ML26020A168
| ML26020A168 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 01/26/2026 |
| From: | David Wrona NRC/NRR/DORL/LPL2-2 |
| To: | Krakuszeski J Duke Energy Progress |
| Sierra T, NRR/DORL/LPL2-2 | |
| References | |
| EPID: L-2025-LLR-0092 | |
| Download: ML26020A168 (0) | |
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January 26, 2026 BRUNSWICK STEAM ELECTRIC PLANT, UNIT 1 - AUTHORIZATION AND SAFETY EVALUATION OF REQUEST FOR ALTERNATIVE ACCEPTANCE OF THROUGH-WALL FLAW IN SERVICE WATER SYSTEM VALVE BODY (EPID: L-2025-LLR-0092)
LICENSEE INFORMATION Recipients Name and Address:
Mr. John A. Krakuszeski Site Vice President Brunswick Steam Electric Plant Duke Energy Progress, LLC 8470 River Rd. SE (M/C BNP001)
Southport, NC 28461 Licensee:
Duke Energy Progress, LLC Plant Name and Unit:
Brunswick Steam Electric Plant (Brunswick), Unit 1 Docket No:
50-325 APPLICATION INFORMATION Submittal Date: November 17, 2025 Submittal Agencywide Documents Access and Management System (ADAMS) Accession No.: ML25321A755 Applicable Inservice Inspection (ISI) Program Interval and Interval Start/End Dates: The fifth ISI interval began on May 11, 2018, and is scheduled to end on May 10, 2028.
Alternative Provision: The licensee requested an alternative under Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(2).
ISI Requirement: The American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) requirements applicable to this request originate in the 2007 Edition through 2008 Addenda of Section XI, IWD-3100, IWD-3500, and IWA-4000.
IWD-3120(b) states that components for which examination reveals flaws that do not meet the standards shall be subjected to supplemental examination, or to a repair/replacement activity.
IWD-3500 describes acceptance standards, and states, in part, that the requirements of IWC-3500, Acceptance Standards, may be used.
IWA-4000 describes the repair/replacement activities to correct an unacceptable flaw.
Discovery of an area below the design minimum wall thickness in the structural portion of an ASME Code Class 1, 2, or 3 component is direct evidence of a flaw in the component.
ASME Code Case N-869, Evaluation Criteria for Temporary Acceptance of Flaws in Class 2 or 3 Piping,Section XI, Division 1, provides analytical evaluation requirements for temporary acceptance of flaws, including through-wall flaws, in piping including elbows, pipe bends, reducers, and branch tees, whose maximum operating pressure is greater than 275 pounds per square inch gauge (psig), without performing a repair/replacement for a limited time, not exceeding the time to the next scheduled refueling outage. This code case has been incorporated by reference into 10 CFR 50.55a via inclusion in Regulatory Guide (RG) 1.147, Revision 21, Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1, with conditions.
ASME Code Case N-513-5, Evaluation Criteria for Temporary Acceptance of Flaws in Moderate Energy Class 2 or 3 Piping and Gate ValvesSection XI, Division 1, provides analytical evaluation requirements for temporary acceptance of flaws, including through-wall flaws, in piping including elbows, pipe bends, reducers, expanders, branch tees, and gate valve body ends, whose maximum operating temperature and pressure do not exceed 200 degrees Fahrenheit (°F) and 275 psig, respectively, without performing a repair/replacement for a limited time, not exceeding the time to the next scheduled refueling outage. This code case has been incorporated by reference into 10 CFR 50.55a via inclusion in RG 1.147, Revision 21, with conditions.
Applicable Code Edition and Addenda: The code of record for the fifth ISI interval of Brunswick, Unit 1 is the 2007 Edition through 2008 Addenda of the ASME Code,Section XI.
By Safety Evaluation dated May 14, 2025 (ML25125A315), the NRC approved the use of the 2021 Edition of ASME Code,Section XI, Nonmandatory Appendix C, Analytical Evaluation of Flaws in Piping, for all applicable pressure-retaining piping and components during the remainder of the Brunswick, Unit 1, fifth ISI interval.
The Brunswick original construction and analysis codes are the 1967 Edition of United States of America Standards (USAS) B31.1 and the 1980 Edition with Winter 1980 Addenda of the ASME Code,Section III. The licensee utilizes the 2007 Edition through 2008 Addenda of the ASME Code,Section III as its current construction code.
Brief Description of the Proposed Alternative: On November 3, 2025, the licensee discovered a leaking flaw on the body of ASME Code Class 3 service water (SW) system valve number 1-E11-PDV-F068A. The external leak from the through-wall flaw is determined to be at a rate of two drops per 30 minutes. The degraded valve is described as 16-inch by 20-inch, 90-degree angled control valve, which connects the Unit 1 residual heat removal (RHR) heat exchanger SW discharge header (Line 1-E11-128-16-046) to the downstream conventional and vital headers drain (Line 1-SW-142-20-157A). The leaking flaw is on the inlet side of the control valve, which is located at the top of a vertical riser, approximately 45 feet from the bottom of the drop. From this low point, the pipe exits into a pipe-tunnel and discharges into the top of the circulating water discharge at near atmospheric conditions. Based on the large elevation difference, and the small pressure drop in the discharge piping, the pressure conditions on the downstream side of this valve are at vacuum. The leaking through-wall flaw is on the upstream side of the valve body, which is currently filled with well-water for layup, and is experiencing approximately two drops per 30 minutes of external leakage. The portion of the piping system containing the through-wall flaw is laid up with well-water while not in service to help prevent brackish water corrosion. The well-water pressure is significantly lower than normal operating pressure. The through-wall flaw location would see normal operating pressure and temperature conditions when the RHR heat exchangers are in service for shutdown cooling or quarterly testing. When quarterly testing occurs, the daily leakage monitoring of the through-wall flaw will take place at that time to ensure monitoring at normal system pressure and temperature.
Licensees Flaw Characterization On November 6, 2025, the licensee performed dye penetrant testing (PT), ultrasonic testing (UT), and borescope visual examination to characterize the leaking flaw in the valve body. The PT determined that the leaking flaw is a pinhole. The PT did not find any additional flaws in the valve body. The UT was used to measure wall thickness of the valve body near the pinhole and around the circumference of the valve body at the inlet flange, and the results showed values at nominal wall thickness of 1 inch. The borescope was used to visually examine the internal surface condition of the valve body and characterize the extent of material degradation internally. From the borescope results, and the known size and contour of the inlet of the valve body, an area of material degradation around the pinhole was conservatively estimated to be approximately 2 inches in axial direction by 2 inches in circumferential direction.
Licensees Proposed Alternative In lieu of IWA-4000 required repair or replacement activities, the licensee proposed alternative evaluation approach and augmented examinations to temporarily accept the degraded SW control valve for continued operation until the valve is replaced during the spring 2028 refueling outage (scheduled for March 4, 2028) or until such time that the analysis conditions used in the evaluation no longer remain valid which requires plant shutdown, whichever occurs first. The licensees proposed alternative is:
- a. The licensee proposed to utilize the design-by-analysis approach in the 2007 Edition with 2008 Addenda of the ASME Code,Section III, NB-3200 to evaluate the structural integrity of the degraded SW control valve. Due to the complexity of valve geometry and to account for future degradation, the licensee also proposed a three-dimensional (3-D) finite element modeling (FEM) and finite element analysis (FEA) under ASME Code,Section III, limit load criteria to calculate the stress field associated with a 100 percent through-wall flaw and non-uniform wall thinning.
- b. To implement compensatory actions consistent with paragraphs 2(e) through 2(i) of ASME Code Case N-869 to monitor growth of, and leakage from, the identified through-wall flaw.
As part of the basis for alternative, the licensee stated that it cannot directly use ASME Code Case N-869 because this code case does not address the evaluation of a flaw on the body of a valve, or ASME Code Case N-513-5 because this code case has different operating pressure and temperature requirements. However, ASME Code Case N-513-5 shares the same scope with the addition of valve body ends. The flaw location in the degraded valve at Brunswick is within the region identified in Code Case N-513-5, where it would be acceptable to use the straight pipe calculations to solve for an allowable flaw size. However, due to the complexity of the valve and to account for future degradation, an FEA under ASME Code,Section III, limit load criteria is utilized instead. The licensee stated that it completed ASME Code Case N-869, Section 5.0, Augmented Examinations, on the most susceptible locations of the affected system within 30 days of the initial detection of pinhole leak on valve 1-E11-PDV-F068A. These inspections included the sister valve on Unit 1, and the two comparable valves on Unit 2, as these are the only locations to check with similar conditions.
Licensees Flooding Analysis The licensee explained that the degraded SW control valve with pinhole leak is in a vertical pipe chase in the northwest corner of the reactor building. The orientation of the leak is on the bottom side of the valve such that any leakage is contained within the pipe chase and collected on the floor of the north core spray pump room. This room contains a 600-gallon capacity sump and a sump pump with a capacity of 50 gallons per minute (gpm). The sump is equipped with a -high-level switch connected to an annunciator to alert operations of high level in the sump, which would indicate leakage exceeding the capacity of the sump pump. Additionally, the north core spray pump room is equipped with an additional level switch and annunciator to alert operations if the water level in the area is above the top of the sump for flooding.
For external flooding events, evaluations postulate the potential for a total of 17 gpm leakage into the north core spray pump area through doors and other sources. This provides 33 gpm margin (50 gpm - 17 gpm) in pump capacity for other leakage sources. The licensee stated that based on the above, limiting the leakage from the valves through-wall flaw to less than 20 gpm is considered reasonable for protecting the north core spray pump room from internal flooding.
According to the licensee, this limit is within the capacity of the area sump pump and provides margin to accommodate other leakages. The daily monitoring of leakage from the through-wall flaw in the valve body in this proposed alternative will identify any increasing trend in leakage that would approach this limit. Annunciator alarms will alert operations of any unexpected leakage increases.
The degraded valve with a through-wall flaw is in piping on the discharge side of all safety related and non-safety related heat exchangers. External leakage at this location will not impact on the heat removal capability of any safety related or non-safety related equipment. The licensee concluded that if the identified leakage exceeds the 20-gpm leak rate limit, repair/replacement activities will be performed to restore the integrity of the valve.
For additional details on the alternative request, refer to the documents located at ADAMS Accession Nos. identified above.
STAFF EVALUATION The NRC staff evaluated the licensees proposed alternative request pursuant to 10 CFR 50.55a(z)(2). The NRC staff focused on whether compliance with the specified requirements of 10 CFR 50.55a(g), or portions thereof, would result in hardship or unusual difficulty, without a compensating increase in the level of quality and safety. On November 25, 2025, via teleconference, the NRC staff verbally authorized this request for alternative, so that the licensee could continue operation with the degraded valve. A detailed safety evaluation of the request for alternative is provided below.
Hardship Justification In its evaluation, the NRC staff assessed whether the licensee provided adequate description and technical information to support the basis for a hardship or unusual difficulty if it were required to comply with the ASME Code repair or replacement of the degraded SW system control valve. The licensee described its basis for hardship as follows: (a) weld repair of the valve is unfeasible based on prior experience with valves of the same material, (b) replacement of the valve cannot be accomplished safely with the unit online, (c) replacement of the valve with the unit online would cause the secondary containment to be inoperable, and replacement of the valve could likely not be completed within the timeframe required to restore operability of the secondary containment, and (d) completion of the valve replacement would require isolation of the conventional SW system discharge header, which would require shutdown of the plant.
Replacement activity while the unit is online or is shutdown would result in personnel exposure to safety hazards and additional dose, and plant risks. Therefore, the NRC staff determines that concerns from unnecessary shutdown of the plant, unnecessary risks to plant operation, personnel exposure to safety hazards, and as low as is reasonably achievable criteria for radiological exposure support the licensees hardship justification.
Reasonable Assurance of Structural Integrity of Degraded Valve In its evaluation, the NRC staff focused on two aspects of the licensees technical basis which includes: (i) use of the ASME Code,Section III, design-by-analysis approach and the FEM and FEA under ASME Code,Section III, limit load criteria to demonstrate that the degraded valve with leaking pinhole remains structurally stable without catastrophic failure, and (ii) the licensee has compensatory actions in place to periodically monitor the flaw growth and leak rate during operation to ensure that the flaw does not exceed the calculated allowable flaw length (axially or circumferentially), or the leakage from the through-wall flaw does not exceed the calculated allowable leak rate. The NRC staffs evaluation is as follows:
Design-by-Analysis Approach and Finite Element Analysis The licensee stated that because the inspections have identified at least one thickness reading below minimum wall thickness (tmin), the primary stress design criteria for service level A (normal) and service level B (upset) conditions are based on the limit load design criteria of ASME Code,Section III, paragraph NB-3228.1, Limit Analysis. The allowable stress, S, is used instead of the ASME Code Class 1 design stress intensity, Sm. This is consistent with the design rules, as the yield stress definition is the equivalent of the local primary membrane stress, which uses an allowable stress of 1.5Sm for Class 1 components or 1.5S for Class 2, Class 3, and B31.1 components. The subject component must support a total load of 150 percent of the applied maximum loads of the service levels A/B without plastically collapsing. That is, the membrane stress across an entire section for a given location does not exceed the defined yield stress of 1.5S. The NRC staff noted that use of the allowable stress for the design stress intensity is consistent with ASME Code,Section III requirement, therefore, is acceptable.
The licensee stated that the subject pipe must support a total load of 150 percent of the applied maximum loads of the service levels A/B without the pipe plastically collapsing.
That is, the membrane stress across an entire section for a given location does not exceed the defined yield stress of 1.5S. The NRC staff noted that the applied loading must be no more than two-thirds of the collapse load and the applied stresses must be within the material yield strength of 1.5S.
For the loading in the service level D faulted condition, the licensee used the limit load design criteria of ASME Code,Section III, Nonmandatory Appendix F, F-1200(a) which is based on F-1341.3. Paragraph F-1341.3 states, in part, that the static or equivalent static loads shall not exceed 90 percent of the limit analysis collapse load using a yield stress which is the lesser of 2.3Sm and 0.7Su, where Su is the ultimate stress. The licensee stated that the subject pipe must support a total load of 111.1 percent of the applied faulted loads without plastically collapsing (i.e., the membrane stress across an entire section for a given location does not exceed the defined yield stress of 2.3S or 0.7Su). The licensee applied additional uniform wall thinning on the FEM until the pipe structure meets the above limit load criteria or plastically collapses, which will be at the point of numerical instability. The total load, as a percentage of nominal load, will be compared to the required 150 percent of the service level A/B loads and 111.1 percent of the service level D loads. The NRC staff noted that the allowable load on the component is established by applying design factors to the limit load such that the onset of gross plastic deformations (plastic collapse) will not occur. The NRC staff further noted that a limit-load analysis performed in accordance with the ASME Code,Section III, consists of using scaled loads (e.g., applying a factor of 1.5) and modeling elastic-plastic material behavior. If the analysis converges for the scaled loads, the design is considered acceptable. The simplified material model for the limit-load analysis method is defined as elastic-plastic with the yield point set equal to 1.5S, where S is the base allowable stress of the material. Therefore, the NRC staff finds that the licensees approach is acceptable.
In its FEM, the licensee included the valve body, the 16-inch raised neck flange, the 16-inch straight pipe, the nominal wall thickness of 1 inch which was based on the field UT, and the initial wall thinning or material degradation area which was modeled as a through-wall hole with dimensions of 2.0 inches long by 2.0 inches wide based on the borescope examination. The licensee did not include either the gusset plate underneath the flaw location or the transition from the 16-inch end of the valve-to-valve body in the FEM. The licensees basis was that the gusset would add more stiffness and wall thickness, and the transition would add additional material that would help reduce the stresses and strains, therefore removing them would be more conservative. The flange face of the 20-inch end of the valve is restrained in the axial and circumferential directions and left unconstrained in the radial direction to allow for expansion due to internal pressure. The free end of the piping is left free, where the bending moment and torque loads are applied. The NRC staff determined that the licensees FEM is acceptable because the model includes the necessary boundary conditions, the necessary pipe configuration, and the nominal wall thickness based on the field measurement.
The licensee stated that maximum internal pressure is applied to the interior surfaces of the FEM. In the licensees FEM analysis, a maximum internal pressure of 320 psig was applied, corresponding to the maximum operating pressure. The NRC staff noted that the use of operating pressure versus design pressure is appropriate in this case because the licensees analysis used a similar methodology and serves the same purpose as an analysis in accordance with ASME Code Cases N-869 and N-513-5, which specify the use of maximum operating pressure rather than maximum design pressure for analyses supporting temporary acceptance of flaws. To properly model the longitudinal stresses caused by pressure on the interior surface of the piping, the licensee applied the pressure induced end-cap load to the unconstrained free end of the valve and piping. According to ASME Code,Section III, Appendix F, the static or equivalent static loads shall not exceed two-thirds for the normal/upset condition or 90 percent for the faulted condition of the limit analysis collapse load. Therefore, the degraded location must support a minimum applied load of 150 percent for the normal/upset condition or 111.1 percent for the faulted condition. The NRC staff noted that the applied loading is consistent with the ASME Code requirements.
From its analysis, the licensee concluded the following: (a) the as-found wall thinning area of the subject valve body meets the criteria for both normal/upset and faulted conditions, (b) a hole size of 6.2 inches by 5 inches in the valve flange meets the limit load design criteria of the ASME Code,Section III, NB-3228.1, and (c) a hole size of 6.2 inches by 5 inches with additional 20 percent uniform thinning around the entire valve flange also meets the limit load. The licensees proposed alternative states, in part, that repair/replacement activities shall be performed no later than when the predicted flaw size from either periodic inspection or by flaw growth analysis exceeds the acceptance criteria (6.2 inches axially or 5 inches circumferentially). The NRC staff determined that the licensees proposed acceptance criterion is smaller and thus more conservative than what the limit load analysis would permit (i.e., a 6.2-inch by 5-inch hole). Therefore, the NRC staff finds that the licensees allowable hole size of 6.2 inches in axial direction or 5 inches in circumferential direction is acceptable for maintaining the structural integrity of the degraded valve because this hole size meets the limit load criteria of the ASME Code,Section III, NB-3228.1.
Compensatory Actions The NRC staff notes that the licensee has the following compensatory actions in place for monitoring the flaw growth and leakage of the identified through-wall flaw in the SW control valve body during operation:
Frequent periodic examinations of no more than 30-day intervals shall be used to determine if the flaw is growing and to establish the time at which the detected flaw will reach the allowable size.
Leakage from through-wall flaw shall be monitored daily to confirm the analysis conditions used in the evaluation remain valid. When the RHR heat exchangers are in service at normal operating temperature and pressure for quarterly testing, the daily leakage check will be performed during this time.
The licensees flooding analysis showed that the leakage from the through-wall flaw in the degraded valve shall be limited to less than 20 gpm. ASME Code repair/replacement activities shall be performed when leakage from the flaw exceeds the acceptance limit of 20 gpm.
If engineering evaluation of examinations reveal flaw growth rate to be unacceptable, an ASME Code repair/replacement activity shall be performed.
ASME Code repair/replacement activities shall be performed no later than when the predicted flaw size from either periodic inspection or by flaw growth analysis exceeds the acceptance criteria (i.e., 6.2 inches axially or 5 inches circumferentially), or during the spring 2028 scheduled refueling outage, whichever occurs first.
The NRC staff finds the licensees compensatory actions are acceptable, and they provide reasonable assurance of structural integrity of degraded valve and flooding concerns until the spring 2028 refueling outage, provided that the flaw size does not exceed 6.2 inches in the axial direction or 5 inches in the circumferential direction, or the leakage from the flaw does not exceed 20 gpm, whichever occurs first.
In summary, the NRC staff determines that: (a) the licensee has demonstrated that the structural integrity of the degraded SW system control valve can be maintained with allowable hole size not exceeding 6.2 inches axially or 5 inches circumferentially, (b) the potential leakage from the through-wall flaw will not affect the safety related structures, systems and components in the vicinity of the degraded valve, and (c) the licensees compensatory measures monitor leakage and flaw growth by periodic inspections and walkdowns. Therefore, the NRC staff finds that the proposed alternative is acceptable.
CONCLUSION As set forth above, the NRC staff has determined that complying with the specified requirements described in the licensees request would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. The proposed alternative provides reasonable assurance of the structural integrity of the degraded SW system control valve. Accordingly, the NRC staff concludes that the licensee has adequately addressed the regulatory requirements set forth in 10 CFR 50.55a(z)(2). Therefore, the NRC staff authorizes the use of the alternative request at Brunswick, Unit 1, up to and for the duration of the spring 2028 refueling outage, which is currently planned to start on March 4, 2028.
All other ASME Code,Section XI requirements for which an alternative was not specifically requested and authorized remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
Principal Contributors: A. Rezai and J. Poehler, NRR Date: January 26, 2026 David Wrona, Chief Plant Licensing Branch LPL II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation cc: Listserv DAVID WRONA Digitally signed by DAVID WRONA Date: 2026.01.26 11:13:17 -05'00'
ML26020A168 NRR-028 OFFICE NRR/DORL/LPL 2-2/PM NRR/DORL/LPL2-2/LA NRR/DNRL/NPHP/BC NAME TSierra ABaxter MMitchell DATE 1/20/2026 01/22/2026 1/20/2026 OFFICE NRR/DORL/LPL2-2/BC NAME DWrona DATE 1/26/2026