WBL-25-020, Cycle 19 Steam Generator Tube Inspection Report

Cycle 19 Steam Generator Tube Inspection Report

ML25141A010
Person / Time
Site:	Watts Bar
Issue date:	05/21/2025
From:	Reneau W Tennessee Valley Authority
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
WBL-25-020
Download: ML25141A010 (1)

Text

Post Office Box 2000, Spring City, Tennessee 37381 WBL-25-020 May 21, 2025 10 CFR 50.4 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Watts Bar Nuclear Plant, Unit 1 Facility Operating License No. NPF-90 NRC Docket No. 50-390

Subject:

Watts Bar Nuclear Plant (WBN) Unit 1 - Cycle 19 Steam Generator Tube Inspection Report In accordance with the requirements of WBN Unit 1 Technical Specification (TS) 5.9.9, ³Steam Generator Tube Inspection Report,' the Enclosure provides the 180 Day Steam Generator Inspection Report for Unit 1 Cycle 19. This report is required to be submitted within 180 days after the initial entry into MODE 4 following the completion of an inspection performed in accordance with TS 5.7.2.12, ³Steam Generator (SG) Program.' The report provides the complete results of the tube inspections.

There are no new regulatory commitments contained in this letter. Please direct any questions concerning this submittal to Jonathan Johnson, WBN Compliance Manager, at jtjohnson0@tva.gov.

Respectfully, William C. Reneau Site Vice President Watts Bar Nuclear Plant TENNESSEE VALLEY AUTHORITY

Reneau, William Christopher Digitally signed by Reneau, William Christopher Date: 2025.05.19 09:26:44 --04'00'

U.S. Nuclear Regulatory Commission WBL-25-020 Page 2 May 21, 2025

Enclosure:

Watts Bar U1R19 180 Day Steam Generator Tube Inspection Report cc (w/ enclosure):

NRC Regional Administrator - Region II NRC Senior Resident Inspector - Watts Bar Nuclear Plant NRC Project Manager +/- Watts Bar Nuclear Plant

WBL-25-020 E 1 of 1 ENCLOSURE Watts Bar U1R19 180 Day Steam Generator Tube Inspection Report

Author:

Connor Rigsby SG Program Engineer Verifier:

Virginia Allen SG Program Engineer Reviewers Robert Himmelspach Watts Bar U1R19 180 Day Steam Generator Tube Inspection Report Rig S by Conn Or Digitally signed by Rigsby, Connor 1

Date: 2025.05.08 10:08:45 -04'00' Signature / Date Allen, Virginia Ann Signature / Date Digitally signed by Allen, Virginia Ann Date: 2025.05.11 00:07:38 -04'00' Himmelspach Robert Digitally signed by Himmelspach, Robert John John Date: 2025.05.12 07:07:40 -04'00' NDE Eddy Current Level III Signature / Date Maxwell Trent T

M 11 Digitally signed by Trent, rent axwe Maxwell 1

Date: 2025.05.12 23:20:23 -04'00' SG Program Manager Signature / Date 1

Introduction In accordance with Watts Bar Nuclear (WBN) Unit 1 Technical Specification Section 5.7.2.12 "Steam Generator Program" and Technical Specification Section 5.9.9 "Steam Generator Tube Inspection Report,"

this report documents the scope and results of the WBN Unit 1 Refueling Outage 19 (U1R19) replacement steam generator (RSG) inspections. In addition, there are fourteen specific reporting requirements associated with the 180 Day Report in the Electrical Power Research Institute (EPRI) Steam Generator Management Program (SGMP): Steam Generator Integrity Assessment Guideline, Revision 5, Attachment G. Each numbered reporting requirement listed below is followed with the associated information based on the inspections performed during WBN U1R19.

The WBN U1R19 inspection, during the fall of 2024, was the fourth in-service inspection (ISi) since steam generator (SG) replacement in 2006. The U1R19 inspection included primary and secondary side inspections. The primary side inspections included 100% eddy current testing of all open SG tubing and visual inspections. The secondary side inspections included sludge lancing, foreign object search and retrieval (FOSAR), and visual inspections.

1.

Design and Operating Parameters The WBN Unit 1 RSGs were installed during the Unit 1 Cycle 7 refueling outage (U1R7 in 2006). The WBN Unit 1 RSGs are of a similar design to the original steam generators (OSG) which had a vertical shell and continuous bend U-tubes with an integral preheater. WBN Unit 1 is a Westinghouse four-loop plant with Westinghouse Model 68 Axial Extent Preheater (AXP) RSGs.

Table 1-1 Steam Generator Design and Operating Parameters SG Model/ Tube Material/# SGs per Unit Westim!house Model 68AXP / Alloy 690TT/ 4

1. of tubes per SG / Nominal Tube Diameter/ tube 5128 / 0.75 in. I 0.043 in.

thickness Support Plate Style / Material Advance Tube Support Grid / 409 Stainless Steel Last Inspection Date 2017 (U1R14)

Effective Full Power Months (EFPM) Since Last 82.15 EFPM (6.84 Effective Full Power Years Inspection (EFPY))

Total Cumulative SG EFPM 193.56 EFPM (16.13 EFPY)

Mode 4 Initial Entrv 12/03/2024 Observed Primarv-to-Secondarv Leak Rate Below Detection Nominal Toot at Full Power Operation 617°F Loose Parts Strainer The Model 68 AXP has a feedwater distribution box with small diameter holes (0.29") acting as strainers to prevent the introduction of significant foreign obiects into the SGs.

Degradation Mechanism Sub-Population The U1R19 condition monitoring and operational assessment (CMOA) considered the perimeter tubes wear rate as different from the interior tubes wear rate.

SG Program Guideline Deviations Since Last None Inspection Steam Generator Schematic See Fiirure 1-1 and Fi1rnre 1-2 below.

2

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NOZ21.fS 2X UP.?ER 1Rll,\\.."J~S HOT LEC BLCit()O't\\tl "0'21.E Figure 1-1: Schematic Design for Watts Bar Unit 1 Model 68AXP Replacement Steam Generators 3

All U-Bend Support Strap are 2" Wide

• AXIAL FLOW HOT SIDE RECIRCULATING

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(Se e Figure 5.5)

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COLD SIDE RECIRCULATING ENTRANCE CROSS FLOW

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,-: II-FEEDWATER ENTRANCE CROSS FLOW Figure 1-2: Tube Support Structure for Watts Bar Unit 1 Model 68AXP Replacement Steam Generators 4

2.

The Scope of Inspections Performed on each SG The U1R19 inspection program addressed the known eddy current signals observed in the Watts Bar Unit 1 RSGs over the past three inspections and potential RSG tube degradation mechanisms relevant to the design and material of the Watts Bar Unit 1 RSG tubing. The inspections were performed with qualified non-destructive examination (NDE) techniques for each potential mechanism. The defined primary side base scope that was implemented in all four SGs included:

100% Bobbin coil inspection of all open tubes in all four RSGs full length.

Array or rotating probe coil (RPC) for all tubes identified in (Reference 1) with a gap velocity

> 6.0 ft/sec for the hot leg (HL) and a gap velocity> 3.5 ft/sec for the cold leg (CL) fluid gap, (minimum of 6 tubes deep around HL periphery and 3 tubes deep around CL periphery).

o HL up to the first support o

CL up to the seventh support 100% Array or +Point to inspect previously reported dings (DNG)/dents (DNT)/distorted dent signals (DDS)> 2 volts plus any newly reported DNG/DNT/DDS > 2 volts in all RSGs.

100% Array or +Point of new and previous bulges (BLG), manufacture burnish marks (MBM),

over expansions (OXP), and absolute drift indications (ADI) in all RSGs. Only BLG/OXP greater than 18 volts (V) in the tubesheet region were inspected.

+Point or Array Special Interest inspection of new and previous wear indications detected with Bobbin.

+Point or Array Special Interest inspections of tube locations with non-resolved Bobbin signals from the base scope inspection to characterize the underlying condition.

In addition to the eddy current inspections, visual inspections were performed on both the primary and secondary sides. Primary side inspections included the entire divider plate to channel head weld and all clad surfaces in both the HL and CL of all four SGs. A total of29 plugs were installed prior to U1R19. All 29 plugs received a visual inspection with no leakage or anomalies identified. The secondary side visuals were performed at the top of tube sheet (TTS) and in the preheater distribution box. The secondary side visuals were conducted to detect foreign objects, assess hard deposit buildup in the tube bundle interior, and to evaluate the effectiveness of the cleanings performed on the four SGs.

No primary or secondary side scope expansion was required for the U1R19 inspections. All primary and secondary side visual inspections were completed satisfactory with no degradation or anomalies reported.

3.

Nondestructive Examination Techniques Utilized for Tubes with Increased Degradation Susceptibility Due to the high fluid gap velocity between the periphery tubes, an Array inspection was performed in each of the four generators to identify foreign object wear and possible loose parts (PLP). The inspection was performed as listed in Section 2 with no foreign object wear or PLP detected.

4.

Nondestructive Examinations Techniques Utilized for Each Degradation Mechanism Found Table 4-1 below provides the eddy current examination technique specification sheets (ETSS) that were used for the detection and sizing of each degradation mechanism considered to be existing for the U1R19 inspection.

5

Table 4-1: NDE Techniques for Each Existing Degradation Mechanism for U1R19 Degradation Mechanism Detection Detection Technique Sizing Probe Sizing Technique Probe Type ETSS Type ETSS Wear at U-Bend Support Bobbin 196044.3 Rev 0 Bobbin 96004.1 Rev 14 Structures Array 117908.5 Rev 1 Array 17908.2 Rev 0 17908.5 Rev 0 Bobbin 196041.1 Rev 8 Bobbin 96004.1 Rev 14 Wear at Horizontal ATSGs 17908.2 Rev 0 Array 117908.5 Rev 1 Array 17908.5 Rev 0 Notes:

(1) The two existing degradation mechanisms are conservatively assumed to be flat wear. A review was performed of indications at various depths which confirmed that the wear characterization for the WBN U1R19 wear scars is flat.

(2) Detection Technique ETSS are SGMP: SG Examination Guideline (Reference 2) Appendix I ETSS (denoted by a leading "I")

whereas Sizing Technique ETSS are Appendix H ETSS.

5.

Location, Orientation (if linear), Measured Size (if available), and Voltage Response for Each Indication.

There were no new degradation mechanisms reported following the WBN U1R19 inspection. The two existing degradation mechanisms are the following:

1. Wear at U-Bend Support Structures

2. Wear at Horizontal Advanced Tube Support Grids (ATSGs)

Table 5-1: Wear Indications <20% Through Wall (TW) at U-Bend Support Structures and ATSGs SGl SG2 SG3 SG4 Total 284 205 209 420 1,118 Table 5-2: Watts Bar U1R19 Horizontal ATSG Wear~ 20% TW)-All SGs SG Row Col Loe Inch Volts lndic

%TW Characterization Resolution 1

84 99 C04 0.82 1.15 PCT 21 Horizontal ATSG Wear Return to Service 1

85 100 C03

-0.91 2.88 PCT 31 Horizontal ATSG Wear Plugged 1

89 96 C03

-0.84 10.69 PCT 53 Horizontal ATSG Wear Plugged C04 0.81 1.25 PCT 21 Horizontal ATSG Wear 1

90 95 Return to Service C03

-0.91 1.2 PCT 21 Horizontal ATSG Wear 1

91 94 C06 0.79 2.59 PCT 29 Horizontal ATSG Wear Plugged 1

96 89 C03

-0.93 1.22 PCT 21 Horizontal ATSG Wear Return to Service 1

97 84 C03

-0.77 1.25 PCT 21 Horizontal ATSG Wear Return to Service 1

102 79 C03 0.86 1.16 PCT 21 Horizontal ATSG Wear Return to Service 1

105 64 C03 0.83 1.53 PCT 23 Horizontal ATSG Wear Return to Service 2

8 77 H08

-0.91 1.02 PCT 20 Horizontal ATSG Wear Return to Service 2

8 127 C03 0.84 1.27 PCT 22 Horizontal ATSG Wear Return to Service C07

-0.89 1.06 PCT 20 2

22 123 Horizontal ATSG Wear Return to Service C03 0.85 1.56 PCT 24 6

SG Row Col Loe Inch Volts Indic

%TW Characterization Resolution 2

28 123 C03 0.89 1.36 PCT 22 Horizontal ATSG Wear Return to Service 2

30 123 C07

-0.87 1.34 PCT 22 Horizontal ATSG Wear Return to Service 2

36 121 C03

-0.88 1.03 PCT 20 Horizontal ATSG Wear Return to Service 2

72 109 C03

-0.94 1.12 PCT 20 Horizontal ATSG Wear Return to Service 2

79 104 C03

-0.92 1.04 PCT 20 Horizontal ATSG Wear Return to Service 2

86 99 C04 0.74 1.05 PCT 20 Horizontal ATSG Wear Return to Service C06

-0.93 1.18 PCT 21 2

87 98 Horizontal ATSG Wear Plugged C03

-0.94 4.3 PCT 36 2

88 95 C03

-0.92 3.06 PCT 32 Horizontal ATSG Wear Plugged 2

89 96 C06

-0.90 1.96 PCT 26 Horizontal ATSG Wear Plugged 2

90 95 C04 0.86 1.24 PCT 21 Horizontal ATSG Wear Return to Service 2

91 94 C03

-0.90 1.71 PCT 25 Horizontal ATSG Wear Return to Service 2

97 86 C03

-0.95 1.04 PCT 20 Horizontal ATSG Wear Return to Service 2

98 79 C03

-0.93 1.01 PCT 20 Horizontal ATSG Wear Return to Service 2

100 81 C04 0.79 1.28 PCT 22 Horizontal ATSG Wear Return to Service 2

101 78 C03

-0.90 1.39 PCT 23 Horizontal ATSG Wear Return to Service 2

105 66 C03 0.83 1.27 PCT 22 Horizontal ATSG Wear Return to Service 3

10 1

C03 0.61 1.14 PCT 21 Horizontal ATSG Wear Return to Service 3

32 5

C03

-0.93 1.04 PCT 20 Horizontal ATSG Wear Return to Service 3

34 5

C03

-0.91 1.34 PCT 22 Horizontal ATSG Wear Return to Service C07

-0.90 1.51 PCT 23 3

60 13 Horizontal ATSG Wear Plugged C03

-0.91 1.15 PCT 21 3

61 114 C06 0.77 2.34 PCT 28 Horizontal ATSG Wear Plugged 3

84 99 C03

-0.85 1.58 PCT 24 Horizontal ATSG Wear Plugged 3

85 28 C03 0.84 1.70 PCT 25 Horizontal ATSG Wear Return to Service 3

85 98 C03 0.88 2.17 PCT 27 Horizontal ATSG Wear Plugged 3

86 99 cos 0.82 1.80 PCT 25 Horizontal ATSG Wear Return to Service 3

89 32 C03 0.78 1.54 PCT 23 Horizontal ATSG Wear Return to Service C04

-0.88 2.17 PCT 27 3

89 96 Horizontal ATSG Wear Plugged C03

-0.86 1.97 PCT 26 3

90 33 C03 0.82 3.09 PCT 32 Horizontal ATSG Wear Plugged 3

90 95 CO2 0.88 2.65 PCT 30 Horizontal ATSG Wear Plugged 3

91 34 C03

-0.97 2.27 PCT 28 Horizontal ATSG Wear Plugged 3

92 35 C03

-0.88 5.82 PCT 41 Horizontal ATSG Wear Plugged C04 0.81 1.71 PCT 25 3

93 36 Horizontal ATSG Wear Return to Service C03

-0.95 1.66 PCT 24 3

96 41 C03 0.81 1.44 PCT 23 Horizontal ATSG Wear Return to Service C04 0.81 1.79 PCT 25 3

97 40 Horizontal ATSG Wear Plugged C03 0.81 2.00 PCT 26 C04 0.80 3.42 PCT 33 3

97 42 Horizontal ATSG Wear Plugged C03

-0.93 1.21 PCT 21 3

100 45 C03

-0.92 1.12 PCT 20 Horizontal ATSG Wear Return to Service 4

9 42 H06 0.79 1.06 PCT 20 Horizontal ATSG Wear Return to Service 4

13 78 ClO 0.65 1.54 PCT 23 Horizontal ATSG Wear Return to Service 4

24 125 C03 0.87 2.34 PCT 28 Horizontal ATSG Wear Plugged 7

SG Row Col Loe Inch Volts Indic

%TW Characterization Resolution 4

27 124 C03

-0.93 1.07 PCT 20 Horizontal ATSG Wear Return to Service 4

36 123 C03

-0.90 1.11 PCT 20 Horizontal ATSG Wear Return to Service 4

44 121 C03 0.80 1.34 PCT 22 Horizontal ATSG Wear Return to Service 4

77 104 C03 0.83 1.69 PCT 24 Horizontal ATSG Wear Return to Service 4

83 100 C03 0.76 1.61 PCT 24 Horizontal ATSG Wear Return to Service 4

87 96 C03

-0.90 1.66 PCT 24 Horizontal ATSG Wear Return to Service 4

89 32 C07 0.85 2.53 PCT 29 Horizontal ATSG Wear Plugged 4

90 33 cos 0.83 2.23 PCT 28 Horizontal ATSG Wear Plugged 4

91 34 C03

-0.87 3.06 PCT 32 Horizontal ATSG Wear Plugged C06 0.83 1.07 PCT 20 4

91 36 Horizontal ATSG Wear Plugged C03

-0.95 2.29 PCT 28 4

92 37 C03

-0.88 2.27 PCT 28 Horizontal ATSG Wear Plugged C06 0.82 2.27 PCT 28 4

93 36 C04 0.88 6.3 PCT 43 Horizontal ATSG Wear Plugged C03

-0.81 3.38 PCT 33 4

94 37 C03

-0.83 11.87 PCT 55 Horizontal ATSG Wear Plugged 4

94 39 C03

-0.86 1.12 PCT 20 Horizontal ATSG Wear Return to Service 4

94 41 C03

-0.88 3.55 PCT 34 Horizontal ATSG Wear Plugged 4

95 42 C03

-0.91 1.64 PCT 24 Horizontal ATSG Wear Return to Service 4

95 86 C03 0.81 1.50 PCT 23 Horizontal ATSG Wear Return to Service 4

96 39 C03

-0.97 1.14 PCT 21 Horizontal ATSG Wear Return to Service 4

96 41 C03

-0.84 1.04 PCT 20 Horizontal ATSG Wear Return to Service 4

96 43 C03

-0.95 1.59 PCT 24 Horizontal ATSG Wear Return to Service 4

96 45 C03

-0.97 2.98 PCT 31 Horizontal ATSG Wear Plugged 4

97 86 C03 0.80 2.47 PCT 29 Horizontal ATSG Wear Plugged 4

97 88 C03 0.78 1.51 PCT 23 Horizontal ATSG Wear Return to Service 4

98 43 C03

-0.88 1.53 PCT 23 Horizontal ATSG Wear Return to Service 4

98 45 C03

-0.84 3.17 PCT 32 Horizontal ATSG Wear Plugged 4

98 85 C03 0.79 1.26 PCT 21 Horizontal ATSG Wear Return to Service 4

99 46 C03

-0.88 1.15 PCT 21 Horizontal ATSG Wear Return to Service 4

102 49 C03 0.34 1.41 PCT 23 Horizontal ATSG Wear Return to Service 4

103 76 C03 0.76 1.37 PCT 22 Horizontal ATSG Wear Return to Service 4

104 61 C03

-0.89 1.84 PCT 25 Horizontal ATSG Wear Return to Service 4

104 67 C03

-0.57 2.42 PCT 29 Horizontal ATSG Wear Plugged C03

-0.81 5.79 PCT 41 4

104 71 Horizontal ATSG Wear Plugged C03 0.81 3.17 PCT 32 4

105 60 C03

-0.91 1.22 PCT 21 Horizontal ATSG Wear Return to Service 4

105 68 C06

-0.88 2.24 PCT 28 Horizontal ATSG Wear Plugged Notes:

(1)

All indications reported by Bobbin were confmned with Array.

(2)

All tubes with a depth of26% TW or greater were plugged.

(3)

All tubes with ATSG wear Pmwth rate ereater than or eaual to 2% TW /EFPY were olueeed (2 tubes).

8

a e - :

a s ar

- en T bl 5 3 W tt B U1R19 U B d S UODO rt St t

rue ure ear 0

W

~ 20°/4 TW)

All SG s SG Row Col Loe Inch Volts Indic(l)

%TW Characterization Resolution 3

81 56 VS4 0.90 1.27 PCT 22 U-Bend Support Structure Wear Return to Service Notes:

(1)

All indications reported bv Bobbin were confmned with Arrav.

6.

A Description of the Condition Monitoring Assessment and Inspection Results for Each Degradation Mechanism Found Condition Monitoring (CM) Assessment Summary The WBN U1R19 inspection was the fourth ISi performed following the replacement of the WBN Unit 1 SGs during U1R7. The WBN U1R19 ISi was conducted after a cumulative SG service of 16.13 EFPY of operation since replacement. The WBN U1R19 inspection was performed after 5 cycles of operation, or 6.84 EFPY, since the last 100% ISi in WBN U1R14. Based on the 100% eddy current inspection, two existing degradation mechanisms were found: mechanical wear at U-Bend Support Structures and mechanical wear at Horizontal ATSGs. No tubes exceeded the CM limits or required in-situ pressure testing to support the CM assessment.

During U1R19, a total of 95 wear indications at U-Bend Support Structures in 60 tubes were identified.

The largest indication was measured to be 22% TW in SG3 R81 / C56 at support VS4. A bobbin probe was used to measure the indication and it was sized using ETSS 96004.1. The depth of indications ranged from 8% TW to 22% TW. Flaw lengths were measured with the array probe and sized with ETSS 17908.2 and ETSS 17908.5. The maximum flaw length recorded was 1.36 inches while the average length was 0.34 inches. All U-Bend Support Structure wear indications were flat. None of the indications exceeded the 51.64% TW CM limit which contains material, burst relation, and NDE measurement uncertainties at 95%

probability and 0.50 confidence level (95/50). None of the U-Bend Support Structure wear indication lengths exceeded the CM bounding limit of 2.5 inches. Since all wear indications were less than 51.64%

TW and 2.5 inches in length, structural performance criteria has been satisfied.

During U1Rl9, a total of 1,121 wear indications at Horizontal ATSGs in 762 tubes were identified. The maximum depth of the largest indication was measured to be 55% TW in SG4 R94 / C37 at support C03.

Four additional indications were reported with depths exceeding 40% TW, all of which were plugged. A bobbin probe was used to measure the indications and indications were sized using ETSS 96004.1. The depth of Horizontal ATSG indications ranged from 8% TW to 55% TW. Flaw lengths were measured with the array probe and sized with ETSS 17908.2 and ETSS 17908.5. The maximum flaw length recorded was 0.41 inches while the average length was 0.26 inches. All Horizontal ATSG wear indications were flat.

None of the indications exceeded the 63.41 % TW CM limit which contains material, burst relation, and NDE measurement uncertainties at (95/50). The longest measured Horizontal ATSG flaw length was 0.41 inches, which slightly exceeds the CM limit bounding length of 0.37 inches. However, this is attributed to probe lead-in and lead-out. Therefore, the CM SG structural performance criteria has been satisfied for the Horizontal ATSG wear degradation mechanism.

Satisfaction of structural integrity implies satisfaction ofleakage integrity at accident conditions since steam line break accident condition pressure differential for pop-through is smaller than 31\\PNoP for pressure-only loading of volumetric flaws. Therefore, CM has been satisfied for degradation associated with Horizontal ATSG wear and U-Bend Support Structure wear indications at the Watts Bar U1R19 inspection.

Projected and As-Found Inspection Results The forward looking operational assessment (OA) was developed following U1R14 (2017) then subsequently revised in 2022 when TSTF-577 was adopted by WBN. The revised OA utilized a volumetric model to determine the max depth indication that could be returned to service while maintaining structural performance criteria until the next scheduled inspection. The model establishes flaw growth based on growth experienced between UlRl 1 and U1R14 by volume-removed methodology. The projected volume-based U1R14 OA results are summarized in Table 6-1.

9

Table 6-1: Prior OA Volume-Based ATSG Wear Projections SG U1R14 Projected EFPY U1R19 Observed EFPY U1R14 Largest Projected U1R19 Largest Observed ATSG Flaw(% TW)

ATSG Flaw(% TW) 1 7.1 6.84 47.4 53 2

7.1 6.84 51.2 36 3

7.1 6.84 49.2 41 4

7.1 6.84 54.0 55 Table 6-1 compares the projected and actual values from WBN U1R19 for the limiting degradation mechanism. The limiting mechanism is Horizontal ATSG wear. Although the two largest indications in SG 1 and SG4 satisfied all performance criteria, the flaw depths exceeded the maximum projected indication sizes. Corrective actions were taken per Section 7. 7.1 of the SGMP: Steam Generator Integrity Assessment Guidelines (Reference 3). This included a revised volume-based OA model for the prior inspection cycle benchmarked to the U1R19 results, growth rates benchmarked to previous projections, and augmenting the U1R19 OA deterministic projections with fully probabilistic and volume-based evaluations. This was performed in order to ensure the deterministic OA performed during U1R19 was acceptable. The WBN U1R19 OA conservatively used simplified statistical methods for projecting the worst-case degraded tube rather than using the volume-based method to support the next operating interval.

7.

The number of Tubes Plugged During the Inspection Outage for Each Degradation Mechanism Found A total of32 tubes were plugged during U1R19. All of the tubes plugged during U1R19 were plugged for Horizontal ATSG wear. Of the 32 tubes plugged, 27 were preventatively plugged and 5 were correctively plugged due to exceeding the WBN TS limit of 40% TW. Table 7-1 provides the total number of tubes plugged for each degradation mechanism at U1R19.

Table 7-1: Total Number of Tubes Plugged During U1R19 for Each Degradation Mechanism SGl SG2 SG3 SG4 Total Plugged for U-Bend Support Structure Wear 0

0 0

0 0

Plugged for Horizontal ATSG Wear 3

3 11 15 32

8.

The Repair Methods Utilized, and the Number of Tubes Repaired by Each Repair Method No repair methods were utilized during WBN U1R19.

9.

Analysis Summary of the Tube Integrity Conditions Predicted to Exist at the Next Scheduled Inspection Relative to the Applicable Performance Criteria Including Analysis Methodology, Inputs, and Results A simplified deterministic OA method was used to predict tube integrity conditions at the next scheduled inspection. In addition, a fully probabilistic and revised volume-based methods were performed to ensure accuracy and conservatism of the simplified deterministic method. These methods were utilized in order to provide added confidence that the SG structural and leakage performance criteria will be maintained until the next scheduled inspection. The deterministic and revised volume-based model evaluated all SGs while the fully probabilistic model only determined probability of burst (POB) and probability ofleakage (POL) 10

for the limiting steam generator, SG4. In all models, a five cycle (7.0 EFPY) interval was justified before the next inspection with conservatism in place. The flaw population in all SGs meet the structural integrity performance criteria for a 3Af>Nopof3750 psid with an applied maximum growth rate for at least 7.0 EFPY of operation. For pressure-only loading of volumetric flaws, satisfaction of the structural integrity implies satisfaction of leakage integrity at accident conditions since steam line break accident condition pressure differential for pop-through is smaller than 3~PNoP.

For the U-Bend Support Structure wear, although a 95th percentile UlR14-UlR19 growth rate (0.497%

TW/EFPY for the limiting SG) can be applied, a conservative limiting growth rate of 2.5% TW/EFPY, which encompasses the maximum growth rate from U1Rl 1-U1Rl4, was used for the UlR19-UlR24 OA.

Regarding Horizontal ATSG wear, to ensure that the UlRl 9-U1R24 OA is bounding, the maximum growth rate of 4.674% TW/EFPY from UlR14-UlR19 was selected rather than the 95th percentile growth rate of the limiting generator which was 1.694% TW/EFPY. This choice was validated by comparing the U1Rl 1-U1R14 growth rate projections with the U1R19 data.

Additional conservatisms are in place for OA model input parameters. For instance, a 5 cycle interval EFPY of 6.85 was projected from UlRl 9-U1R24. However, a conservative value of 7.0 EFPY was used for OA models. Furthermore, a conservative Structural Integrity Performance Criteria (SIPC) of 3750 psid was used rather than the calculated 3~PNoPvalue of 3738 psid.

Deterministic Method Simplified methods of projecting the worst case degraded tube are designed to provide conservative approximations of fully probabilistic calculations that consider the entire projected flaw population and the variety of possible outcomes for a given inspection interval. In the simplified techniques, the worst case flaw is projected using conservative assumptions coupled with uncertainties that are combined using the mixed Arithmetic/Monte Carlo calculation strategies. This method involves a single tube analysis that will provide a conservative estimate for the projected end of cycle (EOC) lower 95th percentile burst pressure.

For the deterministic method, the limiting degradation mechanism was Horizontal ATSG wear. However, both U-Bend Support Structure wear and Horizontal ATSG wear were modeled for 7.0 EFPY using the maximum growth rates previously discussed. Table 9-1 provides maximum depths predicted at the next scheduled inspection for the worst case degraded tubing for both degradation mechanisms.

Table 9-1: Watts Bar U1R19 Deterministic Operational Assessment Summary Degradation Maximum Depth EOC Structural OA Margin to EOC OAinterval Mechanism (Wear)

Predicted at Next Limit (% TW) <1>

Structural Limit (EFPY)

Inspection (% TW)

(%TW)

U-Bend Support 49.08 58.03 8.95 7.0 (Return to Service)

U-Bend Support 39.50 58.03 18.53 7.0 (Undetected)

Horizontal ATSG 67.27 69.08 1.81 7.0 (Return to Service)

Horizontal ATSG 54.72 69.08 14.36 7.0 (Undetected)

Notes:

(1) Structural Limit is based on an assumed maximum length of2.5 inches for U-Bend wear and 0.37 inches for ATSG wear.

11

Supplemental Methods Fully probabilistic methods provide a wider range of inputs that include distributions of detected and undetected flaw sizes and distributions of degradation growth rates, combined with uncertainties for material property, burst relation, and NDE measurement. The OA for Horizontal ATSG and U-Bend Support Structure wear degradation mechanisms is performed using fully probabilistic methods through application of a Westinghouse developed software package referred to as Full Bundle Model (FBM). The assumed quantity and depth distribution of undetected ATSG wear is determined by postulating a total

( detected and undetected) flaw depth distribution which is simulated with the probability of detection (POD) function to produce both detected flaw and undetected flaw size distributions. The total flaw depth distribution is iterated until the simulated detected flaw distribution aligns with the observed detected flaw distribution at UlR19.

A fully probabilistic method was used to predict the conditions at the next inspection for SG4 which is the limiting SG. The number of indications and depth distribution in SG4 bound the remaining SGs. The CL outer perimeter tubes are considered a sub-population in the UlRl 9 FBM due to the growth rate and number of indications. The U1Rl9 FBM conservatively applies the sub-population growth rate to the entire bundle.

For the fully probabilistic method, the limiting degradation mechanism is ATSG wear. The total number of returned to service flaws was 389 while the number of undetected flaws was projected to be 758. The number of returned to service and undetected flaws were inputs into the model. After 7.0 EFPY, the projected POB for ATSG wear is 1.427%, which is below the 5% limit as shown in Table 9-2.

Table 9-2: Watts Bar U1R19 SG4 Five-Cycle Fully Probabilistic OA Results Burst POB(%)

POL(%)

Pressure Leak Rate (gpm)

(osi)

Horizontal ATSG Results 1.427 0.111 4241 0

Maximum Allowed 5.000 5.000 min.

0 3750 Acceptable for Five Cycles?

Yes Yes Yes Yes As shown in Table 9-2, the projected POB and POL were all within the 5% limit for five cycles of operation.

All calculated burst pressures were greater than the minimum 3.Af>Nop of 3750 psid. Thus, the OA supports the next inspection to be performed at the end of 5 operating cycles during U1R24.

In addition to the deterministic OA calculations and fully probabilistic analysis, a volumetric wear evaluation was performed to provide further assurance that the OA is acceptable for a 5-cycle inspection interval. A revised volume-based OA model was created by benchmarking the model to the U1R19 results.

The adjustments formulated a more conservative model used to supplement the previously discussed deterministic method. The volume-based model was adjusted to consider outliers and all indications rather than only the largest depths. The updated volume-based model confirmed that all performance criteria will be satisfied over the next 5-cycles as summarized in Table 9-3.

The deterministic, fully probabilistic, and volume-based methods confirmed that the probability of challenging the CM limit after 7.0 EFPY (84 EFPM) is acceptable for the returned to service flaw population per Reference 3. TV A will perform the next 100% eddy current inspection at WBN Ul during U1R24.

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Table 9-3: Watts Bar UlR19 Volume Based ATSG Wear OA Projections UlR19-UlR24 Largest Projected ATSGEOC SG UlR14-UlR19 EFPY Projected EFPY Depth at U1R24 Structural Limit

(%TW)

(%TW) 1 6.84 7.0 50.3 69.08 2

6.84 7.0 52.3 69.08 3

6.84 7.0 55.3 69.08 4

6.84 7.0 55.3 69.08

10.

The Number and Percentage of Tubes Plugged to Date and the Effective Plugging Percentage in Each SG Table 10-1 below provides the number of tubes plugged and plugging percentage as of the end ofU1R19.

No sleeves have been installed and therefore there is no correction for effective plugging percentage.

Table 10-1: Number and Percentage of Tubes Plugged at Completion ofU1R19 SGl SG2 SG3 Tubes Plugged prior to U1R19 3

5 7

Tubes Plugged for U-Bend Support Structure 0

0 0

Wear During U1R19 Tubes Plugged for Horizontal Support Structure 3

3 11 Wear During U1R19 Total Plugged Tubes to Date 6

8 18 Percentage Plugged to Date 0.12%

0.16%

0.35%

Allowable Percent Tubes Plugged 12%

12%

12%

11.

The Results of Any SG Secondary Side Inspections Scope of Secondary Side Inspection Activities SG4 14 0

15 29 0.57%

12%

Total 29 0

32 61 0.30%

12%

In all four SGs, visual inspections were conducted on the TTS following sludge lancing activities including:

1. Sludge lancing effectiveness and FOSAR in 100% of the annulus.

2. Sludge lancing effectiveness and FOSAR in 100% of the tube lane.

3. All PLPs identified by eddy current program (no PLPs were identified).

FOSAR and Eddy Current Resolution Eddy current inspections capable of detecting foreign objects and PLPs were performed during primary side inspections. This included a 100% full length bobbin probe inspection program and a minimum 6-tube deep array probe peripheral inspection on the HL and 3-tube deep array probe peripheral inspection on the CL to detect foreign objects and foreign object wear. The array probe inspection program went to the seventh support on the CL and the first support on the HL. During the inspections, no foreign object wear or PLPs were detected.

Following sludge lancing, FOSAR was performed in each steam generator to remove remaining foreign objects. The secondary side FOSAR inspections performed in all four SGs included visual examinations of the tube lane, annulus, and periphery tubes (to at least 3-5 tubes into the tube bundle). A total of 21 13

foreign objects were identified through visual inspections at the TTS as summarized in Table 11-1. All foreign objects were either removed or evaluated by size and location as acceptable to remain for the following five cycles of operation. A total of 13 foreign objects were retrieved while 8 foreign objects were not retrieved and were dispositioned to remain. All 8 objects not retrieved were within the limiting size and composition acceptable for five cycles of operation (Reference 1 ). Table 11-1 lists all foreign object dimensions and material types identified on the TTS.

Table 11-1: Watts Bar U1R19 Identified Foreign Objects SG/FO Retrieved?

FO Description Leg Row/Col Dimensions (inch.)

ID 1001 Yes Gasket Material CL 77/116 0.75 X 0.2 X 0.125 2004 No Scale HL 16/4 1.5 X 0.05 X 0.05 2005 No Scale HL 100/73 0.25 X 0.01 X 0.01 4016 Yes Gasket Material CL 1/121 0.4 X 0.125 X 0.125 4027 Yes Wire Bristle CL 2/127 0.063 x 0.06 dia.

4028 Yes Scale CL 86/30 0.2 X 0.17 X 0.01 4029 No Wire Bristle CL 86/30 0.75 x 0.06 dia.

4030 Yes Scale CL 86/30 0.2 X 0.17 X 0.01 4031 No Machine Turning CL 86/30 0.1 X 0.08 X 0.08 4032 No Wire Bristle CL 0/28 0.17 x 0.03125 dia.

4033 Yes Wire Bristle CL 0/19 0.75 x 0.01 dia.

4034 Yes Gasket Material CL 76/21 0.15 X 0.08 X 0.01 4035 No Non-Metallic CL 76/19 0.75 X 0.17 X 0.01 4036 Yes Wire Bristle CL 25/0 1.75 x 0.01 dia.

4037 Yes Gasket Material CL 0/119 0.4 X 0.08 X 0.01 4038 Yes Gasket Material CL 1/23 0.25 X 0.17 X 0.01 4039 No Wire Bristle HL 45/62 0.2 x 0.02 dia.

4040 No Wire Bristle HL 44/62 0.375 x 0.01 dia.

4041 Yes Wire Bristle CL 35/127 0.1 x 0.01 dia.

4042 Yes Gasket Material CL 1/23 0.0 X 0.25 X 0.25 4043 Yes Gasket Material CL 1/119 0.5 X 0.0625 X 0.125 Preheater Box Visual Inspections All four preheater boxes were visually inspected during U1R19. No degradation was found following the completion of the inspection. A total of 31 foreign objects were observed in all SGs. Of the 31 objects, 26 were successfully removed while 5 were left in the preheater boxes. The materials observed included weld slag, scale, sludge rock, gasket material, wire bristles, metallic objects, and non-metallic objects. The 5 remaining foreign objects were determined to be of acceptable dimension and composition that they will 14

not cause tube degradation in the next five cycles of operation should they enter the SGs. The 5 non-retrieved objects in the preheater boxes are listed in Table 11-2.

No degradation was identified during secondary side inspections, including the preheater distribution box.

Table 11-2: Watts Bar U1R19 Unretrieved Preheater Objects SG/FO Retrieved?

FO Description Dimensions (inch.)

ID 3003 No Wire Bristle 0.4 x o.oi dia.

4001 No Gasket Material 0.27 X 0.1 X 0.01 4010 No Gasket Material 1.0 x 0.06 dia.

4015 No Wire Bristle

0. 75x 0.ol dia.

4024 No Metallic Object 0.29 X 0.18 X 0.02

12.

The Scope, Method, and Results of Secondary Side Cleaning Performed in Each SG TTS Sludge Lancing During the WBN U1R19 inspection, sludge lancing was performed at the secondary side TTS in all four steam generators. There are two main purposes of the cleaning process. The first is to remove soft sludge and hardened deposits (such as sludge, scale, and foreign objects) that preferentially form at the TTS. The second is to force and filter out any loose parts or foreign objects that have migrated to the SG secondary side TTS during operation. The mass of deposit material and debris removed by the cleaning process from U1R14 and U1R19 is summarized in Table 12-1 below. The U1R19 weights were 31% greater than the U1R14 weights, which was expected due to the operating interval differences. No tube integrity concerns were identified due to TTS deposits. No water level perturbations were observed during the past fuel cycles.

The main steam pressure remained steady from UlR14-UlR19.

Table 12-1: Watts Bar U1R14 and U1R19 Sludge Lance Deposit Removal Summary RSGOutage Date SGl (lbs.)

SG2 (lbs.)

SG3 (lbs.)

SG4 (lbs.)

Total (lbs.)

U1R14 Spring 2017 8.5 7.5 9.5 7

32.5 U1R19 Fall 2024 10.5 11 8.5 12.5 42.5

13.

The Results of Primary Side Component Visual Inspections Performed in Each SG SG Channel Head Bowl Visual Inspections Visual inspections were performed in the channel head bowl on both the hot and cold leg channels during WBN U1R19. Visual inspections of the SG divider plate, inclusive of the entire divider plate-to-channel head weld and all visible clad surfaces, were performed in accordance with Westinghouse NSAL-12-1.

This inspection was performed using the SG manway channel head bowl cameras. Satisfactory inspection results were observed in all SGs with no indications of cladding surface degradation. No breaches in the cladding or cracking in the divider-to-channel head weld were identified. These inspections are driven by industry operating experience and EPRI guideline recommendations.

Tube Plug Inspections WBN Unit 1 had 29 plugs installed prior to U1R19. All 29 previously installed plugs were inspected with no leakage or degradation detected.

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14.

Any Plant-Specific Reporting Requirements, if Applicable.

There are no plant-specific requirements to report.

References

1. Westinghouse Report, SG-CECO-21-003, Revision 1, "Foreign Object Limits Analysis for the Watts Bar Unit 1 and Unit 2 Replacement Steam Generators," November 2023.

2. Steam Generator Management Program: Pressurized Water Reactor Steam Generator Examination Guidelines: Revision 8, EPRl, Palo Alto, CA: June 2016. 3002007572.

3. Steam Generator Management Program: Steam Generator Integrity Assessment Guidelines, Revision 5. EPRl, Palo Alto, CA: 2021. 3002020909.

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