ML22193A254

SLRA - Audit Report

ML22193A254
Person / Time
Site:	Oconee
Issue date:	08/05/2022
From:	Angela Wu NRC/NRR/DNRL/NLRP
To:	Snider S Duke Energy Carolinas
Wu A
References
EPID L-2021-SLR-0000
Download: ML22193A254 (14)

Text

August 05, 2022 Mr. Steven M. Snider Site Vice President, Oconee Nuclear Station Duke Energy Carolinas, LLC 7800 Rochester Highway Seneca, SC 29672-0752

SUBJECT:

OCONEE NUCLEAR STATION, UNITS 1, 2, AND 3 - REPORT FOR THE LIMITED SCOPE AGING MANAGEMENT AUDIT REGARDING THE SUBSEQUENT LICENSE RENEWAL APPLICATION REVIEW - PWR VESSEL INTERNALS (EPID NO. L-2021-SLR-0000)

Dear Mr. Snider:

By letter dated June 7, 2021 ( ML21158A193), as supplemented by letters dated October 22, 2021 (ML21295A035), October 28, 2021 (ML21302A208), November 11, 2021 (ML21315A012),

December 2, 2021 (ML21336A001), December 15, 2021 (ML21349A005), December 17, 2021 (ML21351A000), January 7, 2022 (ML22010A129), January 21, 2022 (ML22021A000),

February 14, 2022 (ML22045A021), February 21, 2022 (ML22052A002), March 22, 2022 (ML22081A027), March 31, 2022 (ML22090A046), April 20, 2022 (ML22110A207), and April 22, 2022 (ML22112A016), May 11, 2022 (ML22131A023), May 20, 2022 (ML22140A016), May 27, 2022 (ML22147A001), June 7, 2022 (ML22158A028), June 8, 2022 (ML22159A151) July 8, 2022 (ML22189A008), July 18, 2022 (ML22192A062), and July 25, 2022 (ML22206A005), Duke Energy Carolinas, LLC (Duke Energy or the applicant) submitted an application for the subsequent license renewal (SLR) of Renewed Facility Operating License Nos. DPR-38, DPR-47, and DPR-55 for the Oconee Nuclear Station, Units 1, 2, and 3 to the U.S. Nuclear Regulatory Commission (NRC). Duke Energy submitted the application pursuant to Title 10 of the Code of Federal Regulations Part 54, Requirements for Renewal of Operating Licenses for Nuclear Power Plants, for SLR.

The NRC staff completed its aging management audit from May 17-18, 2022, in accordance with the audit plan (ML22111A314). The audit report is enclosed.

If you have any questions, please contact me by e-mail at Angela.Wu@nrc.gov.

Sincerely,

/RA/

Angela Wu, Project Manager License Renewal Projects Branch Division of New and Renewed Licenses Office of Nuclear Reactor Regulation Docket Nos. 50-269, 50-270 and 50-287

Enclosure:

Audit Report cc w/encl: Listserv

SUBJECT:

OCONEE NUCLEAR STATION, UNITS 1, 2, AND 3 - REPORT FOR THE LIMITED SCOPE AGING MANAGEMENT AUDIT REGARDING THE SUBSEQUENT LICENSE RENEWAL APPLICATION REVIEW PWR VESSEL INTERNALS (EPID NO. L-2021-SLR-0000)

DATED: AUGUST 05, 2022 DISTRIBUTION:

E-MAIL:

PUBLIC RidsNrrDnrl Resource RidsNrrPMOconee Resource AWu, NRR/DNRL MJohnson, NRR/DNRL LGibson, NRR/DNRL LRakovan, NMSS/REFS BSmith, NRR/DNRL BThomson, NRR/DNRL SWilliams, NRR/DORL MMarkley, NRR/DORL MWoods, OGC MWright, OGC RRichardson, OEDO SBurnell, HQ/OPA LWilkins, OCA DMcIntyre, HQ/OPA DScrenci, RI/OPA DGasperson, RII/OPA JPelchat, RII/FCO ELea, RII/FCO JNadel, RII/DRP JBaptist, RII/DRS Paul.Guill@duke-energy.com Reene.Gambrell@duke-energy.com Arun.Kapur@duke-energy.com ADAMS Accession No.: ML22193A254

• via eConcurrence NRR-106 OFFICE NRR/DNRL: PM NRR/DNRL: LA NRR/DNRL: BC NAME AWu YEdmonds JTsao for ABuford DATE 07/13/2022 07/26/2022 07/28/2022 OFFICE NRR/DNRL: PM NRR/DNRL: PM NAME LGibson AWu DATE 08/01/2022 08/05/2022

Enclosure AUDIT REPORT Aging Management Audit Oconee Nuclear Station, Units 1, 2, and 3 Subsequent License Renewal Application May 17 - 18, 2022 Division of New and Renewed Licenses Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission

2 U.S. NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION DIVISION OF NEW AND RENEWED LICENSES Docket Nos:

50-269, 50-270 and 50-287 License Nos:

DPR-38, DPR-47, and DPR-55 Licensee:

Duke Energy Carolinas, LCC (Duke Energy)

Facility:

Oconee Nuclear Station (ONS), Units 1, 2, and 3 Location:

Rockville, Maryland Dates:

May 17 - 18, 2022 Approved By:

Angie R. Buford, Chief Vessels and Internals Branch Division of New and Renewed Licenses Lauren K. Gibson, Chief License Renewal Projects Branch Division of New and Renewed Licenses NRC Attendees:

Name Organization Angie Buford Vessels and Internals (NVIB)/Division of New and Renewed Licenses (DNRL)

David Dijamco NVIB/DNRL Emma Haywood NVIB/DNRL Jim Medoff NVIB/DNRL Carol Moyer NVIB/DNRL Cory Parker NVIB/DNRL Lauren Gibson License Renewal Projects Branch (NLRP)/DNRL Marieliz Johnson NLRP/DNRL Angela Wu NLRP/DNRL Christopher Tyree NLRP/DNRL Allen Hiser DNRL

3 TABLE OF CONTENTS AUDIT REPORT......................................................................................................................

TABLE OF CONTENTS...........................................................................................................

ACRONYMS............................................................................................................................

1.

Introduction.......................................................................................................................

2.

Audit Activities..................................................................................................................

SLRA AMP B2.1.7, Pressurized Water Reactor (PWR) Vessel Internals............................

3.

Audit Needs Provided to Duke.........................................................................................

4.

Applicant Personnel Contacted During Audit...................................................................

5.

Exit Meeting......................................................................................................................

4 ACRONYMS AMP aging management program CB core barrel CUF cumulative usage factor EPRI Electric Power Research Institute GALL-SLR NUREG-2191, Generic Aging Lessons Learned for Subsequent License Renewal IASCC irradiation-assisted stress corrosion cracking IE irradiation embrittlement I&E Inspection and evaluation ISG Interim Staff Guidance MRP materials reliability program NAM no additional measures NEI Nuclear Energy Institute NRC U.S. Nuclear Regulatory Commission PWR pressurized-water reactor RAI request for additional information RCI request for confirmation of information SCC stress corrosion cracking SE safety evaluation SER safety evaluation report SLR Subsequent License Renewal SLRA subsequent license renewal application SRP-SLR NUREG-2192, Standard Review Plan for Review of Subsequent License Renewal Applications for Nuclear Power Plants

5 Report for the Aging Management Audit Oconee Nuclear Station, Units 1, 2, and 3 Subsequent License Renewal Application

1. Introduction On May 17-18, 2022, the U.S. Nuclear Regulatory Commission (NRC) staff conducted a limited scope aging management audit for the subsequent license renewal (SLR) of Renewed Facility Operating License Nos. DPR-38, DPR-47, and DPR-55 for Oconee Nuclear Station (ONS),

Units 1, 2, and 3, as submitted by Duke Energy Carolinas, LLC (Duke Energy, applicant).

Following review of Duke Energy responses to RAIs B2.1.7-4 and B2.1.7-5 (ML22045A021) as related to aging management program (AMP) B2.1.7, PWR Vessel Internals, the staff conducted a limited audit to review the applicants bases for its conclusion that the core barrel (CB) assembly vertical seams welds in the top and bottom CB cylinder segments at Oconee Units 1, 2, and 3, and the CB top flange-to-upper cylinder and upper cylinder-to-lower cylinder circumferential seam welds in Oconee Units 1 and 3 do not screen in for stress corrosion cracking (SCC) or fatigue type cracking mechanisms.

The scope of the audit did not include:

anything related to the two Unit 2 CB circumferential welds being elevated up to Primary category status.

anything related to the applicants statements on screening for irradiated-assisted stress corrosion cracking (IASCC) and neutron irradiation embrittlement (IE) mechanisms - in the response to RAI B2.1.7-4, the applicant states that all Oconee CB upper and lower cylinder vertical welds and upper cylinder-to-lower cylinder circumferential welds screen in for IASCC & IE.

CB weld accessibility issues - 2nd round RAI B2.1.7-4a (ML22124A142) addressed this issue.

Audit Assumptions:

For the fatigue screening basis, the staff assumed that the supplemental cumulative usage factor (CUF) analysis for the CB welds discussed with the applicant during the early March 2022 teleconference with the applicant will be posted to the audit portal.

For the SCC screening basis, the staff assumed that the applicant will have posted some sort of site-specific record or unit-specific records that contain the actual alloying ferrite contents for Type 308 or 308L stainless steel weld filler materials used in the fabrication of the CB weld types.

The regulatory bases for the audit was Title 10 of the Code of Federal Regulations (10 CFR)

Part 54, Requirements for Renewal of Operating Licenses for Nuclear Power Plants. The staff also considered the guidance contained in NUREG-2192, Standard Review Plan for Review of Subsequent License Renewal Applications for Nuclear Power Plants (SRP-SLR), dated July 2017, and NUREG-2191. The SRP-SLR allows an applicant to reference in its license renewal application the AMPs described in GALL-SLR Report. By referencing the GALL-SLR

6 Report AMPs, the applicant concludes that its AMPs correspond to those AMPs reviewed and approved in the GALL-SLR Report and that no further staff review is required. If an applicant credits an AMP for being consistent with a GALL-SLR Report program, it is incumbent on the applicant to ensure that the plant program contains all of the elements of the referenced GALL-SLR Report program. The applicant should document this determination in an auditable form and maintain the documentation on-site.

2. Audit Activities A regulatory audit is a planned, license-related activity that includes the examination and evaluation of primarily non-docketed information. A regulatory audit is conducted with the intent to gain greater understanding of an application, to verify information, and, if applicable, to identify information that will require docketing to support the staffs conclusions that form the basis of the licensing or regulatory decision.

Licensing conclusions or staff findings are not made in the audit reports since licensing and regulatory decisions cannot be made solely based on an audit. Therefore, items identified but not resolved within the scope of the audit will be followed using other NRC processes, such as requests for additional information (RAIs), requests for confirmation of information (RCIs), and public meetings. Licensing conclusions, staff findings, and resolution of audit items will be documented in the staffs SER.

Fatigue Screening Activities:

1. Determination and verification of CUF values for CB welds of reference or for the CB assembly as a whole commodity group-based component.

2. Comparison of component-specific CUF value or values to the EPRI MRPs 80 year threshold values for CUF parameters in MRP-189, Revision 3.

3. Determination whether the supplemental CUF analysis being referenced by the applicant is using and applying a CUF threshold on fatigue that is different than that used and cited in MRP-189, Revision 3 (which is referenced in the gap analysis basis of the PWR Vessel Internals AMP (SLRA B2.1.7).

SCC Screening Activities:

1. Determination and verification of ferrite alloying contents values for stainless steel CB welds of reference.

2. Comparison of component-specific ferrite values to the EPRI MRPs 80year threshold value on minimal acceptable ferrite levels in MRP-189, Revision 3.

Prior to the audit, the staff did not have a sufficient basis to conclude that placing the referenced CB welds in the No Additional Measures (NAM) category is a sufficient basis to manage cracking and irradiation embrittlement in the welds per the requirement in 10 CFR 54.21(a)(3).

Under this type of risk-informed, sampling-based program basis, the Unit 2 CB circumferential seam weld types that have been elevated in inspection category status and placed into the programs Primary inspection category do not have any Primary-to-Expansion category interrelationships to the remaining CB welds in Oconee Units 1, 2 and 3 that have been downgraded in inspection category status and placed in the NAM category of the program.

7 Under this type of aging management basis, the referenced CB assembly welds being placed in the NAM category will not be subject to any Primary-based or Expansion-based inspection and evaluation (I&E) criteria during the subsequent period of extended operation; this is regardless of what occurs and may be detected in the Unit 2 Primary CB weld types or in other designated Primary category components of the program (including the Primary category core baffle plates, which were the original, linked Primary components for the designated inaccessible, Expansion category CB welds in MRP-227, Rev. 1-A). The perceived inaccuracy of the new SLRA Table 3.1.2-2 Footnote 3 that was included in the response to RAI B2.1.7-5 complicates the staffs review of the CB NAM inspection category basis. This is beyond scope of the initial issues that were perceived by the staff solely on the review of the applicants response to RAI B2.1.7-4.

The following section discuss the audit activities conducted by the staff:

SLRA AMP B2.1.7, Pressurized Water Reactor (PWR) Vessel Internals Summary of Technical Information in the Application.

The SLRA states that aging management program (AMP) B2.1.7, PWR Vessel Internals is an existing program that, with an enhancement, will be consistent with the program elements in GALL-SLR Report AMP XI.M16A, PWR Vessel Internals, as updated in NRC Interim Staff Guidance (ISG) No. SLR-ISG-2021-01-PWRVI. To verify this claim of consistency, the staff audited the AMP. During the audit, the staff also reviewed the enhancement associated with this AMP. The staff will document its review of the enhancement in the safety evaluation report (SER). The staff will address issues identified but not resolved in this audit report or more complex RVI management issues in the staffs evaluation of SLRA AMP B2.1.7, PWR Vessel Internals in the SER.

Background Information.

The applicants Reactor Vessel Internals AMP is defined as a living, sampling-based condition monitoring program that is based on the latest staff-approved version of Electric Power Research Institute (EPRI) Materials Reliability Program (MRP) Report MRP-227, and any industry supplemental guidelines issued and used to supersede or supplement the inspection and evaluation guidelines in MRP-227. The applicant implements the program in accordance with the industry initiative protocols in the most recent version of Nuclear Energy Institute (NEI)

Report No. NEI 03-08 and the implementation guidance in Chapter 7 of the current version of MRP-227 being used for the AMP. The staff reviewed the basis for the applicants categorizing of components using the EPRI MRPs interactive functionality analysis and failure modes, effects, and critical analysis bases for ranking the components for inspection, as defined in Chapter 2 of MRP-227.

Supplemental Audit - Limited Scope of Audit and Audit Activities.

On May 17 and 18, 2022, the staff performed a supplemental audit of the applicants bases for deriving the final EPRI MRP-227-based inspection categories and I&E criteria for the core barrel (CB) weld components in ONS Units 1, 2, and 3 that are within the scope of the Reactor Vessel Internals AMP (as considered and applied to the proposed 80-year version of the AMP that will be implemented during the subsequent period of extended operation). The scope of the staffs supplemental audit apply to the following CB welds that the applicant has designated for placement in the NAM category of the AMP: (1) CB top flange-to-top cylinder circumferential

8 seam welds in Units 1 and 3, (2) CB top cylinder-to-bottom cylinder circumferential seam welds in Units 1 and 3, and (3) CB top cylinder axial seam welds and bottom cylinder axial seam welds in Units 1, 2, and 3. The staff performed the supplemental audit based on its observation of the applicants responses to staff RAIs B2.1.7-4 and B2.1.7-5, which did not provide sufficient demonstration that these welds were not susceptible to SCC, IASCC, or fatigue cracking mechanisms. More, specifically, the staff noted that the applicants response to RAI B2.1.7-4 identified that the CB top cylinder-to-bottom cylinder circumferential seam welds and CB top cylinder axial seam welds and bottom cylinder axial seam welds in the Oconee unit-specific designs are screened in for both IASCC and that all CB welds screened in for a neutron IE mechanism. As such, the staff limited the scope of its supplemental audit only to the applicants basis for screening of the CB welds for SCC and fatigue type cracking mechanisms. The staff also addressed whether the screening results for assessed SCC and fatigue mechanisms supported the applicants position that the referenced CB assembly weld types could be placed into the NAM category of the version of the AMP based on the screening results for those parameters used to screen for SCC or fatigue. The staff addressed CB weld inspection categorization gaps for assessed IASCC and IE mechanisms and weld accessibility issues through issuance of a supplemental, 2nd round request for additional information (RAI B2.1.7-4a) that was issued to the applicant on May 3, 2022 (ML22124A142). The staff will resolve the matter raised in this RAI in the SER.

This supplemental audit report documents the staff observations of the applicants validity of the proposed NAM category position for the referenced CB welds.

During its supplemental audit, the staff interviewed the applicants staff and reviewed documentation contained in the SLRA and provided by the applicant via the ePortal. The table below lists additional documents that were reviewed by the staff and were found relevant to the program. The staff will document its review of this information in the SER.

Document Title Revision / Date SLRA Appendix B, AMP Section B2.1.7 Reactor Vessel Internals Revision 0 EPRI Non-Proprietary Report No. 3002017168 Materials Reliability Program: Pressurized Water Reactor Internals Inspection and Evaluation Guidelines (MRP-227, Revision 1-A)

June 2020 (ML20175A112)

Nuclear Energy Institute (NEI) Non-Proprietary Report No. 03-08 Guidelines for the Management of Materials Issues Revision 4 (ML20315A536)

EPRI Proprietary Report

((XX))

Materials Reliability Program: Screening, Categorization, and Ranking of Babcock and Wilcox-Designed Pressurized Water Reactor Internals Components Items and Weld (MRP-189, Revision

3)

December 2019 (ML20091K284; a redacted, publicly available version of the report is available in ML20091K282)

EPRI Proprietary Report

((XX))

Materials Reliability Program: PWR Internals Material Aging Degradation Mechanism Screening and Threshold Values (MRP-175, Revision 1)

October 2017 (ML17361A190; a redacted, publicly available version of the report is available in ML1736A188)

Framatome Proprietary Calculation Sheet ((XX))

Oconee Units 1, 2, and 3: Core Barrel Fatigue Evaluation Summary October 1, 2020 Framatome Proprietary Report ((XX))

Oconee-Specific RV Internals Aging Management Strategy Development and Inspection Categorization for SLR August 12, 2020

9 Document Title Revision / Date Framatome Proprietary Presentation ONS 1, 2, and 3 SCC Screening May 17, 2022 Framatome Proprietary Presentation ONS 1, 2, and 3 Core Barrel Fatigue Evaluation May 17, 2022 Framatome Proprietary Presentation ONS Core Barrel cumulative usage factor (CUF) Screening May 17, 2022 Duke Energy Correspondence Letter No.

RA-22-0036 Duke Energy Carolinas, LLC (Duke Energy), Oconee Nuclear Station (ONS), Units 1, 2, and 3, Docket Numbers 50-269, 50-270, and 50-287, Renewed License Numbers, DPR-38, DRP-47, and DPR-55, Subsequent License Renewal Application, Responses to NRC Request for Additional Information February 14, 2022 (ML22045A020; a redacted, publicly available version of the letter is publicly available at ML22045A021)

During the supplemental audit, Framatome Corporation (on behalf of the applicant) presented its basis and results of the SCC, fatigue, and CUF screening analyses that Framatome performed for the referenced CB welds, as given in the last three records cited and referenced in the table above.

The staff observed that Framatome performed supplement CUF calculations using unit-specific CB loading and design transient information as shown in Framatome Proprietary Calculation Sheet, Oconee Units 1, 2, and 3: Core Barrel Fatigue Evaluation Summary. The staff also observed:

The applicant calculated a proprietary CUF value for the CB assemblies in ONS Units 1, 2, and 3 (including the welds in the CB assemblies) that was greater than the EPRI MPR proprietary threshold on CUF, as cited in Table 3-1 of MRP-189, Revision 3.

The methodology and finite element modeling methods for performing the CUF-based fatigue screening analysis in Framatome Proprietary Calculation Sheet, "Oconee Units 1, 2, and 3: Core Barrel Fatigue Evaluation Summary were reasonable and conservative in basis.

Framatome did not draw a conclusion in Framatome Proprietary Calculation Sheet, Oconee Units 1, 2, and 3: Core Barrel Fatigue Evaluation Summary, regarding whether the CB assemblies and the referenced CB welds in the assemblies screened in for the cracking mechanism of fatigue.

As discussed in SLRA AMP B2.1.7 and provided on page B-66 of the SLRA, the applicant reassessed the validity of the referenced EPRI MRP proprietary screening factor for applicability to the fatigue basis for the CB assemblies and referenced welds in the ONS reactor units. The applicant concluded that the EPRI MRP proprietary screening factor on fatigue CUF did not apply to the design of the CB assemblies and welds in the ONS units and was overly conservative for use. Thus, the applicant applied the alternate fatigue (i.e.,

CUF) screening criterion of 1.0 in the ASME Code,Section III, Subsection NG, as the basis for the fatigue screening analysis of the CB assemblies and welds at ONS. However, the staff noted that the applicant did not indicate which SLRA or ONS-specific record contained the applicants justification for using an alternate ASME Code-based fatigue screening criterion instead of the proprietary fatigue screening criterion that is specified and provided

10 in MRP-189, Revision 3. The staff may address this information gap through issuance of an additional RAI.

If use of the fatigue screening criterion in the ASME Code,Section III, Subsection NG (i.e., a screening criterion on CUF of 1.0) is applied as the basis for the screening objective, the proprietary CUF value for the CB assemblies and welds in Framatome Proprietary Calculation Sheet, Oconee Units 1, 2, and 3: Core Barrel Fatigue Evaluation Summary would meet the screening criterion of 1.0 on CUF.

The staff observed that, given the applicants basis and statement in its response to RAI B2.1.7-4 that the CB top cylinder-to-bottom cylinder circumferential seam welds and CB top cylinder axial seam welds and bottom cylinder axial seam welds in the ONS unit-specific designs screen in for mechanism of IASCC, SCC would not be a concern for the staffs evaluation of the inspection category basis for the referenced CB welds; instead, the staff observed that IASCC is the limiting form of SCC for stress corrosion screening and assessment objectives. The staff issuance of RAI B2.1.7-4a addresses the IASCC screening basis matter. The staff will evaluate the applicants response to RAI B2.1.7-4a and the IASCC-inspection category relationships for CB welds in the SER.

3. Audit Needs Provided to Duke On May 3, 2022, the NRC staff provided the audit needs to Duke Energy to facilitate audit discussions. Specifically, the staff requested Duke Energy to post applicable plant records to the portal that demonstrate CUF values for the welds are within the range specified in MRP-189, Rev. 3 for the fatigue mechanism onto the ePortal. Additionally, the staff requested applicable certified material test reports or other types of design records that may demonstrate that the appropriate ferrite alloying content values and loading stress values (including residual stress considerations) for the CB weld types are within the ranges for those parameters in MRP-189, Rev. 3 (for the SCC mechanism assessment).

4. Applicant Personnel Contacted During Audit Name Affiliation Rachel Lee Doss Duke Reene Gambrell Duke Paul Guill Duke Rounette Nader Duke Daniel William Roberts Duke Greg Robison Duke Joe Terrell Duke Justin Byard Framatome Sarah Davidsaver Framatome Ryan Hosler Framatome Philip Opsal Framatone Mark Rinckel Framatome Dave Skulina Framatone Tim Wiger Framatone

11

5. Exit Meeting An exit meeting was held with the applicant on May 18, 2021, to discuss the results of the regulatory audit. As a result of the audit, the staff issued second round RAI B2.1.7-4b (ML22154A200).