NL-23-0745, Refueling Outage 1R24 Steam Generator Tube Inspection Report

Refueling Outage 1R24 Steam Generator Tube Inspection Report

ML23265A249
Person / Time
Site:	Vogtle
Issue date:	09/22/2023
From:	Coleman J Southern Nuclear Operating Co
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
NL-23-0745
Download: ML23265A249 (1)

Text

A Southern Nuclear Regulatory Affairs 3535 Colonnade Parkway Birmingham , AL 35243 205 992 5000 September 22, 2023 Docket No. 50-424 NL-23-0745 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Vogtle Electric Generating Plant - Unit 1 Refueling Outage 1R24 Steam Generator Tube Inspection Report Ladies and Gentlemen:

In accordance with the requirements of Vogtle Electric Generating Plant (VEGP) Technical Specification 5.6.10 as updated by TS Amendment 211 (Adams Accession No. ML21316A055),

Southern Nuclear Operating Company (SNC) submits the enclosed Steam Generator (SG)

Tube Inspection Report for the SG tube inspection performed during the twenty-fourth refueling outage on Unit 1 ( 1R24) as an Enclosure to this letter.

This letter contains no regulatory commitments. If you have any questions, please contact Amy Chamberlain at 205.992.6361.

Respectfully submitted,

~~

Jamie Coleman Regulatory Affairs Director JMC/dsp/cbg

Enclosure:

1R24 Steam Generator Tube Inspection Report cc: Regional Administrator NRR Project Manager - Vogtle 1 & 2 Senior Resident Inspector - Vogtle 1 & 2 RType: CVC?000

Vogtle Electric Generating Plant - Unit 1 Refueling Outage 1R24 Steam Generator Tube Inspection Report Enclosure 1R24 Steam Generator Tube Inspection Report

Enclosure to NL-23-0745 1R24 Steam Generator Tube Inspection Report Introduction The Vogtle Electric Generating Plant (VEGP) Unit 1 is a 4-loop Westinghouse plant with Westinghouse Model F steam generators with lnconel 600 thermally treated tubing. Vogtle Unit 1 refueling outage 24 (1 R24) was conducted after Steam Generator (SG) service equivalent to approximately 1.39 effective full power years (EFPY) from previous SG eddy current inspections. During this operational interval, no tube leakage was reported. Analysis based on conservative assumptions used in the Condition Monitoring (CM) and Operational Assessments (QA) demonstrated that there were no tubes that exceeded the Reg. Guide 1.121 or NEI 97-06 Revision 3 criteria for tube integrity during Cycle 24.

During VEGP 1R24, a total of seven (7) tubes were plugged. None of the indications exceeded the condition monitoring limits identified in the Degradation Assessment. No tubes required in-situ pressure testing. Permanent H* Alternate Repair Criteria (ARC) has been approved for implementation by the NRC. Therefore, SNC and Westinghouse omitted tube end +Point' inspections below top of tubesheet (TTS) -15.2 inches. The scope and results of inspections on each SG are described below.

A. Technical Specification 5.6.1 O.a, the scope of inspections performed on each SG,

• 100% full-length X-probe (Bobbin and Array) examination of tubes in all SGs, tube end to tube end for Row 6 and higher. Straight leg portion of hot leg (HL) and cold leg (CL)

(Rows 1-5). This scope covers the tube support plate (TSP) intersections of high stress (2-sigma) tubes, loose parts, and any possible loose parts (PLPs).

• 100% low row U-bend Bobbin and Array probe examination candy cane from CL Rows 3-5, +Point probe examination of Row 1 and Row 2 U-Bends from the top TSP on the HL to the top TSP on the CL.

• 100% tubesheet expansion transition +Point probe examination of HL tubes in all SGs from the 3-inches above TTS to 3-inches below TTS. This inspection, along with the full-length X-probe inspection, satisfied the required periodic sample that accompanies regulatory approval of H*.

• 100% +Point probe examination of dent and dings ~ 2.0 volts.

• 100% +Point probe examination of the HL tube bulges (BLG) > 42 volts (excluding those below H* distance).

• 100% +Point probe examination of the HL overexpansion (OXP) populations (excluding those below H* distance).

The BLG and OXP indications are defined as follows:

o BLG = differential mix diameter discontinuity signal within the tubesheet of 18 volts or greater as measured by bobbin coil probe.

o OXP = a tube diameter deviation within the tubesheet of 1.5 mils or greater as measured by bobbin coil profile analysis.

• Special Interest +Point probe examination of all I-Codes and as needed to support tube integrity evaluations.

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Enclosure to NL-23-0745 1R24 Steam Generator Tube Inspection Report

• Tube slippage Bobbin probe examination for H* Tube slippage monitoring.

• 100% visual inspection of all installed tube plugs from the primary side.

• Visual inspection in all SGs of channel head primary side HL and CL inclusive of the entire divider plate to channel head weld and all visible clad surfaces.

• Secondary side activities included:

o Sludge lancing o Cleanliness and foreign object search and retrieval (FOSAR)

B. Technical Specification 5.6.1 O.b, the nondestructive examination techniques utilized for tubes with increased degradation susceptibility.

+Point probe inspections were performed for HL tubes in all SGs for TTS +/- 3-inches, Row 1 and Row 2 U-bends from the top TSP on the HL side to the top TSP on the CL side, HL tube BLG and OXP, and dents and dings at specific volts in straight lengths and U-bends. These regions have increased degradation susceptibility to stress corrosion cracking.

X-probe inspections were performed for 100% of the SG tubes. This includes HL and CL periphery and tubelane to identify foreign objects or foreign object wear. These regions are considered to have increased susceptibility to foreign object wear. The 100% X-probe inspection included all potential high stress tubes and dents/dings.

C. Technical Specification 5.6.10.c, for each degradation mechanism found:

1. The nondestructive examination techniques utilized, Table 1: Degradation Found and Techniques Degradation Mechanism Found Technique Used Mechanical wear due to foreign objects X-probe (bobbin or array) - detection

+Point - detection and sizing Mechanical wear at AVB supports X-probe - detection Bobbin - sizing Mechanical wear and wall loss from X-probe - detection secondary side cleanino process +Point- detection and sizino Mechanical wear at TSP X-probe - detection

+Point - sizino ODSCC at the Hot Leg Expansion Transitions +Point - detection and sizing ODSCC at Bulge and Overexpansion X-probe - detection

+Point - detection and sizing ODSCC at Dents and Dings X-probe - detection

+Point - detection and sizing E-2

Enclosure to NL-23-0745 1R24 Steam Generator Tube Inspection Report

2. The location, orientation (if linear), measured size (if available), and voltage response for each indication. For tube wear at support structures less than 20 percent through-wall, only the total number of indications needs to be reported, Mechanical wear due to foreign objects Table 2: Vogtle 1R24 Foreign Object Wear Indications

%TW SG Row Column Location Depth Voltage 1 1 2 BPH+15.12 10 0.11 1 24 66 3C+26.27 9 0.06 1 39 100 TSH+0.24 11 0.11 1 41 97 TSC+0.04 24 0.29 1 41 100 TSH+0.16 16 0.17 1 41 100 TSH+0.09 31 0.42 1 41 101 TSH+0.13 24 0.3 1 41 102 TSH+0.11 24 0.29 1 41 103 TSH+0.42 23 0.28 1 55 82 BPH+0.42 24 0.3 1 56 82 BPH+0.68 INR -

2 6 1 1C+1.14 7 0.07 2 53 48 TSC+0.3 9 0.1 2 54 46 TSC+0.11 15 0.18 3 29 111 BPH-0.15 12 0.13 3 30 111 BPH+0.86 31 0.41 4 38 104 BPH+0.18 DSS -

4 40 57 6H+13.32 8 0.09 4 49 89 BPH+0.3 11 0.09 BPH - Baffle Plate on HL side #C - Tube support plate # on CL side TSH - Tubesheet region on HL side #H - Tube support plate# on HL side TSC - Tubesheet region on CL side INR - Indication Not Reportable DSS - Distorted Support Signal. No change noted with historical lookbacks.

No loose parts were found to remain at any of the foreign object wear locations in Table 2.

Mechanical wear at Anti-vibration bar (AVB) supports In SG1, there are a total of 183 indications for AVB wear with 160 less than 20%

through-wall (TW). In SG2, there are a total of 249 indications for AVB wear with 214 less than 20% TW. In SG3, there are a total of 288 indications with 244 less than 20%

TW. In SG4, there are a total of 243 indications for AVB wear with 212 less than 20%

TW. Tables 3 - 6 include V1 R24 AVB wear indications greater than or equal to 20% TW.

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Enclosure to NL-23-0745 1R24 Steam Generator Tube Inspection Report Table 3: Vogtle 1R24 SG1 AVB Wear Indications> 20%TW SG Row Column Location %TW Depth Voltage 1 26 116 AV5 20 0.85 1 28 115 AV6 25 1.34 1 37 102 AV5 24 1.12 1 38 16 AV4 32 2.18 1 39 48 AV4 23 1.1 1 39 48 AV3 21 0.85 1 40 47 AV4 35 2.21 1 40 47 AV3 33 2.01 1 40 62 AV3 22 0.76 1 41 44 AV3 34 2.21 1 41 44 AV2 22 0.91 1 43 21 AV5 31 1.79 1 43 21 AV4 29 1.58 1 43 83 AV4 20 0.83 1 43 91 AV2 31 1.82 1 44 21 AV3 20 0.84 1 49 28 AV5 21 0.96 1 52 39 AV3 30 1.62 1 52 39 AV4 29 1.48 1 52 39 AV2 22 0.93 1 52 44 AV4 23 1 1 57 45 AV3 36 2.45 1 57 45 AV2 21 0.86 Table 4: Vogtle 1R24 SG2 AVB Wear Indications> 20%TW SG Row Column Location %TW Depth Voltage 2 38 106 AV5 28 1.33 2 39 105 AV5 25 1.22 2 40 93 AV5 20 0.81 2 40 98 AV5 22 0.9 2 40 105 AV5 25 1.24 2 41 33 AV4 24 1.05 2 41 33 AV5 22 0.91 2 41 42 AV5 33 2.08 2 41 42 AV4 27 1.42 2 41 103 AV5 27 1.46 2 42 76 AV5 34 2.06 2 42 76 AV2 26 1.23 2 42 76 AV3 21 0.84 2 42 94 AV4 23 0.92 E-4

Enclosure to NL-23-0745 1R24 Steam Generator Tube Inspection Report 2 42 97 AV4 36 2.52 2 42 97 AV3 21 0.93 2 42 100 AV4 20 0.78 2 43 87 AV5 20 0.86 2 43 91 AV2 28 1.46 2 43 91 AV5 25 1.18 2 46 49 AV3 25 1.13 2 46 50 AV3 34 1.83 2 46 50 AV2 34 1.87 2 46 50 AV4 30 1.5 2 46 50 AV5 27 1.15 2 46 50 AV1 25 1 2 46 58 AV2 30 1.3 2 49 89 AV5 21 0.89 2 49 89 AV4 21 0.93 2 50 84 AV4 35 2.06 2 50 84 AV3 29 1.43 2 50 89 AV4 32 1.78 2 54 84 AV5 32 1.7 2 54 84 AV3 22 0.88 2 54 84 AV4 20 0.75 Table 5: Vogtle 1R24 SG3 AVB Wear Indications> 20%TW SG Row Column Location %TW Depth Voltage 3 39 102 AV2 20 0.61 3 39 35 AV4 22 0.77 3 39 17 AV6 24 1.02 3 39 17 AV3 24 1.02 3 39 35 AV3 29 1.29 3 39 26 AV2 30 1.41 3 39 102 AV5 30 1.24 3 40 30 AV5 20 0.71 3 40 98 AV2 20 0.64 3 40 100 AV2 21 0.73 3 40 104 AV4 22 0.75 3 40 104 AV6 23 0.85 3 40 102 AV2 29 1.29 3 41 19 AV5 29 1.38 3 41 99 AV5 35 1.9 3 42 58 AV3 21 0.73 3 42 21 AV5 22 0.83 3 42 63 AV4 22 0.79 3 42 27 AV5 26 1.04 3 42 35 AV4 28 1.25 3 42 50 AV2 29 1.5 3 42 23 AV4 35 1.84 3 42 50 AV4 36 2.34 E-5

Enclosure to NL-23-0745 1R24 Steam Generator Tube Inspection Report 3 44 26 AV2 30 1.37 3 45 40 AV3 20 0.71 3 45 61 AV4 20 0.67 3 45 67 AV3 20 0.92 3 45 46 AV4 21 0.76 3 45 82 AV4 21 0.69 3 45 49 AV2 23 0.92 3 45 67 AV4 24 1.18 3 45 82 AV3 24 0.92 3 45 64 AV3 25 1.33 3 45 48 AV3 26 1.12 3 45 61 AV5 26 1.03 3 45 49 AV3 27 1.16 3 45 46 AV3 31 1.53 3 45 46 AV2 32 1.66 3 47 45 AV4 25 1.01 3 47 38 AV4 31 1.5 3 47 96 AV4 32 1.47 3 49 34 AV4 29 1.34 3 49 96 AV6 33 1.64 3 50 86 AV5 20 0.65 Table 6: Vogtle 1R24 SG4 AVB Wear Indications> 20%TW SG Row Column Location %TW Depth Voltage 4 28 40 AV5 21 0.62 4 30 9 AV5 32 1.69 4 30 114 AV5 32 1.7 4 33 111 AV6 21 0.67 4 33 111 AV3 22 0.7 4 33 111 AV4 25 0.88 4 36 39 AV3 21 0.82 4 37 107 AV3 20 0.62 4 38 104 AV4 21 0.8 4 39 58 AV4 23 0.79 4 40 82 AV5 21 0.75 4 40 88 AV4 21 0.67 4 40 82 AV3 24 1.02 4 40 95 AV4 25 1.06 4 40 106 AV3 26 0.96 4 40 62 AV4 27 1.11 4 40 62 AV2 27 1.06 4 40 106 AV5 30 1.4 4 40 62 AV3 35 1.86 4 40 82 AV4 37 2.42 4 42 101 AV4 24 0.98 4 42 101 AV5 30 1.46 4 43 101 AV5 30 1.27 E-6

Enclosure to NL-23-0745 1R24 Steam Generator Tube Inspection Report 4 44 97 AV4 22 0.86 4 44 96 AV4 24 0.84 4 44 97 AV5 26 1.15 4 44 97 AV2 26 1.08 4 44 96 AV3 31 1.41 4 45 98 AV5 21 0.64 4 50 63 AV3 25 1.03 4 50 76 AV5 31 1.51 AV# - Location of AVB intersection with the tube (there are up to 6)

Mechanical wear and wall loss from secondary side cleaning process Table 7 lists tube locations and volumetric indications associated with the ultrasonic energy cleaning (UEC) and pressure pulse cleaning (PPC) secondary side cleaning processes.

Based on the nondestructive examination (NOE) uncertainty levels and the results, it is apparent that there has been no measurable progression in the wall loss associated with these historical indications. Further, the mechanisms that caused this form of degradation are no longer applied and therefore no wear progression can occur.

Table 7: Vogtle 1R24 Tube Wall Loss from Secondary Side Cleaning Process

%TW SG Row Col Location Indication Volts Depth 1 1 83 TSH+20.03 PCT 11 0.11 1 1 87 TSH+20.41 PCT 38 0.56 1 58 70 BPH+0.47 PCT 25 0.32 2 1 70 TSC+11.65 PCT 4 0.04 2 1 70 TSC+9.24 PCT 8 0.09 2 1 70 TSC+8.01 PCT 7 0.07 2 1 78 TSC+8.97 PCT 9 0.09 2 1 78 TSC+8.15 PCT 4 0.04 2 1 82 TSC+7.99 PCT 5 0.05 2 16 6 BPC+0.56 PCT 12 0.13 2 16 7 BPC+0.49 PCT 30 0.41 2 1 91 BPC-0.38 PCT DSS -

2 10 101 BPH-0.19 PCT NOD -

DSS - Distorted Support Signal. No change noted with historical lookbacks.

NOD - No Degradation Detected. No change noted with historical lookbacks.

PCT - Volumetric Indication BPH - Baffle Plate on the HL side BPC - Baffle Plate on the CL side Mechanical Wear at TSP There are two (2) indications of mechanical wear at TSP and both are less than 20% TW.

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Enclosure to NL-23-0745 1R24 Steam Generator Tube Inspection Report ODSCC at the Hot Leg Expansion Transitions During the 1R24 SG inspections, five (5) circumferential ODSCC indications were reported at HL TTS expansion transitions. All were detected and sized with the +Point probe. Table 8 includes the ODSCC indications.

Table 8: Vogtle 1R24 ODSCC at Tubesheet Expansion Transitions Max PDA SG Row Column Volts Deg Location Depth%

TW

(%)

4 39 68 0.12 93 TSH-0.18 87 18.6 4 43 64 0.33 75 TSH-0.13 56 18.9 4 43 67 0.08 85 TSH+0.00 31 5.27 4 43 74 0.30 142 TSH-0.10 86 27.1 4 49 67 0.24 74 TSH+0.00 74 34.7 TSH - Tubesheet region on HL side PDA - Percent Degraded Area ODSCC at Tube Overexpansion During 1R24, there was one (1) indication of axial ODSCC at an over expansion within the tubesheet. This indication was detected and sized with the +Point probe. This is a first occurrence of axial ODSCC at this location for Vogtle Unit 1. This type of degradation is expected to be within close proximity to the bottom of the expansion transition - a location that was inspected 100% by +Point probe on the HL side and was covered by the planned inspection scope. No changes in future inspection scopes or intervals would be needed to account for this degradation mechanism. Table 9 includes the ODSCC indication.

Table 9: Vogtle 1R24 Axial ODSCC at Tube Overexpansion

+Point Max Length SG Row Column Voltage Deg Location Depth%

(in)

(Vpp) TW 4 25 74 0.79 91 TSH-1.24 73.9 0.37 ODSCC at Dents and Dings During 1R24, there was one (1) indication of axial ODSCC detected at a freespan ding. This is the first occurrence of axial ODSCC at a ding for Vogtle Unit 1. Table 10 includes the ODSCC indication.

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Enclosure to NL-23-0745 1R24 Steam Generator Tube Inspection Report Table 10: Vogtle 1R24 Axial ODSCC at Dents and Dings

+Point Max Voltage Depth%

SG Row Column (Vpp-) Dea Location TW Lenath (in) 4 14 42 0.14 127 7H+2.51 37.9 0.33

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 Table 11: Vogtle 1R24 Condition Monitoring Summary for Limiting Flaws 1R24 Limiting Flaw CM Limit Mechanism Loe Depth Length Mechanical wear due 48% TW for SG3-R30-C111 31%TW 0.41-inch to foreign objects 1.5-inch flaw Mechanical wear at SG4-R40-C82 0.4-inch 64% TW for 37%TW AVB supports AV4 (assumed) 0.4-inch flaw Mechanical wear and wall loss from SG1-R1-C87 48% TW for 38%TW 1.21-inch secondary side TSH+20.41 1.5-inch flaw cleaning process Mechanical wear at SG4-R44-C21 53%TW 17%TW 0.35-inch TSP 7H-0.58 1.12-inch flaw Circumferential SG4-R49-C67 ODSCC at the HL PDA: 34.7% 171 ° circ PDA: 53%

TSH+0.00 Expansion Transitions SEO: 67.21%

Axial ODSCC at Tube SG4-R25-C7 4 SEO: 62.8% SEL:0.29-TWfor OXP in HL Tubesheet TSH-1.24 TW inch 0.29-inch SEL SEO: 61%

ODSCC at Dents and SG4-R 14-C42 SEO: 31.2% SEL: 0.295-TW for 0.29 Dings 7H+2.51 TW inch 5-inch SEL SEO - Structural Effective Depth SEL - Structural Effective Length For volumetric wear flaws with pressure-only loading condition, tube burst and ligament tearing (i.e., pop-through) are coincident, therefore, satisfaction of the tube burst criteria at 3L'iPNo also satisfies the accident-induced leakage performance criteria (AILPC) at steam line break (SLB) differential pressure.

For all SCC flaws, the burst and ligament tearing pressures are greater than the minimum burst and leakage integrity limits of 4044 psi and 2560 psi, respectively. This includes material property, burst relation, and NOE uncertainties at 0.95 probability and 50%

confidence.

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Enclosure to NL-23-0745 1R24 Steam Generator Tube Inspection Report For existing degradation mechanisms, a comparison of the previous OA projection was compared to the 1R24 inspection results. The following provides a discussion of each comparison.

For potential wear caused by known (legacy) foreign objects remaining in the SGs, the previous 1R23 OA stated that the legacy foreign objects remaining in the SGs will not adversely affect SG tube integrity for at least two full operating cycles. During the 1R24 eddy current inspections no tube wear was reported that was associated with legacy foreign objects. Therefore, the foreign object wear projection methodology remains valid and conservative. During the 1R24 eddy current inspections, there was no new foreign object wear detected.

For AVB wear, the OA projection from the 1R23 assessment predicted an existing AVB wear at a maximum depth of 44% TW for AVB wear inspected in 1R23 (SG2 and 3). The OA projection from the 1R22 assessment predicted an existing AVB wear depth of 49.2% TW for AVB wear inspected in 1R22 (SG 1 and 4 ). The largest existing AVB wear depth reported during 1R24 was 37% TW. The OA projections from the assessments at 1R22 and 1R23 predicted new AVB wear at a maximum depth of 40.4% TW in SGs 1 and 4 and 26% TW in SGs 1 and 3. The largest new AVB wear depth reported across all four SGs during 1R24 was 13%. Therefore, the OA assumptions, inputs, and methodology for AVB wear projections remain valid and conservative.

For wear and wall loss from secondary cleaning, no wear or wall loss progression is expected outside of eddy current depth measurement uncertainty. The maximum increase in legacy wear from secondary side cleaning from 1R23 to 1R24 is 2% TW, well within the measurement uncertainty. Therefore, the OA assumptions, inputs and methodology for these projections remain valid and conservative.

For TSP wear, the end of cycle (EOC) 24 OA projections for TSP wear was determined in the 1R23 assessment to be 26.5% TW. The largest TSP wear depth reported during 1R24 was 17% TW. The OA projection from this assessment predicted new TSP wear at a maximum depth of 17 .5% TW. There were no new indications of TSP wear during 1R24.

Therefore, the OA assumptions, inputs and methodology for TSP wear projections remain valid and conservative.

The EOC-24 simplified worst-case degraded tube Monte Carlo OA projection over 1-cycle for circumferential ODSCC at expansion transitions from 1R23 assessment is a flaw with a maximum depth of 97.1 % TW, a circumferential extent of 182 degrees (1.09 inch), and a PDA of 34.4%. Fully probabilistic analyses were also performed assuming up to nine undetected flaws with OA durations of one and two cycles. The probability of burst (POB) and probability of leakage (POL) for the most limiting case for the 2-cycle OA duration were 0.011 % and 2.104%, respectively. The projected burst pressures for 1- and 2-cycle OA durations were 6949 psi and 6792 psi, respectively. No leakage was projected for the 1-cycle projections, but 0.079 gpm was predicted for the 2-cycle OA duration. The largest circumferential ODSCC indication detected at expansion transitions during 1R24 had a maximum depth of 74%, circumferential extent of 171 degrees, and a PDA of 34.7%. The burst and ligament tearing pressure of this flaw with material, burst relation and NOE uncertainties included at 95/50 are 6989 psi and 9429 psi, respectively. This most limiting E-10

Enclosure to NL-23-0745 1R24 Steam Generator Tube Inspection Report flaw detected during 1R24 was bounded by the 1- cycle Monte Carlo and the 1- and 2-cycle fully probabilistic projections.

The EOC-24 fully probabilistic analysis assumed up to nine undetected flaws at the beginning of Cycle 24. This was derived from a Weibull probability of failure evaluation that predicated an additional two flaws initiating during the 1-cycle. This results in a prediction of eleven circumferential ODSCC indications at 1R23. In reality, five indications were detected. Based on this review, the OA assumptions, inputs, and methodology for circumferential ODSCC projections remain valid and generally conservative.

4. The number of tubes plugged during the inspection outage.

Table 12 presents a summary list of all SG tubes plugged in 1R24.

Table 12: Vogtle 1R24 Plugging List SG Row Column Indication Location Plugging Basis Stabilizer 4 14 42 SAi 7H+2.51 Axial ODSCC No 4 25 74 SAi TSH-1.24 Axial ODSCC No Circumferential 4 39 68 SCI TSH-0.18 Yes - HL ODSCC Circumferential 4 43 64 SCI TSH-0.13 Yes - HL ODSCC Circumferential 4 43 67 SCI TSH 0.0 Yes - HL ODSCC Circumferential 4 43 74 SCI TSH -01 Yes - HL ODSCC Circumferential 4 49 67 MCI TSH 0.0 Yes - HL ODSCC SAi - Single Axial Indication, SCI - Single Circumferential Indications, MCI - Multiple Circumferential Indications D. Technical Specification 5.6.1 O.d, 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 1R24 eddy current inspections did not detect any new wear from foreign objects. For the foreign objects known to be remaining in the SG secondary side following 1R24, the analysis performed establishes that at least two cycles of operating would accrue before the object with greatest potential for tube degradation could potentially exceed the plugging limit of 40% TW.

There is no wear at locations associated with the foreign objects known to be located on the secondary side in all SGs. Regarding new and existing foreign object wear indications, there has either been no observed growth, or no foreign object observed at these locations and no further growth is expected outside of NOE measurement uncertainties.

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Enclosure to NL-23-0745 1R24 Steam Generator Tube Inspection Report Based on application of conservative AVB wear growth rates, the condition of the Vogtle Unit 1 SG tubes has been analyzed with respect to continued operability of the SGs until the end of Cycle 26 without exceeding the limits for structural and leakage integrity. A 2-cycle OA was performed for AVB wear indications existing at 1R24 and assumed undetected flaws. The growth rates were determined by comparative analysis of AVB wear sites for all SGs. The maximum growth rate at 1R24 was 2.19% TW/effective full power years (EFPY). However, in order to provide a level of conservatism, the growth rate from the previous operating interval of 4.0%

TW/EFPY was used for 1R24 OA. The OA duration is conservatively assumed to be 3.0 EFPY, with an expected duration of 2.8 EFPY. The condition monitoring limit for AVB wear is 64% TW while the largest AVB wear indication left in service at 1R24 was 37% TW. The maximum AVB wear indication existing at 1R24 is projected to be 49.0% TW at the next planned inspection (1 R26), which does not include NOE uncertainties. A conservative depth of 20% TW was assumed for an undetected flaw within the OA evaluation. The maximum AVB wear indication assumed to be undetected at 1R24 is projected to be 32.0% TW at 1R26. All AVB wear projections for 2 cycles satisfy the condition monitoring limit of 64% TW.

Mechanical wear at TSP locations was detected in two tubes during 1R24. Based on application of conservative TSP wear growth rates, the condition of the Vogtle Unit 1 SG tubes has been analyzed with respect to continued operability of the SGs until the end of Cycle 26 for existing and assumed undetected flaws, without exceeding the performance criteria. The depth cycle growth per EFPY used was 5.0% TW. The largest TSP wear indication left in service at 1R24 is 17% TW. The maximum TSP wear indication existing at 1R24 is projected to be 32.0% TW at 1R26, which does not include NOE uncertainties. The maximum TSP wear indication assumed to be undetected at 1R24 is projected to be 32.0% TW at 1R26 (not including NOE uncertainty). All existing and undetected TSP wear projections satisfy the condition monitoring limit of 53% TW.

There has been a recurrence of circumferential ODSCC in the hot leg expansion transitions, with five (5) indications detected at 1R24. One (1) Axial ODSCC at a HL freespan ding was detected at 1R24. One (1) indication of Axial ODSCC at a tubesheet overexpansion which was located 1.24-inches below the top of tubesheet. A fully probabilistic OA analysis was performed for all of existing degradation mechanisms for an inspection interval of 2 cycles.

The operational assessment of SCC degradation mechanisms is performed using fully probabilistic methods. The basic methodology for the fully probabilistic analysis is the same for each SCC mechanism, however, the specific inputs for each mechanism may differ. The basic fully probabilistic analysis method includes:

• Determination of beginning of cycle (BOC) flaw distributions o max depth o total length o PDA (for circumferential flaws)

• Flaw characteristic growth rates o based on the EPRI typical default growth rates for sec o corrected for Vogtle Unit 1 hot leg temperature

• Length of cycles

• The remainder of critical inputs to the fully probabilistic model, including number of undetected flaws, tube geometry, material properties, normal operating, accident pressures, and leakage limits.

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Enclosure to NL-23-0745 1R24 Steam Generator Tube Inspection Report BOC flaw distributions account for the differences between destructive analysis results and eddy current measurements. The BOC total length distributions were adjusted for non-destructive examination (NOE) measurement uncertainty through probabilistic simulation, including both the mean regression and standard error. In this way, the BOC lengths are based on site-specific history (when available), but also have been adjusted to account for sizing error to true flaw lengths, as determined by destructive analysis of pulled tubes and laboratory cracks. Similarly, the max depth distributions are derived from the site-specific probability of detection (POD) curves. The Vogtle Unit 1 specific POD distributions account for the correlation of measured voltage amplitudes to true flaw max depth via the ETSS voltage amplitude to true depth distribution correlation (Ahat).

Axial ODSCC at a tubesheet overexpansion has not been previously observed at Vogtle or other domestic A600TT SGs. This degradation mechanism shares the same detection technique, sizing technique, and exam scope as axial ODSCC at the expansion transition. For this reason, the flaw that was detected at 1R24 is included in the populations considered in the OA for axial ODSCC at the expansion transition, and the results are applicable to both mechanisms. This is a conservative assumption because axial ODSCC that exists within the expanded tubesheet region has negligible burst potential and very limited leakage potential.

Potential SCC degradation mechanisms were also evaluated for the next 2 cycles.

The results of the OA for those degradation mechanisms detected during 1R24 are summarized in Table 13. The assessments for all existing degradation mechanisms conclude that all SG performance criteria for structural and leakage integrity (including cumulative leakage for all mechanisms) will be satisfied until the next planned inspection at the end of Cycle 26.

Table 13: Vogtle 1R24 OA Results Summary Burst Pressure at Leak Rate at Degradation POB POL Lower5% Lower5%

OA Duration Mechanism (%) (%) (psi) Caom)

Circ. ODSCC 2 Cycle 0.03 1.79 6690 0.061 HL TTS Axial ODSCC 2 Cycle 0.148 0.055 6373 0.00 Dent/Ding Axial ODSCC 2 Cycle Bulge/Overexp 0.188 0.099 6106 0.00 ansion Acceptance Criterion  ::; 5% :55%  ;:: 4044 psi  ::; 0.35 gpm E-13

Enclosure to NL-23-0745 1R24 Steam Generator Tube Inspection Report E. Technical Specification 5.6.10.e, Number and percentage of tubes plugged to date, and the effective plugging percentage in each.

Table 14: Total Plugged Tubes after Vogtle 1R24 1R24 Total SG # Tubes # Plugged # Plugged  % Plugging 1 5,626 0 31 0.55%

2 5,626 0 31 0.55%

3 5,626 0 42 0.75%

4 5,626 7 97 1.72%

Total 22,504 7 201 0.89%

F. Technical Specification 5.6.10.f, The results of any SG secondary side inspections.

FOSAR inspections were performed at 1R24. A total of forty-eight (48) objects were found during FOSAR and eight (8) were retrieved. The majority of the objects were sludge rocks.

Seven (7) objects required further evaluation to ensure tube integrity for upcoming cycle(s). For the objects remaining in the SG secondary side following Vogtle 1R24, the analysis performed establishes that continued steam generator operation with the foreign objects known to be present in the secondary side will not adversely affect the steam generator tube integrity for at least two full operating cycles, or until the 1R26 outage. Sludge lancing was performed and a total of 71.50 lbs. of deposits were removed.

G. Technical Specification 5.6.10.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.

No tube leakage was reported during this operating interval.

H. Technical Specification 5.6.1 0.h, The calculated accident induced leakage rate from the portion of the tubes below 15.2 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 2.48 times the maximum operational primary to secondary leakage rate, the report should describe how it was determined.

None of the indications reported during the Vogtle 1R24 SG inspections were evaluated to have primary to secondary leakage under accident induced conditions. There was no leakage from the portion of tubing within the H* depth for which to apply the leak rate factor associated with the alternate repair criteria. Since there was no calculated leakage from any other sources, none of the Vogtle 1 SGs installed tube plugs require leakage calculations. Therefore, for these E-14

Enclosure to NL-23-0745 1R24 Steam Generator Tube Inspection Report indications the accident induced leakage rate would be zero, satisfying the accident induced leakage performance criteria.

I. Technical Specification 5.6.1 O.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.

During 1R24, as part of the tube inspection program, 100% of the tubes in all SGs were tested with the bobbin and array probe. The bobbin data collected was screened for large amplitude tubesheet indications of greater than 50 volts with a phase angle between 25° and 50 ° suggestive of tube severance. Both manual and automated data screenings have been performed with SVR as the code to report should a sever-type signal be detected. No SVR call was made for the entirety of the bobbin data collected therefore, no indications of slippage were identified.

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