ML24323A238
| ML24323A238 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 12/05/2024 |
| From: | David Wrona Plant Licensing Branch II |
| To: | Basta L Duke Energy Progress |
| Haeg, T | |
| References | |
| EPID L-2024-LLR-0017 | |
| Download: ML24323A238 (1) | |
Text
December 5, 2024 Laura Basta Site Vice President H. B. Robinson Steam Electric Plant Duke Energy Progress, LLC 3581 West Entrance Road, RNPA11 Hartsville, SC 29550
SUBJECT:
H. B. ROBINSON STEAM ELECTRIC PLANT, UNIT NO. 2 - REGARDING RELIEF REQUEST RA-23-0300 FOR THE FIFTH 10-YEAR INSERVICE INSPECTION INTERVAL (EPID L-2024-LLR-0017)
Dear Laura Basta:
By letter dated February 15, 2024, (Agencywide Documents Access and Management System (ADAMS) Accession No. ML24050A006), as supplemented by letter dated July 26, 2024 (ML24208A108), Duke Energy Progress, LLC (Duke Energy, the licensee) requested relief from certain requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI. Relief request RA-23-0300 pertains to the examination coverage of Class 1 vessel and pipe welds, Class 2 welded attachment welds, and component support welds in the fifth 10-year inservice inspection (ISI) interval of the H. B. Robinson Steam Electric Plant, Unit No. 2 (Robinson), which started on July 21, 2012, and ended on February 19, 2023. The licensee adopted the 2007 Edition through the 2008 Addenda of ASME Code,Section XI as the code of record.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(g)(5)(iii),
the licensee requested relief from the required examination coverage and to use alternative requirements (if necessary) for ISI of the vessel and pipe welds, welded attachments, and component support welds, on the basis that the ASME Code requirements were impractical.
The Nuclear Regulatory Commission (NRC) staff has reviewed the subject request and concludes, as set forth in the enclosed safety evaluation, that it is impractical for the licensee to comply with the ASME Code,Section XI requirements, that the proposed weld examination coverage provides reasonable assurance of structural integrity and leak tightness of the subject welds, and that granting relief pursuant to 10 CFR 50.55a(g)(6)(i) is authorized by law and 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. Accordingly, the NRC staff concludes that the licensee has adequately addressed all the regulatory requirements set forth in 10 CFR 50.55a(g)(6)(i). Therefore, the NRC staff grants RA-23-0300 at Robinson for the fifth 10-year ISI interval that commenced on July 21, 2012, and ended on February 19, 2023.
All other ASME Code,Section XI requirements for which relief was not specifically requested and authorized herein by the NRC staff remain applicable, including the third-party review by the Authorized Nuclear Inservice Inspector.
If you have any questions, please contact the Project Manager, Luke Haeg.
Sincerely, David Wrona, Chief Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-261
Enclosure:
Safety Evaluation cc: Listserv DAVID WRONA Digitally signed by DAVID WRONA Date: 2024.12.05 16:51:56 -05'00'
Enclosure SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO RELIEF REQUEST RA-23-0300 FOR THE FIFTH 10-YEAR INSERVICE INSPECTION INTERVAL DUKE ENERGY PROGRESS, LLC H. B. ROBINSON STEAM ELECTRIC PLANT, UNIT NO 2 DOCKET NO. 50-261
1.0 INTRODUCTION
By letter to the U.S. Nuclear Regulatory Commission (NRC or Commission) dated February 15, 2024, (Agencywide Documents Access and Management System (ADAMS) Accession No. ML24050A006), as supplemented by letter dated July 26, 2024 (ML24208A108), Duke Energy Progress, LLC (Duke Energy, the licensee) requested relief from certain requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),
Section XI. Relief request RA-23-0300 pertains to the examination coverage of Class 1 vessel and pipe welds, Class 2 welded attachment welds, and component support welds in the fifth 10-year inservice inspection (ISI) interval of the H. B. Robinson Steam Electric Plant, Unit No. 2 (Robinson), which started on July 21, 2012, and ended on February 19, 2023. The licensee adopted the 2007 Edition through the 2008 Addenda of ASME Code,Section XI as the code of record.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(g)(5)(iii),
the licensee requested relief from the required examination coverage and to use alternative requirements (if necessary) for ISI of the vessel and pipe welds, welded attachments, and component support welds, on the basis that the ASME Code requirements were impractical.
2.0 REGULATORY EVALUATION
In accordance with 10 CFR 50.55a(g)(4), ASME Code Class 1, 2, and 3 components (including supports) shall meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in the ASME Code,Section XI, 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), inservice 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 Section 50.55a no more than 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 Code,Section XI as incorporated by reference in paragraph (a)(3)(ii) of Section 50.55a), subject to the conditions listed in paragraph (b) of Section 50.55a.
Section 50.55a(g)(5)(iii) of 10 CFR states, in part, that licensees may determine that conformance with certain ASME Code requirements is impractical, and that the licensee shall notify the Commission and submit information in support of the determination. Determination of impracticality in accordance with this section 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 this section 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.
Section 50.55a(g)(6)(i) of 10 CFR states that the Commission will evaluate determinations under paragraph (g)(5) of this section that ASME Code requirements are impractical. The Commission may grant such relief and may impose such alternative requirements as it determines are authorized by law and 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.
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 Commission to grant the relief and authorize the alternatives requested by the licensee.
3.0 TECHNICAL EVALUATION
The NRC staff reviewed the licensees regulatory and technical analysis in support of the relief request from the ISI requirements of the ASME Code that are described in its request (ML24050A006) and supplemental letter (ML24208A108).
3.1 Request for Relief RA-23-0300, ASME Code,Section XI, Category B-A, Items B1.11, B1.12, and B1.30, Pressure Retaining Welds in Reactor Vessel ASME Code Requirement ASME Code,Section XI, Examination Category B-A, Items B1.11, B1.12, and B1.30 require 100 percent volumetric examination, as defined by ASME Code,Section XI, Figures IWB-2500-1, IWB-2500-2, and IWB-2500-4, for reactor pressure vessel (RPV) circumferential shell welds, longitudinal shell welds, and shell-to-flange welds, respectively. ASME Code Case N-768, Alternative Volumetric Coverage Requirements for Ultrasonic Examination of Class 1 and 2 Pressure Vessel Weld Joints Greater Than 2 in.[inch] (50 mm) in ThicknessSection XI, Division 1, as an alternative approved for use by the NRC in RG 1.147, Revision 20, Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1, states that, if greater than 90 percent of the required examination volume in Figures IWB-2500-1, IWB-2500-2, and IWB-2500-4 cannot be achieved, then 100 percent of the reduced examination volume defined in Figures 1, 2, and 4 of Code Case N-768 shall be examined.
Impracticality of Compliance The licensee stated that examinations were limited due to the location of the RPV Core Support Lugs and Keyway/Specimen Slots and design of the RPV resulting in no alternative examination techniques currently available to increase coverage.
Proposed Alternative In accordance with 10 CFR 50.55a(g)(5)(iii), the licensee requested relief from the ASME Code-required 100 percent volumetric examination of RPV circumferential shell welds, longitudinal shell welds, and shell-to-flange welds listed in Table 3.1.1 below:
Table 3.1.1 - ASME Code,Section XI, Examination Category B-A ASME Code Item ID Weld Percent Coverage Obtained Code Case N-768 Coverage Obtained B1.30 101/03 Vessel Flange to Shell Weld 86.87 93.36 B1.11 101/06 Lower Barrel to Lower Head Weld 75 73.90 B1.12 101/22 Lower Shell Long Seam Weld 0° 79.97 77.78 The licensee did not propose alternative examinations for the subject welds; however, the licensee stated that they have performed the required examinations to the extent practical. In addition, the licensee stated that visual test (VT)-2 examinations associated with the Class 1 leakage test are performed each refueling outage and that the volume of coverage obtained during the ultrasonic examinations along with ongoing leakage tests every refueling outage provide adequate assurance that any flaw(s) that might have propagated through the subject welds are identified and repaired prior to returning the plant to power operation. Therefore, the licensee concluded that an acceptable level of quality and safety will have been achieved and public health and safety will not be endangered by allowing the proposed alternative examinations in lieu of the Code requirement.
NRC Staff Evaluation
The ASME Code requires essentially 100 percent volumetric examinations for ASME Code,Section XI, Examination Category B-A Items B1.11, B1.12, and B1.30. However, complete volumetric examinations are restricted by the location of RPV Core Support Lugs and Keyway/Specimen Slots. These conditions preclude the licensee from obtaining full volumetric examinations from both sides of these welds. To gain access for examination, the welds would require design modifications. Imposition of this requirement would create a burden on the licensee, therefore, the ASME Code-required volumetric examinations are considered impractical.
Although less than the essentially 100 percent volumetric examination coverage required by the ASME Code was achieved, examination coverage of the B1.30 Vessel Flange to Shell Weld, B1.11 Lower Barrel to Lower Head Weld, and the B1.12 Lower Shell Long Seam Weld 0° was greater than 75 percent and there were no recordable indications in any of the three welds as reported in Enclosure 2 to RA-23-0300. Additionally, these welds receive a VT-2 examination performed as part of Class 1 leakage tests. Full ASME Code coverage is also achieved on other welds in the same examination categories. Based on the volumetric coverage obtained and considering the licensees performance of ultrasonic techniques employed to maximize this coverage, the NRC staff concludes that, if significant service-induced degradation had occurred in the subject welds, evidence of it would have been detected by the examinations performed.
Furthermore, the NRC staff determined that the examinations performed provide reasonable assurance of structural integrity of the subject welds.
3.2 Examination Category B-J, Pressure Retaining Welds in Piping ASME Code Requirement ASME Code,Section XI, Table IWB-2500-1, Examination Category B-J, Item No. B9.11 requires volumetric and surface examinations of the volume and area defined by Figure IWB-2500-8 in every 10-year ISI interval. The extent of volume or surface examination coverage is defined to be essentially 100 percent (i.e., greater than 90 percent) by IWA-2200(c).
Impracticality of Compliance The licensee stated that it was not possible to obtain greater than 90 percent coverage of the ASME Code-required examination volume for the subject welds due to the plant configuration, cast austenitic stainless steel (CASS) elbows, and/or proximity to an adjacent weld. In Table 1 of Enclosure 1 and sketches, photos, and/or diagrams of Enclosure 2 to RA-23-0300, the licensee described and illustrated the limitations that prevented ultrasonic testing (UT) of each weld to obtain greater than 90 percent coverage. The licensee acknowledged that there are no alternative examination techniques currently available to increase coverage, and there exist no qualified techniques to claim coverage on CASS materials.
The licensee stated that the burden caused by compliance includes major modification of plant components which include redesign and replacement of the welds and their associated components, and/or surrounding components.
Proposed Alternative For each Examination Category B-J pipe weld, the licensee reported the percent coverage obtained from UT of the required examination volume as follows:
Table 3.2.1 - ASME Code,Section XI, Examination Category B-J ASME Code Item ID Component Percent Volume Coverage Obtained B9.11 107/06 Loop A Crossover Leg Elbow to Pipe 50 B9.11 107/09 Loop A Crossover Leg Pipe to Elbow 50 B9.11 107A/06 Loop B Crossover Leg Elbow to Pipe 50 B9.11 107A/07 Loop B Crossover Pipe to Elbow 50 B9.11 116B/18 Elbow to Pipe 87.5 The licensee proposed the above alternative coverage in lieu of the ASME Code essentially 100 percent coverage. No unacceptable indications were identified in the volume examined.
The licensee stated that it performed the UT to the maximum extent possible. Personnel who performed the UT were qualified and the UT procedures used were performance demonstrated in accordance with ASME Code,Section XI, Appendix VIII.
As an extra effort to achieve additional coverage, the licensee performed and illustrated in to RA-23-0300, a best effort UT scan of the CASS elbow side of the weld volume.
No credit was taken for the best effort scan coverage obtained because the best effort scan is not a Code-qualified examination. No unacceptable indications were identified in the volume examined by the best effort scan.
The licensee stated that the subject pipe welds have received the ASME Code system leakage testing and VT-2 visual examination each refueling outage. No leakage has been identified.
As required by ASME Code,Section XI, the subject pipe welds received surface examinations every 10-year ISI interval, and essentially 100 percent coverage of the required examination area was achieved. No unacceptable surface flaws were identified in the area examined.
NRC Staff Evaluation
The NRC staff has evaluated Examination Category B-J pipe welds pursuant to 10 CFR 50.55a(g)(6)(i). The NRC staffs evaluation focused on: (1) whether a technical justification exists to support the determination that the ASME Code requirement is impractical, (2) that imposition of the Code-required inspections would result in a burden to the licensee, and (3) that the licensees proposed alternative (accepting the reduced inspection coverage in this case) provides reasonable assurance of structural integrity and leak tightness of the subject welds.
The NRC staff finds that if these three criteria are met, the requirements of 10 CFR 50.55a(g)(6)(i) will also be met.
As discussed in the submittal, and illustrated in the sketches, the predominant limitations that prevented the licensees UT from achieving essentially 100 percent coverage of the ASME Code-required volume were the metallurgical constraints or the proximity to adjacent weld. For welds 107/06, 107/09, 107A/06, and 107A/07, the licensee performed the UT from the pipe side of the weld (single-sided scan) because scanning from the CASS elbow side of the weld was not possible due to metallurgical constraints. For weld 116B/18, the licensee performed the UT from both sides of the weld (dual-sided scan), but the coverage was limited due to interference from the adjacent weld. The NRC staff determined that the metallurgical constraints or proximity to adjacent welds prevented the licensee to fully scan the required examination volume of the subject welds. Therefore, the NRC staff finds that a technical justification exists to support the determination that achieving essentially 100 percent coverage is impractical.
The licensee proposed that making each weld completely accessible for inspection from both sides or removing metallurgical constraints would require replacement or significant design modification to the weld and its associated components. The NRC staff finds that replacing or reconfiguring the components of the subject welds is the only reasonable means to achieve dual-sided coverage of these welds and that replacement or reconfiguration of the pipe, elbow, and/or adjacent weld constitutes a burden on the licensee.
In evaluating the licensees proposed alternative coverage, the NRC staff assessed whether the licensee obtained as much coverage as reasonably possible, and the methods used for achieving the reported coverage. The NRC staff verified that:
The welds were examined by UT using the appropriate equipment, ultrasonic modes of propagation, probe angles, frequencies, and scanning directions and procedures to obtain maximum coverage.
The coverage calculated was reasonable.
The personnel and procedures utilized for the UT were qualified as required by the ASME Code,Section XI, and the regulation.
The coverage was limited by physical or material constraints.
No unacceptable indications were identified in the volume examined.
Therefore, the NRC staff found that the licensee made every effort to obtain as much coverage as reasonably possible with the ASME Code-required UT.
In addition to the coverage evaluation described above, the NRC staff evaluated the safety significance of the unexamined areas of welds and unachievable coverage. The NRC staff verified that:
The licensees UT has covered, to the extent possible, the regions (i.e., the weld root and the heat affected zone of the base material near the inside diameter surface of the joint) that are typically susceptible to higher stresses and, therefore, potential degradation.
For the austenitic stainless steel welds, the coverage obtained was limited to the volume up to the weld centerline (near-side), because claiming coverage for the volume on the opposite side of the weld centerline (far-side) requires meeting the Appendix VIII of Section XI to the ASME Code required far-side UT performance demonstration. To date, no vendor has been capable of meeting the Appendix VIII far-side UT performance demonstration. The NRC staff verified that the far-side volume was inspected by the best effort examination, no indications were identified, and no credit was taken for the coverage achieved from the best effort examination.
The subject welds also received the required surface examination (essentially 100 percent coverage of the required area were achieved), and no unacceptable surface indications were identified in the area examined.
System leakage test and VT-2 visual examination performed every refueling outage did not identify any leakage.
Therefore, the NRC staff determined that based on the limited coverage achieved by qualified UT, essentially 100 percent coverage obtained by qualified surface examination and system leakage test with associated VT-2 visual examinations, it is reasonable to conclude that if significant service-induced degradation had occurred in Examination Category B-J pipe welds, evidence of it would have been detected by the examinations that the licensee performed.
Therefore, the NRC staff finds that the volumetric examinations performed to the extent possible provide reasonable assurance of structural integrity and leak tightness of Examination Category B-J pipe welds. Compliance with the ASME Code requirements for the subject welds would be a burden on the licensee.
3.3 Examination Category C-C, Welded Attachments for Pressure Vessels, Piping, Pumps, and Valves ASME Code Requirement ASME Code,Section XI, Table IWC-2500-1, Examination Category C-C, Items C3.10 and C3.20 require surface examinations with 100 percent coverage of the area defined by Figures IWC-2500-5 every inspection interval. Note 2 of Examination Category C-C in Table IWC-2500-1 states that the extent of the examination includes essentially 100 percent of the length of the attachment weld at each attachment subject to examination.
Impracticality of Compliance The licensee stated that it was not possible to obtain greater than 90 percent coverage of the ASME Code required examination area for the subject welds due to component configuration and physical interference. In Table 1 of Enclosure 1, and Enclosure 2 to RA-23-0300, the licensee described and illustrated the limitations that prevented liquid penetrant testing (PT) of weld 204/AWS-1-ATT and magnetic particle testing (MT) of welds 212/MS-1A-6017-ATT and 213/MS-1B-1003-ATT. The licensee acknowledged that there are no alternative examination techniques currently available to increase examination coverage.
The licensee stated that the burden caused by compliance includes major modification of plant components which include redesign and replacement of the welds and their associated components.
Proposed Alternative For each Examination Category C-C attachment weld, the licensee reported the percent coverage obtained from surface examinations of the required examination area as follows:
Table 3.3.1 - ASME Code,Section XI, Examination Category C-C ASME Code Item ID Component Percent Surface Coverage Obtained C3.10 204/AWS ATT RHR [residual heat removal] Heat Exchanger A Welded Attachment 75 C3.20 212/MS-1A-6017-ATT Welded Attachment on Loop A Main Steam System 88.9 C3.20 213/MS-1B-1003-ATT Welded Attachment on Loop B Main Steam System 42.7 The licensee proposed the above alternative coverage in lieu of the ASME Code essentially 100 percent coverage of the required examination area. No unacceptable indications were identified in the area examined.
The licensee stated that it performed the surface examinations to the maximum extent possible with personnel qualified in accordance with ASME Code,Section XI.
The licensee state that the VT-3 visual examinations of the welded attachments revealed no relevant conditions.
NRC Staff Evaluation
The NRC staff has evaluated Examination Category C-C welds pursuant to 10 CFR 50.55a(g)(6)(i). The NRC staffs evaluation focused on: (1) whether a technical justification exists to support the determination that the ASME Code requirement is impractical, (2) that imposition of the Code-required inspections would result in a burden to the licensee, and (3) that the licensees proposed alternative (accepting the reduced inspection coverage in this case) provides reasonable assurance of structural integrity and leak tightness of the subject welds. The NRC staff finds that if these three criteria are met, the requirements of 10 CFR 50.55a(g)(6)(i) will also be met.
From a review of RA-23-0300, the NRC staff determined that the configuration of components and physical interferences are the predominant limitations that prevented the licensees surface examination from achieving essentially 100 percent coverage of the ASME Code-required area.
Therefore, the NRC staff finds that a technical justification exists to support the determination that achieving essentially 100 percent coverage is impractical.
The licensee proposed that making each weld completely accessible for surface inspection would require replacement or significant design modification to the weld and its associated components. The NRC staff finds that replacing or reconfiguring the components of the subject welds is the only reasonable means to make them fully accessible for inspection, and that replacement or reconfiguration of the welds and associated components constitutes a burden on the licensee.
In evaluating the licensees proposed alternative coverage, the NRC staff assessed whether the licensee obtained as much coverage as reasonably possible, and the methods used for achieving the reported coverage. From review of submittal, the NRC staff verified that:
The welds were examined by MT or PT using the appropriate equipment to obtain maximum coverage.
The coverage calculated was reasonable.
The personnel who performed MT or PT were qualified as required by the ASME Code,Section XI.
The coverage was limited by component configuration and physical interference.
No unacceptable indications were identified in the area examined.
Therefore, the NRC staff found that the licensee made every effort to obtain as much coverage as reasonably possible.
In addition to the coverage analysis described above, the NRC staff evaluated the safety significance of the unexamined areas of welds and unachievable coverage. The NRC staff verified that the subject welded attachments have received VT-3 visual examinations.
Therefore, the NRC staff determined that based on the limited coverage achieved including the VT-3 visual examinations performed, it is reasonable to conclude that if significant service-induced degradation had occurred in Examination Category C-C welds, evidence of it would have been detected by the examinations that the licensee performed.
Therefore, the NRC staff finds that the surface examinations performed to the extent possible provide reasonable assurance of structural integrity of Examination Category C-C welds.
Compliance with the ASME Code requirements for the subject welds would be a burden on the licensee.
3.4 Request for Relief RA-23-0300, ASME Code,Section XI, Category F-A, Item F1.40, Supports ASME Code Requirement ASME Code,Section XI, Examination Category F-A, Item F1.40, requires 100 percent visual VT-3 examination, as defined by ASME Code,Section XI, Figure IWF-1300-1 of selected Class 1, 2, 3, and MC supports other than piping supports.
Impracticality of Compliance The licensee stated that the examination limitations result from component configuration issues.
The licensee stated the RPV is supported by three supports located on the underside of each of the inlet nozzles (cold leg). Each support bears on a support shoe, which is fastened to the building support structure. Examination access to the RPV supports is through the air ductwork for HVE-6 (Reactor Support Fan) with a robot inside the reactor coolant pump bays. Access to examine the supports is from the ductwork facing the vessel supports with minimal mobility behind the supports, thereby creating a limited visual examination. This is the only access to the supports.
Proposed Alternative In accordance with 10 CFR 50.55a(g)(5)(iii), the licensee requested relief from the ASME Code-required 100 percent visual examination of RPV supports listed in Table 3.4.1 below:
Table 3.4.1 - ASME Code,Section XI, Examination Category F-A ASME Code Item ID Component Percent Coverage Obtained F1.40 101/A Loop A RPV Support 75.12 F1.40 101/B Loop B RPV Support 75.12 F1.40 101/C Loop C RPV Support 73.72 The licensee did not propose any alternative examinations for the subject welds. However, the licensee noted that the VT-3 examinations were performed using the latest technology available at the time of the examination and the examination achieved the maximum amount of coverage possible.
NRC Staff Evaluation
The ASME Code requires 100 percent visual examinations for ASME Code,Section XI, Examination Category F-A Item F1.40 supports. However, visual examinations of these supports at Robinson are limited due to partial accessibility caused by their design and the surrounding interferences. For the licensee to obtain 100 percent of the ASME Code-required examination coverage, the RPV nozzles and surrounding environment need to be redesigned and modified. This would place a burden on the licensee, therefore the ASME Code examinations are considered impractical.
Visual VT-3 examinations on RPV inlet nozzle supports 101/A, 101/B, and 101/C, have been performed to the extent practical, with the licensee obtaining approximately 73 to 75 percent of the ASME Code-required coverage as shown in Table 3.4.1 above.
The NRC staff noted during their review that boron was identified in the area of the RPV supports and requested additional information by email dated Jule 11, 2024 (ML24164A005). As discussed in the supplemental letter of July 26, 2024, the licensee identified two potential sources of leakage associated with the reactor cavity seal. The licensee stated that the leaks are only active when the reactor cavity is flooded (i.e., neither leak is active during normal plant operation). Additionally, the licensee stated that a Permanent Cavity Seal Plate was installed in 2013 to minimize the potential for cavity seal leakage and if leakage does occur, the residual water would evaporate during normal plant operations. Further, the licensee stated that the RPV support structure surfaces are coated with Carbozinc to prevent corrosion of any exposed low alloy steel and that the surfaces are not expected to exhibit corrosion from residual boron deposits without continuous replenishment of borated water as supported by laboratory testing and field experience. Finally, the licensee stated that historical ISI of the RPV supports had consistently reported no visual evidence of significant corrosion.
Based on the remote visual coverage obtained via robotics maneuvered through the ductwork and industry experience regarding residual boron in the reactor cavity spaces producing little evidence of significant corrosion, the NRC staff finds it reasonable to conclude that, if significant service-induced degradation had occurred in the accessible areas, evidence of it would have been detected by the examinations performed.
Furthermore, the staff determined that the examinations performed provide reasonable assurance of structural integrity of the subject welds.
4.0 CONCLUSION
As set forth above, the NRC staff determines that it is impractical for the licensee to comply with the ASME Code,Section XI requirements, that the proposed weld examination coverage provides reasonable assurance of structural integrity and leak tightness of the subject welds, and that granting relief pursuant to 10 CFR 50.55a(g)(6)(i) is authorized by law and 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. Accordingly, the NRC staff concludes that the licensee has adequately addressed all the regulatory requirements set forth in 10 CFR 50.55a(g)(6)(i). Therefore, the NRC staff grants RA-23-0300 at Robinson for the fifth 10-year ISI interval which commenced on July 21, 2012, and ended on February 19, 2023.
All other ASME Code,Section XI requirements for which relief was not specifically requested and authorized herein by the NRC staff remain applicable, including the third-party review by the Authorized Nuclear Inservice Inspector.
Principal Contributors: S. Levitus, NRR A. Rezai, NRR Dated: December 5, 2024
ML24323A238 OFFICE NRR/DORL/LPL2-2/PM NRR/DORL/LPL2-2/LA NRR/DNRL/NPHP/BC NRR/DNRL/NVIB/BC NAME LHaeg ABaxter MMitchell (ABuford for)
ABuford DATE 11/18/2024 11/20/2024 09/26/2024 09/26/2024 OFFICE NRR/DORL/LPL2-2/BC NRR/DORL/LPL2-2/PM NAME DWrona LHaeg DATE 12/05/2024 12/05/2024