ML20055F571
| ML20055F571 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 02/26/2020 |
| From: | Markley M Plant Licensing Branch II |
| To: | Burchfield E Duke Energy Carolinas |
| Mahoney M | |
| References | |
| EPID L-2019-LLR-0028 | |
| Download: ML20055F571 (10) | |
Text
February 26, 2020 Mr. J. Ed Burchfield, Jr.
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 - PROPOSED ALTERNATIVE REQUEST 19-ON-001 TO USE MODIFIED AMERICAN SOCIETY OF MECHANICAL ENGINEERS BOILER AND PRESSURE VESSEL CODE CASE N-853 (EPID NO. L-2019-LLR-0028)
Dear Mr. Burchfield:
By letter RA-19-0028, dated March 21, 2019 (Agencywide Documents Access and Management System Accession No. ML19084A197), Duke Energy Carolinas, LLC (the licensee) submitted Relief Request 19-ON-001 to the U.S. Nuclear Regulatory Commission (NRC or the Commission) for the fifth 10-year inservice inspection (ISI) interval for the Oconee Nuclear Station, Unit Nos. 1, 2 and 3 (Oconee 1, 2 and 3).
Pursuant to Title 10 of the Code of Federal Regulations (10 CFR), Part 50, Paragraph 55a(z)(1),
the licensee requested the NRC to authorize the use of an alternative to the requirements of Section XI of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) for the repair or mitigation of several Alloy 600 nozzle welds at Oconee 1, 2 and 3. Specifically, pursuant to 10 CFR 50.55a(z)(1), the licensee requested to use a proposed alternative on the basis that the proposed alternative would provide an acceptable level of quality and safety.
The NRC staff has concluded that the proposed alternative, in Relief Request 19-ON-001, provides reasonable assurance of structural integrity of the subject components and, therefore, provides an acceptable level of quality and safety. Accordingly, the NRC staff concludes that the licensee has adequately addressed all the regulatory requirements set forth in 10 CFR 50.55a(z)(1). Therefore, the NRC staff authorizes the use of relief request 19-ON-001 at Oconee 1, 2 and 3 for the remainder of the fifth 10-year ISI interval, which are scheduled to end on July 15, 2024.
All other ASME 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.
J. E. Burchfield, Jr.
If you have any questions, please contact the Project Manager, Michael Mahoney at 301-415-3867 or via e-mail at Michael.Mahoney@nrc.gov.
Sincerely,
/RA/
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 w/encl: Distribution via ListServ
Enclosure SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION PROPOSED ALTERNATIVE REQUEST 19-ON-001 TO USE MODIFIED AMERICAN SOCIETY OF MECHANICAL ENGINEERS BOILER AND PRESSURE VESSEL CODE CASE N-853 DUKE ENERGY CAROLINAS, LLC OCONEE NUCLEAR STATION, UNITS 1, 2, AND 3 DOCKET NUMBERS 50-269, 50-270, AND 50-287
1.0 INTRODUCTION
By letter RA-19-0028, dated March 21, 2019 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML19084A197), Duke Energy Carolinas, LLC (the licensee) submitted Relief Request 19-ON-001 to the U.S. Nuclear Regulatory Commission (NRC or the Commission) for the fifth 10-year inservice inspection (ISI) interval for the Oconee Nuclear Station, Unit Nos. 1, 2 and 3 (Oconee 1, 2 and 3).
Pursuant to Title 10 of the Code of Federal Regulations (10 CFR), Part 50, Paragraph 55a(z)(1),
the licensee requested the NRC to authorize the use of an alternative to the requirements of Section XI of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) for the repair or mitigation of several Alloy 600 nozzle welds at Oconee 1, 2 and 3. Specifically, pursuant to 10 CFR 50.55a(z)(1), the licensee requested to use a proposed alternative on the basis that the proposed alternative would provide 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, geometry, and materials of construction of the components.
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, lists the ASME Section XI Code Cases that the NRC has approved for use as voluntary alternatives to the mandatory ASME Boiler and Pressure Vessel (BPV) 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 remainder of the fifth 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 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-PHB-13 1B Hot Leg RTE Mounting Boss Alloy 600 Nozzle Welds 1-PHB-14 1-PHB-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-PHA-13 2A Hot Leg RTE Mounting Boss Alloy 600 Nozzle Welds 2-PHA-14 2-PHA-15 2-PHB-13 2B Hot Leg RTE Mounting Boss Alloy 600 Nozzle Welds 2-PHB-14 2-PHB-15 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-PHA-13 3A Hot Leg RTE Mounting Boss Alloy 600 Nozzle Welds 3-PHA-14 3-PHA-15 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
- Small bore piping (1 inch nominal pipe size) nozzle welds are not given explicit weld IDs on original drawings. These nine specific small bore nozzle welds are located by the nearest documented branch connection butt weld.
3.2 Applicable Code Edition The code of record for the fifth 10-year ISI interval at Oconee 1, 2 and 3 is the ASME Code,Section XI, 2007 Edition and 2008 Addenda. All three units are in the fifth 10-year inspection interval with a scheduled end date of July 15, 2024. The code of construction for Oconee 1, 2, and 3 is ASME B31.7, 1969 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 inservice inspection requirement to perform visual examinations of the specified welds for leakage.
3.3 Licensees Proposed Alternative 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 3.1 of this safety evaluation (SE).
In addition, two deviations are proposed from the requirements of ASME Code Case N-853 as follows:
(1) the new nozzle material may be manufactured from Unified Numbering System (UNS) S31600 material instead of UNS N06690, and (2) the new nozzle may be attached by a full penetration nozzle corner weld instead of a partial penetration J-groove weld.
3.4 Licensees Bases for Use The licensee explains that the welds identified in Section 3.1 of this SE, are unmitigated full penetration welds fabricated from materials susceptible to primary water stress corrosion cracking (PWSCC). As these welds are unmitigated, there exists the potential that flaws may develop at these locations and result in leakage. In accordance with ASME Code Case N-722-1, these welds require frequent visual examination for the identification of any reactor coolant system (RCS) leakage.
The licensee is proposing to apply a welded reinforcing pad (weld pad) on the outside diameter (OD) of the RCS piping using PWSCC-resistant nickel Alloy 52M filler metal. The new weld pad will be welded using the machine gas tungsten arc welding (GTAW) ambient temperature temper bead (ATTB) welding technique. The licensee 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 N-853. The weld pad will be designed and installed in accordance with ASME Code Case N-853, except that the replacement nozzle material will be UNS S31600 or UNS N06690.
Guidance in ASME Code Case N-853 requires the use of UNS N06690 material for replacement nozzles. The licensee proposes, as an option, to use UNS S31600 material for the replacement nozzle. Currently, UNS S31600 material is used in many applications for elevated temperature RSC piping at Oconee 1, 2 and 3. The licensee notes that UNS S31600 is an austenitic stainless steel that has demonstrated operating experience as a more PWSCC-resistant material. The licensee confirmed that the applicable ASME Code allowable stresses and material properties for UNS S31600 will be used in the design of the replacement nozzle. The licensee explained that the reason for the requested use of UNS S31600 is that this material is a more readily available material, given the strict ASME Code Class 1 requirements for materials, and the small volume of material required for these specific locations.
Guidance in ASME Code Case N-853 requires the use of a partial penetration J-groove weld for the attachment of the new nozzle to the reinforcing weld metal buildup. The licensee reasons that the partial penetration J-groove weld is one of many ASME Code approved configurations for attachment of nozzles to piping. The licensee proposes to optionally use a full penetration nozzle corner weld to join the new nozzle to the weld pad. The licensee states that the full penetration nozzle corner weld configuration proposed will be in accordance with ASME Code,Section III, Figure NB-4244(b)-1, detail (a). The licensee also confirms that the full penetration corner weld will be examined in accordance with the 2013 Edition of Section III of the ASME Code and ASME Code Case N-853.
The licensee explains that the reason for the requested optional use of the nozzle corner weld is that field conditions of access and interferences may result in situations where the corner weld is preferable to the J-groove weld, based on dose exposure and installation sequence.
Additionally, the licensee justifies that use of a full penetration corner weld should eliminate the creation of a small pocket area at the base of the nozzle which could over time collect contaminants and create a radiological hot spot in the RCS piping.
At the time that the licensee submitted its request, ASME Code Case N-853 had not yet been approved by the NRC for incorporation by reference in 10 CFR 50.55a, but it had been reviewed by the NRC and was proposed to be approved for unconditional use in a proposed rulemaking in the Federal Register, dated August 16, 2018, (83 FR 40685). Therefore, the licensee requested relief under 10 CFR 50.55a(z)(1) from the defect removal requirements of ASME Code,Section XI, Article IWA-4000.
The licensee states that the identified welds will be mitigated by a repair/replacement activity that meets the requirements of ASME Code Case N-853 with the alternative nozzle material and weld joint geometry requested. The licensee proposes that this repair/replacement activity provides an acceptable level of quality and safety.
3.5 Duration of Proposed Alternative The licensee is requesting to implement this proposed alternative for the remainder of the fifth 10-year ISI interval for Oconee 1, 2 and 3 which is scheduled to end on July 15, 2024. The duration of each physical repair is requested for the remainder of the current licensed operating life of each Oconee unit.
3.6 NRC Staffs Technical Evaluation 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 3.1 of this SE, with two deviations. The first deviation would be that the new nozzle material would be manufactured from stainless steel material instead of the nickel Alloy 690 material, as described in the code case, and the second deviation being the use of a full penetration nozzle corner weld instead of a partial penetration J-groove weld to attach the new nozzle.
Guidance in ASME Code Case 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 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 ASME Code Case N-853, 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 ASME Code Case 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 ASME Code Case N-835.
On August 16, 2018, the NRC staff notes that ASME Code Case N-853 was included in Table 1 of NRC Regulatory Guide (RG) 1.147, Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1, Revision 19, in a proposed rulemaking. The NRC received no public comments on the ASME Code Case N-853 and anticipates publishing the final rule by March of 2020. ASME Code Cases included in Table 1 of RG 1.147 are 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. The NRC staffs rulemaking process for adoption of an ASME Code Case into RG 1.147 is a rigorous process that includes multiple years of NRC staff activity during the development of the ASME Code Case. Voting membership on committees and boards are sought to review and approve the code case as part of the ASME Code approval process and the final step is the NRC rulemaking activity for RG 1.147 revision in 10 CFR 50.55a. Given this review process and history of NRC staff approval, the NRC staff finds the licensees proposed alternative use of ASME Code Case 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 is on the two deviations from ASME Code Case N-853.
The first deviation 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 compared to 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 ASME Code Case 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 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 ASME Code and ASME Code Case N-853. The NRC staff notes that these inspection requirements will meet or exceed the inspection requirements of the original construction code or ASME Code Case 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.
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.
Based on the above, the NRC staff concludes that the licensees proposed alternative to use ASME Code Case N-853 with the two identified deviations provides an acceptable level of quality and safety.
4.0 CONCLUSION
The NRC staff has concluded that the proposed alternative, in Relief Request 19-ON-001, provides reasonable assurance of structural integrity of the subject components and, therefore, provides an acceptable level of quality and safety. Accordingly, the NRC staff concludes that the licensee has adequately addressed all the regulatory requirements set forth in 10 CFR 50.55a(z)(1).
Therefore, the NRC staff authorizes the use of Relief Request 19-ON-001 at Oconee Units 1, 2 and 3 for the remainder of the fifth 10-year ISI intervals, which are scheduled to end on July 15, 2024.
All other ASME 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.
Principal Contributor: J. Collins, NRR Date: February 26, 2020
- By Email OFFICE NRR/DORL/LPL2-1/PM NRR/DORL/LPL2-1/LA NRR/DNRL/NPHP/BC*
NAME MMahoney KGoldstein MMitchell DATE 02/26/2020 02/25/2020 02/19/2020 OFFICE NRR/DORL/LPL2-1/BC NAME MMarkley DATE 02/26/2020