ML25233A223
| ML25233A223 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 08/26/2025 |
| From: | Natreon Jordan NRC/NRR/DORL/LPL2-2 |
| To: | Florida Power & Light Co |
| Shared Package | |
| ML25233A221 | List: |
| References | |
| Download: ML25233A223 (1) | |
Text
VERBAL AUTHORIZATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION 10 CFR 50.55a REQUEST TO USE AN ALTERNATE EVALUATION OF INTAKE COOLING WATER PIPING RELIEF REQUEST 3 ST. LUCIE PLANT, UNIT NO. 2 FLORIDA POWER & LIGHT COMPANY DOCKET NO. 50-389 Technical Evaluation read by Matthew Mitchell, Chief of the Piping and Head Penetration Branch, Office of Nuclear Reactor Regulation By letter dated August 14, 2025 (Agencywide Documents Access and Management System Accession No. ML25226A132), Florida Power & Light (FPL) proposed an alternative to the requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, Subarticle IWD-3120(b); Subarticle IWD-3500; and Article IWA-4000 for St. Lucie, Unit No. 2. Pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(2), FPL submitted a proposed alternative based on ASME Code Case N-513-5 to demonstrate that a degraded piping section in the St. Lucie, Unit No. 2 intake cooling water (ICW) pump discharge piping can remain temporarily in service without performing repair or replacement in accordance with the ASME Code,Section XI. FPL has concluded that complying with the specified ASME Code requirement to repair or replace the degraded piping section at this time would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. FPL requested approval of the proposed alternative until completion of St. Lucie, Unit No. 2 spring 2026 refueling outage, currently scheduled to begin in April of 2026 when the piping will be repaired or replaced in accordance with the ASME Code.
On August 6, 2025, FPL discovered a through-wall flaw on a 36-inch weld neck flange of the ICW pump discharge piping at St. Lucie, Unit No. 2. FPL determined that the flaw, and any subsequent flaw growth, will be outside of the scope of 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. For reference purposes ASME Code Case N-513-5 is conditionally approved by the NRC and allows for temporary acceptance of flaws in moderate energy Class 2 and 3 piping without performing repair or replacement activities in accordance with the ASME Code,Section XI, Article IWA-4000.
FPL measured the flaw, located in the neck region of a 36-inch weld-neck flange, to be 1 inch axially by 1.5 inch circumferentially. On August 9, 2025, FPL ultrasonically took a total of 36 wall thickness measurements around the full circumference of the neck region of the flange; these thickness measurements ranged from 0.592 inches to 0.781 inches, with an average of 0.666 inches. A conservative finite element model was created by applying a 0.150-inch reduction to the actual thickness measurements and extending the through-wall flaw to a rectangle 5 inches axially by 14 inches circumferentially. FPL performed a structural integrity evaluation using the general methodology of ASME Code Case N-513-5 with the addition of ASME Code,Section III, NB-3200 to model the allowable flaw size. FPL stated that the leak has been mitigated by a plug and the current leak rate is between zero and 10 gallons per minute (gpm). The licensee also stated that the maximum level of leak rate poses no risk of challenging the system margin of 1580 gpm for system operability. FPL further stated that even without the plug installed the system would experience a conservatively calculated leakage rate of 796.5 gpm based on a 2-inch diameter hole. FPL stated that any leakage will drain into the intake well, so there is no flooding risk. Additionally, FPL will monitor the leaking location daily to monitor changes in leak rate of the identified flaw. FPL stated that, based on its evaluation and use of the proposed alternative as detailed in its submittal, the structural integrity and functional requirements of the pipe will be maintained.
FPLs submittal also provided a detailed justification of the hardship and unusual difficulty should it be forced to perform ASME Code required repair or replacement of the degraded piping section at this time. FPL noted that for an effective repair, one ICW train would have to be secured for 4 days and extended single train ICW operation presents significant operational hardships that could compromise plant safety margins. FPL stated that plant shutdown activities generically result in additional dose, transients, and plant risk which is not warranted given the acceptable evaluation provided.
Based the results of the FPLs evaluation, the NRC staff finds that: (1) there is adequate margin between the size of the existing flaw in the weld neck flange and the calculated allowable flaw, (2) the existing flaw is expected to be reasonably stable and not grow rapidly during the period of the requested alternative, (3) the leak rate provides a safety margin for the ICW system to perform its intended function, (4) the daily monitoring is acceptable to identify changes in leak rate and/or potential flaw growth, and (5) the hardship justification is acceptable.
The NRC staff finds that the proposed alternative will provide reasonable assurance that the structural integrity of the weld neck flange is maintained until the flaw is repaired during the next refueling outage, which is scheduled to begin April of 2026, or the existing flaw grows to exceed the allowable flaw size, whichever occurs first. FPL will also monitor leakage and flaw growth to ensure that ICW system can perform its intended function.
Authorization read by Kimberly Green (Acting for David Wrona, Chief of the Plant Licensing Branch II-2, Office of Nuclear Reactor Regulation)
As Chief of the Plant Licensing Branch II-2, Office of Nuclear Reactor Regulation, I agree with the conclusions of the Piping and Head Penetration Branch.
The NRC staff finds that the proposed alternative provides reasonable assurance of structural integrity of the subject ICW system piping. The NRC staff finds that complying with the requirements of the ASME Code,Section XI at this time would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. Accordingly, the NRC staff concludes that FPL has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(z)(2). Therefore, as of August 19, 2025, the NRC authorizes the use of the proposed alternative at St. Lucie, Unit No. 2 until the next refueling outage, which is scheduled to begin April 2026, or the existing flaw grows to exceed the allowable flaw size, whichever occurs first.
All other requirements in ASME Code,Section XI, for which relief was not specifically requested and approved in this alternative request remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.