ML26071A239

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End of Cycle 22 Steam Generator Tube Inspection Report in Accordance with Amendment 293 Reporting Requirements
ML26071A239
Person / Time
Site: Millstone 
(NPF-049)
Issue date: 03/11/2026
From: Petty J
Dominion Energy Nuclear Connecticut
To:
Office of Nuclear Reactor Regulation, Document Control Desk
References
25-305
Download: ML26071A239 (0)
v • d • e


Text

March 11, 2026 Dominion Energy Nuclear Connecticut, Inc.

Millstone Power Station 314 Rope Ferry Road, Waterford, CT 06385 Dorn inion Energy.corn U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 3 Serial No.

NSSL/TFO Docket No.

License No.25-305 RO 50-423 NPF-49 END OF CYCLE 22 STEAM GENERATOR TUBE INSPECTION REPORT IN ACCORDANCE WITH AMENDMENT 293 REPORTING REQUIREMENTS During the Millstone Power Station Unit 3 (MPS3) fall 2023 refueling outage (3R22),

inspections were completed on 100% of the steam generator tubes in accordance with Technical Specifications (TS) 6.8.4.g. Initial entry into Mode 4 occurred on November 26, 2023; therefore, a Steam Generator Tube Inspection Report was required to be submitted to the Nuclear Regulatory Commission (NRC) by May 24, 2024, in accordance with MPS3's TS 6.9.1.7.

The report was submitted as required on May 20, 2024 (ML24142A095).

On April 22, 2025, Dominion Energy Nuclear Connecticut (DENC) submitted a license amendment request (LAR) to the NRC requesting adoption of TSTF-577, "Revised Frequencies for Steam Generator Tube Inspections," which is an approved change to the Standard Technical Specifications. The proposed change revises the TS related to steam generator tube inspections and reporting requirements in TS section 6.8.4.g, "Steam Generator (SG) Program," and TS section 6.9.1.7, "Steam Generator Tube Inspection Report," respectively.

The initial inspection period described in the revised SG Program, paragraph 6.8.4.g.d.2, began when the 100% SG tube inspection was completed for MPS3 during the fall 2023 refueling outage (RFO). DENC is required to submit a SG Tube Inspection Report meeting the revised TS 6.9.1. 7 requirements within 30 days after implementation of the license amendment. contains a re-submittal of the EOC22 SG Tube Inspection report which has been modified to the revised MPS3 TS 6.9.1.7 requirements. contains a list of acronyms.

The report addresses the following reporting requirements:

a. The scope of inspections performed on each SG;
b. The nondestructive examination techniques utilized for tubes with increased degradation susceptibility;
c. For each degradation mechanism found:
1. The nondestructive examination techniques utilized;
2. The location, orientation (if linear), measured size (if available), and voltage response for each indication. For tube wear at support structures less than 20 percent through-wall, only the total number of indications needs to be reported;

Serial No.25-305 Docket No. 50-423 Page 2 of 3

3. A description of the condition monitoring assessment and results, including the margin to the tube integrity performance criteria and comparison with the margin predicted to exist at the inspection by the previous forward-looking tube integrity assessment; and
4. The number of tubes plugged during the inspection outage.
d. An analysis summary of the tube integrity conditions predicted to exist at the next scheduled inspection (the forward-looking tube integrity assessment) relative to the applicable performance criteria, including the analysis methodology, inputs, and results;
e. The number and percentage of tubes plugged to date, and the effective plugging percentage in each SG;
f. The results of any SG secondary side inspections;
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;
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 2.49 times the maximum operational primary to secondary leakage rate; the report should describe how it was determined; and
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.

If you have any questions or require additional information, please contact Ms. Lori K. Kelley at (860) 444-6520.

Sincerely,

/~

L:*~

./ James T. Petty Site Vice President - Millstone Power Station Attachments:

1) Millstone Power Station Unit 3, End of Cycle 22 Steam Generator Tube Inspection Report in Accordance with Amendment 293 Reporting Requirements
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 Theo L. Edwards Project Manager U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop O-8C04 11555 Rockville Pike Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station Serial No.25-305 Docket No. 50-423 Page 3 of 3 Millstone Power Station Unit 3 Serial No.25-305 Docket No.

50-423 End of Cycle 22 Steam Generator Tube Inspection Report in Accordance with Amendment 293 Reporting Requirements MILLSTONE POWER STATION UNIT 3 DOMINION ENERGY NUCLEAR CONNECTICUT, INC. (DENC)

Serial No.25-305 Docket No. 50-423, Page 1 of 25 End of Cycle 22 Steam Generator Tube Inspection Report in Accordance with Amendment 293 Reporting Requirements During the Millstone Power Station Unit 3 (MPS3) fall 2023 refueling outage (3R22),

inspections were completed on 100% of the steam generator tubes in accordance with Technical Specifications (TS) 6.8.4.g. Initial entry into Mode 4 occurred on November 26, 2023; therefore, a Steam Generator Tube Inspection Report was required to be submitted to the Nuclear Regulatory Commission (NRC) by May 24, 2024, in accordance with MPS3's TS 6.9.1.7. The report was submitted as required on May 20, 2024 (ML24142A095).

On April 22, 2025, Dominion Energy Nuclear Connecticut (DENC) submitted a license amendment request (LAR) to the NRC requesting adoption of TSTF-577, "Revised Frequencies for Steam Generator Tube Inspections," which is an approved change to the Standard Technical Specifications. The proposed change revises the TS related to steam generator tube inspections and reporting requirements in TS section 6.8.4.g, "Steam Generator (SG) Program," and TS section 6.9.1.7, "Steam Generator Tube Inspection Report," respectively.

The initial inspection period described in the revised SG Program, paragraph 6.8.4.g.d.2, began when the 100% SG tube inspection was completed for MPS3 during the Fall 2023 refueling outage (RFO). DENC is required to submit a SG Tube Inspection Report meeting the revised TS 6.9.1.7 requirements within 30 days after implementation of the license amendment. Re-submittal of this report attachment satisfies the revised MPS3 TS 6.9.1.7 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 U-bends is 2.20 inches. U-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 SG support configuration without dimensions.

All four MPS3 SGs were inspected during the End of Cycle (EOC) 21 refueling outage (April 2022) and had operated for approximately 346.1 Effective Full Power Months (EFPM) prior to that outage. Over cycle 22, the SGs operated for an additional 15.35 EFPM. Therefore, at the time of the inspection, the Unit 3 SGs had accrued approximately 361.4 EFPM of operation as of the EOC22 (October 2023).

Serial No.25-305 Docket No. 50-423, Page 2 of 25 The MPS3 SGs operate with a hot-leg temperature of 617°F and have experienced no detectable primary to secondary leakage.

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 EOC22 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 U-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 1,746 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 prior to EOC21 and repeated during the EOC22 examination. The specific dent/ding scope performed during the EOC22 inspection included 100% of all dents/dings ~ 2 Volts located in the hot leg straight section and 100% of all dents/dings ~ 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.25-305 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 steam generators. 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.

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 3R22.

During 3R22, 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 four SGs during 3R22.

The examination identified no evidence of degradation.

b. The nondestructive examination techniques utilized for tubes with increased degradation susceptibility; 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.

Serial No.25-305 Docket No. 50-423, Page 4 of 25 This evaluation identified 67, 30, 39, and 23 tubes in SGs A, B, C and D, respectively, which may have been improperly heat treated. These tubes were examined full length with array probes (in addition to the full-length bobbin probe) and closely scrutinized during the analysis process.

An additional augmented sample of 25,344 tube locations was inspected with an array coil probe.

The array coil probe sample included full length examinations of the previously mentioned tubes with potentially high residual stress (159), and 40 tubes (10 in each SG) in strategically located positions that also provide an assessment of deposit loading and potential clogging/blockage of the broached openings at tube support intersections.

In addition to the 199 tube full length inspections, 100% of the remaining hot leg top-of-tubesheet (TTS) locations (22,112 tubes), and approximately 13% of the cold leg TTS locations (3,033 tubes) were examined with array probes.

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.

c. For each degradation mechanism found:
1.

The nondestructive examination technique utilized; Table 1: Examination Techniques for Degradation Mechanisms Detected De radation Mechanism AVB Wear Tube Su n Ob*ect Wear

2.

The location, orientation (if linear), measured size (if available), and voltage response for each indication. For tube wear at support structures less than 20 percent through wall, only the total number of indications needs to be reported; The existing degradation mechanisms found during 3R22 included AVB wear, TSP wear, non-support structure volumetric degradation (legacy/new foreign object wear where the object has been removed, fabrication, and maintenance related wear). No corrosion-related degradation, located above the H* distance, was detected in any of the MPS3 SGs during 3R22.

Table 2 contains the listing of all non-support structure volumetric degradation. There were 59 indications recorded in 53 tubes. The indications listed as being caused by a sled were attributed to a historical water lancing delivery device that is no longer used.

Table 2: Summary of Non-Support Structure Volumetric Degradation Axial Gire Max SG Row Col Volts Location Extent Extent Depth Cause

(%TW)

SGA 6

122 0.04 TSH +4.13" 0.14 0.19 5

Foreign Object Wear

SG Row Col Volts location SGA 7

3 0.19 TSC +0.02" SGA 24 7

0.24 04H +3.67" SGA 24 11 0.10 TSH +0.10" SGA 28 112 0.41 01 H +0.53" SGA 29 109 0.12 TSC +0.10" 0.20 01H +0.53" SGA 29 110 0.13 TSC +0.12" SGA 43 103 0.07 TSC +0.65" SGA 47 24 0.25 01C +0.94" 0.18 01C+0.91" SGA 47 25 0.27 01C +1.13" SGA 53 65 0.13 TSC+0.10" SGA 53 66 0.44 TSC +0.05" SGA 54 65 0.12 TSC+0.10" SGA 54 66 0.18 TSC+0.10" SGA 58 47 0.09 TSC +0.58" SGA 58 76 0.08 TSC +0.53" SGA 59 60 0.21 08H -1.73" SG Row Col Volts location SGB 1

119 0.14 TSC + 3.77" 0.09 TSC + 3.82" SGB 1

120 0.06 TSC +4.68" SGB 1

121 0.10 TSC+6.58" SGB 22 118 0.10 TSC+0.77" SGB 44 98 0.31 02H+15.70" SGB 45 99 0.18 06H - 0.94" SG Row Col Volts location SGC 1

5 0.19 TSC+3.19" Axial Circ Extent Extent 0.19 0.34 0.22 0.29 0.19 0.26 0.38 0.34 0.14 0.19 0.43 0.34 0.17 0.24 0.17 0.22 0.24 0.29 0.19 0.29 0.22 0.34 0.12 0.26 0.24 0.31 0.14 0.24 0.14 0.26 0.17 0.29 0.22 0.29 0.24 0.34 Axial Circ Extent Extent 0.26 0.38 0.24 0.34 0.24 0.31 0.53 0.34 0.31 0.31 0.29 0.31 0.22 0.34 Axial Circ Extent Extent 0.26 0.29 Serial No.25-305 Docket No. 50-423, Page 5 of 25 Max Depth Cause (3/4TW) 22 Foreign Object Wear 26 Foreign Object Wear 14 Foreign Object Wear 37 Foreign Object Wear 16 Foreign Object Wear 12 Foreign Object Wear 17 Foreign Object Wear 10 Foreign Object Wear 27 Foreign Object Wear 21 Foreign Object Wear 28 Foreign Object Wear 18 Foreign Object Wear 38 Foreign Object Wear 16 Foreign Object Wear 21 Foreign Object Wear 12 Sled 11 Sled 24 Foreign Object Wear Max Cause Depth 19 Foreign Object Wear 12 Foreign Object Wear 10 Foreign Object Wear 14 Foreign Object Wear 14 Sled 28 Fabrication 21 Foreign Object Wear Max Depth Cause (3/4TW) 12 Foreign Object Wear

SG Row Col Volts Location SGC 3

3 0.20 04C+16.30" SGC 8

61 0.20 TSH +0.60" SGC 20 72 0.08 02H +5.52" SGC 36 13 0.11 TSC +0.55" SGC 38 15 0.10 TSC +0.58" SGC 44 102 0.08 TSC +0.58" SGC 46 34 0.07 TSH +0.38" SGC 47 34 0,08 TSH +0.46" SGC 48 25 0.06 TSH +0.48" SGC 52 77 0.23 TSC +0.07" SGC 52 79 0.34 TSC +0.02" SGC 54 64 0.19 TSH +0.14" SGC 55 68 0.13 TSH +0.67" SGC 56 41 0.08 TSH +0.53" SGC 56 65 0.23 06H+13.25" SGC 56 69 0.24 TSH +0.14" SGC 56 82 0.07 TSC +0.53" SGC 57 44 0.07 TSH +0.55" 0.13 TSC +0.53" SGC 58 48 0.07 TSH +0.55" 0.06 TSC +0.50" SGC 58 49 0.06 TSH +0.48" 0.11 TSC +0.55" SGC 58 76 0.11 TSH+0.50" SGC 59 55 0.06 TSC+0.48" SGC 59 59 0.05 TSC +0.55" SGC 59 68 0.07 TSH +0.55" SG Row Col Volts Location Axial Gire Extent Extent 0.19 0.29 0.29 0.31 0.24 0.24 0.24 0.29 0.22 0.24 0.19 0.24 0.22 0.24 0.22 0.31 0.22 0.36 0.19 0.31 0.22 0.29 0.19 0.34 0.24 0.34 0.29 0.29 0.38 0.26 0.19 0.34 0.19 0.34 0.29 0.29 0.19 0.29 0.34 0.38 0.22 0.34 0.29 0.53 0.19 0.31 0.29 0.34 0.14 0.24 0.19 0.29 0.14 0.29 Axial Circ Extent Extent Serial No.25-305 Docket No. 50-423, Page 6 of 25 Max Depth Cause (3/4TW) 15 Fabrication 23 Foreign Object Wear 7

Fabrication 16 Sled 15 Sled 11 Sled 6

Foreign Object Wear 12 Foreign Object Wear 6

Foreign Object Wear 25 Foreign Object Wear 33 Foreign Object Wear 22 Foreign Object Wear 17 Foreign Object Wear 11 Foreign Object Wear 20 Fabrication 26 Foreign Object Wear 10 Sled 10 Sled 17 Sled 10 Sled 9

Sled 9

Sled 15 Sled 15 Sled 9

Sled 8

Sled 10 Sled Max Depth Cause

(%TW)

SG Row Col Volts Location SGD 46 99 0.21 01 H +0.58" SGD 52 42 0.19 01 H +0.53" SGD 52 91 0.34 01 H +2.52" SGD 58 50 0.06 01C +0.45" SGD 58 51 0.20 01C +0.59" Axial Circ Extent Extent 0.29 0.29 0.24 0.29 0.29 0.34 0.16 0.25 0.21 0.33 Serial No.25-305 Docket No. 50-423, Page 7 of 25 Max Depth Cause

(%TW) 24 Foreign Object Wear 22 Foreign Object Wear 33 Foreign Object Wear 10 Foreign Object Wear 23 Foreign Object Wear Table 3 contains a listing of tube support plate (TSP) and flow distribution baffle (FOB) wear indications that were sized at ~ 20% through wall.

In addition to the TSP and FOB wear indications listed in Table 3, there were an additional 28 indications of TSP and FOB wear that measured < 20% and therefore, are not listed in Table 3.

Table 3: Summary of NON-AVB Support Structure Wear Axial Circ Max SG Row Col Volts Location Extent Extent Depth Cause

(%TW)

SGA 3

112 0.28 06C -0.91" 0.26 0.24 21 TSP Wear SGA 15 74 0.40 07C -0.60" 0.26 0.31 26 TSP Wear Axial Circ Max SG Row Col Volts Location Extent Extent Depth Cause

(%TW)

SGC 17 52 0.53 04H -0.38" 0.26 0.29 29 TSP Wear SGC 48 88 0.42 07C -0.62" 0.24 0.34 28 TSP Wear Axial Circ Max SG Row Col Volts Location Extent Extent Depth Cause (3/4TW)

SGD 17 24 0.81 07C -0.67" 0.32 0.29 38 TSP Wear SGD 35 73 0.45 04H -0.41" 0.24 0.29 30 TSP Wear Table 4 contains a listing of the Anti-Vibration Bar (AVB) wear indications that were sized at

~ 20% through wall. There were an additional 614 AVB wear indications that were sized at

< 20% through wall and therefore, are not listed in Table 4.

Table 4: Millstone 3 EOC22 Inspection Summary - AVB Wear Indications SG Row Col

%TW Elev Volts SG Row Col

%TW Elev Volts A

26 115 24 AV1 -0.52 1.13 A

34 46 28 AV5+0 1.56 A

28 115 29 AVl-0.02 1.68 A

34 46 30 AVG +0.23 1.86 A

30 9

27 AV5 +0.7 1.47 A

34 48 24 AV3 +0.04 1.14 A

30 113 22 AV5 +0.28 0.9 A

34 73 30 AV4+0.04 1.79

SG Row Col 3/4TW Elev Volts A

34 73 31 AV5 -0.21 1.98 A

34 109 22 AV4 +0.02 0.93 A

35 59 25 AV2 +0.02 1.2 A

35 60 29 AV4 +0.04 1.65 A

35 60 26 AV5 -0.23 1.33 A

35 71 26 AV4 -0.26 1.28 A

35 77 21 AV3 -0.11 0.82 A

37 45 32 AV2 +0.02 2.02 A

37 45 24 AV3 +0.17 1.16 A

37 69 20 AV5 -0.02 0.79 A

37 69 22 AV6 -0.04 0.96 A

37 90 21 AV3 +0.02 0.84 A

37 91 22 AV5 -0.06 0.96 A

38 52 26 AV3 +0.19 1.31 A

39 57 27 AV2 -0.02 1.49 A

39 57 20 AV3 -0.11 0.73 A

39 57 22 AV4 +0.04 0.92 A

39 60 22 AV4 +0.06 0.95 A

39 71 23 AV5 -0.28 1.05 A

40 45 26 AV4 +0.11 1.33 A

40 71 22 AV3 -0.17 0.95 A

40 71 25 AV4 -0.26 1.23 A

41 61 23 AV4-0.11 1.06 A

41 102 36 AV4 +0.04 2.72 A

42 33 21 AV3 +0.02 0.86 A

42 53 25 AV4 +0.04 1.24 A

42 53 40 AV5 +0.02 3.31 A

42 53 20 AV6 +0.42 0.75 A

42 77 25 AV4 +0.02 1.24 A

42 93 25 AV4 +0.04 1.22 A

42 93 22 AV5 +0 0.96 A

42 98 25 AV3 +0.07 1.21 A

42 98 28 AV4 +0.02 1.54 A

42 101 23 AV3 +0.02 0.99 A

42 101 29 AV4 +0.02 1.72 A

42 101 20 AV5+0 0.79 A

43 80 20 AV4+0 0.76 A

43 87 21 AV2 +0.09 0.8 A

43 87 21 AV4+0 0.81 SG Row Col A

43 102 A

44 64 A

44 64 A

44 74 A

44 74 A

44 75 A

44 98 A

45 98 A

46 99 A

49 96 A

50 44 A

50 76 A

50 76 A

50 76 A

50 82 A

50 82 A

50 87 A

50 87 A

51 65 A

52 66 A

53 81 B

34 109 B

38 104 B

41 34 B

41 34 B

41 50 B

41 69 B

41 69 B

41 77 B

42 21 B

42 21 B

42 96 B

43 100 B

43 100 B

so 88 B

50 88 B

51 91 B

54 36 B

58 75 Serial No.25-305 Docket No. 50-423, Page 8 of 25

%TW Elev Volts 20 AV4+0 0.74 30 AV2 +0.02 1.76 21 AV3 -0.11 0.87 27 AV5 +0 1.39 20 AV6 +0.25 0.73 21 AV3 +0.02 0.85 20 AV2 -0.19 0.77 21 AV4 +0.04 0.83 20 AV4 +0.02 0.72 20 AV6 +0 0.74 33 AV5 +0.02 2.26 25 AV2 +0.02 1.17 24 AV3 +0.04 1.07 33 AV4 +0.11 2.21 30 AV3 -0.13 1.82 22 AV4 -0.13 0.94 24 AV2 -0.15 1.11 22 AV3 -0.15 0.91 21 AV5 +0.02 0.84 26 AV4 +0.09 1.3 26 AV3 +0.04 1.37 21 AV3 -0.02 0.87 23 AV4-0.18 1.02 32 AV4 +0.44 2.05 32 AV5 +0 2.05 24 AV4 +0.07 1.14 21 AV4 -0.25 0.8 31 AV5 -0.04 1.89 20 AV5 +0 0.72 20 AV4 +0.11 0.73 26 AV5 +0.04 1.29 20 AV2 +0.09 0.73 23 AV3-0.24 1.04 27 AV4-0.04 1.38 21 AV3-0.07 0.85 24 AV4+0 1.07 20 AV4+0 0.76 29 AVS +0.02 1.71 20 AVS-0.04 0.75

SG C

C C

C C

C C

C C

C C

C C

C C

C C

C C

C C

D D

D D

D Row Col

%TW Elev Volts 25 116 23 AV6 +0.56 1

37 15 22 AV2 -0.04 0.97 37 15 26 AV5 +0.26 1.28 39 17 21 AV2 +0 0.8 41 42 26 AV3 +0.05 1.3 41 54 20 AV5 +0.04 0.76 41 62 25 AV2 -0.28 1.26 41 62 30 AV3 +0.46 1.84 41 62 21 AV4 -0.31 0.83 41 62 32 AV4 +0.37 2.05 41 62 29 AV5 -0.32 1.68 42 20 22 AV3 +0 0.97 42 20 24 AV4 -0.02 1.12 42 20 23 AV5 +0.02 0.99 42 20 20 AV6 +0.07 0.75 42 23 20 AV3 +0.07 0.78 42 23 29 AV4 -0.02 1.7 42 23 27 AV5 +0 1.47 49 96 20 AV5 +0 0.78 49 96 24 AV6 -0.12 1.13 56 41 24 AV5 +0.07 1.1 28 114 27 AV2 +0.2 1.4 30 114 23 AV6 +0.2 1.04 37 101 20 AV2 -0.16 0.76 37 106 30 AV4 +0.04 1.74 40 99 26 AV4 -0.02 1.29 SG Row Col 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 D

41 78 D

43 95 D

49 62 D

49 62 D

49 62 D

49 62 D

49 66 D

49 67 D

49 95 D

52 67 D

54 49 D

55 84 Serial No.25-305 Docket No. 50-423, Page 9 of 25 3/4TW Elev Volts 31 AV5 +0.06 1.92 22 AV4 +0.04 0.93 20 AV2 -0.02 0.78 24 AV3 +0.04 1.07 31 AV4 +0.24 1.95 26 AV5 +0.06 1.37 27 AV5 +0.02 1.43 28 AV6 -0.27 1.6 21 AV4 +0.17 0.81 25 AV5 +0 1.19 23 AV3 +0.24 0.98 20 AV5 +0.11 0.79 21 AVl +0.27 0.86 24 AV2 -0.17 1.08 30 AV3 +0.19 1.78 20 AV4 +0.06 0.73 28 AV2 -0.07 1.57 22 AV2 +0.02 0.92 20 AV4 -0.02 0.77 20 AV4 -0.02 0.78 21 AV3 +0.02 0.81 22 AV5 -0.02 0.9

3.

A description of the condition monitoring assessment and results, including the margin to the tube integrity performance criteria and comparison with the margin predicted to exist at the inspection by the previous forward-looking tube integrity assessment; and 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 3R22.

Serial No.25-305 Docket No. 50-423, Page 10 of 25 To perform the Condition Monitoring (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 3R22 Degradation Assessment (DA), the 95/50 CM limit curve of Figure 1 was developed. This limit curve is applicable to the AVB wear indications reported at MPS3 during 3R22.

On Figure 1, the depths of all AVB wear reported during 3R22 are plotted with the assumption that the axial extent of the wear was 2.5 inches (purposely staggered about 2.5" to reveal each SG's findings). 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 MPS3 during 3R22.

On Figure 2, the depths of all TSP and FOB wear reported in each of the four SGs during 3R22 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 3R22.

80

/ 0 oO 40 10 lO 0

100.0 90.0 80.0 70.0 60.0 50.0 40.0 30.0 20.0 10.0

--0.0-

-0.100 05 Serial No.25-305 Docket No. 50-423, Page 11 of 25 Figure 1: CM Limit Curve for AVB Wear CM Limit Curve for AVB Wear ETSS 9604 1.3

( Ml.1rnlt A

SG B SG (

S\l D Figure 2: CM Limit Curve for TSP and FDB Wear CM Limit Curve for TSP/FDB Wear ETSS 96910.1 0.100 0.300 0.500 0.700 0.900 1.100

_._CM Limit SGA SG B SGC SGD 1.300 LSOO

Serial No.25-305 Docket No. 50-423, Page 12 of 25 Volumetric degradation caused by foreign object wear and fabrication processes is evaluated in this section. All these indications (59 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.

53 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.

Figure 3: CM Limit Curve for Volumetric Flaw Using ETSS 21998.1 CM Li mit Curve for VO L lndiations ETSS 21998.1 100.0

.......,._CM limit 90.0

  • SGA
  • SGC
  • SG D 70.0 60.0 50.0 40.0 30.0 20.0 10.0 o.o

-0.100 0.100 0.300 0.500 0.700 0.900 1.100 1.300 1.500

Serial No.25-305 Docket No. 50-423, Page 13 of 25 Figure 4: CM Limit Curve for Foreign Object Wear Flaws Using ETSS 27901.1 100.0 90.0 80.0 70.0 60.0 50.0 40.0 30.0 20.0 10.0 0.0 -

-0.100 0.100 0.300 CM Limit Curve for FOW lndiations ETSS 27901.1 0.500 0.700 0,900 1.100

_.,_ CM Limit SGA A.

SG B SGC SG D 1.300 1.500 Figure 5: CM Limit Curve for Foreign Object Wear Flaw Sized with ETSS 27902.1 CM Limit Curve for FOW lndiations ETSS 27902.1 100.0 90,0 80.0 70.0 60.0 so.a 40.0 30.0 20.0 10.0

---0.0

-0.100 0.100 0.300 0.500 0.700 0.900 1.100

-+- CM limit SGA J.

SG B SG C SG D 1.300 1.500

Serial No.25-305 Docket No. 50-423, Page 14 of 25 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 (3R21 for all four SGs) was performed and the key inputs and assumptions were compared with the results from the current outage (3R22). This review, summarized in Table 7, shows that the as-found conditions were bounded by the projections from the previous OA for all cases.

Table 5: Summary of Prior OA Validation Prior 3R21 (spring 2022) OA Observed during the inspection Assumptions 3R22 Outage projection satisfied AVB Wear 95/50 growth rate of The biggest 95/50 growth rate was Yes 4.0% TW/EFPY 1.564 % TW/EFPY TSP/FDB Maximum growth rate of The Maximum growth rate was Wear 11.0 3/4TW/EFPY 3.13 % TW/EFPY Yes No growth for repeat volumetric degradation due to (foreign No growth observed in non-objects, fabrication related, and support volumetric degradation Non-Support lancing sled).

previously left in service.

Volumetric Yes Degradation If growth occurs, or new A few flaws were newly reported, degradation develops, it will not but none exceeded structural exceed structural performance performance criteria.

criteria prior to 3R22.

Circumferential Probability of Burst < 0.002%

ODSCC No ODSCC was detected Yes Probability of Leakage< 0.074%

Operational Projected: Zero GPM No measurable leakage in any SG Yes Leakage since the last ISi EFPY EFPY :5 1.5 EFPY EFPY = 1.279 Yes 3(NOPD) 3*(1340) = 4020 psid Bounding 3990 psid Yes

Serial No.25-305 Docket No. 50-423, Page 15 of 25

4.

The number of tubes plugged during the inspection outage.

Based on inspection results, two (2) tubes were plugged during the 3R22 outage.

Table 6: Summary of 3R22 Plugging.

SIG Row Col Hot-Leg Cold-Leg Degradation Mechanism SG-A 42 53 Plugged/Stabilized Plugged AVB Wear SG-A 50 76 Plu12:12:ed/Stabilized Plugged AVB Wear

d. An analysis summary of the tube integrity conditions predicted to exist at the next scheduled inspection (the forward-looking tube integrity assessment) relative to the applicable performance criteria, including the analysis methodology, inputs, and results; The OA 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, the 3R22 OA addressed both existing degradation mechanisms and bounding potential degradation mechanisms over the projected inspection interval. Since all four SGs were examined during the 3R22 inspection without finding corrosion related degradation, and with MPS3 planning to adopt TSTF-577 shortly after the 3R22 outage, the 3R22 OA was evaluated for a 3-cycle inspection interval totaling 4.5 EFPY (54 months). This interval is conservative considering that 1.4 EFPY per cycle is typically bounding for MPS3. The MPS3 steam generators (all four SGs) had operated for a single cycle of 1.279 EFPY since the last inspection at 3R21 (spring 2022).

MPS3 existing degradation mechanisms consist of tube wear at supports (AVB and TSP),

tube wear at the FOB, other volumetric degradation, and TTS circumferential ODSCC. Each of the existing wear degradation mechanisms were evaluated using deterministic methodologies. Circumferential TTS ODSCC (although not detected at 3R22 but detected previously during 3R21) was evaluated using a fully probabilistic Monte Carlo methodology.

Anti-Vibration Bar Wear During 3R22, AVB wear was sized using a "fixed curve" for the first time. Use of the fixed curve will smooth out outage to outage variations in AVB wear depths and provide for tighter AVB wear growth rates going forward. To ensure a like-for-like comparison, the previous outage (3R21) AVB wear was resized using the fixed curve for determining 3R22 AVB wear growth rates. The growth rate used for the OA of AVB wear was conservatively based on the SG exhibiting the maximum return to service growth rate. This growth rate is 4.691 % TW/EFPY (in SG-A).

Serial No.25-305 Docket No. 50-423, Page 16 of 25 The beginning of cycle (BOC) AVB wear depth is an upper bound estimate of the AVB wear depth remaining in seNice immediately following the SG tube inspection. The maximum depth of reported AVB wear returned to service during 3R22 was 36% TW. Adjusting the 36% TW depth to conservatively account for NOE sizing uncertainty by applying the sizing performance yields an upper 95/50 depth of 42.1 % TW. Therefore, the OA assumed a limiting BOC23 AVB wear depth of 42.1 % TW.

Adjusting this BOC23 depth (42.1%TW) upward to reflect three fuel cycles of growth (over a conservative duration of 4.5 EFPY), yields the end-of-cycle upper bound depth (EOCUBD) at 3R25:

BOC23 = 42.1%TW maximum %TW of return to service AVB wear at BOC23 EOCUBD = 42.1%TW+ (4.5 EFPY) (4.691 %TW/ EFPY)

EOCUBD = 63.2% TW The maximum projected EOC25 depth is 63.2 % TW which is below the 67% TW structural limit identified in the DA for an AVB wear flaw. Based on this evaluation, AVB wear is not expected to challenge the structural integrity performance criteria in any of the four MPS3 steam generators over the next inspection inteNal, of 4.5 EFPY, until the next scheduled steam generator ECT inspection.

Tube Support Plate (TSP) and Flow Distribution Baffle (FDB) Wear The maximum depth of TSP wear identified during 3R22 and returned to service was 38% TW as sized with +PointTM technique ETSS 96910.1. ConseNatively accounting for the depth sizing uncertainty, the upper bound returned-to-seNice depth was determined to be 51.6 %TW.

No discernible growth of the previously reported TSP wear has occurred since the last ECT inspection (3R21 for all SGs). A conseNative estimate of the maximum growth rate experienced during the past operating cycle was estimated to be 3.0 % TW/EFPY.

Adjusting the BOC23 depth upward to reflect three cycles of growth (assumed duration: 4.5 EFPY), yields the end-of-cycle upper bound depth (EOCUBD) at 3R25:

BOC23 = 51.6%TW upper bound return to seNice depth of TSP/ FOB wear at BOC23 EOCUBD = 51.6% TW + (4.5 EFPY)*(3.0 % TW/EFPY) EOCUBD after 4.5 EFPY EOCUBD = 65.1 3/4TW The maximum length of the MPS3 TSP/ FOB wear as measured with the +PointTM probe was 0.32 inches. Further, the +PointTM probe is known to overestimate the length of degradation, therefore making the longest wear scar less than 0.32 inches. ConseNatively, if the structural length of the limiting flaw will increase to 0.50 inches by the next scheduled

Serial No.25-305 Docket No. 50-423, Page 17 of 25 inspection in 3R25, the structural limit for volumetric degradation (0.50-inch axial length) with limited circumferential extent (<135°) is 69.1 % TW. Since the calculated value of EOCUBO (65.1 % TW) is below this structural limit, there is reasonable assurance that TSP/

FOB wear will not exceed the structural performance criteria prior to the next inspection of any of the MPS3 SGs. As such, no accident leakage or operational leakage concerns exist relative to TSP/ FOB wear for any of the MPS3 SGs.

Table 7: OA for Structure Wear Degradation Mechanism Maximum Depth(%)

Structural Limit Depth(%)

Predicted at 3R25 AVB Wear 63.2 67 TSP/FDB Wear 65.1 69.1 Circumferential ODSCC @TTS A single circumferentially oriented OOSCC indication was identified for the first time, above the H* distance, in the MPS3 SG tubes during the previous 3R21 outage (2022). Therefore, circumferential oriented OOSCC is listed as an existing degradation mechanism. Following the methodology described in the IAGL, a fully probabilistic multi-cycle OA analysis was performed.

The distribution of 3R25 worst-case degraded tube burst pressures resulting from this analysis is shown in Figure 6. This figure demonstrates that the lower 95/50 (i.e., the 5th percentile) burst pressure, 7360 psi satisfies the SIPC limit of 4080 psi; therefore, it is concluded that circumferential OOSCC at the TTS will not cause the structural integrity performance criteria to be exceeded in the MPS3 SGs prior to 3R25. The projected total upper 95/50 leakage (GPM) under limiting accident conditions is zero; therefore, it is concluded that circumferential OOSCC at the TTS will not cause the accident-induced leakage performance criteria to be exceeded prior to 3R25. These conclusions are also presented below in Table 9 in terms of the probability of burst (POB) at 3LiP and the probability of leakage (POL) under accident conditions.

Serial No.25-305 Docket No. 50-423, Page 18 of 25 Figure 6: 3R25 Worst Case Burst Pressure - Circumferential ODSCC @TTS

~

s

..c e 0.20 ~-------------------~,------~

3R25 Min BP 0.15 I

I I

J I

I I

I I

I I I

I I '

I I

I I

n.

a, 0.10 I

~

i E
, u 0.05 3XNOPD: 4080 psi I

I I

I I

I I

I I

I Lower 95/50: 7360 psi

{

I I {

I /

I,

--,( ----

Probability: 0.05

,' I

,' I I

I I

I 0.00 +--___

..... _,.,._=-..::.- ;;;..

  • ----,---"1--.....----......------1 3,000 4,000 5,000 6,000 7,000 8,000 9,000 Projected JR25 Worst Case Burst Pressure (psi)

Table 8: Probabilities of Burst and Leakage at (3*NOPD)

Circumferential ODSCC @TTS Population POB at 3i'lP POL Full Bundle 0.030%

2.03%

SG Program Maximum 5%

5%

Allowable 10,000 The OA also considers two bonding "potential" degradation mechanisms, neither of which have been identified in the MPS3 SGs. These mechanisms which could potentially develop (i.e., "potential" degradation mechanisms) are axial ODSCC at TSPs and axial ODSCC at dent/ dings.

Although no indications of axial ODSCC have been identified in the MPS3 SGs, hypothetical axial ODSCC at tube support plates (TSPs) (which bounds axial ODSCC at tube free-span locations) were evaluated. This degradation mechanism is considered bounding because ECT bobbin probe examination methods are relied upon to detect this mechanism in non-high stress tubes. The bobbin probe probability of detection (POD) is less favorable than that of the +Point' probe. In addition, the lengths of cracks that develop at TSPs are typically greater than the lengths of those that develop elsewhere within the SGs. Even

Serial No.25-305 Docket No. 50-423, Page 19 of 25 though all high stress tubes (Tier-1 tubes), in all four SGs during 3R22, were examined full length using the array probe (in addition to the bobbin probe), this evaluation conservatively assumes that the 3R22 examination relied entirely upon the bobbin probe POD curve for detection of axial ODSCC at TSPs.

Following the methodology described in the IAGL, a fully probabilistic multi-cycle OA analysis was performed. The software simulates the life cycle of a susceptible tube population and generates Monte Carlo projections of both detected and undetected flaws for multiple cycles of operation. The simulation considers inspection POD, new flaw initiation, and growth to calculate burst probability and accident-induced leakage at time points of interest. These key parameters are discussed below.

The distribution of 3R25 worst-case degraded tube burst pressures resulting from this analysis is shown in Figure 7. This figure demonstrates that the lower 95/50 (i.e., the 5th percentile) burst pressure, 4736 psi satisfies the SIPC limit of 4080 psi; therefore, it is concluded that axial ODSCC at tube support plates will not cause the structural integrity performance criteria to be exceeded in the MPS3 SGs prior to 3R25. The projected total upper 95/50 leakage (GPM) under limiting accident conditions is zero; therefore, it is concluded that axial ODSCC at tube support plates will not cause the accident-induced leakage performance criteria to be exceeded prior to 3R25. These conclusions are also presented below in Table 10 in terms of the probability of burst (POB) at 3.6.P and the probability of leakage (POL) under accident conditions.

Figure 7: 3R25 Worst Case Burst Pressure - Axial ODSCC @TSPs 0.25 ~---------------------~,r-------,

~

0.20

~ 0.15

.c e D..

Q)

.2:

1ii

i 0.10 E
s u 0.05 I,

I,,

3R25 Min BP

/,,

I,,

/

,l l

/

Lower 95/50: 4736 psi i,,,,,/

I I,..

--~------ Probability: 0.05 3XNOPD: 4080 psi j I

--~---*1 I

I

~

0.00 +---'""'-==i-=---~--..-------.-~

--r-~

-r-----r-----.-----,,----;

2,000 2,500 3,000 3,500 4,000 4,500 5,000 5,500 6,000 6,500 7,000 Projected 3R25 Worst Case Burst Pressure (psi)

Serial No.25-305 Docket No. 50-423, Page 20 of 25 Table 9: Probabilities of Burst and Leakage at (3*NOPD)

Axial ODSCC @TSPs Population POB at3~P POL Full Bundle 2.19%

1.33%

SG Program Maximum 5%

5%

Allowable Hypothetical axially oriented ODSCC at dent/ ding locations is addressed herein principally because of recent operating experience at Seabrook which has increased industry focus on this mechanism. During the 3R22 outage, all 2: 2 Volt hot-leg dent/ dings and all 2: 5 Volt cold-leg/ U-bend dent/ dings were examined using the +Point' probe. No sec was identified at any dent/ding location.

The same fully probabilistic, multi-cycle OA analysis methodology described in the previous pages was used to evaluate this degradation mechanism. The simulation of axial ODSCC at dent/ dings was benchmarked to cause a detection as early as 3R16, when in fact no dent/ ding ODSCC has ever been detected including the current 3R22 outage. This approach ensures that the Weibull crack initiation function utilized in the analysis is conservative. The shape parameter was selected based upon the research documented in the EPRI PWR Generic Tube Degradation Predictions Reports and the scale parameter was selected to yield at least one detection during 3R16 and subsequent outages 3R18, 3R21, 3R22, and 3R25.

Upon initiation, each crack is assigned a length value, sampled from a suitable length distribution. The length distribution utilized in this evaluation is based upon the measured lengths of MPS3 dents and dings. Because the length and length growth of SCC in SG tubing is dominated by the extent of the residual stress field, it is assumed that the ultimate lengths of cracks that develop within dents/ dings will be limited by the lengths of the dents/

dings themselves. Therefore, no additional length growth was applied within the simulation.

The depth growth rate distribution utilized in this evaluation is the conservative growth rate, for dent/ ding cracks, based on the EPRI 600TT Feasibility Study for Multicycle Operation adjusted to the MPS3 operating temperature (617°F).

The distributions of 3R25 worst-case degraded tube burst pressures resulting from this analysis is shown in Figure 8. This figure demonstrates that the lower 95/50 burst pressure (i.e., the 5th percentile), 7678 psi satisfies the SIPC limit of 4080 psi; therefore, it is concluded that axial ODSCC at dents/ dings will not cause the structural integrity performance criteria to be exceeded in any of the MPS3 SGs prior to 3R25. The projected total upper 95/50 accident leakage (GPM) is zero; therefore, it is concluded that axial ODSCC at dents/ dings will not cause the accident-induced leakage performance criteria to be exceeded prior to 3R25. These conclusions are also presented below in Table 11 in terms of the probability of burst (POB) at 3l'.1P and the probability of leakage (POL) under accident conditions.

~

c

('a

.c Serial No.25-305 Docket No. 50-423, Page 21 of 25 Figure 8: 3R22 Worst Case Burst Pressure - Axial ODSCC @Dents/Dings 0.20 -,--------------------------...-----------,

3R25 Min BP 0.15 I

I I

I I

I I

I I I I,

I I ',

e 0..

a> 0.10

-~ -

..!!l

s E
s u 0.05 Lower 95/50: 7678 psi 1

/

I I,'

I /

13XNOPD: 4080 psi

-f-----

Probability: 0.05 I

/ I

,1 I I

/'

I I

I I

.,./

I I

I I

0.00 +------

.----~

~

"-T-------.-----,__--.--------.----

3,000 4,000 5,000 6,000 7,000 8,000 9,000 Projected 3R25 Worst Case Burst Pressure (psi)

Table 10: Probabilities of Burst and Leakage at (3*NOPD)

Axial ODSCC @Dents/Dings Population POB at3~P POL Full Bundle

< 0.005%

0.008%

SG Program Maximum 5%

5%

Allowable 10,000

e. The number and percentage of tubes plugged to date, and the effective plugging percentage in each SG; Table 11 provides the total number of tubes plugged to date and the effective plugging percentage in each SG.

Prior to 3R22 During 3R22 Total After 3R22 Percentage Overall Percentage Serial No.25-305 Docket No. 50-423, Page 22 of 25 Table 11: Number Tubes Plugged to Date SGA SG B SG C SG D 53 26 23 91 2

0 0

0 55 26 23 91 0.978 0.462 0.409 1.617 0.867 Since no sleeving has been performed in the MPS3 steam generators, the effective plugging percentage is the same as the actual plugging percentage.

f. The results of any secondary side inspections; During 3R22, secondary side activities were performed in SGs A, B, C, and D and included the following:

SG A

  • High pressure sludge lancing removed a total of 41 lbs.

The quantities of sludge removed in each SG is as follows: SG-A (12 lbs.), SG-B (8 lbs.), SG-C (13 lbs.), and SG-D (8 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 Five locations of newly detected wear attributed to foreign objects were observed during 3R22.

o One lodged legacy foreign object was visually confirmed and left in place.

Table 12: 3R22 Foreign Object Tracking FOTS Item Location Description 3R22 Action 3R22 Results Array PLP reported Perform FOSAR at the Legacy PLP on tube 56-44 @01C was INR R56-C44 during 3R21 located affected tube locations and with Array. However, bounding tube 57-44 15 above and outside of perform ECT on affected /

had a PLP. FOSAR at 57-44 removed a 4" 01C +0.61" broached opening. No bounding tubes to check for machine turning. Post removal +Point wear on affected or wear and PLPs.

confirmed part was removed and no wear bounding tubes.

was present.

SG A

A A

A B

B C

C D

D FOTS Item Location Description R51-C68 Irregular Metallic Object R51-C69 identified and removed 17 from periphery during TSC +0.25" the 3R22 post lance examination.

Metallic object identified and removed during the Annulus, 3R22 post lance 19 TSH +0.00 examination. Object was located near the H/L lancing suction foot.

R58-C53 Flex gasket material R58-C54 identified and removed 20 during the 3R22 post TSH +0.00" lance periphery examination Lancing Strainer Parts 22 TTS during 3R22 13 TTS Lancing Strainer Parts during 3R22 R45-C99 Foreign object wear 14 reported in 3R22. No 06H-0.94 ECT signal of foreign object.

Metal block previously Rl-C4 Rl-C5 wedged between 1

blowdown pipe and TSC +3" tube. Caused wear on two tubes 7

TTS Lancing Strainer Parts at 3R22 Metallic object identified R58-C52 24 and removed during the TSC +0.00 3R22 post lance examination 27 TTS Lancing Strainer Parts at 3R22 3R22 Action Perform FOSAR at the affected tube locations and perform ECT on affected /

bounding tubes to check for wear and PLPs.

Perform FOSAR at the affected tube locations and perform ECT on affected /

bounding tubes to check for wear and PLPs.

Perform FOSAR at the affected tube locations and perform ECT on affected /

bounding tubes to check for wear and PLPs.

N/A N/A Perform 2-tube bounding of wear indication. FOSAR not able to reach the location Inspect affected and bounding tubes with ECT to cl1eck for movement of object and/ or active wear. Visually inspect to reconfirm location and fixity of object.

N/A Perform FOSAR at the affected tube locations and perform ECT on affected /

bounding tubes to check for wear and PLPs.

N/A Serial No.25-305 Docket No. 50-423, Page 23 of 25 3R22 Results FOSAR removed a ~1.5" long metallic strip during the post lance inspection. Array on the affected tubes (51-68, 51-69) was NDD.

Yet Array inspection on the bounding tubes detected wear on tube 53-66. Subsequent 2-tube bounding on tube 53-66 detected wear on three more tubes (53-65, 54-65, 54-66).

All bounding tube results associated with tubes (53-65, 54-65, 54-66) were NOD.

Object was removed during FOSAR. No PLPs or wear detected during 100% H/L TTS examination FOSAR removed part from the SG. TTS H/L array did not detect PLP or wear on affected or bounding tubes.

Small sludge related pieces. A few small pieces of flexitallic gasket and metallic fragments.

Small sludge related pieces. A few small pieces of flexita Ilic gasket.

Array was NDD (no wear or PLPs) on bounding tubes. No loose part detected on affected tube.

Array was NDD (no wear) on bounding tubes.

Legacy wear (R1-C5) had not changed.

Part configuration was confirmed to be fixed.

Small sludge related pieces. A few small pieces of flexitallic gasket.

During 3R22 post lance FOSAR, metallic object found next to tube 58-52. Array on affected and bounding tubes was NDD (no wear or PLPs). Item was removed from SG and is considered closed out at 3R22.

Multiple pieces of small sludge related material. Multiple pieces of flexitallic gasket and banding material ranging from ~O. 75" to

~2.5" long.

  • During 3R21 (spring 2022), visual inspections of the feedring, J-nozzles, and feedring supports were completed in all four SGs. In addition to the visual examinations 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.

Therefore, no components in any of the SG steam drums were inspected during 3R22.

Serial No.25-305 Docket No. 50-423, Page 24 of 25 The results of all secondary-side visual examinations performed during 3R22 were satisfactory, with no degradation detected and no foreign objects with the potential to challenge tube integrity are known to remain in any of the SGs.

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 primary to secondary SG leakage was reported during Cycle 22.
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 2.49 times the maximum operational primary to secondary leakage rate, the report should describe how it was determined; and 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 22; therefore, the leakage from this degradation during a limiting accident would have been zero (i.e., 2.49 X 0).

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.

Tube slippage monitoring was performed on all four SGs using the bobbin coil data during 3R22. There was no detection of slippage during the 3R22 examination.

t Positive direction o-f sign corwentJon for reporting indications Figure - 9 Serial No.25-305 Docket No. 50-423, Page 25 of 25 Model F General Support Configuration AV3 AV4 AV6

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TEC Change (08C + 2,00w) t Positive direction ofslgn <:onventlon for repe>tting lndlc:atlons Acronyms MILLSTONE POWER STATION UNIT 3 Serial No.25-305 Docket No. 50-423 DOMINION ENERGY NUCLEAR CONNECTICUT, INC. (DNC)

Serial No.25-305 Docket No. 50-423, Page 1 of 1 Acronyms AVB Anti-Vibration Bar OVR Above Tubesheet Over Expansion BET Bottom of the Expansion Transition OXP Over Expansion BLG Bulge PIO Positive Identification C

Column PLG Tube is plugged CL Cold Leg PLP Possible Loose Part DOH Ding or Dent Signal - Reviewed in PTE Partial Tubesheet Expansion History PWR Pressurized Water Reactor DOI Distorted Dent or Ding Indication PWSCC Primary Water Stress Corrosion DDS Ding or Dent Signal - Non-Cracking Confirming w/RPC R

Row ONG Ding RAD Retest Analyst Discretion ONT Dent Indication RBD Retest - Bad Data ECT Eddy Current Test RIC Retest - Incomplete EFPY Effective Full Power Years RRT Retest - Restricted Tube EPRI Electric Power Research Institute S/N Signal-to-Noise Ratio ETSS Examination Technique SAi Single Axial Indication Specification Sheet sec Stress Corrosion Cracking F/L Full Length SCI Single Circumferential Indication FAC Flow Accelerated Corrosion SG Steam Generator FOB Flow Distribution Baffle SLG Sludge FO Foreign Object SSI Secondary Side Inspection FOTS Foreign Object Tracking System SVI Single Volumetric Indication HL Hot Leg TEC Tube End Cold Leg IAGL Integrity Assessment Guidelines TEH Tube End Hot Leg IGA lntergranular Attack TFH Tangential Flaw-Like Signal - Reviewed INF Indication Not Found in History INR Indication Not Reportable TFS Tangential Flaw-Like Signal - Non-LPI Loose Part Indication Confirming w/RPC LPR Loose Part Removed TSC Top of Tubesheet Cold Leg LPS Loose Part Signal TSH Top of Tubesheet Hot Leg MRPC Motorized Rotating Pancake Coil TSP Tube Support Plate NOD No Detectable Degradation TTS Top ofTubesheet NOE Nondestructive Examination TWO Through-Wall Depth NDF No Degradation Found 3/4TW Percent Through-Wall NEI Nuclear Energy Institute VOL Volumetric Indication NQH Non-quantifiable Indication -

Reviewed in History NQI Non-quantifiable Indication OA Operational Assessment ODSCC Outer Diameter Stress Corrosion Cracking

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