DCL-24-066, Request to Extend the Nrg Approval of Alternative for Use of Full Structural Weld Overlay, REP-RHR-SWOL

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Request to Extend the Nrg Approval of Alternative for Use of Full Structural Weld Overlay, REP-RHR-SWOL
ML24180A205
Person / Time
Site: Diablo Canyon  Pacific Gas & Electric icon.png
Issue date: 06/27/2024
From: Rogers J
Pacific Gas & Electric Co
To:
Office of Nuclear Reactor Regulation, Document Control Desk
References
DCL-24-066, EPID L-2017-LLR-0092
Download: ML24180A205 (1)
v • d • e


Text

m Pacific Gas and Electric C:ompany"'

Justin E. Rogers Station Director iablo Canyon Power Plant Mail code 104/51502 P.O. Box 56 Avila Beach, CA 93424 805.545.3088 Justin.Rooers@poe.com PG&E Letter DCL-24-066 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 10 CFR 50.55a Diablo Canyon Units 1 and 2 Docket No. 50-275, OL-DPR-80 Docket No. 50-323, OL-DPR-82 Request to Extend the NRG Approval of Alternative for Use of Full Structural Weld Overlay, REP-RHR-SWOL, Units 1 and 2

References:

1.
2.
3.
4.

PG&E Letter DCL-17-083, "Request for Approval of Alternative for Application of Full Structural Weld Overlay, REP-RHR-SWOL, Units 1 and 2," dated September 26, 2017 [ML17269A220]

NRC Letter, "Diablo Canyon Power Plant, Units 1 and 2 - Relief Request REP-RHR-SWOL, Request for Approval of Alternative for Application of Full Structural Weld Overlay (EPID L-2017-LLR-0092),"

dated January 2, 2018 [ML17338A131]

PG&E Letter DCL-23-118, "License Renewal Application," dated November 7, 2023 [ML23311A154]

NRG Letter, "Diablo Canyon Nuclear Power Plant, Units 1 and 2 -

Determination of Acceptability and Sufficiency for Docketing and Notice of Opportunity to Request a Hearing Regarding Pacific Gas and Electric Company's Application for License Renewal," dated December 19, 2023 [ML23341A004]

Dear Commissioners and Staff:

In Reference 1, Pacific Gas and Electric Company (PG&E) submitted a request for approval of alternative for application of a full structural weld overlay (SWOL) for the Diablo Canyon Power Plant (DCPP) Units 1 and 2. In Reference 2, the NRG Staff approved the relief request, through the operating license dates of November 2, 2024, for Unit 1, and August 26, 2025, for Unit 2.

In November 2023, PG&E submitted a license renewal application for DCPP, Units 1 and 2 to the NRG (Reference 3), which was determined to be acceptable for review on December 19, 2023 (Reference 4). As a result, PG&E is requesting NRC to extend the approval of the subject SWOLs to the end of the fifth 10-year inservice inspection interval; i.e., May 6, 2035, for Unit 1, and March 12, 2036, for Unit 2.

A member of the STARS Alliance Ca llaway

  • Diablo Canyon
  • Palo Verde
  • Wolf Creek

Document Control Desk Page 2 PG&E Letter DCL-24-066 PG&E requests approval of this request by October 15, 2024, to ensure the approval is in place prior to the current expiration date of the Unit 1 operating license.

The details of the request are provided in the Enclosure.

PG&E makes no new or revised regulatory commitments (as defined by NEI 99-04) in this letter.

If you have any questions regarding this information, please contact Mr. James Morris, Manager, Regulatory Services, at (805) 545-4609.

Sincerely,

~~Z2-----

Justin E. Rogers Station Director rntt/51226940-02 Enclosure Diablo Distribution 6/27/2024 Date cc:

cc/enc:

Anthony Chu, Branch Chief, California Department of Public Health Mahdi 0. Hayes, NRC Senior Resident Inspector Brian Harris, NRC Senior Project Manager Samson S. Lee, NRC Senior Project Manager John D. Monninger, NRC Region IV Administrator State of California, Pressure Vessel Unit A memb er of t he STARS All iance Callaway

  • Diablo Canyon
  • Palo Verde
  • Wolf Cree k

Enclosure PG&E Letter DCL-24-066 10 CFR 50.55a Request to Extend NRC Approval of Proposed Alternative for Use of Full Structural Weld Overlay, REP-RHR-SWOL DCPP Units 1 and 2 In Accordance with 10 CFR 50.55a(z)(1)

- Alternative Provides Acceptable Level of Quality and Safety -

Enclosure PG&E Letter DCL-24-066

1. AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME) CODE COMPONENTS AFFECTED Class 1 piping welds where Structural Weld Overlay (SWOL) was installed are listed in Table 1 below. The requirements of ASME Boiler and Pressure Vessel Code (Code)

Section XI, Table IWB-2500-1, Examination Categories 8-J, are applicable to these welds.

Table 1 - Affected Code Components Unit Weld Description Nominal Materials of Construction*

Designator Size (per ASME Code,Section II) 1 WIB-228 RHR Pipe-to-Elbow Weld 14inch Pipe: SA-376 TP316 Elbow: SA-403 TP316 Weld: SFA-5.9 ER.308 SFA-5.4 E308 2

WIB-245 RHR Pipe-to-Elbow Weld 14 inch Pipe: SA-376 TP316 Elbow: SA-403 TP316 Weld : SFA-5.9 ER308 Notes: RHR = Residual Heat Removal

2. APPLICABLE CODE EDITION AND ADDENDA Diablo Canyon Power Plant (DCPP) Units 1 and 2 are currently completing the fourth 10-year inservice inspection (ISi) interval. The ASME Code of record for this current interval isSection XI, 2007 Edition, with the 2008 Addenda (Reference 1).
3. APPLICABLE CODE REQUIREMENT Fourth ISi inspection Interval Units 1 and 2: ASME Code,Section XI, 2007 Edition with 2008 Addenda, Article IWA-4000 (Reference 1 ).
4. REASON FOR PROPOSED ALTERNATIVE Pacific Gas and Electric Company (PG&E) submitted a request for approval of alternative for application of a full structural weld overlay (SWOL) for the Diablo Canyon Power Plant (DCPP) Units 1 and 2 (Reference 2). The NRG Staff approved the relief request, through the operating license dates of November 2, 2024, for Unit 1, and August 26, 2025, for Unit 2 (Reference 3). PG&E installed the SWOL at weld joint WIB-245 during the Unit 2 twentieth refueling outage (2R20) in 2018, and at weld joint WIB-228 during the Unit 1 twenty-first refueling outage (1 R21) in 2019.

Page 1 of 5

Enclosure PG&E Letter DCL-24-066 In November 2023, PG&E submitted a license renewal application for DCPP Units 1 and 2 to the NRC (Reference 4), which was determined to be acceptable for review on December 19, 2023 (Reference 5). Therefore, PG&E is requesting NRC to extend the approval of the subject SWOLs through the end of the fifth 10-year ISi inspection interval; i.e., May 6, 2035, for Unit 1, and March 12, 2036, for Unit 2.

The SWOL repairs for each subject weld were authorized using a methodology based on Code Case N-740-2 (Reference 6). This approach provides an alternative to replacement of the component as means of restoring full component integrity. The SWOL repairs were evaluated for mitigation of both thermal fatigue and stress corrosion cracking under the conservative assumption that both degradation mechanisms are active. This approach is consistent with the requirements of Code Case N-740-2.

Specifics of the SWOL analysis and evaluation are contained in Section 5 of this Enclosure.

The analysis calculated a cumulative fatigue usage factor of less than unity assuming 60 years of operation with the SWOLs installed. The service life of the SWOL was determined to be greater than 60 years (Reference 7).

5. PROPOSED ALTERNATIVE AND BASIS FOR USE Pursuant to 10 CFR 50.55a(z)(1 ), PG&E proposes an alternative to the ASME Code requirements that are identified in Section 3 of this Enclosure. The alternative consists of use of a SWOL currently installed as authorized (Reference 3).

The SWOL was designed, installed, and examined as detailed in authorized Relief Request REP-RHR-SWOL (Reference 3), during 2R20 in Unit 2, and during 1 R21 in Unit 1. The ASME code examination requirements were met satisfactorily for both units (References 7 and 8).

In accordance with Code Case N-740-2, the SWOL ISi examinations are required to be performed either in the first refueling outage or in the second refueling outage following the application of the overlay. As required, PG&E completed these examinations during the first refueling outage following application of the overlay in each unit. These SWOL examinations were completed during the first Period of the fourth ISi inspection Interval, during Unit 2 twenty-first refueling outage (2R21 ), and during the second Period of the fourth ISi inspection Interval, during Unit 1 twenty-second refueling outage (1 R22).

The ASME code examination were met satisfactorily for both units.

Subsequently, the SWOLs were placed into a population to be examined on a sample basis. The Code Case specifies that twenty-five percent of this population shall be examined once during each inspection interval. With each unit having only one weld in this population this requirement will result in each weld being examined once per inspection interval. Future examinations will continue to follow the requirements of Code Case N-740-2.

Page 2 of 5

Enclosure PG&E Letter DCL-24-066 In September 2018, the following two design reports were submitted to the NRG (Reference 7):

Design Report for the Qualification of the SWOL, Revision 0, dated December 2017.

Impact of Added Second Buffer Layer of Stainless Steel to RHR Weld Overlay, Revision 1, dated August 2018.

The first report concluded that the service life of the installed SWOLs will be greater than 60 years.

In the second report, the impact of the design changes (addition of a second buffer layer) on the original ASME Code qualification and evaluation of the single buffer layer SWOL design was assessed, and it was concluded that the modified SWOL design does not adversely impact the results and conclusions developed for the original SWOL design. Therefore, the modified SWOL design can be considered qualified under all ASME Code requirements that were referenced in the Relief Request [Reference 2].

In addition, PG&E has reviewed the current version of Regulatory Guide 1.193 (Revision 7) against the former Revision 4 referenced and in effect at the time of the authorized Relief Request REP-RHR-SWOL (Reference 3). There are no changes in the NRG basis for not accepting generic use of the subject code case. Specifically, the issues identified in Regulatory Guide 1.193 for Code Case N-740-2 are unchanged. It is concluded that PG&E's basis for relief remains valid with respect to Regulatory Guide 1.193 (Reference 9).

Therefore, the use of this alternative is requested on the basis that the proposed requirements will continue to provide an acceptable level of quality and safety.

6. CONCLUSION As authorized by the NRG (Reference 3), PG&E installed the SWOL at weld joint WIB-245 during 2R20 in 2018, and at weld joint WIB-228 during 1 R21 in 2019.

Implementation of the SWOL alternative to IWA-4000 of ASME Code,Section XI, authorized in REP-RHR-SWOL (Reference 3) produced an effective repair and mitigation of the identified welds and maintains the component geometry. It will also permit Code Case N-740-2 required ASME Code, Appendix VIII, UT examinations as implemented through the Performance Demonstration Initiative (POI) Program. This alternative provides improved structural integrity of the RHR Pipe-to-Elbow Weld.

Accordingly, the use of the alternative continues to provide an acceptable level of quality and safety in accordance with 10 CFR 50.55a(z)(1).

Page 3 of 5

7. DURATION OF PROPOSED ALTERNATIVE Enclosure PG&E Letter DCL-24-066 The provisions of this alternative were approved for the fourth 10-year ISi inspection intervals through the operating license dates of November 2, 2024, for DCPP Unit 1 and August 26, 2025, for DCPP Unit 2 (Reference 3).

PG&E submitted a License Renewal application to extend the operating licenses for both units (Reference 4). As a result, based on the design documentation submitted in Reference 7, PG&E is requesting NRC to extend approval of the subject SWOLs through the end of the fifth 10-year. ISi inspection interval; i.e., May 6, 2035, for Unit 1, and March 12, 2036, for Unit 2.

PG&E requests approval of this request by October 15, 2024, to ensure the approval is in place prior to the current expiration date of the Unit 1 operating license.

8.REFERENCES

1. ASME Boiler and Pressure Vessel Code,Section XI, 2007 Edition, 2008 Addenda.
2. PG&E Letter DCL-17-083, "Request for Approval of Alternative for Application of Full Structural Weld Overlay, REP-RHR-SWOL, Units 1 and 2," dated September 26, 2017 [ML17269A220].
3. NRG Letter, "Diablo Canyon Power Plant, Units 1 and 2 - Relief Request REP-RHR-SWOL, Request for Approval of Alternative for Application of Full Structural Weld Overlay (EPID L-2017-LLR-0092)," dated January 2, 2018 [ML17338A131]
4. PG&E Letter DCL-23-118, "License Renewal Application," dated November 7, 2023 [ML23311A154].
5. NRC Letter, "Diablo Canyon Nuclear Power Plant, Units 1 and 2 - Determination of Acceptability and Sufficiency for Docketing and Notice of Opportunity to Request a Hearing Regarding Pacific Gas and Electric Company's Application for License Renewal," dated December 19, 2023 [ML23341A004]
6. ASME Code Case N-740-2, "Full Structural Dissimilar Metal Weld Overlay for Repair or Mitigation of Class 1, 2, and 3 Items"
7. PG&E Letter DCL-18-050, "Evaluation Documents in Support of Structural Weld Overlay, REP-RHR-SWOL, Unit 2," dated September 11, 2018 [ML18254A426]
8. PG&E Letter DCL-19-054, "Submittal of Acceptance Report Following the Installation of Structural Weld Overlay, REP-RHR-SWOL for Unit 1," dated July 1, 2019 [ML19182A361]

Page 4 of 5

Enclosure PG&E Letter DCL-24-066

9. Regulatory Guide 1.193, "ASME Code Cases Not Approved for Use," Revision 7, dated December 2021 Page 5 of 5
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