ML20268C232
| ML20268C232 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 11/04/2020 |
| From: | Nancy Salgado Plant Licensing Branch III |
| To: | Bryan Hanson Exelon Generation Co |
| Wiebe J | |
| References | |
| EPID L-2019-LLR-0117 | |
| Download: ML20268C232 (10) | |
Text
November 4, 2020 Mr. Bryan C. Hanson Senior Vice President Exelon Generation Company, LLC President and Chief Nuclear Officer (CNO)
Exelon Nuclear 4300 Winfield Road Warrenville, IL 60555
SUBJECT:
CLINTON POWER STATION, UNIT NO. 1 - PROPOSED ALTERNATIVE I4R-06 TO THE REQUIREMENTS OF THE ASME CODE (EPID L-2019-LLR-0117)
Dear Mr. Hanson:
By letter dated December 16, 2019 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML19350C642), as supplemented by letter dated August 13, 2020 (ADAMS Accession No. ML20226A449), Exelon Generation Company, LLC (the licensee) submitted a request to the U.S. Nuclear Regulatory Commission (NRC) for the use of an alternative to certain American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, requirements at Clinton Power Station, Unit No. 1 (Clinton).
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(1), the licensee requested to use alternative I4R-061 on the basis the alternative provides an acceptable level of quality and safety. The licensee proposed to use Boiling Water Reactor Vessel and Internals Project (BWRVIP) guidelines as an alternative to the inservice inspection (ISI) of reactor pressure vessel interior surfaces, attachments, and core support structures.
The NRC staff has reviewed the subject request and concludes, as set forth in the enclosed safety evaluation, that the licensees proposed alternative 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 the proposed alternative in request I4R-06 at Clinton for the duration of the fourth 10-year ISI interval, which commenced on July 1, 2020, and is currently scheduled to end June 30, 2030.
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.
1 The other requests contained in the licensees December 16, 2019, letter have been or will be addressed by separate correspondence.
If you have any questions, please contact the Senior Project Manager, Joel S. Wiebe, at (301) 415-6606 or Joel.Wiebe@nrc.gov.
Sincerely, Nancy L. Salgado, Chief Plant Licensing Branch III Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-461
Enclosure:
Safety Evaluation cc: Listserv Robert F.
Kuntz Digitally signed by Robert F. Kuntz Date: 2020.11.04 08:46:53 -05'00'
Enclosure SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION PROPOSED ALTERNATIVE I4R-06 REGARDING THE INSERVICE INSPECTION OF REACTOR PRESSURE VESSEL INTERIOR SURFACES, ATTACHMENTS, AND CORE SUPPORT STRUCTURES EXELON GENERATION COMPANY, LLC CLINTON POWER STATION, UNIT NO. 1 DOCKET NO. 50-461
1.0 INTRODUCTION
By letter dated December 16, 2019, (Agencywide Documents Access and Management System (ADAMS) Accession No. ML19350C642) as supplemented by letter dated August 13, 2020 (ADAMS Accession No. ML20226A449), Exelon Generation Company, LLC (the licensee) requested relief from the requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (B&PV Code) for Clinton Power Station, Unit No. 1 (Clinton). The licensee proposed to use Boiling Water Reactor Vessel and Internals Project (BWRVIP) guidelines as an alternative to certain requirements of Section XI of the ASME B&PV Code for the inservice inspection (ISI) of reactor pressure vessel interior surfaces, attachments, and core support structures. Pursuant to Title 10 of the Code of Federal Regulations (10 CFR)
Part 50.55a(z)(1), the licensee requested to use the proposed alternative on the basis that the alternative provides an acceptable level of quality and safety.
2.0 REGULATORY REQUIREMENTS The regulations in 10 CFR 50.55a(g)(4) state, in part, that ASME B&PV 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 Section XI of the applicable editions and addenda of the ASME B&PV Code to the extent practical within the limitations of design, geometry, and materials of construction of the components. The interior accessible areas, welded attachments, and the welded core support structures in the reactor pressure vessel (RPV) are categorized as ASME B&PV Code Class 1 components. Therefore, pursuant to 10 CFR 50.55a(g)(4), ISI of these areas and components must be performed in accordance with Section XI of the applicable edition and addenda of the ASME B&PV Code.
The regulations in 10 CFR 50.55a(z), Alternatives to codes and standards requirements, state:
Alternatives to the requirements of paragraphs (b) through (h) of this section
[50.55a] or portions thereof may be used when authorized by the Director, Office of Nuclear Reactor Regulation. A proposed alternative must be submitted and authorized prior to implementation. The applicant or licensee must demonstrate that:
(1) Acceptable Level of Quality and Safety. The proposed alternative would provide an acceptable level of quality and safety; or (2) Hardship without a Compensating Increase in Quality and Safety.
Compliance with the specified requirements of this section [50.55a] would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
Based on the above, and subject to the following technical evaluation, the NRC staff finds that the licensee may propose an alternative to ASME B&PV Code,Section XI, and the NRC staff has the regulatory authority to authorize the licensee's proposed alternative.
3.0 LICENSEES EVALUATION In this safety evaluation (SE), the term reactor vessel internal (RVI) components includes RPV interior surfaces, attachments, and core support structures.
The Components for Which an Alternative is Requested The components for which an alternative is requested are ASME B&PV Code,Section XI, Class 1, Examination Categories B-N-1 and B-N-2, Item Nos. B13.10 (Vessel Interior), B13.20 (Interior Attachments within Beltline Region), B13.30 (Interior Attachments beyond Beltline Region), and B13.40 (Core Support Structure).
Applicable ASME B&PV Code Edition The applicable Code of Record for the fourth 10-year ISI interval for Clinton is the ASME B&PV Code,Section XI, 2013 Edition.
Examination Requirements for Which an Alternative is Requested The ASME B&PV Code, Section Xl, requires the visual examination (VT) of certain RVI components. These examinations are included in Table IWB-2500-1, Categories B-N-1 and B-N-2, and identified with the following item numbers:
B13.10 - Examine accessible areas of the reactor vessel interior each period using a technique which meets the requirements for a VT-3 examination. This includes only those spaces above and below the core made accessible by removal of components during normal refueling outages.
B13.20 - Examine interior attachment welds within the beltline region each interval using a technique which meets the requirements for a VT-1 examination.
B13.30 - Examine interior attachment welds beyond the beltline region each interval using a technique which meets the requirements for a VT-3 examination.
B13.40 - Examine surfaces of the core support structure each interval using a technique which meets the requirements for a VT-3 examination.
These examinations are performed to assess the structural integrity of the RPV interior surfaces, its welded attachments, and the welded core support structures.
Licensees Basis for Requested Alternative In its letter dated December 16, 2019, the licensee requested to use an inspection program (I4R-06) in accordance with the BWRVIP guidelines for B-N-1 and B-N-2 RPV interior surfaces, attachments, and core support structures at Clinton as an alternative to the ASME B&PV Code,Section XI, requirements. The licensee stated that implementation of the alternative inspection program will maintain an acceptable level of quality and safety of the affected welds and components. The proposed alternative includes examination methods, examination volume, frequency, training, successive and additional examinations, flaw evaluations, and reporting.
The BWRVIP guidelines were developed based on inspection data gathered during many inspections of boiling water reactors. The proposed alternative is requested for the fourth 10-year ISI interval for Clinton, which commenced on July 1, 2020, and is currently scheduled to end on June 30, 2030.
Alternative Examination In lieu of the requirements of the applicable Edition of the ASME B&PV Code, Section Xl, the licensee proposed to examine the Clinton RVI components in accordance with the BWRVIP guidelines. The following reports include BWRVIP inspection and evaluation guidelines for the RPV interior surfaces, attachments, and core support structures (not all RVI components listed in these reports are ASME B&PV Code,Section XI, components):
BWRVIP-03, Reactor Pressure Vessel and Internals Examination Guidelines (ADAMS Accession No. ML17054C674)
BWRVIP-18, Revision 2-A, BWR Core Spray Internals Inspection and Flaw Evaluation Guidelines" (ADAMS Accession No. ML16302A123)
BWRVIP-26-A, BWR Top Guide Inspection and Flaw Evaluation Guidelines (ADAMS Accession No. ML043290158)
BWRVIP-27-A, BWR Standby Liquid Control System/Core Plate P Inspection and Flaw Evaluation Guidelines (proprietary)
BWRVIP-38, BWR Shroud Support Inspection and Flaw Evaluation Guidelines (ADAMS Accession No. ML20198H294)
BWRVIP-41, Revision 4-A, BWR Jet Pump Assembly Inspection and Flaw Evaluation Guidelines (ADAMS Accession No. ML19297G509)
BWRVIP-42, Revision 1-A, Low Pressure Coolant Injection System (LPCI) Coupling Inspection and Flaw Evaluation Guidelines (ADAMS Accession No. ML18075A051)
BWRVIP-47-A, BWR Lower Plenum Inspection and Flaw Evaluation Guidelines (ADAMS Accession No. ML043290026)
BWRVIP-48-A, Vessel ID Attachment Weld Inspection and Flaw Evaluation Guidelines (ADAMS Accession No. ML043290379)
BWRVIP-62-A Technical Basis for Inspection Relief for BWR Internal Components with Hydrogen Injection (ADAMS Accession No.ML19178A130)
BWRVIP-76, Revision 1-A, BWR Core Shroud Inspection and Flaw Evaluation Guidelines (ADAMS Accession No. ML15266A189)
BWRVIP-94, Program Implementation Guide (ADAMS Accession No. ML11271A058)
BWRVIP-138, Revision 1-A, Updated Jet Pump Beam Inspection and Flaw Evaluation Guidelines (ADAMS Accession No. ML090760986)
BWRVIP-180, Access Hole Cover Inspection and Flaw Evaluation Guidelines (proprietary)
BWRVIP-183-A, Top Guide Grid Beam Inspection and Flaw Evaluation Guidelines (ADAMS Accession No. ML18078A322)
In Table 2 of the proposed alternative, the licensee provided a comparison of the ASME B&PV Code,Section XI, examination requirements for B-N-1 and B-N-2 Categories of the reactor pressure vessel interior surfaces, attachments, and core support structures with the applicable BWRVIP guidelines listed above. In the Enclosure to the proposed alternative, the licensee provided additional information regarding the BWRVIP inspection guidelines for the following components of the reactor pressure vessel interior surfaces, attachments, and core support structures and their subcomponents representing each of the ASME B&PV Code,Section XI, Item Nos. B13.10, B13.20, B13.30, and B13.40:
Reactor Vessel Interior (B13.10)
Interior Attachments within Beltline (B13.20)
Interior Attachments beyond Beltline (B13.30)
Core Support Structure (B13.40)
For the components included in the above examination categories, the licensee stated that the inspection techniques that are recommended by the BWRVIP inspection guidelines meet or exceed the inspection techniques mandated by the ASME B&PV Code,Section XI, ISI program.
The licensee also stated the BWRVIP guidelines focus on specific and susceptible components, specify appropriate inspection methods capable of identifying known or potential degradation mechanisms, and required reexamination at appropriate intervals. The licensee concluded that implementation of the BWRVIP inspection guidelines for the Clinton RPV interior surfaces, attachments, and core support structures would provide an acceptable level of quality and safety while avoiding duplicate or unnecessary inspections and conserving radiological dose.
4.0 STAFF EVALUATION The NRC staff reviewed the information provided by the licensee in its submittals dated December 16, 2019, and August 13, 2020, regarding its proposed alternative to the ASME B&PV Code,Section XI, ISI requirements and the technical bases for the licensees proposed alternative. The result of the NRC staffs review is described below.
Examination of RVI (Item B13.10)
The ASME B&PV Code requires a VT-3 examination of the RVI which is above and below the core beltline, and which is made accessible during normal refueling outages. For the first inspection interval, the ASME B&PV Code requires inspection at the first refueling outage and at approximately 3-year intervals thereafter. For the second and successive inspection intervals, the ASME B&PV Code requires inspection once each inspection period.
Portions of the various examinations required by the applicable BWRVIP guidelines (referenced in Section 3.0 of this SE) require access to the accessible areas of the reactor vessel during each refueling outage. According to the licensee, BWRVIP examination of core spray piping and spargers, top guide, shroud support, jet pump welds and components, LPCI couplings, lower plenum components, interior attachments, core shroud welds, access hole cover, and top guide beams provides ISI of the ASME B&PV Code defined Item B13.10 RVI. The licensee stated that no inspections of the lower plenum components are planned for the fourth ISI interval because there is no access to the lower plenum without removal of components such as control guide tubes or jet pump mixers. But the licensee also stated that if the lower plenum welds become accessible, inspections will be performed to the extent possible during the refueling outage. This meets the guidelines of BWRVIP-47-A which only requires examination of accessible lower plenum welds.
The licensee stated that the remote camera systems used in these BWRVIP examinations provide an equivalent method of visual examination on a more frequent basis than that required by the ASME B&PV Code. During the BWRVIP examinations, evidence of wear, structural degradation, loose, missing or displaced parts, foreign materials, and corrosion product buildup can be observed. The licensee concluded that the specified BWRVIP guideline requirements meet or exceed the ASME B&PV Code requirements for Item B13.10 examination of the reactor vessel interior.
There is a correlation between the chemical mitigation program implemented and the inspection frequency specified by the BWRVIP alternatives. The licensee stated in its letter dated August 13, 2020, that it uses Online Noble ChemTM (OLNC) to mitigate the effects of intergranular stress corrosion cracking at Clinton. The licensee further stated that it meets the conditions and limitations of BWRVIP-62-A Technical Basis for Inspection Relief for BWR Internal Components with Hydrogen Injection (ADAMS Accession No.ML19178A130) and provided data to show that it meets the criteria of a Category 3a plant as defined in BWRVIP A. Based on the information provided by the licensee, the NRC staff determined that the licensee meets the conditions and limitations of BWRVIP-62-A, which includes the final NRC SE dated April 21, 2010 (ADAMS Accession No. ML100850009), and the final supplemental SE dated July 6, 2018 (ADAMS Accession No. ML18142A019). These conditions and limitations require that plants which use OLNC and wish to claim inspection credit must meet the criteria of a Category 3a plant as defined in BWRVIP-62-A. Based on the licensees stated compliance with BWRVIP-62-A, including the final supplemental SE dated July 6, 2018, the NRC finds that the licensee may adopt the inspection frequencies specified by the BWRVIP alternatives for plants using OLNC.
Based on a comparison of the BWRVIP guideline requirements with the ASME B&PV Code requirements the NRC staff determined that the licensee meets or exceeds the ASME B&PV Code requirements for Item B13.10 examination of the RVI and finds that the licensee proposed alternative provides an acceptable level of quality and safety for the Item B13.10 components.
Examination of Interior Attachments Within Beltline (Item B13.20)
The ASME B&PV Code requires a VT-1 examination of accessible RVI attachment welds within the beltline region during each inspection interval.
The licensee specifically lists the jet pump riser braces and lower surveillance specimen holder brackets as Item B13.20 components which are to be examined in accordance with BWRVIP-48-A. BWRVIP-48-A requires the lower surveillance specimen holder bracket attachment to be examined by VT-1 each inspection interval, which is the same level of inspection and frequency as required by the ASME B&PV Code. BWRVIP-48-A requires an enhanced VT-1 (EVT-1) bare metal examination of 100 percent of the jet pump riser brace attachments during the first 12 years, and then 25 percent EVT-1 examination during each subsequent 6 years. The BWRVIP EVT-1 exams require the same character resolution as the ASME B&PV Code VT-1 examinations, but with a more stringent viewing angle for remote video examination and the performance of a cleaning assessment and cleaning as necessary. The NRC staff finds that the licensee proposed alternative provides an acceptable level of quality and safety for the Item B13.20 components because the proposed alternative provides for equivalent or superior flaw detection and characterization than the ASME B&PV Code requirements.
Examination of Interior Attachments Beyond Beltline (Item B13.30)
The ASME B&PV Code requires a VT-3 examination of accessible reactor vessel interior attachment welds beyond the beltline region during each inspection interval.
The licensee specifically lists the core spray piping support brackets, upper surveillance specimen support brackets, feedwater sparger support brackets, steam dryer hold-down brackets, steam dryer support brackets, guide rod support brackets, as Item B13.30 welded components which are to be examined in accordance with BWRVIP-48-A. The licensee also lists the shroud supports as Item B13.30 welded components which are to be examined in accordance with BWRVIP-38. For the steam dryer hold-down brackets, the guide rod brackets, and the upper surveillance specimen holder brackets, the BWRVIP-48-A requires a VT-3 examination each inspection interval, which is the same level and frequency as required by the ASME B&PV Code. For the steam dryer support brackets and the feedwater sparger brackets, the BWRVIP-48-A requires an EVT-1 examination each inspection interval, which is an enhanced level of inspection, with the same frequency as the ASME B&PV Code. For the core spray piping brackets, the BWRVIP-48-A requires an EVT-1 every four cycles, which is an enhanced level of inspection and an increased frequency compared to the ASME B&PV Code.
For the shroud support welds, the BWRVIP-38 requires either an EVT-1 examination every 6 years, or an ultrasonic (UT) examination, which is an enhanced level of inspection and the same or increased frequency compared to the ASME B&PV Code. For the shroud support leg weld (weld H12), the licensee stated that no inspections are planned during the fourth ISI interval since there is no access without removing other components such as the control rod guide tubes or jet pump mixers. The licensee also stated that if the shroud support leg welds become accessible, then examinations will be performed to the maximum extent practical during that refueling outage. This meets the guidelines of the BWRVIP-38 SE which only requires examination of accessible shroud support leg welds.
The NRC staff finds that the licensee proposed alternative provides an acceptable level of quality and safety for the Item B13.30 components because the proposed alternative provides for equivalent or superior flaw detection and characterization with an examination frequency that is equivalent or more frequent than the ASME B&PV Code requirements.
Examination of Core Support Structure (Item B13.40)
The ASME B&PV Code requires a VT-3 examination of accessible surfaces of the core support structure during each inspection interval.
The licensee specifically lists the shroud support, shroud support legs, shroud vertical welds, and shroud repair tie rods as Item B13.40 components which are to be examined according to the BWRVIP guidelines. For the shroud support, BWRVIP-38 requires either EVT-1 or UT based on as-found conditions, to a maximum 6 years for EVT-1 and 10 years for UT where accessible. The licensee stated that no inspections of the shroud support legs are planned during the fourth ISI interval since there is no access without removing other components such as the control rod guide tubes or jet pump mixers. The licensee also stated that if the shroud support leg welds become accessible, then examinations will be performed to the maximum extent practical during that refueling outage. This meets the guidance of the BWRVIP-38 SE which only requires examination of accessible shroud support leg welds.
For the core shroud vertical welds, BWRVIP-76, Revision 1-A, requires either EVT-1 or UT inspections with a maximum 10-year interval based on inspection of horizontal welds. Since the licensee proposes to inspect the tie rods in lieu of the core shroud horizontal welds, the licensee has established inspection intervals for all core shroud vertical welds at a 10-year interval.
Where BWRVIP-76, Revision 1-A, requires EVT-1 or UT inspection of these components, these methods are more effective in identifying defects than the VT-3 inspection prescribed in the ASME B&PV Code. The licensee also stated that tie rod repairs would be examined in accordance with BWRVIP-76, Revision 1-A, Section 3.5.
The NRC staff finds that for Item B13.40 components, the BWRVIP examination frequency is equivalent or more frequent than that provided by the ASME B&PV Code. The NRC staff also finds that the proposed superior flaw detection and characterization capability, with an equivalent or more frequent examination frequency and the comparable flaw evaluation criteria, provides a level of quality and safety equivalent or superior to the ASME B&PV Code requirements for the Item B13.40 components.
5.0 CONCLUSION
As set forth above, the NRC staff determines that the licensees proposed alternative 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 the proposed alternative in Request No. I4R-06 at Clinton for the remainder of the fourth 10-year ISI interval, which commenced July 1, 2020, and is currently scheduled to end June 30, 2030.
This SE approves only the use of those versions of the BWRVIP topical reports that were requested in the licensee submittals dated December 16, 2019, and August 13, 2020. Use of later versions of BWRVIP topical reports at Clinton for the fourth 10-year ISI interval requires the licensee to submit the revised alternative request for approval prior to its use.
All other requirements of ASME B&PV Code,Section XI, for which an alternative has not been specifically requested remain applicable, including third party review by the Authorized Nuclear In-service Inspector. Any ASME B&PV Code,Section XI, RVI components that are not included in this request for alternative will continue to be inspected in accordance with the ASME B&PV Code,Section XI requirements.
Principal Contributor:
Joel Jenkins, NRR/DNRL/NVIB Dated: November 4, 2020
- via e-mail OFFICE NRR/DORL/LPL3/PM*
NRR/DORL/LPL3/LA*
NRR/DNRL/NVIB/BC(A)*
NAME JWiebe SRohrer JTsao DATE 10/05/2020 09/28/2020 09/03/2020 OFFICE NRR/DORL/LPL3/BC*
NAME NSalgado (RKuntz for)
DATE 11/04/2020