ML25133A127
| ML25133A127 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 05/16/2025 |
| From: | Scott Wall NRC/NRR/DORL/LPL3 |
| To: | Rhoades D Constellation Energy Generation |
| Wall, S | |
| References | |
| EPID L-2025-LLR-0049 RR4 | |
| Download: ML25133A127 (1) | |
Text
May 16, 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:
BRAIDWOOD STATION, UNIT 1 - ISSUANCE OF ALTERNATIVE REQUESTS RR-4 ASSOCIATED WITH POST-MAINTENANCE TESTING OF AIR-OPERATED CONTROL VALVE FOURTH INSERVICE TESTING PROGRAM INTERVAL (EPID L-2025-LLR-0049)
Dear Mr. Rhoades:
By letter dated April 28, 2025 (Agencywide Documents Access and Management System Accession No. ML25118A331), as supplemented by letter dated May 6, 2025 (ML25126A166),
Constellation Energy Generation, LLC (CEG, the licensee) submitted alternative request RR-4 regarding certain inservice testing (IST) requirements of the 2012 Edition of the American Society of Mechanical Engineers (ASME) Operation and Maintenance of Nuclear Power Plants, Division 1, OM Code: Section IST (OM Code) for the IST Program at Braidwood Station, Unit 1, for the Fourth IST Program Interval.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(1) the licensee requested to use the proposed alternative in request RR-4 on the basis that the alternative provides an acceptable level of quality and safety.
The U.S. Nuclear Regulatory Commission (NRC) staff has reviewed the subject request and concludes, as set forth in the enclosed safety evaluation, that CEG has adequately addressed the requirements in 10 CFR 50.55a(z)(1). Therefore, the NRC staff approves the use of RR-4 to support exiting the current 30-day Technical Requirements Manual window.
All other ASME Boiler Pressure Vessel Code or ASME OM Code requirements for which relief was not specifically requested and approved remain applicable.
D. Rhoades 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, Chief Plant Licensing Branch III Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. STN 50-456
Enclosure:
Safety Evaluation cc: Listserv ILKA BERRIOS Digitally signed by ILKA BERRIOS Date: 2025.05.16 11:52:40 -04'00'
Enclosure SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION ALTERNATIVE REQUEST RR-4 POST-MAINTENANCE TESTING OF AIR-OPERATED CONTROL VALVE FOURTH INSERVICE TESTING PROGRAM INTERVAL CONSTELLATION ENERGY GENERATION, LLC BRAIDWOOD STATION, UNIT 1 DOCKET NO. STN 50-456
1.0 INTRODUCTION
By letter dated April 28, 2025 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML25118A331), and supplemented by letter dated May 6, 2025 (ML25126A166), Constellation Energy, LLC (the licensee or CEG) submitted Alternative Request RR-4 to the U.S. Nuclear Regulatory Commission (NRC) regarding certain inservice testing (IST) requirements of the 2012 Edition of the American Society of Mechanical Engineers (ASME) Operation and Maintenance of Nuclear Power Plants, Division 1, OM Code: Section IST (OM Code) for the IST Program at Braidwood Station (Braidwood), Unit 1, for the Fourth IST Interval Program.
Specifically, the licensee requested a one-time alternative to the post-maintenance testing requirements in the ASME OM Code as incorporated by reference in Title 10 of the Code of Federal Regulations (10 CFR), Section 50.55a, Codes and standards, for the Auxiliary Feedwater (AF) air-operated flow control valve 1AF005F at Braidwood, Unit 1, on the basis that the alternative provides acceptable level of quality and safety under 10 CFR 50.55a(z)(1). The licensees submittal requested a one-time allowance in the IST Program to perform a partial manual stroke test of the 1AF005F valve at Braidwood, Unit 1 in lieu of the ASME OM Code required full-stroke exercise following maintenance to repair the valve. The licensee requested the authorization of the proposed alternative by May 19, 2025, to support exiting a 30-day Technical Requirements Manual window.
2.0 REGULATORY EVALUATION
The NRC regulations in 10 CFR 50.55a(f)(4), Inservice testing standards requirement for operating plants, state in part:
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 inservice test 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 NRC regulations in 10 CFR 50.55a(z), Alternatives to codes and standards requirements, state:
Alternatives to the requirements of [10 CFR 50.55a(b) through (h)] or portions thereof may be used when authorized by the Director, Office of Nuclear Reactor Regulation. A proposed alternative must be submitted and authorized prior to implementation. The applicant or licensee must demonstrate that:
(1) Acceptable level of quality and safety. The proposed alternative would provide an acceptable level of quality and safety; or (2) Hardship without a compensating increase in quality and safety. 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.
3.0 TECHNICAL EVALUATION
3.1 Licensees Alternative Request RR-3 Applicable ASME OM Code Edition The applicable Code of record for the Fourth IST Interval Program at Braidwood, Unit 1, is the 2012 Edition of ASME OM Code as incorporated by reference in 10 CFR 50.55a.
ASME OM Code Components Affected In its submittal, the licensee proposed alternative testing for the following valves:
Table 1 Valve Number Description ASME Code Class OM Code Category 1AF005F Unit 1 Aux Feedwater Air Operated Flow Control Valve F 3
B Applicable ASME OM Code Requirements ASME OM Code, Subsection ISTC, Inservice Testing of Valves in Light-Water Reactor Nuclear Power Plants, paragraph ISTC-3540, Manual Valves, states:
Manual valves shall be full-stroke exercised at least once every 2 yr [years],
except where adverse conditions may require the valve to be tested more frequently to ensure operational readiness. Any increased testing frequency shall be specified by the Owner. The valve shall exhibit the required change of obturator position.
Licensees Proposed Alternative The licensees proposal in Alternative Request RR-4 is as follows:
CEG is proposing an alternative partial stroke test in lieu of the code require full-stroke exercise following maintenance to repair to the 1AF005F valve in accordance with 10 CFR 50.55a(z)(1) on the basis that the alternative provides an acceptable level of quality or safety. The partial stroke test better aligns with the function of this specific manual valve and how the manual valve is operated in plant emergency procedures. CEG proposes a test of 1AF005F by full-closing the valve with air, engaging the manual handwheel to ensure valve is full-closed, and failing air to ensure the valve remains closed as required to maintain margin to overfill.
Licensees Basis for Use The licensees basis for use of the proposal in Alternative Request RR-3 is as follows:
The AF system provides cooling water flow to the steam generators [SGs] to allow for decay heat removal during emergency conditions. Performing valve strokes requires closing the associated AF flow-control valve and entry in LCO
[Limiting Condition for Operation] 3.7.5 Required Action for the associated train.
Closing 1AF005F via the handwheel is not required for the AF system to meet its design safety function to provide flow to the SG in accordance with LCO 3.7.5, but further closure of the valve via the handwheel may be necessary to ensure margin to overfill during a SGTR [steam generator tube rupture].
A history of IST required full-stroke and manual valve strokes of 1AF005F using air over the previous 7 years was reviewed. 1AF005F valve was manually stroked successfully during the previous test interval in 2022. The manual stroke was added to the IST program in 2022 following a violation received during the Design Basis Assurance Inspection (ML22164A905). 1AF005F is stroked quarterly with air for stroke time testing. Since 2018, 1AF005F has not exceeded its operating limit in any of these tests.
Despite the 2022 IST manual stroke test interval for the 1AF005F being successful, the 2024 test was unable to be completed during the initial attempt.
While the manual stroke test of the 1AF005F was being performed in November 2024, it was identified that the manual handwheel for the 1AF005F valve became disengaged from the valve actuator. This left the valve in an intermediate position and prevented Operators from being able to manually stroke the valve further. As highlighted in Attachment 2, due to valve position at the time they were also unable to reposition the valve utilizing the air control portion of the actuator. Operators entered LCO 3.7.5, and maintenance was performed to repair a shear pin internal to the valve actuator that was determined to be the cause of the handwheel becoming disengaged from the actuator and locking the valve in place at a mid-position. Operations remotely stroked the valve successfully to demonstrate their ability to control flow to the downstream SG and exit LCO 3.7.5. Similar challenges during the April 2025 performance of the IST manual stroke of the 1AF005F, and the challenges observed at Byron during April 2025, highlight the potential risk of impacting a key design basis safety function by damaging the associated valve actuator and preventing flow control of auxiliary feedwater to the downstream steam generators.
ISTC-3540 requires an observed change in obturator position during the manual exercise test. The proposed post-maintenance test (PMT) will close the valve using the air operator and then ensure the valve is closed using the handwheel.
Utilizing this test method, the handwheel may not move the obturator if the valve fully closes via the air operator. The 1AF005F was evaluated to be not susceptible to stem-disc separation following the requirements of ASME Code Case OMN-28. This valve is tested for supplemental position indication using the air operator to observe changes in flow during the 1B Auxiliary Feedwater Pump Comprehensive Test immediately prior to every refueling outage (every 18 months) and was last successfully performed on 4/12/2024. The supplemental position test performed using the air operator to demonstrate obturator movement is an acceptable alternative to exhibiting the required change when manually stroked for this PMT based on the operation of this valve during execution of plant procedures.
When being operated remotely via air to perform stroke time testing of the 1AF005F, the testing history provides reasonable assurance the AOV is currently operable and ready to perform its safety function to provide feedwater to the 1B SG to remove decay heat from the Reactor Coolant System upon the loss of normal feedwater supply. In the event of a SGTR in the 1B SG, the 1AF013F functions as the primary isolation of feedwater flow. In the event the 1AF013F fails to close, the 1AF005F valve is closed with air and has its manual handwheel closed to ensure isolation. Based on this testing history and the back-up nature of the manual handwheel operation, CEG concludes that the proposed alternative is acceptable and will not result in an adverse consequence to safety.
Licensees Reason for Request The licensees reason for Alternative Request RR-4 is as follows:
In accordance with 10 CFR 50.55a, "Codes and Standards," paragraph (z)(1),
relief is requested from the full-stroke requirement of ASME OM Code ISTC-3540. The basis for this relief request is the alternative to the Inservice Testing (IST) Program testing requirements provide acceptable level of quality and safety.
The 1AF005F valve controls the flow of Auxiliary Feedwater (AF) water to the 1B steam generator (SG). In the event of an accident, the 1AF005F valve can be controlled from the main control room or the remote shutdown panel (RSDP). In the event of a steam generator tube rupture (SGTR) in 1B Steam Generator, feedwater flow to the steam generator from the B AF train will be isolated via the motor-operated isolation valve, 1AF013F, the air-operated control valve, 1AF005F, serves as backup isolation. Step 4 of 1BwEP-3 (Steam Generator Tube Rupture) directs the operator to isolate AF flow to the affected steam generator by closing the associated 1AF013 valves and setting the demanded flow for the associated 1AF005 valves to 0, closing them. In the event the associated 1AF013 does not close as expected, the operator would go to the response not obtained column where they would be directed to close the associated 1AF005 valve using the handwheel, ensuring the valve does not open if instrument air is lost. In this circumstance, the 1AF005 would be taken closed by air from either the instrument air system or the installed safety-related accumulators prior to operators taking field action. During normal plant operation the AF system is in standby with the 1AF005F valve set to control flow at approximately 170 gallons per minute (gpm) upon actuation. Closing of the 1AF005F valve via the handwheel is not required for the AF system to meet its design safety function to provide flow to the SGs in accordance with Limiting Condition for Operation (LCO) 3.7.5 and the Braidwood Station design basis, but ensuring closure of the valve (following closure via instrument air system or installed accumulators) via the handwheel is credited in the safety analysis to ensure margin to overfill during a SGTR.
The 1AF005F valve has two separate actuation methodologies. The valve can be stroked remotely via air or manually via the handwheel. These two methodologies and the actuation sequences are detailed in Attachment 2. Based on the actuator design, the manual handwheel stroke mechanism and air operation stroke mechanism share a common linkage. Degradation of the actuator that impacts the manual handwheel stroke mechanism can affect the air operated stroke mechanism and can ultimately prevent the valve from being capable of changing position remotely via air.
Failure of the 1AF005F valve such that it becomes stuck closed as a result of cycling with the handwheel would prevent the associated train from providing feedwater flow to the 1B steam generator during a plant transient resulting in entry into LCO 3.7.5, Two trains of AF remain OPERABLE.
The 1(2)AF005 valves at Braidwood and Byron share a common valve design, and recent operating experience at both stations demonstrates a trend in challenges with manual actuation of the 1(2)AF005 valves from the handwheel.
[The licensee provided recent operating experience (OPEX) from Braidwood and Byron.]
Based on the above information and component specific operating experience, manually full-stroke exercising the 1AF005F valve utilizing the handwheel has the potential to impact the ability of the valve to be re-positioned and can impact the ability of the Operators to control AF flow remotely. Subsequently, this could challenge the ability of the 1B AF train to provide forward feedwater flow to the 1B steam generator. Full stroking the 1AF005F valve using the handwheel risks failure of the valve in a non-open position. As such, Constellation Energy Generation, LLC (CEG) is proposing an alternative test method to verify successful repair of the 1AF005F actuator. It is the position of CEG that the proposed alternative test method provides an acceptable level of quality and safety.
3.2
NRC Staff Evaluation
In Alternative Request RR-4, the licensee proposed an alternative partial manual stroke test in lieu of the full-stroke manual exercise required by the ASME OM Code, Subsection ISTC, paragraph ISTC-3540, following maintenance to repair the 1AF005F valve at Braidwood, Unit 1 in accordance with 10 CFR 50.55a(z)(1) on the basis that the alternative provides an acceptable level of quality or safety. The licensee asserted that the partial manual stroke test will better align with the function of the 1AF005F valve and how the valve is operated in plant emergency procedures. The licensee proposed a test of the 1AF005F valve by fully closing the valve with air, engaging the manual handwheel to ensure valve is fully closed, and failing air to ensure the valve remains closed.
Paragraph ISTC-3540 in ASME OM Code, Subsection ISTC, requires manual valves to be full-stroke exercised at least once every 2 years, except where adverse conditions may require the valve to be tested more frequently to ensure operational readiness. Paragraph ISTC-3540 also requires that the valve shall exhibit the required change of obturator position. ASME OM Code, Subsection ISTC, paragraph ISTC-3310, Effects of Valve Repair, Replacement, or Maintenance on Reference Values, requires when a valve has been repaired or has undergone maintenance that could affect the valves performance a new reference value shall be determined or the previous value reconfirmed by an inservice test run before the time it is returned to service or immediately if not removed from service. This test is to demonstrate that performance parameters that could be affected are within acceptable limits. Deviations between the previous and new reference values shall be identified and analyzed. Verification that the new values represent acceptable operation shall be documented in the record of tests.
The 1AF005F valve at Braidwood, Unit 1 controls the flow of AF water to the 1B SG. During an SGTR event, feedwater flow to the SG from the AF Train B will be isolated using the motor-operated isolation valve 1AF013F with the air-operated control valve 1AF005F serving as a backup. If the associated 1AF013 valve does not close, the reactor operators would close the 1AF005 valve by air from either the instrument air system or the installed safety-related accumulators prior to the reactor operators taking field action. The licensee stated that closing of the 1AF005F valve using the handwheel is not required for the AF system to meet its design safety function to provide flow to the SGs in accordance with LCO 3.7.5 and the Braidwood Station design basis. However, ensuring closure of the 1AF005F valve (following closure via instrument air system or installed accumulators) using the handwheel is credited in the safety analysis to ensure margin to overfill during an SGTR event.
In Alternative Request RR-4, the licensee stated that the proposed post-maintenance test will close the 1AF005F valve using the air operator and then ensure the valve is closed using the handwheel. The licensee then stated that using this test method, the handwheel may not move the obturator if the valve fully closes using the air operator. The licensee summarized past experience where handwheel operation interfered with the air-operated function of the 1(2)AF005 valves at the Braidwood and Byron nuclear power plants. In a Request for Additional Information dated May 5, 2025 (ML25126A101), the NRC staff requested the licensee to describe its plan to ensure that the air-operated function of the 1AF005F valve at Braidwood, Unit 1 would not been degraded if it was necessary to use the handwheel to fully close the valve manually during the proposed PMT. In its response dated May 6, 2025 (ML25126A166), the licensee stated that for the PMT, the 1AF005F valve will be closed with air, have its handwheel engaged to fully close and gag the valve, and then have air removed to ensure the handwheel maintains the valve closed. Once this function is verified, air will be reapplied, the handwheel will be restored to its normal position ensuring the valve remains closed. The valve will then be returned to its normally open position by normal means of venting air to allow spring force to open the valve. The NRC staff agrees with the licensees position that ensuring the valve remains closed with air applied and then re-opening the valve in this manner demonstrates that handwheel operation did not degrade the air-operated function of the 1AF005F valve.
Based on the information described above, the NRC staff has determined that the proposal in Alternative Request RR-4 to perform a partial manual stroke test as a one-time alternative to the full-stroke manual exercise required by the ASME OM Code, Subsection ISTC, paragraph ISTC-3540, following maintenance to repair the 1AF005F valve at Braidwood, Unit 1 provides an acceptable level of quality or safety. The staff finds that the proposed PMT of the 1AF005F valve as described in Alternative Request RR-4 will provide reasonable assurance of the operational readiness of the 1AF005F valve to perform its intended function following the specific maintenance to repair the valve at this time. Therefore, the NRC staff finds that Alternative Request RR-4 may be authorized in accordance with 10 CFR 50.55a(z)(1).
4.0 CONCLUSION
As set forth above, the NRC staff has determined that the proposal in Alternative Request RR-4 (as supplemented) to perform a partial manual stroke test as a one-time alternative to the full-stroke manual exercise required by the ASME OM Code following maintenance to repair the 1AF005F valve at Braidwood, Unit 1 provides an acceptable level of quality or safety. The staff finds that the proposed PMT of the 1AF005F valve will provide reasonable assurance of the operational readiness of the 1AF005F valve to perform its intended function following the specific maintenance to repair the valve. Accordingly, the NRC staff concludes that the licensee has adequately addressed all the regulatory requirements set forth in 10 CFR 50.55a(z)(1).
Therefore, the NRC staff authorizes Alternative Request RR-4 for the 1AF005F valve at Braidwood, Unit 1, to support exiting the current 30-day Technical Requirements Manual window.
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 Contributor: Thomas Scarbrough, NRR Date: May 16, 2025
SUBJECT:
BRAIDWOOD STATION, UNIT 1 - ISSUANCE OF ALTERNATIVE REQUESTS RR-4 ASSOCIATED WITH POST-MAINTENANCE TESTING OF AIR-OPERATED CONTROL VALVE FOURTH INSERVICE TESTING PROGRAM INTERVAL (EPID L-2025-LLR-0046) DATED MAY 16, 2025 DISTRIBUTION:
PUBLIC RidsNrrDorlLpl3 Resource RidsRgn3MailCenter Resource RidsNrrLASLent Resource RidsAcrs_MailCTR Resource RidsNrrPMBraidwood Resource RidsNrrPMByron Resource RidsNrrDexEmib Resource TScarbrough, NRR Accession No.: ML25133A127
- via memo NRR-028 OFFICE NRR/DORL/LPL3/PM NRR/DORL/LPL3/LA NRR/DEX/EMIB/BC*
NAME SWall SLent SBailey DATE 05/13/2025 5/14/25 05/12/2025 OFFICE NRR/DORL/LPL3/BC NRR/DORL/LPL3/PM NAME IBerrios SWall DATE 05/16/2025 05/16/2025 OFFICIAL RECORD COPY