ML25241A332
| ML25241A332 | |
| Person / Time | |
|---|---|
| Site: | Byron  (NPF-037, NPF-066) |
| Issue date: | 09/04/2025 |
| From: | Ilka Berrios Plant Licensing Branch III |
| To: | Rhoades D Constellation Energy Generation, Constellation Nuclear |
| Wall, S | |
| References | |
| EPID L-2025-LLR-0065 | |
| Download: ML25241A332 (10) | |
Text
September 4, 2025 Mr. David P. Rhoades Senior Vice President Constellation Energy Generation, LLC President and Chief Nuclear Officer Constellation Nuclear 4300 Winfield Road Warrenville, IL 60555
SUBJECT:
BYRON STATION, UNIT NOS. 1 AND 2 - ISSUANCE OF RELIEF REQUEST RP-1 REGARDING ESSENTIAL SERVICE WATER MAKEUP PUMPS VIBRATION LIMITS (EPID L-2025-LLR-0065)
Dear Mr. Rhoades:
By letter dated June 27, 2025 (Agencywide Documents Access and Management System Accession No. ML25178C670), Constellation Energy Generation, LLC (CEG, the licensee) submitted alternative request RP-1 to the U.S. Nuclear Regulatory Commission (NRC). The licensee proposed an alternative to certain inservice testing (IST) requirements of the American Society of Mechanical Engineers (ASME) Code for Operation and Maintenance of Nuclear Power Plants (OM Code), for the fifth IST program at Byron Station, Unit Nos. 1 and 2 (Byron).
The licensee also proposed alternative requests RP-2 and RP-3, which will be addressed by separate NRC staff correspondence.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(2), the licensee requested to use the proposed alternative in request RP-1 on the basis that complying with the requirements of the ASME OM Code would result in hardship without a compensating increase in the 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 alternative RP-1 provides reasonable assurance that the affected components, pumps 0SX02PA and 0SX02PB, are operationally ready, and that CEG has adequately addressed the requirements in 10 CFR 50.55a(z)(2). Therefore, the NRC staff authorizes the use of alternative request RP-1 for the ASME OM 2022 Edition Code of Record Interval at Byron. This alternative applies to the code of record interval, as defined in 10 CFR 50.55a(y), Definitions, that implements the 2022 Edition of the ASME OM Code, as incorporated by reference in 10 CFR 50.55a. Use of this alternative with other codes of record is not authorized.
All other ASME OM Code requirements for which relief has not been specifically requested remain applicable.
If you have any questions, please contact the Senior Project Manager, Scott Wall, at 301-415-2855 or e-mail at Scott.Wall@nrc.gov.
Sincerely, Ilka Berrios, Acting Chief Plant Licensing Branch III Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. STN 50-454, and STN 50-455
Enclosure:
Safety Evaluation cc: Listserv ILKA BERRIOS Digitally signed by ILKA BERRIOS Date: 2025.09.04 15:19:51 -04'00'
Enclosure SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST RP-1 REGARDING ESSENTIAL SERVICE WATER MAKEUP PUMPS VIBRATION LIMITS CONSTELLATION ENERGY GENERATION, LLC BYRON STATION, UNIT NOS. 1 AND 2 DOCKET NOS. STN 50-454 AND STN 50-455
1.0 INTRODUCTION
By letter dated June 27, 2025 (Agencywide Documents Access and Management System Accession No. ML25178C670), Constellation Energy Generation, LLC (CEG, the licensee) submitted alternative request RP-1 to the U.S. Nuclear Regulatory Commission (NRC). The licensee proposed an alternative to certain inservice testing (IST) requirements of the American Society of Mechanical Engineers (ASME) Code for Operation and Maintenance of Nuclear Power Plants, Division 1, OM Code: Section IST (OM Code), for the fifth IST program at Byron Station, Unit Nos. 1 and 2 (Byron). The licensee also proposed alternative requests RP-2 and RP-3, which will be addressed by separate NRC staff correspondence.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) section 50.55a(z)(2), the licensee requested to implement proposed alternative request RP-1 for the essential service water (SX) makeup pumps at Byron on the basis that complying with the ASME OM Code requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
2.0 REGULATORY EVALUATION
The NRC regulations in 10 CFR 50.55a(f)(4), Inservice testing standards requirement for operating units, require, in part, that throughout the service life of a boiling or pressurized water-cooled nuclear power facility, pumps and valves that are within the scope of the ASME OM Code must meet the IST requirements (except design and access provisions) set forth in the ASME OM Code and addenda that become effective subsequent to editions and addenda specified in 10 CFR 50.55a(f)(2) and (3) and that are incorporated by reference in 10 CFR 50.55a(a)(1)(iv), to the extent practical within the limitations of design, geometry, and materials of construction of the components.
The regulations in 10 CFR 50.55a(z) state, in part, that alternatives to the requirements in paragraphs (b) through (h) of 10 CFR 50.55a may be authorized by the NRC if the licensee demonstrates that: (1) the proposed alternative provides an acceptable level of quality and safety, or (2) compliance with the specified requirements 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 and the NRC to authorize the alternative requested by the licensee.
3.0 TECHNICAL EVALUATION
3.1 Licensees Alternative Request RP-1 3.1.1 ASME Code Components Affected 0SX02PA SX Makeup Pump A 0SX02PB SX Makeup Pump B 3.1.2 Applicable Code Editions and Addenda The applicable code of record for the Fifth IST Interval at Byron, is the 2022 Edition of ASME OM Code as incorporated by reference in 10 CFR 50.55a. The Byron Fifth IST interval is scheduled to begin on July 1, 2026.
3.1.3 Applicable Code Requirements ASME OM Code, Subsection ISTB, Inservice Testing of Pumps in Water-Cooled Reactor Nuclear Power Plants - Pre-2000 Plants, Table ISTB-5221-1, Vertical Line Shaft Centrifugal Pump Test Acceptance Criteria specifies the vibration alert range from > 0.325 inch per second (in/sec) to 0.700 in/sec and required action limit of > 0.700 in/sec for vertical line shaft pumps operating at or above 600 revolutions per minute (rpm) for both the Group A and the comprehensive pump tests:
ASME OM Code, paragraph ISTB-6200, Corrective Action, subparagraph (a), Alert Range states:
If the measured test parameter values fall within the alert range of Table ISTB-5121-1, Table ISTB-5221-1, Table ISTB-5321-1, or Table ISTB-5321-2, as applicable, the frequency of testing specified in ISTB-3400 shall be doubled until the cause of the deviation is determined and the condition is corrected, or an analysis of the pump is performed in accordance with (c).
3.1.4 Reason for Request The licensee submitted alternative request RP-1 under 10 CFR 50.55a(z)(2) because the SX makeup pump normal vibration levels have been as high as approximately 0.5 in/sec at the gearbox locations and have exceeded the lower alert range limit of 0.325 in/sec for vertical line shaft pumps operating at or above 600 rpm for both the Group A and the comprehensive test specified in the ASME OM Code, Table ISTB-5221-1. ASME OM Code, subparagraph ISTB-6200(a) requires the frequency of testing to be doubled if the measured test parameter values fall within the alert range. Placing the SX makeup pumps in double test frequency is a hardship because it results in additional man hours, increased pump run time/pump component degradation, confined space entry hazards, and work during inclement weather. The licensee indicates the normal vibration levels of these pumps would place them in double test frequency.
3.1.5 Proposed Alternative and Basis for Use The licensee proposes to increase the lower limit of the alert range as specified in ASME OM Code, Table ISTB-5221-1 from > 0.325 in/sec to > 0.550 in/sec. The licensee does not propose any change to the required action limit (> 0.700 in/sec).
In support of its proposed alternative, the licensee has submitted information about the pump vibrations and the licensees actions to understand and reduce those vibrations. A paper Nuclear Power Plant Safety-Related Pump Issues, in NUREG/CP-0152, Procedures of the Fourth NRC/ASME Symposium on Valve and Pump Testing (ML18057B547) provides guidance on submitting alternative requests to propose alternatives to the ASME OM Code acceptance criteria on pump vibration. The NRC staff summarized the key guidance of the NUREG/CP and the licensees assessment of the SX makeup pumps below.
Vibration History NUREG/CP-0152: The licensee should have sufficient vibration history from IST which verifies that the pump has operated at this vibration level for a significant amount of time, with any spikes in data justified.
The licensee states that the SX makeup pumps are a unique design. A horizontal diesel drives a right-angle gearbox located approximately 39 feet above the pump. The driveshaft from the gearbox to the pump consists of five coupled sections and is located in the pump discharge piping column. Pump thrust is carried by bearings physically located within the gearbox. The pump is submerged in river water. Although these pumps are considered vertical line shaft pumps, their unique design configuration is not addressed by the ASME OM Code. Due to monitoring limitations of this design, and because of the similarity to the requirements for vertical line shaft pumps, vibration is monitored on the gearbox. The limitation of taking the vibration readings at this location is that the resultant vibration readings are not attributable to the pump. Vibration analysis has indicated that the readings obtained are the result of vibrations induced by the diesel engine and gearbox, along with a resonant condition of the gearbox and its foundation. Additionally, the overall vibration levels have remained steady over the past 20 years.
Maintenance and inspection activities have indicated that the angle gearboxes have been operating properly and have not degraded due to vibration. Maintenance and inspection activities on the pumps have indicated that there has not been any pump degradation due to the vibration observed on the gearboxes. Likewise, the pump units have not caused vibration degradation of the gearboxes.
Consultation with Pump Manufacturer/Vibration Expert NUREG/CP-0152: The licensee should have consulted with the pump manufacturer or vibration expert about the level of vibration the pump is experiencing to determine if pump operation is acceptable.
The licensee identified that in 2001, Byron Jackson, the pump manufacturer, had consulted an industry vibration expert and the vendor representative from the gearbox company, in an effort to ensure vibration levels are as low as achievable with this particular design, and to ensure the existing vibration levels are not indicative of pump degradation. These efforts included the following activities:
Field service representatives from the gearbox company supervised the refurbishment of the two gearboxes. Both refurbished units were then installed on the pumps. The units that were refurbished had seen a significant amount of service at vibration levels in excess of the lower alert limit. When inspected, the gearboxes did not show any vibration-related degradation.
Bi-directional support braces were installed on the gearboxes to address the vibration resonance problem.
The gearboxes were precision aligned and the couplings were balance checked upon installation.
Attempts to Lower Vibration NUREG/CP-0152: The licensee should describe attempts to lower the vibration below the defined code absolute levels through modifications to the pump.
The licensee states that due to the adverse quality of the river water in which the pumps operate, the pump impellers have been replaced with stainless steel units and the wear rings replaced with a wear resistant alloy. The licensee reports no documented issues with these new impellers and wear rings since original installation. The new pump assemblies were tested at the vendor's facility and exhibited very low vibration levels.
These collective efforts resulted in some reduction in the vibration levels, however, not enough to remove the pumps from the ASME OM Code alert range. Both pumps have experienced vibration levels at the gearbox locations up to 0.5 in/sec during the Fourth IST Interval. The licensee concluded that those vibration levels recorded at the gearbox locations are normal for the configuration of the subject pumps and do not indicate an unusual condition of the gearbox or the pump. The proposed alternative limit will ensure that required action is taken if vibration levels increase while ensuring the pump is not prematurely declared inoperable.
Spectral Analysis identify all contributors to the vibration levels.
The licensee discussed the performance of spectral analyses in response to a request for additional information issued as part of the review of alternative request RP-1 during the Fourth IST Interval (ML15335A387). In this response, the licensee also stated that spectral analysis will be performed throughout the Fourth IST Interval. Vibration analysis has indicated that the vibration readings obtained are the result of vibration induced by the diesel engine and the gearbox itself, along with a resonant condition of the gearbox and its foundation. The licensee states that during the Fifth IST Interval, advanced analysis techniques, equivalent to spectral analysis, may be performed in lieu of the spectral analysis.
Since the gearbox normally exhibits relatively high vibration levels which are not indicative of degradation, the use of the alert range in ASME OM Code, Table ISTB-5221-1 would result in pumps unnecessarily being placed in double test frequency. Increasing the lower alert range limit for these pumps would ensure the pumps are placed in double test frequency at a vibration level that would be abnormal for the SX makeup pumps' design configuration.
The licensee requests the implementation of alternative request RP-1 during the ASME OM 2022 Edition Code of Record Interval, scheduled to begin on July 1, 2026, at Byron.
Hardship The licensee states that placing the SX makeup pumps in double test frequency is a hardship because it results in additional man hours, increased pump run time/pump component degradation, confined space entry hazards and work during inclement weather. There is not a compensating increase in quality and safety because the pumps have run with this vibration level for the past 20 years.
The licensee stated that the proposed alternative has been authorized for the Byron Fourth IST program interval by an NRC letter dated February 22, 2016 (ML16043A151).
3.2 Staff Evaluation of RP-1 In alternative request RP-1, the licensee proposed an alternative to the requirements in the ASME OM Code, Subsection ISTB, Table ISTB-5221-1, which specifies the vibration alert range from > 0.325 in/sec to 0.700 in/sec and required action limit of > 0.700 in/sec for vertical line shaft pumps operating at or above 600 rpm for both the Group A and the comprehensive pump tests. The licensee proposes to raise the lower vibration alert range limit from > 0.325 in/sec to
> 0.55 in/sec for the SX makeup pumps within the scope of this request, as vibration measurements are frequently about 0.5 in/sec. The licensee proposes no change to the required action limit. ISTB-6200, Corrective Action, requires that if the measured test parameter values fall within the alert range of Table ISTB-5211-1, the frequency of testing shall be doubled until the cause of the deviation is determined and the condition is corrected, or an analysis of the pump is performed.
The proposed alternative is a resubmittal of NRC-authorized alternative request RP-1 for the Byron Fourth IST Interval. The proposed alternative was authorized by NRC staff in a letter dated February 22, 2016 (ML16043A151), on the basis that:
- 1. Vibration History: Documentation of vibration history verifies that the pumps have operated satisfactorily at this vibration level measured at the pump gearbox for a significant period of time without degradation.
- 2. Consultation with Pump Manufacturer/Vibration Expert: The licensee has consulted with the pump vendor and vibration experts. The pumps gearbox vendor provided documentation states that 0.55 in/sec is an acceptable vibration alert range limit. The pump vendor has verified that, when tested at the vendors facility, the replacement stainless steel impellers had very low vibration levels. The material condition of the gearbox was examined and no degradation due to vibration was noted.
- 3. Attempt to Lower Vibration: The licensee has attempted to reduce the vibration level by adding restraints to stiffen the right-angle gearbox and by improving alignment of the gearboxes and couplings.
- 4. Spectral Analysis: The licensee stated that spectral analysis is performed as part of the IST vibration data collection. Any pump vibration concerns are going to be met with more comprehensive special testing and appropriate corrective maintenance will be performed.
In the current alternative request, the licensee has readdressed all four issues and states that the overall vibration levels have remained steady at approximately 0.5 in/sec over the past 20 years and that doubling the test frequency under current conditions does not provide additional assurance as to the condition of the pumps and their ability to perform their safety function.
The NRC staff reviewed this information and agrees with the licensees statement that using the provisions of this request as an alternative to the specific limits of Table ISTB-5221-1 will provide adequate indication of pump performance. In consultation with both the vendor and a vibration expert, the licensee concluded that the normal levels of vibration for these pumps exceed the OM Code limits, but are not an indication of degradation. The NRC staff finds that this additional data and information continue to demonstrate that vibrations in excess of the Code-required lower end of the alert range but lower than the proposed lower end of the alert range have not adversely affected the pump performance. Therefore, increasing the lower end of the alert range from > 0.325 in/sec to > 0.55 in/sec is, in this case, justified. Additionally, NRC staff notes that the licensee proposed alert range (> 0.55 to 0.700 in/sec) remains sufficiently wide so as to be able to identify and assess pump degradation, prior to entering the required action range (> 0.700 in/sec).
Based on its evaluation, the NRC staff has determined that requiring the licensee to meet the requirements for vibration measurement alert range limits for specific pumps at Byron required by the ASME OM Code would result in a hardship without a compensating increase in the level of quality and safety. In consideration of the performance history of these pumps, the consultation of the vendor and a vibration expert, and the acceptance by the NRC staff of similar requests, given the unique design configuration, the NRC staff finds that the proposed alert range limits are acceptable and provides reasonable assurance of operational readiness of these pumps. Therefore, the NRC staff finds that alternative request RP-1 may be authorized in accordance with 10 CFR 50.55a(z)(2) for the applicable pumps at Byron.
The NRC staff notes that the applicable code of record for the Byron Fifth IST interval is the 2022 Edition of the ASME OM Code, as incorporated by reference in 10 CFR 50.55a. The Byron Fifth IST interval is scheduled to begin on July 1, 2026. The ASME OM Code (2022 Edition), Subsection ISTA, paragraph ISTA-3120, Inservice Examination and Test Interval, as incorporated by reference in 10 CFR 50.55a, requires that licensees implement 10-year intervals for their IST programs. The NRC regulations in 10 CFR 50.55a allow licensees to implement the same ASME OM Code as their code of record for two successive IST program intervals. Therefore, the licensee of Byron could implement the 2022 Edition of the ASME OM Code as incorporated by reference in 10 CFR 50.55a for both the Fifth and Sixth IST intervals required by the ASME OM Code, Subsection ISTA, paragraph ISTA-3120.
4.0 CONCLUSION
As described above, the NRC staff has determined that alternative request RP-1 for Byron, as described in the licensees submittal dated June 27, 2025, will provide reasonable assurance that the applicable pumps are operationally ready. The NRC has also determined that the licensee has justified that compliance with the specified ASME OM Code requirements 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 the regulatory requirements set forth in 10 CFR 50.55a(z)(2).
Therefore, the NRC staff authorizes the use of alternative request RP-1 for the ASME OM 2022 Edition Code of Record Interval at Byron. This alternative applies to the code of record interval, as defined in 10 CFR 50.55a(y), Definitions, that implements the 2022 Edition of the ASME OM Code, as incorporated by reference in 10 CFR 50.55a. Use of this alternative with other codes of record is not authorized.
All other ASME OM 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.
Principal Contributors: Yuken Wong, NRR Nicholas Hansing, NRR Date: September 4, 2025
SUBJECT:
BYRON STATION, UNIT NOS. 1 AND 2 - ISSUANCE OF RELIEF REQUEST RP-1 REGARDING ESSENTIAL SERVICE WATER MAKEUP PUMPS VIBRATION LIMITS (EPID L-2025-LLR-0065) DATED SEPTEMBER 4, 2025 DISTRIBUTION:
PUBLIC RidsNrrDorlLpl3 Resource RidsRgn3MailCenter Resource RidsNrrLASLent Resource RidsAcrs_MailCTR Resource RidsNrrPMByron Resource RidsNrrDexEmib Resource YWong, NRR NHansing. NRR Accession No.: ML25241A332 NRR-028 OFFICE NRR/DORL/LPL3/PM NRR/DORL/LPL3/LA NRR/DEX/EMIB/BC NAME SWall SLent SBailey DATE 08/29/2025 09/03/2025 08/28/2025 OFFICE NRR/DORL/LPL3/BC (A)
NRR/DORL/LPL3/PM NAME IBerrios SWall DATE 09/03/2025 09/04/2025 OFFICIAL RECORD COPY