ML25329A094
| ML25329A094 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 12/17/2025 |
| From: | David Wrona NRC/NRR/DORL/LPL2-2 |
| To: | Coffey R Florida Power & Light Co |
| Sierra T, NRR/DORL/LPL2-2 | |
| Shared Package | |
| ML25233A221 | List: |
| References | |
| EPID L-2025-LLR-0078 | |
| Download: ML25329A094 (0) | |
Text
December 17, 2025 Mr. Robert Coffey Executive Vice President, Nuclear and Chief Nuclear Officer Florida Power & Light Company 700 Universe Blvd.
Mail Stop: EX/JB Juno Beach, FL 33408
SUBJECT:
ST. LUCIE PLANT, UNIT NO. 2 - RELIEF REQUEST NO. 3 - ALTERNATE EVALUATION OF INTAKE COOLING WATER PIPING (EPID L-2025-LLR-0078)
Dear Mr. Coffey:
By letter dated August 14, 2025 (Agencywide Documents Access and Management System Accession No. ML25226A132), Florida Power & Light (FPL, the licensee) submitted Relief Request (RR) No. 3 to the U.S. Nuclear Regulatory Commission (NRC) for the St. Lucie Plant (St. Lucie), Unit 2 facility. The licensee requested relief from the requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, Article IWA-4000, Repair/Replacement Activities. Specifically, the licensee requested approval to use an alternative evaluation based on ASME Code Case N-513-5 to demonstrate that a degraded weld-neck flange on the intake cooling water pump discharge piping can temporarily remain in service without repair or replacement activities in accordance with ASME Code,Section XI.
The licensee submitted the proposed alternative evaluation pursuant to Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Section 50.55(a), Codes and standards, paragraph (z)(2), on the basis that complying with the specified ASME Code requirement would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
On August 19, 2025, the NRC verbally authorized the use of RR No. 3 for St. Lucie, Unit 2, until completion of the next refueling outage, which is scheduled for spring 2026. This letter provides the NRCs written safety evaluation for the proposed alternative.
All other ASME Code requirements, as incorporated by reference in 10 CFR 50.55a for which relief or an alternative was not specifically requested, and granted or authorized (as appropriate), in the subject request remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
R. Coffey If you have any questions, please contact the Project Manager, Natreon Jordan, at 301-415-7410 or Natreon.Jordan@nrc.gov.
Sincerely, David Wrona, Chief Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-389
Enclosure:
Safety Evaluation cc: Listserv DAVID WRONA Digitally signed by DAVID WRONA Date: 2025.12.17 14:07:30 -05'00'
Enclosure SAFETY EVALUATION BY THE OFFICE NUCLEAR REACTOR REGULATION RELIEF REQUEST NO. 3 ALTERNATE EVALUATION OF INTAKE COOLING WATER PIPING FLORIDA POWER & LIGHT COMPANY ST. LUCIE PLANT, UNIT NO. 2 DOCKET NO. 50-389
1.0 INTRODUCTION
By letter dated August 14, 2025 (Agencywide Documents Access and Management System Accession No. ML25226A132), Florida Power & Light (FPL, the licensee) submitted Relief Request (RR) No. 3 to request relief from the requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, Article IWA-4000, Repair/Replacement Activities, for St. Lucie Plant, Unit No. 2 (STL2). Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(2), the licensee requested approval to use an alternative evaluation based on ASME Code Case N-513-5 to demonstrate that a degraded weld-neck flange on the intake cooling water (ICW) pump discharge piping can temporarily remain in service without repair or replacement activities, in accordance with the ASME Code,Section XI, on the basis that complying with the specified ASME Code requirement would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
On August 19, 2025 (Package ML25233A221), the U.S. Nuclear Regulatory Commission (NRC) verbally authorized the use of RR No. 3 for STL2 until the completion of the next refueling outage, which is scheduled for spring 2026. The NRC staff determined that the proposed alternative is technically justified and provides reasonable assurance of structural integrity of the subject piping. This safety evaluation documents the technical basis for the NRCs verbal authorization.
2.0 REGULATORY EVALUATION
Adherence to Section XI of the ASME Code is mandated by 10 CFR 50.55a(g)(4), which states, in part, that ASME Code Class 1, 2, and 3 components will meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in the ASME Code,Section XI.
The regulation in 10 CFR 50.55a(z), Alternatives to codes and standards requirements, states, in part, 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 Regulation. A proposed alternative must be submitted and authorized prior to implementation. The applicant or licensee must demonstrate that: (1) the proposed alternative would provide an acceptable level of quality and safety; or (2) 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.
Based on the above, and subject to the following technical evaluation, the NRC staff finds that regulatory authority exists for the licensee to request the use of an alternative and for the NRC to authorize the use of the proposed alternative.
3.0 TECHNICAL EVALUATION
3.1 ASME Code Component Affected The affected component is an ASME Code Class 3 weld-neck flange on the ICW pump discharge piping, located in line I-36-CW-16. The nominal pipe wall thickness is 0.375 inches, and the nominal pipe size is 36 inches. The operating temperature and pressure are 95 degrees Fahrenheit (°F) and 90 pounds per square inch gauge (psig), respectively. The design temperature and pressure are 125 °F and 90 psig, respectively. The pipe is cement lined and fabricated from SA-106, Grade B, and the weld-neck flange is fabricated from SA-105.
3.2
Applicable Code Edition and Addenda
The ASME Code,Section XI, 2019 Edition with no Addenda, is the current code of record for the fifth 10-Year Inservice Inspection interval at STL2. The construction code of record for the ICW piping system at STL2 is the ASME Code,Section III, 1971 Edition with Addenda through Summer 1973.
3.3
Applicable Code Requirement
ASME Code,Section XI, Article IWA-4000, Repair/Replacement Activities.
3.4
Reason for Request
On August 6, 2025, a through-wall flaw was discovered in the ICW piping system for STL2. The flaw is located on the 36 inch weld neck flange line identified as I-36-CW-16 (Figure 1 of FPLs submittal). The flaw was measured 1 inch axially and 1.5-inch circumferentially on the neck region of the weld-neck flange, bordering the flange plate, as shown in Figure 2 of the submittal.
The licensee determined that the existing flaw, and any subsequent growth will be outside 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, due to the location of the flaw. For reference purposes, ASME Code Case N-513-5 is conditionally approved by the NRC and allows for the temporary acceptance of flaws (including through-wall 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.
The licensee stated that it is not possible to determine the cause of the through-wall leak without removing the piping section from service and gaining access to the inside surfaces for examination. However, based on the location of the flaw and the specific system, the licensee indicated that the likely cause of the degradation is general corrosion from localized failure of the cement lining. The licensee reported that the leakage has been mitigated by the application of a temporary plug (Figure 3 of FPLs submittal), which has reduced the leak rate to between 0 and 10 gallons per minute (gpm). FPL stated that this level of leakage has no risk of challenging the system margin of 1,580 gpm allowed to maintain safe operation. Additionally, any leakage will drain into the intake well; therefore, there is no risk for spray or flooding. FPL further stated that even without the installed plug, the system would experience a conservatively calculated leakage rate of 796.5 gpm based on a 2-inch diameter hole.
The licensee proposed to use the methodology of ASME Code Case N-513-5 with the addition of ASME Code,Section III, NB-3200, to validate the structural integrity of the weld-neck flange to allow temporary acceptance of the flaw without repair or replacement, to avoid a forced plant shutdown. The licensee explained that the use of the proposed alternative in lieu of immediate repair or replacement would allow time for safe and orderly long-term repair or replacement actions. FPL also stated that plant shutdown activities result in additional dose, transients, and plant risk, which is not warranted given the evaluations demonstrate that the degraded ASME Code component is shown to retain structural integrity and adequate margin to fulfill its intended safety function. The licensee stated that it will repair or replace the subject pipe in accordance with the ASME Code,Section XI at the next scheduled refueling outage, which is scheduled to start in April of 2026, or prior to exceeding the allowable flaw size, whichever occurs first.
3.5 Proposed Alternative and Basis for Use FPL measured the flaw to be 1 inch axially by 1.5 inch circumferentially. Attachment 1 of the submittal provided an ultrasonic wall-thickness survey taken around the full circumference of the neck region of the flange; these thickness measurements ranged from 0.575 inch to 0.781 inch, with an average of 0.666 inch. 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, Design by Analysis, to evaluate the non-uniform wall thickness and local thinning of the flange and to create a detailed three-dimensional finite element model to establish an allowable flaw size (Attachment 2 of the submittal) for normal, upset, and faulted conditions.
3.6 Structural Integrity The licensee performed a flaw evaluation to demonstrate that the degraded pipe meets the structural integrity requirements of the ASME Code,Section III design by analysis criteria. The licensee evaluated the flaw in the axial and circumferential directions. The licensee enveloped all the ultrasonic thickness (UT) measured weld-neck flange wall thickness values and conservatively bounded the effects of any other areas of erosion/corrosion within the degraded piping section 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, with an additional reduction of 0.5 inch into and vertically on the flange plate. The flaw evaluation also used a conservative application of the primary stress design criteria, upset conditions, and faulted conditions on the piping. Specifically, the criteria for acceptability of normal and upset conditions were determined to be 150 percent of the applied load, and for faulted conditions the acceptability was determined to be 111.1 percent of the applied load.
However, 200 percent was used for both cases to demonstrate further conservatism. The licensee stated that based on the detailed evaluation, the structural integrity and functional requirements of the subject piping will be maintained.
3.7 Monitoring The licensee stated that, consistent with the requirements of ASME Code Case N-513-5, Section 2, it will perform compensatory actions until such time as the flaw is repaired, or the piping section is replaced. Specifically, leakage will be monitored daily, and periodic examinations shall be used to determine if the flaw is growing. If examinations and re-analysis of the Finite Element Analysis reveal that the flaw growth rate to be unacceptable, repair or replace activities shall be performed in accordance with IWA-4000.
The licensee stated that ASME Code Case N-513-5 includes provisions for periodic UT inspection of the flaw not to exceed 30 days if a flaw growth evaluation is not performed. ASME Code Case N-513-5 also requires augmented inspections of at least five similar susceptible locations to that of the flaw.
3.8 Hardship The licensee stated that in order to perform a code repair, it would need to secure the one ICW train for a minimum of 4 consecutive days. While the 2A ICW pump was secured briefly on August 8, 2025, during the initial identification of the flaw and again on August 9, 2025, for the ultrasonic characterization of the flaw, the average containment temperature during each of those isolation periods increased by approximately 3°F, within a 60-to-90-minute period.
Specifically, the peak containment temperature increased from 112°F to 115°F. FPL stated that prolonged operation with a single ICW train could result in challenging the limiting condition for operation 3.6.5 for containment average air temperature of 120°F. Additionally, FPL stated that the current time frame represents the highest-risk period for fibrous algae intrusion in south Florida waters, which would require backwashing the turbine cooling water strainers. The backwash process requires both trains of ICW to be operational. The current ocean temperatures were also at elevated seasonal high levels, placing maximum thermal stress on the ICW system, which serves as the ultimate heat sink for critical plant components. FPL also indicated that regional electricity demand was also currently at a higher-than-normal levels due to extreme summer conditions throughout Florida.
3.9 Duration of Proposed Alternate The proposed alternative is requested until the completion of the next refueling outage, currently scheduled to begin in April 2026. The licensee intends to repair or replace the weld-neck flange during the next refueling outage scheduled to begin in April 2026, using an ASME Code-approved method.
4.0 NRC STAFF EVALUATION The NRC staff has evaluated RR No. 3 pursuant to 10 CFR 50.55a(z)(2). Specifically, the NRC has reviewed flaw characterization, system operability, structural integrity, flooding, and hardship justification for the proposed alternative as follows.
4.1 Flaw Characterization The NRC noted that the actual flaw, which is 1 inch axially by 1.5 inches circumferentially, on the weld-neck flange was conservatively bounded by the 5 inches by 14 inches rectangular flaw assumed for the allowable flaw evaluation. The NRC staff finds FPLs flaw characterization acceptable because the licensee ultrasonically surveyed the full circumference of the weld-neck flange as well as adjacent to the flaw and used a conservative reduction of 0.150 inch from the actual current wall thickness values of the subject pipe segment for the analysis. The NRC staff finds that the licensee appropriately characterized the flaw based on actual measured values and used conservative assumptions in characterizing the flaw.
4.2 System Operability The NRC staff finds that the operability of the 2A ICW system will be maintained as long as the leakage does not exceed 1,580 gpm. Based on the current leak rate of 0 to 10 gpm (with the temporary plug installed), it would be reasonable to assume that the operability of the ICW system would not be challenged for the duration of this relief request. Even in the event of the total failure of the plug, and assuming a 2-inch diameter hole, the licensee calculated that the leakage would be approximately 790 gpm. The NRC staff finds that the operability and functionality of the degraded ICW piping will not be significantly affected because there is sufficient margin in the mass flow rate in the ICW piping to provide cooling to the safety-related equipment. Additionally, the licensees daily monitoring will further ensure that the system leakage will not challenge the ability of the ICW system to fulfill its intended safety function.
4.3 Structural Integrity The licensee evaluated the degraded piping section in accordance with ASME Code Section III, paragraph 3200, Design by Analysis, to assess the effects of the localized wall thickness reduction of the flange on the structural integrity of the piping section. The evaluation derived an allowable rectangular flaw size of 5 inches in the axial direction and 14 inches in the circumferential direction. Additionally, the flaw was extended axially and vertically into the flange plate by 0.5 inch. The wall thickness values used in the evaluation were reduced by 0.150 inch from the actual measured values for the weld-neck flange and the specified wall thickness of the adjoining piping. These assumptions for flaw size and wall thickness conservatively bound the condition of the piping segment with the actual flaw. Additionally, while the licensees evaluation for the criteria for acceptability of normal and upset conditions was determined to be 150 percent of the applied load, and for faulted conditions the acceptability was determined to be 111.1 percent of the applied load, to demonstrate further conservatism, 200 percent of the applied loads was used for normal, upset, and faulted conditions.
As such, the NRC staff finds that the piping segment will remain stable under all design-basis loading-conditions. The NRC staff does not expect the flaw to grow aggressively during the period of time RR No.3 would be in use. Additionally, if the flaw does grow unexpectedly and aggressively, the licensees periodic monitoring and examinations will detect the growth prior to the flaw challenging the structural integrity of the ICW piping. The NRC staff finds that the licensees flaw evaluation has adequately demonstrated the structural integrity of the ICW piping segment.
4.4 Flooding Evaluation The licensee stated that any leakage will drain back into the intake bay. Therefore, the NRC staff finds that flooding in the area where the degraded weld-neck flange is located is not a concern.
4.5 Hardship Justification The NRC staff finds that without the proposed alternative, the licensee would have to shut down the plant to perform the repair or replacement in accordance with the ASME Code,Section XI.
The NRC staff recognizes that a plant shutdown would result in undue risk and add additional doses. An unscheduled mid-cycle plant shutdown and subsequent restart would also add additional loads on various safety-related piping and components. The NRC staff notes that the licensee has demonstrated that the weld-neck flange will maintain structural integrity, that the leakage is being mitigated and that it will be monitored daily for the duration of the relief.
Therefore, the NRC staff finds that complying with the specified ASME Code requirement to repair or replace the degraded piping would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
Based on its review, the NRC staff finds that: (1) there is an adequate margin between the size of the existing flaw and the allowable flaw size for the ICW piping, (2) the existing flaw is expected to be stable and will not challenge the structural integrity of the ICW piping for the period of the requested alternative, (3) the leak rate from the existing flaw is mitigated and the ICW system is capable of performing its intended function, (4) the daily monitoring can adequately detect for any potential unexpected changes in leakage and flaw growth, and (5) the licensees hardship justification is acceptable. Therefore, the NRC staff finds that the proposed alternative in RR No. 3 will provide reasonable assurance of structural integrity for the subject ICW piping until its planned repair or replacement during the spring 2026 refueling outage.
5.0 CONCLUSION
The NRC staff concludes that the proposed alternative provides reasonable assurance of the structural integrity of the subject ICW system piping. The NRC staff finds that complying with the requirements of the ASME Code,Section XI, would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. Accordingly, the NRC staff concludes that the licensee has adequately addressed all the regulatory requirements set forth in 10 CFR 50.55a(z)(2). Therefore, the NRC authorizes the use of RR No. 3 at STL2 until the completion of the spring 2026 refueling outage, or until 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 the proposed alternative remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
Principle Contributor: V. Kalikian, NRR Date: December 17, 2025
ML25329A094 NRR-028 OFFICE NRR/DORL/LPL2-2/PM NRR/DORL/LPL2-2/LA NRR/DNRL/NPHP/BC NRR/DORL/LPL2-2/PM NAME TSierra ABaxter MMitchell NJordan DATE 11/24/2025 12/16/2025 11/14/2025 12/17/2025 OFFICE NRR/DORL/LPL2-2/BC NAME DWrona DATE 12/17/2025