L-2023-023, Revised Steam Generator Tube Inspection Report
| ML23062A351 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 03/03/2023 |
| From: | Strand D NextEra Energy Seabrook |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| L-2023-023 | |
| Download: ML23062A351 (1) | |
Text
March 3, 2023 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Seabrook Station Docket No. 50-443
Subject:
Revised Steam Generator Tube Inspection Repmi L-2023-023
- 1. NextEra Energy Seabrook, LLC letter SBK-L-22054, "License Amendment Request 22-01, Application to Revise Technical Specifications to Adopt TSTF-577, 'Revised Frequencies for Steam Generator Tube Inspections'" June 9, 2022 (ML22160A581)
- 2. NRC Letter from Mr. Justin Poole, NRC Project Manager Seabrook to Mr. Bob Coffey, Executive Vice President, Nuclear Division and Chief Nuclear Officer, Seabrook Station, Unit No. 1 Issuance of Amendment No. 171 RE: Revision to Technical Specifications to Adopt TSTF-577, "Revised Frequencies for Steam Generator Tube Inspections" (EPID: L-2022-LLA-0087 dated December 5, 2022) (ML22287A157)
- 3. NextEra Energy Seabrook, LLC letter SBK-L-22036, "Seabrook Station Steam Generator Tube Inspection Report," April 25. 2022 (ML22115Al58)
In Reference 1, NextEra Energy Seabrook, LLC submitted License Amendment Request 22-01 to adopt TSTF-577, "Revised Frequencies for Steam Generator Tube Inspections." Section 2.1 of the Enclosure to License Amendment Request 22-01 stated that a Steam Generator Tube Inspection Repmi would be submitted within 30 days after implementation of the license amendment to meet revised Technical Specification 6.8.1.7 requirements.
In Reference 2, the NRC issued Amendment No. 171 to revise the "Steam Generator (SG)
Program" and the "Steam Generator Tube Inspection Repmi" Technical Specifications based on TSTF-577. License Amendment No. 171 was required to be implemented within 60 days of issuance.
The Enclosure contains the revised Steam Generator Tube Inspection Report that is updated from Reference 3 to satisfy revised Technical Specification 6.8.1.7 requirements.
NextEra Energy Seabrook, LLC, P.O. Box 300, Lafayette Road, Seabrook, NH 03874
United States Nuclear Regulatory Commission L-2023-005/Page 2 If you have any questions regarding this submittal, please contact Mr. Kenneth Mack, Licensing Manager at (561) 904-3635.
Sincerely, Dianne Strand General Manager Regulatory Affairs Enclosure cc:
NRC Region I Administrator NRC Project Manager NRC Senior Resident Inspector
ENCLOSURE
Seabrook Station OR21 Steam Generator Tube Inspection Report Updated to reflect revised reporting requirements of TSTF-577 Design and Operating Parameters:
L-2023-023 Seabrook Unit 1 is a Westinghouse 4-loop PWR with Model F steam generators. The SGs are U-tube heat exchangers with tube bundles fabricated using thermally-treated Alloy 600 tubing. Each SG contains 5,626 tubes arranged in 59 rows and 122 columns. The tubes have a square pitch arrangement, and nominal tube OD is 0.688" with a 0.040" nominal wall thickness. Internal supports include 8 horizontal tube support structures made of stainless steel where the lowest is a flow distribution baffle (FOB) with drilled holes. The other 7 structures are broached-hole, quatrefoil tube support plates (TSPs ).
There are no inspection ports at the uppermost TSPs. The U-bend region is supported by 3 sets of anti-vibration bars (AVBs ). Rows 1-10 of tubing in each SG were stress relieved in the U-bend region after bending.
The updated Steam Generator Tube Inspection Report for Seabrook Unit 1 is submitted for the inspection of the SGs during refueling outage 21 (hereafter referred to as the OR21 inspection or outage) per Technical Specification (TS) 6.8.1.7, and as discussed in Section 2.1 of the LAR application (Ref 1 ). The OR21 SG inspection was performed in accordance with TS 6.7.6.k. The Seabrook SG Program has no deviations from Mandatory or Needed ( shall) requirements of the EPRI SGMP Guidelines referenced by NEI 97-06 Rev 3. At unit shutdown for the OR21 inspection, the SGs had operated for approximately 27.37 EFPY since installation. This included operation for approximately 1.4 EFPY (16.8 EFPM) during the fuel cycle (cycle 21) leading up to the OR21 inspection. Nominal That is 621 deg F. Initial entry into Mode 4 following completion of the OR21 inspection was made on October 27, 2021. Seabrook's tube sub-populations with increased degradation susceptibility include ones with potential high residual stress, and the presence of ding or dent indications. Portions of tubing which are a few inches above the tubesheet, in the peripheral section of the bundle are also susceptible to wear due to foreign objects because of the relatively high velocity of the secondary-side fluid in this region. Acronyms used in this report are tabulated in Appendix A.
A. Scope of Inspections Performed on each SG The OR21 SG inspection is credited as the implementation outage for TSTF-577 Rev 1. The scope is characterized as 100% full-length enhanced probe exams 1. Since axial ODSCC indications were identified on tubes with dents at TSP intersections at the uppermost support plate in SG-B in OR20, the scope of SG exams in OR21 was also selected to inspect for this degradation mechanism per the requirements of Section 6.7.6.k.d.3 of site Technical Specifications. The OR21 inspection scope met the requirements of the Seabrook Unit 1 Technical Specifications, NEI 97-06 Rev 3 and its referenced EPRI SGMP Guidelines. Unless otherwise noted, the OR21 SG inspection scope on each SG is outlined in Section A of the original SG Tube Inspection Report (Ref 3).
B. NDE techniques utilized for tubes with increased degradation susceptibility This information is outlined in Section A of the original SG Tube Inspection Report (Ref 3) and is summarized in the Table below:
Susceptible population NOE Techniques used High stress tubes
+Point' probe Dings, Dents
+Point' probe, Array probe Peripheral tubes Array probe 1 The enhanced probe inspection method is described in the NRC Final Safety Evaluation for TSTF-577 Rev. 1 (NRC ADAMS Accession No. ML21098A188).
L-2023-023 C. For each degradation mechanism found:
Degradation mechanisms found during the OR21 inspection are provided in Section B of the original SG Tube Inspection Report (Ref 3).
- 1. The non-destructive examination (NDE) techniques utilized NOE techniques used for sizing the tube degradation mechanisms found in OR21 are in Table 1 b of Ref 3. NOE techniques used for detecting tube degradation are found in Table 1a of Ref 3.
- 2. Location, orientation (if linear), measured size (if available), and voltage response for each indication For the axial ODSCC degradation mechanisms found, the information requested is documented in Section D of Ref 3.
For the tube wear degradation mechanisms found, the location, orientation, measured size and voltage response for each indication are provided in Appendix C of Ref 3. This includes indications of tube wear at support structures that are less than 20% TW. Volumetric (wear) indications due to legacy maintenance equipment, TSP wear and foreign object wear were also stratified in Tables 3a, 3b and 3c of Ref 3, as supplemented by the Seabrook Station Response to RAl-4 to Ref 3 (
Reference:
ADAMS Accession No. ML22272A152).
- 3. A description of the condition monitoring assessment and results, including the margin to the tube integrity performance criteria and comparison with the margin predicted to exist at the inspection by the previous forward-looking tube integrity assessment Condition monitoring (CM) assessment and results are described in Sections G1 through G7 of Ref 3. Additional details of CM for the axial ODSCC degradation mechanisms found are located in Appendix B of Ref 3 and supplemented by the Seabrook Station Response to RAl-2 to Ref 3 (
Reference:
ADAMS Accession No. ML22272A152). The margin to the tube integrity performance criteria and comparison with the margin predicted to exist at the inspection by the previous forward-looking tube integrity assessment are summarized in the Table below for the wear degradation mechanisms found.
Degradation Mechanism Max depth CM limit Prior OA max proj'd
(%TW)
(%TW) depth (%TW)
AVB Wear 39 70.7 53.5 TSP Wear 30 52.2 51.3 Note 1 Foreign Object Wear 35 57.8 N/A Note2 Other Volumetric Wear 39 51 N/A Note3 Note 1: Based on OR19 forward-looking assessment since OR20 was a special, limited-scope inspection.
Note 2: There are no FOs at the location which exhibited the maximum % TW depth (R35C80 at 03H in SG-A).
The indication has not changed for several cycles; therefore, no growth is projected.
Note 3: Indication with max depth is attributed to sludge lance equipment used in the past. It has not changed for several cycles, and no growth is projected.
- 4. The number of tubes plugged during the inspection outage Two (2) tubes were plugged for axial ODSCC. Table 4 of Ref 3 provides further tube plugging details during the OR21 inspection outage.
No other tubes were plugged in OR21 for the remaining degradation mechanisms found.
L-2023-023 D. An analysis summary of the tube integrity conditions predicted to exist at the next scheduled inspection (the forward-looking tube integrity assessment) relative to the applicable performance criteria, including the analysis methodology, inputs, and results The forward-looking tube integrity assessment justified operation of the SGs until OR23, as supported by having completed 100% full-length enhanced probe exams in OR21. For existing SCC degradation mechanisms, the assessment used a fully probabilistic analysis (described in the SGMP Integrity Assessment Guidelines) through application of the Westinghouse (proprietary) Full Bundle Model software package. The analysis is the same for each SCC degradation mechanism; however, the specific inputs used for each mechanism may be different. The axial ODSCC degradation mechanisms at TSP and TTS locations are projected to meet the performance criteria until at least OR23.
Conservative growth rate projections of the AVB and TSP wear show that all structural and leakage criteria will continue to be satisfied until at least OR23. The foreign object wear evaluation performed in OR21 was for a 4.5 EFPY interval and does not threaten tube integrity until the next scheduled inspection. All existing mechanisms that were not found during the OR21 inspections do not pose a threat to tube integrity until they are inspected again and re-evaluated at OR23. The requirements for Condition Monitoring are projected to be satisfied over the next (2-cycle) inspection interval for all degradation mechanisms in all SGs. All existing and potential degradation mechanisms are predicted to meet the structural and leakage integrity performance criteria at OR23.
E. The number and percentage of tubes plugged to date, and the effective plugging percentage in each SG See response provided in Section F of the original SG Tube Inspection Report (Ref 3).
F. The results of any SG secondary side inspections The results of secondary side inspections are described in Section G8 of Ref 3 and supplemented by Seabrook Station's Response to RAl-1 to Ref 3 (
Reference:
ADAMS Accession No. ML22272A152). The inspection results for channel head components are described in Section G7 of Ref 3.
G. The primary to secondary leakage rate observed in each SG (if it is not practical to assign the leakage to an individual SG, the entire primary to secondary leakage should be conservatively assumed to be from one SG) during the cycle preceding the inspection which is the subject of the report See response provided in Section H of Ref 3.
H. The calculated accident induced leakage rate from the portion of the tubes below 15.21 inches from the top of the tubesheet for the most limiting accident in the most limiting SG.
In addition, if the calculated accident induced leakage rate from the most limiting accident is less than 2.49 times the maximum operational primary to secondary leakage rate, the report should describe how it was determined See response provided in Section I of Ref 3.
I.
The results of monitoring for tube axial displacement (slippage). If slippage is discovered, the implications of the discovery and corrective action shall be provided See response provided in Section J of Ref 3.
L-2023-023 Appendix A - Additional Information References to recent SG Tube Inspection Reports EOG Outage NRG ADAMS Accession No.
EOC-19 OR19 ML19109A214 EOC-20 OR20 ML20295A551 EOC-21 OR21 ML22115A158 Abbreviations and Acronyms:
AVB Anti Vibration Bar NSAL Nuclear Safety Advisory Letter BLG Bulge OA Operational Assessment CL Cold Leg OD Outside Diameter CM Condition Monitoring ODSCC OD Stress Corrosion Cracking DA Degradation Assessment OXP Over-expansion OBA Design Bases Accident Per Percent Through-Wall ONG Ding PLP Possible Loose Part ONT Dent POB Probability of Burst ECT Eddy Current Testing POL Probability of Leakage EFPM Effective Full Power Months PWSCC Primary Water SCC EFPY Effective Full Power Years SAi Single Axial Indication EOG End-Of-Cycle sec Stress Corrosion Cracking EPRI Electric Power Research Institute SG Steam Generator ETSS Exam Technique Spec Sheet SGMP SG Management Program FOB Flow Distribution Baffle SL Sludge lancing FO Foreign Object SSI Secondary-side inspection FOSAR Foreign object search & retrieval TS Tubesheet GPO (gpd)
Gallons per Day TSC Tube Sheet Cold GPM (gpm) Gallons per Minute TSH Tube Sheet Hot HL Hot Leg TSP Tube Support Plate MNT Maintenance Related TTS Top of Tube Sheet NOD No Degradation Detectable TW Through Wall NEI Nuclear Energy Institute UFSAR Updated Final Safety Analysis Rpt NOPD Normal operating pressure differential VOL Volumetric