CNL-25-108, American Society of Mechanical Engineers Operation and Maintenance Code Request for Alternative BFN-IST-06

American Society of Mechanical Engineers Operation and Maintenance Code Request for Alternative BFN-IST-06

ML25261A131
Person / Time
Site:	Browns Ferry  (DPR-068)
Issue date:	09/18/2025
From:	Hulvey K Tennessee Valley Authority
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
CNL-25-108
Download: ML25261A131 (1)

Text

10 CFR 50.55a 1101 Market Street, Chattanooga, Tennessee 37402 CNL-25-108 September 18, 2025 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Browns Ferry Nuclear Plant, Unit 3 Renewed Facility Operating License No. DPR-68 NRC Docket No. 50-296

Subject:

Browns Ferry Nuclear Plant, Unit 3 - American Society of Mechanical Engineers Operation and Maintenance Code Request for Alternative BFN-IST-06 In accordance with Title 10 of the Code of Federal Regulations (10 CFR) 50.55a, Codes and Standards, paragraph (z)(2), Tennessee Valley Authority (TVA) requests an alternative to the inservice testing (IST) requirements of the American Society of Mechanical Engineers (ASME)

Operation and Maintenance (OM) Code, Section ISTB-3400, Frequency of Inservice Tests.

This alternative request (BFN-IST-06) applies to testing of the standby liquid control (SLC) pumps 3A and 3B for the Browns Ferry Nuclear Plant (BFN), Unit 3.

Due to apparent stem/disc separation of the SLC test line throttle valve (3-THV-63-518) during normal operation of BFN Unit 3 Cycle 22, normal quarterly testing cannot be completed per IST Group B test procedure, and valve repair is necessary to restore normal quarterly pump testing conditions. ASME OM Code ISTB-3400 requires quarterly functional testing of SLC pumps to ensure they are operationally ready. As discussed in the enclosure to this letter, the basis of the request is that compliance with the specified requirements would result in a hardship or unusual difficulty without a compensating increase in the level of quality and safety. Therefore, TVA is submitting this alternative request from ISTB-3400 in accordance with 10 CFR 50.55a(z)(2).

The enclosure to this letter describes the proposed alternative and the basis for use.

TVA requests NRC approval of this alternative request by October 17, 2025, prior to the next scheduled quarterly pump test on October 21, 2025. This request is an alternative from the quarterly IST requirements for Group B pumps until reactor startup for BFN Unit 3 Cycle 23 in spring 2026, during which TVA plans to repair the affected valve and perform the required OM Code testing. If BFN Unit 3 experiences a forced outage prior to the spring outage, TVA will assess whether 3-THV-63-518 can be successfully repaired, depending on the plant conditions and without jeopardizing the health and safety of plant personnel.

U.S. Nuclear Regulatory Commission CNL-25-108 Page 2 September 18, 2025 There are no new regulatory commitments associated with this submittal. Please address any questions regarding this request to Amber V. Aboulfaida, Senior Manager, Fleet Licensing, at avaboulfaida@tva.gov.

Respectfully, Kimberly D. Hulvey General Manager, Nuclear Regulatory Affairs & Emergency Preparedness

Enclosures:

Browns Ferry Nuclear Plant, Unit 3, American Society of Mechanical Engineers Operation and Maintenance Code Request for Alternative BFN-IST-06 cc (Enclosure):

NRC Regional Administrator - Region II NRC Senior Resident Inspector - Browns Ferry Nuclear Plant NRC Project Manager - Browns Ferry Nuclear Plant Digitally signed by Edmondson, Carla Date: 2025.09.18 12:29:20

-04'00'

Enclosure CNL-25-108 Page E1 of 5 Browns Ferry Nuclear Plant, Unit 3 American Society of Mechanical Engineers Operation and Maintenance Code Request for Alternative BFN-IST-06 Inservice Testing of the 3A and 3B Standby Liquid Control Pumps in Accordance with 10 CFR 50.55a(z)(2)

I.

ASME Code Components Affected Site/Unit Pump ID Pump Description Pump Type Code Class OM Group Browns Ferry Nuclear Plant Unit 3 3-PMP-63-6A Standby Liquid Control Pump 3A Positive Displacement 2

B 3-PMP-63-6B Standby Liquid Control Pump 3B Positive Displacement 2

B The standby liquid control (SLC) system provides a means of reactivity control that is independent of control rod movement to ensure and maintain reactor shutdown from the most reactive steady-state operating condition at any time in the core life. The SLC system is not required to shut down the reactor as a backup scram system or to provide operational control of reactivity transients. The SLC system is intended to be used as an extreme measure toward reactivity control. The SLC system is capable of injecting sodium pentaborate (SPB) solution as a buffering agent in the event of a large recirculation break loss-of-coolant accident (LOCA).

The SLC system is required to supply SPB solution for post-LOCA events that involve fuel damage to maintain the suppression pool potential of hydrogen (pH) at or above 7.0 for 30 days. The radiological dose analysis for the design basis accident (DBA) LOCA assumes concentrations of iodine species consistent with a suppression pool at or above 7.0 pH (i.e., re-evolution of iodine to the containment atmosphere is not considered).

The SLC is capable of injecting a neutron absorber solution into the reactor pressure vessel (RPV) at a minimum injection rate of 39 gallons per minute (gpm), under reactor operating pressures ranging from atmospheric to the maximum opening pressure of the reactor relief valves. The SLC system has the capability of injecting into the RPV an SPB solution to bring the reactor from full power to a cold shutdown condition.

To assure the availability of the SLC system, two sets of the components required to actuate the pumps, and explosive valves are provided in parallel for redundancy. The SLC system is required to be operable in the event of a station power failure, so the pumps, valves, and controls are powered from the standby alternating current (AC) power supply in the absence of normal power.

II.

ASME Code Edition and Addenda American Society of Mechanical Engineers (ASME) Operation and Maintenance of Nuclear Power Plants (OM Code), 2020 Edition

Enclosure CNL-25-108 Page E2 of 5 III.

Applicable Code Requirement

Subsection ISTB-3400, Frequency of Inservice Tests, states, An inservice test shall be run on each pump as specified in Table ISTB-3400-1. Table ISTB-3400-1, Inservice Test Frequency, specifies, in part, that a Group B functional test be performed quarterly for Group B pumps.

IV.

Reason for Request

Pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a, Codes and standards, paragraph (z)(2), an alternative is proposed to the quarterly pump test requirements of the ASME OM Code. As explained below, the basis of the request is that compliance with the specified requirements would result in a hardship or unusual difficulty without a compensating increase in the level of quality and safety.

On August 12, 2025, during the performance of SLC pump functional testing on BFN Unit 3, testing was stopped after the 3A pump (3-PMP-63-6A) test due to abnormal indications on the SLC pump discharge pressure instrument (3-PI-63-7B). Initial troubleshooting included flushing the SLC discharge pressures sensing line and calibrating the indicator. Testing re-commenced on August 13, 2025, and again was halted due to abnormal indications.

During this performance, pressure continued to rise even as the SLC test line throttle valve (3-THV-63-518) was opened. Subsequent troubleshooting, including a borescope inspection, identified a stem/disc separation of 3-THV-63-518, which is the Section XI Code Class 2 equivalent and Seismic Class I boundary isolation valve utilized for throttling the quarterly test flow circuit.

SLC pump functional testing was originally due by July 22, 2025, but, due to surveillance schedule conflict and resource availability during a forced outage, was extended by allowed grace period to August 15, 2025. Testing of the 3A SLC pump was completed satisfactorily.

However, due to failure of 3-THV-63-518, testing of the 3B pump (3-PMP-63-6B) was not completed within its required quarterly periodicity, including the grace period, which elapsed at 0000 Central Time on August 16, 2025. This issue was entered into the Tennessee Valley Authority (TVA) Corrective Action Program. A condition report was written to document the inability to perform the quarterly pump test for 3B SLC pump, resulting in the frequency for the required ASME OM Code test not being met as of August 16, 2025.

TVA could not have reasonably avoided this situation. Failure of 3-THV-63-518 (SLC test line throttle valve) was not a foreseeable occurrence. The throttle valve was replaced with a globe valve for improved throttling characteristics to make setting test pressure easier over the old gate valve configuration. The replacement was completed on March 11, 2024, to replace 3-THV-63-518 with a new globe valve. The SLC pump functional test has been performed five times since 3-THV 63-518 was replaced without any deficiencies noted.

Following the last performance of the test with no issues noted, there was no way to have foreseen the valve failure was going to occur. TVA plans to perform extent of condition disassembly and inspection on the SLC test line throttle valves for BFN Units 1 and 2 during their next respective refueling outages.

Based on the condition of 3-THV-63-518, performing pump testing could result in damaging the valve, which is currently in its safety position of locked closed. Degradation or chattering of 3-THV-63-518 from performing pump testing could result in the valve failing to re-close, which would render both loops of SLC inoperable due to a loss of the of the Seismic/Code

Enclosure CNL-25-108 Page E3 of 5 Class 2 Equivalent boundary valve. TVA review of the suspected mechanism of the separation indicates that the failure allows motion of the valve disc with flow with the handwheel full open, and the valve would function as a stop-check if the test was performed.

The closing of the handwheel was able to seat the valve when observed via borescope. TVA determined that there was not a likely failure mode where the disc becomes lodged in the flow stream.

Maintaining 3-THV-63-518 locked closed eliminates the normal testing flow path. Vessel injection through the squib valves (3-FCV-63-8A and 3-FCV-63-8B) is not an acceptable solution for online testing due to the complexity associated with the testing and the potential for injecting sodium pentaborate. An alternate flow path through SLC pump discharge drain valves 3-DRV-63-522 and 3-DRV-63-523 is available but has not historically been utilized for testing. The drain valves are gate valve designs, which are not ideal for throttling and pressure control, and the piping downstream of 3-DRV-63-523 is not rated for the 1150 pounds per square inch gauge (psig) normal test pressure. Additionally, SLC vent valve 3-VTV-63-521 is an alternate throttle valve. However, use of this vent valve and flow path requires flow through 3-THV-63-518 which risks further damage to the valve condition.

Therefore, use of the vent valve, drain valves, or injecting into the reactor vessel are not considered to be desirable alternatives for quarterly testing.

The SLC test line throttle valve is common to both the 3A and 3B SLC pumps. To effect repairs to this valve, both SLC pumps will be declared inoperable, requiring entry into BFN Technical Specification (TS), Limiting Condition for Operation (LCO) 3.1.7, Condition B which requires restoration of at least one SLC pump within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />. If an SLC subsystem is not restored to operable status within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />, BFN Unit 3 would be required to enter TS LCO 3.1.7, Condition C requiring entry to Mode 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and entry to Mode 4 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.

Repairs to 3-THV-63-518 are expected to take 4-6 hours. Pulling the clearances post-repair and performing the SLC pump functional test to restore operability could take another 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.

Additionally, the only benefit online repair would provide is to allow continued testing of the SLC pumps. Periodic testing and maintenance have not identified other deficiencies with the system boundary and normal operation. Test history for these pumps has been acceptable, with periodic maintenance performed to ensure the operational readiness of the pump and driver.

Relief is requested pursuant to 10 CFR 50.55a(z)(2) based on the determination that compliance with the ASME OM Code required quarterly SLC pump functional tests cannot be performed without considerable plant safety and reliability risks prior to significant repairs to address 3-THV-63-518. TVA plans to repair this valve during the BFN Unit 3 Cycle 22 refueling outage (U3R22) in spring 2026 to restore acceptable test alignment, without time pressure and with a focus on quality. As a contingency, the repair scope is included on the forced outage maintenance list and would be performed if a forced outage were to occur prior to the planned refueling outage with scope and plant conditions that allow the repair.

Enclosure CNL-25-108 Page E4 of 5 V.

Proposed Alternative and Basis for Use The proposed alternative requests to defer the requirements to perform Group B quarterly pump tests as required by ISTB-3400 for the 3A and 3B SLC pumps until the end of the U3R22 outage. This will allow performance of the biennial comprehensive pump tests (CPT) and periodic pump verification tests (PPVT) for the 3A and 3B SLC pumps during the refueling outage, and the Group B quarterly pump tests will resume as scheduled following repair of the Unit 3 SLC test line throttle valve (3-THV-63-518) and reactor startup from the U3R22 outage.

Previous IST trends for the 3A and 3B SLC pumps are in Attachment 1 (Tables 1 - 7) and show the operational readiness of the pumps to perform their intended safety function. The last 4 years of data from the quarterly Group B testing and the last 10 years of data from the CPT for the 3A and 3B SLC pumps indicate there is no current pump degradation. The recorded values for pump vibration, flow, and discharge pressure during the review period were within ASME OM Code and design limits. Therefore, it is unlikely that the upcoming quarterly pump tests would produce a failing value for any test parameter.

Periodic maintenance of each pump is performed to disassemble, inspect pump internals, and refurbish as necessary in accordance with the BFN Preventive Maintenance Program.

The 3A SLC pump was internally inspected in March 2022, and it had previously been replaced in March 2014. The 3B SLC pump was internally inspected in March 2024 and in March 2016. During the last two inspections, the as-found pump internals were in good condition with only periodic refurbishment needed. The available data supports the conclusion that the pumps are capable of performing their design functions until their next scheduled internal inspections. These observations are supported by the historical pump trends.

Repairs to 3-THV-63-518 are planned for the upcoming spring 2026 refueling outage because repair of the valve requires tagging the 3A and 3B SLC pumps, rendering them inoperable.

Under current conditions, performing the Group B quarterly test for the 3A and 3B SLC pumps would constitute a hardship without a compensating increase in the level of quality and safety.

The proposed alternative to ISTB-3400 provides reasonable assurance of pump operational readiness and provides an acceptable level of quality and safety.

VI.

Duration of Proposed Alternative The performance of the Group B test for the 3B SLC pump was originally scheduled for July 22, 2025, but went late August 15, 2025 (with grace period), during system troubleshooting. The 3A SLC pump test was completed August 12, 2025. The last complete test of both pumps - 3A and 3B - was on April 22, 2025. The next due date from the base 91-day interval is October 21, 2025. Therefore, TVA is requesting NRC approval of this relief request by October 17, 2025, prior to the expiration of the normal quarterly testing frequency window (without grace).

This request, upon NRC approval, will be applied at BFN Unit 3 until the end of the U3R22 outage, currently scheduled to be completed in March 2026. This timeframe provides an adequate window of opportunity to perform the CPTs and PPVTs during the spring refueling outage, after repairs have been made to the SLC test line throttle valve (3-THV-63-518). The performance of the quarterly IST Group B functional pump tests for the components included in this request will resume at the normal frequency following the U3R22 outage.

Enclosure CNL-25-108 Page E5 of 5 VII.

Precedents The following precedents are similar to the proposed alternative request in that they approved deferring the quarterly IST testing until the next refueling outage when plant conditions were suitable to perform the test.

On January 16, 2025, the NRC approved a similar alternative request for the Vogtle Unit 2 charging pumps 2A and 2B (Reference 1).

On December 19, 2024, the NRC approved a similar alternative request for the Farley Unit 2 charging pumps 2A, 2B, and 2C and mini-flow isolation valves (Reference 2).

On April 25, 2023, the NRC approved a similar alternative request for components in the high-pressure coolant injection system at Monticello (Reference 3).

On October 4, 2018, the NRC approved a similar alternative request for Millstone Unit 3 charging pump 3C (Reference 4).

VIII.

References

1. NRC Letter to Southern Nuclear Operating Company, Vogtle Electric Generating Plant, Unit 2 - RE: Authorization of Proposed Alternative for Inservice Testing of the 2A and 2B Charging Pumps (EPID L-2025-LLR-0000), dated January 16, 2025 (ML25010A381)

2. NRC Letter to Southern Nuclear Operating Company, Joseph M. Farley Nuclear Plant, Unit 2 - RE: Authorization of Proposed Alternative RR-PR-04 Inservice Testing of the 2A, 2B, and 2C Charging Pumps and Mini-Flow Isolation Valves (EPID L-2024-LLR-0068), dated December 19, 2024 (ML24351A040)

3. NRC Letter to Northern States Power Company, Monticello Nuclear Generating Plant - Authorization and Safety Evaluation for Alternative Request PR-08 (EPID L-2022-LLR-0088), dated April 25, 2023 (ML23107A285)

4. NRC Letter to Dominion Energy Nuclear Connecticut, Millstone Power Station, Unit No 3 - Alternative Request P-06 for C Charging Pump Test Frequency (EPID L-2018-LLR-0078), dated October 4, 2018 (ML18275A012)

Enclosure CNL-25-108 Page E-A1 of 3 - Browns Ferry Nuclear Plant, Unit 3 Standby Liquid Control Pump Test History Table 1 - 3A SLC Pump Quarterly Group B History Exam Date Q (gpm)

P (psig)

Acceptable Range (Q) 4/22/2025 55 1150 48.1 to 58.7 gpm 2/13/2025 50.6 1150 48.1 to 58.7 gpm 10/22/2024 52.8 1150 48.1 to 58.7 gpm 7/23/2024 57.2 1150 48.1 to 58.7 gpm 4/23/2024 52.8 1150 48.1 to 58.7 gpm 1/23/2024 50.6 1155 48.1 to 58.7 gpm 10/10/2023 52.8 1150 48.1 to 58.7 gpm 7/18/2023 56.1 1150 48.1 to 58.7 gpm 4/18/2023 52.8 1150 48.1 to 58.7 gpm 1/20/2023 53.9 1150 48.1 to 58.7 gpm 10/18/2022 50.6 1150 48.1 to 58.7 gpm 7/19/2022 52.8 1150 48.1 to 58.7 gpm 4/19/2022 53.9 1150 48.1 to 58.7 gpm 1/18/2022 56.1 1150 48.1 to 58.7 gpm 10/6/2021 57.2 1150 48.1 to 58.7 gpm 7/20/2021 57.2 1150 48.1 to 58.7 gpm 4/20/2021 55 1150 48.1 to 58.7 gpm 1/20/2021 53.9 1150 48.1 to 58.7 gpm Table 2 - 3A SLC Pump Comprehensive Pump Test Hydraulic History Exam Date Q (gpm)

P (psig)

Acceptable Range (Q) 3/10/2024 53.9 1155 50.8 to 56.6 gpm 3/21/2022 55 1150 50.8 to 56.6 gpm 3/4/2020 51.7 1160 50.8 to 55.0 gpm 3/22/2018 53.9 1150 50.8 to 55.0 gpm 3/22/2016 53.35 1180 50.8 to 55.0 gpm 3/15/2014 52.8 1140 50.8 to 55.0 gpm Table 3 - 3A SLC Pump Comprehensive Pump Test Vibration History Exam Date Pump Inboard Bridge Vibration (DV)

DV Normal Range (in/sec)

Pump Outboard Bridge Vibration (EV)

EV Normal Range (in/sec) 3/10/2024 0.180 0.5552 0.166 0.3360 3/21/2022 0.147 0.3250 0.137 0.3250 3/4/2020 0.162 0.3250 0.157 0.3250 3/22/2018 0.153 0.3250 0.140 0.3250 3/22/2016 0.197 0.3250 0.143 0.3250 3/14/2014 0.182 0.3250 0.123 0.3250

Enclosure CNL-25-108 Page E-A2 of 3 Table 4 - 3B SLC Pump Quarterly Group B History Exam Date Q (gpm)

P (psig)

Acceptable Range (Q) 4/22/2025 55 1150 48.02 to 58.68 gpm 2/13/2025 52.8 1150 48.02 to 58.68 gpm 10/22/2024 55 1150 48.02 to 58.68 gpm 7/23/2024 55 1150 48.02 to 58.68 gpm 4/23/2024 55 1150 48.02 to 58.68 gpm 1/23/2024 52.8 1150 48.02 to 58.68 gpm 10/10/2023 52.8 1150 49.0 to 59.8 gpm 7/18/2023 53.9 1150 49.0 to 59.8 gpm 4/18/2023 50.6 1150 49.0 to 59.8 gpm 1/20/2023 53.9 1150 49.0 to 59.8 gpm 10/18/2022 50.6 1150 49.0 to 59.8 gpm 7/19/2022 57.2 1150 49.0 to 59.8 gpm 4/19/2022 55 1150 49.0 to 59.8 gpm 1/18/2022 52.8 1150 49.0 to 59.8 gpm 10/6/2021 55 1150 49.0 to 59.8 gpm 7/20/2021 57.2 1150 49.0 to 59.8 gpm 4/20/2021 55 1150 49.0 to 59.8 gpm 1/21/2021 53.9 1150 49.0 to 59.8 gpm Table 5 - 3B SLC Pump Comprehensive Pump Test Hydraulic History Exam Date Q (gpm)

P (psig)

Acceptable Range (Q) 3/10/2024 55 1155 50.7 to 56.5 gpm 3/21/2022 52.8 1150 51.7 to 56.0 gpm 3/4/2020 52.8 1220 51.7 to 56.0 gpm 3/22/2018 52.8 1150 51.7 to 56.0 gpm 3/22/2016 53.35 1180 51.7 to 56.0 gpm 3/14/2014 52.8 1145 51.7 to 56.0 gpm Table 6 - 3B SLC Pump Comprehensive Pump Test Vibration History Exam Date Pump Inboard Bridge Vibration (DV)

DV Normal Range (in/sec)

Pump Outboard Bridge Vibration (EV)

EV Normal Range (in/sec) 3/10/2024 0.100 0.3185 0.121 0.3413 3/21/2022 0.116 0.2081 0.128 0.2400 3/4/2020 0.120 0.2081 0.119 0.2400 3/22/2018 0.116 0.2081 0.126 0.2400 3/22/2016 0.127 0.2081 0.136 0.2400 3/14/2014 0.112 0.2081 0.114 0.2400

Enclosure CNL-25-108 Page E-A3 of 3 Table 7 - SLC Pump Periodic Verification Test History Exam Method UNID Exam Date Q (gpm)

P (psig)

Acceptance Criteria (NOTE

1)

PPVT 3-PMP-63-6A 3/10/2024 51.7 1330 P > 1325 psid, Q > 48.4 gpm PPVT 3-PMP-63-6B 3/10/2024 55 1330 P > 1325 psid, Q > 48.4 gpm NOTE 1:

The required minimum discharge pressure setting for pump periodic verification test (PPVT) was determined by subtracting 1 standard atmosphere (14.69595 psi) from the minimum value (1223 psia). That value (1208.31 psig) was rounded up to 1220 psig for readability and margin.

Testing at 1325 psig to satisfy Surveillance Requirement (SR) 3.1.7.7 flow and head requirements is expected to demonstrate sufficient flow to meet the requirement of the PPVT. If the requirement of PPVT is not met at the pressure required for SR 3.1.7.7, then the procedure has steps to lower discharge pressure and retest using an alternative procedural attachment.