MRP Materials Reliability Program MRP (via )

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1 MRP Materials Reliability Program MRP (via ) DATE: May 28, 2015 TO: FROM: SUBJECT: Materials Reliability Program (MRP) Technical Advisory Group (TAG) Materials Reliability Program (MRP) Integration Committee (IC) Bernie Rudell, MRP Chairman Anne Demma, EPRI, MRP Program Manager Implementation of NEI Needed and Good Practice Interim Guidance Requirements for Management of Thermal Fatigue REFERENCES: 1. MRP Letter, MRP , Notification of Recent Thermal Fatigue Operating Experience, February 16, Materials Reliability Program: Management of Thermal Fatigue in Normally Stagnant Non-Isolable Reactor Coolant System Branch Lines (MRP-146, Revision 1, ), June Materials Reliability Program: Management of Thermal Fatigue in Normally Stagnant Non-Isolable Reactor Coolant System Branch Lines Supplemental Guidance (MRP- 146S, January Materials Reliability Program: Assessment of Residual Heat Removal Mixing Tee Thermal Fatigue in PWR Plants (MRP-192, Revision 2, ), August Materials Reliability Program: Integrated Fatigue Management Guideline (MRP-148, Revision 1), , November Materials Reliability Program: Fatigue Management Handbook, Revision 1 (MRP-235), , December 2009 ENCLOSURES: 1. NEI Needed and Good Practice Interim Guidance for Management of Thermal Fatigue 2. MRP Letter , Notification of Recent Thermal Fatigue Operating Experience, February 16, The purpose of this letter is to inform the MRP Technical Advisory Group (TAG) and Integration Committee (IC) representatives that the Primary Materials Management Program (PMMP) Executive Committee has endorsed implementation of new NEI Needed and Good Practice requirements defined in enclosure 1. These new requirements are applicable to

2 2 of 5 MRP the thermal fatigue management program guidelines described in references 2, 3 and 4. These guideline changes are the result of analysis by the Thermal Fatigue Focus Group (TFFG) of recent operating experience summarized in reference 1 and provided in enclosure 2 for convenience. It is expected that TAG / IC representatives will communicate these new requirements to the responsible engineering program owner at each Pressurized Water Reactor (PWR) plant site for implementation in accordance with NEI requirements and the schedules provided. Background Management of fatigue resulting from the interaction of thermally stratified fluids in reactor coolant system piping was first recognized in operating experience during the 1980s. Industry response to management of this fatigue mechanism was based on a combination of testing, analysis and Operating Experience (OE) assessments. This work resulted in development of thermal fatigue management guidelines of references 2, 3 and 4. These thermal fatigue management guidelines have historically been effective in detecting related cracking well in advance of exceeding allowable flaw dimensions. However, as communicated in reference 1, there has been a significant increase in the number of thermal fatigue cracks, as well as the occurrence of cracks that exceed allowable limits. In response to this operating experience, the Thermal Fatigue Focus Group (TFFG) was formed. This group includes U.S. and International representatives from mechanical and Non-Destructive Examination (NDE) disciplines. The TFFG was tasked with analyzing each fatigue event to identify unexpected characteristics, determine the underlying causes and to develop near term actions designed to prevent unacceptable consequences. This Interim Guidance letter communicates those actions. This added guidance is designed to minimize the probability of thermal fatigue cracks that exceed allowable flaw dimensions or result in forced or extended outages. This Interim Guidance provides additional examination requirements only and does not address mitigation of the causes of thermal fatigue in normally stagnant branch lines or thermal Mixing Tees. In general, susceptibility of a component to thermal fatigue is a property of the system design and operation. MRP-146 and MRP-192 do include practical suggestions for reducing thermal fatigue susceptibility. In some cases, cost effective measures for mitigation have not been developed and fatigue management is dependent on conservative prediction, timely detection and repair. Therefore, the TFFG is also tasked with identifying the research necessary to understand and effectively mitigate or manage the factors underlying the recent events. This longer term effort can reduce the occurrence of thermal fatigue events. The recommended research will be prioritized and managed by the appropriate Technical Advisory Committee (TAC) and Integration Committee.

3 3 of 5 MRP Operating Experience Evaluation As described above, each of the recent Operating Experience (OE) Events was analyzed by the Thermal Fatigue Focus Group (TFFG) to identify actions to prevent thermal fatigue cracking from exceeding allowable limits or resulting in forced or extended outages. In addition to those necessary actions, a number of beneficial observations were made during this analysis. The following observations are provided for consideration by engineers responsible for management of thermal fatigue: A. Thermal fatigue management guidelines, MRP-146 and MRP-146(S) are designed to manage the effects of thermal fatigue due to interaction of hot turbulent coolant with cooler fluid in stagnant Reactor Coolant System (RCS) branch lines. Fatigue contributions due to periodic operations such as chemistry sampling or vibration, must also be identified and assessed by fatigue program owners in the determination of appropriate inspection requirements. Use of Integrated Fatigue Management guidance as identified in MRP-148 and the Fatigue Management Handbook, MRP-235 are valuable tools to help manage fatigue degradation at operating units. In addition, Fatigue management training is currently being developed for presentation during the November 2015 MRP meetings. Program owners are encouraged to take advantage of these resources. B. In several of the recent operating events, cracking re-occurred after modifications had been made to mitigate thermal fatigue. In one instance, the mitigative insulation was compromised during subsequent outages. In other instances, contributing causes of the initial events were not addressed in corrective action plans. The potential for reoccurrence of cracking caused by degraded mitigation or unrecognized causal factors can be reduced by performing follow-up nondestructive examinations (NDE) and system inspections to validate effectiveness of mitigation and cause diagnoses. C. Repairs performed during original construction can increase local stresses and increase the likelihood of crack initiation and growth compared to the conditions assumed in the design. Responsible engineers can utilize repair history to identify locations of increased susceptibility. D. In one recent operating event, RHR mixing Tee cracks were detected during an MRP- 192 re-examination that followed a period of minimal apparent fatigue usage. This experience demonstrates that implementation of Good Practice examination schedules described in MRP-192 provide confidence in prevention of unacceptable cracking in RHR mixing Tees. E. Four of the recent operating events resulted in forced outages and emergent repairs that were directly caused by leakage through isolation valves that had a function of preventing thermal fatigue in downstream components. Thermal fatigue program owners should be cognizant of the performance history of valves that function to

4 4 of 5 MRP prevent thermal mixing, and to ensure prompt maintenance when needed. This practice is beneficial to any plant system. F. Several recent events attributed to thermal fatigue involved isolated fatigue cracks that were not associated with generalized craze cracking. This condition is not represented in the EPRI MRP thermal fatigue mockups, and may not be detected by general area examinations as was previously considered reasonable. Examinations should include coverage in areas where deeper cracking has been observed in the Operating Experience. G. Several recent events involved detection of thermal fatigue cracks that resulted in Code allowable limits being exceeded or forced outages. Due to the challenging morphology of thermal fatigue cracks, greater engagement between engineering staff and examiners in preparing for examinations (e.g. Pre-job briefing and hands on mockup training), evaluation of examinations results (review by NDE level III) and debriefing of examination findings can improve NDE performance and reduce operating risks. Recording and evaluation of indications in accordance with the guidance of the applicable qualified procedure, coupled with a Level III examiner review, will also reduce risk of detection errors. (Note: Revision of the Thermal Fatigue UT procedures referenced in MRP-146 is planned to better align with ASME Code Section XI, Appendix VIII qualified procedures). H. Piping supports were initially designed without recognizing the (MRP-146) thermohydraulic phenomena in normally isolated branch lines. Consequently, thermal movement of these lines may be different than was anticipated in the original design. Engineering inspections can reveal evidence of excess load conditions by assessing pipe support condition and indications of pipe contact with the fixed environment. Summary Thermal fatigue management guidelines have been historically effective in preventing pressure boundary leakage. However, based on lessons learned and with a commitment to continuous improvement in the area of materials degradation management, changes to current industry guidance is necessary. Specifically, Enclosure 1 provides new NEI Needed and Good Practice guidance requirements that supplement existing thermal fatigue management guidelines for normally isolated Reactor Coolant System (RCS) Branch lines and Residual Heat Removal (RHR) system mixing Tees.

5 5 of 5 MRP A summary of these new requirements is provided in the table below Level Enclosure 1 Paragraph Type Condition of Applicability Required Action Completion G.P All Fatigue Assessments G.P Needed Needed Mixing Tee s DH * >1 to <4 DH * >1 to <4 Needed DH * Needed Needed Needed Needed Needed UH * >1 to =2 UH * >2 to =4 NDE process NDE process NDE process Review and validate Assumptions none Future Examinations Include additional volume none Prior History of cyclic operational out-flow Continuing cyclic operational out-flow use of Generic Analyses for relaxation, MRP-146, With a potential for cold inleakage With a potential for cold inleakage regardless of screening All Needed MRP-146 examinations All Needed MRP-146 examinations All Needed MRP-146 examinations One time exam to verify component condition Examination every other refueling outage One time examination and result reporting to MRP Examine with increased volume every refueling One time exam and result reporting to MRP Examination volume specification Examination coverage calculation Examination coverage review After 6/1/2016 after 6/1/2016 After 6/1/2016 after 6/1/2016 After 6/1/2016 After 10/1/2015 After 10/1/2015 After 10/1/2015 * MRP-146 classifies branch line configurations as either Up Horizontal (UH), Horizontal (H) or Down Horizontal DH If you or your team have any questions on these recommendations, please contact Mike McDevitt, EPRI Thermal Fatigue Focus Group Lead (mmcdevitt@epri.com; ), or Mike Hoehn, Chairman of the MRP Technical Support Advisory Committee (MRP TS-TAC) (mhoehn@ameren.com). Bernie Rudell Chairman, Materials Reliability Program Anne Demma EPRI MRP Program Manager cc: Thermal Fatigue Focus Group Members MRP Technical Support Technical Advisory Committee MRP Inspection Technical Advisory Committee Andrew McGehee, BWRVIP Bob Carter, BWRVIP

6 Enclosure 1 NEI Needed and Good Practice Interim Guidance for Management of Thermal Fatigue 1. Good Practice Interim Guidance 1.1. Validation of Thermal Fatigue Management Assumptions Thermal fatigue is a dynamic aging mechanism that is sensitive to plant configuration and operating history. Key assumptions made in determining component life and inspection requirements may be subject to design and operational changes and may warrant periodic monitoring to ensure analysis validity. Assumptions may include insulation, piping supports and operational practices Good Practice: Validation of Thermal Fatigue Management Assumptions Analyses performed in support of MRP-146 and MRP-192 examination plans should be reviewed to identify key assumptions. This may include plant screening evaluations and corrective action documents related to thermal fatigue. Key assumptions should be evaluated to determine if periodic inspections or monitoring is appropriate to ensure analysis integrity Expanded MRP-192 Examination Volume Requirement MRP-192 Section 3 specifies examination volumes that include the mixing Tee downstream weld, and all other welds within 4 pipe diameters downstream of the mixing Tee weld. Non-destructive and destructive examinations performed following recent OE identified cracking in the perpendicular branch inlet pipe to the mixing Tee. Computational simulations of thermal transients in mixing Tees have also observed relatively large magnitude thermal cycles in the upstream pipe inner surface. The extent to which thermally stratified eddies penetrate upstream piping is dependent on flow velocities and Mixing Tee geometry. It is possible that under low branch flow conditions, cracking could initiate at upstream piping welds. Based on these observations, the recommended MRP-192 examination volume specified in Section 3 is being expanded to include areas of observed and potential cracking.

7 Enclosure Good Practice: Expanded MRP-192 Examination Volume Requirement In addition to the examination volumes specified in Section 3 of MRP-192, Revision 2, it is recommended that future MRP-192 examinations also include the Mixing Tee weld to the upstream piping as shown in Figure 1. Combined flow direction Perpendicular Piping Flow Good Practice Recommendation: In addition to current MRP-192 revision 2 recommendations, also perform Volumetric Examination of the two upstream welds joining the mixing tee to upstream piping Figure 1 Revised volumetric examination recommendations.

8 Enclosure 1 2. Needed Interim Guidance 2.1. Down Horizontal (DH) Branch Lines subject to cyclic operational out-flow The introduction to Section 2 of MRP-146 identifies that the analytical models used for identification of thermal fatigue susceptibility are not applicable to DH lines where inleakage or out-leakage is present. Recent operating experience has identified at least one through wall cracking event involving a 2-inch Nominal Pipe Size (NPS) drain line where fatigue failure was likely to have been accelerated by thermally stratified, cyclic chemistry sampling in the DH branch line. This OE identifies the need for near term actions to limit the potential of unacceptable cracking. Continuous or slowly varying leakage through closed valves or other fixed mechanical boundaries does not constitute cyclic outflow for purposes of this concern Needed Requirement: One Time Examination of Down Horizontal (DH) Branch Lines >1-inch NPS to <4-inches NPS that have had a prior history of cyclic operational out-flow. Normally stagnant DH branch lines where cyclic out flow operations have occurred in the past, shall be examined in accordance with requirements and examination volumes specified in MRP-146 to ensure acceptable elbow and piping condition. This one-time examination requirement shall be performed no later than the first refueling outage starting after June 1, Examinations meeting the requirements of MRP-146, and performed after June 1, 2013 may be credited for meeting this Needed requirement, if determined to be acceptable by the responsible engineer. This determination should consider the adequacy of volumetric coverage consistent with the intent of section in this letter. This one time examination is not required if the incremental fatigue usage of piping due to thermally stratified outflow has been conservatively analyzed and shown to be negligible. These examinations ensure piping integrity subsequent to previous cyclic outflow operations. Results of these examinations do not require EPRI-MRP review for Guideline management purposes and may be reported in the annual MRP-219 outage surveys Needed Requirement: Periodic Examination of Down Horizontal (DH) Branch Lines >1-inch NPS and <4-inches NPS that have a continuing potential for cyclic operational out-flow Normally stagnant DH branch lines where cyclic out flow operations are expected to occur in the future, shall be examined every other refueling outage

9 Enclosure 1 subsequent to cyclic out flow operation and the first refueling outage starting after June 1, Examinations shall conform to the requirements and volumes specified in MRP-146. If the fatigue contribution due to outflow is evaluated with all other usage, including MRP-146 effects, and shown to remain within acceptable limits, this examination schedule may be relaxed by the owner. Examinations may be deferred following operating cycles where cyclic operational out-flow does not occur Down Horizontal (DH) Branch Lines Previously Exempted by MRP-146 Paragraph , MRP-146(S) Generic Analysis Recent Operating Experience identified through wall cracking in Down Horizontally attached branch lines within 6-years of a previous examination where no cracks had been detected. The examination frequency for these branch lines had been relaxed under MRP-146 Paragraph using MRP-146(S) paragraphs and A.2.4. This experience draws into question the conservatism of extending examination schedules based on the analysis of MRP-146 Paragraph Other factors may have contributed to this premature cracking event. In order to assess the extent of condition from a potentially non-conservative analysis method, a one-time examination will be necessary. (Note: Branch lines with examination requirements based on MRP-170 software or other analysis alternatives under MRP-146 and MRP-146(S) are not subject to this one time examination requirement) Needed Requirement: One Time Examination of Down Horizontal (DH) Branch Lines Previously Exempted by the Generic Analysis option described in MRP-146 paragraph Down Horizontal (DH) branch lines that were determined not to have significant thermal fatigue based on generic analysis described in MRP-146 Paragraph and MRP-146(S) Paragraphs and A.2.4 shall undergo a one-time examination in accordance with the requirements specified in MRP-146 Paragraph and the Needed NDE guidance contained in section 2.4 of this letter. This examination shall be performed no later than the first refueling outage commencing after June 1, Examinations meeting the requirements of MRP-146, and performed after June 1, 2013 may be credited for meeting this needed requirement, if determined to be acceptable by the responsible engineer. This determination should consider the adequacy of volumetric coverage consistent with the intent of section of this letter.

10 Enclosure 1 Plants may return to the current examination schedules after completion of this extent of condition examination. Results from these examinations shall be communicated to the EPRI MRP Technical Support Advisory Committee for an assessment of whether the relaxation methodology under MRP-146 Paragraph should be revised Up Horizontal (UH) Piping subject to Thermal Fatigue in the vertical pipe section Up Horizontal (UH) piping with NPS of 2-inches and smaller was observed to be resistant to turbulent swirl penetration in mockup testing and simulations underlying the current MRP-146 guidance. This resistance to development of swirl penetration in the vertical pipe was assumed to result in resistance to thermal fatigue associated with cold in-leakage. MRP-146 Section excludes examination requirements for vertical piping based on this presumption. However, in two recent operating events, cracking was discovered in 1 ½ inch NPS lines that had been excluded from examination requirements under MRP-146 Section screening criteria. This recent OE has revealed an unanticipated mode of thermal cycling and cracking that also occurred at an unexpected location in the vertical pipe to RCS nozzle interface. As a result of this experience, UH lines less than 2-inches NPS that may be subjected to cold in-leakage as defined in MRP-146 section 2.1 can no longer be exempted from examination on the basis of diameter alone. The required examination volume for these lines include vertical pipe sections where cracking was identified in the OE, in addition to the MRP-146 examination volume from which the line had previously been exempted. It is not known if lines somewhat larger than 2-inches may be susceptible to vertical pipe cracking from this mode of thermal fatigue. Therefore, a one-time examination of vertical pipe for lines greater than 2-inches NPS and not larger than 4-inches NPS is needed to establish the extent of this thermal fatigue mode. This operating experience does not diminish the validity of other bases for exclusion of UH/H lines from examination in MRP-146 Section Branch piping of diameters 1-inch NPS and less remain exempted from examination based on engineering judgement that temperature differentials across small diameter pipe wall will be limited by conduction and as a result will suppress significant cyclic stresses Needed Requirement: Periodic Examination of Up Horizontal (UH) configured Piping greater than 1- inch NPS and not larger than 2-inches NPS and having the potential of cold inleakage.

11 Enclosure 1 Normally stagnant UH piping, with nominal pipe sizes greater than 1-inch NPS and not larger than 2 -inches NPS and having a potential for cold inleakage shall be examined every refueling outage commencing with the first refueling outage starting after June 1, Examinations shall conform to the requirements of MRP-146 as augmented in this Interim Guidance letter. The examination volume shall include the areas described in Section of MRP-146, the pipe to nozzle (butt) weld and the vertical pipe base metal up to two pipe diameters above the weld or to the elbow if it is less than 2D from the weld as shown in figure 2. Examination of socket welds is not required Needed Requirement: One Time Examination of UH Configured Piping greater than 2-inches NPS and not larger than 4-inches NPS and having the potential of previous cold in-leakage. Up-Horizontal (UH) normally stagnant piping with nominal pipe sizes (NPS) of between 2 and 4 inches and having the potential for cold in-leakage, shall be examined using the examination requirements of MRP-146 as augmented in this Interim Guidance letter. This one-time examination shall include the pipe to nozzle (butt) weld, and the vertical pipe base metal up to 2 pipe diameters above the weld or to the elbow if it is less than 2D from the weld as shown in figure 2. Examination of socket welds is not required. This examination shall be performed not later than the first refueling outage commencing after June 1, Examinations performed after June 1, 2013 may be credited for meeting this needed requirement, if the additional volume was examined and the examination is determined acceptable by the responsible engineer. This determination should consider the adequacy of volumetric coverage consistent with the intent of section of this letter. Results from these examinations shall be communicated to the EPRI MRP Technical Support Advisory Committee for an assessment of whether branch lines between 2 and 4 inches NPS are susceptible to this thermal fatigue mode.

12 Enclosure 1 Figure 2 Detailed view of the additional examination volume for Up Horizontal configured branch lines between 1 and 4 inches NPS that also have potential for in-leakage Non Destructive Examination Process Improvements Recent Operating Experience in thermal fatigue as well as other NDE applications have identified that greater engagement between inspection program owners and examiners is key to effective examinations and understanding of detection limitations. New requirements have been published in several examination areas such as Dissimilar Metal Welds, and Reactor Pressure Vessel Head penetrations that implement greater engineering engagement. Several of the recent thermal fatigue events have involved missed crack detection opportunities which resulted in plant shutdown and reliability challenges. In some cases, lack of emphasis on examination coverage may have contributed to non-detection of operationally significant cracks. MRP-146 Section states that it is not necessary to examine 100% of the recommended volume based on the generalized nature of thermal fatigue. However, recent Operating Experience has revealed instances where cracking was limited to small volumes such that 100% examination coverage would be critical to prevent exceeding allowable crack dimensions. As a result of these observations, examination process changes are required for implementation. These process changes shall be implemented for Needed thermal fatigue

13 Enclosure 1 examinations no later than the first refueling outage following October 1, These requirements are not applicable to examinations performed prior to that date Needed Requirement: Examination Volume Specification For locations to be inspected in accordance with MRP-146 and as augmented in this interim guidance letter, Component examination sketches indicating the required coverage volumes of MRP-146 figures 2-11 through 2-19, and as augmented by this interim guidance (figure 2), shall be developed and provided to the examiners. These sketches shall be included in the completed thermal fatigue examination work package or applicable procedure. These sketches shall separately identify both the base metal examination volume and weld examination volume requirements. Butt weld volume requirements shall be established consistent with MRP-146 Figures 2-16 and The base metal examination volume includes all required piping and fitting volumes exclusive of the specified weld volumes Needed Requirement: Examination Documentation Limitations and Coverage Calculations Examiners shall document the actual coverage obtained and calculate the percentage of required volumes examined for both the base metal and weld volumes. These results shall be provided for review by the responsible engineer Needed Requirement: Examination Volume Coverage Essentially 100% of the examination volumes specified in MRP 146 and this Interim Guidance, shall be inspected. If the achieved examination coverage of the required base metal volume was not greater than 90%, or if the achieved examination coverage of the required weld volume was not greater than 90%, then the Responsible Engineer shall be informed and a Corrective Action Program (CAP) item shall be generated to document the coverage limitation and assess the actual coverage obtained. The Responsible Engineer shall assess the potential risk from cracking in the unexamined volumes and determine if compensatory measures such as alternate examination techniques or weld crown removal are warranted. CAP items need not be replicated in subsequent examinations if coverage limitations are unchanged. Coverage limitations should be included in subsequent thermal fatigue examination briefings.

14 Enclosure 2 MRP Letter , Notification of Recent Thermal Fatigue Operating Experience, February 16, Note Since publication of MRP letter on February 16, 2015, Dominion Virginia Power destructively examined the weld volume containing crack like indications identified in the loop-c drain line elbow of the North Anna Nuclear Power Station, Unit- 1. The destructive examination determined that no crack was actually present.

15 Enclosure 2 MRP Materials Reliability Program MRP (via ) February 16, 2015 TO: FROM: SUBJECT: PWR Plant Site Vice Presidents David Czufin, TVA, PMMP Chairman Robin Dyle, EPRI, PMMP Manager Anne Demma, EPRI, MRP Program Manager Notification of Recent Thermal Fatigue Operating Experience The PWR Materials Management Program (PMMP) Executive Committee is issuing this notification of recent operating experience in piping and components potentially exposed to thermal stratification fatigue. This experience has revealed potential EPRI Materials Reliability Program (MRP) Guidance gaps. The MRP has formed a Thermal Fatigue Focus Group (TFFG) which will develop and recommend NEI Interim Guidance in May, This preliminary information is provided for review and consideration to the U.S. PWR fleet, with a specific focus on plants with Spring 2015 refueling outages. There are no new Materials Initiative (NEI 03-08) requirements associated with this communication. In the 23 years prior to 2013, there were three thermal fatigue cracking events reported in plants subject to MRP thermal fatigue management guidelines. Since 2013, there have been ten relevant events, eight of which had thermal fatigue as the primary causal factor. Three of these events were detected through leakage and four others involved cracks with excessive depths or in locations not previously considered to be susceptible to thermal fatigue. In response to this trend the MRP established the TFFG to evaluate these events in total and revise guidance that will improve performance and reliability. Recent operating experience is presented in Attachment 1. The purpose of this letter is to inform you of the collective operating experience, and to share examples of beneficial practices so that members may take into account that experience in near term outages as appropriate while the TFFG develops interim guidance. It is important that stations review the recent thermal fatigue operating experience for opportunities to mitigate risk at your facility. Some utilities with outages this spring are considering walk-downs of potential thermal fatigue locations; others are reviewing system configurations and operating conditions to identify potential high risk locations and determine if any additional volumetric inspections or examination should be considered.

16 Enclosure 2 2 of 5 MRP I wanted to make sure you were aware of this recent operating experience, the planned Interim Guidance that will be issued in May 2015, and recommend if you have a planned spring outage, you perform a review with engineering for any site specific risks that might warrant additional inspections. If you or your team have any follow-up questions, you may contact Mike McDevitt, EPRI Thermal Fatigue Focus Group Lead (mmcdevitt@epri.com; ), Mike Hoehn, Chairman of the MRP Technical Support Advisory Committee (mhoehn@ameren.com) or myself. Chairman, PMMP Attachment cc: MRP TAG & IC members

17 3 of 5 MRP Attachment: Operating Experience Summary Enclosure 2 The following table summarizes recent fatigue operating experiences. Not all events are attributed to thermal fatigue; however each event offers insight into fatigue management program effectiveness. Date Plant Event Discovery Learning Point Nov 2013 Nov 2013 Apr 2014 Sep 2014 Sep 2014 Oct 2014 Oct 2014 Nov 2014 Dec 2014 Dec 2014 TMI-1 ONS-1 MNS-2 MNS-1 MNS-1 MNS-1 Perry (BWR) ONS-1 NAPS-1 NAPS-1 Part-wall cracking in CL drain line Through-wall cracking in CL SI Line Part-wall cracking in CL SI Line Part-wall cracking in CL SI Line Part-wall cracking in CL SI Line Part-wall cracking in RHR mixing tee Through-wall cracking in RWCU regen heat exchanger mixing tee Part-wall cracking in CL drain line Through-wall cracking in CL drain elbow Part-wall cracking in CL drain line MRP-146 Inspection Through-wall Leak MRP-146 Inspection Extent of Condition Extent of Condition MRP-192 Inspection Through-wall Leak MRP-146 Inspection Through-wall Leak Extent of Condition Significant elements of these fatigue cracking events are discussed below: Vibration was primary cause of repeat cracking event NDE program weaknesses prevented timely detection Updated NDE procedures employed Updated NDE procedures employed Cracking located outside of current inspection zone guidance Updated NDE procedures employed Cracking located outside of current inspection zone guidance Updated NDE procedures employed Not specifically addressed in guidance. Cold in-leakage to any hot system is a Thermal Fatigue risk Updated NDE procedures employed Inspection frequency was insufficient to manage fatigue Oconee Nuclear Station, Unit-1, November 2013 On November 11, 2013 Oconee Unit-1 was forced off-line due to through wall leakage in the 1B2 High Pressure Injection safe end to pipe weld. The cause of this crack was concluded to be vibration fatigue, however, this weld fell within the management guidance of MRP-146 and had been volumetrically examined in 2012 as part of committed inspections with no rejectable indications detected. Subsequent reviews of radiography performed in 2011 confirmed that the crack had gone undetected in the 2012 UT examinations. In this event NDE improvements would have prevented component failure and the forced outage. As a result, volumetric examination process weaknesses were identified and procedure improvements were implemented. As part of the Extent of Condition assessment, components examined using the previous procedures were scheduled for reexamination in the next outages, including Duke plants at other sites. TBD

18 Enclosure 2 4 of 5 MRP McGuire Nuclear Station, Unit-2, April 2014 On 4/1/14 while performing scheduled ONS-1 Extent of Condition examinations using the improved NDE processes, an 85% part through wall axial crack was identified in the loop-d, 1 ½ inch High Pressure Injection pipe to nozzle weld. The cause of this crack was determined to be due to Thermal Fatigue due to a legacy in-leakage issue. Isolation valve leak by creating cold inleakage contributed to the event. Repairs were implemented with limited impact to the planned refueling outage. This weld had been examined as required by MRP-146 during the previous refueling outage with no rejectable indications detected. The volumetric examination improvements and job briefings implemented as a result of the November 2013 Oconee experience are likely to have prevented an on-line leakage and forced outage event. The planned Extent of Condition examinations for NDE were supplemented with plans to examine all likekind HPI nozzle to pipe welds regardless of Thermal Fatigue Management Program susceptibility guidance. McGuire Nuclear Station, Unit-1 September 2014 On September 27, 2014 ultrasonic testing as part of the McGuire Unit-2 Extent of Condition detected 50-55% through wall flaws in the 1B and 1C High Pressure Injection pipe to nozzle welds. These welds were previously screened out from being considered susceptible to swirl penetration fatigue using MRP-146 methodology on the basis that stratification and cycling will not be sustained in piping less than 2-inch nominal pipe size. Furthermore, indications in both HPI injection lines were located outside of the MRP-146 examination volume that would have been applicable had the piping configuration screened in under MRP-146. The cause of these indications was determined to be thermal fatigue at the interface between cold inleakage and primary coolant in the main loop. MRP-146 failed to anticipate the potential interaction at injection nozzles in small diameter piping attached to the top of the main reactor coolant loop. Rigorous Extent of Condition plans may have prevented forced outages and revealed a gap in the Industry s Thermal Fatigue management program. North Anna Nuclear Power Station, Unit-1, December 2014 On December 23, 2014 RCS pressure boundary leakage in the loop-b cold leg drain line forced shutdown of North Anna Unit-1. Volumetric examination of the other cold leg drain elbows revealed a second crack-like indication in Loop-C. Some weld crown surface conditioning was performed to improve crack characterization. These components had been inspected 5-years earlier with no relevant indications detected. Assessment tools provided in MRP-146(S) had been used to extend the default inspection period of every other outage to once per 10-years. Consequently, a gap in MRP-146 methodology, the 2009 volumetric examinations or an unaccounted contributing fatigue mechanism must have existed. Note that these lines are used for drawing RCS Chemistry samples. MRP-146 does not account for fatigue usage contributions other than cyclic swirl penetration. Chemistry sampling has been implicated as being a contributing factor in previous cracking events. (In 2009, Beaver Valley Power Station Unit-1 found multiple cracks in a cold leg drain line that were partially attributed to usage from chemistry sampling). Valve leak-by may also have contributed to this event. While the root cause of the North Anna event has not yet been determined, the forced outage might have been

19 Enclosure 2 5 of 5 MRP prevented by improved guidance for examination scheduling, improved NDE requirements and/or more comprehensive assessment of operational fatigue contributions. Oconee Nuclear Station, Unit-1, November 2014 On November 13th, 2014 flaws ranging in depth up to 17% were identified during augmented MRP-146 UT examinations in the extrados of the elbow in the Oconee Unit-1 loop B2 cold leg drain line. The cracking characteristics and location were generally consistent with a previous leak event of this same elbow in Following the 2000 through wall leakage and forced outage event, downstream piping was insulated to reduce differential cyclic temperatures and significantly reduce accumulation of fatigue usage. Analysis performed in accordance with MRP-146(S) would have allowed relaxation of the inspection period to once per 6 years, however, the schedule was not reduced. Visual inspection of the piping revealed that at some time since 2000, the mitigative insulation had been compromised. The compromised insulation is likely to have had a role in the event recurrence. Had the degraded insulation been identified to the fatigue program owner, minor maintenance might have prevented this pressure boundary damage. Perry Nuclear Power Plant, October 2014 On October 5, 2014 a leak was detected in a 6-inch piping branch tee connecting regenerative heat exchanger outlet and bypass flow in the Reactor Water Cleanup (RWCU) system. This was a repeat of a previous through wall leak in the same weld 6 years earlier. During power operation, cold bypass around the regenerative heat exchanger is normally isolated. However, known isolation valve leakage permitted cold bypass to continuously enter the heated cleanup return at the Tee connection. The temperature differential between these fluids (300F) is sufficient to result in an aggressive thermal fatigue condition. The apparent cause evaluation of this thru-wall leakage event concluded that bypass isolation valve leakage resulted in thermal fatigue failure of the mixing tee weld. This event has characteristics in common with both MRP- 192 governing fatigue usage at mixing locations of Residual Heat Removal systems and MRP- 146 addressing cold inleakage into hot flow streams. In this instance, application of thermal fatigue management concepts to configurations outside the scope of published guidelines would have prevented this leakage event. McGuire Nuclear Station, Unit-1, October 2014 On October 10, 2014 during thermal fatigue ultrasonic examinations in accordance with MRP- 192, multiple ID connected, axial and circumferential, and craze crack indications were identified in an 8 inch, Schedule 20 stainless steel RHR mixing tee. The maximum crack depth was approximately 22%, which is consistent with expectations of an inspection based management program. The mixing Tee inspection period of 6-years was calendar based on MRP-192 prescribed guidance. The previous examination in 2008 did not detect degradation. However, the estimated fatigue usage in the period since 2008 was very low. The 2014 examination employed improved NDE methods which may have contributed to detection. MRP- 192 is a Good Practice program under the Materials Initiative NEI This operating experience highlights the importance of continued focus and improvement of methodologies as plants continue to age and accumulate fatigue usage.