NL-25-0375, Refueling Outage 2R24 Steam Generator Tube Inspection Report
| ML25269A150 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 09/26/2025 |
| From: | Coleman J Southern Nuclear Operating Co |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| NL-25-0375 | |
| Download: ML25269A150 (1) | |
Text
Regulatory Affairs 3535 Colonnade Parkway Birmingham, AL 35243 205 992 5000 September 26, 2025 Docket Nos.: 50-425 NL-25-0375 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Vogtle Electric Generating Plant - Unit 2 Refueling Outage 2R24 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 194 (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 2 (2R24) as an Enclosure to this letter.
This letter contains no NRC commitments. If you have any questions, please contact Ryan Joyce at 205.992.6468.
Respectfully submitted, Jamie M. Coleman Regulatory Affairs Director Southern Nuclear Operating Company JMC/btr/cbg
Enclosure:
2R24 Steam Generator Tube Inspection Report cc: Regional Administrator NRR Project Manager - Vogtle 1 & 2 Senior Resident Inspector - Vogtle 1 & 2 RType: CVC7000 Digitally signed by JAMIEMCO Date: 2025.09.26 10:00:12 -05'00'
Vogtle Electric Generating Plant - Unit 2 Refueling Outage 2R24 Steam Generator Tube Inspection Report Enclosure to NL-25-0375 2R24 Steam Generator Tube Inspection Report
Enclosure to NL-25-0375 2R24 Steam Generator Tube Inspection Report E-1 TABLE OF CONTENTS 1.0 Introduction/Design.............................................................................................................. 2 2.0 Scope of Inspections Performed on Each SG (Technical Specification Section 5.6.10.a)..... 2 3.0 The Nondestructive Examination Techniques Listed for Tubes with Increased Degradation Susceptibility (Technical Specification Section 5.6.10.b)............................................................ 3 4.0 The Nondestructive Examination Techniques Utilized for Each Degradation Mechanism Found (Technical Specification Section 5.6.10.c.1).................................................................... 3 5.0 Location, Orientation, Measured Size, and Voltage Responses of Each Indication For tube wear at support structures less than 20 percent through-wall, only the total number of indications needs to be reported, (Technical Specification 5.6.10.c.2)....................................... 4 6.0 Condition Monitoring Assessment and Results, Margin to Tube Integrity Performance Criteria, and Comparison with the Margin Predicted to Exist at the Inspection by Prior Assessments (Technical Specification Section 5.6.10.c.3)......................................................... 8 7.0 Tubes Repaired or Plugged During the Inspection Outage (Technical Specification Section 5.6.10.c.4).................................................................................................................................. 9 8.0 Repair Methods Utilized and Number of Tubes Repaired by Each Repair Method............... 9 9.0 Analysis Summary of Tube Integrity Conditions Predicted to Exist at Next Scheduled Inspection (the forward-looking tube integrity assessment) relative to the applicable performance criteria, including the analysis methodology, inputs, and results. (Technical Specification Section 5.6.10.d)................................................................................................... 9 10.0 Number and Percentage of Tubes Plugged (or repaired) to Date and Effective Plugging Percentage in Each SG (Technical Specification Section 5.6.10.e)...........................................12 11.0 SG Secondary Side Inspection Results Summary (Technical Specification 5.6.10.f).........12 12.0 Scope, Method, and Results of Secondary-Side Cleaning Performed in Each SG............12 13.0 Results of Primary Side Component Visual Inspection Performed in Each SG..................12 14.0 Plant-Specific Reporting Requirements.............................................................................12
Enclosure to NL-25-0375 2R24 Steam Generator Tube Inspection Report E-2 1.0 Introduction/Design The Vogtle Electric Generating Plant (VEGP) Unit 2 is a 4-loop Westinghouse plant with Westinghouse Model F steam generators with Inconel 600 thermally treated tubing. Vogtle Unit 2 refueling outage 24 (2R24) was conducted after Steam Generator (SG) service equivalent to approximately 2.80 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 (OA) 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 2R24, a total of nine (9) tubes were plugged. None of the indications exceeded the condition monitoring limits identified in the Degradation Assessment and therefore did not require 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.
2.0 Scope of Inspections Performed on Each SG (Technical Specification Section 5.6.10.a) x 100% full-length X-probe (Bobbin and Array) examination of tubes in all SGs, tube end to tube end for Row 7 and higher. Straight leg portion of cold leg (CL) and hot leg (HL)
(Rows 1-6).
x 100% low Row U-bend Bobbin and Array probe examination candy cane from CL Rows 3-6, +Point probe examination of Row 1 and Row 2 U-Bends from the top tube support plate (TSP) on the HL to the top TSP on the CL.
x 100% tubesheet expansion transition +POINT probe examination of HL tubes in all SGs from the TTS (+3/-3 inches). This inspection, along with the full length X-probe inspection, satisfied the required periodic sample that accompanies regulatory approval of H*.
x 100% +POINT of the HL tube bulge (BLG) and overexpansion (OXP) populations in all four SGs. 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.
x 100% +Point probe examination of dents and dings 2 volts.
x Special Interest +Point probe examination of all I-Codes and as needed to support tube integrity evaluations.
x Tube slippage Bobbin probe examination for H* Tube slippage monitoring.
x 100% visual inspection of all installed tube plugs from the primary side in all SGs.
x 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.
x Secondary side activities included:
o Sludge lancing o Cleanliness and foreign object search and retrieval (FOSAR)
Enclosure to NL-25-0375 2R24 Steam Generator Tube Inspection Report E-3 3.0 The Nondestructive Examination Techniques Listed for Tubes with Increased Degradation Susceptibility (Technical Specification Section 5.6.10.b) 100% +Point of HL tubes from TTS (+3/-3 inches), 100% +Point of DNT/DNG 2.0 volts, 100%
+Point of HL BLG/OXP above H* distance, and 100% +Point of Row 1 and Row 2 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.
4.0 The Nondestructive Examination Techniques Utilized for Each Degradation Mechanism Found (Technical Specification Section 5.6.10.c.1)
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 secondary side cleaning process X-probe - detection
+Point - detection and sizing Mechanical wear at TSP X-probe - detection
+Point-sizing Outside Diameter Stress Corrosion Cracking (ODSCC) at Dents and Dings X-probe - detection
+Point - detection and sizing
Enclosure to NL-25-0375 2R24 Steam Generator Tube Inspection Report E-4 5.0 Location, Orientation, Measured Size, and Voltage Responses of Each Indication For tube wear at support structures less than 20 percent through-wall, only the total number of indications needs to be reported, (Technical Specification 5.6.10.c.2)
Mechanical wear due to foreign objects Table 2 lists tube wear indications attributable to mechanical wear due to foreign objects.
Table 2: Vogtle 2R24 Foreign Object Wear Indications SG Row Column Location
%TW Depth Length (in)
Voltage 1
47 84 TSH+0.14 11 0.19 0.11 1
47 85 TSH+0.17 9
0.19 0.09 4
12 57 TSH+0.41 22 0.17 0.26 4
42 93 TSC+0.93 23 0.17 0.28 4
46 87 TSC+0.60 28 0.48 0.36 4
46 87 TSC+6.09 17 0.42 0.20 4
46 87 TSC+6.85 21 0.17 0.25 4
57 68 BPC+0.36 30 0.30 0.40 4
58 51 BPH+0.78 37(1) 0.37 0.54 BPC - Baffle Plate on CL side BPH - Baffle Plate on HL side TSC - Tubesheet region on CL side TSH - Tubesheet region on HL side Notes:
(1) This was the only indication of foreign object wear newly reported at 2R24. Lookback showed no indication of previous wear. This tube was preventatively plugged and stabilized.
Mechanical wear at Anti-vibration bar (AVB) supports In SG1, there are a total of 110 indications for AVB wear with 94 less than 20% through-wall (TW). In SG2, there are a total of 182 indications for AVB wear with 165 less than 20% TW. In SG3, there are a total of 80 indications with 71 less than 20% TW. In SG4, there are a total of 216 indications for AVB wear with 181 less than 20% TW. Table 3 - 6 includes V2R24 AVB wear indications greater than or equal to 20%TW.
Enclosure to NL-25-0375 2R24 Steam Generator Tube Inspection Report E-5 Table 3: Vogtle 2R24 SG1 AVB Wear Indications 20%TW SG Row Column Location
%TW Depth Voltage 1
32 17 AV5 21 0.53 1
41 20 AV2 22 0.71 1
41 20 AV5 21 0.65 1
41 23 AV5 20 0.5 1
42 20 AV2 22 0.76 1
43 100 AV3 20 0.63 1
43 100 AV4 23 0.82 1
44 23 AV3 27 0.86 1
44 23 AV5 31 1.21 1
46 26 AV4 20 0.64 1
46 58 AV5 21 0.74 1
47 27 AV2 24 0.9 1
48 27 AV3 23 0.84 1
49 36 AV2 22 0.86 1
49 36 AV5 30 1.48 1
50 29 AV5 49 4.18 Table 4: Vogtle 2R24 SG2 AVB Wear Indications 20%TW SG Row Column Location
%TW Depth Voltage 2
38 39 AV5 22 0.72 2
39 43 AV2 24 0.85 2
39 43 AV3 22 0.75 2
40 48 AV4 21 0.68 2
40 52 AV2 20 0.63 2
40 52 AV3 29 1.17 2
42 74 AV2 29 1.36 2
42 74 AV3 27 1.2 2
44 72 AV5 21 0.77 2
49 74 AV3 23 0.9 2
49 91 AV2 27 1.38 2
50 70 AV4 21 0.76 2
51 74 AV3 30 1.43 2
51 89 AV4 34 2.12 2
51 89 AV5 33 2.02 2
51 91 AV5 28 1.54 2
53 88 AV5 31 1.72
Enclosure to NL-25-0375 2R24 Steam Generator Tube Inspection Report E-6 Table 5: Vogtle 2R24 SG3 AVB Wear Indications 20%TW SG Row Column Location
%TW Depth Voltage 3
32 12 AV5 20 0.77 3
39 72 AV3 27 1.39 3
39 72 AV4 31 1.73 3
41 77 AV4 23 0.97 3
41 77 AV5 22 0.88 3
43 82 AV5 35 2.04 3
43 82 AV6 23 0.94 3
46 36 AV4 29 1.41 3
50 31 AV5 20 0.68 Table 6: Vogtle 2R24 SG4 AVB Wear Indications 20%TW SG Row Column Location
%TW Depth Voltage 4
30 9
AV5 25 1.06 4
39 64 AV1 20 0.71 4
39 64 AV2 21 0.79 4
39 64 AV3 28 1.31 4
39 64 AV6 31 1.63 4
43 68 AV3 25 1.06 4
43 68 AV4 28 1.34 4
43 68 AV5 25 1.09 4
43 69 AV5 21 0.79 4
43 95 AV3 23 0.9 4
43 95 AV4 20 0.67 4
44 42 AV5 25 0.82 4
44 54 AV2 21 0.58 4
44 54 AV5 31 1.14 4
45 32 AV3 22 0.82 4
45 58 AV3 30 1.55 4
45 66 AV5 20 0.72 4
46 31 AV3 29 1.44 4
48 57 AV5 20 0.72 4
49 93 AV4 21 0.64 4
49 93 AV5 26 0.9 4
50 70 AV3 25 0.99 4
51 54 AV4 24 1
4 51 55 AV3 22 0.9 4
51 76 AV2 24 0.76 4
51 76 AV3 21 0.61 4
51 76 AV5 33 1.5
Enclosure to NL-25-0375 2R24 Steam Generator Tube Inspection Report E-7 SG Row Column Location
%TW Depth Voltage 4
52 45 AV3 24 0.76 4
52 45 AV4 23 0.74 4
52 66 AV2 22 0.77 4
52 71 AV2 22 0.85 4
52 71 AV3 25 1.03 4
52 72 AV2 32 1.67 4
53 74 AV4 20 0.7 4
55 41 AV5 25 1.08 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 these nondestructive examination (NDE) 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 2R24 Tube Wall Loss from Secondary Cleaning Process SG Row Col Location Indication
%TW Depth Volts 1
1 42 TSH+10.44 PCT 11 0.12 1
1 45 TSH+10.20 PCT 13 0.14 1
1 46 TSH+10.41 PCT 21 0.25 1
1 78 TSH+9.53 PCT 16 0.18 1
1 78 TSH+11.26 PCT 10 0.10 1
1 78 TSC+11.94 PCT 13 0.14 1
1 78 TSC+12.14 PCT 24 0.29 2
1 46 TSC+10.55 PCT 21 0.25 3
1 112 TSC+18.28 PCT 22 0.27 PCT - Volumetric Indication Mechanical Wear at TSP There is one indication of mechanical wear at TSP that is less than 20% TW.
ODSCC at Dents and Dings During 2R24, there were 2 indications of axial ODSCC detected at a dent by the +Point probe.
Table 8 includes the ODSCC indication. The dent itself was measured at 2.25 volts at SG1 -
Row 58-Column 63 and 2.56 volts at SG1 - Row 58 Column 64 with the bobbin probe.
Enclosure to NL-25-0375 2R24 Steam Generator Tube Inspection Report E-8 Table 8: Vogtle 2R24 Axial ODSCC at TSP Dent SG Row Column
+Point Voltage (Vpp)
Deg Location Max Depth
(% TW)
Length (in) 1 58 63 0.14 81 7H+0.53 37.9 0.24 1
58 64 0.13 67 7H+0.64 36.3 0.24 7H - Support Plate 7 HL 6.0 Condition Monitoring Assessment and Results, Margin to Tube Integrity Performance Criteria, and Comparison with the Margin Predicted to Exist at the Inspection by Prior Assessments (Technical Specification Section 5.6.10.c.3)
The condition monitoring conclusions are summarized in the following Table 9. No tubes required in situ pressure or leak testing to demonstrate structural and leakage integrity.
Therefore, the SG performance criteria for structural and leakage integrity were satisfied for all degradation mechanisms for the preceding Vogtle Unit 2 SG operating interval from 2R22 to 2R24.
Table 9: Vogtle 2R24 Condition Monitoring Summary For Limiting Flaws Degradation Mechanism Sizing ETSS Sizing Probe 2R24 Limiting Flaw CM Limit Margin to Limit Depth Length Mechanical wear due to foreign objects 21998.
1 R4
+Point 37% TW 0.48-inch 55% TW for 0.50-inch flaw 18 % TW Mechanical wear at AVB supports I96041.
1 R8 Bobbin 49% TW 0.40-inch 67% TW for 0.4-inch flaw 18 % TW Mechanical wear from secondary side cleaning process 21998.
1 R4
+Point 24% TW 0.38-inch 49% TW for 1.5-inch flaw 25 % TW Mechanical wear at TSP 96910.
1 R12
+Point 15% TW 0.24-inch 54% TW for 1.12-inch flaw 39 % TW Axial ODSCC at Dents I28432 R2
+Point 38% TW 0.24-inch 61.7% TW for 0.24-inch flaw 24% TW 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 3PNO 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 4065 psi and 2560 psi, respectively. This includes material property, burst relation, and NDE uncertainties at 0.95 probability and 50% confidence. For existing degradation mechanisms, a comparison of the previous OA projection was compared to the 2R24 inspection results. Table 10 and the following information provides comparison results.
Enclosure to NL-25-0375 2R24 Steam Generator Tube Inspection Report E-9 Table 10: Comparison of Previous OA Projections to 2R24 Results Mechanism 2R22 Projection to 2R24
(%TW) 2R24 Limiting Flaw AVB Wear - Existing 51 49 AVB Wear - New 32 15 TSP Wear - Existing 37 15 TSP Wear - New 37 none For existing SCC mechanisms, the previous OA projections were confirmed to be conservative by comparing the projected 2R24 flaws to the 2R24 inspection results. No indications of circumferential ODSCC at the expansion transition were reported at 2R24; therefore, the 2R22 OA projections are inherently bounding. For Axial ODSCC at dents and dings, the previous OA projections for simulated flaws at end of cycle (EOC) 24 were compiled and compared to the inspection results. It was found that the EOC distributions were very conservative relative to the inspection results. The EOC distributions were projected to have 95th percentile values of approximately 85-90% TW and 0.5-inch. This is well bounding of the detected values of 36-37%TW and 0.24-inch. The Weibull failure curve from the prior OA projected more flaws at 2R24 than the two actual detections.
7.0 Tubes Repaired or Plugged During the Inspection Outage (Technical Specification Section 5.6.10.c.4)
Table 11 presents a summary list of all SG tubes plugged in 2R24.
Table 11: Vogtle 2R24 Plugging List SG Row Col Indication Location Plugging Basis Stabilizer 1
58 63 SAI 7H+0.53 Axial ODSCC No - axial indication 1
58 64 SAI 7H+0.64 Axial ODSCC No - axial indication 1
50 29 PCT AV5 AVB Wear > 40% TW Yes - accelerated wear 4
58 49 NDD BPH Bound PLP - Preventative Yes 4
58 50 PLP BPH PLP w/o FOSAR -
Preventative Yes 4
58 51 SVI BPH+0.78 FOW - Preventative Yes 4
57 49 NDD BPH Bound PLP - Preventative Yes 4
57 50 NDD BPH Bound PLP - Preventative Yes 4
57 51 NDD BPH Bound PLP - Preventative Yes SAI - Single Axial Indication, PCT - Percent Through-Wall, NDD - No Degradation Detected SVI - Single Volumetric Indication, FOW-Foreign Object Wear, PLP - Possible Loose Part 8.0 Repair Methods Utilized and Number of Tubes Repaired by Each Repair Method Nine (9) tubes plugged and seven (7) stabilized at 2R24.
9.0 Analysis Summary of Tube Integrity Conditions Predicted to Exist at Next Scheduled Inspection (the forward-looking tube integrity assessment) relative to the applicable performance criteria, including the analysis methodology, inputs, and results. (Technical Specification Section 5.6.10.d)
The 2R24 eddy current inspections detected one new indication of foreign object wear in one tube (SG4 R58C51), on the top surface of the hot leg baffle plate. The depth was measured as
Enclosure to NL-25-0375 2R24 Steam Generator Tube Inspection Report E-10 37% TW using ETSS 21998.1. This wear was not associated with a legacy foreign object.
Lookback of the array data shows no sign of wear at the last inspection in 2022 (2R22). The tube with this newly reported indication was preventively plugged and stabilized at 2R24.
Following identification of the wear, a PLP was identified by +Point at the adjacent tube. No other surrounding tubes exhibited evidence of a PLP or wear by +Point. The tube closest to the PLP (SG4 R58C50) was plugged and stabilized, and the five adjacent tubes were also preventively plugged and stabilized to form a protective plugged tube/stabilizer box. Therefore, no in-service tubes are expected to wear as a result of the PLP at this location. There was no apparent growth in legacy foreign object wear over the previous operating interval and no growth is expected in the future since the loose parts that caused the legacy wear are no longer present. Therefore, the legacy foreign object wear indications do not pose a threat to the SG structural integrity over the next operating interval, to 2R26.
The Operational Assessment for tube wear mechanisms was performed using conservative methods to project EOC flaw depths for each active mechanism. A 2-cycle OA was performed for AVB wear indications existing at 2R24 and assumed undetected flaws. The growth rates were determined by comparative analysis of AVB wear sites for all SGs. The maximum growth rate observed between 2R22 and 2R24 was 4.64% TW/EFPY. However, in order to provide a level of conservatism, the growth rate from the previous operating interval of 5.21% TW/EFPY was used for 2R24 OA. The largest return to service flaw and assumed undetected flaw are projected to be less than the 70% TW Material Structural Limit at the next planned inspection.
Structural and leakage performance criteria for detected and undetected AVB wear is satisfied using deterministic OA methods until the next planned inspection at 2R26.
Mechanical wear at TSP locations was detected in one tube during 2R24. Comparison of the 2R24 depth with historical results shows there is no significant change in the flaw identified at Vogtle Unit 2. The observed changes in depth are within the uncertainty range of the sizing techniques used. Therefore, there is essentially no recent growth in the TSP wear at Vogtle Unit 2 as of 2R24. TSP wear growth from similar plants has shown typical TSP wear growth rates to be bounded by 5% TW/EFPY. Therefore, a conservative growth rate of 5.0% TW/EFPY over the upcoming operating interval was used for the OA. The return to service flaw and assumed undetected flaw are projected to be less than the 63% TW Material Structural Limit at the next planned inspection. Structural and leakage performance criteria for detected and undetected TSP wear is satisfied using deterministic OA methods until the next planned inspection at 2R26.
No indications of circumferential ODSCC in the hot leg expansion transitions were detected during Vogtle 2R24. Axial ODSCC at a HL dent was detected at 2R24 in 2 tubes. A fully probabilistic OA analysis was performed for all 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:
x Determination of beginning of cycle (BOC) flaw distributions o max depth o total length o PDA (for circumferential flaws) x Flaw characteristic growth rates o based on the EPRI typical default growth rates for SCC
Enclosure to NL-25-0375 2R24 Steam Generator Tube Inspection Report E-11 o corrected for Vogtle Unit 2 hot leg temperature x
Length of cycles x
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.
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 (NDE) 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 POD curves. The Vogtle Unit 2 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).
Potential SCC degradation mechanisms were also evaluated for the next 2 cycles. All results show that all SG performance criteria for structural and leakage integrity will be satisfied until the next planned inspection at the end of Cycle 26.
Table 12: Results Summary Degradation Mechanism Inspection Interval EFPY 2R26 EOC Depth Projection,
%TW Material Structural Limit(2),
%TW Margin to Limit, %TW AVB Wear, Existing(1) 2-Cycle 2.9 59 70 11 AVB Wear, Undetected 2-Cycle 2.9 38 70 32 TSP Wear, Existing(1) 2-Cycle 2.9 47.5 63 15.5 TSP Wear, Undetected 2-Cycle 2.9 33.5 63 29.5 Foreign Object Wear(3) 2-Cycle 2.9 37 62 25 Secondary Side Cleaning Wear(3) 2-Cycle 2.9 24 62 38 Degradation Mechanism Inspection Interval EFPY Prob. Of Burst Prob. Of Leakage Burst Pressure Leak Rate Lower 5%
Circ. ODSCC Exp. Trans.
2-Cycle 2.9 0.160%
1.751%
6234 psi 0.023 gpm Axial ODSCC Dents/Dings 2-Cycle 2.9 0.401%
0.129%
5555 psi 0.00 gpm Combined 2-Cycle 2.9 n/a 1.88%
n/a 0.023 gpm Acceptance Criterion 5%
5%
4065 psi 0.35 gpm Margin to Limit (bounding or combined) 4.60%
3.12%
1490 psi 0.327 gpm Notes:
- 1. NDE adjusted depth
- 2. Structural Limit with material property and burst relation uncertainties calculated through Monte Carlo simulations
- 3. Maximum depth of measured flaws at 2R24. No growth expected over next 2 cycles.
Enclosure to NL-25-0375 2R24 Steam Generator Tube Inspection Report E-12 10.0 Number and Percentage of Tubes Plugged (or repaired) to Date and Effective Plugging Percentage in Each SG (Technical Specification Section 5.6.10.e)
Table 13: Total Plugged Tubes after Vogtle 2R24 SG
- Tubes 2R24
- Plugged Total
- Plugged
% Plugging 1
5,626 3
10 0.18%
2 5,626 0
16 0.28%
3 5,626 0
7 0.12%
4 5,626 6
34 0.60%
Total 22,504 9
67 0.298%
11.0 SG Secondary Side Inspection Results Summary (Technical Specification 5.6.10.f)
FOSAR inspections were performed at 2R24. A total of 14 objects were found during FOSAR and 2 were retrieved. 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 2 operating cycles, or until the 2R26 outage.
12.0 Scope, Method, and Results of Secondary-Side Cleaning Performed in Each SG Top of tubesheet sludge lancing, with post-cleanliness inspections of the tubelane, annulus, and pre-defined in-bundle hot leg columns was performed in all SGs. Sludge lancing was performed and a total of 119.5 lbs of deposits were removed. Removal of 32.5 lbs. in SG 1, 24.75 lbs. in SG 2, 44.75 lbs. in SG 3 and 17.5 lbs. in SG 4.
13.0 Results of Primary Side Component Visual Inspection Performed in Each SG A 100% visual inspection of tube plugs in all four SGs was performed from the primary side during Vogtle 2R24. Prior to the 2R24 inspection, Vogtle Unit 2 had 58 total tubes plugged. No evidence of plug degradation, excessive boron deposits, or wetness was noted during the plug visual examination. A visual inspection of the SG channel head bowl was performed for all SGs during 2R24 based on Westinghouse Nuclear Safety Advisory Letter (NSAL) NSAL-12-1, Revision 1, and industry operating experience. Visual inspections were performed in each hot leg and cold leg channel head that focused on divider plate assemblies and welds, the tubesheet, tube-to-tubesheet welds, channel heads, nozzle inner radii, and all visible clad surfaces. The purpose of the visual inspections is to look for evidence of cracking or loss of materials (e.g., rust stains).
Satisfactory results were observed in all channel heads with no areas of defects or unusual discolorations noted.
14.0 Plant-Specific Reporting Requirements Technical Specification Section 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.
Technical Specification Section 5.6.10.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
Enclosure to NL-25-0375 2R24 Steam Generator Tube Inspection Report E-13 maximum operational primary to secondary leakage rate, the report should describe how it was determined.
None of the indications reported during the Vogtle 2R24 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 2 SGs installed tube plugs require leakage calculations. Therefore, for these indications the accident induced leakage rate would be zero, satisfying the accident induced leakage performance criteria.
Technical Specification Section 5.6.10.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 2R24, 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.