RS-25-095, Relief Request RR-4 Associated with the Fourth Inservice Testing 10-Year Interval
| ML25118A331 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 04/28/2025 |
| From: | Steinman R Exelon Generation Co |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| RS-25-095 | |
| Download: ML25118A331 (1) | |
Text
4300 Winfield Road Warrenville, IL 60555 630 657 2000 Office April 28, 2025 10 CFR 50.55a RS-25-095 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555-0001 Braidwood Station, Unit 1 Renewed Facility Operating License No. NPF-72 NRC Docket No. STN 50-456
Subject:
Relief Request RR-4 Associated with the Fourth Inservice Testing 10-Year Interval In accordance with 10 CFR 50.55a, "Codes and standards," paragraph (z)(1), Constellation Energy Generation, LLC (CEG) requests U.S. Nuclear Regulatory Commission (NRC) approval of the attached relief request associated with the current Fourth Inservice Testing (IST) Interval for Braidwood Station, Unit 1 (Braidwood) on the basis that the alternative provides acceptable level of quality and safety. Specifically, relief is requested to allow a one-time change to the post-maintenance testing of the Unit 1 Auxiliary Feedwater (AF) air operated flow control valve 1AF005F per American Society of Mechanical Engineers (ASME) Operation and Maintenance (OM) Code 2012.
Proposed relief request RR-4 to implement an alternative post-maintenance testing method is provided in Attachment 1. CEG requests authorization of the proposed requested alternative by May 19, 2025 to support exiting D30-day Technical Requirements Manual window.
There are no regulatory commitments contained within this letter.
Should you have any questions concerning this letter, please contact Brian Seawright at 779-231-6151.
Respectfully, Rebecca L. Steinman Sr. Manager Licensing Constellation Energy Generation, LLC
- Steinman, Rebecca Lee Digitally signed by Steinman, Rebecca Lee Date: 2025.04.28 15:59:22
-05'00'
U.S. Nuclear Regulatory Commission April 28, 2025 Page 2 Attachments:
- 1) 10 CFR 50.55a Relief Request RR-4, Revision 0
- 2) Actuation Methodology for 1(2)AF005A-H cc:
Regional Administrator - NRC Region III NRC Senior Resident Inspector - Braidwood Station Illinois Emergency Management Agency - Department of Nuclear Safety
ATTACHMENT 1 Braidwood Station Unit 1 10 CFR 50.55a Relief Request RR-4, Revision 0 (Page 1 of 5)
10 CFR 50.55a Relief Request RR-4 Revision 0 (Page 2 of 5)
Proposed Alternative In Accordance with 10 CFR 50.55a(z)(1)
--Alternative Provides Acceptable Level of Quality and Safety--
1.0 ASME CODE COMPONENTS AFFECTED Valve Number Description Safety Class Category 1AF005F Unit 1 Aux Feedwater Air Operated Flow Control Valve F 3
B 2.0 APPLICABLE CODE EDITION AND ADDENDA American Society of Mechanical Engineers (ASME) Operation and Maintenance (OM)
Code 2012 Edition, no Addenda 3.0 APPLICABLE CODE REQUIREMENT ISTC-3540, "Manual Valves" Manual valves shall 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. Any increased testing frequency shall be specified by the Owner.
The valve shall exhibit the required change of obturator position.
4.0 REASON FOR REQUEST 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
10 CFR 50.55a Relief Request RR-4 Revision 0 (Page 3 of 5) 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. Recent operating experience (OPEX) is outlined below:
A. Byron performed 2BOSR 0.5-2.AF.3-1, Unit 2 Auxiliary Feedwater Valves Train A Indication Test on 4/7/2025, the handwheel of 2AF005B became difficult to operate until it eventually began to freely spin with the valve approximately 25% open. The valve was unable to re-positioned manually in the field or remotely. The valve was declared inoperable per LCO 3.7.5 because the 2A AF train could not forward feedwater flow to the SG.
B. Byron performed 2BOSR 0.5-2.AF.3-1, Unit 2 Auxiliary Feedwater Valves Train A Indication Test on 4/7/2025, the handwheel of the 2AF005D became increasingly difficult to operate at approximately 50%. At that time, Operations stopped further valve manipulation and engaged maintenance for troubleshooting. The performance of the full range manual stroke could not be completed. However, the valve was returned to the full-open position and stroked remotely to verify it could provide forward feedwater flow to the SG as required by LCO 3.7.5.
10 CFR 50.55a Relief Request RR-4 Revision 0 (Page 4 of 5)
C. Braidwood Station attempted to perform a manual stroke of AF flow control valves on Unit 1 in April 2025. 1AF005A-E were tested satisfactorily with no issues noted. Based on recent OPEX from Byron Station, operators were instructed to immediately stop, re-open the valve and return the handwheel to Neutral, and abandon the test if any increased resistance was noted. During the test of 1AF005F, operators encountered increased resistance. The test was incomplete, and Operations entered TRM 3.7.g for 1AF005F. An Issue Report (IR# 4858175) was generated to address the resistance encountered during the aborted surveillance through the stations Corrective Action Program.
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.
5.0 PROPOSED ALTERNATIVE AND BASIS FOR USE 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.
The AF system provides cooling water flow to the steam generators to allow for decay heat removal during emergency conditions. Performing valve strokes requires closing the associated AF flow-control valve and entry in LCO 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.
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.
10 CFR 50.55a Relief Request RR-4 Revision 0 (Page 5 of 5)
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.
6.0 DURATION OF PROPOSED ALTERNATIVE This submittal requests a one-time allowance to IST Program testing to perform a partial stroke test in lieu of the code require full-stroke exercise following maintenance to repair to the 1AF005F valve.
ATTACHMENT 2 Braidwood Station Unit 1 Actuation Methodology for 1(2)AF005A-H (Page 1 of 3)
Actuation Methodology for 1(2)AF005A-H (Page 2 of 3)
Although RR-4 is specific to the 1AF005F valve, the following explanation if the actuation methodology applies to all AF005 valves in both units.
The 1(2)AF005 valves have two separate actuation methodologies, remote via air and manual via the handwheel.
For air operation, the crosshead must be in neutral position. With the crosshead in the neutral position, the actuator stem Plate Stem can move the main lever (Figure 1) through the full range of motion and allow full valve stroke. While in the neutral position, the crosshead does not interact/interfere with the handwheel lever (Figure 1). While at the full open or at the full closed position, the crosshead would be located at the respective end of the slot in the handwheel lever.
For manual operation, the handwheel is turned, which turns the power screw and then allows the crosshead to move along the power screw and interact with the main lever through the handwheel lever. The crosshead will contact the handwheel lever at either end of the slot and move the valve to the desired location which in-turn, locks the valve in that position. During handwheel operation to take the valve closed, the actuator stem is drawn out thus compressing the actuator spring which results in a resistive force. It is important to note that once manual operation of the valve is initiated and the crosshead falls outside of the neutral position, air operation in the opposite direction is no longer achievable and air operation in desired direction may be impacted due to interference between the handwheel lever and crosshead. Specifically, if the action is taken to close the valve using the handwheel, once the valve is taken 25% closed the valve may not be taken open via air. There is also potential for interference between the handwheel lever and crosshead that would prevent the valve from being taken further closed via air.
Manual operation of the 1(2)AF005 valves with the handwheel has the potential to impact Operations ability to operate the valve remotely via air.
Actuation Methodology for 1(2)AF005A-H (Page 3 of 3)
Figure 1. Handwheel Lever and Main Lever Interface