Elbow skewed cracks – NDE challenge: cracks with complex skewed paths difficult to

detect

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Inspection TAC Deliverables

To respond to the OE, Inspection TAC plans include:– Revise the thermal fatigue examination procedureDevelop a cover sheet for use with PDI UT-2 Revise the generic thermal fatigue examination procedure

– Revise MRP-23, MRP-36 (CBT)– Fabricate 7 additional mockups– Add thermal fatigue mockups to Virtual UT System

Deliverables scheduled for December 2017

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