ML23048A304
| ML23048A304 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry, Watts Bar, Sequoyah  |
| Issue date: | 03/08/2023 |
| From: | David Wrona Plant Licensing Branch II |
| To: | Jim Barstow Tennessee Valley Authority |
| Green K | |
| References | |
| EPID L-2022-LLR-0045, EPID L-2022-LLR-0046, EPID L-2022-LLR-0047 | |
| Download: ML23048A304 (26) | |
Text
March 8, 2023 Mr. James Barstow Vice President, Nuclear Regulatory Affairs and Support Services Tennessee Valley Authority 1101 Market Street, LP 4A-C Chattanooga, TN 37402-2801
SUBJECT:
TENNESSEE VALLEY AUTHORITY - REQUEST FOR RELIEF FROM THE REQUIREMENTS OF THE ASME BOILER AND PRESSURE VESSEL CODE REGARDING WELD EXAMINATION COVERAGE (EPID L-2022-LLR-0045,
-0046, -0047)
Dear Mr. Barstow:
By letter dated April 25, 2022, the Tennessee Valley Authority (TVA, the licensee) submitted a request to the Nuclear Regulatory Commission (NRC) for relief from certain American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPV Code),Section XI requirements at Browns Ferry Nuclear Plant (Browns Ferry), Units 1, 2, and 3, Sequoyah Nuclear Plant (Sequoyah), Units 1 and 2, and Watts Bar Nuclear Plant (Watts Bar), Units 1 and 2.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(g)(5)(iii),
TVA requested relief and to use alternative requirements for inservice inspection (ISI) items on the basis that the code requirement is impractical.
The NRC staff has reviewed the subject request and concludes, as set forth in the enclosed safety evaluations, that granting relief is authorized by law, will not endanger life or property or the common defense and security, and is otherwise in the public interest, giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility. Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in the regulations at 10 CFR 50.55a(g)(5)(iii). Therefore, the NRC staff grants relief from the ASME BPV Code examination requirements for the welds included in:
BFN-0-ISI-31 for Browns Ferry, Units 1, 2, and 3, for the first period of the third, fifth and fourth 10-year ISI intervals, respectively, which are currently scheduled to end on January 31, 2026; SQN-19-ISI-1 at Sequoyah, Units 1 and 2, for first period of the fourth 10-year ISI interval, which is currently scheduled to end on September 3, 2025; and WBN-19-ISI-1 at Watts Bar, Units 1 and 2, for the first period of the third and first 10-year ISI intervals, respectively, which are currently scheduled to end on May 26, 2026.
J. Barstow All other ASME BPV Code,Section XI requirements for which relief was not specifically requested and approved in this relief request remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
If you have any questions, please contact Ms. Kimberly Green at 301-415-1627 or via email at Kimberly.Green@nrc.gov.
Sincerely, David J. Wrona, Chief Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-259, 50-260, 50-296 50-327, 50-328 50-390, 50-391
Enclosures:
- 1. Safety Evaluation for BFN-0-ISI-31
- 2. Safety Evaluation for SQN-19-ISI-1
- 3. Safety Evaluation for WBN-19-ISI-1 cc: Listserv David J.
Wrona Digitally signed by David J. Wrona Date: 2023.03.08 12:42:57 -05'00'
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST BFN-0-ISI-31 REGARDING WELD EXAMINATION COVERAGE TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT, UNITS 1, 2, AND 3 DOCKET NOS. 50-259, 50-260, AND 50-296
1.0 INTRODUCTION
By letter dated April 25, 2022 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML22115A235), the Tennessee Valley Authority (TVA or the licensee),
submitted Relief Request BFN-0-ISI-31 to the U.S. Nuclear Regulatory Commission (NRC or Commission) for the third, fifth, and fourth 10-year inservice inspection (ISI) interval at Browns Ferry Nuclear Plant, Units 1, 2, and 3 (Browns Ferry), respectively. The licensee requested relief from the examination coverage requirements of Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME BPV Code), applicable to certain ASME Code Class 1 and 2 component weld examinations at Browns Ferry, Units 1, 2, and 3.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(g)(5)(iii),
the licensee requested relief on the basis that achieving the ASME BPV Code-required volumetric examination coverage for the subject welds in Relief Request BFN-0-ISI-31 is impractical.
2.0 REGULATORY EVALUATION
Pursuant to 10 CFR 50.55a(g)(4), Inservice inspection standards requirement for operating plants, components (including supports) that are classified as ASME Code Class 1, Class 2, and Class 3 must meet the requirements, except design and access provisions and preservice examination requirements set forth in Section XI of editions and addenda of the ASME BPV Code that become effective subsequent to editions specified in paragraphs (g)(2) and (3) of 10 CFR 50.55a, which are incorporated by reference in paragraph (a)(1)(ii) of 10 CFR 50.55a to the extent practical within the limitations of design, geometry, and materials of construction of the components.
Pursuant to 10 CFR 50.55a(g)(4)(ii), Applicable ISI Code: Successive 120-month Intervals, in-service examination of components and system pressure tests conducted during successive 120-month inspection intervals must comply with the requirements of the latest edition and addenda of the ASME Code incorporated by reference in paragraph (a) of 10 CFR 50.55a 18 months before the start of the 120-month inspection interval (or the optional ASME Code Cases listed in NRC Regulatory Guide (RG) 1.147, Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1, when using ASME BPV Code,Section XI, as incorporated by reference in paragraph (a)(3)(ii) of 10 CFR 50.55a, subject to the conditions listed in paragraph (b) of 10 CFR 50.55a.
Pursuant to 10 CFR 50.55a(g)(5)(iii), ISI Program Update: Notification of impractical ISI Code requirements, if the licensee has determined that conformance with a ASME Code requirement is impractical for its facility, the licensee must notify the NRC and submit, as specified in 10 CFR 50.4, information to support the determinations. Determinations of impracticality in accordance with 10 CFR 50.55a(g)(5)(iii) must be based on the demonstrated limitations experienced when attempting to comply with the ASME Code requirements during the ISI interval for which the request is being submitted. Requests for relief made in accordance with 10 CFR 50.55a(g)(5)(iii) must be submitted to the NRC no later than 12 months after the expiration of the initial or subsequent 120-month inspection interval for which relief is sought.
Pursuant to 10 CFR 50.55a(g)(6)(i), Impractical ISI requirements: Granting of relief, the Commission will evaluate determinations under paragraph 10 CFR 50.55a(g)(5) that ASME BPV Code requirements are impractical. The Commission may grant such relief and may impose such alternative requirements as it determines are authorized by law, will not endanger life or property or the common defense and security, and are otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility.
Based on the above, and subject to the following technical evaluation, the NRC staff finds that regulatory authority exists for the licensee to request and the NRC to grant the relief requested by the licensee.
3.0 TECHNICAL EVALUATION
3.1 Summary of Request Relief Request BFN-0-ISI-31 is for multiple ASME BPV Code Class 1 and 2 component welds associated with ASME BPV Code, Examination Categories B-D and R-A, for Browns Ferry. The licensee stated that for the subject welds in Relief Request BFN-0-ISI-31, it was impractical to meet the ASME BPV Code-required examination coverage. Specifically, due to component design configurations or interference by other items, it was not possible to perform examinations to the extent required by the ASME BPV Code. When examined, the welds listed in this enclosure of this request did not receive the required code volume coverage. The licensee stated that conformance would require using radiography as an alternative that would result in numerous work-related stoppages and increased radiation exposure due to the shutdown and startup of other work in the areas. The licensee explained that water may need to be drained from some systems or components where radiography is performed, which increases the radiation dose rates over a much broader area than the weld being examined. Therefore, the licensee determined there is significant impracticality associated with the performance of modifications to the welds or surrounding areas; or the use of radiography in order to increase the examination coverage.
The licensee indicated that it performed the ASME BPV Code-required examinations to the maximum extent possible. Due to design limitation, there are no viable alternative volumetric examination techniques currently available to increase the coverage. Therefore, pursuant to 10 CFR 50.55a(g)(5)(iii), the licensee requested relief on the basis that achieving the ASME BPV Code-required volumetric examination coverage for the subject components in BFN-0-ISI-31 is impractical.
During the Unit 1 third 10-year ISI interval, the Unit 2 fifth 10-year ISI interval, and the Unit 3 fourth 10-year ISI interval, the applicable ASME BPV Code of Record is ASME Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, 2007 Edition through 2008 Addenda, as modified by 10 CFR 50.55a, Codes and Standards. The ASME BPV Code,Section XI, Mandatory Appendix VIII requirements and use of the performance demonstration initiative (PDI) requirements at Browns Ferry were in accordance with the 2007 Edition through 2008 Addenda of Section XI, as modified by 10 CFR 50.55a for the limited examinations contained in the request. For all three units, the first period of the current 10-year ISI interval ended on January 31, 2019. The ISI interval is currently scheduled to end on January 31, 2026.
The licensee also cited use of ASME Code Case N-613-1, Ultrasonic Examination of Full Penetration Nozzles in Vessels, Examination Category B-D, Item Nos. B3.10 and B3.90, Reactor Nozzle-To-Vessel Welds, Figs. IWB-2500-7(a), (b), and (c),Section XI, Division I.
ASME Code Case N-613-1 is an NRC-approved alternative that can be used by a licensee, as referenced in Regulatory Guide (RG) 1.147, Revision 20 (ML21181A222).
Additionally, the licensee cited use of ASME Code Case N-716-1, Alternative Piping Classification and Examination Requirements,Section XI, Division 1. ASME Code Case N-716-1 is also an NRC-approved alternative authorized for use by the licensee for Examination Category R-A components, as referenced in RG 1.147.
For clarity, the NRC staffs evaluation of Relief Request BFN-0-ISI-31 is documented according to each of the applicable ASME Code-required examination categories.
3.2 Examination Category B-D, Pressure-Retaining Reactor Vessel Nozzle-To-Vessel Welds 3.2.1 Applicable ASME Code Requirements The examination requirements for Examination Category B-D, Item Number B3.90 are delineated in ASME BPV Code,Section XI, Table IWB-2500-1, and require the volumetric examination coverage depicted in Figure IWB-2500-7. Examinations performed per Table IWB-2500-1, Examination Category B-D, Full Penetration Welded Nozzles in Vessels, Item No. B3.90, Reactor Vessel Nozzle-to-Vessel Welds, encountered limitations on various nozzle-to-vessel welds on each unit. These welds included reactor water recirculation outlet (N1), reactor water recirculation inlet (N2), steam outlet (N3), core spray (N5), head spray (N6),
vent (N7), jet pump (N8), control rod drive (N9), and standby liquid control (N10) nozzles. Per ASME Code Case N-613-1, Item B3.90 nozzle-to-vessel welds previously ultrasonically examined using the examination volumes of Figures IWB-2500-7(a), (b), and (c) may be examined using the reduced examination volumes as specified in ASME Code Case N-613-1, Figure 1.
Tables 1, 2, and 3 below provide a summary of licensees examinations for Examination Category B-D welds for which the licensee is seeking relief.
Table 1 - Examination Category B-D Welds with Limited Volumetric Coverage for Browns Ferry, Unit 1 Item No.
Component ID and Description Limitation/Coverage Examination Results B3.90 N1A-NV (28 Reactor Water Recirculation Outlet Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 35.6% coverage No Recordable Indications B3.90 N2D-NV (12 Reactor Water Recirculation Inlet Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 38.5% coverage No Recordable Indications B3.90 N2E-NV (12 Reactor Water Recirculation Inlet Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 38.5% coverage No Recordable Indications B3.90 N2G-NV (12 Reactor Water Recirculation Inlet Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 38.5% coverage No Recordable Indications B3.90 N3D-NV (26 Steam Outlet Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 39.9% coverage No Recordable Indications B3.90 N5A-NV (10 Core Spray Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 26.8% coverage No Recordable Indications B3.90 N6A-NV (6 Head Spray Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 54.1% coverage No Recordable Indications B3.90 N7-NV (4 Vent Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 73.6% coverage No Recordable Indications Table 2 - Examination Category B-D Welds with Limited Volumetric Coverage for Browns Ferry, Unit 2 Item No.
Component ID and Description Limitation/Coverage Examination Results B3.90 N1B-NV (28 Reactor Water Recirculation Outlet Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 42.2% coverage No Recordable Indications B3.90 N2A-NV (12 Reactor Water Recirculation Inlet Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 45.0% coverage No Recordable Indications B3.90 N2C-NV (12 Reactor Water Recirculation Inlet Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 45.0% coverage No Recordable Indications B3.90 N2H-NV (12 Reactor Water Recirculation Inlet Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 45.0% coverage No Recordable Indications B3.90 N3B-NV (26 Steam Outlet Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 42.3% coverage No Recordable Indications B3.90 N5B-NV (10 Core Spray Nozzle to Shell Weld)
Geometric Nozzle Design Configuration and Insulation Support Ring 36.0% coverage No Recordable Indications B3.90 N7-NV (4 Vent Nozzle to Head Weld)
Geometric Nozzle Design Configuration 50.9% coverage No Recordable Indications B3.90 N9-NV (4 Control Rod Drive Hydraulic System Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 54.2% coverage Previously Recorded Indication Observed With No Changes Table 2 - Examination Category B-D Welds with Limited Volumetric Coverage for Browns Ferry, Unit 2 Item No.
Component ID and Description Limitation/Coverage Examination Results B3.90 N10-NV (1.5 Standby Liquid Control System Nozzle to Head Weld)
Geometric Nozzle Design Configuration 89.9% coverage No Recordable Indications Table 3 - Examination Category B-D Welds with Limited Volumetric Coverage for Browns Ferry, Unit 3 Item No.
Component ID and Description Limitation/Coverage Examination Results B3.90 N1A-NV (28 Reactor Water Recirculation Outlet Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 44.9% coverage No Recordable Indications B3.90 N2B-NV (12 Reactor Water Recirculation Inlet Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 45.0% coverage No Recordable Indications B3.90 N2D-NV (12 Reactor Water Recirculation Inlet Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 45.0% coverage No Recordable Indications B3.90 N2F-NV (12 Reactor Water Recirculation Inlet Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 45.0% coverage No Recordable Indications B3.90 N3B-NV (26 Steam Outlet Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 42.3% coverage No Recordable Indications B3.90 N5A-NV (10 Core Spray Nozzle to Shell Weld)
Geometric Nozzle Design Configuration and Insulation Support Ring 33.7% coverage No Recordable Indications B3.90 N8A-NV (4 Jet Pump Instrumentation Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 81.0% coverage No Recordable Indications B3.90 N2G-NV (12 Reactor Water Recirculation Inlet Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 45.8% coverage No Recordable Indications B3.90 N2H-NV (12 Reactor Water Recirculation Inlet Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 45.8% coverage No Recordable Indications B3.90 N2J-NV (12 Reactor Water Recirculation Inlet Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 45.8% coverage No Recordable Indications B3.90 N3C-NV (26 Steam Outlet Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 42.3% coverage No Recordable Indications B3.90 N3D-NV (26 Steam Outlet Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 42.3% coverage No Recordable Indications B3.90 N6A-NV (6 Head Spray Nozzle to Shell Weld)
Geometric Nozzle Design Configuration 44.9% coverage No Recordable Indications ASME Code,Section XI, IWA-2200(c) defines essentially 100 percent as greater than 90 percent coverage of the examination volume or surface area, as applicable.
3.2.2 Licensees Reason for Request Due to component design configuration and limitations, the licensee was unable to obtain the ASME BPV Code-required volumetric examination coverage for the components identified in its submittal. The licensee stated that the subject welds were examined to the extent practical due to limited access. The licensee stated that its determination is based on actual demonstrated limitations experienced when attempting to comply with the ASME BPV Code examination coverage requirements. The licensee clarified that further coverage would require extensive design modifications.
The licensee also explained that Examination Category B-D Welds, Item B3.90, Reactor Vessel Nozzle To Vessel Welds, are Class 1 pressure retaining welds and that the examinations were limited due to the configuration of the geometric design.
3.2.3 NRC Staff Evaluation of Examination Category B-D Welds The NRC staff has evaluated Relief Request BFN-0-ISI-31 pursuant to 10 CFR 50.55a(g)(6)(i).
The NRC staffs evaluation focused on whether: (1) sufficient technical justification exists to support the determination that the ASME BPV Code requirements are impractical; (2) imposition of the Code-required examinations would result in a burden to the licensee; and (3) the licensees proposed alternative (i.e., accepting the reduced inspection coverage in these cases and periodic system pressure tests and VT-2 visual examinations performed during each refueling outage in accordance with Examination Category B-P of Table IWB-2500-1) provides reasonable assurance of structural integrity and leak tightness of the subject welds. The NRC staff determined that if these three criteria are met, then the requirements of 10 CFR 50.55a(g)(6)(i) (i.e., that granting the requested relief will not endanger life or property or the common defense and security, and is otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility) will also be met.
Impracticality of Compliance The design of Browns Ferry, Units 1, 2, and 3 provides access for examinations; however, component design configurations with conditions resulting in examination limitations (for example, those from support interference and/or geometric configurations of welds) did not allow for the full required examination volume coverage. The licensee explained that when examined, the welds listed in its submittal did not receive the required ASME BPV Code volume coverage due to their component design configurations or interference by other items. These conditions resulted in scanning access limitations that prohibited obtaining essentially 100-percent examination coverage (i.e., greater than 90 percent) of the required examination volumes. When this situation occurred, 100 percent of the accessible volumes of each weld were examined to the extent practicable. Consequently, according to the licensee, every weld was examined as required by applicable procedures and regulations to the extent practicable.
The licensee documented these impediments to achieving the required volumetric examination coverages in diagrams provided in its submittal and illustrated the problematic geometry surrounding the subject welds.
Based on its review of the submittal, including the provided diagrams, the NRC staff finds that due to geometric limitations associated with the aforementioned welds, it was impractical to meet the ASME BPV Code-required essentially 100 percent volumetric examination coverage for the subject welds during the first period of its third, fifth, and fourth 10-year ISI interval for Browns Ferry, Units 1, 2, and 3, respectively.
Burden of Compliance The licensee stated that for each weld in the scope of this request, it is not possible to obtain ultrasonic (UT) interrogation of greater than 90 percent of the required code examination volume without extensive weld or component design modifications and that examinations have been performed to the maximum extent possible. The licensee explained that using radiography as an alternative would result in numerous work-related stoppages and increased radiation exposure due to the shutdown and startup of other work in the areas. Further that the water may need to be drained from some systems or components where radiography is performed, which increases the radiation dose rates over a much broader area than the weld being examined.
The licensee determined that obtaining essentially 100-percent coverage is not feasible and is impractical without adding additional burden consisting of significant redesign work and increased radiation exposure.
The NRC staff finds that replacing, reconfiguring, or modifying the components of the subject welds, or the use of radiography in order to increase the examination coverage are the only reasonable means to achieve greater than 90 percent of the required ASME BPV Code examination volume and that replacement or reconfiguration, or use of radiography of the subject components constitutes a burden on the licensee.
Structural Integrity and Leak Tightness The NRC staffs review considered whether the licensees achieved examination coverage for the subject welds in Examination Category B-D, Item Number B3.90 provides reasonable assurance of structural integrity and leak tightness of the subject welds. This was based on:
(1) the examination coverages achieved and (2) safety significance of unexamined volumes and unachievable coverages (e.g., the presence or absence of known active degradation mechanisms and essentially 100-percent coverage achieved for similar welds in similar environments subject to similar degradation mechanisms).
In evaluating the licensees achieved examination coverage, the NRC staff assessed whether the licensee obtained as much coverage as reasonably possible and the manner in which the licensee reported the coverage achieved. From review of submittal, the NRC staff determined that:
The welds were examined using the appropriate equipment, UT modes of propagation, probe angles, frequencies, and scanning directions to obtain maximum coverage.
The coverage was calculated in a reasonable manner.
The personnel and UT procedures utilized for the examination were qualified as required by the ASME Code,Section XI.
The coverage was limited by geometric configuration of the components that limited access to the required examination volume.
No unacceptable indications were identified.
The NRC staff reviewed the licensees figures for the reactor vessel nozzle-to-vessel welds identified above in Table 1, 2, and 3, showing the examination coverage and limitations due to the configuration of the nozzle forgings. Based on its review, the NRC staff found that the licensee made an appropriate effort to obtain as much coverage as reasonably possible with the ASME BPV Code-required volumetric examinations. In addition to the coverage analysis described above, the NRC staff evaluated the safety significance of the unexamined volumes of welds and unachievable coverage. Based on its review of the submittal, the NRC staff determined that the licensees volumetric examinations have covered, to the extent possible, the regions that are typically susceptible to higher stresses and, therefore, more susceptible to potential degradation. No unacceptable indications were detected in the volumes examined by the licensee. Therefore, based on the coverage achieved by the qualified UT and the examination of the subject welds to the extent possible, the staff finds it reasonable that if significant service-induced degradation had occurred, evidence of it would have been detected by the examinations that the licensee performed.
The NRC staff also finds that, in addition to the required volumetric examinations, the subject welds have received and will continue to receive the ASME Code,Section XI, Table IWB-2500-1, Examination Category B-P, required system leakage test. Despite reduced coverage of the required examination volume of the subject welds, the NRC staff finds that this system leakage test will provide additional assurance that any pattern of degradation, if it were to occur, would be detected and that the licensee will be able to take appropriate corrective actions. Additionally, the staff noted that there is continuous monitoring instrumentation, which is required to be operable by Browns Ferry Technical Specification (TS) 3.4.5, RCS Leakage Detection Instrumentation, to assure that early detection of any reactor coolant system (RCS) pressure boundary leakage is identified and meets BFN TS 3.4.4, RCS Operational Leakage.
The NRC staff also determined that the examinations performed, despite the limited coverage obtained by the licensee, provide reasonable assurance of the structural integrity for the subject component welds in Examination Category B-D, Item Number B3.90. Furthermore, the continued performance of the periodic required VT-2 examinations during the system pressure tests provides additional assurance of structural integrity and leak tightness of the subject welds. Compliance with the ASME BPV Code requirements for these welds would be a burden on the licensee without a commensurate increase in safety. Therefore, the NRC staff finds that the risk associated with granting the requested relief would be acceptably low and the licensees request acceptable.
3.3 Examination Category R-A, Pressure-Retaining Welds in Piping 3.3.1 Applicable ASME Code Requirements The Class 1 piping welds in Examination Category R-A, for which the licensee is seeking relief, were selected for examination under the Browns Ferry Risk-Informed Inservice Inspection (RI-ISI) Program in accordance with ASME Code Case N-716-1. The examination requirements for Examination Category R-A, Item Numbers R1.16 and R1.20 are delineated in ASME BPV Code,Section XI, Nonmandatory Appendix R, Table R-2500-1, and require the volumetric examination coverage depicted in Figures IWB-2500-8(c) or IWB-2500-9, -10, -11, as applicable plus an additional 0.5 inch beyond the base metal thickness transition or counterbore for Item Number R1.16.
Tables 4 and 5 below provide a summary of licensees examinations for Examination Category R-A welds for which the licensee is seeking relief.
Table 4 - Examination Category R-A Welds with Limited Coverage for Browns Ferry, Unit 2 Item No.
Component ID and Description Limitation/Coverage Examination Results R1.16 TCS-2-406, 12 Core Spray System Pipe-to-Valve Valve Side Configuration 48.5% coverage No Recordable Indications Table 5 - Examination Category R-A Welds with Limited Coverage for Browns Ferry, Unit 3 Item No.
Component ID and Description Limitation/Coverage Examination Results R1.20 RWCU-3-001-042, 6 Reactor Water Cleanup Pipe-to-Valve Geometric Valve Configuration 37.6% coverage No Recordable Indications 3.3.2 Licensees Reason for Request Due to component design configuration and limitations the licensee was unable to obtain the ASME BPV Code-required examination coverage for the components identified in its submittal, without extensive design modifications. The licensee stated that the subject welds were examined to the extent practical due to limited access. The licensee stated that its determination is based on actual demonstrated limitations experienced when attempting to comply with the ASME Code examination requirements.
The licensee also explained that Examination Category R-A welds, Item Numbers R1.16 and R1.20 pipe-to-valve welds are Class 1 pressure-retaining welds, and the examinations were limited due to the configuration of the geometric design.
3.3.3 NRC Staff Evaluation of Examination Category R-A Welds The ASME BPV Code requires 100 percent of the defined examination volumes for Class 1 circumferential piping welds. However, examination coverage of the subject welds is limited due to the plants original construction design, which results in a geometrical configuration or obstruction that prevents complete examination. To increase coverage, a design modification would be necessary to accomplish the required inspection volume and the level of effort required to accomplish such modification to the plant would be excessive. Therefore, the licensee has shown that it is impractical to meet the ASME BPV Code-required volumetric coverage of the subject welds.
As shown in the technical descriptions and sketches provided in the licensees submittal, examinations of the subject welds have been performed to the extent practical, with the licensee obtaining volumetric coverage ranging from approximately 37.6 to 48.5 percent of the ASME BPV Code-required volumes (see Tables 4 and 5 above). Volumetric examinations on the subject welds were conducted with equipment, procedures, and personnel that have been performance demonstrated to the requirements outlined in ASME Code,Section XI, Appendix VIII. The licensees UT scanning techniques included combinations of 35 to 70-degree shear waves and 25 to 70-degree refracted longitudinal waves, as applicable on the subject welds. The UT examinations showed no recordable indications.
Additionally, the licensee performed examinations on similar components subject to the same degradation mechanism, i.e., intergranular stress corrosion cracking (IGSCC):
TCS-2-406 weld in Unit 2 was UT examined in the fifth 10-Year ISI Interval, first period, during the U2R19 refueling outage. Three additional examinations were performed on similar components subject to the same degradation mechanism in the Residual Heat Removal and Reactor Water Recirculation systems. Although not examined for Code Case N-716-1 credit, these representative examinations provide additional assurance that IGSCC is not occurring in a similar operating environment. For each of the three additional exams, essentially 100 percent coverage was obtained, and no indications were recorded.
RWCU-3-001-042 weld in Unit 3 was UT examined in the fourth 10-year ISI Interval, first period, during the U3R18 refueling outage in 2018 to meet the requirements of the RI-ISI Program under ASME Code Case N-716-1. During U3R18, there were two additional welds examined on the same line of piping as RWCU-3-001-042 that obtained 100 percent coverage with zero indications identified. These two welds that were examined for Code Case N-716-1 credit (R1.20) provide additional assurance that IGSCC is not occurring in a similar operating environment.
The staff finds that the licensees maximum examination coverage of the accessible volume of these R-A welds, coupled with applicable leakage monitoring and required system pressure tests with VT-2 visual examinations, as outlined in the licensees request for relief, provides reasonable assurance of structural integrity of the subject welds.
4.0 CONCLUSION
As set forth above, the NRC staff has determined that granting relief pursuant to 10 CFR 50.55a(g)(6)(i) is authorized by law, will not endanger life or property or the common defense and security, and is otherwise in the public interest given due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility. Furthermore, the NRC staff concluded that the examinations performed to the extent practical provide reasonable assurance of structural integrity of the subject components. Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(g)(5)(iii). Therefore, the NRC staff grants relief from the ASME BPV Code examination requirements for the welds included in Relief Request BFN-0-ISI-31 for Browns Ferry, Units 1, 2, and 3, for the first period of the third, fifth, and fourth 10-year ISI intervals, respectively.
All other ASME Code,Section XI requirements for which relief was not specifically requested and approved in this relief request remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
Principal Contributors: O. Yee M. Burton Date: March 8, 2023
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST SQN-19-ISI-1 REGARDING WELD EXAMINATION COVERAGE TENNESSEE VALLEY AUTHORITY SEQUOYAH NUCLEAR PLANT, UNITS 1 AND 2 DOCKET NOS. 50-327 AND 50-328
1.0 INTRODUCTION
By letter dated April 25, 2022 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML22115A235), the Tennessee Valley Authority (TVA or the licensee),
submitted Relief Request SQN-19-ISI-1 to the U.S. Nuclear Regulatory Commission (NRC or Commission) for the first period of the fourth 10-year Inservice Inspection (ISI) interval for Sequoyah Nuclear Plant (Sequoyah), Units 1 and 2. The licensee requested relief from the examination coverage requirements of Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME BPV Code), applicable to certain ASME Code Class 1 and 2 component weld examinations at Sequoyah, Units 1 and 2.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(g)(5)(iii),
the licensee requested relief on the basis that achieving the ASME BPV Code-required volumetric examination coverage for the subject welds in Relief Request SQN-19-ISI-31 is impractical.
2.0 REGULATORY EVALUATION
Pursuant to 10 CFR 50.55a(g)(4), Inservice inspection standards requirement for operating plants, components (including supports) that are classified as ASME Code Class 1, Class 2, and Class 3 must meet the requirements, except design and access provisions and preservice examination requirements set forth in Section XI of editions and addenda of the ASME BPV Code that become effective subsequent to editions specified in paragraphs (g)(2) and (3) of 10 CFR 50.55a, which are incorporated by reference in paragraph (a)(1)(ii) of 10 CFR 50.55a to the extent practical within the limitations of design, geometry, and materials of construction of the components.
Pursuant to 10 CFR 50.55a(g)(4)(ii), Applicable ISI Code: Successive 120-month Intervals, in-service examination of components and system pressure tests conducted during successive 120-month inspection intervals must comply with the requirements of the latest edition and addenda of the ASME Code incorporated by reference in paragraph (a) of 10 CFR 50.55a 18 months before the start of the 120-month inspection interval (or the optional ASME Code Cases listed in NRC Regulatory Guide (RG) 1.147, Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1, when using ASME BPV Code,Section XI, as incorporated by reference in paragraph (a)(3)(ii) of 10 CFR 50.55a, subject to the conditions listed in paragraph (b) of 10 CFR 50.55a.
Pursuant to 10 CFR 50.55a(g)(5)(iii), ISI Program Update: Notification of impractical ISI Code requirements, if the licensee has determined that conformance with a ASME Code requirement is impractical for its facility, the licensee must notify the NRC and submit, as specified in 10 CFR 50.4, information to support the determinations. Determinations of impracticality in accordance with 10 CFR 50.55a(g)(5)(iii) must be based on the demonstrated limitations experienced when attempting to comply with the ASME Code requirements during the ISI interval for which the request is being submitted. Requests for relief made in accordance with 10 CFR 50.55a(g)(5)(iii) must be submitted to the NRC no later than 12 months after the expiration of the initial or subsequent 120-month inspection interval for which relief is sought.
Pursuant to 10 CFR 50.55a(g)(6)(i), Impractical ISI requirements: Granting of relief, the Commission will evaluate determinations under paragraph 10 CFR 50.55a(g)(5) that ASME BPV Code requirements are impractical. The Commission may grant such relief and may impose such alternative requirements as it determines are authorized by law, will not endanger life or property or the common defense and security, and are otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility.
Based on the above, and subject to the following technical evaluation, the NRC staff finds that regulatory authority exists for the licensee to request and the NRC to grant the relief requested by the licensee.
3.0 TECHNICAL EVALUATION
3.1 Licensees Request 3.1.1 ASME Code Components Affected ASME Code Class 1, Category B-D, Item No. B3.110, RCW-21 and RCW-15 pressurizer nozzle-to-vessel welds.
3.1.2 Applicable Code Editions and Addenda The fourth 10-year ISI intervals for Sequoyah, Units 1 and 2, end on September 3, 2025, and comply with the 2007 Edition through 2008 Addenda, as modified by 10 CFR 50.55a, Codes and Standards, of ASME BPV Code,Section XI.
3.1.3 Applicable Code Requirements The examination requirement for Examination Category B-D, Item No. B3.110, per ASME BPV Code,Section XI, Table IWB-2500-1 requires a volumetric examination of essentially 100 percent of the weld length for nozzle-to-vessel welds as shown in ASME Code,Section XI, Figures IWB-2500-7(a) through (d).
In addition, ASME BPV Code,Section XI, IWA-2200(c) defines essentially 100 percent as greater than 90-percent coverage of the examination volume or surface area, as applicable.
3.1.4 Licensees Reason for the Request The licensee was unable to meet the ASME BPV Code examination requirements as the pressurizer nozzles do not allow for full ASME Code ultrasonic (UT) examination due to geometric design configurations. The pressurizer nozzle welds and components would need to be modified to perform a full ASME Code-required UT examination of the welds.
3.1.5 Licensees Proposed Alternative The licensee proposed to perform system pressure tests and visual inspections of the welds in addition to continuing UT examinations to the maximum extent possible. The licensee notes that both welds are inside containment and must undergo periodic reactor coolant system (RCS) pressure tests. The RCS is also monitored for leakage inside containment.
3.1.6 Duration of the Request The licensee submitted this request for the first period of the fourth 10-year ISI interval. The fourth ISI interval for Sequoyah, Units 1 and 2, is currently scheduled to end on September 3, 2025.
3.2
NRC Staff Evaluation
The licensee has requested relief from the essentially 100 percent volumetric coverage requirements described in ASME BPV Code,Section XI and its ISI program because the design configurations of the subject welds limit access for volumetric inspection. In order to effectively increase the examination coverage to meet ASME Code requirements, the components would require significant modifications.
The NRC staff reviewed the partial UT weld examination to understand the level of assurance provided concerning weld structural integrity. The licensee stated that it performed UT examinations on these welds to the maximum extent feasible. Due to the bend radius on the flange side and the thickness of the flange, the following examination volumes were scanned for RCW-21: axial composite coverage of 45.1 percent; circumferential composite coverage of 68.3 percent. The following examination volumes were scanned for RCW-15: axial composite coverage of 68.3 percent; circumferential composite coverage of 88.5 percent.
The licensee documented the impediment to full examination in several diagrams, illustrating the problematic geometry surrounding the subject welds.
The NRC staff determined the coverage achieved represents a sufficiently large area, such that, if significant degradation were present in the weld, it is likely that the degradation would have been detected. Evidence of significant service-induced degradation in the weld, if it were to occur, would likely be detected in the portions of the welds that were examined because the examined volume is the same material as the unexamined volume, is under the same loading conditions, and is exposed to the same reactor coolant environment. Based on operating experience at similar locations to date, the NRC staff determined that the likelihood that a degradation mechanism unique to Sequoyah, Units 1 and 2, and located only in the unexamined portion of the weld is acceptably low.
The licensee stated that it would be a burden to meet the ASME Code-required 100-percent volumetric examination coverage for the subject welds due to their design. The staff determined that relieving the nature of the impediment would require significant burden and would be impractical. Therefore, Relief Request SQN-19-ISI-1 meets the requirements for relief for impracticality described in the regulations at 10 CFR 50.55a(g)(6)(i).
Based on the volumetric coverage obtained, the resistance of material to relevant degradation mechanisms, and examination results, the NRC staff finds that there is reasonable assurance of structural integrity of the subject component. In addition, the staff notes that nearly identical relief requests were approved for this weld during the first, second, and third 10-year ISI intervals. In light of the above, the staff finds that because the coverage achieved was as high as practical, this coverage provides reasonable assurance that no general degradation mechanism is active within the weld, and that to improve coverage would require undue burden.
4.0 CONCLUSION
As set forth above, the NRC staff has determined that granting relief in accordance with 10 CFR 50.55a(g)(6)(i) is authorized by law, will not endanger life or property or the common defense and security, and is otherwise in the public interest, giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility.
Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in the regulations at 10 CFR 50.55a(g)(5)(iii). Therefore, the NRC staff grants relief from the ASME BPV Code examination requirements for the welds included in Relief Request SQN-19-ISI-1 for Sequoyah, Units 1 and 2, for the first period of the fourth 10-year ISI interval.
All other ASME Code,Section XI requirements for which relief was not specifically requested and approved in this relief request remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
Principal Contributors: C. Parker D. Widrevitz Date: March 8, 2023
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST WBN-19-ISI-1 REGARDING WELD EXAMINATION COVERAGE TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT, UNITS 1 AND 2 DOCKET NOS. 50-390 AND 50-391
1.0 INTRODUCTION
By letter dated April 25, 2022 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML22115A235), the Tennessee Valley Authority (TVA or the licensee),
submitted Relief Request WBN-19-ISI-1 to the U.S. Nuclear Regulatory Commission (NRC or Commission) for the first period of the third and first 10-year Inservice Inspection (ISI) intervals for Watts Bar Nuclear Plant (Watts Bar), Units 1 and 2, respectively. The licensee requested relief from the examination coverage requirements of Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME BPV Code), applicable to certain ASME Code Class 1 and 2 component weld examinations at Watts Bar, Units 1 and 2.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(g)(5)(iii),
the licensee requested relief on the basis that achieving the ASME BPV Code-required volumetric examination coverage for the subject welds in Relief Request WBN-19-ISI-1 is impractical.
2.0 REGULATORY EVALUATION
Pursuant to 10 CFR 50.55a(g)(4), Inservice inspection standards requirement for operating plants, components (including supports) that are classified as ASME Code Class 1, Class 2, and Class 3 must meet the requirements, except design and access provisions and preservice examination requirements set forth in Section XI of editions and addenda of the ASME BPV Code that become effective subsequent to editions specified in paragraphs (g)(2) and (3) of 10 CFR 50.55a, which are incorporated by reference in paragraph (a)(1)(ii) of 10 CFR 50.55a to the extent practical within the limitations of design, geometry, and materials of construction of the components.
Pursuant to 10 CFR 50.55a(g)(4)(ii), Applicable ISI Code: Successive 120-month Intervals, in-service examination of components and system pressure tests conducted during successive 120-month inspection intervals must comply with the requirements of the latest edition and addenda of the ASME Code incorporated by reference in paragraph (a) of 10 CFR 50.55a 18 months before the start of the 120-month inspection interval (or the optional ASME Code Cases listed in NRC Regulatory Guide (RG) 1.147, Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1, when using ASME BPV Code,Section XI, as incorporated by reference in paragraph (a)(3)(ii) of 10 CFR 50.55a, subject to the conditions listed in paragraph (b) of 10 CFR 50.55a.
Pursuant to 10 CFR 50.55a(g)(5)(iii), ISI Program Update: Notification of impractical ISI Code requirements, if the licensee has determined that conformance with a ASME Code requirement is impractical for its facility, the licensee must notify the NRC and submit, as specified in 10 CFR 50.4, information to support the determinations. Determinations of impracticality in accordance with 10 CFR 50.55a(g)(5)(iii) must be based on the demonstrated limitations experienced when attempting to comply with the ASME Code requirements during the ISI interval for which the request is being submitted. Requests for relief made in accordance with 50.55a(g)(5)(iii) must be submitted to the NRC no later than 12 months after the expiration of the initial or subsequent 120-month inspection interval for which relief is sought.
Pursuant to 10 CFR 50.55a(g)(6)(i), Impractical ISI requirements: Granting of relief, the Commission will evaluate determinations under paragraph 10 CFR 50.55a(g)(5) that ASME BPV Code requirements are impractical. The Commission may grant such relief and may impose such alternative requirements as it determines are authorized by law, will not endanger life or property or the common defense and security, and are otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility.
Based on the above, and subject to the following technical evaluation, the NRC staff finds that regulatory authority exists for the licensee to request and the NRC to grant the relief requested by the licensee.
3.0 TECHNICAL EVALUATION
3.1 Summary of Request Relief Request WBN-19-ISI-1 is for multiple ASME BPV Code Class 1 and 2 component welds associated with multiple ASME Code, Examination Categories, for Watts Bar. The licensee stated that for the subject welds in Relief Request WBN-19-ISI-1, it was impractical to meet the ASME BPV Code-required examination coverage. Specifically, due to component design configurations or interference by other items, it was not possible to perform examinations to the extent required by the ASME BPV Code. When examined, the welds listed in this enclosure of this request did not receive the required code volume coverage. The licensee stated that conformance would require using radiography as an alternative that would result in numerous work-related stoppages and increased radiation exposure due to the shutdown and startup of other work in the areas. The licensee explained that water may need to be drained from some systems or components where radiography is performed, which increases the radiation dose rates over a much broader area than the weld being examined. Therefore, the licensee determined there is significant impracticality associated with the performance of modifications to the welds or surrounding areas; or the use of radiography in order to increase the examination coverage.
The licensee indicated that it performed the ASME BPV Code-required examinations to the maximum extent possible. Due to design limitation, there are no viable alternative volumetric examination techniques currently available to increase the coverage. Therefore, pursuant to 10 CFR 50.55a(g)(5)(iii), the licensee requested relief on the basis that achieving the ASME BPV Code-required volumetric examination coverage for the subject components in Relief Request WBN-19-ISI-1 is impractical.
During the Unit 1 third 10-year ISI interval and the Unit 2 first 10-year ISI interval, the applicable ASME BPV Code of Record is ASME Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, 2007 Edition through 2008 Addenda, as modified by 10 CFR 50.55a, Codes and Standards. The ASME BPV Code,Section XI, Mandatory Appendix VIII requirements and use of the performance demonstration initiative (PDI) requirements at Watts Bar were in accordance with the 2007 Edition through 2008 Addenda of Section XI, as modified by 10 CFR 50.55a for the limited examinations contained in the request. For both units, the first period of the current 10-year interval ended on May 26, 2019. The ISI interval is currently scheduled to end on May 26, 2026.
Additionally, the licensee cited use of ASME Code Case N-716-1, Alternative Piping Classification and Examination Requirements,Section XI, Division 1. ASME Code Case N-716-1 is also an NRC-approved alternative authorized for use by the licensee for Examination Category R-A components, as referenced in RG 1.147.
For clarity, the NRC staffs evaluation of Relief Request WBN-19-ISI-1 is documented according to each of the applicable ASME Code-required examination categories.
3.2 Examination Category B-D, Full Penetration Welded Nozzles In Vessels, Examination Category C-A, Pressure-Retaining Welds In Pressure Vessels, and Examination Category C-B, Pressure-Retaining Nozzle Welds In Pressure Vessels 3.2.1 Applicable ASME Code Requirements The examination requirements for Examination Category B-D, Item Number B3.110 are delineated in ASME BPV Code,Section XI, Table IWB-2500-1, and require the volumetric examination coverage depicted in Figure IWB-2500-7. Examinations performed per Table IWB-2500-1, Examination Category B-D, Full Penetration Welded Nozzles in Vessels, Item No. B3.110, Pressurizer Nozzle-to-Vessel Welds, encountered limitations on various nozzle-to-vessel welds in Watts Bar, Unit 2. These welds included a 4-inch pressurizer spray nozzle to head weld, and a 6-inch pressurizer relief nozzle-to-head weld for Watts Bar, Unit 2.
Table 1 below provides a summary of licensees examinations for Examination Category B-D welds for which the licensee is seeking relief.
Table 1 - Examination Category B-D Welds with Limited Volumetric Coverage for Watts Bar, Unit 2 Item No.
Component ID and Description Limitation/Coverage Examination Results B3.110 4 Pressurizer Spray Nozzle to Head Weld Geometric Nozzle Design Configuration 63.8% coverage No Recordable Indications B3.110 6 Pressurizer Relief Nozzle to Head Weld Geometric Nozzle Design Configuration 63.7% coverage No Recordable Indications The examination requirements for Examination Category C-A, Item Number C1.30 are delineated in Table IWC-2500-1, and require the volumetric examination coverage depicted in Figure IWC-2500-2. Examinations performed per Table IWC-2500-1, Examination Category C--A, Pressure Retaining Welds In Pressure Vessels, Item No. C1.30, Tubesheet-to-Shell Weld, encountered limitations on the steam generator shell-to-tube sheet weld in Watts Bar, Unit 2.
Table 2 below provides a summary of licensees examinations for Examination Category C-A weld for which the licensee is seeking relief.
Table 2 - Examination Category C-A Welds with Limited Volumetric Coverage for Watts Bar, Unit 2 Item No.
Component ID and Description Limitation/Coverage Examination Results C1.30 Steam Generator Shell to Tube Sheet Weld Obstructions from Sludge Lance Ports, Bottom Blowdowns and Shell Drains 88.8% coverage No Recordable Indications The examination requirements for Examination Category C-B, Item Number C2.21 are delineated in Table IWC-2500-1, and require volumetric examination coverages depicted in Figure IWC-2500-4(a), (b), or (d). Examinations performed per Table IWC-2500-1, Examination Category C-B, Pressure Retaining Nozzle Welds In Pressure Vessels, Item No. C2.21, Nozzle-to-Shell (Nozzle to Head or Nozzle to Nozzle) Weld, encountered limitations on the 32 main steam nozzle-to-head weld in Watts Bar, Unit 2 during the volumetric examination only.
The surface examination of this weld, required by Table IWC-2500-1, was completed with no limitations.
Table 3 below provides a summary of licensees examinations for Examination Category C-B weld for which the licensee is seeking relief.
Table 3 - Examination Category C-B Welds with Limited Volumetric Coverage for Watts Bar, Unit 2 Item No.
Component ID and Description Limitation/Coverage Examination Results C2.21 32 Main Steam Nozzle to Head Weld Geometric Nozzle Design Configuration 75.0% coverage No Recordable Indications ASME Code,Section XI, IWA-2200(c) defines essentially 100 percent as greater than 90 percent coverage of the examination volume or surface area, as applicable.
3.2.2 Licensees Reason for Request Due to component design configuration and limitations the licensee was unable to obtain the ASME Code-required volumetric examination coverage for the components identified in its submittal. The licensee stated that the subject welds were examined to the extent practical due to limited access. The licensee stated that its determination is based on actual demonstrated limitations experienced when attempting to comply with the ASME BPV Code examination coverage requirements. The licensee clarified that further coverage would require extensive design modifications.
The licensee explained that Examination Category B-D Welds, Item B3.110, are Class 1 pressure retaining welds and the examinations were limited due to the configuration and geometric design of the components. Furthermore, Examination Category C-A Welds, Item C1.30, and Examination Category C-B Welds, Item C2.21, are Class 2 pressure retaining welds and the examinations were limited due to obstructions or the configuration and geometric design of the component. The summary of the examination results is provided above in Tables 1, 2, and 3.
3.2.3 NRC Staff Evaluation of Examination Category B-D, C-A, and C-B Welds The NRC staff has evaluated Relief Request WBN-19-ISI-1 pursuant to 10 CFR 50.55a(g)(6)(i).
The NRC staffs evaluation focused on whether: (1) a technical justification exists to support the determination that the ASME BPV Code requirement is impractical; (2) imposition of the Code-required examinations would result in a burden to the licensee; and (3) the licensees proposed alternative (accepting the reduced inspection coverage in these cases, and periodic system pressure tests and VT-2 visual examinations performed during each refueling outage in accordance with Examination Category B-P of Table IWB-2500-1 or Examination Category C-H of Table IWC-2500-1) provides reasonable assurance of structural integrity and leak tightness of the subject welds. The NRC staff determined that if these three criteria are met, then the requirements of 10 CFR 50.55a(g)(6)(i) (i.e., that granting the requested relief will not endanger life or property or the common defense and security, and is otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility) will also be met.
Impracticality of Compliance The design of Watts Bar, Unit 2 provides access for examinations; however, component design configurations with conditions resulting in examination limitations (for example, those from support interference and geometric configurations of welds) did not allow for the full required examination volume coverage. The licensee explained that when examined, the welds listed in its submittal did not receive the required ASME BPV Code volume coverage due to their component design configurations or interference by other items. These conditions resulted in scanning access limitations that prohibited obtaining essentially 100-percent examination coverage (i.e., greater than 90 percent) of the required examination volumes. When this situation occurred, 100 percent of the accessible volumes of each weld were examined to the extent practicable. Consequently, according to the licensee, every weld was examined as required by applicable procedures and regulations to the extent practicable. The licensee documented these impediments to achieving the required volumetric examination coverages in diagrams provided in its submittal, and illustrated the problematic geometry surrounding the subject welds.
Based on its review of the submittal, including the provided diagrams, the NRC staff finds that due to geometric limitations associated with the aforementioned welds, it was impractical to meet the ASME BPV Code-required essentially 100 percent volumetric examination coverage for the subject welds during the first period of the first 10-year ISI interval for Watts Bar, Unit 2.
Burden of Compliance The licensee stated that for each weld in the scope of this request, it is not possible to obtain ultrasonic (UT) interrogation of greater than 90 percent of the required code examination volume without extensive weld or component design modifications and that examinations have been performed to the maximum extent possible. The licensee explained that using radiography as an alternative would result in numerous work-related stoppages and increased radiation exposure due to the shutdown and startup of other work in the areas. Further that the water may need to be drained from some systems or components where radiography is performed, which increases the radiation dose rates over a much broader area than the weld being examined.
The licensee determined that obtaining essentially 100-percent coverage is not feasible and is impractical without adding additional burden consisting of significant redesign work and increased radiation exposure.
The NRC staff finds that replacing, reconfiguring, or modifying the components of the subject welds; or the use of radiography in order to increase the examination coverage are the only reasonable means to achieve greater than 90 percent of the required ASME BPV Code examination volume and that replacement or reconfiguration; or use of radiography of the subject components constitutes a burden on the licensee.
Structural Integrity and Leak Tightness The NRC staffs review considered whether the licensees achieved examination coverage for the subject welds in the following examination categories provides reasonable assurance of structural integrity and leak tightness of the subject welds. This was based on: (1) the examination coverage achieved and (2) safety significance of unexamined volumes and unachievable coverage (e.g., the presence or absence of known active degradation mechanisms and essentially 100-percent coverage achieved for similar welds in similar environments subject to similar degradation mechanisms),
Examination Category B-D, Item Number B3.110 Examination Category C-A, Item Number C1.30 Examination Category C-B, Item Number C2.21 In evaluating the licensees achieved examination coverage, the NRC staff assessed whether the licensee obtained as much coverage as reasonably possible and the manner in which the licensee reported the coverage achieved. From review of submittal, the NRC staff determined that:
The welds were examined using the appropriate equipment, ultrasonic modes of propagation, probe angles, frequencies, and scanning directions to obtain maximum coverage.
The coverage was calculated in a reasonable manner.
The personnel and UT procedures utilized for the examination were qualified as required by the ASME Code,Section XI.
The coverage was limited by geometric configuration of the components that limited access to the required examination volume.
No unacceptable indications were identified.
The NRC staff reviewed the licensees figures for the 4 pressurizer spray nozzle-to-head weld, 6 pressurizer relief nozzle-to-head weld, and 32 main steam nozzle-to-head welds identified above in Table 1, 2, and 3, showing the examination coverage and limitations due to the design and configuration of the nozzles. Additionally, the NRC staff reviewed the licensees figures for the steam generator shell to tube sheet weld identified above in Table 2, showing the examination coverage and limitations due to the obstructions from sludge lance ports, bottom blowdowns and shell drains. Based on its review, the NRC staff found that the licensee made an appropriate effort to obtain as much coverage as reasonably possible within the ASME BPV Code-required volumetric examination. In addition to the coverage analysis described above the NRC staff evaluated the safety significance of the unexamined volumes of welds and unachievable coverage. Based on its review of the submittal, the NRC staff determined that the licensees volumetric examinations have covered, to the extent possible, the regions that are typically susceptible to higher stresses and, therefore, more susceptible to potential degradation. No unacceptable indications were detected in the volumes examined by the licensee. Therefore, based on the coverage achieved by the qualified UT and the examination of the subject welds to the extent possible, the staff finds it reasonable that if significant service-induced degradation had occurred, evidence of it would have been detected by the examinations that the licensee performed.
The NRC staff also finds that, in addition to the required volumetric examinations, the subject welds in Examination Category B-D have received and will continue to receive the ASME Code,Section XI, Table IWB-2500-1, Examination Category B-P, required system leakage test.
Furthermore, the NRC staff finds that, in addition to the required volumetric examinations, the subject welds in Examination Category C-A and Examination Category C-B have received and will continue to receive the ASME BPV Code,Section XI, Table IWC-2500-1, Examination Category C-H, required system leakage test. Despite reduced coverage of the required examination volume of the subject welds, the NRC staff finds that these system leakage tests will provide additional assurance that any pattern of degradation, if it were to occur, would be detected and the licensee will be able to take appropriate correction actions.
Therefore, the NRC staff also determined that the examinations performed, despite the limited coverage obtained by the licensee, provide reasonable assurance of the structural integrity for the subject component welds in (1) Examination Category B-D, Item Number B3.110, (2) Examination Category C-A, Item Number C1.30, and (3) Examination Category C-B, Item Number C2.21. Furthermore, the continued performance of the periodic required VT-2 examinations during the system pressure tests provides additional assurance of structural integrity and leak tightness of the subject welds. Compliance with the ASME BPV Code requirements for these welds would be a burden on the licensee without a commensurate increase in safety. Therefore, the NRC staff finds that the risk associated with granting the requested relief would be acceptably low and the licensees request acceptable.
3.3 Examination Category R-A, Pressure-Retaining Welds in Piping 3.3.1 Applicable ASME Code Requirements The Class 1 piping welds in Examination Category R-A for which the licensee is seeking relief were selected for examination under the Watts Bar Risk-Informed Inservice Inspection (RI-ISI)
Program in accordance with ASME Code Case N-716-1. The examination requirements for Examination Category R-A, Item Numbers R1.11, R1.16, and R1.20 are delineated in ASME BPV Code,Section XI, Nonmandatory Appendix R, Table R-2500-1, and require the volumetric examination coverage depicted in Figures IWB-2500-8(c) or IWB-2500-9, -10, -11, as applicable, plus an additional 0.5 inch beyond the base metal thickness transition or counterbore for Items Numbers R1.11 and R1.16.
Tables 4 and 5 below provide a summary of licensees examinations for Examination Category R-A welds for which the licensee is seeking relief.
Table 4 - Examination Category R-A Welds with Limited Coverage for Watts Bar, Unit 1 Item No.
Component ID and Description Limitation/Coverage Examination Results R1.16/
R1.11 SIF-D090-08, 10 Pipe to Valve Valve Configuration 75% coverage No Recordable Indications R1.16/
R1.11 SIF-D092-10, 10 Pipe to Valve Valve Configuration 75% coverage No Recordable Indications R1.20 SIS-075, 6 Elbow to Pipe Welded Nameplate Pipe Side 87.5% Coverage No Recordable Indications R1.20 SIF-D091-04, 6 Elbow to Pipe Valve Configuration 75% coverage No Recordable Indications R1.20 SIF-D087-21, 6 Elbow to Pipe Valve Configuration 75% coverage No Recordable Indications Table 5 - Examination Category R-A Welds with Limited Coverage for Watts Bar, Unit 2 Item No.
Component ID and Description Limitation/Coverage Examination Results R1.11 SIF-B-T095-01, 1.5 Pipe to Nozzle Geometric Nozzle Design Configuration 75% Coverage No Recordable Indications R1.11 RCF-D144-07, 3 Valve to Pipe Valve Configuration 75% coverage No Recordable Indications R1.11 RCF-D144-03, 3 Valve to Pipe Valve Configuration 75% coverage No Recordable Indications 3.3.2 Licensees Reason for Request Due to component design configuration and limitations the licensee was unable to obtain the ASME BPV Code-required examination coverage for the components identified in its submittal, without extensive design modifications. The licensee stated that the subject welds were examined to the extent practical due to limited access. The licensee stated that its determination is based on actual demonstrated limitations experienced when attempting to comply with the ASME Code examination requirements.
The licensee also explained that Examination Category R-A welds, Item Numbers R1.16 and R1.20 pipe-to-valve welds are Class 1 pressure-retaining welds and the examinations were limited due to the configuration of the geometric design.
3.3.3 NRC Staff Evaluation of Examination Category R-A Welds The ASME BPV Code requires 100 percent of the defined examination volumes for the Examination Category R-A Welds listed in Tables 4 and 5. However, examination coverage of the subject welds is limited due to the plants original construction design which results in a geometrical configuration or obstruction that prevents complete examination. To increase coverage, a design modification would be necessary to accomplish the required inspection volume and the level of effort required to accomplish such modification to the plant would be excessive. Therefore, the licensee has shown that it is impractical to meet the ASME BPV Code-required volumetric coverage of the subject welds.
As shown in the technical descriptions and sketches provided in the licensees submittal, examinations of the subject welds have been performed to the extent practical, with the licensee obtaining volumetric coverage ranging from approximately 75 to 87.5 percent of the ASME BPV Code-required volumes (see Tables 4 and 5 above). Volumetric examinations on the subject welds were conducted with equipment, procedures, and personnel that have been performance demonstrated to the requirements outlined in ASME Code,Section XI, Appendix VIII. The licensees UT scanning techniques included combinations of 45, 60, and 70-degree shear waves and 60-degree refracted longitudinal waves, as applicable on the subject welds. The UT examinations had no recordable indications. The NRC staff finds that the licensees system leakage monitoring, pressure tests, and VT-2 visual examinations provide further assurance that significant degradation, if it is present, would be detected and corrected.
The NRC staff finds that the licensees maximum examination coverage of the accessible volume of these R-A welds, coupled with applicable leakage monitoring and required system pressure tests with VT-2 visual examinations, as outlined in the licensees request for relief, provides reasonable assurance of structural integrity of the subject welds.
4.0 CONCLUSION
S As set forth above, the NRC staff has determined that granting relief pursuant to 10 CFR 50.55a(g)(6)(i) is authorized by law, will not endanger life or property or the common defense and security, and is otherwise in the public interest given due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility. Furthermore, the NRC staff concluded that the examinations performed to the extent practical provide reasonable assurance of structural integrity of the subject components. Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(g)(5)(iii). Therefore, the NRC staff grants relief from the ASME Code examination requirements for the welds included in Relief Request WBN-19-ISI-1 for Watts Bar, Unit 1 and 2, for the first period of the third and first 10-year ISI intervals, respectively, which are currently scheduled to end on May 26, 2026.
All other ASME Code,Section XI requirements for which relief was not specifically requested and approved in this relief request remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
Principal Contributors: M. Burton O. Yee Date: March 8, 2023
ML23048A304 OFFICE NRR/DORL/LPLII-2/PM NRR/DORL/LPLII-2/LA NRR/DNRL/NVIB/BC(A)
NAME KGreen RButler DWidrevitz DATE 02/14/23 02/22/23 12/12/22 OFFICE NRR/DNRL/NPHP/BC NRR/DORL/LPLII-2/BC NAME MMitchell DWrona DATE 12/22/22 03/08/2023