ML23285A074
| ML23285A074 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 10/20/2023 |
| From: | Markley M Plant Licensing Branch II |
| To: | Snider S Duke Energy Carolinas |
| Williams S | |
| References | |
| EPID L-2023-LLR-0024 | |
| Download: ML23285A074 (1) | |
Text
October 20, 2023 Mr. Steven M. Snider 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 - RELIEF REQUEST (RA-23-0018) TO UTILIZE CODE CASE N-853, WITH DEVIATIONS (EPID L-2023-LLR-0024)
Dear Mr. Snider:
By letter dated May 4, 2023, Duke Energy Carolinas, LLC (Duke Energy, the licensee) submitted relief request RA-23-0018 to the U.S. Nuclear Regulatory Commission (NRC) for the use of an alternative to certain American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPV Code),Section XI requirements at the Oconee Nuclear Station, Units 1, 2, and 3 (Oconee 1, 2, and 3) for the sixth 10-year inservice inspection interval (ISI).
Specifically, Duke Energy proposed to use ASME Code Case N-853, PWR Class 1 Primary Piping Alloy 600 Full Penetration Branch Connection Weld Metal Buildup for Material Susceptible to Primary Water Stress Corrosion Cracking Section XI, Division 1 with deviations.
Pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(1), the licensee requested to use the proposed alternative on the basis that the proposed alternative provides an acceptable level of quality and safety.
The NRC staff has reviewed the subject request, and concludes, as set forth in the enclosed safety evaluation, that the Duke Energy has adequately addressed the regulatory requirements set forth in 10 CFR 50.55a(z)(1). Therefore, the NRC staff authorizes the proposed alternative in relief request RA-23-0018 for the sixth 10-year ISI program interval for Oconee 1, 2, and 3, which is scheduled to begin on July 15, 2024, and end on July 14, 2034.
All other ASME BPV Code Section XI, requirements for which relief was not specifically requested and approved remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
If you have any questions, please email Shawn.Williams@nrc.gov.
Sincerely, Michael T. Markley, Chief Plant Licensing Branch II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-269, 50-270, and 50-287
Enclosure:
Safety Evaluation cc: Listserv John G. Lamb Digitally signed by John G. Lamb Date: 2023.10.20 10:59:34 -04'00'
Enclosure SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION PROPOSED ALTERNATIVE REQUEST RA-23-0018 RELATED TO THE USE OF CODE CASE N-853 WITH DEVIATIONS FOR THE SIXTH 10-YEAR INSERVICE INSPECTION INTERVAL DUKE ENERGY CAROLINAS, LLC (DUKE ENERGY)
OCONEE NUCLEAR STATION, UNIT NOS. 1, 2, AND 3 DOCKET NOS. 50-269, 50-270, AND 50-287
1.0 INTRODUCTION
By letter dated May 4, 2023 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML23124A384), Duke Energy Carolinas, LLC (Duke Energy, the licensee) submitted to the U.S. Nuclear Regulatory Commission (NRC) relief request RA-23-0018 for the sixth 10-year inservice inspection (ISI) interval for the Oconee Nuclear Station, Units 1, 2, and 3 (Oconee 1, 2, and 3).
Specifically, Duke Energy proposed to use ASME Code Case N-853, PWR Class 1 Primary Piping Alloy 600 Full Penetration Branch Connection Weld Metal Buildup for Material Susceptible to Primary Water Stress Corrosion Cracking Section XI, Division 1 with deviations.
Pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(1), the licensee requested to use the proposed alternative on the basis that the proposed alternative provides an acceptable level of quality and safety.
2.0 REGULATORY EVALUATION
Pursuant to 10 CFR 50.55a(g)(4), Inservice inspection standards requirement for operating plants, ASME Code Class 1, 2, and 3 components (including supports) must meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in the ASME Code,Section XI, Rules for lnservice Inspection [lSI] of Nuclear Power Plant Components, to the extent practical within the limitations of design.
Pursuant to 10 CFR 50.55a(z)(1), Alternatives to codes and standards requirements, alternatives to the requirements of paragraphs (b) through (h) of Section 50.55a, or portions thereof, may be used when authorized by the NRC if the licensee demonstrates that the proposed alternative would provide an acceptable level of quality and safety.
Regulatory Guide, 1.147, Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1 Revision 19 (ML19128A244), lists the ASME Section XI Code Cases that the NRC has approved for use as voluntary alternatives to the mandatory ASME Code provisions that are incorporated by reference into 10 CFR 50.55a, Codes and Standards.
Based on the above, and subject to the following technical evaluation, the NRC staff finds that regulatory authority exists for the NRC to authorize the licensees proposed alternative for the sixth 10-year ISI interval for Oconee 1, 2, and 3. Accordingly, the NRC staff reviewed and evaluated the licensees request pursuant to 10 CFR 50.55a(z)(1).
3.0 TECHNICAL EVALUATION
3.1 ASME Code Components Affected by the Proposed Alternative Table 1: ASME Code Components Affected Oconee Unit 1 Weld ID Description 1-PHA-13 1A Hot Leg Resistance Temperature Element (RTE) Mounting Boss Alloy 600 Nozzle Welds 1-PHA-14 1-PHA-15 1-PIA1-12 Cold Leg RTE Mounting Boss Alloy 600 Nozzle Welds 1-PIA2-12 1-PIB1-12 1-PIB2-12 Oconee Unit 2 Weld ID Description 2-PIA1-12 Cold Leg RTE Mounting Boss Alloy 600 Nozzle Welds 2-PIA2-12 2-PIB1-12 2-PIB2-12 Oconee Unit 3 Weld ID Description 3-PHB-13 3B Hot Leg RTE Mounting Boss Alloy 600 Nozzle Welds 3-PHB-14 3-PHB-15
- Nearest Nozzle Butt Welds 3-RC-286-11 3-RC-286-58V 3B Hot Leg Flow Meter Alloy 600 Nozzle Welds 3-PIA1-9 Cold Leg RTE Mounting Boss Alloy 600 Nozzle Welds 3-PIA2-9 3-PIB1-11 3-PIB2-9
- Nearest Nozzle Butt Weld 3-50-37-1 3B1 Cold Leg Level Tap Alloy 600 Nozzle Weld 3-PIA1-10 Three Cold Leg Drain Alloy 600 Nozzle Welds 3-PIA2-10 3-PIB2-10 Note *: Small Bore Piping (1 nominal pipe size) nozzle welds are not given explicit weld IDs on original drawings. These three specific Small Bore Nozzle Welds are located by the nearest documented branch connection butt weld.
Materials of construction for all locations referenced above are:
- Reactor Coolant System Piping (RCS) - SA-106 Grade C (P-No. 1)
- Alloy 600 Nozzle - SB-166 UNS N06600 (P-No. 43)
- Alloy 82/182 Dissimilar Metal Weld (DMW) - ERNiCr-3, Spec. SFA 5.14 / ENiCrFe-3, Spec. SFA 5.11 (F-No. 43) 3.2 Applicable Code Edition The code of record for the current fifth 10-year ISI interval for Oconee 1, 2, and 3 is the ASME Code,Section XI, 2007 Edition with the 2008 Addenda. All three units are currently in their fifth 10-year ISI interval with a scheduled end date of July 14, 2024. The code of construction for Oconee 1, 2, and 3 is ASME B31.7, 1960 Edition, and was later reconciled to the ASME Code,Section III, 1983 Edition, no Addenda.
The licensee must also apply ASME Code Case N-722-1 as required by 10 CFR 50.55a(g)(6)(ii)(E) as an augmented ISI requirement to perform visual examinations of the specified welds for leakage.
The licensee must also apply ASME Code Case N-853.
The applicable ASME Code Section XI of record for the sixth 10-year ISI interval at Oconee 1, 2, and 3 was determined in accordance with the requirement of 10 CFR 50.55a(g)(4)(ii), which
- states, Successive 120-month inspection intervals must comply with the requirements of the latest edition and addenda of the Code incorporated by reference in paragraph (a) of this section 18 months before the start of the 120-month inspection interval.
The fifth 10-year ISI interval for Oconee 1, 2, and 3 is scheduled to end on July 14, 2024.
Therefore, the sixth 10-year ISI interval code of record for Oconee 1, 2, and 3 complies with the requirements of the latest edition and addenda of the Code incorporated by reference in 10 CFR 50.55a on January 15, 2023, which is ASME Code Section XI, 2019 Edition. The current scheduled start date of the sixth 10-year ISI interval for Oconee 1, 2, and 3 is July 15, 2024, with a scheduled end date of July 14, 2034.
3.3 Proposed Alternative and Basis of Use 3.3.1 Alternative Repair Technique The Licensee stated:
Duke Energy is proposing to apply a welded reinforcing pad on the Outer Diameter of the RCS piping using Primary Water Stress Corrosion Cracking (PWSCC) resistant nickel Alloy 52M (ERNiCrFe-7A) filler metal. The new weld pad is welded using the machine Gas Tungsten Arc Welding Ambient Temperature Temper Bead welding technique. Duke Energy is proposing to attach a PWSCC resistant nozzle to the new weld pad with a full penetration nozzle corner weld using a non-temper bead manual welding technique, using PWSCC resistant nickel Alloy 52M filler metal, or with a "J" groove partial penetration weld as described in ASME Code Case (CC) N-853. The welded pad is designed and installed in accordance with CC N-853 except that the replacement nozzle material is UNS S31600 or UNS N06690.
Oconee received approval applicable to the fifth 10-year ISI interval from the NRC safety evaluation dated February 26, 2020 (ML20055F571) to preemptively apply a mitigation/repair using the rules of CC N-853 with a PWSCC resistant nozzle attached to the new weld pad with a full penetration nozzle corner weld using a non-temper bead manual welding technique, using PWSCC resistant nickel Alloy 52M filler metal, or with a "J" groove partial penetration weld as described in CC N-853. The welded pads are to be designed and installed in accordance with CC N-853 except that the replacement nozzle material is UNS S31600 or UNS N06690. The new welded pad provides a full structural primary pressure boundary repair that takes no structural credit for either the existing 82/182 weld or the Alloy 600 nozzle material.
The licensee stated that the requested relief from IWA-4000 is based on the use of CC N-853 (with the noted deviations described herein) which provides an alternative with an acceptable level of quality and safety. Additionally, the licensee describes that the subject welds are mitigated or repaired by application of a PWSCC resistant reinforcing pad and attachment of a PWSCC resistant nozzle and that the use of CC-853 as guidance for the repair/replacement activity provides an acceptable level of quality and safety.
Duke Energy is requesting relief applicable from the defect removal requirements of ASME Code,Section XI, Article IWA-4000 for the sixth 10-year ISI interval. The duration of each physical repair is requested for the remainder of the current licensed operating life of each Oconee unit (as described in section 3.4 of this safety evaluation.).
3.3.2 Alternative Acceptance Criteria Oconee received approval applicable to the fifth 10-year ISI interval from the NRC safety evaluation dated February 7, 2022 (ML22028A365) to use ASME Code,Section XI, IWB-3514 as an alternative acceptance criteria for disposition of defects detected during volumetric inspection via ultrasonic testing (UT) of the stress corrosion cracking resistant Alloy 52M weld pad in lieu of the ASME Code,Section III, NB-5330 criteria specified in CC N-853.
The licensee is requesting relief under 10 CFR 50.55a(z)(1) from the ASME Code,Section XI CC N-853 inspection requirements with the method stated herein based on the use of CC N-853 (with the noted deviations described herein) that provides an alternative with an acceptable level of quality and safety. The licensee stated that the subject welds will be preemptively mitigated or repaired by application of a PWSCC resistance reinforcing pad and attachment of a PWSCC resistant nozzle, and that the use of CC N-853 as guidance for the repair/replacement activity, as modified, provides an acceptable level of quality and safety.
Duke Energy is requesting relief to continue to use the alternative acceptance criteria for volumetrically inspecting weld pads for the identified affected components during Oconee 1, 2, and 3s sixth 10-year ISI interval.
3.4 Duration of Proposed Alternative The licensee is requesting to implement this proposed alternative for the sixth 10-year ISI interval for Oconee 1, 2, and 3 which is scheduled to start on July 15, 2024, and end on July 14, 2034. The duration of each physical repair is requested for the remainder of the current licensed operating life of each Oconee unit. The repairs are designed to meet the requirements of CC N-853 (with the noted deviations described herein), ASME Code,Section III, and ASME Code,Section XI. The design considers operation until the end of the current renewed operating license for each unit as shown below.
Table 2: Oconee Nuclear Station Subsequent Operating Reactor License Expiration Dates Docket Number License Expires Unit 1 05000269 02/06/2033 Unit 2 05000270 10/06/2033 Unit 3 05000287 07/19/2034 3.5
NRC Staff Evaluation
3.5.1 Alternative Repair Technique The NRC staff has reviewed and evaluated the licensees request on the basis that the proposed alternative would provide an acceptable level of quality and safety. The licensees proposed alternative is to use ASME Code Case N-853 to repair or proactively mitigate the Alloy 600 nozzle welds identified in Section 1.0 of the licensees submittal with two allowed deviations to the requirements of the CC N-853. One deviation is that the new nozzle material may be manufactured from stainless steel material instead of the nickel alloy 690 material described in the code case, and the second deviation is the use of a full penetration nozzle corner weld instead of a partial penetration J-groove weld to attach the new nozzle.
The CC N-853 is an alternative to the defect removal requirements of Article IWA-4000 of Section XI of the ASME Code. It allows a licensee to modify a full penetration branch connection, which is susceptible to PWSCC, by deposition of a branch connection weld metal buildup and weld a branch connection to the weld metal buildup using base material and weld metal that is more resistant to PWSCC. A branch connection weld metal buildup is essentially a weld pad that is applied over a branch connection nozzle, associated full penetration butt weld and RCS primary piping in sufficient size to handle structural design and analytical evaluation of any postulated flaws through the PWSCC materials underneath the weld pad. In accordance with paragraph 2(d)(1) of the code case, the design, fabrication and installation of the replacement nozzle, and replacement nozzle weld shall be in accordance with the requirements of the licensees construction code. However, per the same paragraph of CC N-853 the replacement nozzle design shall be a partial penetration weld. Further, paragraph 1.2(e) specifies that the replacement nozzle base material shall be UNS N06690. These items are areas for which the licensee is proposing deviations from CC N-853.
On March 16, 2020, a final rule was published in the Federal Register (85 FR 14736) that incorporates by reference NRC Regulatory Guide 1.147, Revision 19 (ML19128A244). The NRC staff notes that CC N-853 was included in Table 1, and it was authorized by the NRC to be used by licensees without conditions, as an alternative to the ASME Code if all requirements of the code case are met. As such, the NRC staff finds the licensees proposed alternative to use CC N-853 would provide an acceptable level of quality and safety. Therefore, the remaining focus of the NRC staff review of the licensees proposed alternative repair is on the two deviations from CC N-853.
The first deviation the licensee described was to allow the optional use of an austenitic stainless steel (UNS S31600) in lieu of the nickel alloy 690 (UNS N06690) for the replacement nozzle in conjunction with a full penetration corner weld. The NRC staff agrees that the use of UNS S31600 versus UNS N06690 provides similar resistance to PWSCC over the projected design life of the repairs as proposed by the licensee. Further, since the licensee will ensure all applicable ASME Code allowable stresses and material properties for UNS S31600 will be used in the design of the replacement nozzle, the NRC staff finds this deviation is acceptable for use with CC N-853 to address mitigation against PWSCC for the proposed design life of the repair.
Therefore, the NRC staff finds that this deviation would provide an acceptable level of quality and safety.
The second deviation described by the licensee was to allow the optional use of a full penetration nozzle corner weld instead of a partial penetration J-groove weld when an austenitic stainless steel nozzle would be used in accordance with the licensees proposed alternative.
The NRC staff notes that the licensee confirmed that the full penetration nozzle corner weld will be designed and installed in accordance with ASME Code,Section III, Figure NB-4244(b)-1 detail (a). The NRC staff finds that this meets or exceeds the licensees original construction code requirements for the installation of this weld joint. The NRC staff also noted the licensees confirmation that the full penetration corner weld will be examined in accordance with the 2013 Edition of Section III of the CC N-853. The NRC staff notes that these inspection requirements will meet or exceed the inspection requirements of the original construction code or CC N-853 for the partial penetration weld joint and are acceptable to provide reasonable assurance of structural integrity of the joint for the licensees proposed duration of the repair. Therefore, the NRC staff finds that this deviation would provide an acceptable level of quality and safety.
3.5.2 Alternative Acceptance Criteria The NRC staff evaluated proposed alternative RA-23-0018 pursuant to 10 CFR 50.55a(z)(1), to determine whether the alternative acceptance criteria for volumetrically inspecting the weld pad provides an acceptable level of quality and safety.
The licensee confirmed that it will comply with the CC N-853, Section 3, paragraph (d)(3) requirements with the following proposed conditions when performing UT to accept the weld pads installed on the nozzle components listed in Section 1.0 of Enclosure to Alternative RA-23-0018. The NRC staffs evaluation of the licensees proposed conditions is discussed below.
If the results of the examination are acceptable under NB-5330 criteria, [the licensee] will follow CC N-853 required subsequent ISI for that weld pad (i.e.,
visual examination).
The NRC staff finds the licensees proposed inspection acceptable because no planar fabrication defects regardless of length or depth will be left in service that requires periodic volumetric monitoring. The CC N-853-required subsequent visual examinations is adequate to verify leak tightness of the weld pad and associated components of the repaired nozzle during plant operating license.
If a defect is detected in a weld pad that is rejectable under NB-5330 but acceptable under IWB-3514, [the licensee] will perform a subsequent, one-time volumetric examination of that weld pad during the first or second refueling outage following installation. If the volumetric examination shows no indication of crack growth or new cracking, the weld pad is placed into a population (per unit) to be examined on a sample basis. Twenty-five percent of this population shall be added to the ISI program and shall be examined volumetrically once each inspection interval If during the subsequent, one-time volumetric examination of a weld pad, or subsequent examinations, there is an indication of crack growth or new cracking,
[the licensee] will evaluate the condition of the weld pad in accordance with Section XI of the ASME Code and take action (e.g., repair, subsequent re-examination, etc.) in accordance with ASME Code requirements.
The NRC staff finds the inspection described in Section 5.3 of the licensees proposed alternative - including all conditions specified as applicable and solely limited to N-853 weld pads - acceptable because the location and vicinity of the planar fabrication defects left in service under IWB-3514 will receive periodic volumetric examinations during plant operating license, and the licensee will take corrective action if it identifies, through subsequent examination and monitoring, the planar fabrication defects are growing or new defects are identified in the area or volume scanned.
In conclusion, NRC staff notes that the implementation of this proactive mitigation will address a safety concern of PWSCC susceptibility of the reactor coolant pressure boundary for the remaining design life of the repair. Therefore, given the basis above, the NRC staff concludes that the licensees proposed alternative to use CC N-853 with the two identified deviations and alternative volumetric inspection criteria provides an acceptable level of quality and safety.
4.0 CONCLUSION
The NRC staff has determined that the proposed alternative in the licensees request referenced above would provide 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 proposed alternative RA-23-0018 at Oconee 1, 2, and 3 for the sixth 10-year ISI interval, which is scheduled to begin on July 15, 2024, and end on July 14, 2034.
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 Contributors: Mathew Burton, NRR Jay Collins, NRR Date: October 20, 2023
ML23285A074 OFFICE NRR/LPL2-1/PM NRR/LPL2-1/PM NRR/LPL2-1/LA NRR/DNRL/NPHP/BC NAME ZTurner SWilliams KGoldstein MMitchell DATE 10/11/2023 10/16/2023 10/16/2023 10/10/2023 OFFICE NRR/LPL2-1/BC NRR/LPL2-1/PM NAME MMarkley (JLamb for)
SWilliams DATE 10/20/2023 10/20/2023