W3F1-2025-0004, Entergy Operations, Inc - Response to Request for Additional Information – Steam Generator Tube Inspection Report for the 25th Refueling Inspection Performed During Operating Cycle 25 / Refuel 25

Entergy Operations, Inc - Response to Request for Additional Information – Steam Generator Tube Inspection Report for the 25th Refueling Inspection Performed During Operating Cycle 25 / Refuel 25

ML25042A396
Person / Time
Site:	Waterford
Issue date:	02/11/2025
From:	Couture P Entergy Operations
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
W3F1-2025-0004
Download: ML25042A396 (1)

Text

Phil Couture Senior Manager Fleet Regulatory Assurance - Licensing 601-368-5102

Entergy Operations, Inc., 1340 Echelon Parkway, Jackson, MS 39213 W3F1-2025-0004 TS 6.9.1.5 February 11, 2025 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001

Subject:

Response to Request for Additional Information -

Steam Generator Tube Inspection Report for the 25th Refueling Inspection Performed During Operating Cycle 25 / Refuel 25 Waterford Steam Electric Station, Unit 3 NRC Docket Nos. 50-382 Renewed Facility Operating License Nos. NPF-38 In accordance with Waterford Steam Electric Station, Unit 3 (WF3) Technical Specification 6.9.1.5, "Steam Generator Tube Inspection Report," Entergy Operations, Inc. (Entergy) submitted the Steam Generator Tube Inspection Report for the 25th Refueling Outage (Reference 1). Entergy received a Request for Additional Information (RAI) (Reference 2).

Response to the RAI is provided in the Enclosure.

This letter contains no new regulatory commitments. Should you have any questions or require additional information, please contact me at 601-368-5102.

Respectfully, Phil Couture PC/chm

W3F1-2025-0004 Page 2 of 2

Enclosure:

Response to Request for Additional Information

References:

1) Entergy letter to NRC, WF3, "Steam Generator Tube Inspection Report for the 25th RF Inspection Performed During Operating Cycle 25 /

Refuel 25," (ML24204A270), dated July 22, 2024

2) NRC Email to Entergy, WF3, "Request for Additional Information, Review of Steam Generator Tube Inspection Report for the 25th RF Inspection," (ML25017A282), dated January 17, 2025 cc:

NRC Region IV Regional Administrator NRC Senior Resident Inspector NRC Project Manager Designated State Official WF3 ANI Inspector

Enclosure W3F1-2025-0004 Response to Request for Additional Information

W3F1-2025-0004 Enclosure Page 1 of 4 TABLE OF CONTENTS

1.0 BACKGROUND

................................................................................................................. 2 2.0 REGULATORY BASIS....................................................................................................... 2 3.0 NRC REQUEST AND ENTERGY RESPONSE................................................................. 2 3.1 Request for Additional Information - 1........................................................................... 2 3.1.1 NRC Request.......................................................................................................... 2 3.1.2 Entergy Response................................................................................................... 2 3.2 Request for Additional Information - 2........................................................................... 3 3.2.1 NRC Request.......................................................................................................... 3 3.2.2 Entergy Response................................................................................................... 3

4.0 REFERENCES

................................................................................................................... 4

W3F1-2025-0004 Enclosure Page 2 of 4 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION

1.0 BACKGROUND

By letter dated July 22, 2024 (ML24204A270), Entergy Operations, Inc. (the licensee),

submitted information summarizing the results of the Fall 2023 steam generator (SG) inspections performed at Waterford Steam Electric Station, Unit 3 (WF3), during the 25th refueling outage (RFO25).

To complete its review of the inspection report, the NRC staff requests the following additional information:

2.0 REGULATORY BASIS WF3 Technical Specification (TS) 6.9.1.5, Steam Generator Tube Inspection Reports, requires Entergy Operations to submit a Tube Inspection Report to the NRC within 180 days after entry into MODE 4 following a steam generator inspection performed in accordance with TS 6.5.9, Steam Generator (SG) Program.

3.0 NRC REQUEST AND ENTERGY RESPONSE 3.1 Request for Additional Information - 1 3.1.1 NRC Request Based on review of the detection and sizing technique information provided in the RFO25 (Reference 1) and RFO21 report (Reference 3), it is the NRC staffs understanding that WF3 does not have a plant-representative broached tube support plate (TSP) wear calibration standard.

1. Please confirm whether the NRC staffs understanding is correct.

2. If the staffs understanding is correct, and the calibration standard wear scars used in RFO21 and RFO25 are at a different orientation or width compared to a TSP land, please discuss whether the difference(s) could result in bobbin coil under sizing of TSP wear depths. For example, could a wear flaw on a calibration standard of a given depth produce a larger amplitude signal compared to the same depth wear from a narrower TSP land?

3. If a plant-representative broached TSP wear calibration standard has not been used for past inspections, please discuss if use of that type of standard is being considered for future steam generator tube inspections.

3.1.2 Entergy Response

1. The NRC staffs understanding is correct that WF3 does not have a plant-representative (i.e., plant-specific) broached tube support plate wear calibration standard.

2. Note that this issue does not apply to WF3 as a 3-point fixed curve, rather than a calibration standard, was implemented at both the RFO21 and RFO25 inspections.

For inspections where a calibration standard is used any differences between the wear scars on the standard and actual wear in the tube has a potential to impact

W3F1-2025-0004 Enclosure Page 3 of 4 depth measurements. The variety of the actual wear lengths, widths, depths, shapes, orientations, number of land contacts that are impacted, taper angle/length/orientation, etc., is very large, and there is no practical way to make a calibration standard that will cover all possible wear morphologies that can transpire over the life of the steam generator.

However, the two main contributors to the magnitude of a wear signal are the volume of the tubing material missing and the depth of the wear, and a narrower TSP land is expected to have a negligible impact. Typical calibration standards have single wear scars that taper from zero to the max depth therefore returning conservative results of the wear depth(s). The presence of multiple wear scars at the same elevation in the tube would result in an overall conservative Bobbin sizing due to the higher amplitudes. Deep tapered wear or flat wear would also be sized conservatively.

3. At this time, WF3 does not have plans to utilize a plant-representative TSP wear calibration standard in the near future. The use of one will be considered for future inspections based on lead-times, cost, and effectiveness of the current sizing curve (curve created for the RFO 25 inspections).

3.2 Request for Additional Information - 2 3.2.1 NRC Request In the operational assessments performed in section 3.5 of the RFO25 report, ten Monte Carlo simulations were performed with 100,000 trials each, and the results of the ten simulations were averaged to calculate the probability of survival (POS).

1. Please discuss the range of POS results of the ten simulations.

2. Please discuss how the results of this calculation method might differ from performing one Monte Carlo simulation with 1,000,000 trials.

3.2.2 Entergy Response

1. The range of POS results for the ten simulations were as follows:

a. For the limiting SG AVB (Anti-Vibration Bar) Wear, the ranges were 0.9963 - 0.9970

b. For the limiting SG TSP Wear, Rows 1-2, the ranges were 0.9765 - 0.9781

c. For the limiting SG TSP Wear, Rows 3+, the ranges were 0.9951 - 0.9975

2. Performing the calculation with 1,000,000 trials would not provide any difference in the results.

For Monte Carlo simulations increasing the number of trials will increase the accuracy at the expense of increased simulation length. The standard process is to increase the number of trials (e.g., 1,000, 10,000, 100,000, etc.) until the results become stable with little variance between runs. Simulations of 100,000 trials are sufficiently accurate, needing only a single simulation where increasing trials even further will not provide a statistically different result. Running multiple simulations and determining the average is a defense-in-depth strategy to ensure the most favorable result is not used in the Operational Assessment (OA).

W3F1-2025-0004 Enclosure Page 4 of 4

4.0 REFERENCES

1.

Entergy letter to NRC, WF3, "180 Day Steam Generator Tube Inspection Report for the 21st Refueling Outage," (ML17325B762), November 21, 2017

2.

NRC Email to Entergy, WF3, "Request for Additional Information, Review of Steam Generator Tube Inspection Report for the 25th RF Inspection," (ML25017A282), dated January 17, 2025

3.

Entergy letter to NRC, WF3, "Steam Generator Tube Inspection Report for the 25th RF Inspection Performed During Operating Cycle 25 / Refuel 25," (ML24204A270), dated July 22, 2024