ML24145A186
| ML24145A186 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 05/30/2024 |
| From: | Hipolito Gonzalez NRC/NRR/DORL/LPL1 |
| To: | Rhoades D Constellation Energy Generation |
| References | |
| EPID L-2023-LLR-0065 | |
| Download: ML24145A186 (1) | |
Text
May 30, 2024 NINE MILE POINT NUCLEAR STATION, UNIT 1-AUTHORIZATION AND SAFETY EVALUATION FOR ALTERNATIVE RELIEF NO. I5R-12 CONCERNING THE INSTALLATION OF A FULL STRUCTURAL WELD OVERLAY ON REACTOR PRESSURE VESSEL RECIRCULATION INLET NOZZLE N2E SAFE END-TO-NOZZLE DISSIMILAR METAL WELD (EPID L-2023-LLR-0065)
LICENSEE INFORMATION Recipients Name and Address:
David P. Rhoades Senior Vice President Constellation Energy Generation, LLC President and Chief Nuclear Officer Constellation Nuclear 4300 Winfield Rd Warrenville, IL 60555 Licensee:
Constellation Energy Generation, LLC (CEG)
Plant Name and Unit:
Nine Mile Point Nuclear Station, Unit 1 (Nine Mile Point, Unit 1)
Docket No.:
50-220 APPLICATION INFORMATION Application Date: December 4, 2023 Application Agencywide Documents Access and Management System (ADAMS)
Accession No.: ML23338A232 Licensee Proposed Alternative No. or Identifier: I5R-12 Applicable Inservice Inspection (ISI) Program Interval and Interval Start/End Dates: The fifth 10-year ISI interval for Nine Mile Point, Unit 1 began on August 23, 2019, and is scheduled to end August 22, 2029.
Alternative Provision: The applicant requested an alternative under Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(1), Acceptable level of quality and safety.
ISI Requirement: American Society of Mechanical Engineer (ASME) Boiler and Pressure Vessel Code (ASME Code),Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, IWA-4411, IWA-4411(a), IWA-4411(b), IWA-4412, IWA-4221(c), IWA-4222, IWA-4420, and IWA-4611.
Applicable Code Edition and Addenda: The applicable Code of record for the fifth 10-year ISI interval at Nine Mile Point, Unit 1 is ASME Code,Section XI, 2013 Edition.
Background:
During automated encoded ultrasonic testing examination of N2E safe end-to-nozzle dissimilar metal weld (DMW) 32-WD-208 during the last refueling outage (N1R27), an axial flaw was discovered in the Alloy 82/182 weld metal and adjacent 316 stainless steel safe end. The flaw had attributes that were indicative of intergranular stress corrosion cracking (SCC). In lieu of performing an ASME Code repair/replacement activity in accordance with IWA-4000 and IWB-3640, CEG submitted proposed alternative I5R-11 (ML23083B991) to apply a design (leakage barrier) weld overlay (WOL) using Alloy 52M until a full structural weld overlay (FSWOL) could be performed at the next refueling outage (N1R28). The alternative used guidance based on ASME Code Case N-740-2, Full Structural Dissimilar Metal Weld Overlay for Repair or Mitigation of Class 1, 2, and 3 ItemsSection XI, Division 1 and ASME Code,Section XI, 2013 Edition, Nonmandatory Appendix Q, Weld Overlay Repair of Classes 1, 2, and 3 Austenitic Stainless Steel Piping Weldments. On March 31, 2023 (ML23090A130),
the U.S. Nuclear Regulatory Commission (NRC) verbally authorized the use of Relief Request I5R-11 at Nine Mile Point, Unit 1, on the basis that the proposed alternative provided for an acceptable level of quality and safety, and the structural integrity and leak tightness of the subject overlaid weld would be maintained until the end of the next refueling outage (N1R28).
The final safety evaluation was issued on June 22, 2023 (ML23156A682).
Subsequent to the verbal approval of Relief Request I5R-11, during the examination of the completed leakage barrier WOL, the licensee discovered three laminar weld indications, one of which did not meet the acceptance criteria in Code Case N-740-2. On April 13, 2023 (ML23103A404), the licensee submitted I5R-14 requesting to use the WOL acceptance criteria in Section XI, Nonmandatory Appendix Q in lieu of the acceptance criteria specified in Code Case N-740-2, which was specified in I5R-11. On April 14, 2023 (ML23104A347), the NRC verbally authorized the use of Relief Request I5R-14 at Nine Mile Point, Unit 1, on the basis that the proposed alternative provided for an acceptable level of quality and safety, and the structural integrity and leak tightness of the subject overlaid weld would be maintained until the end of the next refueling outage (N1R28). The final safety evaluation was issued on June 22, 2023 (ML23156A683).
Brief Description of the Proposed Alternative:
The licensees proposed alternative is to apply an Alloy 52M FSWOL over the dissimilar metal Alloy 82/182 weld and existing leakage barrier WOL on DMW 32-WD-208, as described above.
The FSWOL will be designed in accordance with the guidance of Code Case N-740-2 as detailed in the licensees request dated December 4, 2023. Attachment 3 of the "NMP1L3563, Submittal of Relief Request I5R-12, Revision 0, Concerning the Installation of a Full Structural Weld Overlay on Reactor Pressure Vessel Recirculation Inlet Nozzle N2E Safe End-to-Nozzle [[Topic" contains a listed "[" character as part of the property label and has therefore been classified as invalid. (32-WD-208)|December 4, 2023, letter]] provides a comparison of the proposed alternative to Code Case N-740-2 and provides additional technical justifications for the alternative.
The proposed alternative has been requested in accordance with the provisions of 10 CFR 50.55a(z)(1). The proposed alternative would provide for an acceptable level of quality and safety.
For additional details on the licensees request, please refer to the documents located at the ADAMS accession numbers identified above.
STAFF EVALUATION In lieu of performing an ASME Code repair/replacement activity in accordance with IWA-4000, CEG proposed to apply an FSWOL using Alloy 52M weld filler material during refueling outage N1R28. The applicable edition of ASME Code,Section XI for the fifth ISI interval at Nine Mile Point, Unit 1 is the 2013 Edition.Section XI, Nonmandatory Appendix Q provides requirements for WOLs on stainless steel pipe welds. However, Appendix Q only addresses stainless steel-to-stainless steel welds using stainless steel weld filler material to apply an overlay. Although many of the design and inspection attributes of Appendix Q are applicable to the FSWOL proposed on N2E safe end-to-nozzle DMW 32-WD-208, the subject weld covers low alloy steel, stainless steel and Alloy 82/182 weld metal. In addition, Appendix Q does not provide for the use alloy 52M weld filler material or the use of the ambient temperature temper bead welding technique, which are necessary to install a FSWOL on a DMW such as 32-WD-208. Code Case N-740-2, which is not endorsed by the NRC for generic use, provides general requirements, design, installation, and examination criteria for FSWOLs using Alloy 52M weld filler materials and includes criteria for temper bead welding. Although not yet endorsed by the NRC, Code Case N-740-2 has been used as a basis for several NRC approved alternatives at multiple U.S.
nuclear power plants.
As described above, the licensee installed a leakage barrier WOL on the subject flawed weld using guidance based on Code Case N-740-2 and ASME Code,Section XI, Nonmandatory Appendix Q. In short, the licensee installed part of an FSWOL during its last refueling outage (N1R27) to ensure that structural integrity and leak tightness of the weld would be maintained until the next refueling outage (N1R28) when completion of an FSWOL can be performed. Weld overlays have been used extensively to mitigate SCC flaws in boiling-water reactors (BWRs) and pressurized-water reactors for decades. The leakage barrier alternatives I5R-11 and I5R-14 were approved by the NRC for one cycle. The previously installed leakage barrier WOL has a length that is sufficient for an FSWOL; therefore, the ambient temperature temper bead welding required for the FSWOL has been completed. In addition, ER309L weld metal was used for sulfur mitigation on the stainless steel safe end and Alloy 82 bridge beads were installed over the original weld. The remainder of the leakage barrier WOL used Alloy 52 weld filler material.
These techniques are consistent with WOLs that have been installed in other BWRs.
The licensee will perform a surface and volumetric examination on the previously installed leakage barrier WOL to verify its integrity before adding additional weld layers to complete the FSWOL. The NRC staff notes that the laminar weld flaw that was identified in the leakage barrier WOL and accepted via NRC approval of alternative I5R-14 is contained in a portion of the WOL that is not susceptible to degradation and is not in proximity to the DMW. In addition, the flaw met the acceptance criteria of ASME Code Section XI, Nonmandatory Appendix Q. Two additional laminar flaws were also identified; however, those flaws were acceptable per Code Case N-740-2. Therefore, the NRC finds that the NRC evaluations of the leakage barrier portion of the proposed FSWOL remain valid. For additional information regarding the NRC staffs review and approval of the leakage barrier WOL, see NRC final safety evaluations for Relief Requests I5R-11 and IR5R-14 referenced above in the background section.
After installation of the leakage barrier WOL in N1R27, ultrasonic examination showed that the initial flaw had extended to the interface of the original Alloy 82/182 weld and the Alloy 82 bridge beads applied during installation of the leakage barrier WOL. The NRC staff notes that
volumetric and surface examinations will confirm the integrity of the leakage barrier WOL prior to installing the remaining weld layers needed to complete the FSWOL.
The weld filler material used to complete the FSWOL is Alloy 52. Alloy 52 is highly resistant to SCC and is the same material used for the outer layers of the leakage barrier WOL installed during N1R27. The NRC staff is unaware of any instances of SCC in Alloy 52 weld metal in U.S. or foreign nuclear plants. The NRC staff notes that the original weld flaw is axial. As such, it is highly unlikely that the flaw could propagate any significant distance into the low alloy steel nozzle or the low carbon stainless steel safe end as these materials are typically not considered susceptible to SCC.
The licensee estimates that an additional 0.26 inch of WOL will be added during N1R28 to complete the 0.76-inch minimum design thickness for the FSWOL thickness. The licensees design of the FSWOL requires that a design analysis be complete in accordance with ASME Code,Section XI, IWA-4311, Material, Design, or Configuration Changes. The design requires that the axial length and end slope of the WOL covers the weld and heat-affected zones on each side of the weld, as well as any SCC susceptible base material adjacent to the weld and provide for load redistribution from the item into the WOL and back into the item without violating applicable stress limits of NB-3200. Post weld volumetric examinations will be performed on the FSWOL volume, including the initial flaw found in the base material during N1R27. These flaw dimensions will be used to determine the life of the FSWOL. The NRC staff notes that the required service life of the proposed FSWOL is somewhat limited because the Nine Mile Point, Unit 1 operating license will expire at the end of the current inspection interval on August 22, 2029. The crack growth and design requirements in Code Case N-740-2 are consistent with those found in ASME Code,Section XI, Nonmandatory Appendix Q. ASME Code Section XI, Appendix Q has been endorsed by the NRC. Therefore, the NRC staff finds that the licensees design criteria is acceptable.
The licensees examination procedures will be qualified in accordance with Code Case N-653-2, Qualification Requirements for Full Structural Overlaid Wrought Austenitic Piping WeldsSection XI, Division 1, in lieu of ASME Code,Section XI, Mandatory Appendix VIII, Performance Demonstration for Ultrasonic Examination Systems, as specified in Code Case N-740-2. Code Case N-653-2 is endorsed by the NRC staff in Regulatory Guide 1.147, Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1, and is, therefore, acceptable to use.
The examination volume used by the licensee for the initial examination of the completed FSWOL is that shown in Code Case N-740-2, figure 1(a). This examination volume is equivalent to that shown in ASME Code,Section XI, Nonmandatory Appendix Q, figure Q-4300-1. The acceptance standards of ASME Code,Section XI, IWB-3514 will be met as specified in Appendix Q and Code Case N-740-2. However, Code Case N-740-2 provides additional limitations. Appendix Q, Q-4000(c)(1) requires that laminar flaws meet the acceptance standards of table IWB-3514-3, which allows a laminal flaw area of 7.5-in2, but does not have the limitation in Code Case N-740-2 that no linear dimension of a laminar flaw area shall exceed the greater of 3 inches (76 mm) or 10 percent of the pipe circumference. The NRC staff previously approved the use of ASME Code,Section XI, Appendix Q acceptance standards for the leakage barrier WOL alternative (Relief Request I5R-14). Given the NRC staffs previous approval of the use of Appendix Q acceptance standards for the leakage barrier WOL and the endorsement of ASME Code,Section XI, Appendix Q by the NRC staff for stainless steel
FSWOLs, the NRC staff finds that the licensees use of ASME Code,Section XI, Appendix Q acceptance standards is acceptable.
The preservice examination volume used in the proposed alternative is that shown in Code Case N-740-2, Figure 2 which is identical to that shown in NRC endorsed ASME Code,Section XI, Appendix Q, figure Q-4300-1. The proposed alternative implements the acceptance standards that are listed in Code Case N-740-2, which specifies the acceptance standards in ASME Code,Section XI, IWB-3514. These acceptance standards are consistent with those listed in ASME Code,Section XI, Appendix Q, which has been endorsed by the NRC staff and are, therefore, acceptable.
Based on the above, the NRC staff finds that the licensees proposed alternative provides reasonable assurance of structural integrity and leak tightness of subject weld and is, therefore, acceptable.
CONCLUSION The NRC staff has determined that the licensees proposed alternative provides an acceptable level of quality and safety.
The NRC staff concludes that the licensee has adequately addressed the regulatory requirements set forth in 10 CFR 50.55a(z)(1).
The NRC staff authorizes the use of the licensee's proposed alternative at Nine Mile Point, Unit 1, for the remainder of the fifth 10-year ISI interval that began on August 23, 2019, and ends on August 22, 2029. This end date also coincides with the end of the current Nine Mile Point, Unit 1 operating license. Furthermore, the NRC staff authorizes the FSWOL that is to be installed in accordance with provisions of Relief Request I5R-12, to remain in place for the remaining operating license of the plant or the design life, whichever is shorter.
All other ASME Code,Section XI requirements for which an alternative was not specifically requested and authorized remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
Principal Contributor: Robert Davis Date: May 30, 2024 Hipólito González, Chief Plant Licensing Branch I Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation cc: Listserv HIPOLITO GONZALEZ Digitally signed by HIPOLITO GONZALEZ Date: 2024.05.30 10:29:10 -04'00'
ML24145A186 NRC-001 OFFICE NRR/DORL/LPL1/PM NRR/DORL/LPL1/LA NRR/DNRL/NPHP/BC NAME RGuzman KEntz (PBlechman for)
MMitchell DATE 05/27/2024 5/28/2024 05/24/2024 OFFICE NRR/DORL/LPL1/BC NAME HGonzález DATE 05/30/2024