L-2024-044, Revised Steam Generator Tube Inspection Reports

Revised Steam Generator Tube Inspection Reports

ML24079A176
Person / Time
Site:	Turkey Point
Issue date:	03/19/2024
From:	Catron S Florida Power & Light Co
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
L-2024-044
Download: ML24079A176 (1)

Text

FPL U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Re:

Turkey Point Nuclear Plant, Units 3 and 4 Docket Nos. 50-250 and 50-251 Subsequent Renewed Facility Operating Licenses DPR-31 and DPR-41 Revised Steam Generator Tube Inspection Reports

References:

March 19, 2024 L-2024-044 10 CFR 50.36

1.

Turkey Point Nuclear Generating Unit Nos. 3 and 4 - Issuance of Amendment Nos. 297 And 290 Regarding Conversion to Improved Standard Technical Specifications (EPID L-2021-LLl-0002),

September 27, 2023 (ADAMS Accession No. ML23234A192)

2.

Florida Power & Light Company letter L-2024-025, Notification of Improved Standard Technical Specifications (ITS) Implementation, February 22, 2024 (ADAMS Accession No. ML24054A022)

3.

Turkey Point, Unit 3 - Steam Generator Tube Inspection Report [TP3-32], (ADAMS Accession No. ML22126A104)

4.

Turkey Point Nuclear Generating Station, Unit 4 - U4R33 Steam Generator Tube Inspection Report, (ADAMS Accession No. ML22277A803)

In Reference 1, Florida Power & Light Company (FPL) received authorization to implement Improved Standard Technical Specifications (ITS) at Turkey Point Nuclear Plant (Turkey Point) Units 3 and 4.

Included within were revised steam generator (SG) tube inspection and reporting requirements modeled after Technical Specification Task Force Traveler (TSTF) 577-A, Revision 1, Revised Frequencies for Steam Generator Tube Inspections (ADAMS Accession No. ML21099A086). Per the implementation notes for TSTF-577-A, Revision 1, "a SG Tube Inspection Report satisfying the TSTF-577 revised requirements must be submitted within 30 days after implementation of the license amendment." In Reference 2, FPL notified the NRC of ITS implementation at Turkey Point effective February 19, 2024. to this letter contains the revised SG tube inspection report for Turkey Point Unit 3 PT3-32. contains the revised SG tube inspection report for Turkey Point Unit 4 PT 4-33. Enclosures 1 and 2 supplement the SG tube inspection reports for Turkey Point Units 3 and 4 dated May 6, 2022 and October 4, 2022, respectively (Reference 3, Reference 4).

Should you have any questions regarding this submission, please contact Mr. Kenneth Mack, Fleet Licensing Manager, at 561-904-3635.

Steve Catr n Licensing a tt Regulatory Compliance Director - Nuclear Fleet Florida Power & Light Company Florida Power & Light Company 15340 Endeavor Dr. Jupiter, FL, 33478

Enclosures:

cc:

USNRC Regional Administrator, Region II USNRC Project Manager, Turkey Point Nuclear Generating Station USNRC Senior Resident Inspector, Turkey Point Nuclear Generating Station Ms. Cindy Becker, Florida Department of Health L-2024-044 Page 2 of 2

Turkey Point Nuclear Plant Docket Nos. 50-250 and 50-251 Turkey Point Unit 3, Cycle TP3-32, Steam Generator Tube Inspection Report (Updated to Reflect Revised Reporting Requirements of TSTF-577-A, Revision 1)

(6 pages follow)

L-2024-044

Turkey Point Unit 3 Docket No. 50-250 TP3-32 Steam Generator Tube Inspection Report Updated per revised reporting requirements of TSTF-577-A, Rev 1 Design and Operating Parameters:

L-2024-044 Page 1 of 6 Turkey Point Unit 3 is a Westinghouse 3-loop PWR with Model 44F steam generators (SGs). The SGs are U-tube heat exchangers with tube bundles fabricated using thermally treated Alloy 600 tubing. Each SG contains 3,214 tubes arranged in 45 rows and 92 columns, in a square-pitch configuration. Nominal tube OD is 0.875" with a 0.050" nominal wall thickness. Each SG tube bundle is supported by one drilled-hole flow distribution baffle (FOB) and 6 quatrefoil, broached-hole tube support plates (TSPs) all fabricated from stainless steel. Two (2) sets of anti-vibration bars (AVBs) in the U-bends also provide tube bundle support (AV1/4, AV2/3). Rows 1-8 of tubing in each SG were stress relieved in the U-bend region after bending. A schematic of a typical Model 44F SG is shown in Figure 1 of ADAMS Accession No. ML23095A171.

This updated SG Tube Inspection Report for Turkey Point Unit 3 is submitted for the inspection of the SGs during refueling outage 32 (hereafter referred to as the TP3-32 inspection or outage). In its conversion to the Improved Standard Technical Specifications (ITS), Turkey Point has incorporated "Revised Frequencies for Steam Generator Tube Inspections" (TSTF-577-A Rev 1 ). The updated SG Tube Inspection Report is completed per section 5.6.5 of the Turkey Point Technical Specifications (License Amendments 297 and 290) and meets the reporting requirements for implementing TSTF-577. The inspection in TP3-32 was performed in accordance with Technical Specification 5.5.6 and was the initial inspection (implementation outage) for TSTF-577. At unit shutdown for the TP3-32 inspection, the SGs had operated for approximately 31.5 EFPY since installation. Nominal That during the last cycle was 611 °F. Initial entry into Mode 4 following completion of the TP3-32 inspection was made on November 10, 2021. A list of acronyms used in this report is provided in Appendix A 1.

A. Scope of Inspections Performed on each SG Unless otherwise noted, the TP3-32 SG inspection scope (primary, secondary) on each SG is outlined in Section A of the original SG Tube Inspection Report (Ref 3). The scope is characterized as 100%

full-length bobbin probe exams along with inspection of targeted areas having tubes with increased degradation susceptibility with an enhanced probe. The TP3-32 inspection scope was selected to meet the requirements of plant Technical Specifications, NEI 97-06 Rev 3 and its referenced EPRI SGMP Guidelines. The TP3-32 SG inspection is credited as the implementation outage for TSTF-577. The scope meets the requirements of section 5.5.6.d.2 of the Turkey Point Technical Specifications to "inspect 100% of the tubes in each SG at least every 54 effective full power months".

Scope Expansion: Expansion of the inspection scope was conducted in TP3-32 due to an axial ODSCC indication identified in the U-bend of a low row tube (R 1 C 13) in SG-3A. (This is described in section 8 of Ref 3.) Since the TP3-32 scope did not utilize 100% full-length enhanced probes, a special inspection of the low row U-bends in each SG was conducted1 in TP3-33 as required by section 5.5.6.d.3 of Technical Specifications.

1 Ref. ADAMS Accession No. ML23299A122 for the TP3-33 SG Tube Inspection Report.

Turkey Point Unit 3 Docket No. 50-250 B. NDE techniques utilized for tubes with increased degradation susceptibility L-2024-044 Page 2 of 6 This information is outlined in Section A of the original TP3-32 SG Tube Inspection Report (Ref 3) and is summarized in the Table below:

Susceptible population NOE Techniques High stress tubes

+Point' HL tubesheet program Array Dings, Dents

+Point', Array Peripheral tubes Array Low row U-bends

+Point' Bulges, Over-expansions Array C. For each degradation mechanism found:

Degradation mechanisms found during the TP3-32 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 TP3-32 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 degradation mechanisms found in TP3-32 (low row U-bend axial ODSCC, wear), this information is described in Section D of Ref 3. For tube wear degradation, the location, orientation, measured size, and voltage response for each indication are provided in Appendix B of Ref 3. This includes tube wear indications at support structures that are less than 20%TW.

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 results for the TP3-32 inspection are described in sections G.1 and G.2 of Ref 3 for all degradation mechanisms found. The axial ODSCC and wear indications were evaluated against CM screening charts and fell below the limits for burst and leakage. The prior inspection was in TP3-29. The previous forward-looking tube integrity assessment (OA) was revised at the TP3-31 outage to extend the inspection interval from 2 cycles to 3 cycles via an exigent license amendment (Ref. ADAMS Accession No. ML20104B527). A comparison of the worst-case tube predictions for the PT3-32 inspection to the actual detected degradation depths shows the revised 3-cycle OA wear depths conservatively predicted the actual best-estimate wear depths for the deepest indications as well as the upper 95/50 wear depths. This is summarized in the Table below for the wear degradation mechanisms.

Turkey Point Unit 3 Docket No. 50-250 Degradation Mechanism AVB wear TSP wear (broached)

TSP wear (edge)

FOB wear Volumetric wear (in freespan)

TP3-32 max NOE Previous OA max proj'd depth (%TW) 95/50 depth (% TW) 48 60.5 15 57.5 19 65.5 14 Note 2 53.6 23 N/A Note 1 Note 1: Historical review shows that freespan volumetric is not an active mechanism.

Note 2: Max depth was 14%, not 17% as previously reported in section G.2 of Ref 3.

L-2024-044 Page 3 of 6 EOC structural limit (%TW) 64.9 66.6 66.6 71.4 N/A Note 1 For benchmarking the TP3-32 axial ODSCC indication in the low-row U-bend, the most relevant analysis case from the revised 3-cycle OA for comparing with the TP3-32 NOE results, is the case for the +Point' exam for the presence of axial ODSCC at dings/dents

>5 volts. Results show that the probabilistic OA model was conservative for the number and depths of sec indications. Therefore, the previous OA methods and input assumptions for axial ODSCC were confirmed to remain acceptable.

The degradation mechanisms observed during the subsequent TP3-33 inspection (for axial ODSCC, reported in ADAMS Accession No. ML23299A122) were confirmed to be bounded by the TP3-32 OA, and the tube integrity criteria were not challenged by the TP3-33 CM inspection results.

4. The number of tubes plugged during the inspection outage Five (5) tubes were plugged during the TP3-32 inspection outage. Table 2 of Ref 3 provides the degradation mechanism attributed to each plugged tube.

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 A deterministic forward-looking tube integrity assessment (OA) was completed for the TP3-32 results for each wear degradation mechanism based on site-specific structural limits, degradation growth rates, predicted burst pressures and accident-induced leakage. Since the scope of the TP3-33 exam was specific for potential stress corrosion cracking (SCC) in the U-bend region, the TP3-3~ OA was updated for existing wear. Using a 3-cycle inspection interval in the assessment, the tube integrity conditions predicted to exist at the next scheduled inspection (TP3-35) is summarized in the Table below. Note: The TP3-33 recalculated OA projections were bounded by (lower than) the values calculated at TP3-32 for each mechanism.

Degradation Mechanism TP3-32 NOE max depth TP3-32 OA EOC structural returned to svc (% TW) projections (% TW) limit (%TW)

AVB wear 36 59.6 64.9 TSP wear (broached) 15 57.3 66.6 TSP wear (edge) 19 47.2 66.6 FOB wear 14 57.2 71.4 Volumetric freespan wear Note 1 N/A N/A N/A Note 1: Tube with volumetric freespan wear was removed from service in TP3-32.

Turkey Point Unit 3 Docket No. 50-250 L-2024-044 Page 4 of 6 A probabilistic forward-looking tube integrity assessment (OA) was completed at the TP3-32 inspection for the axial ODSCC degradation mechanism detected on tube R1C13 in the low-row U-bend region of SG-A. Axial ODSCC was classified as an existing mechanism for the low-row U-bends after the TP3-32 exams. Since a re-inspection was required per section 5.5.6.d.3 of Technical Specifications after one cycle, the TP3-32 OA calculated the results after 1-cycle and 3-cycles of operation, to be applied depending on re-inspection results of TP3-33. The input distributions of the updated (Covid skip) 3-cycle OA (ADAMS Accession No. ML20098F341) were used in the TP3-32 OA with no significant change made, given the excellent benchmark achieved with the CM NOE results of TP3-32. The key parameters/input distributions for probability of detection (POD), growth rate, structural length, and Weibull initiation function remain unchanged.

The POD used in the EPRI feasibility study was used in the OA based on good industry cracking experience. The "typical" default growth rates in the SGMP Integrity Assessment Guidelines were used in the model since they provide reasonable conservative estimates.

Results of the TP3-32 OA (probabilistic forward-looking tube integrity assessment) predicted zero (0) detected indications of axial U-bend ODSCC with a POB close to zero (0), meeting the structural and leakage performance criteria for a 1-cycle operating interval. The 3-cycle OA also predicted excellent results: one detected indication, max NOE depth -61 % and POB < 2%.

At the TP3-33 inspection, CM results confirmed no SCC indications (Ref. ADAMS Accession No. ML23299A122), validating the results of the 1-cycle probabilistic model used in TP3-32. The input distributions of TP3-32 were used in the TP3-33 OA model and updated with TP3-33 CM results.

The updated (TP3-33) OA model was re-run for both 1-cycle and 3-cycle operation with results (tabulated below) that are similar to the ones reported by the TP3-32 probabilistic OA.

Operating Period Note 1 No. of detected NOE depth (best POB at 3xNOPD indication at EOC estim.) at EOC (%TW) atEOC 1-cycle (thru EOC-32) 0 39.4 0.0003 3-cycles (thru EOC-34) 1 59.1 0.0117 Note 1: No sec was observed at TP3-33 (EOC-32). 100% enhanced probe exams are scheduled at TP3-35.

In summary, the tube integrity assessment results justify operation of the SGs for existing and potential mechanisms through TP3-35. In all cases, the 95/50 leak rate was negligible and the POB will not exceed the structural integrity performance criteria. Therefore, the margin requirements for both burst and leakage integrity satisfy the NEI 97-06 acceptance criteria until the next inspection in TP3-35.

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 G.4 of Ref 3. The inspection results for channel head components are described in Section G.3 of Ref 3.

Turkey Point Unit 3 Docket No. 50-250 L-2024-044 Page 5 of 6 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 18.11 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 1.82 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 Slippage monitoring was conducted during the 100% SG tube inspection in TP3-32. See response provided in Section J of Ref 3.

Turkey Point Unit 3 Docket No. 50-250 L-2024-044 Page 6 of 6 APPPENDIX A1 -Additional Information Abbreviations and Acronyms:

ARC Alternate Repair Criteria NEI Nuclear Energy Institute AVB Anti Vibration Bar OA Operational Assessment (forward-BAC Baffle plate cold looking tube integrity assessment)

BAH Baffle plate hot OD Outside Diameter BLG Bulge ODSCC OD Stress Corrosion cracking CL Cold Leg OXP Over-expansion CM Condition Monitoring POB Probability of burst ONG Ding SAi Single Axial Indication ONT Dent sec Stress Corrosion Cracking ECT Eddy Current Testing SG Steam Generator EFPY Effective Full Power Years SGMP SG Management Program EPRI Electric Power Research Institute TS Tubesheet FOB Flow Distribution Baffle TSP Tube Support Plate FO Foreign Object TTS Top of Tube Sheet HL Hot Leg TW Through Wall ISPT In-Situ Pressure Test

Turkey Point Nuclear Plant Docket Nos. 50-250 and 50-251 Turkey Point Unit 4, TP4-33, Steam Generator Tube Inspection Report (Updated to Reflect Revised Reporting Requirements of TSTF-577-A, Revision 1)

(6 pages follow)

L-2024-044

Turkey Point Unit 4 Docket No. 50-251 TP4-33 Steam Generator Tube Inspection Report Updated per revised reporting requirements of TSTF-577-A, Rev 1 Design and Operating Parameters:

L-2024-044 Page 1 of 6 Turkey Point Unit 4 is a Westinghouse 3-loop PWR with Model 44F steam generators (SGs). The SGs are U-tube heat exchangers with tube bundles fabricated using thermally treated Alloy 600 tubing. Each SG contains 3,214 tubes arranged in 45 rows and 92 columns, in a square-pitch configuration. Nominal tube OD is 0.875" with a 0.050" nominal wall thickness. Each SG tube bundle is supported by one drilled-hole flow distribution baffle (FOB) and 6 quatrefoil, broached-hole tube support plates (TSPs) all fabricated from stainless steel. Two (2) sets of anti-vibration bars (AVBs) in the U-bends also provide tube bundle support (AV1 /4, AV2/3). Rows 1-8 of tubing in each SG were stress relieved in the U-bend region after bending. A schematic of a typical Model 44F SG is shown in Figure 1 of ADAMS Accession No. ML23095A171.

This updated SG Tube Inspection Report for Turkey Point Unit 4 is submitted for the inspection of the SGs during refueling outage 33 (hereafter referred to as the TP4-33 inspection or outage). In its conversion to the Improved Standard Technical Specifications (ITS), Turkey Point has incorporated "Revised Frequencies for Steam Generator Tube Inspections" (TSTF-577-A Rev 1 ). The updated SG Tube Inspection Report is completed per section 5.6.5 of the Turkey Point Technical Specifications (License Amendments 297 and 290) and meets the reporting requirements for implementing TSTF-577. The inspection in TP4-33 was performed in accordance with Technical Specification 5.5.6 and was the initial inspection (implementation outage) for TSTF-577. At unit shutdown for the TP4-33 inspection, the SGs had operated for approximately 31.27 EFPY since installation. Nominal That during the last cycle was 610 °F. Initial entry into Mode 4 following completion of the TP4-33 inspection was made on April 7, 2022. A list of acronyms used in this report is provided in Appendix A2.

A. Scope of Inspections Performed on each SG Unless otherwise noted, the TP4-33 SG inspection scope (primary, secondary) on each SG is outlined in Section A of the original SG Tube Inspection Report (Ref 4). The scope is characterized as 100%

full-length enhanced probe exams. The TP4-33 inspection scope was selected to meet the requirements of plant Technical Specifications, NEI 97-06 Rev 3 and its referenced EPRI SGMP Guidelines. The TP4-33 SG inspection is credited as the implementation outage for TSTF-577. The scope meets the requirements of section 5.5.6.d.2 of the Turkey Point Technical Specifications to "inspect 100% of the tubes in each SG at least every 54 effective full power months".

Scope Expansion: Since the base scope exams included a 100% full-length inspection of all tubes in each SG with an enhanced probe, expansion of the inspection scope was not required when a single axially-oriented, crack-like ODSCC indication (SAi) was identified in the U-bend of a tube (R9C80) in SG-C.

Turkey Point Unit 4 Docket No. 50-251 B. NDE techniques utilized for tubes with increased degradation susceptibility L-2024-044 Page 2 of 6 This information is outlined in Section A of the original TP4-33 SG Tube Inspection Report (Ref 4) and is summarized in the Table below:

Susceptible population NOE Techniques High stress tubes

+Point' HL tubesheet program Array Dings, Dents

+Point', Array Peripheral tubes Array Low row U-bends

+Point' Bulges, Over-expansions Array

Turkey Point Unit 4 Docket No. 50-251 C. For each degradation mechanism found:

L-2024-044 Page 3 of 6 Degradation mechanisms found during the TP4-33 inspection are provided in Section B of the original SG Tube Inspection Report (Ref 4).

1. The non-destructive examination (NOE) techniques utilized NOE techniques used for sizing the tube degradation mechanisms found in TP4-33 are in Table 1 b of Ref 4. NOE techniques used for detecting tube degradation are found in Table 1a of Ref 4.

2. Location, orientation (if linear), measured size (if available), and voltage response for each indication For degradation mechanisms found in TP4-33 (U-bend axial ODSCC, wear), this information is described in Section D of Ref 4. For tube wear degradation, the location, orientation, measured size, and voltage response for each indication are provided in Appendix B of Ref

4. This includes tube wear indications at support structures that are less than 20% TW.

Corrections to the TSP wear indications in SG-C were also submitted for TP4-33 (Ref.

ADAMS Accession No. ML23089A051).

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 for the TP4-33 inspection are described in Sections G.1 through G.4 of Ref 4 for all degradation mechanisms found. The previous inspection was conducted in TP4-31. 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 (OA) are summarized in the Table below for the wear degradation mechanisms. All detected tube indications were smaller than the critical sizes for burst and therefore posed no challenges to tube structural integrity. No indications were required to be in-situ pressure tested to demonstrate that CM was satisfied.

Degradation TP4-33 Max NOE Previous OA max proj'd EOC structural limit Mechanism depth (%TW) 95/50 depth (% TW)

(%TW)

AVB wear 31 50.5 64.9 TSP wear (broached) 16 Note 2 50.8 66.6 TSP wear (edge) 20 35.2 66.6 FOB wear 12 45.1 71.4 FO wear at TTS 39 N/A Note 1 N/A Note 1: There were no FOs reported at locations with FO wear. Therefore, no growth is projected since there is no source of future wear on the tubes.

Note 2: Max depth was 16%, not 17% as previously reported in section G.2 of Ref 4.

4. The number of tubes plugged during the inspection outage Seven (7) tubes were plugged during the TP4-33 inspection outage. Table 2 of Ref 4 provides the degradation mechanism attributed to each plugged tube.

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

Turkey Point Unit 4 Docket No. 50-251 L-2024-044 Page 4 of 6 A deterministic forward-looking tube integrity assessment (OA) was completed for each wear degradation mechanism. The inspection interval used in the assessment is 2 cycles. The tube integrity conditions predicted to exist at the next scheduled inspection (TP4-35) is summarized in the Table below.

Degradation TP4-33 NOE max depth TP4-33 OA EOC structural Mechanism returned to svc (% TW) projections (% TW) limit (%TW)

AVB wear 25 41.1 64.9 TSP wear (broached) 16 43.9 66.6 TSP wear (edge) 20 39.4 66.6 FOB wear 12 45.6 71.4 FO wear at TTS Note 1 25 N/A N/A Note 1: There were no FOs reported at locations with FO wear. Therefore, no growth is projected since there is no source of future wear on the tubes.

A probabilistic forward-looking tube integrity assessment (OA) was completed for the axial ODSCC degradation mechanism detected on tube R9C80 in the U-bend region of SG-C. The probabilistic OA used a Monte Carlo simulation model for axial ODSCC in the U-bend and was benchmarked to outage results.

The key input parameters for each OA input distribution (probability of detection (POD), growth rate, structural length, and Weibull initiation function) were modified for the Turkey Point Unit 4 data. A reasonable conservative fit to a dataset for ETSS 10413.2 was used to define the POD for array probe inspections of the U-bend region. The "typical" default sec growth rates given in the SGMP Integrity Assessment Guidelines give reasonable conservative estimates of industry experience for axial ODSCC data, as demonstrated in the EPRI feasibility study on A600TT plants. Given the limited experience with axial ODSCC in LI-bends, the "bounding" default growth rate curve is used in the TP4-33 OA to ensure a conservative benchmark of the NOE results. The axial structural length distribution was developed for SCC in the U-bend region from existing distribution for other locations (ODSCC at TSP, TTS). The upper 95th percentile on sec length is used which is about four times longer than the structural length of the detected axial ODSCC indication in R9C80.

The Weibull initiation function was varied until a good benchmark was achieved, which compared favorably with the actual TP4-33 inspection results. The model is calibrated to produce at least two initiations at the prior inspection (TP4-31) but with no detections calculated on average. After the current 2-cycle inspection interval, the OA predicts Oto 1 axial ODSCC detections, a maximum NOE depth of 37% TW and POB of 0.25% with the array probe at TP4-35. Therefore, the margin requirements for both burst and leakage integrity satisfies the NEI 97-06 acceptance criteria for a 2-cycle inspection interval.

In summary, the tube integrity assessment results justify operation of the SGs for the current 2-cycle inspection interval through TP4-35, and as supported by having completed 100% full-length enhanced probe exams in TP4-33. The projected limiting indication sizes through TP4-35 are calculated to meet, with adequate margins, the structural integrity performance criterion for the tubes. The projected leak rates associated with the observed degradation were determined to be negligible. Therefore, the tube integrity requirements of NEI 97-06 Rev 3 will be met for the planned operating interval until the next tube inspection.

Turkey Point Unit 4 Docket No. 50-251 L-2024-044 Page 5 of 6 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 4).

F. The results of any SG secondary side inspections The results of secondary side inspections are described in Section G.6 of Ref 4. The inspection results for channel head components are described in Section G.5 of Ref 4.

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 4.

H. The calculated accident induced leakage rate from the portion of the tubes below 18.11 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 1.82 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 4.

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 4.

Turkey Point Unit 4 Docket No. 50-251 L-2024-044 Page 6 of 6 APPPENDIX A2 - Additional Information Abbreviations and Acronyms:

ARC Alternate Repair Criteria NEI Nuclear Energy Institute AVB Anti Vibration Bar OA Operational Assessment (forward-BAC Baffle plate cold looking tube integrity assessment)

BAH Baffle plate hot OD Outside Diameter BLG Bulge ODSCC OD Stress Corrosion cracking CL Cold Leg OXP Over-expansion CM Condition Monitoring POB Probability of burst ONG Ding SAi Single Axial Indication ONT Dent sec Stress Corrosion Cracking ECT Eddy Current Testing SG Steam Generator EFPY Effective Full Power Years SGMP SG Management Program EPRI Electric Power Research Institute TS Tubesheet FOB Flow Distribution Baffle TSP Tube Support Plate FO Foreign Object TTS Top of Tube Sheet HL Hot Leg TW Through Wall ISPT In-Situ Pressure Test