ML22300A100
| ML22300A100 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 10/27/2022 |
| From: | O'Connor M Dominion Energy Nuclear Connecticut |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| 22-274 | |
| Download: ML22300A100 (1) | |
Text
Dominion Energy Nuclear Connecticut, Inc.
Millstone Power Station 314 Rope Ferry Road, Waterford, CT 06385 DominionEnergy.com U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 OCT*2 7 2022 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.
MILLSTONE POWER STATION UNIT 3 ft Dominion j a,, Energy Serial No.
. NSSL/TFO Docket No.
License No.22-274 RO 50-423 NPF-49 END OF CYCLE 21 STEAM GENERATOR TUBE INSPECTION REPORT In accordance with the Millstone Power Station Unit 3 Technical Specification (TS)
Section 6.9.1.7, Dominion Energy Nuclear Connecticut, Inc. hereby submits the End of Cycle 21 (EOC21) Steam Generator (SG) Tube Inspection report.
The report is submitted within 180 days after initial entry into MODE 4 following completion of the spring 2022 SG inspections performed in accordance with TS 6.8.4.g, "Steam Generator (SG) Program." Initial entry into Mode 4 occurred on May 18, 2022. contains the EOC21 SG Tube Inspection report. Attachment 2 contains a list of acronyms.
The report addresses the following reporting requirements:
- a. The scope of inspections performed on each SG,
- b. Degradation mechanisms found,
- c. Nondestructive examination techniques utilized for each degradation mechanism,
- d. Location, orientation (if linear), and measured sizes (if available) of service induced indications,
- e. Number of tubes plugged during the inspection outage for each degr~dation mechanism,
- f.
The number and percentage of tubes plugged to date and the effective plugging percentage in each steam generator,
- g. The results of condition monitoring, including the results of tube pulls and in-situ
- testing,
- h. 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,
- i.
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 2.49 times the maximum operational primary to secondary leakage rate, the report should describe how it was determined; and
- j.
The results of monitoring for tube axial displacement (slippage).
If slippage is discovered, the implications of the discovery and corrective action shall be provided.
Serial No.22-274 Docket No. 50-423 Page 2 of 2 If you have any questions or require additional information, please contact Mr.
Dean E. Rowe at (860) 444-5292.
Sincerely, Michael J. O'Connor Site Vice President - Millstone Attachments:
- 1) Millstone Power Station Unit 3, End of Cycle 21 Steam Generator Tube Inspection Report
- 2) Acronyms Commitments made in this letter: None cc:
U. S. Nuclear Regulatory Commission Region I 475 Allendale Road, Suite 102 King of Prussia, PA 19406-1415 R. V. Guzman Senior Project Manager - Millstone Power Station U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 08-C 2 11555 Rockville Pike Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station Millstone Power Station Unit 3 Serial No.
22-27 4 Docket No.
50-423 End of Cycle 21 Steam Generator Tube Inspection Report MILLSTONE POWER STATION UNIT 3 DOMINION ENERGY NUCLEAR CONNECTICUT, INC. (DENC)
Serial No.
22-27 4 Docket No.
50-423, Page 1 of 25 End of Cycle 21 Steam Generator Tube Inspection Report Transmittal of this report satisfies Millstone Power Station Unit 3 (MPS3) Technical Specification (TS) 6.9.1.7 which specifies that a report shall be submitted within 180 days after the initial entry into MODE 4 following completion of an inspection performed in accordance with TS 6.8.4.g, Steam Generator (SG) Program. During MPS3's spring 2022 refueling outage (3R21 ), steam generator inspections were completed in accordance with TS 6.8.4.g. Initial entry into Mode 4 occurred on May 18, 2022; therefore, this report is required to be submitted to the NRG by November 14, 2022.
This attachment provides a summary of the MPS3 SG inspection results and specific responses to each of the TS 6.9.1.7 reporting requirements. Attachment 2 contains a list of acronyms.
Introduction MPS3 is a four loop Westinghouse pressurized water reactor with Westinghouse Model F SGs. Each SG was fabricated with 5626 U-bend thermally treated lnconel 600 tubes. The tubing is nominally 0.688 inches outside diameter with a 0.040-inch nominal wall thickness.
During SG fabrication, the tubes were hydraulically expanded over the full depth of the 21.23-inch thick tubesheet. The tubesheet was drilled on a square pitch with 0.98 inch spacing. There are 59 rows and 122 columns in each SG. The radius of row 1 Li-bends is 2.20 inches. Li-bends in rows 1 through 10 were stress relieved after being formed.
The secondary side tube support structures include eight 405 stainless steel support plates and six upper support bars (anti-vibration bars) made of chrome plated lnconel 600. The first or lower support plate is a partial plate with drilled tube holes, commonly referred to as a flow distribution baffle.Figure 9 contains a schematic depicting the general arrangement of the steam generator support configuration without dimensions.
SG-A and SG-C were last inspected during the Fall 2017 refueling outage (EOC18) and had operated for 297.1 EFPM prior to that outage.
SG-B and SG-D were last inspected during the Spring 2019 refueling outage (EOC19) and had operated for 313.9 EFPM preceding that outage.
At the time of this inspection, the Unit 3 SGs have accrued approximately 346.1 Effective Full Power Months (EFPM) of operation as of the End of Cycle (EOG) 21 (April 2022). Consequently, SGs A and C had operated for 49 EFPM since the last inspection of those SGs and SGs B and D had operated for 32.2 EFPM since those SGs were last inspected. An inspection for SGs A and C was planned for the Fall 2020 outage, but it was deferred to Spring 2022 in accordance with License Amendment No. 277.
The MPS3 SGs operate with a hot-leg temperature of 617°F and have experienced no detectable primary to secondary leakage.
Each of the MPS Unit 3 SGs was screened to identify any low row indications of improper heat treatment.
None were identified.
All four SGs were also screened for long row indications of improper heat treatment (-2 sigma tubes) and associated high residual stress.
This evaluation identified 67, 30, 39, and 23 tubes in SGs A, B, C and D, respectively, which
Serial No.22-274 Docket No.
50-423, Page 2 of 25 may have been improperly heat treated. These tubes were examined full length with array probes and closely scrutinized during the analysis process.
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 EOC21 examination.
TS 6.9.1.7 Reporting Requirements This section provides responses to each of the reporting requirements specified in MPS3 TS 6.9.1. 7.
Bold wording represents TS verbiage.
The required information is provided immediately following the restatement of each reporting requirement.
A report shall be submitted within 180 days after the initial entry into MODE 4 following completion of an inspection performed in accordance with TS 6.8.4.g, Steam Generator (SG} Program. The report shall include:
- a. The scope of inspections performed on each SG, One hundred percent of the operational tubes in all four SGs were inspected full length using eddy current examination techniques.
The majority of the tubing length was examined with bobbin probes. The Li-bends of rows 1 and 2 (955 in-service tubes) were examined with a +Point' probe technique in addition to the bobbin probe examination of the straight legs of the tubes. An additional augmented sample of 1,736 tube locations was examined with a +Point' probe. The augmented sample inspections were performed in areas of special interest including hot leg expansion transitions, tube overexpansion locations, dents/dings, as well as locations where the bobbin probe response was ambiguous.
As a result of concerns for possible degradation at dent/ding locations, the special interest scope of dents/dings with a +Point' probe was increased significantly. The specific dent/ding scope performed during the EOC21 inspection included 100% of all dents/dings 2:
2 Volts located in the hot leg straight section and 100% of all dents/dings 2:5 Volts in the U-bend and cold-leg sections of the tubes.
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).
Serial No.
22-27 4 Docket No.
50-423, Page 3 of 25 At MPS Unit 3, 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 MPS Unit 3 are 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 MPS Unit 3. 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.
No scope expansions were required; however, the base scope was augmented with additional rotating probe (including magnetically bias probes) to resolve ambiguous indications consistent with the special interest criteria.
An additional augmented sample of 25,345 tube locations was inspected with an array coil probe. The array coil probe sample included 100% of the hot leg top-of-tubesheet (TTS) locations (22,070 tubes), and approximately 13% of the cold leg TTS locations (2,949 tubes). The extent of the TTS examinations was from the first support structure detected above the secondary face of the tubesheet to 15.2 inches below the secondary face of the tubesheet; except for the tubes categorized as high residual stress tubes.
For the high residual stress tubes, the extent included the entire full length of the tubes.
A License Amendment Request (LAR) to implement a Permanent Alternate Repair Criteria (PARC) for tube degradation near the tube end was approved for use prior to the 3R15 outage. The PARC excludes the lower portion of the tubes (more than 15.2 inches below the top of the tubesheet on both the hot and cold leg sides) from augmented inspection (i.e.,
array or rotating probe) requirements. Furthermore, tubes with degradation (other than tube slippage) more than 15.2 inches below the top of the tubesheet do not require plugging.
Thus, that portion of the tube adjacent to the tube ends, (where linear indications were identified during 3R12), was not required to be inspected with array or +Point' probes during 3R21.
During 3R21, each primary channel head in all four SGs was visually examined prior to the installation of eddy current probe manipulators. This examination revealed no evidence of degradation, no evidence of plug leakage, and no foreign objects. The proper tube number, plug type, and plug position were verified for all previously installed plugs.
Westinghouse issued a Nuclear Safety Advisory Letter, NSAL-12-1 regarding SG channel head degradation. The recommended action is to perform a visual scan of both hot and cold legs of the inside surface of the channel head. Key areas of inspection include the channel head cladding, the divider plate-to-channel head weld and the visible portion of the weld at the top of the channel head bowl drain tube. The purpose of the inspection is to detect any gross defects such as indications in welds, missing weld filler material, a breach of the weld metal, unusual discoloration of the weld metal, dings or gouges, etc.
A video camera visual examination in accordance with the requirements of NSAL-12-1 was conducted on all fours SGs during 3R21.
The examination identified no evidence of degradation.
Serial No.22-274 Docket No.
50-423, Page 4 of 25 During 3R21, secondary side activities were performed in SGs A, B, C, and D and included the following:
SG A
A B
B B
- High pressure sludge lancing removed a total of 159 lbs. The quantities of sludge removed in each SG is as follows: SG-A (44 lbs.), SG-B (33 lbs.), SG-C (45 lbs.), and SG-D (37 lbs.).
- Post-sludge lancing visual examination of the TTS annulus and no-tube lane to assess as-left material condition and cleanliness, and to identify and remove any retrievable foreign objects.
- Visual investigation of accessible locations having eddy current indications potentially related to foreign objects, and if present, removal of those retrievable foreign objects.
o Five foreign objects were removed individually from the SGs (see Table 1 ).
o An abundance of objects was also removed by sludge lancing. These objects include scale, small pieces of Flexitallic gasket, and hard deposits.
o Two locations of newly detected foreign object wear were observed during 3R21. The presence of the foreign objects causing the wear was not observed.
o One lodged legacy foreign object was visually confirmed and left in place Table 1: 3R21 Foreign Object Tracking FOTS Item Location Description 3R21 Action 3R21 Results Irregularly ECT not required since shaped metallic located in periphery 14 Annulus object found in annulus Object removed annulus during from SG by FOSAR 3R21 post lance Perform FOSAR inspection 16 TTS Lancing Strainer N/A Pieces of scale and Parts at 3R21 Flexitallic gasket R56-C65 Metallic piece of Array was NOD (no Perform array on wear) on R57-C65 scale discovered affected/bounding tubes affected/bounding tubes.
8 R56-C64 by SSI in outer R57-C64 periphery tubes Perform FOSAR Object removed
@TSH at 3R21 from SG by FOSAR Irregularly Array was NOD (no R59-C66 shaped metallic Perform array on wear) on object discovered affected/bounding tubes affected/bounding tubes.
9 R59-C67 by SSI in outer
@TSC periphery tubes Perform FOSAR Object removed at 3R21 from SG by FOSAR 10 TTS Lancing Strainer N/A Pieces of scale and Parts at 3R21 Flexitallic gasket
SG C
C D
D D
FOTS Item Location Description Metal block previously R1-C4 wedged between 1
R1-C5 blowdown pipe
@TSC +3" and tube.
R1-C4 plugged.
4 TTS Lancing Strainer Parts at 3R21 Array PLP caused by Irregularly R55-C69 shaped metallic 18 R56-C69 piece of scale
@TSC discovered by SSI in outer periphery tubes at 3R21 Array PLP R57-C65 caused by soft, 22
@TSC non-metallic
+0.38" objects in periphery tubes 23 TTS Lancing Strainer Parts at 3R21 3R21 Action Inspect affected and bounding tubes (2-tube bounding) with ECT to check for movement of object and/or active wear.
Visually inspect to reconfirm location and fixity of object.
N/A Inspect PLP with +Point Perform array/+Point on affected/bounding tubes Perform SSI if +Point confirms Inspect PLP with +Point Perform array/+Point on affected/bounding tubes Perform SSI if +Point confirms N/A Serial No.
22-27 4 Docket No.
50-423, Page 5 of 25 3R21 Results Array was NDD (no wear) on bounding tubes.
Part configuration was confirmed to be fixed at 3R21 Pieces of scale and Flexitallic gasket
+Point confirmed array PLP No wear detected on affected/bounding tubes Object removed from SG by FOSAR
+Point confirmed array PLP No wear detected on affected/bounding tubes Object removed from SG by FOSAR Pieces of scale and Flexitallic gasket
- During 3R21, visual inspections of the feedring, J-nozzles, and feedring supports were completed in all four SGs. External inspections focused on weld integrity, structural orientation, and any unexpected flow patterns. All external surfaces appeared structurally sound and in proper working order with no apparent degradation observed. J-nozzle overspray was observed on some of the riser barrels. The overspray appeared as a discoloration of the riser barrel surface with no significant material loss noted. Internal inspections were performed on all the J-nozzles in each SG by visually inspecting the interface between the feedring and the J-nozzle. All nozzles appeared structurally sound with no significant FAG observed.
- During 3R21, specific components associated with the feedring (tees, reducers, elbows, piping, etc.) in SGs B and D were ultrasonically (UT) examined. The UT inspection results revealed no signs of significant wall loss or degradation.
The results of all secondary-side visual examinations performed were satisfactory, with no degradation detected.
- b. Degradation mechanisms found, Serial No.
22-27 4 Docket No.
50-423, Page 6 of 25 The existing degradation mechanisms found during 3R21 included AVB wear, TSP wear, non-support structure volumetric degradation (legacy foreign object wear where the object has been removed, fabrication and maintenance related wear).
Corrosion-related degradation, located above the H* distance, was also detected for the first time in the MP3 steam generators.
- c. Nondestructive examination techniques utilized for each degradation mechanism, Table 2 identifies the examination techniques used for each identified degradation mechanism.
Table 2: Examination Techniques for Degradation Mechanisms Detected Degradation Mechanism Technique Used AVB Wear Bobbin Detection and Sizing Tube Support Plate Wear Bobbin Detection and +Point Sizinq Volumetric Including Foreign Object Wear Bobbin/Array Detection and +Point Sizinq Top-of-Tubesheet ODSCC Arrav/+Point Detection and +Point Sizinq
- d. Location, orientation (if linear), and measured sizes (if available) of service induced indications, A total of 88 Non-AVB Volumetric Wear indications were recorded during the examination, with 57 of those recording wall losses of < 20%.
The 31 indications that recorded wall losses of ~20% are listed in Table 3.
There was a total of 736 AVB wear indications reported in all SGs with 589 of those sized at< 20% through wall. The 147 indications with wall losses of ~20% are listed in Table 4.
Table 3: Summary of Non-AVB Wear Volumetric Degradation ~0%
Max Circ Depth Axial Length Length SG Row Col Volts Location (3/4TW)
(in)
(in)
Cause SGA 2
109 0.25 06 -0.59 23 0.32 0.29 TSP Wear SGA 3
112 0.29 06C -0.99 25 0.32 0.33 TSP Wear SGA 7
3 0.22 TSC +0.13 25 0.32 0.39 Foreign Object Wear SGA 15 68 0.26 07C -0.75 23 0.32 0.33 TSP Wear SGA 15 74 0.44 07(-0.57 36 0.27 0.25 TSP Wear SGA 23 76 0.25 03C +0.32 22 0.16 0.42 TSP Wear SGA 24 7
0.22 04H +3.63 25 0.16 0.33 Foreign Object Wear SGA 28 112 0.41 01H +0.51 37 0.35 0.37 Foreign Object Wear
SG Row Col Volts Location SGA 35 71 0.26 08(-0.93 SGA 47 24 0.27 01C +0.91 0.2 01C+0.93 SGA 47 25 0.3 01C +1.15 SGA 59 60 0.21 08H -1.65 SGB 1
119 0.18 TSC + 4.03 SGB 44 98 0.45 02H + 15.76 SGC 8
61 0.23 TSH +0.45 SGC 17 52 0.59 04H -0.35 SGC 17 70 1.21 06H -0.56 SGC 35 97 0.21 05H -.067 SGC 48 88 0.46 07C -0.88 SGC 52 77 0.26 TSC +0.08 SGC 52 79 0.31 TSC +0.08 SGC 54 64 0.21 TSH +0.13 SGC 56 65 0.25 06H +13.36 SGC 56 69 0.25 TSH +0.11 SGD 17 24 0.68 07(-064 SGD 35 73 0.39 04H - 0.43 SGD 46 99 0.21 01H + 0.59 SGD 52 42 0.22 01H + 0.56 SGD 52 91 0.33 01H + 2.48 SGD 58 51 0.21 01C + 0.59 Max Depth Axial Length
(%TW)
(in) 21 0.24 28 0.27 23 0.27 30 0.27 24 0.27 21 0.27 29 0.24 25 0.27 33 0.24 45 0.27 20 0.27 27 0.27 28 0.27 31 0.32 24 0.16 24 0.32 27 0.21 36 0.29 26 0.27 24 0.21 25 0.32 32 0.32 24 0.27 Circ Length (in) 0.33 0.35 0.33 0.33 0.33 0.37 0.33 0.33 0.31 0.29 0.37 0.42 0.29 0.39 0.42 0.29 0.33 0.33 0.31 0.33 0.27 0.29 0.35 Serial No.22-274 Docket No.
50-423, Page 7 of 25 Cause TSP Wear Foreign Object Wear Foreign Object Wear Foreign Object Wear Foreign Object Wear Foreign Object Fabrication Foreign Object Wear TSP Wear TSP Wear TSP Wear TSP Wear Foreign Object Wear Foreign Object Wear Foreign Object Wear Fabrication Foreign Object Wear TSP Wear TSP Wear Foreign Object Foreign Object Foreign Object Foreign Object
Serial No.
22-27 4 Docket No.
50-423, Page 8 of 25 Table 4: Millstone 3 EOC21 Inspection Summary - AVB Wear Indications ~20% TW SG Row Col AVB No.
Amplitude Wear Depth (Volts)
(3/4TW)
A 26 115 AVl 1.2 27 A
28 115 AVl 1.49 33 A
30 9
AV5 1.46 30 A
30 113 AV5 0.95 24 A
34 46 AV5 1.32 29 A
34 46 AV6 1.63 32 A
34 48 AV3 1.16 27 A
34 73 AV4 1.67 33 A
34 73 AV5 1.79 35 A
34 109 AV4 0.9 23 A
35 59 AV2 1.25 28 A
35 60 AV4 1.4 30 A
35 60 AV5 1.13 26 A
35 71 AV4 1.26 28 A
35 77 AV3 0.69 20 A
37 45 AV2 1.88 35 A
37 45 AV3 1.06 25 A
37 69 AV5 0.77 20 A
37 69 AV6 0.91 23 A
37 90 AV3 0.94 24 A
37 91 AV5 1.06 25 A
37 106 AV4 0.77 20 A
38 52 AV3 1.02 25 A
39 57 AV2 1.46 31 A
39 57 AV3 0.82 22 A
39 57 AV4 0.96 24 A
39 60 AV4 0.97 24 A
39 71 AV5 0.83 21 A
40 45 AV4 1.29 28 A
40 71 AV3 0.87 22 A
40 71 AV4 1.12 26 A
40 94 AV5 0.53 20
SG Row Col A
41 61 A
41 102 A
42 33 A
42 53 A
42 53 A
42 77 A
42 93 A
42 93 A
42 98 A
42 98 A
42 101 A
42 101 A
42 101 A
42 102 A
42 102 A
42 102 A
43 87 A
43 87 A
43 102 A
44 64 A
44 64 A
44 74 A
44 74 A
44 98 A
45 98 A
45 99 A
46 99 A
46 99 A
49 96 A
50 44 A
50 50 A
50 76 A
50 76 A
50 76 AVB No.
Amplitude (Volts)
AV4 0.97 AV4 2.01 AV3 0.75 AV4 1.12 AV5 2.18 AV4 1.05 AV4 1.05 AV5 0.96 AV3 1.15 AV4 1.37 AV3 1.01 AV4 1.5 AV5 0.75 AV3 2.21 AV4 2.49 AV5 1.02 AV4 0.77 AV5 0.9 AV4 0.78 AV2 1.29 AV3 0.72 AV5 1.29 AV6 0.78 AV2 0.88 AV4 0.78 AV4 0.72 AV4 0.79 AV5 0.77 AV6 0.84 AV5 1.82 AV4 0.74 AV2 1.11 AV3 0.99 AV4 1.62 Serial No.
22-27 4 Docket No.
50-423, Page 9 of 25 Wear Depth
(%TW) 24 37 20 26 37 26 25 24 27 30 25 31 20 38 40 25 21 23 21 29 20 28 21 23 21 20 21 21 23 34 20 27 25 33
SG Row Col -
A 50 82 A
50 82 A
50 87 A
50 87 A
51 65 A
52 66 A
53 81 B
33 109 B
34 109 B
38 104 B
41 34 B
41 34 B
41 50 B
41 69 B
42 21 B
42 98 B
42 98 B
43 100 B
43 100 B
50 88 B
50 88 B
54 36 C
25 116 C
37 15 C
37 15 C
39 17 C
39 17 C
39 17 C
41 42 C
41 54 C
41 54 C
41 62 C
41 62 AVB No.
Amplitude (Volts)
AV3 1.4 AV4 0.81 AV2 0.98 AV3 0.75 AV5 0.86 AV4 1.17 AV3 1.38 AV3 0.79 AV3 0.85 AV4 1.26 AV4 1.73 AV5 1.65 AV4 1.02 AV5 1.72 AV5 1.3 AV2 1.63 AV3 2.43 AV3 1.2 AV4 1.36 AV3 0.92 AV4 1.07 AV5 1.78 AV6 0.73 AV2 0.89 AV5 1.09 AV2 0.72 AV4 0.83 AV5 0.69 AV3 1.12 AV3 0.7 AV5 0.93 AV2 0.99 AV3 0.71 Serial No.22-274 Docket No.
50-423, Page 10 of 25 Wear Depth (3/4TW) 31 22 24 20 23 27 29 20 22 27 33 32 24 31 26 32 39 25 28 20 22 34 21 24 28 21 23 21 27 20 25 26 22
SG Row Col C
41 62 C
41 62 C
41 62 C
41 62 C
41 65 C
41 65 C
42 20 C
42 20 C
42 20 C
42 23 C
42 23 C
42 23 C
49 96 C
49 96 C
50 93 C
56 41 D
24 117 D
28 114 D
30 114 D
37 106 D
37 106 D
37 106 D
40 99 D
40 99 D
40 102 D
40 103 D
40 103 D
40 103 D
40 103 D
41 26 D
41 26 D
41 39 D
41 39 AVB No.
Amplitude (Volts)
AV3 1.43 AV4 0.77 AV4 1.58 AV5 1.64 AV4 0.63 AV5 0.83 AV3 0.93 AV4 1.09 AV5 0.97 AV3 0.77 AV4 1.45 AV5 1.22 AV5 0.91 AV6 1.07 AV6 1.29 AV5 1.03 AV1 0.76 AV2 1.2 AV6 0.73 AV3 0.71 AV4 1.59 AV5 0.9 AV4 1.01 AV5 1.5 AV4 0.9 AV2 0.75 AV3 1.07 AV4 1.91 AV5 1.24 AV5 1.48 AV6 1.54 AV3 0.81 AV4 0.85 Serial No.
22-27 4 Docket No.
50-423, Page 11 of 25 Wear Depth
(%TW) 32 22 34 34 20 24 24 26 25 21 31 28 25 27 27 25 21 28 21 20 33 23 26 32 24 21 27 36 29 31 32 22 22
SG Row Col D
41 39 D
41 78 D
41 78 D
49 62 D
49 62 D
49 62 D
49 66 D
49 67 D
49 67 D
49 95 D
49 95 D
49 95 D
52 67 D
54 49 D
55 84 AVB No.
Amplitude (Volts)
AV5 1.2 AV3 0.85 AV4 0.73 AV1 0.92 AV2 0.87 AV3 1.52 AV2 1.6 AV2 0.95 AV3 0.82 AV2 0.71 AV3 0.73 AV4 0.67 AV4 0.81 AV3 0.83 AV5 0.91 Serial No.
22-27 4 Docket No.
50-423, Page 12 of 25 Wear Depth
(%TW) 28 23 21 23 22 31 33 25 22 20 20 20 22 23 24 During 3R21, corrosion-related degradation, above the H* distance, was detected for the first time in the MP3 steam generators. This single indication was detected on the hot-leg side of SGA in tube 10-63 at TSH +0.32". The indication was detected with the array probe (as part of the 100% TTS examination performed in each SG). The indication was confirmed using the +Point' probe and characterized as circumferentially oriented ODSCC degradation. The indication measured 10% TW with a circumferential length of 0.42 inches.
During 3R21, tube 10-63 in SGA was stabilized (using the shorter TTS stabilizer) and plugged on both ends.
Table 5: Summary of 3R21 Corrosion Related Degradation Location SGA, Tube 10-63 at TSH + 0.32" Orientation Circumferential ODSCC Amplitude (300 kHz +Point'}
0.36 Volts Maximum NOE Depth 10%TW Circumferential Extent 59 Degrees, 0.42 inches Percent Degraded Area (PDA}
0.59
- e. Number of tubes plugged during the inspection outage for each degradation mechanism, Based on inspection results, four (4) tubes were plugged during the 3R21 outage.
SIG Row Col SG-A 10 63 SG-A 42 102 SG-B 42 98 SG-C 17 70 Table 6: Summary of 3R21 Plugging Hot-Leg Cold-Leg Plugged/Stabilized Plugged Plugged Plugged/Stabilized Plugged/Stabilized Plugged Plugged Plugged Serial No.22-274 Docket No.
50-423, Page 13 of 25 Degradation Mechanism ODSCC AVB Wear AVB Wear TSP Wear
- f. The number and percentage of tubes plugged to date and the effective plugging percentage in each steam generator.
Table 9 provides the total number of tubes plugged to date and the effective plugging percentage in each SG.
Table 7: Number Tubes Plugged to Date SGA SG B SGC SGD Prior to 3R21 51 25 22 91 During 3R21 2
1 1
0 Total After 3R21 53 26 23 91 Percentage 0.942 0.462 0.409 1.617 Overall Percentage 0.857 Since no sleeving has been performed in the MPS3 steam generators, the effective plugging percentage is the same as the actual plugging percentage.
- g. The results of condition monitoring, including the results of tube pulls and in-situ
- testing, No tubes were pulled, and no in-situ pressure tests were performed.
The condition monitoring assessment concluded that the structural integrity, operational leakage, and accident induced leakage performance criteria were not exceeded during the operating interval preceding 3R21.
To perform the CM assessment for AVB wear, a CM limit curve was developed using the EPRI Flaw Handbook Calculator. Since the circumferential extent of AVB wear is <135°, it is appropriate to use the EPRI Flaw Handbook "Part-Through wall Axial Volumetric Degradation" flaw model to evaluate the CM limit. The Flaw Handbook Calculator uses Monte Carlo methods to model the various uncertainties. The CM limit includes material property uncertainties, model uncertainties, and NOE depth sizing uncertainties to establish a curve of allowable NOE measured depths (i.e., the CM limit curve).
Using the input parameters summarized in the DA, the 95/50 CM limit curve of Figure 1 was developed. This limit curve is applicable to the AVB wear indications reported at MP3 during 3R21.
Serial No.
22-27 4 Docket No.
50-423, Page 14 of 25 On Figure 1, the depths of all AVB wear reported during 3R21 are plotted with the assumption that the axial extent of the wear was 2.5 inches. This is a very conservative assumption representative of the upper limit of near-parallel contact between the AVBs and tubes. It should also be noted that there is no significant reduction in the depth limit curve from 2.5 inches to 3 inches and beyond. Since all the reported AVB wear depths (including the maximum, 40% TW), lie below the CM Limit Curve, the CM requirements for structural integrity are satisfied for AVB wear.
To perform the CM assessment for TSP and FOB wear, a CM limit curve was developed using the EPRI Flaw Handbook Calculator. Monte Carlo methods were used to incorporate material property uncertainties, model uncertainties and NOE depth sizing uncertainties to establish a curve of allowable NOE measured depths. Because of eddy current coil "look-ahead," the +Point' probe overestimates the length of degradation. Therefore, the lengths as-measured are upper-bound estimates of the actual flaw length, and no additional allowance for length sizing uncertainty is included in the CM curve.
Using the input parameters summarized in the DA, together with the EPRI Flaw Handbook
"<135° Part-Through-wall Axial Volumetric Degradation" model, the 95/50 CM limit curve of Figure 2 was developed. This limit curve is applicable to the TSP wear indications (including any baffle plate wear) reported at MP3 during 3R21.
On Figure 2, the depths of all TSP and FOB wear reported in each of the four SGs during 3R21 are plotted using the +Point' measured axial lengths and depths. Since all the reported TSP/FOB wear depths lie below the CM Limit Curve, the CM requirements for structural integrity are satisfied for TSP and FOB wear at 3R21.
R:l 70 G) s,
,JJ 3J 2,
I~
()
()_\
100.0 90.0 80.0 70.0 60.0 50.0 40.0 30.0 20.0 10.0 Figure 1: CM Limit Curve for AVB Wear CM Limit Curve for AVB Wea r ETSS 96041.3 i;i l ~~
7.!,
Serial No.
22-27 4 Docket No.
50-423, Page 15 of 25 CMLimit
. SGA SG O
. ~GC
I I
I...
CM Limit Curve for TSP/FDB Wear ETSS 96910.1 t
_.J, CM Limit
Serial No.22-274 Docket No.
50-423, Page 16 of 25 Volumetric degradation caused by foreign object wear and fabrication processes is evaluated in this section. All these indications (54 total) are identified in Figure 3 through Figure 5 along with the ETSSs that were used to measure each indication. A unique CM limit curve was developed to capture the sizing uncertainty for each unique ETSS used. Each CM limit curve in this section is based on use of the EPRI Flaw Handbook "<135° Part-Through-wall Axial Volumetric Degradation" model.
4 of the volumetric flaws (fabrication indication) were sized using ETSS 21998.1. Since the flaws lie below the 95/50 CM limit curve illustrated in Figure 3, the CM requirements for structural integrity are satisfied.
48 of the volumetric flaws were sized as foreign object wear using ETSS 27901.1. Since the flaws lie below the 95/50 CM limit curve illustrated in Figure 4, the CM requirements for structural integrity are satisfied.
2 of the volumetric flaws were sized as foreign object wear using ETSS 27902.1. Since the flaws lie below the 95/50 CM limit curve illustrated in Figure 5, the CM requirements for structural integrity are satisfied.
100 i '"
80 I 70 I
I 60 I so 30 20 Figure 3: CM Limit Curve for Volumetric Flaw Using ETSS 21998.1 J
I I*
CM Lim it Curve for Vol Indica tions ETSS 21998.1
~
CMLimit 5G B 5GC o~---~---~-------------------~
0.2 0.4 0.6 0.8 1.2 1.4
Serial No.
22-27 4 Docket No.
50-423, Page 17 of 25 Figure 4: CM Limit Curve for Foreign Object Wear Flaws Using ETSS 27901.1 CM Limit Curve for Foreign Object Wear ETSS 27901.1 100
-+CMUm;t 90 j
, SGA SG B 80
- I ::
70 I
f 60 -
1 ~1 50
- o I
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l 30
- I I. I
- 20 1=. '
10
- *
- I* :
- 1.
0 0
0.2 o.*
0.6 0.8 1.2 1.*
Figure 5: CM Limit Curve for Foreign Object Wear Flaw Sized with ETSS 27902.1 CM Limit Curve for Foreign Object Wear ETSS 27902.1 60 50 40 -
30 20 0.2 0.4 0.6 0.8
......,___ CM Limit SGA I
, I SGC 1.2
-1 I
i l I
1.4
Serial No.22-274 Docket No.
50-423, Page 18 of 25 A single circumferential ODSCC indication was identified, during the 100% TSH array probe examination, on the hot-leg in SGA, tube 10-63 at TSH +0.32". The indication was confirmed using the +Point' probe and characterized as circumferential ODSCC. A review of the prior inspection data was inconclusive in determining if the flaw was present in history, as the indication's response was influenced by adjacent hard sludge deposits.
During 3R21, since the array probe signal exhibited rotation towards the flaw-plane, the indication was reported as circumferential ODSCC.
The indication's +Point' voltage measured 0.36 Volts. Using ETSS 21410.1, the indication measured 10% TW with a circumferential extent of 59 degrees (0.42 inches). A very conservative estimate of the indication's actual PDA of 0.59 was taken to be 2.0 for evaluation purposes. Applying the ETSS uncertainty parameters to determine the upper 95/50 PDA value yields the following:
ETSS 21410.1 PDA uncertainty parameters
- Slope = 1.05
- Intercept = -0.011
- StdErr = 13.43 Upper 95/50 = (EOC21 PDA) *(Slope)+ (Intercept)+ (1.645) *(StdErr)
Upper 95/50 = (2.0) *(1.05) + (-0.011) + (1.645) *(13.43)
Upper 95/50 = 24.2 PDA Since the upper 95/50 PDA (24.2 PDA) does not exceed the conservative EOC structural limit of 77 PDA calculated using the EPRI Flaw Handbook Calculator, it is concluded that the circumferential ODSCC indication satisfied the SIPC.
To assess this indication against the AILPC, the upper 95/50 maximum through wall depth must be compared to the pop-through depth. The ETSS 21410.1 depth sizing uncertainty is first applied to the determine the upper 95/50 depth as follows:
ETSS 21410.1 Depth uncertainty parameters
- Slope= 1.0
- Intercept = 0.0
- StdErr = 13.8 Upper 95/50 = (EOC21 Depth) *(Slope)+ (Intercept)+ (1.645) *(StdErr)
Upper 95/50 = (10) *(1.0) + (0.0) + (1.645) *(13.8)
Upper 95/50 = 32. 7 % TW The pop-through depth of a circumferential crack of up to 300 degrees is greater than 90% TW. Therefore, it is concluded that the circumferential ODSCC indication would not have leaked during a limiting accident, thus satisfying the AILPC.
Serial No.
22-27 4 Docket No.
50-423, Page 19 of 25 In summary, both condition monitoring structural and leakage integrity have been demonstrated for the circumferential ODSCC indication located in SGA, tube 10-63, at outage 3R21.
It is a requirement of the IAGL that current inspection results be used to validate prior operational assessment (OA) inputs and assumptions. This ensures that any adjustments that may be necessary going forward are incorporated into the current outage OA. A review of the most recent OA for each steam generator (3R20 OA Deferral for SGs A/C and 3R19 OA for SGs B/D) was performed and the key inputs and assumptions were compared with the results from the current outage (3R21 ). This review, summarized in Table 8, shows that the as-found conditions were bounded by the projections from the previous OA for all cases with exception of the SG-B upper 95/50 AVB wear growth rate. Specifically, the SG-B upper 95/50 AVB wear growth rate (at 3R21) measured 1.23 %TW/EFPY compared to the 3R19 projected growth rate of 1.1 % TW/EFPY.
This comparison provides the basis for concluding that the prior OA assumptions were appropriate with exception of the higher than predicted SG-B upper 95/50 AVB wear growth.
To correct this issue, the largest upper 95/50 AVB wear growth rate (from all four SGs) should have been used instead of the largest growth rate from the two SGs examined at 3R19 (SGs B/D). Going forward (as performed in this OA), the growth rates in all four SGs were evaluated, and the SG exhibiting the largest upper 95/50 AVB wear growth rate was used to project structural integrity, for AVB wear, in all SGs.
Table 8: Summary of Prior QA Validation Assumed or calculated in the Observed during the Prior inspection 2020 OA Deferral (SG A/C) or projection the 3R19 OA (SG BID) 3R21 Outage satisfied SG NC: 95/50 = 2.2 % TW/EFPY 95/50 growth rate of 1.519 Yes 3/4TW/EFPY AVB Wear SG BID: 95/50 = 1.1 % TW/EFPY 95/50 growth rate of 1.23 No 3/4TW/EFPY SG NC: Maximum growth rate of Maximum growth rate of 2.2 Yes TSP/FDB 5.5 % TW/EFPY 3/4TW/EFPY Wear SG B/D: Maximum growth rate of Maximum growth rate of 3.7 5.0 % TW/EFPY 3/4TW/EFPY Yes SG NC: Minimum projected margin Minimum observed margin between 3R18 depth and 61%TW structural between EOC depth and the 95/50 depth (axial length 2.5 inch) is Yes structural limit is 4.6 % TW TSP/FDB 16%TW Wear Minimum observed margin between SG B/D: Minimum projected margin 3R19 depth and 61%TW structural between EOC depth and the 95/50 depth (axial length 2.5 inch) is Yes structural limit is 6.5 % TW 25%TW
No growth over the operating period from 3R18 to 3R21 (SG A/C) or Non-from 3R 19 to 3R21 (SG B/D) for repeat degradation left in-service.
Support Volumetric If growth occurs or new degradation Degradation develops, it will not exceed structural performance criteria prior to 3R21.
Operational Projected: 0 gpm Leakage SG A/C: 4.2 EFPY from 3R18 to 3R21 EFPY SG B/D: 3.0 EFPY from 3R19 to 3R21 3(NOPD) 3 * (1340) = 4020 psid Serial No.22-274 Docket No.
50-423, Page 20 of 25 No growth observed in non-support volumetric degradation previously left in service.
Yes A few flaws were newly reported, but none exceeded structural performance criteria.
No measurable leakage in any SG Yes since the last ISi 4.081 EFPY Yes 2.682 EFPY Yes Bounding 3960 psid Yes The Operational Assessment must demonstrate that the three performance criteria will not be exceeded prior to the next scheduled examination in each steam generator. Consistent with the Dominion Fleet Administrative Procedure for performing CMOAs, this operational assessment addresses degradation mechanisms known to exist in the MP3 steam generators: {AVB wear, TSP/FOB wear, volumetric degradation (from foreign object wear or fabrication/maintenance damage) and TTS circumferential ODSCC}, together with the impact of these mechanisms over the upcoming operating interval. Since all four SGs were examined during the 3R21 outage (spring 2022), the next scheduled tube inspection (in all SGs) is planned for 3R22; resulting in a single fuel cycle operating interval of assumed 1.5 EFPY, a conservative measure considering that 1.4 EFPY per cycle is typically bounding for MP3.
Table 9: OA for Structure Wear Degradation Mechanism Maximum Depth(%)
Structural Limit Depth(%)
Predicted at 3R22 AVB Wear 51 61 TSP/FDB Wear 66.5 69.6
Serial No.22-274 Docket No.
50-423, Page 21 of 25 Figure 6: 3R22 Worst Case Burst Pressure - Circumferential ODSCC @TTS
~
- c
.c 0.20 ~--------------------
~
---* 3R22 Min BP 0.15 I
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a, 0.10 I
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- , u 0.05 1 3XNOPD; 4020 psi I
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Lower 95/50: 8434 psi I I I '
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/---- Probability: 0.05
/ 1
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0.00 +-----1----~--
- ,.=
- :.c....__~-L..--~--~---1 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 Projected 3R22 Worst Case Burst Pressure (psi)
Table 10: Probabilities of Burst and Leakage at (3*NOPD)
Circumferential ODSCC @TTS Population POB POL Full Bundle
< 0.002%
0.074%
SG Program Maximum 5%
5%
Allowable 11,000
Serial No.
22-27 4 Docket No.
50-423, Page 22 of 25 Figure 7: 3R22 Worst Case Burst Pressure - Axial ODSCC @TSPs
- c CV
..Q
~
- 0..,
~
CV :i E
- , u 0.25 ~-----------------------~ -----,
0.20 0.15 0.10 0.05 I,
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3R22 Min BP
/
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Lower 95/50: 6476 psi 1 I
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3XNOPD: 4020 psi
_________ !,/ ~---
p b b'l't o 05 l
,,*j-ro a 11 y:
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--~--*-
I 0.00 +-----------._,,-,_,,-"ll'.=--=---'--------~---~-----*-~---~-------1 2,000 3,000 4,000 5,000 6,000 7,000 8,000 Projected JR22 Worst case Burst Pressure (psi)
Table 11: Probabilities of Burst and Leakage at (3*NOPD)
Axial ODSCC @TSPs Population POB at 3Af>
POL Full Bundle 0.238%
0.12%
SG Program Maximum 5%
5%
Allowable 9,000
Serial No.
22-27 4 Docket No.
50-423, Page 23 of 25 Figure 8: 3R22 Worst Case Burst Pressure -Axial ODSCC @Dents/Dings 0.20 -r---------------------------.-,
3R22 Min BP 0.15 I
I I
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I,
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I
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- c (0
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a..
11> 0.10
.2:
jg
- I E
- I u
0.05 1 3XNOPD: 4020 psi I
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Lower 95/50: 9851 psi 1
/
I
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I,
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Probability: 0.05 ------/-----
/ I
/ I I
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0.00 +--------~---~- - - ----=='---~---.&.~---1 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 Projected 3R22 Worst Case Burst Pressure (psi)
Table 12: Probabilities of Burst and Leakage at (3*NOPD)
Axial ODSCC @Dents/Dings Population POB at 3LlP POL Full Bundle
< 0.002%
0.0%
SG Program Maximum 5%
5%
Allowable 11,000
- h. 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 primary to secondary SG leakage was reported during Cycle 21.
- i.
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 2.49 times the maximum operational primary to secondary leakage rate, the report should describe how it was determined;
Serial No.22-274 Docket No.
50-423, Page 24 of 25 For the purposes of the condition monitoring assessment, and in accordance with the permanent alternate repair criteria, the accident leakage attributed to degradation within the tubesheet below the H* dimension must be estimated by applying a factor of 2.49 to the operational leakage.
There was no recordable operational leakage during Cycle 21; therefore, the leakage from this degradation during a limiting accident would have been zero (i.e., 2.49 X 0).
- j. The results of monitoring for tube axial displacement (slippage). If slippage is discovered, the implications of the discovery and corrective action shall be provided.
Tube slippage monitoring was performed on all four SGs using the bobbin coil data during 3R21. There was no detection of slippage during the 3R21 examination.
1 Positive direction ot sign cotwentfon for reporting indications
~ "'.
Figure - 9 Model F General Support Configuration AV6 Serial No.22-274 Docket No.
50-423, Page 25 of 25
... - - *- Location of 08H F4======;=:~=========* -
OSC SlgnConvlintion 0711
~=:z:s=:11111\111:111111:iii--===ii=..---llllllllflt -
07C 04H 03H 02H on, TSH TEH J,CI.
03C W=:::::=~==;::===::=====-====;:,1- -
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!=::;=======~=-===-==-=:a..;M -
01C TSC TEC Change (OSC + 2,00"')
f Positive direction ohlgl'I conventfoo for reporting tndkatlons
Serial No.22-274 Docket No. 50-423 Acronyms MILLSTONE POWER STATION UNIT 3 DOMINION ENERGY NUCLEAR CONNECTICUT, INC. (DNC)
Serial No.22-274 Docket No. 50-423, Page 1 of 1 Acronyms AVB Anti-Vibration Bar BET Bottom of the Expansion Transition BLG Bulge C
Column CL Cold Leg DDH Ding or Dent Signal - Reviewed in History DDI Distorted Dent or Ding Indication DDS Ding or Dent Signal - Non-Confirming w/RPC DNG Ding DNT Dent Indication ECT Eddy Current Test EFPY Effective Full Power Years EPRI Electric Power Research Institute ETSS Examination Technique Specification Sheet F/L Full Length FAC Flow Accelerated Corrosion FDB Flow Distribution Baffle FO Foreign Object FOTS Foreign Object Tracking System HL Hot Leg IGA Intergranular Attack INF Indication Not Found INR Indication Not Reportable LPI Loose Part Indication LPR Loose Part Removed LPS Loose Part Signal MRPC Motorized Rotating Pancake Coil NDD No Detectable Degradation NDE Nondestructive Examination NDF No Degradation Found NEI Nuclear Energy Institute NQH Non-quantifiable Indication -
Reviewed in History NQI Non-quantifiable Indication OA Operational Assessment ODSCC Outer Diameter Stress Corrosion Cracking OVR Above Tubesheet Over Expansion OXP Over Expansion PID Positive Identification PLG Tube is plugged PLP Possible Loose Part PTE Partial Tubesheet Expansion PWR Pressurized Water Reactor PWSCC Primary Water Stress Corrosion Cracking R
Row RAD Retest Analyst Discretion RBD Retest - Bad Data RIC Retest - Incomplete RRT Retest - Restricted Tube S/N Signal-to-Noise Ratio SAI Single Axial Indication SCC Stress Corrosion Cracking SCI Single Circumferential Indication SG Steam Generator SLG Sludge SSI Secondary Side Inspection SVI Single Volumetric Indication TEC Tube End Cold Leg TEH Tube End Hot Leg TFH Tangential Flaw-Like Signal - Reviewed in History TFS Tangential Flaw-Like Signal - Non-Confirming w/RPC TSC Top of Tubesheet Cold Leg TSH Top of Tubesheet Hot Leg TSP Tube Support Plate TTS Top of Tubesheet TWD Through-Wall Depth
% TW Percent Through-Wall VOL Volumetric Indication