ML20224A457

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Connecticut. Inc. Millstone Power Station Unit 3, Proposed License Amendment Request for a One-Time Extension of the Millstone Unit 3 Steam Generator Inspections
ML20224A457
Person / Time
Site: Millstone Dominion icon.png
Issue date: 08/11/2020
From: Mark D. Sartain
Dominion Energy Co
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
20-272
Download: ML20224A457 (60)
v • d • e


Text

Dominion Energy Nuclear Connecticut, Inc.

5000 Dominion Boulevard, Glen Allen, VA 23060 Dominion DominionEnergy.com August 11, 2020 Energy U. S. Nuclear Regulatory Commission Serial No.: 20-272 Attention: Document Control Desk NRA/SS: RO Washington, DC 20555-0001 Docket No.: 50-423 License No.: NPF-49 DOMINION ENERGY NUCLEAR CONNECTICUT. INC.

MILLSTONE POWER STATION UNIT 3 PROPOSED LICENSE AMENDMENT REQUEST FOR A ONE-TIME EXTENSION OF THE MILLSTONE UNIT 3 STEAM GENERATOR INSPECTIONS Pursuant to 10 CFR 50.90, Dominion Energy Nuclear Connecticut, Inc. (DENC} requests an amendment to the Millstone Power Station Unit 3 (MPS3} Facility Operating License Number NPF-49, in the form of a change to the technical specifications (TSs}. This license amendment request (LAR) proposes to revise MPS3 TS 6.8.4.g, "Steam Generator (SG} Program," Item d.2, to extend, on a one-time basis, the requirement to inspect each steam generator (SG) at least every 48 effective full power months or every other refueling outage (whichever results in more frequent inspections) for SGs A and C.

This extension would allow DENC to defer the MPS3 inspections for SGs A and C from the fall of 2020 (Refueling Outage 20) to the spring of 2022 (Refueling Outage 21 ).

In the fall of 2020, MPS3 will begin its Refueling Outage 20. To meet the requirements of TS 6.8.4.g Item d.2, the outage scope includes a planned inspection of the MPS3 SGs A and C. An estimated one hundred individuals from vendor locations across the U.S.,

are required to be onsite to perform activities related to the SG inspections. However, on January 31, 2020, the United States (U.S.} Department of Health and Human Services declared a public health emergency (PHE) for the U.S. in response to the worldwide spread of the Coronavirus Disease 2019 (COVID-19). Subsequently, on March 11, 2020, the COVID..:19 outbreak was characterized as a pandemic by the World Health Organization and declared a national emergency on March 13, 2020. In response to the pandemic, the Centers for Disease Control and Prevention (CDC} issued recommendations advising isolation activities (e.g., social distancing, group size limitations, self-quarantining, etc.) to help limit the spread of the COVID-19 virus.

Although infection rates have decreased in some parts of the country, infection rates in other parts of the U.S. continue to rise.

Steam generator inspections require many workers to be in close proximity to each other in a high temperature environment, for extended periods of time (which increases the likelihood for involved individuals to contract and spread the COVID-19 virus).

Additionally, SG inspections require the support of a specialty vendor that maintains a unique and complex set of qualifications. If the vendor's qualified personnel contract the virus, a situation could occur where the necessary technical knowledge would not be available to complete the inspections (due to the likelihood of affecting additional individuals working in close proximity). Therefore, in response to the continuing COVID-19 pandemic, in the interest of personnel health and safety, compliance with CDC recommendations, and to preclude the potential for transmittal and spread of the COVID-

Serial No.20-272 Docket No. 50-423 Page 2 of 3 19 virus, DENC requests to extend, on a one-time basis, the TS-required inspection of the MPS3 SGs A and C, from the fall of 2020 (Refueling Outage 20) to the spring of 2022 (Refueling Outage 21 ). provides DENC's description and assessment of the proposed change.

Attachments 2 and 3 provide the marked-up and clean TS pages, respectively, for the proposed change. Attachment 4 contains the operational assessment, which demonstrates that the proposed change to the SG inspection schedule is appropriate and does not impact the safe operation of the plant.

DENG has evaluated the proposed amendment and has determined it does not involve a significant hazards consideration as defined in 10 CFR 50.92. The basis for this determination is included in Attachment 1. DENG has also determined that operation with the proposed change will not result in a significant increase in the amount of effluents that may be released offsite or a significant increase in individual or cumulative occupational radiation exposure. Therefore, the proposed amendment is eligible for categorical exclusion from an environmental assessment as set forth in 10 CFR 51.22(c)(9).

Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment is needed in connection with approval of the proposed change. The LAR has been reviewed and approved by the Facility Safety Review Committee.

DENG requests approval of the proposed change by September 15, 2020. Should you have any questions or require additional information, please contact Shayan Sinha at (804) 273-4687.

Respectfully, i<<Ja~-

Mark D. Sartain Vice President - Nuclear Engineering and Fleet Support COMMONWEALTH OF VIRGINIA )

)

COUNTY OF HENRICO )

The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by Mr. Mark D. Sartain, who is Vice President- Nuclear Engineering and Fleet Support of Dominion Energy Nuclear Connecticut, Inc. He has affirmed before me that he is duly authorized to execute and file the foregoing document in behalf of that company, and that the statements in the document are true to the best of his knowledge and belief.

Acknowledged before me this / J fl.. day of A-u5u 5t , 2020.

My Commission Expires: / ~ I/~/ I/ ')..O Notary Public

Serial No.20-272 Docket No. 50-423 Page 3 of 3 Commitments contained in this letter: None Attachments:

1. Description and Assessment of Proposed Change
2. Marked-up Technical Specification Page
3. Retyped Proposed Technical Specification Page
4. Operational Assessment Addressing Fall 2020 SG A and C Inspection Deferral cc: U.S. Nuclear Regulatory Commission Region I 2100 Renaissance Blvd, Suite 100 King of Prussia, PA 19406-2713 R. V. Guzman NRC Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 08 C2 11555 Rockville Pike Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station Director, Radiation Division Department of Energy and Environmental Protection 79 Elm Street Hartford 1 CT 06106-5127

Serial No.20-272 Docket No. 50-423 ATTACHMENT 1 DESCRIPTION AND ASSESSMENT OF PROPOSED CHANGE DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 3

Serial No.20-272 Docket No. 50-423 Attachment 1, Page 1 of 22 DESCRIPTION AND ASSESSMENT OF PROPOSED CHANGE 1.0

SUMMARY

DESCRIPTION Pursuant to 10 CFR 50.90, Dominion Energy Nuclear Connecticut, Inc. (DENC) requests an amendment to the Millstone Power Station Unit 3 (MPS3) Facility Operating License Number NPF-49, in the form of a change to the technical specifications (TSs).

This license amendment request (LAR) proposes to revise MPS3 TS 6.8.4.g, "Steam Generator (SG) Program," Item d.2, to extend, on a one-time basis, the requirement to inspect each steam generator (SG) at least every 48 effective full power months or every other refueling outage (whichever results in more frequent inspections) for SGs A and C. This extension would allow DENC to defer the MPS3 inspections for SGs A and C from the fall of 2020 (Refueling Outage 20 or 3R20) to the spring of 2022 (Refueling Outage 21 or 3R21 ).

In the fall of 2020, MPS3 will conduct its Refueling Outage (RFO) 20. To meet the requirements of TS 6.8.4.g, Item d.2, the outage scope includes a planned inspection of the MPS3 SGs A and C. An estimated one hundred individuals from vendor locations across the U.S., are required to be onsite to perform activities related to the SG inspections. However, on January 31, 2020, the United States (U.S.) Department of Health and Human Services declared a public health emergency (PHE) for the U.S. in response to the worldwide spread of the Coronavirus Disease 2019 (COVID-19).

Subsequently, on March 11, 2020, the COVID-19 outbreak was characterized as a pandemic by the World Health Organization and declared a national emergency on March 13, 2020. In response to the pandemic, the Centers for Disease Control and Prevention (CDC) issued recommendations advising isolation activities (e.g., social distancing, group size limitations, self-quarantining, etc.) to help limit the spread of the COVID-19 virus. Although infection rates have decreased in some parts of the country, infection rates in other parts of the U.S. continue to rise.

Steam generator inspections require many workers to be in close proximity to each other in a high temperature environment, for extended periods of time (which increases the likelihood for involved individuals to contract and spread the COVID-19 virus).

Additionally, SG inspections require the support of a specialty vendor that maintains a unique and complex set of qualifications. If the vendor's qualified personnel contract the virus, a situation could occur where the necessary technical knowledge would not be available to complete the inspections (due to the likelihood of affecting additional individuals working in close proximity). Therefore, in response to the continuing COVID-19 pandemic, in the interest of personnel health and safety, compliance with CDC recommendations, and to preclude the potential for transmittal and spread of the COVID-19 virus, DENG requests to extend, on a one-time basis, the TS-required inspection of the MPS3 SGs A and C, from the fall of 2020 to the spring of 2022.

Serial No.20-272 Docket No. 50-423 Attachment 1, Page 2 of 22 2.0 DETAILED DESCRIPTION 2.1 System Design and Operation The MPS3 Reactor Coolant System (RCS) consists of four coolant loops.

Each loop contains a reactor coolant pump (RCP), two loop stop valves, loop piping, instrumentation, and a SG. The SGs are Westinghouse Model F, and each SG is a vertical shell, U-tube heat exchanger that is the heat transfer interface between the primary and secondary loops. The purpose of the SGs is to generate high quality steam for the secondary plant by transferring heat from the reactor coolant to the secondary side water.

The SGs are divided into two main portions: the primary side and the secondary side. The primary side consists of a cast hemispherical chamber, internally partitioned by a divider plate, which separates the chamber into inlet and outlet chambers. The primary and secondary sides are separated by the tubesheet and the U-tubes. The tubesheet is penetrated by 5626 lnconel-600 thermally treated U-tubes, which are welded to the tubesheet.

The tubes are supported at intervals by horizontal support plates. The location of each tube is marked in accordance with an established grid system, i.e., row and column number. The marking of the tubes facilitates identification of tubes for plugging or inspection, thereby minimizing radiation exposure and time required for the activity.

Reactor coolant enters the primary side of the SG into the inlet chamber. The coolant then enters the U-tubes, flows up and through the tubes, and exits into the outlet chamber, where it returns to the RCP. The secondary side of the SG contains feedwater, recirculating water (hot water drainage from the first and second stage separators), and steam. The boundaries for the secondary side consist of the upper and lower shell, the top of the tubesheet, and the outside of the U-tubes. An access opening for inspection and maintenance is provided in each section of the SG channel head.

2.2 Current Technical Specification Requirements Applicable SG TS requirements are included in the following TS sections:

TS 3.4.6.2.c, "Reactor Coolant System Operational LEAKAGE," limits primary to secondary leakage through any one SG to 150 gallons per day.

TS 3.4.5, "Steam Generator Tube Integrity," states that SG tube integrity shall be maintained and all SG tubes satisfying the tube plugging criteria shall be plugged in accordance with the SG Program.

Serial No.20-272 Docket No. 50-423 Attachment 1, Page 3 of 22 TS Surveillance Requirement (SR) 4.4.5.1 requires verification of SG tube integrity in accordance with the Steam Generator Program. TS SR 4.4.5.2 requires verification that each inspected SG tube that satisfies the tube plugging criteria is plugged in accordance with the SG Program prior to entering hot shutdown following a SG tube inspection.

The SG inspection scope is governed by TS 6.8.4.g, "Steam Generator (SG)

Program" requirements. TS 6.8.4.g, Item a, requires that a condition monitoring assessment be performed during each outage in which the SG tubes are inspected, to confirm that the performance criteria are being met.

TS 6.8.4.g, Item b, ensures SG tube integrity is maintained by meeting specified performance criteria for structural and leakage integrity, consistent with the plant design and licensing basis. Meeting SG performance criteria provides reasonable assurance of maintaining tube integrity at normal and accident conditions. TS 6.8.4.g, Item c, provides SG tube plugging criteria and TS 6.8.4.g, Item d, includes provisions regarding the scope, frequency, and methods of SG tube inspections. Specifically, TS 6.8.4.g, Item d.2 states, in part, "after the first refueling outage following SG installation, inspect each SG at least every 48 effective fu II power months or at least every other refueling outage (whichever results in more frequent inspections)."

2.3 Description of Proposed Change A note (denoted by an asterisk) will be added to TS 6.8.4.g, Item d.2), to allow DENC to defer, on a one-time basis, inspections of the MPS3 SGs A and C, from the fall of 2020 (Refueling Outage 20) to the spring of 2022 (Refueling Outage 21). The proposed change is as follows (added text is shown below in bold type):

2. After the first refueling outage following SG installation, inspect each SG at least every 48 effective full power months or at least every other refueling outage (whichever results in more frequent inspections).*
  • As approved by License Amendment No. XXX, inspection of the Millstone Unit 3 SGs A and C may be extended, on a one-time basis, from fall 2020 (Refueling Outage 20) to spring 2022 (Refueling Outage 21).

A TS markup of the proposed change is provided in Attachment 2. A clean (retyped) version of the proposed TS change is provided in Attachment 3.

Serial No.20-272 Docket No. 50-423 Attachment 1, Page 4 of 22 2.4 Reason for Proposed Change In the fall of 2020, MPS3 will begin its RFO 20. To meet the requirements of TS 6.8.4.g Item d.2, the outage scope includes a planned inspection of the MPS3 SGs A and C. An estimated one hundred individuals from vendor locations across the U.S., are required to be onsite to perform activities related to the SG inspections. However, on January 31, 2020, the U.S.

Department of Health and Human Services declared a PHE for the U.S. in response to the worldwide spread of the Coronavirus Disease 2019 (COVID-19). Subsequently, on March 11, 2020, the COVID-19 outbreak was characterized as a pandemic by the World Health Organization and declared a national emergency on March 13, 2020. In response to the pandemic, the CDC issued recommendations advising isolation activities (e.g., social distancing, group size limitations, self-quarantining, etc.) to help limit the spread of the COVID-19 virus. Although infection rates have decreased in some parts of the country, infection rates in other parts of the U.S. continue to rise ..

DENC has implemented practices beyond the CDC recommendations.

These include self-screening questions of all workers prior to reporting to work, temperature monitoring and maximizing remote-enabled employees.

MPS3 personnel have performed a review of all activities for the fall 2020 RFO to defer any activities that are not critical to nuclear safety or reliable generation, thus minimizing the number of people who must travel to the site.

Steam generator inspection~ require many workers to be in close proximity to each other in a high temperature environment, for extended periods of time (which increases the likelihood for involved individuals to contract and spread the COVID-19 virus). Additionally, SG inspections require the support of a specialty vendor that maintains a unique and complex set of qualifications. If the vendor's qualified personnel contract the virus, a situation could occur where the necessary technical knowledge would not be available to complete the inspections (due to the likelihood of affecting additional individuals working in close proximity).

The use of fiber-optic cable running from the MPS3 Containment to the MPS Building 512 allows DENC to perform some SG inspection-related functions outside the protected area. However, a significant number of individuals must still enter containment to perform their activiites, including closure crews, water lancing crews, acquisition perso.nnel, and secondary side inspection (SSI) and foreign object search and retrieval (FOSAR) personnel.

Consequently, in response to the pandemic declarations, in the interest of personnel health and safety, and to preclude the potential for transmittal and spread of the COVID-19 virus, DENC is requesting, on a one-time basis, extension of the TS-required inspection of the MPS3 SGs A and C, from the

Serial No.20-272 Docket No. 50-423 Attachment 1, Page 5 of 22 fall of 2020 (Refueling Outage 20 or 3R20) to the spring of 2022 (Refueling Outage 21 or 3R21 ). The MPS3 SGs B and D were inspected during Refueling Outage 19 (spring 2019) and are therefore not required to be inspected during the upcoming Refueling Outage 20. Consequently, the TS-required inspection schedule for SGs Band Dis not affected by the proposed change.

3.0 TECHNICAL EVALUATION

MPS3 TS 6.8.4.g requires that after the first RFO following SG installation, each SG must be inspected at least every 48 effective full power months (EFPM) or at least every other RFO (whichever results in more frequent inspections). MPS3 SGs A and C were last inspected during the fall 2017 RFO (3R18) and would therefore need to be inspected during the fall 2020 RFO (3R20) to comply with the " ... at least every other refueling outage ... " portion of the TS 6.8.4.g requirement. MPS3 TS 6.8.4.g further stipulates that commencing with the third inspection period during the remaining life of the SGs, 100% of the tubes in each SG must be inspected every 72 EFPM. During the fall 2017 RFO, 100% of the MPS3 A and C SG tubes were inspected. MPS3 SGs are now in the 4th Inspection period (duration 72 EFPM). The spring 2019 RFO (3R19) was the first outage of the 4th period.

Due to personnel health and safety issues associated with the COVID-19 pandemic as discussed above, DENG is requesting a one-time change to MPS3 TS 6.8.4.g requirements to defer the SG A and C inspections by one operating cycle until the spring 2022 RFO (3R21 ).

3.1 Operational Assessment Summary The Dominion Energy Steam Generator Program requires a "forward looking" operational assessment (OA) be performed to determine if the SG tubing will continue to meet specific structural and leakage integrity performance criteria throughout the operating period preceding the next inspection. Nuclear Energy Institute (NEI), document 97-06, "Steam Generator Program Guidelines," (Reference 8.1) and TS 6.8.4.g establish the following SG performance criteria:

Structural Integrity - Margin of 3.0 against burst under normal steady state power operation, and a margin of 1.4 against burst under the most limiting design basis accident. Additional requirements are specified for non-pressure accident loads.

  • Operational Leakage - RCS operational primary-to-secondary leakage through one SG shall not exceed 150 gallons per day (gpd).

Serial No.20-272 Docket No. 50-423 Attachment 1, Page 6 of 22

  • Accident Induced Leakage - The primary to secondary accident induced leakage rate for any design basis accident, other than a steam generator tube rupture, shall not exceed the leakage rate assumed in the accident analysis in terms of total leakage rate for all steam generators and leakage rate for an individual steam generator. MPS3's accident induced leakage performance criteria is 500 gpd through the faulted SG (Main Steam Line Break or MSLB) and one gallon per minute total for all SGs.

An OA (Reference 8.6) confirming there is reasonable assurance that the performance criteria identified above will continue to be met throughout the requested examination deferral period is provided in Attachment 4. The OA was developed in accordance with the following MPS3 and industry inspection requirements documents:

  • Dominion Energy Fleet-wide SG Program
  • Electric Power Research Institute (EPRI) Steam Generator Integrity Assessment Guidelines (IAG) (Reference 8.2)
  • Dominion Energy SG Condition Monitoring and Operational Assessment (CMOA) Procedure The OA provides an evaluation of MPS3 SGs A and C with the purpose of demonstrating the primary side examinations currently planned for the end of cycle (EOC) 20 for MPS3 (fall 2020) may be safely deferred by one additional operating cycle (EOC21, spring 2022).

SGs 8 and D were inspected more recently (EOC19, spring 2019) than SGs A and C, and the OA performed following the EOC19 inspection concluded SGs 8 and D could be safely operated until their next scheduled primary side inspection (EOC21, spring 2022). Consequently, the OA does not include any additional analysis of SGs 8 and D.

Table 1A below provides a brief description of the MPS3 SG inspections performed, or to be performed, from the fall 2014 RFO through the spring 2022 RFO. As discussed above, the purpose of the OA is to determine if the planned EOC20 SG A and C primary side inspections may be safely deferred until EOC21. Table 1A shows the as-planned scope prior to deferral, and Table 1B shows the proposed scope following deferral. In addition to the deferral of the SG A and C primary inspection scope, the secondary side

Serial No.20-272 Docket No. 50-423 Attachment 1, Page 7 of 22 inspections planned for the four SGs in EOC20 would also be deferred to EOC21. The "full primary side inspection scope" referred to in Tables 1A and 1B includes:

  • 100% full length bobbin probe examinations (excluding low row U-bends) 100% hot leg tubesheet region array probe exams Array probe exams of the cold leg periphery tubesheet region~ 2 tubes deep (approximately 13% of all tubes)

Hot leg array probe exams of tubes categorized as high residual stress tubes (during 3R18 in SGs A and C)

  • Full length array probe exams of tubes categorized as high residual stress tubes (during 3R19 in SGs Band D and future inspections)
  • Motorized rotating probe coil (+Point') examinations:

100% of low row U-bends 50% of hot leg dents/dings ~ 2 volts plus the five largest voltage cold leg and U-bend dents/dings Miscellaneous areas of special interest

Serial No.20-272 Docket No. 50-423 Attachment 1, Page 8 of 22 Table 1A: Millstone Unit 3 Inspection Scope Timeline Inspection Scope Refueling Cumulative Outage Date EFPY SGA 5GB SGC SGD

  • Full primary side
  • TTS SSI / FOSAR
  • Full primary side
  • TTS SSI / FOSAR inspection scope
  • DMT Chemical inspection scope
  • DMT Chemical Fall 3R16 22.02
  • TTS SSI / FOSAR Cleaning
  • TTS SSI / FOSAR Cleaning 2014
  • SSI Upper Internals
  • DMT Chemical
  • DMT Chemical Cleaning Cleaning
  • TTS SSI / FOSAR
  • Full primary side
  • TTS SSI / FOSAR
  • Full primary side
  • DMT Chemical Cleaning inspection scope
  • DMT Chemical inspection scope Spring
  • TTS SSI / FOSAR Cleaning
  • TTS SSI / FOSAR 3R17 23.39 2016
  • SSI Upper Internals
  • DMT Chemical
  • DMT Chemical Cleaning Cleaning Fall
  • Full primary side
  • TTS SSI / FOSAR
  • Full primary side
  • TTS SSI / FOSAR 3R18 24.76 inspection scope inspection scope 2017
  • SSI Upper Internals
  • TTS SSI / FOSAR
  • TTS SSI / FOSAR Spring
  • TTS SSI / FOSAR
  • Full primary side
  • TTS SSI / FOSAR
  • Full primary side 3R19 26.16 inspection scope inspection scope 2019
  • SSI Upper Internals
  • TTS SSI / FOSAR
  • TTS SSI / FOSAR C
  • Full primary side
  • TTS SSI / FOSAR
  • Full primary side
  • TTS SSI / FOSAR cu Fall inspection scope inspection scope a:

3R20 2020 27.56* roC

  • TTS SSI / FOSAR
  • TTS SSI / FOSAR *5,
  • SSI Upper Internals 0
  • TTS SSI I FOSAR
  • Full primary side
  • TTS SSI / FOSAR
  • Full primary side C cu Spring inspection scope inspection scope a:

3R21 2022 28.96* roC

  • TTS SSI / FOSAR
  • TTS SSI / FOSAR *5,
  • SSI Upper Internals 0
  • Estimate (Note: The acronyms included in the above and following tables and text are defined in the OA provided in Attachment 4)

Serial No.20-272 Docket No. 50-423 Attachment 1, Page 9 of 22 Table 1B: Millstone Unit 3 Inspection Proposed 3R20 and 3R21 Scope Inspection Scope Refueling Cumulative Outage Date EFPY SGA SGB SGC SGD

  • None
  • None
  • None
  • None C cu a:

-0 3R20 Fall 2020 27.56* Q)

(/)

0 Cl.

2 0..

  • Full primary side C
  • Full primary side
  • Full primary side
  • Full primary side cu inspection scope inspection scope inspection scope inspection scope a:

Spring -0 3R21 28.96*

  • TTS SSI I FOSAR
  • TTS SSI / FOSAR
  • TTS SSI / FOSAR
  • TTS SSI I FOSAR Q) 2022 (/)

0 Cl.,

  • SSI Upper Internals
  • SSI Upper Internals 2 0..
  • Estimate

Serial No.20-272 Docket No. 50-423 Attachment 1, Page 10 of 22 The degradation mechanisms assessed during the most recent inspections are identified in the respective 180-day reports for EOC18 and EOC19 (References 8.3 and 8.7, respectively). The degradation mechanisms previously identified (i.e., "existing") in the MPS3 SGs, and the inspection method and scope used to detect these mechanisms, are summarized in Table 2. Apart from tube-end stress corrosion cracking (SCC), which is covered by MPS3 Permanent Alternate Repair Criteria (PARC), each degradation mechanism identified in the table is evaluated within the OA.

Table 2: Existing Millstone Unit 3 Degradation Mechanisms Mechanism Detection Strategy Anti-vibration bar (AVB} wear

  • 100% bobbin probe examination of AVB/tube intersections Foreign object wear
  • Cold leg periphery and 100% hot leg array probe examination of the tubesheet region
  • 100% full length bobbin probe examination Tube support plate (TSP} and Flow
  • 100% bobbin probe examination of distribution baffle (FDB) wear TSP /FOB/tube intersections Wear from a legacy maintenance
  • Cold leg periphery and 100% hot leg array process (sled sludge lancing) that has probe examination of the tubesheet region not been implemented for many years
  • Inspection for this degradation mechanism ends is not required under the MP3 technical specification PARC The OA concludes with reasonable assurance that each of the evaluated existing degradation mechanisms will not violate structural or leakage performance criteria prior to 3R21.

The OA also considers three other degradation mechanisms (Table 3), none of which have been identified in the MPS3 SGs. These are considered to be bounding among the mechanisms which could potentially develop (i.e.

"potential" degradation mechanisms).

Serial No.20-272 Docket No. 50-423 Attachment 1, Page 11 of 22 Table 3: Evaluated Potential Degradation Mechanisms Mechanism Detection Strategy Axial ODSCC at TSPs

  • 100% bobbin probe examination of TSP /tube intersections.
  • 100% array probe examination of hot leg TSP /tube intersections in high stress tubes (SGs A and C, 3R18}

Axial ODSCC at Dents/Dings

  • 50% +Point' probe examination of hot leg dents/dings ~ 2 Volts and the 5 largest voltage cold leg dents/dings Circumferential OD stress corrosion
  • 100% hot leg array probe examination cracking (ODSCC) at the hot leg top of of the tubesheet region tubesheet (TTS)

Axially oriented, outer diameter-initiated sec (ODSCC) at the tube support plates (TSPs) is bounding in this context because eddy current testing bobbin probe examination methods are relied upon to detect this mechanism in non-high stress tubes. The bobbin probe probability of detection (POD) is generally less favorable than that of the +Point' or array probes. In addition, the lengths of cracks that develop at TSPs are typically greater than the lengths of those that develop elsewhere within SGs.

Axially oriented ODSCC at dent/ding locations is addressed herein principally because of recent operating experience at Seabrook Station, which has increased industry focus on this mechanism. Axial ODSCC at dents/dings is not bounding per se (i.e., the cracks are short, growth rates are low).

However, because the routine MPS3 dent/ding examinations utilize sampling, an explicit operational assessment (OA) of this hypothetical mechanism must consider longer operating intervals between inspections. Thus, this is a bounding degradation mechanism.

Among circumferentially oriented SCC degradation mechanisms, ODSCC at the top of tubesheet (TTS) is considered to be bounding because the inspection POD for OD initiated SCC is not as favorable as that for ID initiated flaws. In addition, ID-initiated sec within the tubesheet region is less challenging to structural and leakage integrity due to the presence of the tubesheet.

The OA evaluates whether the lower 95/50 (i.e., the 5th percentile) burst pressure for each of the potential degradation mechanisms above satisfy the structural integrity performance criteria (SIPC) limits and demonstrate that the mechanisms would not cause the structural integrity performance criteria to be exceeded in SG A or C prior to 3R21.

Serial No.20-272 Docket No. 50-423 Attachment 1, Page 12 of 22 Since operational leakage is already limited by the technical specifications limit, a more restrictive operational leakage limit is not required. The projected total upper 95/50 leakage under limiting accident conditions for each of the potential degradation mechanisms is zero. Therefore, it is concluded these mechanisms will not cause the accident induced leakage performance criteria (AILPC) to be exceeded prior to 3R21. Since degradation is not projected to exceed the AILPC through 3R21, there is reasonable assurance that normal operating conditions will not result in exceeding the operational leakage performance criteria. Although there are no known conditions of concern, sensitivity to primary-to-secondary leakage events will continue under existing MPS3 monitoring procedures.

Table 4 summarizes the projected margin to SIPC and AILPC discussed in the OA:

Table 4: SGs A and C Integrity Margin Summary SIPC AILPC Degradation Mechanism Limit 3R21 Projection Limit 3R21 Projection AVB wear 61.2 %TW 52.1 %TW 500 GPD Zero Leakage TSP/FDB wear 68.9%TW 64.3 %TW 500 GPD Zero Leakage Axial ODSCC 4020 psi 5262 psi Zero Leakage 500 GPD

@TSPs (3xNOPD 1 ) (Lower 95%/50%) (Upper 95%/50%)

Axial ODSCC 4020 psi 4743 psi Zero Leakage 500 GPD

@Dents/Dings (3xNOPD 1 ) (Lower 95%/50%) (Upper 95%/50%)

Circumferential 4020 psi 7420 psi Zero Leakage 500 GPD ODSCC@TTS (3xNOPD 1 ) (Lower 95%/50%) (Upper 95%/50%)

1 Minimum acceptable burst pressure Based on the above, there is reasonable assurance the SIPC and AILPC will remain satisfied in SGs A and C throughout the period preceding 3R21, for a total operating duration of three cycles between primary side inspections.

Additional information relevant to this operational assessment summary is provided below:

MPS3 Tube Plugging. The total number of tubes plugged along with the driver for each is provided in Tables 5 and 6:

Serial No.20-272 Docket No. 50-423 Attachment 1, Page 13 of 22 Table 5: Total Number of SG Tubes Plugged in Millstone Unit 3 SGA SGB SGC SG D Total Total Tubes Plugged 51 25 22 91 189 Through 3R19 Percent Tubes Plugged 0.907% 0.444% 0.391% 1.617% 0.84%

Through 3R19 Allowable Percent 10% 10% 10% 10% 10%

Tubes Plugged Table 6: Millstone Unit 3 SG Tube Plugging by Degradation Mechanisms Degradation Mode Total Tubes Plugged AVB Wear 77 Foreign Objects/ Foreign Object Wear 59 TSP Wear 9 Pre-service 10 Tube-end sec 23 Other* 11

  • Bottom of the expansion transition (BET) being more than 1" below the top of tubesheet (TTS), ID Chatter, tube restriction/ obstruction, and U-bend tangent signal.

No tubes have required plugging in MPS3 steam generators since 3R18 (2017), when a total of two tubes were plugged to address AVB wear and foreign object wear.

High Stress Tubes: A total of 67 Tier 1 tubes exist in MPS3 SG A and a total .

of 39 Tier 1 high stress tubes exist in in SG C. During EOC18, DENG examined the entire hot leg straight length of tubing with array probes. No relevant indications were noted. When analyzing potential stress corrosion cracking degradation mechanisms, the attached OA utilizes the POD associated with the bobbin probe method of examination for the purposes of defining a pre-existing flaw size used for probabilistic crack growth analysis.

The bobbin probe (POD) is less favorable than that of the +Point' or array probes. In addition, the lengths of the cracks that develop at TSPs are typically greater than the length of those that develop elsewhere within the SGs. Although hot leg TSPs in high stress tubes were examined using an array probe during 3R18, the evaluation in the OA conservatively assumes

Serial No.20-272 Docket No. 50-423 Attachment 1, Page 14 of 22 that the 3R 18 examination relied entirely on the bobbin probe to detect axial ODSCC at SG A and C TSPs.

Deposit Loading: Deposit loading has been aggressively managed including performance of chemical cleaning (Deposit Minimization Treatment or DMT) in 3R 16 and 3R 17 and deposit mapping during each outage since that time.

No adverse trends in deposit loading currently exist in any MPS3 SG.

Chemistry Transients: Throughout the current operating cycle between 3R 19 and the present time, no chemistry excursions that would cause MPS3 to approach or exceed Technical Specification limits or Action Level values have occurred.

Introduction of FME: No known foreign materials that pose a threat to tube integrity are known to exist in any of the MPS3 SGs. No incidents of foreign material introduction to the MPS3 primary or secondary fluid systems are known to have occurred throughout the operating interval since 3R18 (fall 2017).

Flaw profiling to meet condition monitoring: Flaw profiling was not required during 3R18 to demonstrate condition monitoring criteria was met.

3.2 Mitigation Strategy The TS limit on primary-to-secondary leakage is 150 gpd through any one SG. The limit of 150 gpd per SG is based on the operational leakage performance criterion prescribed in NEI 97-06, Steam Generator Program Guidelines. The limit is based on operating experience with SG tube degradation mechanisms that result in tube leakage. The operational leakage rate criterion, in conjunction with the implementation of the Steam Generator Program, is an effective measure for minimizing the frequency of SG tube ruptures.

There are several methods available to identify and quantify primary-to-secondary leakage in the plant. These methods include chemistry samples by the continuous radiation monitoring via Nitrogen-16 (N-16) radiation monitor, Main Condenser Air Ejector radiation monitor, and SG blowdown radiation monitor. The advantage of continuous radiation monitors is they provide instant response during a primary-to-secondary leak. Additionally, the N-16 radiation monitor can provide evidence to determine from which SG the leak is originating.

The N-16 Main Steam Radiation monitor is the primary means of monitoring and assessing primary-to-secondary leakage, augmented by the Main Condenser Air Ejector radiation monitor. The N-16 Main Steam Radiation monitor consists of four channels, one installed in each steam generator main

Serial No.20-272 Docket No. 50-423 Attachment 1, Page 15 of 22 steam supply line. These channels continuously monitor for evidence of primary-to-secondary leakage and are augmented by periodic performance of primary-to-secondary system leakage calculations (typically performed once per 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> at normal operation, but frequency varies based on plant conditions). Current calculations indicate no detectable leakage has been identified in any MPS3 SG. If primary-to-secondary leakages reaches 5 gpd as indicated by chemistry sampling, increased monitoring is initiated and entry into MPS3 Abnormal Operating Procedure (AOP) 3576, "Steam Generator Tube Leak," (Reference 8.5) is required. AOP 3576 is also entered if primary-to-secondary leakage is indicated by the N-16, Main Condenser Air Ejector, or SG Slowdown radiation monitors. The N-16 radiation monitor's lower alarm setpoint corresponds to 30 gpd. In addition to requiring additional monitoring, AOP 3576 directs equipment configuration changes based on the magnitude of the primary-to-secondary leakage. If a leak rate of 75 gpd in any SG is sustained for one hour (as indicated by chemistry samples or receipt of the N-16 radiation monitor's higher setpoint alarm), procedural actions require plant shutdown to be initiated.

The Loose Parts Monitoring System (LPMS), in conjunction with the associated programmatic procedures, comprise the MPS3 Loose Part Detection Program described in Regulatory Guide 1.133, Revision 1. The LPMS monitors for evidence indicative of a loose part that could cause fuel damage or SG tube damage, which could then lead to SG tube leakage. If a loose part is suspected, diagnostic steps are taken to determine whether a loose part is present and assess the safety significance of any identified loose parts. If the presence of a loose part is confirmed and is evaluated to have safety significance, it will be reported to the NRC in accordance with 10 CFR 50.73.

The above monitoring and mitigative actions will provide assurance that should a SG tube leak develop in MPS3 SGs A or C during the proposed extended inspection interval, the condition will be identified and managed to ensure public safety is assured. The leakage limits imposed are consistent with EPRI recommendations and conservatively below the TS prescribed shutdown criteria of 150 gpd.

Serial No.20-272 Docket No. 50-423 Attachment 1, Page 16 of 22

4.0 REGULATORY EVALUATION

The proposed LAR adds a note to MPS3 TS 6.8.4.g Item d.2), to allow DENG to defer, on a one-time basis, inspections of the MPS3 SGs A and C, from the fall of 2020 (Refueling Outage 20) to the spring of 2022 (Refueling Outage 21 ). The following regulatory requirements have been reviewed and the No Significant Hazards Consideration Determination is provided below.

4.1 Applicable Regulatory Requirements/Criteria Technical Specifications - Section 50.36 of Title 10 of the Code of Federal Regulations (10 CFR), establishes the regulatory requirements related to the content of the TSs. Pursuant to 10 CFR 50.36, TSs are required to include items in the following five specific categories related to station operation: (1) safety limits, limiting safety system settings, and limiting control settings; (2) limiting conditions for operation (LCOs); (3) surveillance requirements; (4) design features; and (5) administrative controls. In 10 CFR 50.36(c)(5),

administrative controls are stated to be, "the provisions relating to organization and management, procedures, recordkeeping, review and audit, and reporting necessary to assure the operation of the facility in a safe manner." This also includes the programs established by the licensee and listed in the administrative controls section of the TS for the licensee to operate the facility in a safe manner. For MPS3, the requirements for performing SG tube inspections and repair are contained in TS 3/4.4.5, "Steam Generator Tube Integrity" and TS 6.8.4.g, "Steam Generator (SG) Program."

The TSs for pressurized-water reactor plants require that a SG program be established and implemented to ensure SG tube integrity is maintained. For MPS3, TS 6.8.4.g, Item a, requires that a condition monitoring assessment be performed during each outage in which the SG tubes are inspected, to confirm that the performance criteria are being met. TS 6.8.4.g, Item b, ensures SG tube integrity is maintained by meeting specified performance criteria for structural and leakage integrity, consistent with the plant design and licensing basis. TS 6.8.4.g, Item c, provides SG tube plugging criteria and TS 6.8.4.g, Item d, includes provisions regarding the scope, frequency, and methods of SG tube inspections. Of relevance to the proposed changes, TS 6.8.4.g, Item d.2, requires, in part, that "After the first refueling outage following SG installation, inspect each SG at least every 48 effective full power months or at least every other refueling outage (whichever results in more frequent inspections)."

10 CFR Requirements/General Design Criteria (GDC) - 10 CFR 50, Appendix A, "General Design Criteria for Nuclear Power Plants," Criteria 14, 15, 30, 31, and 32, define the requirements for the RCS pressure boundary with respect to structural and leakage integrity. Steam generator tubing and tube repairs constitute a major fraction of the RCS pressure boundary surface area. Steam generator tubing and associated repair techniques and components, such as

Serial No.20-272 Docket No. 50-423 Attachment 1, Page 17 of 22 plugs and sleeves, must be capable of maintaining reactor coolant inventory and pressure.

Criterion 14, "Reactor Coolant Pressure Boundary" The reactor coolant pressure boundary shall be designed, fabricated, erected, and tested so as to have an extremely low probability of abnormal leakage, or rapidly propagating failure, and of gross rupture.

Criterion 15, "Reactor Coolant System Design" The reactor coolant system and associated auxiliary, control, and protection systems shall be designed with sufficient margin to assure that the design conditions of the reactor coolant pressure boundary are not exceeded during any condition of normal operation, including anticipated operational occurrences.

Criterion 30, "Quality of reactor coolant pressure boundary" Components, which are part of the reactor coolant pressure boundary, shall be designed, fabricated, erected, and tested to the highest quality standards practical. Means shall be provided for detecting and, to the extent practical, identifying the location of the source of reactor coolant leakage.

Criterion 31, "Fracture prevention of reactor coolant pressure boundary" The reactor coolant pressure boundary shall be designed with sufficient margin to assure that when stressed under operating, maintenance, testing, and postulated accident conditions (1) the boundary behaves in a nonbrittle manner and (2) the probability of rapidly propagating fracture is minimized. The design shall reflect consideration of service temperatures and other conditions of the boundary material under operating, maintenance, testing, and postulated accident conditions and the uncertainties in determining (1) material properties, (2) the effects of irradiation on material properties, (3) residual, steady state and transient stresses, and (4) size of flaws.

Criterion 32, "Inspection of reactor coolant pressure boundary" Components, which are part of the reactor coolant pressure boundary, shall be designed to permit (1) periodic inspection and testing of important areas and features to assess their structural and leak-tight integrity, and (2) an appropriate material surveillance program for the reactor pressure vessel.

The reactor coolant system (RCS) pressure boundary is designed, fabricated and constructed to have an exceedingly low probability of gross rupture or significant uncontrolled leakage throughout its design lifetime. RCS pressure boundary components have provisions for the inspection testing and surveillance of critical areas, by appropriate means, to assess the structural and leak-tight integrity of the boundary components during their service lifetime.

The SG tubes function as an integral part of the RCS pressure boundary and, in addition, isolate fission products in the primary coolant from the secondary coolant and the environment. SG tube integrity means the tubes are capable

Serial No.20-272 Docket No. 50-423 Attachment 1, Page 18 of 22 of performing these safety functions in accordance with the plant design and licensing bases. All applicable regulatory requirements will continue to be satisfied as a result of the proposed license amendment.

As part of the plant-licensing basis, applicants for operating licenses are required to analyze the consequences of postulated design-basis accidents (OBA) such as a SG tube rupture and a main steam line break (MSLB). These analyses consider primary-to-secondary leakage that may occur during these events and must show that the offsite radiological consequences do not exceed the applicable limits of the 10 CFR 50.67 guidelines for offsite doses, GDC 19 criteria for control room operator doses, or some fraction thereof, as appropriate, to the accident or the NRG-approved licensing basis (e.g., a small fraction of these limits). No accident analysis for MPS3 is being changed because of the proposed amendment; thus, no radiological consequences of any accident analysis are being changed. The proposed change to TS 6.8.4.g, Item d.2, stays within the GDC requirements for the SG tubes and maintains the accident analysis and consequences for the postulated DBAs for SG tubes.

4.2 No Significant Hazards Consideration Determination Pursuant to 10 CFR 50.90, Dominion Energy Nuclear Connecticut, Inc. (DENC) is requesting an amendment to the Millstone Power Station Unit 3 (MPS3)

Facility Operating License Number NPF-49, in the form of a change to the technical specifications (TSs). This license amendment request proposes to revise MPS3 TS 6.8.4.g, "Steam Generator (SG) Program," to extend, on a one-time basis, the requirement to inspect each steam generator (SG) at least every 48 effective full power months or every other refueling outage (whichever results in more frequent inspections) for SGs A and C. This extension would allow DENC to defer the MPS3 inspections for SGs A and C from the fall of 2020 (Refueling Outage 20) to the spring of 2022 (Refueling Outage 21 ).

DENC has evaluated whether a significant hazards consideration is involved with the proposed amendment by focusing on the three standards set forth in 10 CFR 50.92, "Issuance of Amendment," as discussed below:

(1) Does the proposed change involve a significant increase in the probability or consequences of an accident previously evaluated?

Response: No An operational assessment (OA) has been performed that concludes MPS3 SGs A and C will continue to meet structural and leakage integrity performance criteria with margin throughout the operating period preceding the next inspection in spring 2022. In addition, the proposed change does not implement physical changes to any plant structure, system or component; hence, no new failure modes are introduced.

Therefore, the probability of an accident previously evaluated is not

Serial No.20-272 Docket No. 50-423 Attachment 1, Page 19 of 22 significantly increased. The proposed change does not involve a significant increase in the consequences of any previously evaluated accident. The proposed change does not involve an increase to the Technical Specification allowable iodine limit for primary coolant activity nor does it impact any of the underlying assumptions of the steam generator tube rupture (SGTR) accident analysis. As such, the consequences of a SGTR event are not affected by the change.

Therefore, the proposed change does not involve a significant increase in the probability or consequences of an accident previously evaluated.

(2) Does the proposed change create the possibility of a new or different accident from any accident previously evaluated?

Response: No The proposed change does not alter the design function or operation of the MPS3 SGs A and C or the ability of the SGs to perform their design function. The SG tubes continue to meet the SG Program performance criteria. No plant physical changes are being implemented that would result in plant operation in a configuration outside the plant safety analyses or design basis. The proposed change does not introduce any changes or mechanisms that create the possibility of a new or different kind of accident. Furthermore, MPS3 SGs A and C will continue to meet its specific structural and leakage integrity performance criteria throughout the operating period preceding the next inspection in spring 2022. Finally, no new effects on existing equipment are created, nor are any new malfunctions introduced.

Therefore, based on the above evaluation, the proposed change does not create the possibility of a new or different kind of accident from any accident previously evaluated.

(3) Does the proposed change involve a significant reduction in a margin of safety?

Response: No Extending the MPS3 inspection schedule for SGs A and C does not involve changes to any limit on accident consequences specified in the M PS3 licensing bases or applicable regulations, does not modify how accidents are mitigated, and does not involve a change in a methodology.

A forward-focused OA of MPS3 SGs A and C was performed that demonstrates there is reasonable assurance that the structural integrity and accident-induced leakage performance criteria will remain satisfied in SGs A and C throughout the period preceding the spring 2022 refueling

Serial No.20-272 Docket No. 50-423 Attachment 1, Page 20 of 22 outage inspection for a total operating duration of three cycles between primary side inspections. The OA also identified projected margin to the structural integrity and accident-induced leakage performance criteria prior to the spring 2022 refueling outage for each evaluated degradation mechanism.

Therefore, operation of the facility in accordance with the proposed change will not involve a significant reduction in a margin of safety.

Therefore, DENG concludes the proposed amendment presents no significant hazards consideration under the standards set forth in 10 GFR 50.92(c) and, accordingly, a finding of "no significant hazards consideration" is justified.

5.0 ENVIRONMENTAL CONSIDERATION

The proposed amendment meets the eligibility criterion for categorical exclusion set forth in 10 GFR 51.22(c)(9) as follows:

(i) The proposed change involves no significant hazards consideration.

As described in Section 4.2 above, the proposed change involves no significant hazards consideration.

(ii) There are no significant changes in the types or significant increase in the amounts of any effluents that may be released off-site.

The proposed LAR adds a note to MPS3 TS 6.8.4.g Item d.2, to allow DENG to defer, on a one-time basis, inspections of the MPS3 SGs A and G, from the fall of 2020 (Refueling Outage 20) to the spring of 2022 (Refueling Outage 21 ). The proposed change does not alter the design function or operation of SGs A and G or the ability of these SGs to perform its design function. SGs A and G will continue to meet specific structural and leakage integrity performance criteria throughout the operating period preceding the next inspection in spring 2022. As such, the proposed change does not involve the installation of any new equipment or the modification of any equipment that may affect the types or amounts of effluents that may be released off-site. The proposed change will have no impact on normal plant releases and will not increase the predicted radiological consequences of accidents postulated in the UFSAR.

Therefore, there are no significant changes in the types or significant increase in the amounts of any effluents that may be released off-site.

(iii) There is no significant increase in individual or cumulative occupational radiation exposure.

Serial No.20-272 Docket No. 50-423 Attachment 1, Page 21 of 22 The proposed LAR adds a note to MPS3 TS 6.8.4.g Item d.2), to allow DENG to defer, on a one-time basis, inspections of the MPS3 SGs A and C, from the fall of 2020 (Refueling Outage 20) to the spring of 2022 (Refueling Outage 21 ). The proposed change does not implement plant physical changes or result in plant operation in a configuration outside the plant safety analyses or design basis. Furthermore, SGs A and C will continue to meet specific structural and leakage integrity performance criteria throughout the operating period preceding the next inspection in spring 2022. Therefore, there is no significant increase in individual or cumulative occupational radiation exposure associated with the proposed change.

Based on the above, DENG concludes that, pursuant to 10 CFR 51.22(b ), no environmental impact statement or environmental assessment need be prepared in connection with the proposed amendment.

6.0 CONCLUSION

The proposed LAR adds a note to MPS3 TS 6.8.4.g Item d.2), to allow DENG to defer, on a one-time basis, inspections of the MPS3 SGs A and C, from the fall of 2020 (Refueling Outage 20) to the spring of 2022 (Refueling Outage 21 ).

The proposed change will not result in plant operation in a configuration outside the current design basis and does not affect the safety analyses. The structural integrity and known degradation mechanisms of the SG A and C tubes have been evaluated, and it has been determined the SG tube integrity performance criteria will continue to be met until the spring 2022 refueling outage, when the next inspections will be performed.

Therefore, DENG concludes, based on the considerations discussed herein, that (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.

7.0 PRECEDENTS A similar LAR requesting deferral of SG inspections for one cycle is currently under review by the NRC as noted below:

7.1 Letter from Exelon Generation to the NRC, dated July 10, 2020, Application for Revision to TS 5.5.9, "Steam Generator (SG) Program," for a One-Time Deferral of Steam Generator Tube Inspections. ADAMS Accession No. ML20195B158

Serial No.20-272 Docket No. 50-423 Attachment 1, Page 22 of 22 The following letters are recent precedence for one-time changes to SG inspection frequencies:

7.2 Letter from NRC to Florida Power and Light Company dated April 16, 2020, Turkey Point Nuclear Generating Unit No. 3 - Issuance of Exigent Amendment No. 291 Concerning the Deferral of Steam Generator Inspections (EPID L-2020-LLA-0067). ADAMS Accession No. ML20104B527 7.3 Letter from NRC to Exelon Generation dated May 1, 2020, Braidwood Station, Unit 2- Issuance of Amendment No. 209 Re: One-Time Extension of Steam Generator Inspections [COVID-19] (EPID L-2020-LLA-0069).

ADAMS Accession No. ML20111A000 7.4 Letter from NRC to Virginia Electric Power Company dated May 7, 2020, Surry Power Station, Unit Nos. 1 and 2, Issuance of Exigent Amendment Nos. 299 and 299 to Revise Technical Specification 6.4.Q, "Steam Generator (SG) Program," to Allow a One-Time Deferral of the Surry Unit No. 2 SG "B" Spring 2020 Refueling Outage Inspection (EPID No. L-2019-LLA-0071 ). ADAMS Accession No. ML20115E237

8.0 REFERENCES

8.1 Nuclear Energy Institute (NEI) 97-06 Revision 3, "Steam Generator Program Guidelines," January 2011 8.2 Electric Power Research Institute (EPRI) Report 3002007571, "Steam Generator Management Program: Steam Generator Integrity Assessment Guidelines," Revision 4, June 2016 8.3 DENC Letter 18-116 dated April 19, 2018, "Millstone Power Station Unit 3, End of Cycle 18 Steam Generator Tube Inspection Report," (ADAMS Accession No. ML18114A105) 8.4 Millstone Power Station Unit 3, Final Safety Analysis Report, Revision 33

-06/30/20 8.5 Millstone Unit 3 Abnormal Operating Procedure, AOP 3576, "Steam Generator Tube Leak," Rev. 009 8.6 Millstone Unit 3 Steam Generator Operational Assessment SGs A and C Fall 2020 Inspection Deferral, Revision 0.

8.7 DENC Letter 19-375 dated September 19, 2019, "Millstone Power Station Unit 3, End of Cycle 19 Steam Generator Tube Inspection Report,"

(ADAMS Accession No. ML19275D254)

Serial No.20-272 Docket No. 50-423 ATTACHMENT 2 MARKED-UP TECHNICAL SPECIFICATION PAGE DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 3

Serial No.20-272 Docket No. 50-423 Attachment 2, Page 1 of 1 Jtmuary 11, 2013 ADMINISTRATIVE CONTROLS PROCEDURES AND PROGRAMS (Continued)

d. Provisions for SG tube inspections: Periodic SG tube inspections shall be pe1fomied. The number and portions ofthe tubes inspected and methods of inspection shall be performed with the objective of detecting flaws of any type (e.g., volumetric flaws, axial and circumferential crack.c;) that may be present along the length of the tube, from the tube-to-tubesheet weld at the tube inlet to the tube-to-tubesheet weld at the tube outlet, and that may satisfy the applic.:i.ble tube plugging criteria. Portions of the tube below 15.2 ,...r inches below the top of the tubesheet are excluded from this requirement. The tube-to-tubesheet weld is not part of the tube. In addition to meeting the requirements of d.l, d.2, and d.3 below, the inspection scope, inspection methods, and inspection intervals shall be such as to ensure that SG tube integrity is maintained until the next SG inspection. A degradation assessment shall be performed ,.,r to determine the type and location of flaws to which the tubes may be susceptible atid, based on this assessment, to determine which inspection methods need to be employed and at what locations.
1. Inspect 100% of the tubes in each SG duri11g the first refueling outage following SG installation.
2. Afterthe first refueling outage following SGinstallation, inspect each SG at least every 48 effective full power months or east every other refueling outage (whichever results in more frequent inspect10 . In addition, the minimum number of tubes inspected at each scheduled inspection shall be the number of tubes in all SGs divided by the number of SG inspection outages scheduled in each inspection period as defined in a, b, and c below. If a degradation assessment indicates the potential for a type of degradation to occur at a location not previously inspected with a technique capable of detecting this type of degradation at this location and that may satisfy the applicable tube plugging criteria, the minimum number oflocations inspected with such a capable inspection technique during the remainder of the inspection period may be prorated. The fraction of locations to be inspected for this potential type of degradation at this location at the end of the
  • As approved by License Amendment No. XXX, inspection of the Millstone Unit 3 SGs A and C may be extended, on a one-time basis, from fall 2020 (Refueling Outage 20) to spring 2022 (Refueling Outage 21 ).

MILLSTONE - UNIT3 6-17c Amendment No. 69, 86-, ~ , ~

2,13, 245, 2,19, 252,255, ~

Serial No.20-272 Docket No. 50-423 ATTACHMENT 3 RETYPED PROPOSED TECHNICAL SPECIFICATION PAGE DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 3

Serial No.20-272 Docket No. 50-423 Attachment 3, Page 1 of 1 ADMINISTRATIVE CONTROLS PROCEDURES AND PROGRAMS (Continued)

d. Provisions for SG tube inspections: Periodic SG tube inspections shall be performed. The number and portions of the tubes inspected and methods of inspection shall be performed with the objective of detecting flaws of any type (e.g., volumetric flaws, axial and circumferential cracks) that may be present along the length of the tube, from the tube-to-tubesheet weld at the tube inlet to the tube-to-tubesheet weld at the tube outlet, and that may satisfy the applicable tube plugging criteria. Portions of the tube below 15.2 inches below the top of the tubesheet are excluded from this requirement. The tube-to-tubesheetweld is not part of the tube. In addition to meeting the requirements of d.1, d.2, and d.3 below, the inspection scope, inspection methods, and inspection intervals shall be such as to ensure that SG tube integrity is maintained until the next SG inspection. A degradation assessment shall be performed to determine the type and location of flaws to which the tubes may be susceptible and, based on this assessment, to determine which inspection methods need to be employed and at what locations.
1. Inspect 100% of the tubes in each SG during the first refueling outage following SG installation.
2. After the first refueling outage following SG installation, inspect each SG at least every 48 effective full power months or at least every other refueling outage (whichever results in more frequent inspections)*. In addition, the minimum number of tubes inspected at each scheduled inspection shall be the number of tubes in all SGs divided by the number of SG inspection outages scheduled in each inspection period as defined in a, b, and c below. If a degradation assessment indicates the potential for a type of degradation to occur at a location not previously inspected with a technique capable of detecting this type of degradation at this location and that may satisfy the applicable tube plugging criteria, the minimum number oflocations inspected with such a capable inspection technique during the remainder of the inspection period may be prorated. The fraction of locations to be inspected for this potential type of degradation at this location at the end of the
  • As approved by License Amendment No. XXX, inspection of the Millstone Unit 3 SGs A and C may be extended, on a one-time basis, from fall 2020 (Refueling Outage 20) to spring 2022 (Refueling Outage 21 ).

MILLSTONE - UNIT 3 6-17c Amendment No. 69-, 86, ~ , B-8, 213,215,219,252,255,;§6

Serial No.20-272 Docket No. 50-423 ATTACHMENT 4 OPERATIONAL ASSESSMENT ADDRESSING FALL 2020 SG A AND C INSPECTION DEFERRAL DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 3

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 1 of 29 Millstone Unit 3 Steam Generator Operational Assessment for SGs A and C Fall 2020 Inspection Deferral Revision 0 Date: 7-27-2020 Date: 7-27-2020 U)

Date: 7 /Po jio U>

Date: 7-28-ZC/LO Date: tt~8f3 .. f}D!J{)

Page 1 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 2 of 29 Table of Contents 1.0 PURPOSE .................................................................................................................................... 4

2.0 BACKGROUND

............................................................................................................................ 4 2.1 Inspection Timeline ........................................................................................................... 4 2.2 Degradation Mechanisms ................................................................................................. 4 2.3 Regulatory Requirements ................................................................................................. 5 3.0 OPERATIONAL ASSESSMENT .................................................................................................. 8 3.1 Existing MP3 Degradation Mechanisms ........................................................................... 8 3.1.1 AVB Wear .......................................................................................................... 8 3.1.2 Foreign Objects and Foreign Object Wear ......................................................... 9 3.1.3 TSP/FOB Wear ................................................................................................ 10 3.1 .4 Tube Damage due to Maintenance Process .................................................... 11 3.2 Important Potential Degradation Mechanisms ................................................................ 12 3.2.1 Axial ODSCC at Tube Support Plates .............................................................. 12 3.2.2 Axial ODSCC at Dents/Dings ........................................................................... 17 3.2.3 Circumferential ODSCC at Top-of-Tubesheet ................................................. 22 3.3 Secondary Side Internals ................................................................................................ 26 3.4 Projected Accident Leakage ........................................................................................... 26 3.5 Operational Leakage ...................................................................................................... 27 3.6 Operational Assessment Conclusion .............................................................................. 27

4.0 REFERENCES

........................................................................................................................... 28 5.0 ABBREVIATIONS AND ACRONYMS ........................................................................................ 29 Page 2 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 3 of 29 List of Figures Figure 3-1: Bobbin Probe POD for Axial ODSCC @TSPs .................................................................... 13 Figure 3-2: Simulated Initiation of Axial ODS CC @TSPs ..................................................................... 14 Figure 3-3: Initial Length Distribution -Axial ODSCC @TSPs ............................................................. 14 Figure 3-4: Length Growth Rate Distribution - Axial ODS CC @TSPs .................................................. 15 Figure 3-5: Depth Growth Rate Distribution - Axial ODSCC @TSPs ................................................... 15 Figure 3-6: 3R21 Worst Case Burst Pressure-Axial ODSCC @TSPs ................................................ 16 Figure 3-7: +Point' Probe POD for Axial ODSCC @Dents/Dings ...................................................... 19 Figure 3-8: Simulated Initiation of Axial ODS CC @Dents/Dings ........................................................... 19 Figure 3-9: Limiting Length Distribution - Axial ODSCC @Dents/Dings ............................................... 20 Figure 3-10: Depth Growth Rate Distribution - Axial ODS CC @Dents/Dings ...................................... 20 Figure 3-11: 3R21 Worst Case Burst Pressure - Axial ODS CC @Dents/Dings ................................... 21 Figure 3-12: Array Probe POD for Circumferential ODSCC @TTS ...................................................... 23 Figure 3-13: Simulated Initiation of Circumferential ODSCC @TTS ..................................................... 23 Figure 3-14: Initial Length Distribution - Circumferential ODSCC @TTS ............................................. 24 Figure 3-15: Length Growth Rate Distribution - Circumferential ODSCC @TTS ................................. 24 Figure 3-16: Depth Growth Rate Distribution - Circumferential ODS CC @TTS ................................... 25 Figure 3-17: 3R21 Worst Case Burst Pressure - Circumferential ODS CC @TTS ............................... 25 List of Tables Table 2-1: Millstone Unit 3 Inspection Scope Timeline ........................................................................... 6 Table 2-2: Existing MP3 Degradation Mechanisms ................................................................................ 7 Table 2-3: Evaluated Potential Degradation Mechanisms ...................................................................... 7 Table 3-1: Basic Inputs ............................................................................................................................ 8 Table 3-2: Probabilities of Burst and Leakage -Axial ODSCC @TSPs ............................................... 16 Table 3-3: +Point' Probe Examinations of Dents/Dings in SGs A and C ............................................ 18 Table 3-4: Probabilities of Burst and Leakage-Axial ODSCC @Dents/Dings .................................... 21 Table 3-5: Probabilities of Burst and Leakage - Circumferential ODSCC @TTS ..... ;........................... 26 Table 3-6: SGs A and C Integrity Margin Summary .............................................................................. 27 Page 3 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 4 of 29 1.0 PURPOSE This report provides an operational assessment (OA) of Millstone Unit 3 (MP3) steam generators (SGs) A and C. The purpose is to demonstrate that the primary side examinations currently planned for refueling outage 3R20 (end of Cycle 20, fall 2020) may be safely deferred by one additional operating cycle to 3R21 (spring 2022).

SGs Band D were inspected more recently (3R19, spring 2019) than SGs A and C, and the OA performed following the 3R 19 inspection [3.e] concluded that SGs B and D could be safely operated until their next scheduled primary side inspection during 3R21. Consequently, this OA does not include any additional analysis of SGs B and D.

2.0 BACKGROUND

2.1 Inspection Timeline Table 2-1 provides a brief description of the MP3 SG inspections performed or to be performed from the fall 2014 outage through the spring 2022 outage. As discussed above, the purpose of this OA is to determine if the planned 3R20 SG A and C primary side inspections may be safely deferred until 3R21. The table shows the scope as-planned prior to the deferral. In addition to the deferral of the primary inspection scope, the secondary side inspections planned for all four SGs during 3R20 would also be deferred to 3R21. The "full primary side inspection scope" referred to in the table includes:

  • 100% full length bobbin probe examinations (excluding low row u-bends)
  • 100% hot leg tubesheet region array probe exams
  • Array probe exams of the cold leg periphery tubesheet region ~2 tubes deep (approximately 13% of all tubes)
  • Hot leg array probe exams of tubes categorized as high residual stress tubes (during 3R 18 in SG A and C)
  • Full length array probe exams of tubes categorized as high residual stress tubes (during 3R19 in SG Band D, and future inspections)
  • Motorized rotating probe coil (+Point') examinations:

100% of low row u-bends 50% of hot leg dents/dings ~2 volts plus the five largest voltage cold leg and u-bend dents/dings Miscellaneous areas of special interest 2.2 Degradation Mechanisms The degradation mechanisms targeted by the most recent inspections are identified in the respective 180-day reports [3.g, 3.h] for 3R18 and 3R19. The degradation mechanisms previously identified in the MP3 SGs (i.e., "existing" mechanisms) and the inspection methods and scopes used to detect these mechanisms are summarized in Table 2-2. With the exception of tube-end stress corrosion cracking (SCC) which is covered by the MP3 PARC, each degradation mechanism identified in this table is evaluated within this OA.

Page 4 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 5 of 29 The OA also considers three other degradation mechanisms (Table 2-3), none of which have been identified in the MP3 SGs. These are considered to be bounding among the mechanisms which could potentially develop (i.e. "potential" degradation mechanisms).

Axially oriented, OD-initiated SCC (ODSCC) at TSPs is bounding in this context 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 generally less favorable than that of the

+Point' or array probes. In addition, the- lengths of cracks that develop at TSPs are typically greater than the lengths of those that develop elsewhere within SGs.

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. Axial ODSCC at dents/dings is not bounding per se (i.e., the cracks are short, growth rates are low);

however, because the routine MP3 dent/ding examinations utilize sampling, an explicit operational assessment (OA) of this hypothetical mechanism must consider longer operating intervals between inspections. Thus, from that perspective it becomes a bounding degradation mechanism.

Among circumferentially oriented sec degradation mechanisms, ODSCC at the top of tubesheet (TTS) is considered to be bounding because the inspection POD for OD initiated SCC is not as favorable as that for ID initiated flaws. In addition, ID initiated SCC within the tubesheet region is less challenging to structural and leakage integrity due to the presence of the tubesheet.

2.3 Regulatory Requirements Technical Specification 6.8.4.g and the Dominion Energy SG program [3.a] require that a "forward looking" operational assessment be performed to determine if the steam generator tubing will continue to meet specific structural and leakage integrity performance criteria throughout the operating period preceding the next inspection. NEI 97-06 [1] and Technical Specification TS 6.8.4.g establish these steam generator performance criteria:

  • Structural Integrity - Margin of 3.0 against burst under normal steady state power operation and a margin of 1.4 against burst under the most limiting design basis accident. Additional requirements are specified for non-pressure accident loads.
  • Accident Induced Leakage - Leakage shall not exceed the value assumed in the limiting accident analysis: 500 GPO through the faulted SG (MSLB) and one gallon per minute total for all SGs (3. b).

The OA herein was performed in accordance with the following Millstone and industry requirement documents:

  • Dominion Energy SG condition monitoring and operational assessment (CMOA) procedure

[3.f]

Page 5 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 6 of 29 Table 2-1: Millstone Unit 3 Inspection Scope Timeline Refueling Cumulative Inspection Scope Outage Date EFPY SGA SGB SGC SGD

  • Full primary side
  • Full primary side

inspection FOSAR inspection FOSAR scope

  • DMT Chemical scope
  • DMT Chemical
  • TTSSSI/ Cleaning
  • TTS SSI / Cleaning Fall 3R16 22.02 FOSAR FOSAR 2014
  • DMT Chemical Internals Cleaning
  • DMT Chemical Cleaning
  • Full primary side
  • Full primary side FOSAR inspection FOSAR inspection
  • DMT Chemical scope
  • DMT Chemical scope Cleaning
  • TTS SSI I Cleaning

Spring 3R17 23.39 FOSAR FOSAR 2016

  • DMT Chemical Internals Cleaning
  • DMT Chemical Cleaning
  • Full primary side
  • Full primary side

inspection FOSAR inspection FOSAR Fall 3R18 24.76 scope scope 2017

  • TTSSSI/
  • TTSSSI/ Internals FOSAR FOSAR
  • TTSSSI/
  • Full primary side
  • TTS SSI/
  • Full primary side FOSAR inspection FOSAR inspection Spring 3R19 26.16 scope
  • SSI Upper scope 2019
  • TTS SSI I Internals
  • TTS SSI I FOSAR FOSAR
  • Full primary side
  • TTSSSI/
  • Full primary side
  • TTS SSI I inspection FOSAR inspection FOSAR C ro Fall scope scope a::

3R20 27.56*

  • TTS SSI I cuC 2020 '6>

FOSAR FOSAR

Internals

  • Full primary side
  • Full primary side FOSAR inspection FOSAR inspection C ro Spring scope scope a::

3R21 28.96*

  • TTSSSI/
  • TTS SSI I cuC 2022 '6>

FOSAR FOSAR

Internals

  • Estimate Page 6 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 7 of 29 Table 2-2: Existing MP3 Degradation Mechanisms Evaluated in Mechanism Detection Strategy Section Anti-vibration bar (AVB) wear

  • 100% bobbin probe examination of 3.1.1 AVB/tube intersections Foreign object wear
  • Cold leg periphery and 100% hot leg 3.1.2 array probe examination of the tubesheet region
  • 100% full length bobbin probe examination Tube support plate (TSP) and
  • 100% bobbin probe examination of 3.1.3 Flow distribution baffle (FOB) TSP/FOB/tube intersections wear Wear from a legacy maintenance
  • Cold leg periphery and 100% hot leg 3.1.4 process (sled sludge lancing) that array probe examination of the has not been implemented for tubesheet region many years
  • Inspection for this degradation N/A at tube ends mechanism is not required under the MP3 technical specification permanent alternate repair criteria (PARC)

Table 2-3: Evaluated Potential Degradation Mechanisms Evaluated in Mechanism Detection Strategy Section Axial ODSCC at TSPs

  • 100% bobbin probe examination of 3.2.1 TSP/tube intersections.
  • 100% array probe examination of hot leg TSP/tube intersections in high stress tubes (SGs A and C, 3R18)

Axial ODSCC at Dents/Dings

  • 50% +Point' probe examination of 3.2.2 hot leg dents/dings and largest voltage cold leg dents/dings Circumferential OD stress
  • 100% hot leg array probe examination 3.2.3 corrosion cracking (ODSCC) at of the tubesheet region the hot leg top of tubesheet (TTS)

Page 7 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 8 of 29 3.0 OPERATIONAL ASSESSMENT The following sections summarize the evaluations performed for the degradation mechanisms discussed in Section 2.2. Table 3-1 identifies basic input information used in the evaluation.

Table 3-1: Basic Inputs Assumed Operating Duration from 4.2 EFPY 3R18 to 3R21 Tube OD 0.688 inch Tube Wall Thickness 0.040 inch Primary Side Hot Leg 617 °F Temperature (TH) 1 Nominal Full Power Steady State 1340 psi Primary to Secondary Pressure Differential (NOPD)

MSLB Pressure Differential 2560 psi (MSLB PD) 3.1 Existing MP3 Degradation Mechanisms The degradation mechanisms discussed in this section are those which have been previously identified within the Millstone Unit 3 SGs.

3.1.1 AVB Wear The AVB wear indications identified in SGs A and C during the 3R 18 inspection were evaluated through 3R20 in [3.d]. The evaluation herein addresses AVB wear relative to tube integrity requirements for a projected operating interval of three cycles for SGs A and C (i.e., 3R18 to 3R21). This corresponds to an operating duration of 4.2 EFPY which reflects a conservative assumption of 1.4 EFPY each for Cycles 20 and 21.

MP3 SG operating experience demonstrates that AVB wear is a mature and docile degradation mechanism. Relatively few AVB wear flaws are newly identified during inspections and the depths of newly identified AVB wear are consistently small (<20% TW). Consequently, AVB wear that has not yet initiated is not limiting with respect to the projection of future tube integrity. This evaluation will focus on flaws that have already initiated, whether the wear has been detected or not.

The beginning of cycle (BOC) A VB wear depth must be an upper bound estimate of the depth of wear remaining in service immediately following the SG tube inspection. This value must account for the fact that NOE processes have imperfect PODs, and must account for known flaws left in service following the tube inspection. Consistent with [2.a], the limiting BOC AVB wear depth is the 1

This value is based upon operating primary and secondary pressure data through 6-16-2020 Page 8 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 9 of 29 upper 95%/50% uncertainty-adjusted depth of the largest flaw left in service, or the depth at 95%

POD, whichever is larger.

Bobbin probe technique ETSS 96041.1 was relied upon during the 3R 18 inspection for the detection of AVB wear. For this technique, the depth at 95% POD is conservatively estimated to be 26%TW [3.c, Table 7-1]. The maximum depth of reported AVB wear returned to service in SGs A and C during 3R18 was 35%TW. Adjusting the 35%TW depth to conservatively account for NOE sizing uncertainty yields an upper bound depth (UBD) value of 42.9% TW:

BOC19 UBD = upper 95%/50% depth of maximum reported in-service AVB wear depth at the beginning of Cycle 19 BOC19 UBD = (0.99)(35)+(2.73)+(1.645)(3.36) adjust for sizing uncertainty, ETSS 96041.3 [3.c]

BOC19 UBD = 42.9%TW Since this value is more limiting than the depth at 95% POD, the limiting BOC19 UBD AVB wear depth was 42.9% TW.

Adjusting the BOC19 UBD depth upward to reflect three operating cycles of growth (assumed total duration: 4.2 EFPY), yields the EOC21 UBD. The growth rate used is the largest 95%/50% value among the four MP3 steam generators at the most recent inspection: 2.2% TW/EFPY (SG A, 3R18):

EOC21 UBD = BOC19 UBD + (4.2 EFPY)(2.2% TW/EFPY)

EOC21 UBD = 52.1%TW The projected EOC21 UBD must be compared with the appropriate structural limit. In this case the appropriate limit conservatively accounts for uncertainties in material strength and in the burst pressure relationship. The structural limit for a conservatively assumed 2.5 inch long AVB wear flaw is 61.2% TW [2.b]. Since the projected value of EOC21 UBD is less than 61.2% TW, it is concluded that AVB wear will not challenge the structural integrity performance criteria in SG A or C going forward to the next inspection in 3R21.

Per reference [2.a], the onset of pop-through leakage for axially oriented volumetric flaws with limited circumferential extent such as AVB wear is coincident with burst. Since A VB wear is not projected to exceed the structural performance criteria prior to 3R21, there is reasonable assurance that neither the operational leakage criteria nor the accident-induced leakage criteria would be violated by AVB wear in SG A or C in the event of a limiting accident prior to 3R21.

3.1.2 Foreign Objects and Foreign Object Wear The most recent primary side tube inspections performed in each MP3 SG included array probe examinations of all periphery cold leg locations (~2 tubes deep) and all hot leg locations up to the first support structure. This examination provides excellent foreign object and foreign object wear detection capabi.lity. Also, although not specifically qualified to detect foreign object wear at the TTS, the bobbin probe does provide a significant detection capability at these locations, and is the primary means of detection elsewhere in the tube bundle. All tubes in SGs A and C were examined full length with bobbin probes (except for the u-bends in the low rows which were examined with

+Point' or array probes). In addition, sludge lancing and visual inspections were performed at the TTS in all four SGs during 3R19, providing added assurance that no new foreign objects were left in service in a high flow region of the SG (i.e., periphery, no tube lane).

Page 9 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 10 of 29 The vast majority of foreign object wear identified during 3R18 was reported and/or present during previous inspections and has exhibited no growth since initial detection. The OA performed following the 3R 18 SG A and C inspection [3.d] concluded that with one exception, there were no foreign objects remaining near any of the foreign object related degradation that was reported and returned to service during 3R18. The exception is an object that is wedged between tube SGC R1 C4 (plugged during 3R08) and the blowdown pipe on the cold leg. This object was first observed during 3R08 and has been monitored during each inspection since that time. The surrounding tubes were examined during 3R 18 with array probes to identify any indication of change or new wear. A wear indication in SGC R1 CS, initially reported during 3R08 in the vicinity but not in contact with the object, has exhibited no signal change since it was initially detected. All other surrounding tubes showed no indication of a foreign object or foreign object wear during 3R18.

Since the objects that caused the wear in the tubes that were returned to service are no longer present at the locations of the wear indications, there is no mechanism to cause future growth.

Therefore, there is reasonable assurance that these flaws will not violate the structural and leakage performance criteria going forward to 3R21.

The potential development of new foreign object wear during the operating period through 3R21 must be considered. It is difficult to predict if and when foreign object wear will occur. However, by examining the aggregate operating history of the MP3 SGs with respect to foreign object wear, a judgment of the risk can be developed.

Since 3R5, several dozen foreign objects have been identified during secondary side visual examinations. Since 3R6 when significant rotating probe inspection samples at the TTS were first employed at MP3, many dozens of PLP indications have been identified by eddy current inspection. Despite the large number of objects identified and the long operating period preceding large scale rotating probe inspections, no degradation exceeding the structural performance criteria. has been identified. The absence of flaws which exceed the structural criteria is due to the tendency for the objects to migrate (due to operation and/or sludge lancing), the small mass of the objects, and the continued removal of objects during each outage.

Through the years, the number of objects identified within the SG secondary side has consistently declined as objects have been removed by FOSAR efforts and sludge lancing operations. The scarcity of newly identified foreign objects during the 3R 18 inspection is the result of FME diligence through the years. This significantly reduces the future risk of tube degradation by foreign objects.

The results of FOSAR, array probe examinations, and .bobbin coil examinations provide reasonable assurance that deferral of the SGs A and C examinations to 3R21 will not generate foreign object wear which exceeds the SG integrity performance criteria. In the unlikely event that significant degradation does occur, primary to secondary leakage monitoring procedures in place at MP3 provide a high degree of confidence of safe unit shutdown without challenging the SIPC or AILPC.

3.1.3 TSP/FDB Wear The TSP/FOB wear indications identified in SGs A and C during the 3R 18 inspection were evaluated through 3R20 in [3.d]. The evaluation herein addresses TSP/FOB wear relative to tube integrity requirements for a projected operating interval of three cycles for SGs A and C (i.e., 3R18 to 3R21).

Page 10 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 11 of 29 Only two newly reported TSP/FOB wear flaws were identified during 3R18 and their depths were small (11 %TW and 15%TW). Consequently, TSP/FOB wear that has not yet initiated is not limiting with respect to the projection of future tube integrity. This evaluation will focus on flaws that have already initiated, whether the wear has been detected or not.

During 3R 18, ETSSs 96004.1 and 96042.1 were relied upon for the detection of TSP/FOB wear.

Both methods provide excellent detection capability for this mechanism (i.e., depth at 95% POD is

<15%TW [3.c, Table 7-1]). Therefore, the maximum wear depth returned to service following the 3R18 SG inspection provides a reliable estimate of the limiting BOC wear depth.

The deepest TSP wear flaw returned to service during 3R18 was 27%TW. Adjusting the 27%TW depth to conservatively account for NOE sizing uncertainty (ETSS 96910.1 ). yields a UBD value of 41.2%TW:

BOC19 UBD = upper 95%/50% depth of maximum reported in-service TSP/FOB wear depth at the beginning of Cycle 19 BOC19 UBD = (0.95)(27)+(6.7)+(1.645)(5.36) adjust for sizing uncertainty [3.c]

BOC19 UBD = 41.2%TW Adjusting the BOC19 UBD depth upward to reflect three operating cycles of growth (4.2 EFPY),

yields the EOC21 UBD. A conservative growth rate assumption of 5.5% TW/EFPY [3.d] is used for this purpose:

EOC21 UBD = BOC19 UBD + (4.2 EFPY)(5.5%TW/EFPY)

EOC21 UBD = 64.3%TW The projected EOC21 UBD must be compared with the appropriate structural limit. In this case the appropriate limit conservatively accounts for uncertainties in material strength and in the burst pressure relationship. The structural limit for a conservatively assumed 0.5 inch long [3.d]

TSP/FOB wear flaw is 68.9%TW [2.b]. Since the projected value of EOC21 UBD is less than 68.9% TW, it is concluded that TSP/FOB wear will not challenge the structural integrity performance criteria in SG A or C going forward to the next inspection during 3R21.

Since TSP/FOB wear is not projected to exceed the structural performance criteria prior to 3R21, there is reasonable assurance that neither the operational leakage criteria nor the accident-induced leakage criteria would be violated by TSP/FOB wear in SG A or C in the event of a limiting accident prior to 3R21.

3.1.4 Tube Damage due to Maintenance Process Tube wear resulting from a sludge lancing process used in the 1990s is identified as an existing degradation mechanism within the context of the MP3 SG Program. The process that caused the damage is no longer used and the sludge lancing processes utilized since that time do not cause tube damage. There is no mechanism for the existing degradation to advance during operation or for new degradation to occur during operation; therefore, there is reasonable assurance that tube damage caused by this degradation mechanism will not violate the structural or leakage performance criteria prior to 3R21.

Page 11 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 12 of 29 3.2 Important Potential Degradation Mechanisms 3.2.1 Axial ODSCC at Tube Support Plates Although no indications of axial ODSCC have been identified in the MP3 SGs, hypothetical axial ODSCC at tube support plates (TSPs) is evaluated in this section. As discussed earlier, this degradation mechanism is considered to be 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' or array probes. In addition, the lengths of cracks that develop at TSPs are typically greater than the lengths of those that develop elsewhere within SGs. Although hot leg TSPs in high stress tubes were examined using an array probe during 3R 18, this evaluation conservatively assumes that the 3R 18 examination relied entirely on the bobbin probe to detect axial ODSCC at SG A and C TSPs.

Following the methodology described in [2.a], a fully probabilistic multi-cycle OA analysis was performed. Framatome software (MultiFram [4.a]), 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 POD curve describing bobbin probe detection of axial ODSCC at TSPs (ETSS 128413) that was used in this evaluation is shown in Figure 3-1. This POD curve was developed using Surry Unit 2 ECT noise measurements in conjunction with the MAPOD methodology described in [2.d].

Surry Unit 2 noise is more limiting than that of MP3 therefore the use of this POD curve is conservative.

For this evaluation the simulation of axial ODSCC at TSPs was benchmarked to cause axial ODSCC detection during 3R18, when in fact no ODSCC was detected during this or any other 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 [2.c]

and the scale parameter was selected to yield at least one detection during 3R 18. Figure 3-2 illustrates the number of crack initiations that were generated within the simulation and shows that the first initiation occurred before 3R 13, more than five fuel cycles prior to 3R 18.

Upon initiation, each crack is assigned an initial length, sampled from a suitable length distribution.

The length distribution utilized in this evaluation (Figure 3-3) is based upon industry analyses of all axial ODSCC identified at TSPs in US plants' I600TT tubing. Even though the length distribution is based on cracks that were in-service for various periods of time, the lengths are conservatively treated as the initial lengths of newly initiated cracks. Within the simulation, additional length growth is applied by sampling from the generic length growth distribution provided in [2.a], adjusted to reflect the higher hot leg operating temperature of MP3 (Figure 3-4). Similarly, the depth growth rate distribution utilized in this evaluation was developed by adjusting the generic depth growth rates of [2.a] to MP3's higher operating temperature. The resulting distribution is shown in Figure 3-5. Recent industry analyses performed in support of potential technical specification inspection interval changes has confirmed that the actual behavior of SCC in I600TT is bounded by these generic distributions.

The distribution of 3R21 worst-case degraded tube burst pressures resulting from this analysis is shown in Figure 3-6. This figure demonstrates that the lower 95%/50% (i.e., the 5th percentile) burst pressure, 5,262 psi satisfies the SIPC limit of 4,020 psi; therefore, it is concluded that axial Page 12 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 13 of 29 ODSCC at TSPs will not cause the structural integrity performance criteria to be exceeded in SG A or C prior to 3R21. The projected total upper 95%/50% leakage under limiting accident conditions is zero; therefore, it is concluded that axial ODSCC at TSPs will not cause the accident-induced leakage performance criteria to be exceeded prior to 3R21. These conclusions are also presented below in terms of the probability of burst (POB) and the probability of unacceptable leakage under accident conditions (POL) (see Table 3-2).

Figure 3-1: Bobbin Probe POD for Axial ODSCC @TSPs 1.0 0.9 0.8 C:

0.7

.2 u(1) 0.6 4) 0 0 0.5 a::>-

0 (I:$ 0.4

.0 e

0..

0.3

0.2 Median

22 % TW 0.1 95/50: 73 %TW 0.0 0 10 20 30 40 50 60 70 80 90 100 Depth (%TW)

Page 13 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 14 of 29 Figure 3-2: Simulated Initiation of Axial ODSCC @TSPs 10 9

8 "O

.m 7 *

t
:!

.s 6 Ill

~

u f

u (I) 5 -

.2!:

i:, 4 .

  • E 0 3 - *
  • 2 -
  • 0 --------,------.----..---------.-------.-----.--------.------.-------~

3R12 3R13 3R14 3R15 3R16 3R17 3R18 3R19 3R20 3R21 Refueling Outage Figure 3-3: Initial Length Distribution - Axial ODSCC @TSPs 1.0 0.9 0.8 0.7

~

~

sl'O 0.6

.0 e

CL (I) 0.5

.2!:

Jg

, 0.4 E

u 0.3

0.2 Median

0.48 inch 0.1 95/50: 0.79 inch 0.0 0.0 0.1 0.2 0.3 0.4' 0.5 0.6 0.7 0.8 0.9 1.0 Initial Length (inch)

Page 14 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 15 of 29 Figure 3-4: Length Growth Rate Distribution - Axial ODSCC @TSPs 1.0 0.9 0.8 0.7

~

s 0.6

'°

.Q e

0..

Q) 0.5

.i::!

i:::, 0.4 E

u 0.3

0.2 Median

0.047 in/EFPY 0.1 95/50: 0.136 in/EFPY 0.0 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 Length Growth Rate (inch/EFPY)

Figure 3-5: Depth Growth Rate Distribution - Axial ODSCC @TSPs 1.0 0.9 0.8 0.7

=

a

'°

.Q 0.6 e

0..

0.5 (I)

~

'° 0.4

S E

(,)

0.3

0.2 Median

5.25 %TW/EFPY 0.1 95/50: 15.3 % TW/EFPY 0.0 0 5 10 15 20 25 30 Depth Growth Rate (% TW/EFPY)

Page 15 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 16 of 29 Figure 3-6: 3R21 Worst Case Burst Pressure - Axial ODSCC @TSPs 0.50 - . - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ,

0.45 0.40 0.35

~

s'° 0.30

.0 e

0..

(l) 0.25

.G:

lg

, 0.20 E

u 0.15 3xNOPD: 4020 psi 0.10 j J

t I

I 0.05 j I

Probability: 0.05 I

I 0.00 4--------,.---------~~~::=:;i::___ _--,--_j__ _~-----.------J 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 Projected 3R21 Worst Case Burst Pressure (psi)

Table 3-2: Probabilities of Burst and Leakage - Axial ODSCC @TSPs Population POB at 3xNOPD POL at MSLB PD Full Bundle 1.14% 0.83%

SG Program 5% 5%

Maximum Allowable Page 16 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 17 of 29 3.2.2 Axial ODSCC at Dents/Dings Hypothetical axial ODSCC at dents and dings is evaluated in this section. As discussed earlier, this potential degradation mechanism is considered herein because of recent Seabrook operating experience and because the routine MP3 dent/ding examinations utilize sampling. Sampling extends the operating interval that must be considered in an explicit OA.

For the integrity analysis of dent/ding cracking, the population of dents/dings in SGs A and C was segregated into two groups to align with the 50% sample examined during every other outage.

Table 3-3 summarizes recent dent/ding inspection history for these two groups. The "1 st Half' includes dents/dings most recently examined during 3R 16, while the "2 nd Half' refers to those most recently examined during 3R 18. The probability of burst (POB) and accident leakage (POL) at 3R21 was evaluated for each sub-population and the results were combined to determine the overall POB and POL for this degradation mechanism, discussed below.

It should be noted that the dent/ding inspections performed at MP3 have been principally focused on the hot leg because sec is much more likely to occur on the hot leg (as is demonstrated by the Seabrook experience). Initial detection of SCC in any MP3 dent/ding location would require an expansion of the scope to include all dent/dings, including those on the cold leg.

The same fully probabilistic, multi-cycle OA analysis methodology described in the previous section was used to evaluate this degradation mechanism. The key input parameters are discussed below.

The POD curve describing +Point' probe detection (ETSS 128432) of axial ODSCC at dents/dings that was used in this evaluation is shown in Figure 3-7. This POD curve was developed using MP3 ECT noise measurements in conjunction with the MAPOD methodology described in [2.d].

For this evaluation the simulation of axial ODSCC at dents/dings was benchmarked to cause axial ODSCC detection in the "2 nd Half' during 3R18, when in fact no ODSCC was detected during this or any other 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 [2.c] and the scale parameter was selected to yield at least one detection during 3R18. The same Weibull function was used for the evaluation of both the "1 st Half' and "2 nd Half' sub-populations. Figure 3-8 illustrates the number of crack initiations that were generated within the simulation and shows that the first initiation occurred before 3R12, more than six fuel cycles prior to 3R18. Since this initiation function was applied for the evaluation of each sub-population, the total initiations evaluated for SGs A and C is double that of each sub-population; a total of 24 initiations by 3R21.

Upon initiation, each crack is assigned a length value, sampled from a suitable length distribution.

The length distribution utilized in this evaluation (Figure 3-9) is based upon the measured lengths of MP3 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 and 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 of the Seabrook dent/ding cracks as determined by Westinghouse, adjusted to the MP3 operating temperature. The resulting distribution is shown in Figure 3-10.

The distributions of 3R21 worst-case degraded tube burst pressures resulting from this analysis for each sub-population and for the population as a whole are shown in Figure 3-11. This figure Page 17 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 18 of 29 demonstrates that the combined lower 95%/50% burst pressure, 4,743 psi satisfies the SIPC limit of 4,020 psi; therefore, it is concluded that axial ODSCC at dents and dings will not cause the structural integrity performance criteria to be exceeded in SG A or C prior to 3R21. The projected total upper 95%/50% accident leakage for the sub-populations and for the population as a whole is zero; therefore it is concluded that axial ODSCC at dents and dings will not cause the accident-induced leakage performance criteria to be exceeded prior to 3R21. These conclusions are also presented below (Table 3-4) in terms of the probability of burst (POB) and the probability of unacceptable leakage under accident conditions (POL).

Table 3-3: +Point' Probe Examinations of Dents/Dings in SGs A and C Refueling Sub-Population Outage Date st nd 1 Half 2 Half 100% Hot Leg DNTs/DNGs, 3R16 Fall 2014 Largest Cold Leg DNTs/DNGs Spring 3R17 2016 100% Hot Leg DNTs/DNGs, 3R18 Fall 2017 Largest Cold Leg DNTs/DNGs Spring 3R19 2019 3R20* Fall 2020 Spring 100% Hot Leg DNTs/DNGs, 100% Hot Leg DNTs/DNGs, 3R21*

2022 Largest Cold Leg DNTs/DNGs Largest Cold Leg DNTs/DNGs

  • Reflects deferral of 3R20 inspection Page 18 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 19 of 29 Figure 3-7: +Point' Probe POD for Axial ODSCC @Dents/Dings 1.0 0.9 0.8 s::::

0.7 0

(.)

~ 0.6 0

0 0.5

s~

n, 0.4

..0 g

0..

0.3

0.2 Median

53 % TW 0.1 95/50: 83 % TW 0.0 0 10 20 30 40 50 60 70 80 90 100 Depth (%TW)

Figure 3-8: Simulated Initiation of Axial ODSCC @Dents/Dings 30 - . - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ,

"1st Half' plus 112nd Half' 25 Each Sub*Population 5

0 -+-----.-------,----...-----.----

3R12 3R13 3R14 3R15 3R16 3R17 3R18 3R19 3R20 3R21 Refueling Outage Page 19 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 20 of 29 Figure 3-9: Limiting Length Distribution - Axial ODSCC @Dents/Dings 1.0

.. MP3 Dent/Ding Measurements 0,9

-Log Normal Fit 0.8 0.7

E:
s

('0 0.6

..0 e

0..

(1) 0.5

.i?;

Jg

, 0.4 E

0 0.3

0.2 Median

0.36 inch 0.1 95/50: 0.60 inch 0.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Limiting Length (inch)

Figure 3-10: Depth Growth Rate Distribution - Axial ODSCC @Dents/Dings 1.0 0.9 0.8 0.7

~

a

('0 0.6

..0 e

Q.

Q) 0.5 4!

('0

'3 0.4 E

0 0.3

0.2 Median

2.6 %TW/EFPY 0.1 95/50: 11.1 %TW/EFPY 0.0 0 5 10 15 20 25 30 Depth Growth Rate (% TW/EFPY)

Page 20 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 21 of 29 Figure 3-11: 3R21 Worst Case Burst Pressure - Axial ODSCC @Dents/Dings 0.50 -.-----------------------------!-----.

0.45 1st Half I

                  • 2nd Half  !

/

0.40

- - Full Bundle . /

0.35

./

~ /

E I\'!

.0 e

0.30

/

0..

0.25 /

/

(l,)

.i::

~

..~:' ,~

, 0.20  !

E Lower 95/50: 4743 psi ,.l

s  :

t

(.)

/

0.15 l.

t t

3xNOPD: 4020 psi /

0.10 I

./

0.05  ! 1

.:~.r( ..Pr~~ability: 0.05

.;;;:::~;*::::::~:.:::f.*******,....

0.00 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 Projected 3R21 Worst Case Burst Pressure (psi)

Table 3-4: Probabilities of Burst and Leakage - Axial ODSCC @Dents/Dings Population POB at 3xNOPD POL at MSLB PD st 1 Half 0.84% 2.32%

nd 2 Half 0.35% 0.75%

Full Bundle 1.19% 3.06%

SG Program 5% 5%

Maximum Allowable Page 21 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 22 of 29 3.2.3 Circumferential ODSCC at Top-of-Tubesheet No circumferentially oriented SCC has been identified in the MP3 SG tubes beyond the tube end region. Hypothetical circumferential ODSCC at the TTS is evaluated in this section. As discussed earlier, this mechanism is bounding of other potential circumferential degradation.

Following the methodology described in [2.a], a fully probabilistic multi-cycle OA analysis was performed. Framatome software (MultiCirc [4.b]), simulates the life-cycle of a susceptible tube population in the manner discussed in Section 3.2.1. The key parameters for this degradation mechanism are discussed below.

The POD curve describing array probe detection (ETSS 20400.1) of circumferential ODSCC at the TTS used in this evaluation is shown in Figure 3-12. This POD curve was developed using MP3 ECT noise measurements in conjunction with the MAPOD methodology described in [2.d].

For this evaluation the simulation of circumferential ODSCC at TTS was benchmarked to cause detection of this mechanism during 3R 18, when in fact no ODS CC was detected during this or any other 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 [2.c] and the scale parameter was selected to yield at least one detection during 3R18. Figure 3-13 illustrates the number of crack initiations that were generated within the simulation and shows that the first initiation occurred before 3R 12, more than 6 fuel cycles prior to 3R 18.

Upon initiation, each crack is assigned an initial length, sampled from a suitable length distribution.

The length distribution utilized in this evaluation (Figure 3-14) is based upon industry analyses of circumferential ODSCC in support of the industry's generic technical specification change initiative

[5]. Even though the length distribution is based on cracks that were in-service for various periods of time, the lengths are conservatively treated as the initial lengths of newly initiated cracks. Within the simulation, additional length growth is applied by sampling from the generic length growth distribution provided in [2.a], adjusted to reflect the higher hot leg operating temperature of MP3 (Figure 3-15). Similarly, the depth growth rate distribution used was developed by adjusting the generic depth growth rates of [2.a] to MP3's higher operating temperature. The resulting distribution is shown in Figure 3-16. Recent industry work performed in support of potential technical specification inspection interval changes has confirmed that the actual behavior of SCC in I600TT is bounded by these generic distributions.

The distribution of 3R21 worst-case degraded tube burst pressures resulting from this analysis is shown in Figure 3-17. This figure demonstrates that the lower 95%/50% (i.e., the 5th percentile) burst pressure, 7,420 psi satisfies the SIPC limit of 4,020 psi; therefore, it is concluded that circumferential ODSCC at the TTS will not cause the structural integrity performance criteria to be exceeded in SG A or C prior to 3R21. The projected total upper 95%/50% leakage under limiting accident conditions is zero; therefore it is concluded that circumferential ODSCC at the TTS will not cause the accident-induced leakage performance criteria to be exceeded prior to 3R21. These conclusions are also presented below (Table 3-5) in terms of the probability of burst (POB) and the probability of unacceptable leakage under accident conditions (POL).

Page 22 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 23 of 29 Figure 3-12: Array Probe POD for Circumferential ODSCC @TTS 1.0 0.9 0.8 C 0.7 0

g

~ 0.6 Q

....0 0.5

~

E 0.4

.0 g

0..

0.3

0.2 Median

27 %TW 0.1 95/50: 67 %TW 0.0 0 10 20 30 40 50 60 70 80 90 100 Depth (%TW)

Figure 3-13: Simulated Initiation of Circumferential ODSCC @TTS 8

7 -

6 -

"O (l)

.1'S!

£: 5 - *

  • ti)

.!ii::

0

~

0 4 -

(l)

~

E:,

s:,

3 -

  • u 2
  • 1 - * * *
  • 0 +-------.----~----.------.-----,----...------.-------.-----.---

3R12 3R13 3R14 3R15 3R16 3R17 3R18 3R19 3R20 3R21 Refueling Outage Page 23 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 24 of 29 Figure 3-14: Initial Length Distribution - Circumferential ODSCC @TTS 1.0 0.9 0.8 0.7

~

sl'O 0.6

.0 e

0..

0.5 Q)

.i::

J::,

S!

0.4 E

u 0.3

0.2 Median

0.41 inch 0.1 95/50: 1.0 inch 0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Initial Length (inch)

Figure 3-15: Length Growth Rate Distribution - Circumferential ODSCC @TTS 1.0 0.9 0.8 0.7

~

1:::
s l'O 0.6

.0 e

a.

Q) 0.5

.i::

J::,

E S!

0.4 u 0.3

0.2 Median

0.047 in/EFPY 0.1 95/50: 0.136 in/EFPY 0.0 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 Length Growth Rate (lnch/EFPY)

Page 24 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 25 of 29 Figure 3-16: Depth Growth Rate Distribution - Circumferential ODSCC @TTS 1.0 0.9 0.8 0.7

E:
0 (IS 0.6

.0 e

0..

<l) 0.5

~

.!:1

, 0.4 E

u 0.3

0.2 Median

5.25 % TW/EFPY 0.1 95/50: 15.3 %TW/EFPY 0.0 0 5 10 15 20 25 30 Depth Growth Rate (% TW/EFPY)

Figure 3-17: 3R21 Worst Case Burst Pressure - Circumferential ODSCC @TTS 0.50 - . . - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

0.45 0.40 0.35

~

E

~ 0.30 e

0..

<l> 0.25 j

, 0.20 E

u 0.15 3xNOPD: 4020 psi 0.10 I I

I I

I 0.05 I I

I

  • I 0.00 -l-------.----.....-------,.----1------.----~=.:.:.:_----,._..,L__~------I 0 2.000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 Projected 3R21 Worst Case Burst Pressure (psi)

Page 25 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 26 of 29 Table 3-5: Probabilities of Burst and Leakage - Circumferential ODSCC @TTS Population POB at 3xNOPD POL at MSLB PD Full Bundle 0.014% 1.82%

SG Program 5% 5%

Maximum Allowable 3.3 Secondary Side Internals The absence of secondary side structural degradation, and minimal to no advancement of FAC at J-nozzle/feedring interfaces [3.d, 3.e], provides a high level of confidence that tube degradation caused by secondary subcomponent deterioration will not occur in any of the steam generators prior to 3R21.

3.4 Projected Accident Leakage In the sections above, the evaluation of each postulated degradation mechanism demonstrated that there is reasonable assurance that the AILPC will not be exceeded prior to 3R21. However, the permanent alternate repair criteria (PARC) for tube end cracks incorporated into the MP3 technical specifications requires additional consideration with respect to accident-induced leakage.

Implementation of the PARC makes it necessary to postulate primary to secondary leakage through tube end cracks in in-service tubes during the next operating interval, both during normal operations and during a main steam line break. The PARC establishes a correlation between leakage measured during normal operation and the expected accident induced leakage. The limiting accident is projected to increase existing operational leakage by a factor of 2.49. If other sources of accident induced SG leakage are identified as part of the OA, the factor only applies to the operational leakage from the tube end cracking contribution. The operational leakage administrative limit is reduced as necessary such that the factor of 2.49 times the tube end leakage, plus any other postulated accident leakage contributions, would not exceed the accident leakage limit. As discussed earlier, there is reasonable assurance that no degradation outside the tube-end region will contribute to leakage during an accident. However, one potential source of other postulated accident leakage is leakage through installed plugs.

Although only one tube removed from service in the history of the MP3 SGs had throughwall degradation that could contribute to leakage in this context, it is assumed that there is a leak path through all plugged tubes. Using this assumption, and assuming that all installed mechanical plugs leak, yields a conservative estimate of potential primary-to-secondary leakage of approximately 0.0004 GPM at room temperature [3.e]. The AILPC is 500 GPO (0.34722 GPM) through the faulted SG. If the upper bound estimate of plug leakage is subtracted from this accident limit, the remaining leakage allowance available for tube end cracks is 0.3468 GPM. Dividing by 2.49 yields an administrative limit of 0.139 GPM, but since operational leakage is already limited by the technical specifications to 0.104 GPM, a more restrictive operational leakage limit is not required.

Page 26 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 27 of 29 3.5 Operational Leakage In the absence of degradation projected to exceed the AILPC through 3R21, there is reasonable assurance that normal operating conditions will not lead to a violation of the operational leakage performance criteria. Although there are no known conditions of concern, sensitivity to primary-to-secondary leakage events will continue under Millstone's conservative monitoring procedures.

3.6 Operational Assessment Conclusion There is reasonable assurance that the structural and leakage integrity performance criteria will remain satisfied in SG A and SG C throughout the period preceding 3R21, for a total operating duration of three cycles between primary side inspections. Table 3-6 summarizes the projected margin to SIPC and AILPC at 3R21 for each degradation mechanism quantitatively evaluated.

Table 3-6: SGs A and C Integrity Margin Summary SIPC AILPC Degradation Mechanism Limit 3R21 Projection Limit 3R21 Projection AVB wear 61.2 3/4TW 52.1 3/4TW 500 GPO Zero Leakage TSP/FOB wear 68.9 3/4TW 64.3 %TW 500 GPO Zero Leakage 4020 psi 5262 psi Zero Leakage Axial ODSCC @TSPs 2 500 GPO (3xNOPD ) (Lower 95%/50%) (Upper 95%/50%)

4020 psi 4743 psi Zero Leakage Axial ODSCC @Dents/Dings 2 500 GPO (3xNOPD ) (Lower 95%/50%) (Upper 95%/50%)

4020 psi 7420 psi Zero Leakage Circumferential ODSCC @TTS 2 500 GPO (3xNOPD ) (Lower 95%/50%) (Upper 95%/50%)

2 Minimum acceptable burst pressure Page 27 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 28 of 29

4.0 REFERENCES

1. NEI 97-06, "Steam Generator Program Guidelines," Rev. 3, March 2011
2. EPRI Documents
a. EPRI Report 3002007571, "SG Integrity Assessment Guidelines, Revision 4,"

June 2016

b. EPRI Report 3002003048, "Steam Generator Management Program: Flaw Handbook Calculator (SGFHC) for Excel 2010 v1 .O," June 2014
c. EPRI Report 3002000475, "SGMP: PWR Generic Tube Degradation Predictions," December 2013
d. EPRI Report 3002010334, "Model Assisted Probability of Detection Using R (MAPOD-R), Version 2.1," September 2017
3. Dominion Energy Documents
a. Dominion Energy Fleet Administrative Procedure ER-AA-SGP-101, "Steam Generator Program," Rev. 0
b. ERC No. 25212-ER-08-0063, Revision 00, "Millstone 3 Main Steam Line Break Accident Affected Steam Generator Primary to Secondary Leak Rate," October 2008
c. Dominion Energy ETE-MP-2019-1005, "Steam Generator Degradation Assessment Refueling Outage 3R19," Revision 0, Spring 2019
d. Dominion Energy ETE-MP-2017-1169, "Millstone Unit 3 Steam Generator Integrity Condition Monitoring and Operational Assessment (3R18)", Revision 0, November 2017
e. Dominion Energy ETE-MP-2019-1036, "MP3 SG Integrity CMOA (R19),"

Revision 0, May 2019

f. Dominion Energy Fleet Administrative Procedure ER-AA-SGP-103, "Steam Generator Condition Monitoring and Operational Assessments," Revision 0
g. Dominion Energy, "Dominion Energy Nuclear Connecticut, Inc., Millstone Power Station Unit 3, EOC 18 SG Tube Inspection Report," Serial No.18-116, April 2018
h. Dominion Energy, "Dominion Energy Nuclear Connecticut, Inc., Millstone Power Station Unit 3, EOC 19 SG Tube Inspection Report," Serial No.19-375, September 2019
4. Framatome Documents
a. Framatome Document 32-9038747-000, "Validation of Multi-Cycle Probabilistic Integrity Assessment Software - Multifram" Page 28 of 29

Serial No.20-272 Docket No. 50-423 Attachment 4, Page 29 of 29

b. Framatome Document 32-9313861-000, "Validation of Multi-Cycle Probabilistic Integrity Assessment Software - MultiCircV1"
5. lntertek AIM-190610636-2-1, "Feasibility Study for the Potential to Extend Inspection Intervals for the A600TT Fleet," December 2019 5.0 ABBREVIATIONS AND ACRONYMS AILPC Accident Induced Leakage Performance Criteria LPS Loose Part Signal ARC Alternate Repair Criteria MAA Multiple Axial Anomaly AVB Anti-Vibration Bar MBH Manufacturing Burnish Mark BET Bottom of Expansion Transition MSLB Main Steam Line Break BLG Bulge NDF No Degradation Found BOC Beginning Of Cycle NOPD Normal Operating Pressure Differential BPC Baffle Plate Cold NTE No Tube Expansion BPH Baffle Plate Hot OA Operational Assessment CDS Computer Data Screening OD Outer Diameter CM Condition Monitoring Assessment ODSCC Outer Diameter Stress Corrosion Cracking CMOA Condition Monitoring and Operational Assessment OVR Over Roll DA Degradation Assessment OXP Over Expansion DDH Distorted Dent w/lndication PARC Permanent Alternate Repair Criteria DDI Distorted Dent w/lndication PDA Percent Degraded Area DDS Distorted Dent w/lndication PIT Pit DMT Deposit Minimization Treatment PLP Possible Loose Part DNT Dent POD Probability Of Detection ECT Eddy Current Test PTE Partial Tube Expansion EFPY Effective Full Power Years PVN Permeability Variation EOC End Of Cycle PWSCC Primary Water Stress Corrosion Cracking ETSS Examination Technique Specification Sheet QDA Qualified Data Analyst FAC Flow Assisted Corrosion REOC Replacement End Of Cycle FDB Flow Distribution Baffle RPC Rotating Pancake Coil (generic term for all rotating probes)

FK Foreign Object Tracking System Key SAA Single Axial Anomaly FOSAR Foreign Object Search And Retrieval sec Stress Corrosion Cracking FOTS Foreign Object Tracking System SG Steam Generator GPD Gallons Per Day SIPC Structural Integrity Performance Criteria HRS High Residual Stress SSI Secondary Side Inspection ID Inner Diameter TSC Tube Sheet Cold INF Indication Not Found TSH Tube Sheet Hot INR Indication Not Reportable TSP Tube Support Plate LGV Local Geometry Variation TTS Top of Tubesheet LPM Loose Part Monitoring VOL Volumetric WAR Wear Page 29 of 29

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