ML25114A223
| ML25114A223 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 04/24/2025 |
| From: | Jenkins B Dominion Energy Co, Dominion Energy South Carolina |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| 25-122 | |
| Download: ML25114A223 (1) | |
Text
Serial No.25-122 Docket No. 50-395
Enclosure:
page 1 of 23 V. C. Summer Unit 1 STEAM GENERATOR TUBE INSPECTION REPORT FOR THE FALL 2024 REFUELING OUTAGE In accordance with V. C. Summer Power Station Unit 1 (VCS) Technical Specification (TS) 6.9.1.12, Dominion Energy is submitting this Steam Generator Tube Inspection Report which describes the results of the previously complete VCS Steam Generator (SG) examinations. During the VCS Fall 2024 End-of-Cycle 28 (EOC28) refueling outage (1R28), SG inspections were completed in accordance with TS 6.8.4.k for all three SGs, designated as SG-A, SG-B, and SG-C. Based upon entry into Mode 4, exceeding 200°F, on October 27, 2024, a report was required to be submitted by April 25, 2025.
All three SGs were last inspected during the Spring 2020 refueling outage (EOC25). Just prior to the EOC25 shut down, all SGs had a cumulative operating time of 267.97 EFPM. Over Cycles 26 through 28, the SGs operated for an additional 48.06 EFPM. Therefore, at the time of this inspection (EOC28),
the Unit 1 SGs had a cumulative operating time of approximately 316.03 EFPM since installation.
The three VCS Unit 1 SGs are replacement Westinghouse Model Delta 75 which were installed in Fall of 1994. Each of the replacement steam generators contains 6,307 Thermally Treated Alloy 690 tubes with nominal 0.6875 x 0.040 wall thickness. Stress relief was performed during fabrication on the U-bends of the first 17 rows of tubing. The straight sections of the tubing are supported by nine tube support plates made of 1.125 thick, SA-240, Type 405 stainless steel. The tube support plates (TSP) have trefoil broached holes. The u-bend sections of the tubing are supported by four sets of anti-vibration bars (AVB) made of SA-240, Type 405 stainless steel. A flow distribution baffle (FDB) plate is located between the tubesheet and the lowest support plate. The D-75 steam generators contain a sludge collector above each primary separator which is designed to reduce the accumulation of sludge at the tubesheet. The tube-to-tubesheet joints are formed by a full depth hydraulic expansion and a weld to the primary cladding on the tubesheet.
The nominal Thot during Cycles 26, 27, and 28 at full power was 619.6oF.
The SG feedring has spray-nozzles (spray cans) which serve as loose parts catching mechanisms due to the many 0.25 diameter holes.
The VCS Unit 1 SGs have experienced no reportable primary-to-secondary leakage since replacement in 1994.
There were no deviations taken from Mandatory and/or Needed (Shall) requirements important to tube integrity from the EPRI Guidelines referenced by NEI 97-06 during the examination or the cycles preceding the EOC28 examination.
Figure 5 contains a schematic depicting the arrangement of the steam generators without dimensions.
In the discussion below, Bold Italicized wording represents TS verbiage and the required information is provided directly below each reporting requirement. A list of acronyms is contained in Table 14 at the end of this report.
6.9.1.12 A report shall be submitted within 180 days after the initial entry into MODE 4 following completion of an inspection performed in accordance with specification 6.8.4.k. The report shall include:
Serial No.25-122 Docket No. 50-395
Enclosure:
page 2 of 23
- a. The scope of inspections performed on each SG, Primary Side The in-service tubing in each SG was inspected with bobbin coil probes over the full length. In addition to detection and sizing of degradation, the bobbin coil inspections, data was taken for deposit mapping, Top of Tubesheet sludge height reporting, and monitoring for tube-to-tube contact/wear.
An array probe examination was conducted on 100% of the tubes on the hot leg and approximately 75% cold leg (this includes the outer 30 rows for the tubesheet periphery and the no-tube lane) for the top of the tubesheet. The extent of the array probe inspection for the top of the tubesheet was -6 of the top of the tubesheet to +6 for outside the Flow Distribution Baffle (FDB) cutout region and to the 1st TSP for inside the FDB cutout region. Array probe scope provided an increased detection capability for potential foreign objects. Additionally, 44 tubes were examined on the Hot-Leg from 5-inches above the 9th TSP to the Hot Leg tube end for deposit mapping and broached hole blockage of TSPs.
In addition to the bobbin coil and array probe scope, 187 examinations were performed with a +Point' probe. The +Point' probe included 37 preplanned locations (29 low row U-bends in SG-B and 8 historical BLG indications) and 150 special interest locations. The special interest locations included the sizing of structure wear, one legacy foreign object wear indication, and all new dent indications.
It should be noted that both terms Dent and Ding refer to a plastic deformation of the tube that results in a reduction in the tube diameter. The two different terms were used to differentiate between the location of the signals. Historically (early generation designs) the term dent referred to local tube diameter reductions due to corrosion products from carbon steel (typically, drilled carbon steel tube support plates).
The term ding referred to local tube diameter reductions due to mechanical means (manufacturing, vibration, incidents during maintenance activities, or impact from foreign objects). Since the eddy current signals from both dents and dings are similar, the location of the indication was used to differentiate which term was used (dent for indications at supports and ding for all free span indications).
At VCS, the referenced dent signals do not represent the same phenomena as classical denting on older generation units caused by drilled carbon steel support plate corrosion damage. Since the VCS unit is not similar in design (i.e., quatrefoil stainless steel tube support plate design vs. drilled hole carbon steel tube support plate design) these same denting issues do not directly apply to the VCS unit. Tube support plate areas are not susceptible to denting caused by corrosion of the tube support plates. However, the historical nomenclature assigned to these signals has existed in the database since the steam generators were installed and has remained unchanged since that time.
The primary side work scope also included video / visual examinations (as-found / as left) of the entire hot leg and cold leg channel head bowl (including the tubesheet cladding and welds) in each SG and internal surfaces as recommended by Nuclear Safety Advisory Letter (NSAL) 12-1 Revision 1. In addition, all previously installed tube plugs were inspected. SG tube plug and channel head examinations conducted during 1R28 outage were all performed satisfactorily and did not identify any abnormal conditions. While performing the as-found inspection in SG-C cold leg, flakes were discovered in the bottom of the SG bowl. The evaluation of the reported flakes concluded that the flakes are not a material of detrimental concerns for the steam generator.
Secondary Side During 1R28 examination, the following secondary side activities were performed in all three SGs:
Top of tubesheet and sludge collector water lancing.
Serial No.25-122 Docket No. 50-395
Enclosure:
page 3 of 23 Table 1: SG Sludge Lancing SG A SG B SG C Sludge Collector 82 lbs 65 lbs 27 lbs Top of Tubesheet 36 lbs 46 lbs 73 lbs Total 118 lbs 111 lbs 100 lbs Post-lancing visual examination of the tube bundle from the entire periphery and no tube lane.
Additionally, inner bundle passes were performed across both the hot-leg and cold-legs to pass through the kidney region of each steam generator.
Visual examination of historical foreign object-related locations.
Visual investigation of any accessible locations having eddy current signals potentially related to foreign objects, and removal of retrievable foreign objects.
Steam drum visual inspections to evlauate the material conditions and cleanliness of key components such as:
o Drain pipes o Internal manways o Welds o Deck plates o Ladders o Feedwater ring, feed ring components, spray-nozzles, and support straps o Instrumentation taps (level transmitters, etc.)
o Primary separators and sludge collectors o Downcomer barrels o Swirl vanes o Secondary Separators o Steam Outlet Nozzle (flow limiting venturi)
Top of 9th Tube Support Plate (TSP) inspections:
o Non-tube lane inspections o Inner Bundle passes (Hot Leg and Cold Leg) perpendicular to the no-tube lane approximately every 10 columns. This included looking down into broached holes for broached hole blockage.
o Drops to lower supports for view around broaches from the no-tube lane.
Foreign Object Search and Retrieval was performed in all SGs. The objects identified in Table 15 include foreign objects removed or remaining in the SGs during 1R28 FOSAR and water lancing activities.
The results of all secondary-side visual inspections were performed satisfactorily, with no degradation identified. The inspections of the 9th TSP on the hot leg during the inner bundle passes did identify some broached hole blockage and flakes of deposits on the 9th TSP or in broached holes.
- b. Degradation mechanism found.
During the 1R28 examination for VCS SGs, anti-vibration bar (AVB) wear, TSP wear, FDB wear, and legacy foreign object wear were detected during the SG tube examination.
Prior to 1R28, fixed curves were developed for sizing TSP and AVB in the VC Summer RF28 inspection. To provide a reference when evaluating wear growth rates for the Operational Assessment (OA), all existing wear from the previous inspections (RF18 through RF25) were resized using these
Serial No.25-122 Docket No. 50-395
Enclosure:
page 4 of 23 fixed curves. The plan is to use these fixed curves for all support wear in future VC Summer SG inspections. Their implementation does not create inspection transients and eliminates the need for retest when TSP or AVB wear is identified in the tubes acquired without a wear standard. Furthermore, results obtained from one inspection to another using the fixed curve approach are more reliable, so the estimated wear growth rate is more accurate.
Anti-Vibration Bar (AVB) Wear During 1R28, a total of four (4) AVB wear indications were detected in three (3) tubes across all SGs combined. Three (3) AVB wear indications were reported in SG-A, zero (0) indications reported in SG-B, and one (1) indication reported in SG-C. All reported AVB wear was repeat wear, meaning no new AVB wear was reported. The maximum AVB wear depth was 11%TW. None of the AVB wear indications exceeded the Condition Monitoring (CM) limit. Table 2 summarizes the current inspection results for AVB wear.
Table 2: 1R28 AVB Wear SG Total Repeat New Repeat New Tubes / Indications Tubes / Indications Tubes / Indications Max %TW Max %TW A
2 / 3 2 / 3 0 / 0 11 N/A B
0 / 0 (1) 0 / 0 0 / 0 N/A N/A C
1 / 1 1 / 1 0 / 0 7
N/A All 3 / 4 3 / 4 0 / 0 11 N/A Notes:
- 1. One indication in SG-B from 1R25 (9%TW at 90-29 AV2) was reported as Indication not Found (INF) by bobbin in 1RF28.
TSP Wear During 1R28, a total of one hundred thirty (130) TSP wear indications were detected in one hundred seven (107) tubes across all SGs combined. There were thirty-seven (37) TSP wear indications reported in SG-A, sixty-three (63) indications reported in SG-B, and thirty (30) indications reported in SG-C. Of these, there were seven (7) new TSP indications and one hundred twenty-three (123) repeat indications. The maximum depth of repeat TSP wear was 27%TW. The maximum depth of new TSP wear was 17%TW. None of the TSP wear indications exceeded the Condition Monitoring (CM) limit.
Table 3 summarizes the current inspection results for TSP wear.
Table 3: 1R28 TSP Wear SG Total Repeat New Repeat New Tubes / Indications Tubes / Indications Tubes / Indications Max %TW Max %TW A
35 / 37 33 / 35 2 / 2 19 11 B
46 / 63 44 / 61 2 / 2 21 16 C
26 / 30 23 / 27 3 / 3 27 17 All 107 / 130 100 / 123 7 / 7 27 17 FDB Wear There were zero (0) FDB wear indications reported in SG-A, zero (0) indications in SG-B, and four (4) indications in SG-C. Of these, there was one (1) new FDB indication and three (3) repeat indications.
The maximum depth of repeat FDB wear was 33%TW which had a 1R25 resized depth of 30%TW
Serial No.25-122 Docket No. 50-395
Enclosure:
page 5 of 23 using the fixed curve exhibiting little growth over the prior 3-cycles. The maximum depth of new FDB wear was 12%TW. None of the FDB wear indications exceeded the Condition Monitoring (CM) limit as discussed in Section 9.0. Table 4 summarizes the current inspection results for FDB wear.
Table 4: 1R28 FDB Wear SG Total Repeat New Repeat New Tubes / Indications Tubes / Indications Tubes / Indications Max %TW Max %TW A
0 / 0 0 / 0 0 / 0 N/A N/A B
0 / 0 0 / 0 0 / 0 N/A N/A C
4 / 4 3 / 3 1 / 1 33(1) 12 All 4 / 4 3 / 3 1 / 1 33 12 Notes:
- 1. The max depth of 33%TW was in SG-C (35-92) which had a 1RF25 resized depth of 30%TW using the fixed curve.
Foreign Object Wear (FOW)
The examination techniques used for detection of foreign object wear included the 100% bobbin coil examination, the TTS Array examinations, and the Secondary Side Inspections (SSI) examinations of the annulus, bundle periphery and the inner bundle passes. The TTS Array examination bounded all previously identified TTS foreign object wear.
No new foreign object wear was detected in any SG at 1RF28. Table 5 summarizes the current inspection results for foreign object wear.
Table 5: 1R28 Foreign Object Wear SG Total Repeat New Repeat New Tubes / Indications Tubes / Indications Tubes / Indications Max %TW Max %TW A
0 / 0 0 / 0 0 / 0 N/A N/A B
1 / 1 1 / 1 0 / 0 27 N/A C
0 / 0 0 / 0 0 / 0 N/A N/A Dents All dents/dings (> 5 Volts or new at 1R28) were examined with the +PointTM probe. No signs of corrosion related degradation were associated with any dent/ding. There were nineteen (19) new dents reported during 1R28. SG-A had one (1) new dent located at TSP 9 hot leg, SG-B had six (6) new dents with five (5) located at TSP 8 hot leg and one (1) located at TSP 9 hot leg, and SG-C had twelve (12) new dents with four (4) located at TSP 8 hot leg and eight (8) located at TSP 9 hot leg. All nineteen (19) of the new dents were examined using the +PointTM probe. Additionally, all new dents are located around the outer periphery. The most probable cause of the new dents is thought to be repeated mechanical impact resulting from flow-induced excitation of the tubes. With flow blockage in the upper TSP on the hot leg side, elevated cross flow velocities could be occurring.
- c. Nondestructive examination techniques utilized for each degradation mechanism, Table 5 below shows the examination techniques for each degradation mechanism in 1R28.
Serial No.25-122 Docket No. 50-395
Enclosure:
page 6 of 23 Table 5 SG Tube Degradation Mechanisms and Associated NDE Techniques Classification Degradation Mechanism(s)
Primary Detection method Existing AVB Wear Bobbin - Detection and Sizing TSP Wear Bobbin - Detection and Sizing FDB Wear Bobbin and/or Array - Detection Bobbin - Sizing Potential FOW Bobbin and/or Array - Detection
+PointTM - Sizing Proactive - Relevant Pitting Bobbin and TTS Sludge Inspection using Array Proactive - Non-Relevant Tube-to-Tube wear (TTW)
Bobbin U-bend Stress Corrosion Cracking (SCC)
U-Bend Sampling using +PointTM Freespan and Dent/Ding Outer Diameter Stress Corrosion Cracking (ODSCC)
Bobbin and Dent/Ding Sampling using
+PointTM PWSCC (Hot Leg Tubesheet)
Hot Leg Inspections using Array
- d. Location, orientation (if linear), and measured sizes (if available) of service induced indications, Tables 6, 7, 8, and 9 provide the location and measured sizes of service-induced indications relative to each degradation mechanism.
Legacy AVB wear, TSP wear, and FDB wear indications detected during previous outages were resized using fix curves and used as the basis for evaluating growth rates.
Serial No.25-122 Docket No. 50-395
Enclosure:
page 7 of 23 Table 6: 1R28 AVB Wear SG Row Col Volts Elev New Offset 1R25
%TW Wear Depth (% TW)
Resized 1R25 1R28 A
19 140 0.17 AV7
+0.39 13 11 11 A
26 139 0.10 AV2
-0.69 10 8
7 A
26 139 0.14 AV7
+0.88 12 10 10 B
90 29 n/a AV2
+0.09 11 9
INF (1)
C 26 3
0.10 AV2
-0.56 6
7 7
Notes:
- 1. The AVB indication from 1R25 (9%TW at 90-29 AV2) was reported as Indication not Found (INF) by bobbin in 1R28.
Table 7: 1R28 TSP Wear SG Row Col Volts Elev New Offset 1R25
%TW Wear Depth (% TW)
Resized 1R25 1R28 A
1 16 0.10 05C
-0.57 9
7 10 A
1 52 0.10 04C
-0.55 10 9
10 A
1 58 0.09 03C
-0.55 11 9
9 A
1 60 0.10 03C
-0.51 10 9
10 A
1 60 0.23 03C 0.47 19 17 19 A
1 66 0.17 03C 0.41 15 13 15 A
1 78 0.17 06C
-0.05 16 15 15 A
1 82 0.12 03C
-0.56 12 11 11 A
1 88 0.21 07C
-0.05 20 18 18 A
2 1
0.23 07C
-0.67 19 17 19 A
2 3
0.08 07C 0.39 10 9
8 A
2 5
0.12 05C
-0.6 12 10 11 A
2 59 0.17 07C
-0.07 14 13 15 A
2 79 0.18 07C
-0.09 17 16 16 A
2 87 0.15 07C
-0.05 16 15 14 A
3 54 0.13 07C 0.52 13 11 12 A
3 66 0.18 08C
-0.07 17 15 16 A
3 108 0.16 05C 0.37 17 15 14 A
3 140 0.14 07C 0.35 13 11 13 A
4 81 0.10 07C 0.45 11 9
10 A
4 99 0.11 05C 0.47 14 12 11
Serial No.25-122 Docket No. 50-395
Enclosure:
page 8 of 23 A
4 103 0.07 05C
-0.56 11 9
7 A
4 103 0.08 05C 0.49 13 11 9
A 6
1 0.12 04C
-0.48 13 12 11 A
6 85 0.11 08C
-0.6 11 A
6 93 0.11 05C 0.42 12 10 11 A
8 131 0.11 06C 0.42 12 10 11 A
15 2
0.11 05C 0.49 11 A
17 2
0.16 05C 0.44 16 14 15 A
61 12 0.08 04C
-0.53 11 9
8 A
67 24 0.14 07C 0.47 13 11 13 A
77 122 0.16 07C 0.35 15 14 14 A
91 28 0.14 07C
-0.6 15 13 13 A
96 55 0.16 06C 0.43 16 14 14 A
101 62 0.10 08C 0.45 13 11 10 A
115 62 0.08 09H 0.37 12 11 8
A 115 72 0.14 08C 0.3 15 13 13 B
1 2
0.05 05C
-0.62 4
4 5
B 1
2 0.12 05C 0.39 13 13 11 B
1 2
0.11 06C
-0.67 12 12 11 B
1 2
0.15 06C 0.37 15 14 14 B
1 8
0.18 07H 0.39 16 B
1 14 0.15 07H
-0.58 15 14 14 B
1 28 0.13 07H
-0.6 13 12 12 B
1 28 0.08 07H 0.42 8
7 8
B 1
140 0.09 06C
-0.72 8
7 9
B 1
140 0.11 06C 0.39 13 12 11 B
2 17 0.09 07H 0.4 9
8 9
B 2
31 0.20 05C 0.39 16 15 17 B
2 31 0.13 06C 0.44 12 11 12 B
2 61 0.11 04C
-0.58 10 9
11 B
2 111 0.16 07C 0.4 14 14 14 B
2 113 0.26 06C
-0.05 20 21 21 B
2 113 0.25 07C
-0.05 19 20 20 B
3 4
0.07 06C
-0.65 10 10 7
B 3
46 0.26 07C
-0.54 21 21 21 B
3 46 0.15 08C
-0.6 14 14 14 B
3 54 0.10 06C 0.46 10 10 10 B
3 76 0.09 07C
-0.56 8
8 9
B 3
80 0.15 06C 0.39 15 15 14 B
3 84 0.17 07C 0.42 17 17 15 B
3 88 0.15 07C
-0.53 16 16 14
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Enclosure:
page 9 of 23 B
3 90 0.10 07C 0.36 11 11 10 B
3 112 0.10 07C 0.43 13 12 10 B
4 117 0.06 07C 0.53 9
8 6
B 5
84 0.09 07C 0.39 12 10 9
B 5
88 0.09 05C
-0.54 8
7 9
B 5
88 0.21 07C
-0.57 18 16 18 B
5 88 0.09 07C 0.54 11 9
9 B
5 88 0.10 08C
-0.63 9
8 10 B
5 88 0.10 08C 0.54 10 8
10 B
5 90 0.08 07C
-0.59 8
7 8
B 5
90 0.11 07C 0.47 13 12 11 B
5 90 0.08 08C
-0.63 8
7 8
B 5
90 0.13 08C 0.5 14 12 12 B
5 116 0.13 07C 0.42 14 12 12 B
6 75 0.10 07C
-0.52 11 9
10 B
6 125 0.09 05C 0.47 11 9
9 B
10 121 0.07 08C
-0.6 7
6 7
B 10 121 0.05 08C 0.44 6
5 5
B 12 139 0.05 06C
-0.74 11 10 5
B 20 139 0.07 03H
-0.48 13 12 7
B 34 9
0.10 06C 0.48 11 9
10 B
39 120 0.08 08C 0.42 8
7 8
B 45 12 0.11 03H
-0.54 12 10 11 B
54 121 0.11 07C
-0.65 10 8
11 B
56 11 0.12 03H
-0.63 14 12 11 B
64 13 0.14 07C 0.4 14 12 13 B
69 126 0.15 07C 0.35 9
8 14 B
94 45 0.09 09C 0.43 8
7 9
B 95 110 0.08 08C
-0.68 11 9
9 B
98 47 0.13 09C 0.47 12 B
99 44 0.11 09C 0.43 10 8
11 B
99 106 0.07 07C
-0.66 8
7 7
B 108 47 0.06 07H
-0.67 9
8 6
B 108 47 0.10 07H 0.37 11 9
10 B
108 63 0.11 08C 0.45 10 8
11 B
110 89 0.08 08C
-0.7 9
8 8
B 114 75 0.09 04H 0.51 9
8 9
B 115 74 0.13 06H 0.47 14 12 12 C
1 4
0.09 06C 0.37 7
8 9
C 1
8 0.15 07C 0.4 12 13 14 C
1 16 0.10 06C
-0.51 8
8 10
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Enclosure:
page 10 of 23 C
1 16 0.10 06C 0.49 8
9 10 C
1 82 0.10 08H 0.47 9
10 10 C
1 94 0.22 06H 0.47 17 18 18 C
1 112 0.25 06C
-0.56 15 17 20 C
1 112 0.14 06C 0.49 11 12 13 C
2 137 0.09 08C 0.29 5
5 10 C
3 54 0.13 06C
-0.56 12 C
5 52 0.16 06C
-0.58 14 18 14 C
6 25 0.10 07C
-0.54 8
8 10 C
6 25 0.09 07C 0.46 9
10 9
C 6
79 0.20 06C
-0.56 17 C
6 107 0.09 05C
-0.53 8
11 9
C 7
54 0.17 06C
-0.63 12 15 15 C
25 36 0.18 07C 0.49 14 15 16 C
30 137 0.08 08C 0.44 9
12 8
C 48 15 0.08 08C 0.37 8
9 8
C 52 19 0.09 08C 0.39 10 10 9
C 82 113 0.09 07C
-0.53 9
9 9
C 83 116 0.17 07C
-0.55 12 15 15 C
96 95 0.12 07C
-0.56 11 C
104 55 0.38 08C 0.38 23 26 27 C
104 67 0.13 08C
-0.6 11 11 12 C
105 78 0.12 07C
-0.68 11 15 11 C
105 78 0.07 08C 0.35 8
10 7
C 107 98 0.07 08C 0.44 7
8 7
C 110 73 0.34 08C 0.33 21 23 25 C
114 83 0.07 09H 0.49 7
8 7
Table 8: 1R28 FDB Wear SG Row Col Volts Elev New Offset 1R25
%TW Wear Depth (% TW)
Resized 1R25 1R28 C
31 92 0.13 BPH 0.49 12 C
32 89 0.23 BPH 0.48 13 17 19 C
34 91 0.12 BPH 0.47 8
11 11 C
35 92 0.58 BPH 0.48 23 30 33
Serial No.25-122 Docket No. 50-395
Enclosure:
page 11 of 23 Table 9: 1R28 Foreign Object Wear SG Row Col Volts Elev New Offset Wear Depth (% TW) 1R25 1R28 B
92 87 0.17 TSH
+0.03 26 27
- e. Number of tubes plugged during the inspection outage for each degradation mechanism, No tubes were plugged during this examination.
- f. The number and percentage of tubes plugged to date, and the effective plugging percentage each steam generators, and Table 10 provides the plugging totals and percentages to date.
Table 10 - Tube Plugging Summary Steam Generator SG-A SG-B SG-C Total Prior to 1R28 13 3
6 22 Plugged in 1R28 0
0 0
0 Total 13 3
6 22
% Plugged 0.206%
0.048%
0.095%
0.116%
Since no sleeving has been performed in the VCS Unit 1 SGs, the effective plugging percentage is the same as the actual plugging percentage.
- g. The results of condition monitoring, including results of tube pulls and in-situ testing.
None of the tube degradation identified in VCS Unit 1 SGs during the 1R28 outage violated the structural integrity performance criteria; thereby providing reasonable assurance that none of these flaws would have leaked during a limiting design basis accident. Therefore, tube pulls and in-situ pressure testing were not necessary.
The Condition Monitoring (CM) Assessment for each detected degradation mechanism was determined using the methodology described below in Table 11.
Table 11 - CM Methodology CM (Mechanism)
Methodology Structural Limit AVB Wear Monte Carlo CM Curve TSP wear Monte Carlo CM Curve FDB wear Monte Carlo CM Curve Foreign Object Wear Monte Carlo CM Curve Presented below in Figure1, Figure 2, Figure 3, and Figure 4 are the 95/50 CM limit curves for AVB wear, TSP wear, FDB wear, and foreign object wear, respectively, reported at VC Summer during
Serial No.25-122 Docket No. 50-395
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page 12 of 23 1RF28. Each CM curve accounts for material property uncertainties, burst relational uncertainties, and NDE depth sizing uncertainties as required.
As illustrated in Figure 1 through Figure 4 the wear indications for each degradation mechanism (AVB wear, TSP wear, FDB wear, and foreign object wear) all plot below the CM limit curve, demonstrating that CM is satisfied for each of these mechanisms at 1RF28.
Serial No.25-122 Docket No. 50-395
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page 13 of 23 Figure 1 - AVB Wear CM Limit Figure 2 - 1R28 TSP Wear CM Limit
Serial No.25-122 Docket No. 50-395
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page 14 of 23 Figure 3 - 1R28 FDB Wear CM Limit Figure 4 - 1R28 Foreign Object Wear CM Limit (Object Not Present)
Serial No.25-122 Docket No. 50-395
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page 15 of 23 The 1R28 inspection results were compared to the predictions from the 1R25 Operational Assessment (OA). This ensures that any adjustments that may be necessary going forward are incorporated into the OA for the 1R28 inspection. A review of the most recent OAs for the VCS Unit 1 SGs was performed. This review is summarized in Table 12 and provides the basis for concluding that the prior OA assumption was appropriate.
Table 12 - Summary of Prior Operational Acceptance Validation Degradation Mechanism 1R25 OA Prediction Observed During 1R28 Cycle Length 4.5 Effective Full Power Year (EFPY) 4.0 EFPY AVB Wear (1)
Maximum projected depth of 26.37 %TW Maximum depth of 15.77 %TW FDB / TSP Wear(1)
Maximum projected depth of 43.7 %TW Maximum depth of 35.6 %TW Foreign Object Wear Will not exceed High Probability Limit of 55%TW for one (1) inch length No new foreign object wear observed at 1RF28 and no change in existing FO wear.
Operational Leakage Projected: <150 GPD No measurable leakage over past operating cycles 26, 27, or 28 Notes:
- 1. AVB, FDB and TSP projected and observed depths are after adjusting for the ETSS sizing regression parameters.
An arithmetic methodology was used in the forward-looking integrity assessment for structure wear as summarized below.
The high probability (HP) depth is the structural depth adjusted downward to correct for burst relational uncertainty and material property uncertainty. The high probability depth is also referred to as the EOC allowable depth. The high probability depths for AVB wear, TSP wear, and FDB wear, for this operational assessment, were determined using a 3P value of 3825 psi. A 3P of 3825 psi bounds the maximum pressure differentials experienced in the VCS SGs during operation of cycles 25 through 28.
Note that the bounding length (used to determine the HP limiting depth) for each degradation mechanism is conservative given that the bounding length exceeds the actual support length/thickness.
Table 12 - High Probability Depth Degradation Mechanism Bounding Length (inch)
HP Depth
(%TW)
AVB wear 1.0 60 TSP wear 1.5 59 FDB wear 1.5 59
Serial No.25-122 Docket No. 50-395
Enclosure:
page 16 of 23 AVB The highest growth rate for AVB wear was from 2020 to 2024 with a growth rate of 0.76%TW/EFPY.
Bobbin probe technique ETSS 96041.1 Rev. 8 was relied upon during 1R28 for detection of AVB wear.
Correcting the maximum 2024 AVB wear depth of 11% TW for NDE regression error results in a best estimate depth of 15.77%TW. Increasing this depth by the upper 95th sizing uncertainty produced an upper 9th depth of 21.38%. Growing this indication by 0.76%TW/EFPY over a 4.5 EFPY operating peroid, results in an upper 95th EOC depth of 24.8%TW. Since this depth is less than 60%TW HP depth for AVB wear, reasonable assurance is provided that structural integrity for AVB wear will be maintained over upcoming Cycles 29, 30, and 31. Should VC Summer be granted the Tech Spec extension to operate for an additional two operating cycles of 1.5 EFPY each, the upper 95th EOC AVB wear becomes 27.08%TW. With this EOC depth also less than the 60%TW HP depth, reasonable assurance continues to be provided that structural integrity will be maintained for AVB wear over additional Cycles 32 and 33.
TSP Wear The maximum growth rate for TSP wear based on 1R28 results is 1.5 %TW/EFPY. Bobbin probe technique ETSS 9604.1 Rev. 14 was relied upon during 1R28 for detection of TSP wear. Correcting the maximum 2024 TSP wear depth of 27%TW for NDE regression error (ETSS 96004.1, R14) results in a best estimate depth of 29.66%TW. Increasing this depth by the upper 95th sizing uncertainty produces an upper 95th depth of 36.54%TW. Growing this indication by 1.5 %TW/EFPY over a 4.5 EFPY operating period, results in an upper 95th EOC depth of 43.29%TW. Since this depth is less than the 59%TW HP depth for TSP wear, reasonable assurance is provided that structural integrity for TSP wear will be maintained over upcoming Cycles 29, 30, and 31. Should VC Summer be granted the Tech Spec extension to operate for an additional two operating cycles of 1.5 EFPY each, the upper 95th EOC TSP wear becomes 47.79%TW. With this EOC depth also less than the 59%TW HP depth, reasonable assurance continues to be provided that structural integrity will be maintained for TSP wear over additional Cycles 32 and 33.
FDB Wear SG-C is the only steam generator with FDB wear, four (4) indications to date. The depth of the deepest return to service FDB wear indication at 1R28 was 33%TW based upon the bobbin depth. During 1R28, no tubes were plugged because of FDB wear. The maximum growth rate for FDB wear based on 1R28 results is 0.75 %TW/EFPY. However, as a conservative measure, the maximum growth rate for TSP wear based on 1R28 results (1.5 %TW/EFPY) will be used to evaluate FDB wear. Bobbin probe technique ETSS 96042.1 Rev. 4 was relied upon during 1R28 for detection of FDB wear. Correcting the maximum 2024 FDB wear depth of 33%TW for NDE regression error (ETSS 96042.1, R4) results in a best estimate depth of 33.5%TW. Increasing this depth by the upper 95th sizing uncertainty produces an upper 95th depth of 38.78%TW. Growing this indication by 1.5 %TW/EFPY over a 4.5 EFPY operating period, results in an upper 95th EOC depth of 45.53%TW. Since this depth is less than the 59%TW HP depth for FDB wear, reasonable assurance is provided that structural integrity for FDB wear will be maintained over upcoming Cycles 29, 30, and 31. Should VC Summer be granted the Tech Spec extension to operate for an additional two operating cycles of 1.5 EFPY each, the upper 95th EOC FDB wear becomes 50.03%TW. With this EOC depth also less than the 59%TW HP depth, reasonable assurance continues to be provided that structural integrity will be maintained for FDB wear over additional Cycles 32 and 33.
Foreign Object Wear No new foreign object wear indications were detected during the examination performed in 1R28, there was no growth to any existing foreign object wear indication, and no known foreign objects that are causing tube wear remain in any of the steam generators. It is impossible to predict wear rates of unknown foreign objects that could possibly enter the steam generator during the ensuing operating
Serial No.25-122 Docket No. 50-395
Enclosure:
page 17 of 23 interval; however, operating experience has shown that leakage from foreign objects initially leads to low level leakage and that the primary-to-secondary leakage monitoring program is capable of identifying leakage at very low levels. If leakage is detected, the VCS procedures require a unit shutdown when necessary to avoid the potential of tube rupture.
Summary of Operational Assessment The OA provides reasonable assurance that the performance criteria will be met over operating cycles 29, 30, and 31. Should VCS be granted Tech Spec extension, per propose TSTF-577, to operate for an additional two operating cycles 1.5 EFPY each, reasonable assurance continues to be provided that both structural and leakage requirements will be maintained over additional Cycles 32 and 33. These results have considered conservative assumptions for growth rates, cycle length, and differential pressure (3P) and summarized below in Table 13.
Table 13 - OA Projected Condition During EOC31 and EOC 33 Degradation Mechanism Limit EOC 31 EOC 33 AVB Wear 60%
24.8%
27.08%
TSP Wear 59%
43.29%
47.79%
FDB Wear 59%
45.53%
50.03%
Serial No.25-122 Docket No. 50-395
Enclosure:
page 18 of 23 Table 14 - Acronyms AILPC Accident Induced Leakage Performance Criteria NDD No Degradation Detected ARC Alternate Repair Criteria NDE Non Destructive Examination AVB Anti-Vibration Bar NOPD Normal Operating Pressure Differential BLG Bulge NTE No Tube Expansion BOC Beginning Of Cycle OA Operational Assessment BPC Baffle Plate Cold OD Outside Diameter BPH Baffle Plate Hot ODSCC Outer Diameter Stress Corrosion Cracking CM Condition Monitoring Assessment OVR Over Roll DNG Ding OXP Over Expansion DNT Dent PARC Permanent Alternate Repair Criteria ECT Eddy Current Test PDA Percent Degraded Area EFPM Effective Full Power Months PLP Possible Loose Part EOC End Of Cycle POD Probability Of Detection ETSS Examination Technique Specification Sheet PWSCC Primary Water Stress Corrosion Cracking EWM Entangled wire mass SCC Stress Corrosion Cracking FAC Flow Assisted Corrosion SG Steam Generator FDB Flow Distribution Baffle SIPC Structural Integrity Performance Criteria FO Foreign Object SSI Secondary Side Inspection FOW Foreign Object Wear TS Technical Specification FOSAR Foreign Object Search And Retrieval TSC Tube Sheet Cold GPD Gallons Per Day TSH Tube Sheet Hot HP High Probability TSP Tube Support Plate HRS High Residual Stress TTS Top of Tubesheet ISI In-Service Inspection TW Through Wall LPM Loose Part Monitoring VOL Volumetric LPS Loose Part Signal WAR Wear MBM Manufacturing Burnish Mark
Serial No.25-122 Docket No. 50-395
Enclosure:
page 19 of 23 Table 15: Foreign Object Summary at 1R28 SG FOTS Item #
Row Col Elevation Object (Dimensions in inches)
Historical (Yes/No)
Removed (Yes/No)
Comments A
12 35 72 TSH A001: Wire 0.4 Length X 0.05 Width X 0.05 Height Yes No Part Found in 1R25 No part found in 1R25 and suspected removed from lancing.
In 1R28, Array performed on affected / bounding tubes and no wear was detected. Continue to monitor affected /
bounding tubes with ECT next ISI outage.
A 13 42 69 TSH A003: Metallic Object 0.2 Length X 0.125 Width X 0.125 Height Yes (seen 1R21)
No During 1R28, part found in same configuration and location as found in 1R25. Array performed on affected / bounding tubes and no wear was detected. At next ISI outage perform ECT on affected / bounding tubes, along with SSI, to verify part configuration.
A 16 65 58 TSH +0.26 A011: Metallic Object 0.07 Length X 0.08 Width X 0.08 Height 1R25 PLP with VLP in Util2 Yes (seen 1R21)
No Object visually confirmed at location and remains fixed in place. SSI/ECT results reaffirm that this historical object has not changed tube integrity conditions (i.e., no wear or other degradation detected). At next ISI outage perform ECT on affected / bounding tubes, along with FOSAR, to verify part configuration.
67 58 TSH +0.26 1R28 PLP A
39 109 78 BPH +0.77 Gasket Material/Round Sludge Ball Yes (seen 1R24)
Tubes Plugged at 1R24 (seen in 1R25)
Visually seen in 1R25 with no change in configuration. No visual inspection of part in 1R28. ECT results in 1R28 provide reasonable assurance that the configuration of the part has not changed. No further evaluation required. Going forward, continue to inspect bounding tubes with array to provide reasonable assurance that the configuration of the part has not changed.
108 77 110 77 A
42 52 61 BPH +0.38 Metallic Debris 0.63 Length X 0.25 Width X 0.10 thickness Yes (seen 1R24)
Yes (removed 1R24)
Although object was removed from SG at 1R24, the affected
/ bounding tubes were monitored with ECT at 1R28, and no wear was detected. Going forward, continue to monitor LPS for affected / bounding tubes with ECT.
A 51 31 86 01H +0.70 ECT PLP Tube 31-86 @ 01H Yes (1R25 ECT PLP)
Tube plugged at 1R25 Affected tube is plugged and no ECT indications in surrounding tubes in 1R28. Going forward, continue ECT on bounding tubes. No SSI is required, and the area is inaccessible to current tooling.
A 52 11 2
TSH Wire 0.06 Diameter x 1.0 Length No Not found Small wire was found during post lancing quick look. After an additional water lancing flush, the small piece of wire was no longer there. The small wire may have flushed away; however, if it did not flush away it does not pose a concern for tube integrity per engineering assessment. No future actions required.
13 2
15 2
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Enclosure:
page 20 of 23 SG FOTS Item #
Row Col Elevation Object (Dimensions in inches)
Historical (Yes/No)
Removed (Yes/No)
Comments A
54 31 20 TSH Gasket Strip 1.0 Length x 0.18 Width x 0.03 Thickness No No During FOSAR, gasket material was being brought out to the No Tube Lane (NTL) from the inner bundle where it was originally located and the part dropped from the grabbers as it entered the NTL. SSI team could not locate part after considerable amount of time was spent looking for it.
Dispositioned to remain in SG based on engineering assessment of part. Going forward, no further actions required since current location of part is unknown.
32 19 30 19 A
56 SGA 1RF28 Lancing Strainer Parts Yes At 1R28, the objects found in the lancing strainers consisted of foil like material, graphite pieces, metallic pieces (from the flow straightener valve), sludge related materials, and flexitallic gasket material. While most of these objects are relatively benign in regards for potential to cause tube wear (sludge, foil, and graphite), the metallic flow modulator pieces and flexitallic gasket material are types of objects that have potential to cause wear. Potential wear of these parts, should they enter the SG shortly after 1R28 and over the next five cycles, is evaluated by engineering.
A 57 SGA FW Spray Nozzle 17 Loose Parts Yes While performing visuals of the upper internals in the steam drum, loose parts were found in FW Spray Nozzle 17. These parts are from the damaged flow modulators that were replaced in 1R26. Parts were removed from nozzle with pliers.
Potential wear from flow modulator pieces is evaluated by engineering.
B 4
92 87 TSH Legacy foreign object from 1R18 and legacy PLP from 1R21 Yes No Part Found in 1R24 Legacy LPW indication (tube 92-87) sized with +Point at 1R28. Results show little change in %TW depth (26%TW in 1R25 to 27%TW in 1R28). 1R24 LPS dispositioned to INF at 1R25. Continue to monitor LPW with ECT at the next ISI outage.
93 88 93 86 B
13 61 40 TSH ECT PLP Tube 61-40 @ TSH Yes No Part Found in 1R24 Investigated by SSI at 1R24 and no part was found. Affected
/ bounding tubes were monitored with ECT in 1R25 and 1R28 and no wear was detected in any of the tubes and no PLPs were detected in any of the bounding tubes. 1R25 LPS dispositioned to INR at 1R28. No future actions required.
Serial No.25-122 Docket No. 50-395
Enclosure:
page 21 of 23 SG FOTS Item #
Row Col Elevation Object (Dimensions in inches)
Historical (Yes/No)
Removed (Yes/No)
Comments B
17 114 83 01H ECT PLP Tube 114-83 @ 01H Yes (1R25 PLP)
Tube plugge d in 1R25 Tube 114-83 was plugged and stabilized at 1RF25 due to a suspect loose part inside the broached opening. ECT results in 1RF28 reaffirm that tube integrity conditions have not changed for the bounding tubes (i.e., no wear or other degradation detected). Going forward, continue to inspect bounding tubes with array to provide reasonable assurance that the configuration of the suspect loose part has not changed.
B 18 SGB 1R28 Lancing Strainer Parts Yes At 1R28, the objects found in the lancing strainers consisted of foil like material, graphite pieces, metallic pieces (from the flow straightener valve), sludge related materials, and flexitallic gasket material. While most of these objects are relatively benign in regards for potential to cause tube wear (sludge, foil, and graphite), the metallic flow modulator pieces and flexitallic gasket material are types of objects that have potential to cause wear. Potential wear of these parts, should they enter the SG shortly after 1R28 and over the next five cycles, is evaluated by engineering.
C 10 110 91 01C ECT PLP Tube 110-91 @ 01C Yes Tubes plugged at 1R24 Affected tubes with PLPs were plugged at 1R24. Location inaccessible by SSI. Therefore, bounding tubes were monitored with ECT in 1R28. Region was bounded by Array and no PLPs or wear was detected in 1R28. No evidence of part moving away from plugged tubes. Continue to monitor bounding tubes with ECT next ISI outage.
111 92 C
13 76 53 TSH ECT PLP Tube 76-53 @ TSH Yes (1R25 LPS)
No Part Found in 1R24 Investigated by SSI at 1R24 and no part was found. 1R25 LPS location was monitored with ECT in 1R28. Region was bounded by Array and no wear was detected in any of the tubes and no PLPs were detected in in any of the bounding tubes. Continue to monitor LPS location with ECT.
C 18 62 13 TSH Metallic Object (0.08 thick x 0.18 wide x 0.18 long)
No No Object found in the annulus at TTS during post lance SSI in 1R28. Due to the characteristics of the object (flat and non-magnetic), it could not be removed with the FOSAR tooling.
Dispositioned to remain in SG based on engineering assessment of part. Visually inspect to confirm part configuration next ISI outage.
C 19 86 25 TSH +0.30 Metallic Items No Yes Metallic objects found during post lance SSI in 1R28. Objects were removed. Inspect tube with LPR next inspection (pre-planned bounding not required). If NDD next inspection, no further action required going forward.
85 24 TSH +0.00 C
20 69 20 TSH Irregular Object (0.13 thick x 0.25 wide x 0.25 long)
No No Irregular shaped object identified during post lance SSI in 1R28 but not found during FOSAR; assumed to remain in the SG and bounded by engineering evaluations.
70 19 TSH 68 19 TSH
Serial No.25-122 Docket No. 50-395
Enclosure:
page 22 of 23 SG FOTS Item #
Row Col Elevation Object (Dimensions in inches)
Historical (Yes/No)
Removed (Yes/No)
Comments C
21 98 41 TSH Metallic Item (0.03 thick x 0.25 wide x 0.5 long)
No No Metallic object found during post lance SSI in 1R28. FOSAR team was unable to retrieve the part and indicated it was small enough to fit between the tubes. Dispositioned to remain in SG based on engineering assessment. At next ISI outage perform ECT on affected/bounding tubes, along with FOSAR, to verify part configuration.
100 41 TSH 99 40 TSH C
22 35 70 TSH Potential Metallic Item (0.12 thick x 0.18 wide x 0.15 long)
No No Potential metallic object found during post lance SSI in 1R28.
FOSAR team unable to remove part. Part is embedded in hard TTS deposit and did not move when camera pulled past.
Dispositioned to remain in SG based on engineering assessment. At next ISI outage perform ECT on affected/bounding tubes, along with FOSAR, to verify part configuration.
34 69 TSH 33 70 TSH C
24 33 70 TSH Small Wire Embedded in Hard Deposit (0.08 diameter x 0.3 long)
No No Object found during post lance SSI in 1R28. FOSAR team unable to remove part. Part is embedded in hard TTS deposit and did not move when camera pulled past. Dispositioned to remain in SG based on engineering assessment. At next ISI outage perform ECT on affected/bounding tubes, along with FOSAR, to verify part configuration.
32 69 TSH C
25 SGC 1R28 Lancing Strainer Parts Yes At 1R28, the objects found in the lancing strainers consisted of foil like material, graphite pieces, metallic pieces (from the flow straightener valve), sludge related materials, and flexitallic gasket material. While most of these objects are relatively benign in regards for potential to cause tube wear (sludge, foil, and graphite), the metallic flow modulator pieces and flexitallic gasket material are types of objects that have potential to cause wear. Potential wear of these parts, should they enter the SG shortly after 1R28 and over the next five cycles, is evaluated by engineering.
Serial No.25-122 Docket No. 50-395
Enclosure:
page 23 of 23 Figure 5 - General Arrangement