AEP-NRC-2024-77, U2C28 Steam Generator Tube Inspection Report

U2C28 Steam Generator Tube Inspection Report

ML24295A135
Person / Time
Site:	Cook
Issue date:	10/21/2024
From:	Scarpello M Indiana Michigan Power Co
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
AEP-NRC-2024-77
Download: ML24295A135 (1)

Text

INDIANJl MICHIGAN POW/ER" An MP Company BOUNDLESS ENERGY-October 21, 2024 Docket No.: 50-316 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Donald C. Cook Nuclear Plant Unit 2 U2C28 Steam Generator Tube Inspection Report Indiana Michigan Power Cook Nuclear Plant One Cook Place Bridgman, Ml 49106 indianamichiganpower.com AEP-NRC-2024-77 10 CFR 50.4 Technical Specification (TS) 5.6. 7 of Appendix A, to the Donald C. Cook Nuclear Plant (CNP) Unit 2 Operating License requires a report to be submitted within 180 days after initial entry into Mode 4 following the completion of an inspection performed in accordance with TS 5.5. 7, Steam Generator (SG) Program. Such an inspection was completed during the U2C28 refueling outage, following which CNP Unit 2 entered Mode 4 on April 27, 2024. This report details specific attributes of the inspection in accordance with TS 5.6. 7. Consistent with these requirements, Indiana Michigan Power Company, the licensee for CNP Unit 2, is submitting the Cook Nuclear Plant U2C28 Steam Generator Tube Inspection Report as an enclosure to this letter.

There are no new regulatory commitments made in this submittal. Should you have any questions, please contact me at (269) 466-2649.

Sincerely, iwt.0,a,-&

Michael K. Scarpello Regulatory Affairs Director BMC/sjh

Enclosure:

Cook Nuclear Plant U2C28 Steam Generator Tube Inspection Report c:

EGLE - RMD/RPS J. B. Giessner - NRC Region Ill NRC Resident Inspector N. Quilico - MPSC R. M. Sistevaris - AEP Ft. Wayne, w/o enclosures S. P. Wall - NRC Washington, D.C.

A. J. Williamson - AEP Ft. Wayne, w/o enclosures

ENCLOSURE TO AEP-NRC-2024-77 Cook Nuclear Plant U2C28 Steam Generator Tube Inspection Report

Cook Nuclear Plant U2C28 Steam Generator Tube Inspection Report Page 1 of 7

1. Design and Operating Parameters Table 1: Steam Generator (SG) Design and Operating Parameters SG Model Westinghouse Model 54F (also referred to as 51F)

Tube Material Alloy 690 thermally treated Number of SGs per Unit 4

Number of Tubes 3592 tubes per SG Nominal Tube Diameter / Wall Thickness 0.875 inches / 0.050 inches Support Plates Broached Quatrefoil ASME SA-240 Type 405 stainless steel Last Inspection U2C23 (Fall 2016)

Effective Full Power Months (EFPM) Since Last Inspection 78.3 EFPM Cumulative EFPM of Steam Generators 321.8 EFPM (at start of U2C28)

Mode 4 Entry Date 4/27/2024 Observed Primary-to-Secondary Leak Rate No primary-to-secondary leakage detected THOT During the Prior Inspection Period 606.4 °F (Normal Operating Temperature) 650 °F (Design Temperature)

Loose Parts Strainer A single basket type strainer is installed in the suction line to each main feed pump Tube Sub-Populations with Increased Degradation Susceptibility Tubes near periphery and no-tube lane (increased susceptibility to foreign object wear)

Deviations from Steam Generator Management Program (SGMP) Guidelines Since the Last Inspection Secondary Water Chemistry Guidelines, Rev. 8:

Deviation due to not meeting the 2018 implementation date. Guidelines were fully implemented in 2019.

Cook Nuclear Plant U2C28 Steam Generator Tube Inspection Report Page 2 of 7 Table 1: Steam Generator (SG) Design and Operating Parameters Steam Generator Schematic:

Cook Nuclear Plant U2C28 Steam Generator Tube Inspection Report Page 3 of 7

2. Scope of Inspections Inspections performed on all four SGs during the U2C28 refueling outage included:

100% eddy current testing (ECT) of all in-service tubes Visual inspection of channel head interior surfaces and all installed tube plugs Visual inspection of secondary side top-of-tubesheet region Additionally, visual inspections were performed inside the steam domes of SG 22 and SG 23.

No scope expansions were required.

3. Nondestructive Examination (NDE) Techniques Utilized for Tubes with Increased Degradation Susceptibility In all four SGs, the outer tubes around the periphery and no-tube lanes were visually inspected at the top-of-tubesheet (TTS) region.

In all four SGs, a sample of the TTS region was inspected with a rotating pancake coil (RPC) probe. The sample included a band around the periphery and no-tube lane (approximately four tubes deep). The extent of examination encompassed three inches below TTS to three inches above TTS.

4. NDE Techniques Utilized for Degradation Mechanisms Found The only degradation mechanism detected was support wear. Support wear was found at anti-vibration bars (AVBs), tube support plates (TSPs), and the flow distribution baffle (FDB). Table 2 lists the NDE technique and corresponding Examination Technique Specification Sheet (ETSS) utilized for each degradation mechanism found.

Table 2: NDE Techniques Degradation Mechanism Detection Technique Sizing Technique Support Wear - AVB Bobbin ETSS I96041.1 Bobbin ETSS 96004.1 Support Wear - TSP Bobbin ETSS I96043.4 Bobbin ETSS 96004.1 Support Wear - FDB Bobbin ETSS I96043.4 Bobbin ETSS 96004.1

5. Degradation Indications Table 3 shows the total number of support wear indications reported by bobbin probe. Additional investigation with an RPC probe determined 36 of the TSP wear indications contained multi-land wear. Each indication 20% through-wall (TW) or greater is listed in Table 4.

Table 3: Number of Support Wear Indications SG AVB Wear TSP Wear FDB Wear Maximum % TW 21 0

16 0

20 22 2

3 0

12 23 1

115 1

22 24 0

27 0

17

Cook Nuclear Plant U2C28 Steam Generator Tube Inspection Report Page 4 of 7 Table 4: Indications 20% TW SG Tube (Row-Col)

Elevation (TSP +/- inches)

Flaw Type

% TW Bobbin Voltage (V) 21 6-53 06H -0.67 TSP wear 20 0.34 23 1-25 05C TSP wear 22 0.39 23 1-58 06C TSP wear 20 0.34

6. Condition Monitoring Assessment All indications found during the U2C28 inspection satisfied the condition monitoring (CM) requirements for structural integrity and accident induced leakage integrity. No in-situ pressure testing was required.

Table 5 summarizes each limiting flaw depth observed during U2C28 compared to the applicable CM limit as well as the flaw depth projected in the previous operational assessment.

Table 5: Condition Monitoring Results Degradation Mechanism Maximum U2C28 Flaw Depth (% TW)

Condition Monitoring Limit (% TW)

Projected U2C28 Flaw Depth (% TW)

AVB Wear 17 46.1 31.8 TSP Wear 22 42.9 30.8 FDB Wear 13 42.9 not included Condition Monitoring for AVB Wear The CM limit for a 0.8 inch axial thinning condition applicable to AVB wear is 46.1% TW using the NDE technique uncertainties for ETSS 96004.1 at 4350 psi. The largest AVB wear flaw reported during U2C28 was 17% TW. The longest measured length was 0.4 inches. Therefore, the structural integrity performance criterion was satisfied.

For these volumetric wear flaws with an axial length greater than 0.25 inches and pressure-only loading condition, tube burst and ligament tearing (i.e., pop-through) are coincident. Therefore, the accident-induced leakage performance criterion was also satisfied.

Condition Monitoring for TSP and FDB Wear The TSP has a nominal design thickness of 1.125 inches. The FDB has a nominal design thickness of 0.75 inches. The CM limit for a 1.125 inch uniform thinning condition is 42.9% TW using the NDE technique uncertainties for ETSS 96004.1 at 4350 psi. The largest TSP wear flaw reported during U2C28 was 22% TW.

The largest FDB wear flaw reported during U2C28 was 13% TW. Therefore, the structural integrity performance criterion was satisfied for both TSP and FDB wear.

All TSP and FDB wear reported at U2C28 was conservatively evaluated as flat wear. Any locations with multi-land wear were conservatively evaluated using the combined bobbin indication depth.

For these volumetric wear flaws with pressure-only loading condition, tube burst and ligament tearing (i.e.,

pop-through) are coincident. Therefore, the accident-induced leakage performance criterion was also satisfied.

7. Number of Tubes Plugged During the Inspection Outage No tubes were plugged during U2C28.

Cook Nuclear Plant U2C28 Steam Generator Tube Inspection Report Page 5 of 7

8. Repair Methods Utilized No tube repairs were completed during U2C28.

9. Operational Assessment An operational assessment (OA) was completed to evaluate continued operation through the end of operating cycle 32, which coincides with the start of the U2C33 refueling outage. The OA evaluated all existing degradation mechanisms using simplified deterministic calculations and a bounding operating period of 7.5 effective full power years (EFPY). Structural limits used in the OA were conservatively based on an operating pressure differential of 1600 psid.

Table 6 summarizes the OA results for each degradation mechanism, including the largest returned-to-service (RTS) flaw. The OA illustrates reasonable assurance that tube integrity will be maintained until the U2C33 refueling outage.

Table 6: Operational Assessment Summary Degradation Mechanism Growth Rate

(% TW/EFPY)

Largest RTS Flaw (% TW)

U2C33 Projection

(% TW)

Structural Limit

(% TW)

AVB Wear 0.97 17 33.9 45.5 TSP/FDB Wear 1.11 22 39.9 43.6 Operational Assessment for AVB wear A growth rate evaluation was completed for AVB wear. Since only three data points exist, a log-normal distribution fit was utilized. The upper 95th percentile growth rate from the log-normal distribution fit was 0.90% TW/EFPY. For the OA projection, the more conservative growth rate of 0.97% TW/EFPY from the previous OA was used.

The largest AVB wear flaw in U2C28 measured 17% TW using the bobbin sizing technique ETSS 96004.1. The maximum length of an AVB wear flaw was 0.4 inches. For the structural limit used in the OA, a conservative length of 0.8 inches was used.

Adjusting for NDE uncertainties, the worst-case AVB wear flaw at U2C33 is projected to be 33.9% TW, which is less than the 45.5% TW structural limit.

Operational Assessment for TSP and FDB Wear FDB wear is accounted for and evaluated as part of the OA for TSP wear. FDB wear is bounded by TSP wear due to the lower thickness of the FDB and the lower maximum wear depth observed.

A growth rate evaluation was completed by comparing to indication depths reported during U2C23. The upper 95th percentile growth rate was determined to be 0.735% TW/EFPY. The maximum growth rate was determined to be 1.08% TW/EFPY. For the OA projection, the more conservative growth rate of 1.11%

TW/EFPY from the previous OA was used.

The largest TSP wear flaw in U2C28 measured 22% TW using the bobbin sizing technique ETSS 96004.1. For the OA calculation, all flaws were assumed to be the full thickness of the TSP (1.125 inches).

Adjusting for NDE uncertainties, the worst-case TSP wear flaw at U2C33 is projected to be 39.9% TW, which is less than the 43.6% TW structural limit.

Cook Nuclear Plant U2C28 Steam Generator Tube Inspection Report Page 6 of 7

10. Total Number of Tubes Plugged Table 7 shows the current number of tubes plugged in the Unit 2 steam generators.

Table 7: Total Tubes Plugged SG Number of Tubes Number of Tubes Plugged Plugging Percentage 21 3,592 1

0.03%

22 3,592 8

0.22%

23 3,592 6

0.17%

24 3,592 4

0.11%

Total 14,368 19 0.13%

11. Secondary Side Inspections Visual inspections of the steam dome upper internals were performed on SG 22 and SG 23. The scope included the main deck plate region, primary and secondary moisture separators, sub-deck plate region, and the feedwater ring and nozzle. Some areas of missing magnetite were observed on select components in both steam domes. In SG 23, a through-wall hole was identified in the wall of the riser barrel on one of the primary moisture separators. There were no conditions observed that represent a challenge to structural integrity or to the continued operability of the steam generators.

After water lancing, the top-of-tubesheet region was visually inspected in each SG. The scope included the annulus region, no-tube lane, and multiple in-bundle passes in the hot leg and cold leg of each SG. Possible loose part (PLP) signals from eddy current were visually investigated. Hard sludge accumulation was identified in areas of each SG. This is not considered a new or abnormal condition.

Table 8 provides the list of known foreign objects (FOs) left in the steam generators following the U2C28 refueling outage. Sludge piles and sludge rocks are not included. An evaluation determined that all FOs remaining in the SGs are acceptable for at least five cycles of operation.

Table 8: Foreign Objects Remaining in Steam Generators FO #

SG Description Size (inches)

Location 21001 21 wire bristle Length 0.5 Diameter 0.06 Cold Leg Tube Sheet Column: 27-28, Row: 40 21002 21 wire bristle Length 0.2 Diameter 0.1 Hot Leg Tube Sheet Column: 44-45, Row: 7-8 21003 21 wire bristle Length 0.3 Diameter 0.1 Hot Leg Tube Sheet Column: 54-55, Row: 3-4 22001 22 fiber material Length 0.75 Diameter 0.125 Cold Leg Tube Sheet Column: 98 Row: 5 22005 22 wire bristle Length 2 Diameter 0.125 Hot Leg Tube Sheet Column: 46 Row: 2 22006 22 wire bristle Length 1.5 Diameter 0.0625 Hot Leg Tube Sheet Column: 46 Row: 4 22007 22 wire Length 4.2 Diameter 0.125 Cold Leg Tube Sheet Column: 55-59 Row: 2-6

Cook Nuclear Plant U2C28 Steam Generator Tube Inspection Report Page 7 of 7 Table 8: Foreign Objects Remaining in Steam Generators FO #

SG Description Size (inches)

Location 23001 23 scale Length 0.5 Height 0.2 Hot Leg Tube Sheet Column: 18 Row: 37 23002 23 machine remnant Length 0.5 Diameter 0.025 Hot Leg Tube Sheet Column: 34 Row: 38 23003 23 wire bristle Length 0.5 Diameter 0.0625 Hot Leg Tube Sheet Column: 34 Row: 38 23005 23 gasket material Length 0.25 Diameter 0.0625 Hot Leg Tube Sheet Column: 34 Row: 16 23006 23 wire bristle Length 1.5 Diameter 0.0625 Hot Leg Tube Sheet Column: 46 Row: 4 23007 23 machine turning Length 0.4 Height 0.1 Cold Leg Tube Sheet Column: 36 Row: 40 23008 23 wire bristle Length 1 Diameter 0.0625 Hot Leg Tube Sheet Column: 56 Row: 39 24001 24 wire bristle Length 0.3 Diameter 0.2 Hot Leg Tube Sheet Column: 44-45 Row: 6-7 24002 24 wire bristle Length 0.25 Diameter 0.1 Hot Leg Tube Sheet Column: 44-45 Row: 4-5 24004 24 wire bristle Length 1 Diameter 0.063 Hot Leg Tube Sheet Column: 47-48 Row: 3 24005 24 wire bristle Length 0.5 Diameter 0.031 Hot Leg Tube Sheet Column: 54-55 Row: 6-7 24006 24 wire bristle Length 0.125 Diameter 0.1 Hot Leg Tube Sheet Column: 66 Row: 18 24008 24 bridging legacy Length 0.35 Diameter 0.1 Hot Leg Tube Sheet Column: 42 Row: 7

12. Secondary Side Cleaning Water lancing was performed in each SG. In total, approximately 47.5 pounds of material was removed.

13. Primary Side Visual Inspections Each of the steam generator channel heads (hot leg and cold leg sides) were visually inspected. The scope included tubesheet cladding, channel head cladding, divider plate, stub runner, nozzle dam rings, and all associated welds. The inspections looked for evidence of gross defects such as degraded welds, unusual discoloration, dings, or gouges. No discrepancies or anomalous conditions were identified.

A visual inspection was performed on all previously installed tube plugs. No degraded tube plugs were identified.

14. Plant-Specific Reporting Requirements Cook Nuclear Plant has no plant-specific reporting requirements.