ML23297A026

Proposed Alternatives to ASME Code Section XI Subsection IWE Requirements for Torus Metallic Liner Inspections

ML23297A026
Person / Time
Site:	Brunswick
Issue date:	11/27/2023
From:	David Wrona NRC/NRR/DORL/LPL2-2
To:	Krakuszeski J Duke Energy Progress
References
EPID L-2022-LLR-0089
Download: ML23297A026 (12)

Text

November 27, 2023 John A. Krakuszeski Site Vice President Brunswick Steam Electric Plant Duke Energy Progress, LLC 8470 River Rd. SE (M/C BNP001)

Southport, NC 28461

SUBJECT:

BRUNSWICK STEAM ELECTRIC PLANT, UNIT NOS. 1 AND 2 - PROPOSED ALTERNATIVES TO ASME CODE SECTION XI SUBSECTION IWE REQUIREMENTS FOR TORUS METALLIC LINER INSPECTIONS (EPID L-2022-LLR-0089)

Dear Mr. Krakuszeski:

On December 15, 2022, Duke Energy Progress, LLC (Duke Energy, the licensee) submitted a request (RA-22-0308) to the U.S. Nuclear Regulatory Commission (NRC) for the performance of alternatives to certain American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (BPV) Code,Section XI, Subsection IWE, Requirements for Class MC [metal containment] and Metallic Liners of Class CC [concrete containment] Components of Light-Water Cooled Plants, requirements for the third 10-year containment inservice inspection (CISI) interval at Brunswick Steam Electric Plant (Brunswick), Unit Nos. 1 and 2.

Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(1),

Duke Energy requested to perform alternatives on the basis that the proposed alternative examinations and acceptance criterion provide an acceptable level of quality and safety.

The NRC staff has reviewed the subject request and concludes, as set forth in the enclosed safety evaluation, that the proposed alternatives would provide an acceptable level of quality and safety. Accordingly, the NRC staff concludes that Duke Energy has adequately addressed all regulatory requirements set forth in 10 CFR 50.55a(z)(1). Therefore, the NRC staff authorizes the proposed alternatives to certain requirements of the ASME Code,Section XI, Subsection IWE, 2007 Edition through the 2008 Addenda regarding CISI examinations at Brunswick, Unit Nos. 1 and 2, for the third 10-year CISI interval (May 11, 2018, through May 10, 2028). This request relates to alternative examination and acceptance criterion of the submerged surfaces of torus bays for Brunswick, Unit Nos. 1 and 2.

All other ASME BPV Code,Section XI, requirements for which relief was not specifically requested and approved remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.

J. Krakuszeski If you have any questions, please contact the Project Manager, Luke Haeg.

Sincerely, Digitally signed by David David J. J. Wrona Date: 2023.11.27 Wrona 12:37:14 -05'00' David J. Wrona, Chief Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-325 and 50-324

Enclosure:

Safety Evaluation cc: Listserv

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REQUEST FOR ALTERNATIVES TO ASME CODE SECTION XI SUBSECTION IWE REQUIREMENTS FOR TORUS METALLIC LINER INSPECTIONS DUKE ENERGY PROGRESS, LLC BRUNSWICK STEAM ELECTRIC PLANT, UNIT NOS. 1 AND 2 DOCKET NOS. 50-325 AND 50-324

1.0 INTRODUCTION

By letter dated December 15, 2022 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML22349A655), Duke Energy Progress, LLC (the licensee) requested alternatives to certain requirements of the 2007 Edition through 2008 Addenda of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (BPV) Code,Section XI, Subsection IWE, Requirements for Class MC [metal containment] and Metallic Liners of Class CC [concrete containment] Components of Light-Water Cooled Plants, for the third 10-year containment inservice inspection (CISI) interval at Brunswick Steam Electric Plant (Brunswick),

Unit Nos. 1 and 2.

Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(1), the licensee submitted Relief Request Serial # RA-22-0308 proposing alternative examination and acceptance criterion of the Brunswick, Unit Nos. 1 and 2 torus submerged metallic liner surfaces on the basis that the alternatives provide an acceptable level of quality and safety.

In June 2023, the Nuclear Regulatory Commission (NRC) staff conducted a virtual regulatory audit to support its review of the RA-22-0308. During the regulatory audit, the NRC staff reviewed documents and held discussions with the licensee. The regulatory audit summary was summarized in an NRC letter dated July 28, 2023 (ML23201A204).

By letter dated August 18, 2023 (ML23232A000), the licensee submitted responses (referred to as the supplement henceforth in this safety evaluation) to an NRC request for additional (RAI) information (ML23202A065).

2.0 REGULATORY EVALUATION

The NRC regulations in 10 CFR 50.55a(g)(4), Inservice inspection standards requirement for operating plants, requires that components that are classified as Class MC pressure retaining components and their integral attachments, and components that are classified as Class CC pressure retaining components and their integral attachments, must meet the requirements set forth in Section XI of the ASME BPV Code, Rules for lnservice Inspection of Nuclear Power Enclosure

Plant Components. The regulations require that all inservice inspections conducted during the first 10-year interval, and subsequent intervals, comply with the requirements in the latest edition and addenda of Section XI of the ASME BPV Code, incorporated by reference into 10 CFR 50.55a(b), on the date 18 months prior to the start of the 10-year interval, subject to the conditions listed in 10 CFR 50.55a(b)(2), Conditions on ASME BPV Code,Section XI, to the extent practical within the limitation of design, geometry, and materials of construction of the components.

The NRC regulations in 10 CFR 50.55a(z), Alternatives to codes and standards requirements, states that:

Alternatives to the requirements of paragraphs (b) through (h) of [10 CFR 50.55a]

or portions thereof may be used when authorized by the Director, Office of Nuclear Reactor Regulation. A proposed alternative must be submitted and authorized prior to implementation. The applicant or licensee must demonstrate that:

(1) Acceptable level of quality and safety. The proposed alternative would provide an acceptable level of quality and safety; or (2) Hardship without a compensating increase in quality and safety.

Compliance with the specified requirements of this section would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

3.0 TECHNICAL EVALUATION

3.1 Licensees Alternative Request Serial # RA-22-0308 Relief Request Serial # RA-22-0308 contained three proposed alternatives:

1. In lieu of the acceptance criteria of the ASME Code,Section XI, IWE-3513, Visual Examination, VT-3, subparagraph (a), the licensee proposed that a relevant condition be defined as substrate pit corrosion that causes the remaining torus liner wall thickness to be less than 145 percent of the design minimum allowable wall thickness. The licensee stated that a relevant condition that exceeds this proposed acceptance criterion will require evaluation, corrective measures, or repair/replacement activity to the extent necessary to meet the acceptance standards of IWE-3122, Acceptance, prior to continued service.

2. In lieu of the successive inspection in accordance with IWE-2420, Successive Inspections, subparagraph (b), the licensee proposed to perform an inspection at a frequency not to exceed every third inspection period from the previous visual (VT-3) examination (e.g., ~10 years in lieu of the IWE-2420(b) ~3 years frequency).

3. When protective coating is restored to the torus submerged surfaces prior to return to service, the licensee proposed that reexamination during the next inspection period in accordance with Table IWE-2500-1, Examination Category E-C, is not required, (i.e., using the acceptance standard of IWE-3520,

Standards for Examination Category E-C, Containment Surfaces Requiring Augmented Examination, and VT-1 examination are not required).

3.1.1 Applicable Code Edition and Addenda The applicable Edition and Addenda of the ASME BPV Code,Section XI, for Brunswick, Unit Nos. 1 and 2, is the 2007 Edition through the 2008 Addenda for the fifth 10-year inservice inspection (ISI) interval, which commenced on May 11, 2018, and is currently scheduled to end on May 10, 2028.

The NRC staff noted that the fifth ISI interval for piping and vessels corresponds to the third 10-year containment ISI (CISI) interval. As such, the third CISI interval has the same beginning and end dates as the fifth 10-year ISI interval and uses the same 2007 Edition through the 2008 Addenda of the ASME BPV Code,Section XI.

Relief Request Serial # RA-22-0308 is applicable to the third 10-year CISI.

The licensee noted that the third CISI end date is subject to change in accordance with IWA-2430(c) of the ASME BPV Code,Section XI.

3.1.2 ASME Code Components Affected The affected ASME Code components are Brunswick, Unit Nos. 1 and 2 suppression chamber (torus) submerged surfaces of the metallic liners as identified in Section 1 of Enclosure 1 of RA-22-0308.

3.1.3 Applicable Code Requirements IWE-2500, Table IWE-2500-1, Examination Category E-A, Item Number E1.12, Wetted Surfaces of Submerged Areas, requires that 100 percent of wetted surfaces of submerged areas receive a VT-3 examination once each inspection interval in accordance with the acceptance standards in IWE-3510, Standards for Examination Category E-A, Containment Surfaces. Deferral of inspection to the end of the interval is permissible.

IWE-3513, Visual Examination, VT-3, states, in part, that relevant conditions1 shall require correction or evaluation to meet the requirements of IWE-3122 prior to continued service. In accordance with IWE-3513(a), relevant conditions include pressure-retaining component corrosion that exceeds 10 [percent] of the nominal wall thickness.

IWE-3122.3, Acceptance by Engineering Evaluation, subparagraph (a) states, in part, that a component whose examination detects flaws or areas of degradation that do not meet the acceptance standards of IWE-3500 [Acceptance Standards] are acceptable for continued service without a repair/replacement activity if an engineering evaluation indicates that the flaw or area of degradation is nonstructural in nature or has no unacceptable effect on the structural integrity of the component.

1 relevant condition, is defined in Article IWA-9000 as a condition observed during a visual examination that requires supplemental examination, corrective measure, correction by repair /replacement activities, or analytical evaluation.

IWE-3122.3(b) states, in part, that when flaws or areas of degradation are accepted by engineering evaluation, the area containing the flaw or degradation shall be reexamined in accordance with IWE-2420(b), (c), and (d).

IWE-2420(b) requires that when examinations result in detection of areas of flaws, or degradation, or conditions that require an engineering evaluation and the component is acceptable for continued service, the areas containing such flaws, areas of degradation, or conditions shall be reexamined during the next inspection period in accordance with Table IWE-2500-1, Examination Category E-C, Containment Surfaces Requiring Augmented Examination.

3.1.4 Licensees Proposed Alternatives, Bases for Use, and Reason for Request The licensee stated that the nominal wall thickness of the torus metallic liner plate is 3/8-inch (0.375 inch or 375 mils), and the torus is backed by reinforced concrete. The licensee further stated that relevant conditions for the torus liner, consistent with IWE-3513(a), includes substrate pit corrosion and general area degradation of the torus metallic liner that exceed a depth of 37 mils (0.037 inch, i.e., 10 percent of the nominal wall thickness). The licensee stated that the torus metallic liner remains fully capable of performing its intended design function with local substrate pit corrosion that does not result in a remaining wall thickness of less than 187 mils (0.187 inch, tmin = 0.1875 inch, or 50 percent of the nominal wall thickness) and with general area corrosion that does not result in a remaining wall thickness of less than 250 mils (0.250 inch, tmin = 0.25 inch, or 66 percent of the nominal wall thickness).

The licensee stated that to perform both (i) successive examination of submerged surfaces previously receiving protective coating repairs, and (ii) scheduled examination of the remaining submerged surfaces during a single refueling outage, creates an unnecessary challenge to personnel safety and radiation exposure. The licensee further stated that to complete the submerged surface inspections, divers manually clean the torus liner surfaces to be examined and a filtration system must be used to attain water clarity before divers can perform torus liner visual examinations under water.

The licensee explained that using a filtration system to attain water clarity results in unnecessary worker radiation exposure and radioactive material disposal. To attain the needed water clarity, the full volume of water in the torus must be circulated several times through the filtration system. This activity typically generates depleted filters, which requires handling and disposal of highly radioactive material.

According to the licensee, restoration of protective coatings on the submerged surfaces of the torus liner is implemented, as necessary, when examination results reveal areas of degradation that do not meet the acceptance criteria of IWE-3500. The licensee considers surfaces where protective coatings have been restored no longer warrant successive inspections in accordance with IWE-2420(b) and that restoration of a protective coating following an examination provides reasonable assurance that continued degradation of these submerged surfaces is arrested and mitigated.

Section 4 of Enclosure 1 of RA-22-0308 discusses the inspection results and current examination status of the torus liners of Brunswick, Unit Nos. 1 and 2. Section 5 of Enclosure 1 of RA-22-0308 discusses the proposed alternatives and basis for use. The licensees supplement provided additional details.

3.1.5 Duration of Proposed Alternatives The licensee requested that the proposed alternatives be effective for the duration of Brunswick, Unit Nos. 1 and 2, third 10-year CISI interval, which is currently scheduled to end no later than May 10, 2028. In response to RAI-9(2) in its supplement, the licensee stated that the duration of the proposed alternatives would not extend to the Brunswick, Unit Nos. 1 and 2, fourth 10-year CISI interval, which is scheduled to begin on May 11, 2028.

3.2 NRC Staff Evaluation The NRC staff focused its evaluation on: (1) the three proposed alternatives, (2) the proposed inspection during the remainder of the third 10-year CISI interval, (3) proposed corrective actions, and (4) defense-in-depth measures.

3.2.1 Proposed Alternatives 3.2.1.1 Proposed Acceptance Criterion for Relevant Conditions The ASME Code,Section XI, IWE-3513(a) specifies that the pressure-retaining component corrosion or erosion (degradation) that exceeds 10 percent of the nominal wall thickness shall require correction or evaluation to meet the requirements of IWE-3122 prior to continued service. The nominal torus liner wall thickness is 0.375 inch. Therefore, the depth of degradation is limited to 0.0375 inch (10 percent of 0.375 inch).

The licensee proposed acceptance criterion is that if the remaining wall thickness, at a pitted location, is less than 145 percent of the design minimum allowable torus liner nominal wall thickness, the pit corrosion will be considered as a relevant condition. In response to RAI-3 and RAI-7 as shown in its supplement, the licensee stated that substrate pit corrosion is defined as a 1-inch diameter area with a minimum thickness in the pit area of 3/16 inch and the average remaining wall thickness in the pit area of 1/4 inch.

The 145 percent of the design minimum allowable wall thickness of 0.1875 inch is 0.2719 inch (145 percent of 0.1875 inch). In response to RAI-8 as shown in its supplement, the licensee stated that the material allowance for future pitting corrosion is 0.084 inch (45 percent of 0.1875 inch). The licensee further stated that any metal loss that exceeds the depth of 0.084 inch would be characterized as a relevant condition. As a comparison, the proposed allowable metal loss of 0.084 inch is about 2.24 times the 0.0375 inch that is allowed per the ASME Code,Section XI, IWE-3122.3.

The licensee stated that once an indication exceeds 0.084 inch, it will take corrective action, such as restoring the protective coating on the pitted location to prevent further degradation.

The NRC staff noted that if corrosion does occur, under the proposed alternative, 0.291 inch of the torus wall thickness would remain (0.375 inch - 0.084 inch), which is 77.6 percent of the torus wall design thickness ((0.291 inch / 0.375 inch) x 100 percent). This remaining wall thickness is equal to 155.2 percent ((0.291 inch / 0.1875 inch) x 100 percent) of the minimal wall thickness.

The licensee imposed a limitation on the use of the proposed acceptance criterion. In response to RAI-8(2) as shown in its supplement, the licensee stated that the proposed acceptance criterion does not apply to discovered corroded areas of the torus metallic liner that have not been recoated to prevent further corrosion degradation.

The NRC staff finds the proposed acceptance criterion acceptable because with the postulated metal loss of 0.084 inch, the torus liner would still maintain 155.2 percent of the minimum wall thickness for the remainder of the third CISI interval.

3.2.1.2 Proposed Alternate Examination As stated above, the licensee proposed to: (1) perform an inspection at a frequency not to exceed every third inspection period from the previous visual (VT-3) examination, and (2) not to perform VT-1 examination. The licensee stated that the corrosion rate is 7.5 mils/year based on operating experience. In response to RAI-8 as shown in its supplement, the licensee stated that considering the 0.084 inch of liner material available for future corrosion and a corrosion rate of 7.5 mils/year, an uncoated pitted area (i.e., protective coating was not applied, or the applied protective coating failed) would not be expected to violate the design minimum wall thickness for approximately 11.2 years (0.084 inch / 0.0075 inch/year). As such, in lieu of performing a successive examination in the subsequent inspection period per the ASME Code,Section XI, IWE-2420(b), the licensee proposed that inspection at a frequency not to exceed every third inspection period from the previous visual (VT-3) examination.

In response to RAI-5 as shown in its supplement, the licensee stated that it will apply the proposed acceptance criterion to discovered exposed substrate areas and corrosive pit indications on the submerged surfaces of the torus liner. The licensee also stated that this new acceptance criteria will be applied to the exposed substrate areas and corrosive pit indications discovered with previously restored protective coatings and to the areas of exposed substrate corrosion left uncoated during the second inspection interval in the 2016 Unit 1 refueling outage.

The licensee stated that any discovered corrosive pit indications that exceed the proposed acceptance criterion will be dispositioned in accordance with the requirements of IWE-3122.2, Acceptance by Corrective Measures or Repair/Replacement Activity, or IWE-3122.3 prior to continued service.

The NRC staff noted that the ASME Code,Section XI, IWE-1241, Examination Surface Areas, requires augmented inspection in accordance with Table IWE-2500-1, Examination Category E-C for surface areas that are subject to accelerated degradation and aging. Examination Category E-C requires the use of the VT-1 examination during the augmented examination. As an alternative, the licensee proposed that when protective coating is restored, reexamination during the next inspection period in accordance with Table IWE-2500-1, Examination Category E-C, is not required, meaning that the use of the acceptance standard of IWE-3520 and VT-1 examination are not required.

However, the licensee imposed a limitation on its proposed alternative examination. In response to RAI-8(4) in its supplement, the licensee stated that for discovered indications that do not receive protective coating restoration and are determined acceptable by engineering evaluation in accordance the ASME Code,Section XI, IWE-3122.3, the inspection frequency will be in accordance with IWE-2420. The NRC staff determined that the licensee-imposed limitation will ensure that the proposed acceptance criterion will be applied judiciously and appropriately.

In addition, the NRC noted that as discussed in RA-22-0308 and the supplement, the inspection results from the second and third CISI intervals do show many corroded locations. Several indications were within the 37 mils depth (e.g., 10 percent of design thickness). Some of the indications exceeded the ASME Code limit of 37 mils depth. The maximum depth for the pitted corrosion was 131 mils as presented in response to RAI-5(1) in the supplement. The NRC staff noted that the degradation mechanism of pitted indications is general corrosion, not stress

corrosion cracking or fatigue. This means that if a pitted location becomes 100 percent through wall, the corroded location will start with a pin hole. The pin hole may enlarge, and leakage may increase. However, the torus would not be likely to fail catastrophically for the remainder of the third CISI interval because the growth of the degradation would be localized and slow. In addition, the torus is backed and supported by reinforced concrete. The torus would still maintain its designed function for the remainder of the third CISI interval. The NRC staff noted that the licensees operating experience has shown that the previously implemented protective coating restoration has mitigated the corroded locations. The licensee described that the corrosion rate of 7 mils/year is based on operating experience. The licensee will examine the degraded locations within three periods (10-year CISI interval) to monitor the condition of the torus liners.

Based on the above evaluation, the NRC staff finds that the augmented examination per Table IWE-2500-1, Examination Category E-C, Item No. E4.11, Visible Surfaces, augmented visual (VT-1) examinations are unnecessary subject to the allowance for pitting depth of 0.084 inch (45 percent of 0.1875 inch) as described in the licensees response to RAI-8.

3.2.1.3 Proposed Inspection In response to RAI-10 in its supplement, the licensee discussed the inspections performed in the earlier refueling outages and the proposed inspections in the remaining refueling outages of the third CISI interval as shown in Attachments 1 and 2 of the supplement.

The NRC staff evaluated the proposed inspections scheduled for the remaining outages in the third CISI interval. Brunswick, Unit No. 1 has three remaining refueling outages in 2024, 2026 and 2028. Brunswick, Unit No. 2 has two remaining refueling outages in 2025 and 2027.

Brunswick, Unit No. 1 As shown in Attachment 1 of its supplement, for Brunswick, Unit No. 1, the licensee stated that it had scheduled VT-1 examination of torus bays 05, 06, 07, and 08. However, the licensee proposed not to perform VT-1 examination if degradation is detected by VT-3 examination in the spring of 2024 refueling outage.

In response to RAI-5 as shown in its supplement, the licensee clarified that during the upcoming 2024 Brunswick, Unit No. 1 refueling outage, 6 of the 12 remaining torus bays with uncoated corroded areas from the 2016 refueling outage are currently scheduled for examination and protective coating restoration. During the 2026 Brunswick, Unit No. 1 refueling outage, the six remaining torus bays with uncoated corroded areas from the 2016 refueling outage are scheduled for examination and protective coating restoration. In response to RAI-6 as shown in its supplement, the licensee emphasized that the proposed alternative does not apply to discovered exposed substrate areas and corrosive pit indications in Brunswick, Unit No. 1 torus bays that have not received protective coating restoration.

The licensee stated that if the torus examinations performed during the 2024 and 2026 refueling outages reveal that the uncoated corroded areas remain bounded by the current engineering calculation, it may apply additional analysis of the remaining uncoated corroded areas which may support extending torus examinations until the refueling outage, which is the last refueling outage of the third CISI interval.

Brunswick, Unit No. 2 As shown in Attachment 2 of its supplement, for Brunswick, Unit No. 2, the licensee stated that it has scheduled inspections of torus bays 10, 11, 12, 13, 14, 15, and 16, and restore protective coating of any exposed substrate areas in the spring 2025 refueling outage. If the licensee could not complete the inspection, the licensee proposed to defer the inspection and protective coating restoration to the spring 2027 refueling outage, which is the last refueling outage of the third CISI interval.

Based on the inspection plan for the remaining third CISI interval, the NRC staff determined that the licensee will have completed inspections of all 16 torus bays of both Brunswick, Unit Nos. 1 and 2. In addition, the licensee will have applied protective coating restoration on the detected indications. The NRC staff finds that based on the results from inspections performed in the third CISI interval, the torus liners of Brunswick, Unit Nos. 1 and 2 will have sufficient wall thickness to perform their design functions during the remaining third CISI interval.

3.2.2 Corrective Actions In response to RAI-4 in its supplement, the licensee stated that protective coating restoration repairs are performed by a specialty vendor using qualified coating material. When coating defects are identified, the licensee will clean and prepare the corroded area and adjacent coating for spot application of the new coating. The license stated that the new coating material it uses has proven industry success of greater than 20 years without failure.

In response to RAI-6(3) in its supplement, the licensee stated that before the end of the CISI third interval for Brunswick, Unit No. 1, protective coating restoration will be applied to the discovered exposed substrate areas and corrosive pit indications in the submerged surfaces of the torus metallic liner in all 16 torus bays. For the Brunswick, Unit No. 2 torus, the licensee stated that it has performed the protective coating restoration on all exposed pitted areas as discussed in Attachment 2 of the supplement.

In response to RAI-7(4) in its supplement, the licensee stated that typical corrective actions would be to apply protective coating to the pitted areas that are within or exceed the proposed alternate acceptance criterion. The licensee further stated that if protective coating were not able to be applied, the condition would be entered into the corrective action program and an engineering evaluation performed in accordance with the ASME Code,Section XI, IWE-3122.3.

In response to RAI-7(5), the licensee stated that for discovered indications whose metal loss depth is within the proposed acceptance criterion, the indication will be accepted for continued service in accordance with the ASME Code,Section XI, IWE-3122.1, Acceptance by Examination. For these discovered indications, the licensee stated that the protective coating restoration will typically be reapplied to arrest further degradation. However, the licensee stated that it will not need to perform corrective measures or evaluation on these indications in accordance with IWE-3122.2 or IWE-3122.3, because the indications are accepted for service.

The NRC staff finds that the licensees corrective action is acceptable because: (1) the licensee will restore protective coating on all indications that are detected and if the protective coating is not restored, the indication will be dispositioned under the corrective action program and IWE-3122.3, and (2) the licensee is using a coating material that has proven success of a minimum of 20 years.

3.2.3 Defense-in-Depth Measures to RA-22-0308 showed that the Brunswick torus liners are backed by reinforced concrete. The NRC staff noted that if a 100 percent through wall hole were to occur, there would be leakage from the hole to the interface between the liner and reinforced concrete. However, the torus would not catastrophically fail within the remainder of the third CISI interval based on the licensees corrosion calculation.

In addition, in response to RAI-2 in the supplement, the licensee stated that the plant Technical Specification (TS) and Technical Requirements Manual (TRM) Section 5.5.2, Primary Coolant Sources Outside Containment, describe the program for control to minimize leakage from those portions of systems outside primary containment that could contain highly radioactive fluids during serious transients or accidents. The licensee explained that these systems are periodically tested and inspected to determine the system leakage rates. The leakage rates of all the systems are summed to obtain a total engineered safety feature (ESF) leakage. The licensee has a plant procedure that provides a management standard acceptance criteria 1 gallon per minute (gpm) total ESF leakage. The licensee stated that leakage between 1 and 20 gpm can be accepted and that the 20 gpm leak rate is used as input to the various radiological dose calculations.

The NRC staff determined that the torus liners are structurally supported by reinforced concrete which will minimize the potential for catastrophic failure. In addition, the licensees TS, TRM, and leak management procedure monitors potential leakage. The NRC staff finds that these defense-in-depth measures will support the structural integrity of the torus liners.

4.0 CONCLUSION

As set forth above, the NRC staff has determined that the licensee has demonstrated, in Relief Request Serial # RA-22-0308, that the proposed alternatives will provide an acceptable level of quality and safety. Accordingly, the NRC staff concludes that the licensee meets the regulatory requirements set forth in 10 CFR 50.55a(z)(1). Therefore, the NRC staff authorizes the use of Relief Request Serial # RA-22-0308 at the Brunswick Steam Electric Plant, Unit Nos. 1 and 2, for the remainder of the third 10-year CISI interval that ends on May 10, 2028.

All other ASME BPV Code,Section XI, requirements, as incorporated by reference in 10 CFR 50.55, for which an alternative was not specifically requested and granted or authorized (as appropriate) remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.

Principal Contributors: J. Tsao, NRR A. Istar, NRR B. Lee, NRR D. Widrevitz, NRR Date: November 27, 2023

ML23297A026 OFFICE NRR/DORL/LPL2-2/PM NRR/DORL/LPL2-2/LA NRR/DEX/ESEB/BC NRR/DSS/SCPB/BC NAME LHaeg RButler (ABaxter for) ITseng BWittick DATE 10/23/2023 10/26/2023 9/22/2023 10/5/2023 OFFICE NRR/DNRL/NVIB/BC NRR/DORL/LPL2-2/BC NRR/DORL/LPL2-2/PM NAME ABuford DWrona LHaeg DATE 11/9/2023 11/17/2023 11/27/2023