TXX-2002, Exigent License Amendment Request (LAR) 20-003 Revision to Technical Specification (TS) 5.5.9, Unit 1 Model D76 and Unit 2 Model D5 Steam Generator Program

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Exigent License Amendment Request (LAR)20-003 Revision to Technical Specification (TS) 5.5.9, Unit 1 Model D76 and Unit 2 Model D5 Steam Generator Program
ML20101M879
Person / Time
Site: Comanche Peak  Luminant icon.png
Issue date: 04/10/2020
From: Thomas McCool
Vistra Energy
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
CP-20200260, TXX-20025
Download: ML20101M879 (89)


Text

Thomas P. McCool Site Vice President Luminant P.O. Box 1002 6322 North FM 56 Glen Rose, TX 76043 o 254.897.6042 CP-20200260 TXX-20025 U. S. Nuclear Regulatory Commission Ref 10 CFR 50.90 ATTN: Document Control Desk 10 CFR 50.91(b)(1)

Washington, DC 20555-0001 04/10/2020

SUBJECT:

COMANCHE PEAK NUCLEAR POWER PLANT DOCKET NOS. 50-445 AND 50-446 EXIGENT LICENSE AMENDMENT REQUEST (LAR)20-003 REVISION TO TECHNICAL SPECIFICATION (TS) 5.5.9, UNIT 1 MODEL D76 AND UNIT 2 MODEL D5 STEAM GENERATOR (SG) PROGRAM

Dear Sir or Madam:

Pursuant to 10CFR50.90 and 10 CFR 50.91, Vistra Operations Company LLC (Vistra OpCo) hereby requests an exigent amendment to the Comanche Peak Nuclear Power Plant (CPNPP) Unit 1 Operating License (NPF-87) and CPNPP Unit 2 Operating License (NPF-89) by incorporating the attached change into the CPNPP Units 1 and 2 Technical Specifications. The one-time exigent license amendment is required due to unforeseen issues as a result of the current COVID-19 virus pandemic.

The proposed change will revise Technical Specification 5.5.9 entitled UNIT 1 MODEL D76 AND UNIT 2 MODEL D5 STEAM GENERATOR (SG) PROGRAM. The proposed change will implement a one-time change to Unit 2 steam generator inspection frequency. This one-time exigent license amendment is required to minimize CPNPP Unit 2 spring 2020 refueling outage scope to limit personnel exposure to the COVID-19 virus pandemic.

The Enclosure provides a description and assessment of the proposed changes. Attachment 1 provides the existing TS pages and marked TS pages to show the proposed changes. No change is proposed to the current TS Bases as a result of this license amendment request. Attachment 2 provides an Operational Assessment describing the impact of deferring the Unit 2 steam generator inspections for spring 2020 refueling outage to the fall 2021 refueling outage.

Vistra OpCo has determined that the proposed change does not involve a significant hazards consideration pursuant to 10 CFR 50.92(c), and there are no significant environmental impacts associated with the change. The CPNPP Station Operations Review Committee has reviewed the proposed license amendment. In accordance with 10 CFR 50.91(b)(1), a copy of the proposed license amendment is being forwarded to the State of Texas.

6555 SIERRA DRIVE IRVING, TEXAS 75039 o214-812-4600 VISTRAENERGY.COM

TXX-20025 Page 2 of 2 NRC staff review and approval of the proposed amendment is requested by April 19, 2020, prior to CPNPP Unit 2 entering MODE 4. Once approved, the amendment shall be implemented immediately.

This letter contains no new regulatory commitments.

If you have any questions regarding this submittal, please contact James E. Barnette at (254} 897-5866 or james.barnette@luminant.com.

I state under penalty of perjury that the foregoing is true and correct.

Executed on April 10, 2020.

Sincerely, Thomas 11:

Enclosure LICENSE AMENDMENT REQUEST (LAR} 20-003, REVISION TO TECHNICAL SPECIFICATION (TS}

5.5.9, "UNIT 1 MODEL D76 AND UNIT 2 MODEL D5 STEAM GENERATOR (SG} PROGRAM" . CPNPP TECHNICAL SPECIFICATION 5.5.9, UNIT 1 MODEL D76 AND UNIT 2 MODEL D5 STEAM GENERATOR (SG} PROGRAM TECHNICAL SPECIFICATION PAGES

2. COMANCHE PEAK UNIT 2 STEAM GENERATOR OPERATIONAL ASSESSMENT TO SUPPORT DEFERRAL OF PLANNED INSPECTIONS FROM 2RF18 TO 2RF19 c- Scott Morris, Region IV [Scott.Morris@nrc.gov]

Dennis Galvin, NRR [Dennis.Galvin@nrc.gov]

John Ellegood, Senior Resident Inspector, CPNPP [John.Ellegood@nrc.gov]

Neil Day, Resident Inspector, CPNPP [Neil.Day@nrc.gov]

Mr. Robert Free [robert.free@dshs.state.tx.us]

Environmental Monitoring & Emergency Response Manager Texas Department of State Health Services Mail Code 1986 P. 0. Box 149347 Austin TX, 78714-9347

Enclosure to TXX-20025 Page 1 of 18 1.0

SUMMARY

DESCRIPTION 2.0 DETAILED DESCRIPTION 2.1 System Design and Operation 2.2 Current Technical Specification Requirements 2.3 Reason for Proposed Change 2.4 Description of Proposed Change

3.0 TECHNICAL EVALUATION

4.0 REGULATORY EVALUATION

4.1 Applicable Regulatory Requirements 4.2 Precedent 4.3 No Significant Hazards Consideration Determination 4.4 Conclusions

5.0 ENVIRONMENTAL CONSIDERATION

S

6.0 REFERENCES

ATTACHMENTS Attachment 1 Technical Specification Pages Attachment 2 Comanche Peak Unit 2 Steam Generator Operational Assessment to Support Deferral of Planned Inspections from 2RF18 to 2RF19

Enclosure to TXX-20025 Page 2 of 18 1.0

SUMMARY

DESCRIPTION Proposed License Amendment Request (LAR)20-003 is to revise Technical Specification 5.5.9, Unit 1 Model D76 and Unit 2 Model D5 Steam Generator (SG) Program for Comanche Peak Nuclear Power Plant (CPNPP) Unit 2.

Vistra OpCo is requesting this change to defer the 100% inspection scope currently required for the third sequential inspection period from 2RF18 (April 2020) to 2RF19 (October 2021). This change is requested to minimize COVID-19 virus exposure at CPNPP during 2RF18.

No changes to the Comanche Peak Nuclear Power Plant Final Safety Analysis Report are anticipated as a result of this License Amendment Request.

2.0 DETAILED DESCRIPTION 2.1 System Design and Operation Steam Generator (SG) tubes in pressurized water reactors have a number of important safety functions. SG tubes are an integral part of the reactor coolant pressure boundary (RCPB) and, as such, are relied on to maintain reactor coolant system pressure and inventory. As part of the RCPB, SG tubes are unique as they transfer heat from the primary (Reactor Coolant System (RCS)) to the secondary (Main Feedwater (MFW)). In addition, SG tubes isolate radioactive fission products in the RCS from MFW.

The steam generator tube rupture (SGTR) accident is the limiting design basis event for a SG. The analysis of a SGTR event assumes a bounding primary to secondary leakage rate equal to the TS operational leakage rate limit, plus the leakage rate from a double-ended rupture of a single tube. The analysis for design basis accidents and transients other than a SGTR assume the SG tubes retain their structural integrity (i.e., they are assumed not to rupture). In these analyses, the steam discharge to the atmosphere is based on the total primary to secondary leakage from all SGs or is assumed to increase to the limit as a result of accident induced conditions. For accidents that do not involve fuel damage, the reactor coolant activity level is assumed to be equal to TS limits. For accidents that assume fuel damage, reactor coolant activity is a function of the amount of activity released from damaged fuel.

Steam generator tube integrity is necessary to ensure SG tubes are capable of performing their intended safety functions. Concerns relating to integrity of SG tubes stem from the fact that SG tubes are subject to a variety of degradation mechanisms. Steam generator tubes have experienced tube degradation related to corrosion phenomena, such as wastage, pitting, intergranular attack, and stress corrosion cracking, along with other mechanically induced phenomena such as wear. These degradation mechanisms can impair tube integrity if they are not managed effectively. When degradation of the tube wall reaches a prescribed criterion for action, the tube is considered defective and corrective action is taken, such as plugging or repair. Note not all plants have approved repair techniques. Therefore, references to "repair" are bracketed in the Standard Technical Specifications.

Enclosure to TXX-20025 Page 3 of 18 The industry, working through the Electric Power Research Institute (EPRI)

Steam Generator Management Program (SGMP), has implemented a generic approach to managing SG performance referred to as "Steam Generator Degradation Specific Management" (SGDSM).

The overall program is described in NEI 97-06, "Steam Generator Guidelines, which is supported by a number of EPRI guidelines, such as:

  • PWR Primary-to-Secondary Leak Guidelines
  • PWR Primary Water Chemistry Guidelines
  • PWR Secondary Water Chemistry Guidelines NEI 97-06 and the EPRI Guidelines define a comprehensive, performance based approach to managing SG performance.

2.2 Current Technical Specification Requirements The current Technical Specification proposed to be changed is TS 5.5.9, Steam Generator (SG) Program.

TS 5.5.9.d.2 currently states, For the Unit 2 model D5 steam generators (Alloy 600 thermally treated) 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).

TS 5.5.9.d.2.c currently states, During the remaining life of the SGs, inspect 100% of the tubes every 72 effective full power months. This constitutes the third and subsequent inspection periods.

See Attachment 1 to TXX-20025 for TS 5.5.9 - Current Technical Specification.

2.3 Reason for Proposed Change Operating experience supports a longer inspection period for plants with 600TT tubes. In addition, the current inspection practices permit a simplified inspection routine, with fixed periods for 100% inspection of the SG tubes. Delaying performance of the current inspection regime for one refueling outage due to COVID-19 virus concerns is warranted when the potential for infection is weighed against the historical performance of the 600TT steam generators on CPNPP Unit 2.

Vistra OpCo initiated dialog with the NRC on a technical specification change process in March 2020 and is making a good faith effort to submit this license amendment request in a timely manner following the escalation of federal and state guidelines for COVID-19 virus response. Vistra OpCo has communicated with the NRC Staff regarding this request. Accordingly, Vistra OpCo requests this amendment be processed under exigent circumstances pursuant to 10 CFR 50.91(a)(6) to avoid potential unnecessary personnel exposure to COVID-19 virus which could also expose the general public to COVID-19 virus.

Enclosure to TXX-20025 Page 4 of 18 Consistent with the Statement of Considerations accompanying issuance of 10 CFR 50.91(a)(6), the circumstances here result in a net increase in safety or reliability (51 Federal Register 7744, 7756 (Mar. 6, 1986). Staff implementing guidance expresses a preference for a license amendment, if possible over NOED, where possible. See Inspection Manual Chapter 410, Section 6.03. In this case, the proposed balances opportunity to improve public safety and reliability with public participation in the NRCs technical specification change process.

2.4 Description of Proposed Change The proposed change will revise TS 5.5.9:

TS 5.5.9.d.2 will state, This is a one-time change to TS 5.5.9.d.2 for CPNPP Unit 2 Cycle 19, for the Unit 2 model D5 steam generators (Alloy 600 thermally treated) after the first refueling outage following SG installation, inspect each SG at least every 54 effective full power months or at least every other refueling outage (whichever results in more frequent inspections).

TS 5.5.9.d.2.c will state, This is a one-time change to TS 5.5.9.d.2.c for CPNPP Unit 2 Cycle 19, during the remaining life of the SGs, inspect 100% of the tubes every 90 effective full power months. This constitutes the third and subsequent inspection periods.

See Attachment 1 to TXX-20025 for TS 5.5.9 - Markup Technical Specification.

3.0 TECHNICAL EVALUATION

3.1 General Evaluation of Proposed Change The proposed change provides for compliance with federal recommendations regarding exposure to COVID-19 virus as low as possible while still conducting inspection and maintenance that will ensure the health and safety of the public.

Power generated by CPNPP Unit 2 is a vital national and state asset during the current pandemic.

The proposed change adds verbiage addressing the one-time deferral of CPNPP Unit 2 steam generator inspections. Based on Unit 2 600TT steam generator historical performance and current condition there is reasonable expectation that deferring the currently called for inspection for one refueling cycle will not impact public health or safety.

The current TS requirement is to inspect 100% of the tubes during each sequential period of 120 EFPM, 96 EFPM, and 72 EFPM, and each SG must be inspected at least every 48 EFPM or at least every other refueling outage (whichever results in more frequent inspections).

Significant operating experience has been gained over the course of 27 years of CPNPP Unit 2 plant operation with the 600TT steam generators and provides justification for this one-time inspection deferral. CPNPP Unit 2 operating experience has shown no propensity for rapidly increasing crack initiation rates in Alloy 600TT SG tubes.

Enclosure to TXX-20025 Page 5 of 18 The proposed one-time change that defers steam generator tube inspections for one refueling cycle can be demonstrated to meet the structural integrity and accident induced leakage performance criteria even for SGs that have experienced cracking. Based on this operating experience, the proposed TS change to defer tube inspections for one refueling cycle is acceptable.

3.2 CPNPP Unit 2 Specific Evaluation of Proposed Change Recent operational experience is summarized as follows:

1. Primary to secondary leakage The Operational Assessment performed following 2RF17 stated, Structural and leakage performance criteria were satisfied based on the inspection results. Hence, the CM requirements are satisfied. There was no primary-to-secondary operating leakage during the preceding inspection interval. An operational assessment of the current inspection results shows that the structural and leakage integrity will be satisfied for the next cycle and that it is acceptable to continue operation until the next planned inspection in spring 2020 (2RF18) for degradation mechanisms detected during 2RF17 and for existing degradation mechanisms previously detected at CPNPP Unit 2. There was no primary-to-secondary leakage observed during Cycle 17.
2. Summarize the most recent primary and secondary inspections, degradation description and location The most recent full scope SG inspection occurred during 2RF16. A smaller inspection scope was performed during 2RF17 to address circumferential cracking mechanisms found during 2RF16. The inspection scope and degradation mechanisms found during each inspection are as follows:

2RF16 SG Inspection Scope (performed in All SGs unless otherwise stated)

  • 50% full-length bobbin o Including all previously existing flaws
  • 100% full-length bobbin of all high stress tubes o +Point of all hot leg and cold TSP and TTS expansion transitions in all high stress tubes
  • 100% hot leg TTS +POINT (+3 to H* depth) in SG 2-03
  • 50% hot leg TTS +POINT (+3 to H* depth) in SG 2-01, SG 2-02, and SG 2-04
  • 100% hot bulges/overexpansion inside tubesheet H* region
  • 50% +Point of Row 1 and Row 2 U-bends
  • 50% +Point of dents and dings greater than 5 volts o Dents/dings less than 5volts inspected with bobbin coil as part of bobbin program o 50% dents/dings 2-5volts at or below TSP 07C with +Point on cold leg side
  • 100% TTS hot leg and cold leg periphery tubes with +Point

Enclosure to TXX-20025 Page 6 of 18

  • 100% +Point of cold leg Rows 21 to 49 at PBP-B in SG 2-02 and SG 2-03
  • 50% +Point probe of tubes expanded into Preheater Baffle Plate D
  • Channel Head visual inspections in all SGs (hot and cold legs)
  • Hot leg and cold leg tube plug visual inspections
  • Sludge Lance and FOSAR in all four SGs
  • Visual inspection of all waterboxes
  • Visual inspection of PBP Plate B in Rows 21-49 in SG 2-01 and SG 2-04
  • Upper bundle visual inspections in SG 2-01 During the 2RF16 inspections the following degradation mechanisms were reported
  • AVB Wear
  • Preheater baffle plate wear
  • Foreign object wear above tubesheet
  • Circumferential PWSCC at bulges/overexpansions within hot leg tubesheet (3 indications in 2 tubes)
  • Circumferential PWSCC at hot leg tubesheet expansion transition (1 indication in 1 tube)
  • One primary channel head cladding anomaly in SG 2-01 cold leg (historical)
  • One primary tubesheet cladding anomaly in SG 2-02 hot leg 2RF17 SG Inspection Scope (performed in All SGs unless otherwise stated)
  • 100% hot leg TTS +POINT (+3 to H* depth) in SG 2-03
  • 50% hot leg TTS +POINT (+3 to H* depth) in SG 2-01, SG 2-02 and SG2-04
  • 100% hot bulges/overexpansion inside tubesheet H* region in SG 2-03
  • 50% hot bulges/overexpansion inside tubesheet H* region in SG 2-01, SG 2-02 and SG2-04
  • Channel Head visual inspections
  • Hot leg and cold leg tube plug visual inspections
  • Visual inspection of Steam Drum Upper Internals in all 4 SGs During the 2RF17 inspections the following degradation mechanisms were reported
  • Foreign object wear above tubesheet
  • One primary channel head cladding anomaly in SG 2-02 cold leg (historical)
  • One primary tubesheet cladding anomaly in SG 2-02 hot leg Sludge lancing and foreign object search and retrieval (FOSAR) activities were not performed during 2RF17.

Enclosure to TXX-20025 Page 7 of 18

3. Number of tubes plugged including reason for plugging During 2RF16, SG 2-03 had three tubes plugged due to circumferential primary water stress corrosion cracking (PWSCC). No tubes were plugged during 2RF17 as a result of the base scope and special interest inspections. Currently the cumulative total number of plugged SG tubes on CPNPP for Unit 2 in all four SGs is 96 which is equal to 0.53% of the total number of tubes.
4. Relevant operating experience that may have impacted SG tube integrity There have been no thermal or hydraulic events on CPNPP, Unit 2 that may have impacted SG tube integrity since 2RF16.

Previous inspection condition monitoring is as follows:

1. For each degradation mechanism detected compare the most limiting as found condition to tube performance criteria.

The following degradation mechanisms exist in CPNPP Unit 2 Steam Generators; Identified during 2RF16 inspection

a. Wear at anti-vibration bars (AVB) supports No tubes were plugged due to AVB wear prior to inspection. The maximum depth of all AVB wear was 39% through wall (TW). The Condition Monitoring (CM) wear limit is 67.1% TW.

For volumetric wear flaws with pressure-only loading condition, tube burst and ligament tearing (i.e., pop-through) are coincident, therefore, satisfaction of the tube burst criteria at 3PNO also satisfies the AILPC at SLB differential pressure. Therefore, the SG performance criteria for structural and leakage integrity were demonstrated.

b. Wear at Preheater Baffle Plates (PBP)

The maximum depth of all PBP wear was 7% TW. The CM wear limit for PBP is 51.2% TW.

For volumetric wear flaws with pressure-only loading condition, tube burst and ligament tearing (i.e., pop-through) are coincident, therefore, satisfaction of the tube burst criteria at 3PNO also satisfies the AILPC at SLB differential pressure. Therefore, the SG performance criteria for structural and leakage integrity were demonstrated.

c. Wear at Quatrefoil Tube Support Plates (TSP)

The maximum depth of all quatrefoil TSP wear was 16% TW. The CM wear limit for quatrefoil TSP is 51.2% TW.

For volumetric wear flaws with pressure-only loading condition, tube burst and ligament tearing (i.e., pop-through) are coincident, therefore, satisfaction of the tube burst criteria at 3PNO also satisfies the AILPC at SLB differential pressure. Therefore, the SG performance criteria for structural and leakage integrity were demonstrated.

Enclosure to TXX-20025 Page 8 of 18

d. Wear due to foreign objects The maximum depth of all new foreign objects wear indications was 14% TW. The CM wear limit for foreign objects is 55.8% TW. Prior to 2RF16 the largest flaw to remain in service was 28% TW. The CM wear limit for foreign objects with an axial flaw length of 0.5 inches using ETSS 21998.1 +POINT probe sizing technique is 55.8% TW.

For volumetric wear flaws with pressure-only loading condition, tube burst and ligament tearing (i.e., pop-through) are coincident, therefore, satisfaction of the tube burst criteria at 3PNO also satisfies the AILPC at SLB differential pressure. Therefore, the SG performance criteria for structural and leakage integrity were demonstrated.

e. Circumferential primary water stress corrosion cracking (PWSCC) at bulges/overexpansions with the hot leg tubesheet Three indications found in SG 2-03 within the hot leg tubesheet below the top of the tubesheet. The largest percent degraded area (PDA) was 4.2% and the CM limit was 74%.
f. Circumferential PWSCC at hot leg tubesheet expansion transitions One indication found in SG 2-03 within the top of the hot leg tubesheet expansion transition. As found PDA was 11.5% and the CM limit was 74%.

Identified during 2RF17 inspection

a. Wear due to foreign objects The maximum depth of all foreign objects wear indications was 17%

TW with axial extent of 0.32 inches. The CM wear limit for foreign objects with an axial flaw length of 0.5 inches is 49.4% using ETSS 96911.1 pancake coil sizing technique.

For volumetric wear flaws with pressure-only loading condition, tube burst and ligament tearing (i.e., pop-through) are coincident, therefore, satisfaction of the tube burst criteria at 3PNO also satisfies the AILPC at SLB differential pressure. Therefore, the SG structural and leakage performance criteria are satisfied for foreign object wear.

b. Circumferential PWSCC at bulges/overexpansions with the hot leg tubesheet and Circumferential PWSCC at hot leg tubesheet expansion transitions Because of the indications found in 2RF16 inspections for these degradation methods were required in 2RF17. No indication of circumferential PWSCC were reported, thus no CM for these degradation mechanisms was required.

Enclosure to TXX-20025 Page 9 of 18

2. For all SG tubes that required flaw profiling, demonstrate how condition monitoring was met.

Condition monitoring was met by not exceeding any through wall limits for the above degradation mechanisms. Flaw profiling was not required to demonstrate condition monitoring.

Operational assessment during an additional operating cycle is as follows:

List of terms used in this assessment; POB = Probability of Burst (%)

POL = Probability of Leakage (%)

Pb = Burst Pressure (psi)

LR = Leakage Rate (gpm)

TW = Through wall NDE = Non-destructive examination CM = Condition Monitoring PBP = Preheater Baffle Plates FDB = Flow Distribution Baffle TSP = Tube Support Plate POD = Probability of flaw Detection

1. List mechanisms considered and reason for consideration Existing Degradation Mechanisms
a. Projected Tube Wear at AVBs Existing 55.3% TW with burst pressure of 5075 psi. Criterion is less than 69.4% TW with burst pressure greater than or equal to 3909 psi.

Undetected 38.4% TW with burst pressure of 6438 psi. Criterion is less than 69.4% TW with burst pressure greater than or equal to 3909 psi.

Prediction of existing AVB Wear at 2RF19 starts with 39% TW is projected to be no worse than 38.4% TW with a burst pressure of 5075 psi. The bounding load limit is 69.4% TW with a burst pressure greater than or equal to 3909 psi.

Prediction of undetected AVB Wear at 2RF19 starts with 17% TW is projected to be no worse than 55.3% TW with a burst pressure of 6438 psi. The bounding load limit is 69.4% TW with a burst pressure greater than or equal to 3909 psi.

Deferring AVB Wear inspections until 2RF19 will not violate SG tube integrity performance criteria.

b. Projected Tube Wear at Tube Support Plates (PBP and TSP)

Existing 51.1% TW with burst pressure of 5063 psi. Criterion is less than 63.7% TW with burst pressure greater than or equal to 3909 psi.

Undetected 57.6% TW with burst pressure of 4465 psi. Criterion is less than 63.7% TW with burst pressure greater than or equal to 3909 psi.

Enclosure to TXX-20025 Page 10 of 18 Prediction of existing PBP Wear at 2RF19 starts with 7% TW is projected to be no worse than 42.6% TW with a burst pressure of 5938 psi. The bounding load limit is 65.9% TW with a burst pressure greater than or equal to 3909 psi.

Prediction of undetected PBP Wear at 2RF19 starts with 9% TW is projected to be no worse than 53.6% TW with a burst pressure of 4981 psi. The bounding load limit is 65.9% TW with a burst pressure greater than or equal to 3909 psi.

Deferring PBP Wear inspections until 2RF19 will not violate SG tube integrity performance criteria.

Prediction of existing TSP Wear at 2RF19 starts with 16% TW is projected to be no worse than 51.1% TW with a burst pressure of 5063 psi. The bounding load limit is 63.7% TW with a burst pressure greater than or equal to 3909 psi.

Prediction of undetected TSP Wear at 2RF19 starts with 13% TW is projected to be no worse than 57.6% TW with a burst pressure of 4465 psi. The bounding load limit is 63.7% TW with a burst pressure greater than or equal to 3909 psi.

Deferring TSP Wear inspections until 2RF19 will not violate SG tube integrity performance criteria.

c. Projected Tube Wear Due to Foreign Objects Existing 28% TW (NDE). Criterion is less than 55.8% TW (CM).

No foreign objects remain within the vicinity of the affected tubes and no flaw growth has occurred since initial identification. Therefore, there is no mechanism for future flaw growth.

Deferring Tube Wear from Foreign Objects inspections until 2RF19 will not violate SG tube integrity performance criteria.

d. Projected Circumferential PWSCC Indications Existing with POB of 1.67%, POL of 2.72%, Pb of 4604 psi, and LR of 0.146 gpm. Criterion POB less than or equal to 5%, POL less than or equal to 5%, Pb greater than or equal to 3909 psi, and LR less than or equal to 0.3472 gpm.

Deferring Projected Circumferential PWSCC inspections until 2RF19 will not violate SG tube integrity performance criteria.

Potential Degradation Mechanisms

a. Axial ODSCC at Tube Support Plates for High Stress Tubes Potential with POB of 0.617%, POL of 0.847%, Pb of 5291 psi, and LR of 0 gpm. Criterion POB less than or equal to 5%, POL less than or equal to 5%, Pb greater or equal to 3909 psi, and LR less than or equal to 0.3472 gpm.

Enclosure to TXX-20025 Page 11 of 18 Deferring Axial ODSCC at Tube Support Plates for High Stress Tubes inspections until 2RF19 will not violate SG tube integrity performance criteria.

b. Circumferential ODSCC at top of Tubesheet Expansion Transitions Potential with POB of 0.63%, POL of 2.14%, Pb of 5584 psi, and LR of 0.05 gpm. Criterion POB less than or equal to 5%, POL less than or equal to 5%, Pb greater or equal to 3909 psi, and LR less than or equal to 0.3472 gpm.

Deferring Circumferential ODSCC at top of Tubesheet Expansion Transitions inspections until 2RF19 will not violate SG tube integrity performance criteria.

c. Axial PWSCC at top of Tubesheet Expansion Transitions Potential with POB of 1.29%, POL of 0.64%, Pb of 4767 psi, and LR of 0 gpm. Criterion POB less than or equal to 5%, POL less than or equal to 5%, Pb greater or equal to 3909 psi, and LR less than or equal to 0.3472 gpm.

Deferring Axial PWSCC at top of Tubesheet Expansion Transitions inspections until 2RF19 will not violate SG tube integrity performance criteria.

d. Axial ODSCC at top of Tubesheet Expansion Transitions & Sludge Pile Potential with POB of 1.17%, POL of 0.42%, Pb of 4757 psi, and LR of 0.0014 gpm. Criterion POB less than or equal to 5%, POL less than or equal to 5%, Pb greater or equal to 3909 psi, and LR less than or equal to 0.3472 gpm.

Deferring Axial ODSCC at top of Tubesheet Expansion Transitions &

Sludge Pile inspections until 2RF19 will not violate SG tube integrity performance criteria.

Leakage Integrity The existing and potential stress corrosion cracking (SCC) mechanisms have been evaluated against condition monitoring criteria of less than 5%

POL. Following EPRI SG IAGL guidance the circumferential PWSCC and circumferential ODSCC POLs are combined for a total 4.76% which is bounded by the less than 5% CM limit.

The predicted primary to secondary leakage based on not performing SG inspections until 2RF19 is calculated to be no more than 68.3 gpd. This value is bounded by the TS primary to secondary leakage limit of 150 gpd and the administrative limit of 75 gpd (Action Level 2 - be in MODE 3 in 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />).

Enclosure to TXX-20025 Page 12 of 18 Channel Head Indications Combined aerated and deaerated corrosion rate for CPNPP Unit 2 SGs is 0.00087 inch per cycle. Projected total wall loss through 2RF19 is 0.0166 inch. The allowable surface flaw depth is 0.10 inch. Predicted total wall loss of 0.0166 inch is bounded by allowable depth of 0.10 inch.

Foreign Object Evaluation CPNPP Unit 2 SG foreign object inventory with all four SGs will not reach minimum tube wall thickness at any location by deferring foreign object inspection to 2RF19. No retrieval, inspection, or plugging is necessary prior to 2RF19.

Secondary Side Integrity Steam drum inspection interval is every 12 years. The inspection was last performed during 2RF17 (fall or 2018). That inspection yielded no evidence of progressing degradation. No impact on deferring inspections to 2RF19.

2. Inspection strategy details at last inspection for each item considered above The inspection strategy is to perform a 100% tube inspection of all CPNPP Unit 2 SGs during 2RF19 in the fall of 2021.
3. CPNPP Unit 2 SG Alloy 600TT tubing;
a. Number of high stress tubes remaining in service In 2003, a total 73 high stress tubes were identified in CPNPP Unit 2 SGs. Nine of the 73 tubes have been plugged, resulting in 64 high stress tubes remaining in service.
b. How tubes that could have remained unidentified as high stress after screening are considered in inspection strategy Inspection of the 64 high stress SG tubes on CPNPP Unit 2 includes full-length bobbin coil inspections and targets +POINT probe inspection of areas more susceptible to degradation.

CPNPP Unit 2 SG tubes not identified with high residual stress are inspected in accordance with TS 5.5.9 requirements.

c. Operational experience related to the high stress tubes that remain in service Most recently, during 2RF16 in 2017 one high stress SG tube presented PWSCC indication and was plugged. No other SCC indications have presented on CPNPP Unit 2 SGs.

Enclosure to TXX-20025 Page 13 of 18 This operational assessment (Attachment 2) reviewed all existing degradation mechanisms and evaluated detected and undetected flaws. Potential degradation mechanisms were reviewed. The methodology assumes the degradations have occurred and are undetected until 2RF19. Overall, data supports deferral of CPNPP Unit 2 SG inspections until 2RF19.

Mitigating strategies are as follows:

1. Administrative limits versus Technical Specification (TS) limits TS 3.4.13, RCS Operational LEAKAGE is limited to 150 gallons per day primary to secondary LEAKAGE through any one steam generator (SG).

The current administrative limit is 75 gpd for Action Level 2 entry which requires MODE 3 entry within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Action Level 2 entry will be changed to 50 gpd.

2. Increased monitoring between operating cycles Increased monitoring can be correlated to TS 3.4.13, RCS Operational LEAKAGE, surveillance requirement (SR) 3.4.13.1, Verify RCS operational LEAKAGE is within limits by performance of RCS water inventory balance. The frequency requirement is once per 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> in accordance with the Surveillance Frequency Control Program (SFCP). At CPNPP this SR is performed once per day during steady state operations.

This is not a new requirement it is provided to illustrate that CPNPP performs an RCS water inventory balance more frequently than what is required by the SFCP.

Increased monitoring can also be correlated to TS 3.4.13, RCS Operational LEAKAGE, surveillance requirement (SR) 3.4.13.2, Verify primary to secondary LEAKAGE is 150 gallons per day through any one SG. The frequency requirement is once per 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> in accordance with the Surveillance Frequency Control Program (SFCP). At CPNPP this SR is performed once per day during steady state operations. This is not a new requirement it is provided to illustrate that CPNPP performs an RCS water inventory balance more frequently than what is required by the SFCP.

CPNPP has adopted the EPRI PWR Primary-To-Secondary Leak Guidelines provide two methodologies for responding to power operation primary-to-secondary leakage: Rate of Change, and Constant Leakage.

Rate of Change methodology evaluates the leakage and the rate of leakage change. Constant Leakage methodology only considers leakage. CPNPP has determined to use the Constant Leakage methodology for primary-to-secondary leakage response. The following actions are taken in response to increasing primary-to-secondary leakage.

  • Increased Monitoring: Mode 1 normal operation plant condition entered when leakage has been detected but is not in a range that can be accurately monitored by most online radiation monitors, does not necessarily indicate imminent risk to steam generator tube integrity, but warrants additional attention. This condition is entered when the total primary-to-secondary leakage is greater than or equal to 5 gpd.

Enclosure to TXX-20025 Page 14 of 18

  • Action Level 1: The plant condition entered when leakage has increased to a condition that requires frequent monitoring by the radiation monitoring system with periodic bench marking by laboratory analyses. Action Level 1 is entered when primary-to-secondary leakage is greater than or equal to 30 gpd.
  • Action Level 2: Plant condition entered when primary-to-secondary leakage is greater than or equal to 75 gpd in any steam generator AND is sustained for greater than 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. Be in Mode 3 within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of entering Action Level 2.
  • Action Level 3: Plant condition entered when primary-to-secondary leakage in any steam generator is greater than or equal to 100 gpd.

Commence prompt and controlled plant shut down and be at less than or equal to 50% power within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and be in Mode 3 within the next 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> (total of 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />).

3. Procedure changes that will be implemented between operating cycles
a. ABN-106, High Secondary Activity Procedure currently uses 75 gpd to determine whether to monitor and continue operation or shutdown. The procedure will be changed to use 50 gpd as the determination leak rate.
b. ODA-102, Conduct of Operations Procedure contains a table with a list of procedures that require directing a trip or down power. This table will be revised to use 50 gpd vice 75 gpd for unit down power.
c. COP-732, Primary to Secondary Leakage Procedure contains a note listing the leakage values to be used when developing a correlation graph using the Condenser Off Gas radiation monitor to determine primary to secondary leakage. One of the values is 75 gpd, this will be changed to 50 gpd.
d. CHM-113, Primary to Secondary Leakage Procedure requires entry into Action Level 2 when primary to secondary leakage is greater than or equal to 75 gpd in any steam generator and is sustained for greater than one hour. Action Level 2 requires MODE 3 entry within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. The 75 gpd value will be changed to 50 gpd.
e. CHM-113-12, Primary to Secondary Leakage Data Sheet The data sheet will replace the 75 gpd value with 50 gpd when using tritium analysis method for primary to secondary leakage.
f. CHM-101-11, Chemistry Checklist MODE 5 to MODE 4 The mode change restraint for primary to secondary leakage is 75 gpd and will be changed to 50 gpd.
g. CHM-101-12, Chemistry Checklist MODE 4 to MODE 3 The mode change restraint for primary to secondary leakage is 75 gpd and will be changed to 50 gpd.

Enclosure to TXX-20025 Page 15 of 18

h. CHM-101-13, Chemistry Checklist MODE 3 to MODE 2 The mode change restraint for primary to secondary leakage is 75 gpd and will be changed to 50 gpd.
i. RPI-621, Response to Primary to Secondary Leakage Action Level 2 entry criteria will be changed from 75 gpd to 50 gpd.

See Attachment 2 to TXX-20025 for Comanche Peak Unit 2 Steam Generator Operational Assessment to Support Deferral of Planned Inspections from 2RF18 to 2RF19 Based on this operating data, the one-time TS change to defer the CPNPP Unit 2 SG tube inspections from 2RF18 to 2RF19 (for 18 months) is acceptable.

4.0 REGULATORY EVALUATION

4.1 Applicable Regulatory Requirements The regulatory basis for Technical Specifications 5.5.9, ASteam Generator (SG)

Program@ is to ensure that SG tube integrity is maintained. In addition, the SG Program shall include the following:

Section 182a of the Atomic Energy Act requires applicants for nuclear power plant operating licenses to include technical specifications as part of the license.

The Commission's regulatory requirements related to the content of the technical specifications are contained in Title 10, Code of Federal Regulations (10 CFR),

Section 50.36, "Technical Specifications," of 10 CFR Part 50 "Domestic Licensing of Production and Utilization Facilities." The technical specification requirements in 10 CFR 50.36 include the following categories: (1) safety limits, limiting safety systems settings and control settings, (2) limiting conditions for operation, (3) surveillance requirements, (4) design features, and (5) administrative controls.

As stated in 10 CFR 50.59(c)(1)(i), a licensee is required to submit a license amendment pursuant to 10 CFR 50.90 if a change to the technical specifications is required. Furthermore, the requirements of 10 CFR 50.59 necessitate that the NRC approve technical specification changes before the changes are implemented. Vistra OpCos submittal meets the requirements of 10 CFR 50.59(c)(1)(i) and 10 CFR 50.90.

General Design Criterion (GDC) 14 "Reactor Coolant Pressure Boundary (RCPB)," of Appendix A "General Design Criteria for Nuclear Power Plants," to 10 CFR Part 50 requires, among other things, that the reactor coolant pressure boundary shall be designed, fabricated, erected, and tested so as to have an extremely low probability of abnormal leakage, of rapidly propagating failure, and of gross rupture. The proposed change continues to provide steam generator tube inspections that will contribute to a robust RCPB.

GDC 15, AReactor Coolant System (RCS) 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

Enclosure to TXX-20025 Page 16 of 18 pressure boundary are not exceeded during any condition of normal operation, including anticipated operational occurrences. The proposed change does not negatively impact steam generator tube integrity during normal operation or anticipated operational occurrences.

GDC 30, AQuality of reactor coolant pressure boundary,@ requires that components which are part of the RCPB shall be designed, fabricated, erected, and tested to the highest quality standards practical. The proposed change does not reduce quality standards for steam generator design, fabrication, or testing.

GDC 31, Fracture prevention of reactor coolant pressure boundary, requires the RCPB 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 proposed change does not alter the fracture prevention design of the steam generator tubes.

GDC 32, Inspection of reactor coolant pressure boundary, the steam generator tubes are designed to permit periodic inspection and testing to assess their structural and leaktight integrity. The proposed change does not eliminate periodic inspection or testing of the steam generator tubes.

4.2 Precedent None cited 4.3 No Significant Hazards Consideration Determination Vistra OpCo has evaluated whether or not a significant hazards consideration is involved with the proposed amendment by focusing on the three standards set forth in 10 CFR 50.92, AIssuance of amendment,@ as discussed below:

1. Do the proposed changes involve a significant increase in the probability or consequences of an accident previously evaluated?

Response: No The proposed change calls for a one-time change in inspection frequencies for steam generator tube inspections and associated reporting requirements. Inspection frequencies are not an initiator to a steam generator tube rupture accident, or any other accident previously evaluated. As a result, the probability of any accident previously evaluated is not significantly increased. The steam generator tubes inspected by the Steam Generator (SG) Program continue to be required to meet the SG Program performance criteria and to be capable of performing any functions assumed in the accident analysis. As a result, the consequences of any accident previously evaluated are not significantly increased.

Enclosure to TXX-20025 Page 17 of 18 Therefore, the proposed change does not involve a significant increase in the probability or consequences of an accident previously evaluated.

2. Do the proposed changes create the possibility of a new or different kind of accident from any accident previously evaluated?

Response: No The proposed change calls for a one-time change in inspection frequencies for steam generator tube inspections and associated reporting requirements. The proposed change does not alter the design function or operation of the steam generators or the ability of a steam generator to perform the design function. The steam generator tubes continue to be required to meet the Steam Generator (SG)

Program performance criteria. The proposed change does not create the possibility of a new or different kind of accident due to credible new failure mechanisms, malfunctions, or accident initiators that not considered in the design and licensing bases.

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

3. Do the proposed changes involve a significant reduction in a margin of safety?

Response: No The proposed change calls for a one-time change in inspection frequencies for steam generator tube inspections and associated reporting requirements. The proposed change does not change any of the controlling values of parameters used to avoid exceeding regulatory or licensing limits. The proposed change does not affect a design basis or safety limit, or any controlling value for a parameter established in the FSAR or the license.

Therefore, the proposed change does not involve a significant reduction in a margin of safety.

Based on the above evaluations, Vistra OpCo concludes that the propose amendment presents no significant hazards consideration under the standards set forth in 10 CFR 50.92(c) and, accordingly, a finding of Ano significant hazards consideration@ is justified.

4.4 Conclusions In conclusion, based on the considerations discussed above, (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 adverse to the common defense and security or to the health and safety of the public.

Enclosure to TXX-20025 Page 18 of 18

5.0 ENVIRONMENTAL CONSIDERATION

S Vistra OpCo has determined that the proposed amendment would change requirements with respect to the installation or use of a facility component located within the restricted area, as defined in 10 CFR 20, or would change an inspection or surveillance requirement. However, the proposed amendment does not involve (i) a significant hazards consideration, (ii) a significant change in the types or significant increase in the amount of effluent that may be released offsite, or (iii) a significant increase in the individual or cumulative occupational radiation exposure. Accordingly, the proposed change meets the eligibility criterion for categorical exclusion set forth in 10 CFR 51.22(c)(9). Therefore, pursuant to 10 CFR 51.22(b), an environmental assessment of the proposed change is not required.

6.0 REFERENCES

6.1 TSTF-449, Revision 4, "Steam Generator Tube Integrity," April 14, 2005, (ADAMS Accession No. ML051090200).

6.2 TSTF-510, Revision 2, "Revision to Steam Generator Program Inspection Frequencies and Tube Sample Selection," March 1, 2011, (ADAMS Accession No. ML110610350).

6.3 TSTF-577, Revision 0a, DRAFT " Performance Based Frequencies for Steam Generator Tube Inspections," September 18, 2019, (ADAMS Accession No. ML19301A001).

6.4 UNIT 2 SIXTEENTH REFUELING OUTAGE (2RF16) STEAM GENERATOR 180 DAY REPORT (ML17313A447) 6.5 UNIT 2 SEVENTEENTH REFUELING OUTAGE (2RF17) STEAM GENERATOR 180 DAY REPORT (ML19171A190)

Attachment 1 to TXX-20025 Page 1 of 12 Attachment 1 to TXX-20025 Technical Specifications

1. Technical Specification 5.5.9, Unit 1 Model D76 and Unit 2 Model D5 Steam Generator (SG) Program - Current
2. Technical Specification 5.5.9, Unit 1 Model D76 and Unit 2 Model D5 Steam Generator (SG) Program - Markup

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Attachment 1 to TXX-20025 Page 12 of 12 INSERT A This is a one-time change to TS 5.5.9.d.2 for CPNPP Unit 2, Cycle 19 for the Unit 2 model D5 steam generators (Alloy 600 thermally treated) after the first refueling outage following SG installation, inspect each SG at least every 54 effective full power months.

INSERT B "This is a one-time change to TS 5.5.9.d.2.c for CPNPP Unit 2, Cycle 19, during the remaining life of the SGs, inspect 100% of the tubes every 90 effective full power months.

This constitutes the third and subsequent inspection periods.

to TXX-20025 Page 1 of 57 Attachment 2 to TXX-20025 Comanche Peak Unit 2 Steam Generator Operational Assessment to Support Deferral of Planned Inspections from 2RF18 to 2RF19 to TXX-20025 Page 2 of 57 Westinghouse Non-Proprietary Class 3 SG-CDMP-20-13 April 2020 Revision 0 Comanche Peak Unit 2 Steam Generator Operational Assessment to Support Deferral of Planned Inspections from 2RF18 to 2RF19

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 3 of 57 Westinghouse Non-Proprietary Class 3 SG-CDMP-20-13 Revision 0 Comanche Peak Unit 2 Steam Generator Operational Assessment to Support Deferral of Planned Inspections from 2RF18 to 2RF19 April 2020 Author: Signature/Date Bradley T. Carpenter *Electronically Approved Component Design & Management Programs Author: Signature/Date Jay R. Smith *Electronically Approved OSG/RSG Engineering Chemistry Author: Signature/Date Levi Y. Marcus *Electronically Approved Component Design & Management Programs Verifier: Signature/Date Hermann O. Lagally *Electronically Approved Component Engineering & Chemistry Operations Approved: Signature/Date Michael E. Bradley, Manager *Electronically Approved Component Design & Management Programs

©2020 Westinghouse Electric Company LLC All Rights Reserved

  • Electronically Approved Records are Authenticated in the Electronic Document Management System SG-CDMP-20-13 Revision 0 Page 2 of 56
      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 4 of 57 04/10/2020
      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 5 of 57 Westinghouse Non-Proprietary Class 3 Record of Revisions Revision Number Description 0 Initial Issue SG-CDMP-20-13 Revision 0 Page 4 of 56
      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 6 of 57 Westinghouse Non-Proprietary Class 3 Table of Contents 1 Introduction .................................................................................................................... 8 1.1 Steam Generator Configuration...................................................................................... 8 1.2 Summary of Operation and Plan .................................................................................... 9 1.3 Steam Generator Performance Criteria .......................................................................... 9 1.3.1 Structural Integrity Performance Criteria (SIPC) ................................................... 9 1.3.2 Operational Primary-to-Secondary Leakage Performance Criteria ...................... 11 1.3.3 Accident Induced Leakage Performance Criteria (AILPC) .................................. 11 1.3.4 H* Alternate Repair Criteria Considerations ........................................................ 12 2 Steam Generator Outage Summary .............................................................................. 13 2.1 Sequential Inspection Periods ...................................................................................... 13 2.2 2RF17 Inspection Plan and Results .............................................................................. 14 2.2.1 2RF17 Inspection Plan .......................................................................................... 14 2.2.2 2RF17 Inspection Results ..................................................................................... 14 2.2.3 Secondary Side Inspection and Maintainance ...................................................... 14 2.3 2RF16 Inspection Plan and Results .............................................................................. 14 2.3.1 Base Scope Inspection .......................................................................................... 14 2.3.2 Inspection Expansion ............................................................................................ 15 2.3.3 Inspection Results ................................................................................................. 15 2.3.4 Secondary Side Inspection and Maintainance ...................................................... 16 2.4 Tube Repair Summary.................................................................................................. 16 2.5 Channel Head Indications ............................................................................................ 16 2.6 Tube Plug Visual Examinations ................................................................................... 17 3 Condition Monitoring ................................................................................................... 23 3.1 Existing Degradation Mechanisms ............................................................................... 23 3.1.1 Tube Wear at AVBs .............................................................................................. 23 3.1.2 Tube Wear at Tube Support Plates ....................................................................... 24 3.1.3 Tube Wear Due to Foreign Objects ...................................................................... 24 3.1.4 Circumferential PWSCC within Tubesheet and at Expansion Transitions .......... 25 3.2 Channel Head Indications ............................................................................................ 26 3.3 Tube Plug Visual Examinations ................................................................................... 27 3.4 Secondary Side Integrity .............................................................................................. 27 3.5 Condition Monitoring Conclusion................................................................................ 27 4 Operational Assessment ............................................................................................... 29 4.1 Existing Degradation Mechanisms ............................................................................... 30 4.1.1 Tube Wear at AVBs .............................................................................................. 30 4.1.2 Tube Wear at Tube Support Plates ....................................................................... 33 4.1.3 Tube Wear Due to Foreign Objects ...................................................................... 36 4.1.4 Circumferential PWSCC Indications .................................................................... 36 4.2 Potential Degradation Mechanisms .............................................................................. 38 4.2.1 Axial ODSCC at Tube Support Plates for High Stress Tubes .............................. 39 4.2.2 Circumferential ODSCC at Top of Tubesheet ...................................................... 41 4.2.3 Axial PWSCC at Top of Tubesheet ...................................................................... 42 4.2.4 Axial ODSCC at Top of Tubesheet ...................................................................... 44 4.3 Leakage Integrity .......................................................................................................... 46 4.4 Channel Head Indications ............................................................................................ 47 4.5 Foreign Object Evaluation............................................................................................ 48 SG-CDMP-20-13 Revision 0 Page 5 of 56
      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 7 of 57 Westinghouse Non-Proprietary Class 3 4.6 Secondary Side Integrity .............................................................................................. 50 4.7 High Stress Tubes ......................................................................................................... 50 4.7.1 Potential for Unidentified High Stress Tubes ....................................................... 50 4.7.2 Inspections Performed to Address Potentially Missed High Stress Tubes ........... 51 4.7.3 High Stress Tube Cracking at Comanche Peak Unit 2 ......................................... 51 4.7.4 Inspection Strategy (Prior and Future) .................................................................. 51 4.8 Final Operational Assessment Conclusion ................................................................... 52 5 References .................................................................................................................... 55 SG-CDMP-20-13 Revision 0 Page 6 of 56
      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 8 of 57 Westinghouse Non-Proprietary Class 3 List of Tables Table 1-1. Structural and Condition Monitoring Limits for Volumetric Flaws ...................................11 Table 2-1. CPNPP Unit 2 SG Sequential Inspection Periods, Primary Side Inspection History & Plan

.......................................................................................................................................................18 Table 2-2. Historical Secondary Side Visual Inspections - Comanche Peak Unit 2 ...........................19 Table 2-3: Summary of Indication History ...........................................................................................19 Table 2-4. History of SG Tube Plugging in CPNPP Unit 2 through 2RF16 .......................................20 Table 2-5. History of Sludge Removal from CPNPP Unit 2 SGs .......................................................21 Table 3-1. Historical AVB Wear at CPNPP Unit 2 .............................................................................24 Table 3-2. Summary of Tube Support Plate Wear Indications in 2RF16 ............................................24 Table 3-3. Summary of Foreign Object Wear Indications Reported in 2RF16 and 2RF17 ................25 Table 3-4. Summary of Historical Circumferential PWSCC...............................................................26 Table 4-1. Circumferential PWSCC at Tubesheet Locations Fully Probabilistic OA Results ............38 Table 4-2. Industry SCC Experience in A600TT Tubing ....................................................................39 Table 4-3. Axial ODSCC at TSP (2-Sigma Tubes) Fully Probabilistic OA Results ...........................41 Table 4-4. Circumferential ODSCC at TTS Fully Probabilistic OA Results ......................................42 Table 4-5. Axial PWSCC at Expansion Transition Fully Probabilistic OA Results ...........................44 Table 4-6. Axial ODSCC at Expansion Transition Fully Probabilistic OA Results ...........................46 Table 4-7. OA Calculated POL by SCC Mechanism ..........................................................................46 Table 4-8. OA Predicted Leakages by SCC Mechanism .....................................................................47 Table 4-9. OA Results Summary Table for Tube Wear Mechanisms .................................................53 Table 4-10. OA Results Summary Table for SCC Mechanisms .........................................................54 List of Figures Figure 2-1. SG 2-01 Cold Leg Channel Head Cladding Anomaly Historical Inspection Results .......22 Figure 2-2. SG 2-02 Hot Leg Channel Head Cladding Anomaly Near Tube R1-C109 Inspection Results ...........................................................................................................................................22 Figure 4-1: CNPP Unit 2 AVB Wear Historical Growth Rate Distribution ........................................31 SG-CDMP-20-13 Revision 0 Page 7 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 9 of 57 Westinghouse Non-Proprietary Class 3 1 Introduction Steam generator (SG) inspections were most recently performed at Comanche Peak Nuclear Power Plant (CPNPP) Unit 2 during refueling outage 17 (2RF17) in December 2018 and prior to that during 2RF16 in April 2017. The next planned SG inspections are scheduled to be performed during 2RF18 in April 2020. However, in response to the government mandates associated with the COVID-19 virus pandemic to the population exposure by physical separation and limiting large gatherings of personnel, Luminant is pursuing regulatory approval of a deferral of the 2RF18 planned inspection scope by one operating cycle. This report documents the technical viability of deferring SG inspections by one cycle to 2RF19 currently planned for October 2021.

Per NEI 97-06 (Reference 1), a Condition Monitoring (CM) assessment, which evaluates structural and leakage integrity characteristics of each SG at the end of the last operating period, is to be performed following each inspection. This evaluation is backward-looking and compares the observed SG tube eddy current indication parameters against leakage and structural integrity criteria of Reference 1. Condition Monitoring evaluations were completed for the 2RF16 and 2RF17 outages and are summarized within this report. Inspection results are summarized in the publicly available 180-day SG inspection reports (Reference 5 and Reference 6) that are issued by the utility following the completion of each SG inspection. This report does not change any Condition Monitoring conclusions from the 2RF16 or 2RF17 outages and merely summarizes them to succinctly provided the background that CM has been met by standard methods for all indications detected during recent inspections for CPNPP Unit 2.

Additionally, an Operational Assessment (OA), or forward-looking evaluation is used to project the inspection results and trends to confirm that the SG performance criteria will be met during the operating period until the next inspection. Operational Assessments were previously completed to justify SG tube integrity up to 2RF18. This report investigates the addition of one cycle to the Operational Assessment in order to conclude that SG tube integrity is maintained at least up to 2RF19 at which point the next SG inspections would occur.

Evaluations performed within this document would become the SG OA evaluations of record, should the 2RF18 inspection deferral be processed.

1.1 Steam Generator Configuration The CPNPP Unit 2 Nuclear Steam Supply System (NSSS) has four Westinghouse Model D-5 SGs each with 4570 thermally treated Alloy 600 (A600TT) U-tubes. Each U-tube has a nominal outside diameter (OD) of 0.750 inch, and a nominal tube wall thickness of 0.043 inch. The U-bend region in Rows 1 through 9 were stress relieved following heat treatment. The tubesheet is 21.23 inches thick with a full depth hydraulic expansion of the tubes in both the hot leg (HL) and the cold leg (CL). Approximately 0.75 inch of the tube at both ends was tack expanded prior to tube-end welding. On the hot leg side, the U-tubes are supported by seven tube support plates (TSPs). A flow distribution baffle (FDB) plate located between the tubesheet and the first TSP helps distribute the secondary side flow over the tubesheet. On the cold leg side there are four TSPs, six preheater baffle plates (PBPs) and the FDB. The FDB and the lowest five preheater baffle plates are 0.75 inch thick whereas the TSPs and the top preheater baffle plate are 1.12 inches thick. The FDB and the preheater baffle plates have round drilled holes whereas the TSPs have quatrefoil broached holes. All plates are made of Type 405 stainless steel. In the U-bend, the tubes are SG-CDMP-20-13 Revision 0 Page 8 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 10 of 57 Westinghouse Non-Proprietary Class 3 supported by two (2) sets of chrome-plated Inconel anti-vibration bars (AVBs). To reduce tube vibration, 140 tubes in each SG were hydraulically expanded at the B and D preheater baffle plates.

This field modification was performed before the initial startup of CPNPP Unit 2.

1.2 Summary of Operation and Plan CPNPP Unit 2 began commercial operation in April 1993. At the end of the current operating cycle (Cycle 18), the plant and SGs have accumulated 24.04 effective full power years (EFPY) of operation. The duration for Cycle 17 and Cycle 18 were provided from Reference 7 and are summarized below.

EFPD EFPY EFPM U2C17 498.481 1.365 16.377 U2C18 451.080 1.235 14.820 Since Cycle 17 and Cycle 18 are completed, the actual cycle lengths can be applied for evaluations performed in this report rather than the typical conservative assumption of 1.45 EFPY/cycle.

Cycle 19 will be projected as 1.45 EFPY which is judged to be conservative based on past cycle lengths for CPNPP Unit 2. Therefore, the total duration from Cycle 16 to Cycle 19 is 4.05 EFPY.

The nominal primary side fluid pressure at CPNPP Unit 2 is 2235 psig. The lowest value of the steam pressure for Cycles 16 through 18 was 932 psig based on review of the 2RF17 OA, 2RF16 OA, and the current Cycle 18 plant conditions (Reference 8). Therefore, the bounding differential pressure across the SG tubes is 1303 psi, not including line and pressure losses from the main steam pressure tap to the top of the SG tube bundle. The primary hot leg temperature for Cycle 18 did not exceed 618°F over the four SGs which is the design basis Thot temperature for CPNPP2 (Reference 8).

There was no primary-to-secondary side leakage observed during Cycles 16, 17 or 18 at CPNPP2.

1.3 Steam Generator Performance Criteria NEI 97-06, Revision 3 (Reference 1) specifies the performance criteria for structural integrity and leakage integrity that must be met for CM and OA.

1.3.1 Structural Integrity Performance Criteria (SIPC)

The structural criteria were based on demonstrating capability to meet the pressure loading of 3 times the normal operating condition pressure differential (3PNO) or 1.4 times the limiting accident condition (steam line break - SLB) pressure differential (1.4PSLB). Reference 1 includes the structural integrity performance criteria (SIPC) and is defined as follows:

All in-service steam generator tubes shall retain structural integrity over the full range of normal operating conditions (including startup, operation in the power range, hot standby, and cooldown and all anticipated transients included in the design specification) and design basis accidents. This includes retaining a safety factor of 3.0 against burst under normal steady state full power operation primary-to-secondary pressure differential and a safety SG-CDMP-20-13 Revision 0 Page 9 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 11 of 57 Westinghouse Non-Proprietary Class 3 factor of 1.4 against burst applied to the design basis accident primary-to-secondary pressure differentials. Apart from the above requirements, additional loading conditions associated with the design basis accidents, or combination of accidents in accordance with the design and licensing basis, shall also be evaluated to determine if the associated loads contribute significantly to burst or collapse. In the assessment of tube integrity, those loads that do significantly affect burst or collapse shall be determined and assessed in combination with the loads due to pressure with a safety factor of 1.2 on the combined primary loads and 1.0 on axial secondary loads.

The CPNPP Unit 2 normal primary side pressure is 2235 psig and the lower bound secondary side pressure at full load operating condition from Cycle 18 is 932 psig (Reference 8). This results in the full load operating pressure differential (PNO) of 1303 psi. Three times the normal operating pressure differential (3PNO) is 3909 psi. The limiting tube differential pressure at SLB conditions is taken as 2560 psi to determine limits for the leakage integrity performance criteria.

The differential pressure used for tube structural integrity is the limiting value of 3PNO (3909 psi) and 1.4 PSLB (3584 psi). Therefore, a tube differential pressure of 3909 psi corresponding to 3PNO is used as the minimum burst pressure requirement for satisfaction of the structural integrity performance criteria. There are no non-pressure loads conditions applicable to CPNPP2 for the expected existing and potential degradation mechanisms. This performance criteria differential pressure is consistent with the value from 2RF17 and bounds the value from 2RF16.

The applied steam pressure values are considered to be conservative since they do not account for steam line losses between the SGs and the steam pressure measurement point nor does it consider pressure drops within the SGs that result from steam flow through components such as the primary and secondary moisture separators.

Degradation specific structural limits (SL) and condition monitoring (CM) limits were determined in accordance with recommended industry guidance provided in References 3 and 4. The structural limits are derived from the burst pressure equations provided in Reference 4 for the applicable degradation mechanism and includes the burst relation and material strength uncertainties at 0.95 probability and 50% confidence (95/50). The condition monitoring limit is also derived from the Reference 4 burst pressure equations and includes the 95/50 uncertainties for burst relation, material strength and non-destructive examination (NDE) flaw sizing.

Therefore, the NDE measured flaw size can be compared directly to the condition monitoring limit.

Table 1-1 provides the structural and condition monitoring limits for volumetric degradation mechanisms. These values were most recently calculated in the CPNPP Unit 2 Degradation Assessment (Reference 19).

Demonstration of the structural integrity and leakage performance criteria for cracking mechanisms are based on satisfaction of the minimum burst pressure requirement associated with 3PNO and the ligament tearing pressure at steam line break conditions (2560 psi). When fully probabilistic methods are used for Operational Assessment, the probability of burst (POB) and probability of leakage (POL) each must be satisfied at 5% or less.

SG-CDMP-20-13 Revision 0 Page 10 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 12 of 57 Westinghouse Non-Proprietary Class 3 Table 1-1. Structural and Condition Monitoring Limits for Volumetric Flaws Axial SL Degradation Burst Equation Extent CM Depth Depth(1)

Mechanism Model (inch) (%TW)

(%TW)

AVB Wear Axial Thinning(2) 0.5 69.4 66.8 Wear at Broached TSP Axial Thinning(2) 1.125 63.7 54.3 Wear at Preheater Axial Thinning(2) 0.75 65.9 56.8 Baffle Plates Uniform Thinning 0.75 63.6 54.3 0.25 79.6 66.2 Volumetric Indication / 0.5 69.4 55.8 Axial Thinning(2)

Foreign Object Wear 1.0 64.3 50.5 1.5 62.6 48.7 (1) Structural Limit includes burst relation and material strength uncertainties at 0.95 probability and 50% confidence.

(2) Axial thinning model applies to flaws of limited axial extent and circumferential extents less than 135 degrees.

1.3.2 Operational Primary-to-Secondary Leakage Performance Criteria The operational leakage performance criterion from plant Technical Specifications (Reference 18) is as follows:

The RCS operational primary-to-secondary leakage through any one steam generator shall be limited to 150 gallons per day (gpd).

1.3.3 Accident Induced Leakage Performance Criteria (AILPC)

The accident-induced leakage performance criterion (AILPC) from the Reference 1 guideline is as follows:

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 SGs and leakage rate for an individual steam generator. Leakage is not to exceed 1 gpm per steam generator, except for specific types of degradation at specific locations when implementing alternate repair criteria as documented in the Steam Generator Program technical specifications.

For Comanche Peak Unit 2, the leakage limit during a steam line break (limiting accident condition) is 0.3472 gpmRT (room temperature) in the affected SG. Since this is more limiting than the value of 1 gpmRT, the plant-specific value shall be used as the allowable. The flow rate, pressure, and temperature conditions used in the determination of the accident induced leakage rate shall be consistent with those assumed in the accident analysis of the plant. Observed and potential flaws will be evaluated for their leakage potential with depths and lengths adjusted to 95% probability with 50% confidence, using the methods provided in the SG Integrity Assessment Guidelines (Reference 3).

SG-CDMP-20-13 Revision 0 Page 11 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 13 of 57 Westinghouse Non-Proprietary Class 3 1.3.4 H* Alternate Repair Criteria Considerations CPNPP Unit 2 has implemented an alternate repair criteria (ARC) to address flaws within the hydraulically expanded portion of the tubesheet, referred to as H*. The Comanche Peak Unit 2 permanent H* ARC license amendment was approved by the NRC in 2012 (Reference 17) and first implemented during the CPNPP 2RF14 steam generator inspection in 2014. H* is the minimum engagement distance of the tubesheet hydraulic expansion between the tube and tubesheet. The H* distance ensures the structural and leakage integrity of the tube-to-tubesheet joints. The approved H* license amendment excludes the portions of tubing below the H* distance from inspection and plugging requirements on the basis that flaws below the H* distance are not detrimental to the structural and leakage integrity of the tube-to-tubesheet joints. The H* distance for CPNPP Unit 2 is 14.01 inches measured downward from the top of the tubesheet.

The permanent ARC defines a length of tube that assures structural and leakage integrity. Tube burst cannot occur due to the constraint provided by the tubesheet. Although the leakage from cracks below the H* distance must be considered. A factor of 3.16 will be applied to the portion of observed normal operating leakage that cannot be associated with degradation mechanisms outside the tubesheet expansion region to calculate the accident induced leakage from within the tubesheet region. The resulting calculated accident induced leakage will be added to the predicted leakage from other degradation mechanisms that have been detected and that have the potential to result in accident induced leakage for evaluation against the accident induced leakage performance criteria.

With NRC approval of the H* alternate repair criteria (Reference 17), Luminant made a commitment to the NRC to address leakage through the tubesheet joint during OA evaluations.

Specifically, the commitment is as follows:

For the operational assessment (OA), the difference between the allowed accident induced leakage from sources other than the tubesheet expansion region will be divided by 3.16 and compared to the observed operational leakage. An Administrative limit will be established to not exceed the calculated value.

The value 3.16 is the H* leak rate factor that is used to convert operational leakage from the tubesheet below the H* distance to accident induced leakage at steam line break conditions.

The total accident induced leakage includes predicted leakage from all sources, including tubesheet leakage from the tubesheet region. The total accident induced leakage must not exceed the steam line break leakage limit of 0.3472 gpmRT as specified in the plant licensing basis. The accident induced leakage from the tubesheet region is the operational leakage increased by a factor of 3.16.

The calculation described in the above commitment determines whether an administrative operational leakage limit is necessary to ensure that the total calculated accident induced leakage does not exceed the 0.3472 gpmRT limit when considering leakage from the tubesheet below the H* distance.

SG-CDMP-20-13 Revision 0 Page 12 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 14 of 57 Westinghouse Non-Proprietary Class 3 2 Steam Generator Outage Summary 2.1 Sequential Inspection Periods The SG Integrity Assessment Guidelines (Reference 3), SG Examination Guidelines (Reference 2) and plant Technical Specifications (Reference 18) provide guidance on inspection scope and sequential periods. The inspection scope depends on the sequential inspection period and the operating history of the SGs. The first sequential period of 120 effective full power months (EFPM) in length ended during plant operation in Fuel Cycle 9. The final SG inspection during the first sequential period was during 2RF08. The final SG inspections of the second sequential inspection period were during 2RF14. The SGs were not inspected during 2RF09, 2RF11, and 2RF13, all of which were in the second sequential inspection period. The first inspection of the third sequential period was during 2RF16.

The plant Technical Specifications have been updated to incorporate the generic Technical Specification change known as TSTF-510 (Reference 20). This change redefines the durations of the second and subsequent sequential inspection periods as 96 and 72 EFPM, respectively.

Table 2-1 lists the recent history of SG primary inspections and the plans for the upcoming inspections. It also lists the cycle lengths and cumulative EFPMs in the inspection periods. Outage 2RF18 was intended to be the third and final inspection of the third sequential inspection period.

Luminant is submitting a License Amendment Request to request a one-time Technical Specification change to extend the third sequential inspection period by 18 EFPM to include 2RF19. This would permit CPNPP Unit 2 to defer SG inspections from 2RF18 to 2RF19 and still meet the Technical Specification requirement to inspect 100% of the tubes within each sequential inspection period. Should the 2RF18 SG inspections be deferred to 2RF19, CPNPP Unit 2 intends to implement a 100% bobbin and tubesheet inspection scope during 2RF19.

The overall SG inspection plan for CPNPP Unit 2 was altered by the identification of circumferential primary water stress corrosion cracking (PWSCC) during the 2RF16 outage. As a result, +POINT'1 probe inspection of the hot leg (HL) top of tubesheet (TTS) was performed during 2RF17 per Technical Specification requirements. Originally, SG inspections were not intended to be performed at CPNPP Unit 2 during 2RF17.

Table 2-2 provides the historical inspection scopes for secondary side components including steam drum components (i.e., primary/secondary moisture separators and internal subcomponents),

preheater waterbox components and its subcomponents, and sludge lancing history. Should the 2RF18 SG inspections be deferred to 2RF19, the 2RF18 planned secondary side activities would be performed in 2RF19.

1

+POINT is a trademark or registered trademark of Zetec, Inc. Other names may be trademarks of their respective owners.

SG-CDMP-20-13 Revision 0 Page 13 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 15 of 57 Westinghouse Non-Proprietary Class 3 2.2 2RF17 Inspection Plan and Results 2.2.1 2RF17 Inspection Plan The 2RF17 inspection plan satisfied the requirements of both the Technical Specifications and the Electric Power Research Institute (EPRI) Nondestructive Examination (NDE) Guidelines (Reference 2). The primary inspection scope is summarized in Table 2-1. Inspections were limited to tubesheet examinations via +POINT probe due to the detection of circumferential PWSCC during 2RF16. No bobbin inspections were performed during 2RF17. No expansion to the base scope was implemented during 2RF17. Secondary side inspection activities included steam drum inspections.

2.2.2 2RF17 Inspection Results The total number of indications by type and outage at CPNPP Unit 2 are summarized in Table 2-3. No bobbin inspections were performed during 2RF17, and therefore no new tube wear at support structures was detected. The tubesheet inspection program did not detect any new SCC indications.

Tube slippage monitoring is required to support implementation of the H* alternate repair criteria and is performed through the course of routine bobbin coil inspections as planned by the SG program. Bobbin coil inspections were not planned and performed during 2RF17, and therefore full slippage monitoring was not performed. However, the hot leg top of tubesheet +POINT probe inspections can detect if tube slippage has occurred. Tube slippage was not reported during the

+POINT probe inspection programs during 2RF17.

2.2.3 Secondary Side Inspection and Maintenance The SG secondary side maintenance activities performed during 2RF17 included top-down visual inspection of all four upper steam drum regions, including the primary and secondary moisture separator components, swirl vanes, tangential nozzles, riser barrels, downcomer barrels, auxiliary feedwater nozzle, and general area. Small amounts of incipient erosion were observed in various components. However, this amount of degradation is judged to be quite small in comparison to the expected structural margin of the component and is consistent with the condition found during the previous inspections in 2RF08.

Tubesheet sludge lancing and FOSAR were not performed during 2RF17. Foreign objects that remained in the SGs at the conclusion of the 2RF16 outage were either assessed at that time to remain in the SG for 2 cycles or were re-assessed at 2RF17 to remain in the SG to 2RF18. Section 4.5 describes the extension of these evaluations until 2RF19.

2.3 2RF16 Inspection Plan and Results 2.3.1 Base Scope Inspection SG-CDMP-20-13 Revision 0 Page 14 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 16 of 57 Westinghouse Non-Proprietary Class 3 The 2RF16 inspection plan satisfied the requirements of both the Technical Specifications and the Electric Power Research Institute (EPRI) Nondestructive Examination (NDE) Guidelines (Reference 2). The inspections followed the standard inspection strategy implemented at CPNPP Unit 2 which include 50% full length bobbin and 50% inspection of the top of tubesheet. Further details on the primary inspection plan by outage can be seen in Table 2-1. The secondary side inspection scope is summarized in Table 2-2.

2.3.2 Inspection Expansion Circumferential PWSCC indications were reported in SG 2-03 during 2RF16. This is a new degradation mechanism for the Comanche Peak Unit 2 SGs. This occurred in three separate tubes in SG 2-03 at or below the top of the tubesheet (TTS). Therefore, in accordance with Reference 3 inspection expansion requirements and to support the SG tube integrity assessments, CPNPP Unit 2 completed the following expansions of the base inspection during 2RF16:

100% +POINT probe inspection of HL TTS from +3.00/-15.00 inches in SG 2-03 100% +POINT probe inspection of all known BLG/OXP locations in SGs 2-01, 2-02 and 2-04

+POINT probe inspection of HL TTS from 3.00/-15.00 for all tubes which have not been tested in either 2RF14 or 2RF16. This will achieve 100% coverage of +POINT probe inspection on the HL TTS in the last three (3) sequential outages for SGs 2-01, 2-02, and 2-04.

2.3.3 Inspection Results The indications by type and outage at CPNPP Unit 2 are summarized in Table 2-3.

There were 331 AVB wear indications detected. The largest of these flaws returned to service was 39%TW. No tubes were plugged because of AVB wear.

There were 4 TSP/PBP wear indications detected. The largest of these flaws returned to service was 16%TW. No tubes were plugged because of TSP/PBP wear.

There were 12 foreign object wear indications detected. The largest of these flaws returned to service was 28%TW. No tubes were plugged because of foreign object wear.

Four indications in three tubes of circumferential PWSCC were detected during +POINT probe inspections of the tubesheet. Three of these were at identified BLG/OXP locations within the tubesheet, and one was at an expansion transition. The largest of these flaws had a maximum depth of 69%TW and a circumferential length of 60 degrees. All three tubes were plugged and stabilized as stress corrosion cracking (SCC) indications are plugged on detection per plant Technical Specifications.

Tubesheet slippage monitoring was performed during 2RF16 as required by the implementation of the H* alternate repair criteria using automated analysis of the eddy current data. The results were spot-checked by eddy current analysts. No slippage was detected in any of the tubes inspected.

SG-CDMP-20-13 Revision 0 Page 15 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 17 of 57 Westinghouse Non-Proprietary Class 3 2.3.4 Secondary Side Inspection and Maintenance SG secondary side maintenance activities were performed during 2RF16 that included tubesheet sludge lancing, tubesheet and upper tube bundle visual inspections and FOSAR. The secondary side inspections were performed in all four SGs. Additionally, all SG waterboxes and Baffle Plate B were inspected and showed no evidence of erosion-corrosion. Baffle Plate B scope was limited in SG 2 & 3 compared to SG 1 & 4.

A total of 13.0 pounds of sludge was removed from the four SGs by sludge lancing during 2RF16.

Taking into account that in 2RF14 processes removed a large amount of deposits, the decrease from the 2RF14 amount is reasonable and is consistent with the prior history of sludge removal from CPNPP Unit 2. The sludge removal history is summarized in Table 2-5.

During 2RF16, all PLPs reported from eddy current inspection were reviewed by FOSAR, if possible. Areas of the tube bundle accessible for retrieval include the top of the tubesheet and a large portion of the area over PBP-B. FOSAR was conducted for all accessible PLPs located in these areas. The video inspection also resulted in the identification of parts located on the tubesheet and on PBP-B. The parts judged to have possibly caused tube wear (based on size and location) were identified and eddy current inspection of the potentially affected tubes was conducted. All objects removed from the SGs were reviewed to see if any visible wear could be seen. None of the objects had any visible signs of wear.

2.4 Tube Repair Summary A total of three tubes were plugged during 2RF16, all three in SG 3. All three tubes required plugging due to circumferential PWSCC indications. These three tubes also required stabilization.

No tubes were plugged during 2RF17.

Table 2-4 summarizes the list of tubes plugged in each SG and the cause of plugging. As shown in the table, the cumulative total number of tubes plugged in all SGs is 96, which is equal to 0.53%

of the total number of tubes.

2.5 Channel Head Indications During the SG channel head bowl video scan in 2RF14, a discoloration was observed in the cladding of SG 1. The discoloration was apparently caused by a flaw in the cladding which was located in the vicinity of the joint between the channel head shell and the tubesheet near the peripheral tube in Row 36 Column 100 on the cold leg side. It was determined that there was a breach in the cladding at this location and that the discoloration resulted from oxidation of the carbon steel base metal surface behind the cladding. The reported flaw was estimated, by review of the images taken of the flaw, to be approximately 5/8-inch long and approximately half as wide.

This anomaly was re-inspected during 2RF16 and 2RF17 and estimated to be the same size as in 2RF14. Figure 2-1 provides images of the inspection results for each of these three inspections.

In 2RF16 a discoloration in SG 2 hot leg was seen near the tube-to-tubesheet weld of R1-C109.

The discoloration appeared to have been apparently caused by a small breech in the tubesheet cladding causing oxidation of the carbon steel base metal. This anomaly was not visible upon SG-CDMP-20-13 Revision 0 Page 16 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 18 of 57 Westinghouse Non-Proprietary Class 3 review of the primary channel head visual inspection. A re-inspection of this anomaly was performed during 2RF17 and showed no apparent change in size or character. Figure 2-2 provides images of the inspection result for 2RF16 and 2RF17.

2.6 Tube Plug Visual Examinations During both 2RF16 and 2RF17 SG inspections, visual examinations were performed on previously installed tube plugs in accordance with the requirements in Section 6.10 of the EPRI SG Examinations Guidelines (Reference 2). No anomalous conditions, such as plug degradation or leakage, were reported from the examinations.

SG-CDMP-20-13 Revision 0 Page 17 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation)

Attachment 2 to TXX-20025 Page 19 of 57 Westinghouse Non-Proprietary Class 3 Table 2-1. CPNPP Unit 2 SG Sequential Inspection Periods, Primary Side Inspection History & Plan Outage 2RF08 2RF09 2RF10 2RF11 2RF12 2RF13 2RF14 2RF15 2RF16 2RF17 2RF18(3) 2RF19(3)

Oct-Date Apr-05 Apr-08 Oct-09 Apr-11 Oct-12 Apr-14 Oct-15 Apr-17 Dec-18 Apr-20 Oct-21 06 History vs. Plan History Plan SG Cumulative EFPY 10.21 11.64 13.04 14.5 15.91 17.33 18.71 20.14 21.52 22.86 24.10 25.55 Cycle EFPM 16.56 17.21 16.86 17.5 16.89 17.03 16.55 17.16 16.54 16.14 14.88 17.4 Cumulative EFPM (for 111.56 8.77 25.63 43.13 60.02 77.05 93.59 17.16 33.7 49.84 64.72 17.4 Period)

Sequential Inspection First Fourth Period of 120, 90, 72, Second Period Third Seq. Insp. Period of 72 EFPM Period Period 72, 72, .. EFPM 100 % of Tubes over the inspection 100%/p Required Scope 50% 50% within 45 EFPM(1) Remaining 50%(1) period eriod Bobbin Full Length 55% 55% 55% 34% 50% NA 55%

No Eddy Current Inspection Performed No Eddy Current Inspection Performed No Eddy Current Inspection Performed

+Point Inspection of 50% 50% 50% 34% 50% NA 50%

No Eddy Current Inspection Row 1-2 U-bend 100%

+Point Inspection at (2) (SG 3) 50% 50% 50% 33% 100% 100%

HL Top of Tubesheet 50% No EC (others) Insp Performed

+Point Inspection of (skip) 50% 50% 50% 50% 50% NA 50%

Dings/Dents > 5 Volts

+Point Inspection of 50% 50% 50% 50% 50% NA 50%

Exp. Tubes at Baffle D

+Point Inspection of 50% 50% 50% 100% 100% NA 100%

Exp. Tubes at Baffle B (1) Based on the implementation of Technical Specifications in place prior to the license approval of TSTF 510.

(2) 2RF16 Scope expansion based on circumferential PWSCC: 100% +POINT probe inspection of HL TTS in SG 3, 100% +POINT probe inspection of all known BLG/OXP locations in SG 1, SG 2 and SG 4, and +POINT probe inspection of HL TTS for all tubes that were not inspected in either 2RF14 or 2RF16. This achieved 100% coverage of +POINT probe inspection on the HL TTS in three (3) sequential outages for SG 1, SG 2, and SG 4.

(3) Planned activities are shown. Should 2RF18 SG inspections be deferred, Comanche Peak intends to implement a 100% bobbin and tubesheet inspection scope during 2RF19.

SG-CDMP-20-13 Revision 0 Page 18 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 20 of 57 Westinghouse Non-Proprietary Class 3 Table 2-2. Historical Secondary Side Visual Inspections - Comanche Peak Unit 2 SG 2RF12 2RF13 2RF14 2RF15 2RF16 2RF17 2RF18(2) 1 -- -- -- -- -- X --

Steam Drum 2 -- -- -- -- -- X --

Inspection(1) 3 -- -- -- -- -- X --

4 -- -- -- -- -- X --

1 -- -- -- -- X -- X 2 -- -- X -- X(3) -- X Preheater/Waterbox 3 -- -- -- -- X(3) -- X 4 X -- -- -- X -- X 1 -- -- -- -- X -- --

2 -- -- X -- -- -- --

Upper Bundle TSP 3 -- -- -- -- -- -- X 4 X -- -- -- -- -- --

Sludge Lance/FOSAR 1/2/3/4 X -- X -- X -- X (1) Steam drum inspections were performed in 2RF08 and 2RF17.

(2) Planned activities during 2RF18 are shown. Should 2RF18 inspections be deferred, these inspection activities would be performed during 2RF19.

(3) Preheater Baffle Plate B inspections on SG 2 & 3 were reduced scope compared to SG 1 & 4 Table 2-3: Summary of Indication History AVB TSP FO Wear Wear Wear PWSCC 2RF12 286 2 8 0 2RF14 329 3 12 0 2RF16 331 4 10 3 (1) (1) 2RF17 - - 12 0 (1) No inspections performed for this mechanism SG-CDMP-20-13 Revision 0 Page 19 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 21 of 57 Westinghouse Non-Proprietary Class 3 Table 2-4. History of SG Tube Plugging in CPNPP Unit 2 through 2RF16 SG SG SG SG Outage Date EFPY Total Percent 2-01 2-02 2-03 2-04 Pre- Pre-0.000 5 3 3 9 20 0.11%

Service Service 2RF01 Nov-94 0.910 0 0 0 0 0 0.00%

2RF02 Mar-96 2.090 0 0 0 0 0 0.00%

2RF03 Nov-97 3.489 3 5 0 0 8 0.04%

2RF04 Apr-99 4.706 1 0 0 4 5 0.03%

2RF05 Oct-00 6.138 3 0 0 1 4 0.02%

2RF06 Apr-02 7.520 0 4 7 0 11 0.06%

2RF07 Oct-03 8.825 3 0 0 1 4 0.02%

2RF08 Apr-05 10.205 5 2 4 2 13 0.07%

2RF09 Oct-06 11.639 No SG Inspection 0 0.00%

2RF10 Apr-08 13.044 1 7 3 2 13 0.07%

2RF11 Oct-09 14.502 No SG Inspection 0 0.00%

2RF12 Apr-11 15.910 0 2 1 0 3 0.02%

2RF13 Oct-12 17.329 No SG Inspection 0 0.00%

2RF14 Apr-14 18.709 2 10 0 0 12 0.07%

2RF15 Oct-15 20.139 No SG Inspection 0 0.00%

2RF16 Apr-17 21.509 0 0 3 0 3 0.02%

2RF17 Dec-18 22.862 0 0 0 0 0 0.00%

Total 23 33 21 19 96 0.53%

Percent 0.50% 0.72% 0.46% 0.42% 0.53%

SG-CDMP-20-13 Revision 0 Page 20 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 22 of 57 Westinghouse Non-Proprietary Class 3 Table 2-5. History of Sludge Removal from CPNPP Unit 2 SGs Comanche Peak Unit 2 - Pounds of Sludge Removed SG SG SG SG Outage Method Total 2-01 2-02 2-03 2-04 2RF01 SL 2.5 3.0 3.0 3.0 11.5 2RF02 No Sludge Lancing Performed 2RF03 SL 3.7 4 4.5 6 18.2 2RF04 SL 3 4 3 3 13 2RF05 SL 5.5 3.5 5.5 3.5 18 2RF06 SL 4 6 3 2 15 2RF07 No Sludge Lancing Performed 2RF08 SL 10 8 7.5 9 34.5 2RF09 No Sludge Lancing Performed 2RF10 SL 8.3 6.8 9.3 6.5 30.9 2RF11 No Sludge Lancing Performed 2RF12 SL 6.5 6.5 9.5 6.5 29 2RF13 No Sludge Lancing Performed 2RF14 SL* 2.8 2.8 2.8 2.8 11.2 2RF14 SL 13 16 18 20.5 67.5 2RF15 No Sludge Lancing Performed 2RF16 SL 3.5 2.5 2.5 4.5 13.0 2RF17 No Sludge Lancing Performed Total 62.8 63.1 68.6 67.3 261.8 Key: SL = Sludge Lancing Note: SL* - Sludge Lancing in 2RF14 was performed once before ASCA and CODE cleaning, then again following the cleaning.

SG-CDMP-20-13 Revision 0 Page 21 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 23 of 57 Westinghouse Non-Proprietary Class 3 2RF14 2RF16 2RF17 Figure 2-1. SG 2-01 Cold Leg Channel Head Cladding Anomaly Historical Inspection Results 2RF16 2RF17 Figure 2-2. SG 2-02 Hot Leg Channel Head Cladding Anomaly Near Tube R1-C109 Inspection Results SG-CDMP-20-13 Revision 0 Page 22 of 56
      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 24 of 57 Westinghouse Non-Proprietary Class 3 3 Condition Monitoring Condition Monitoring is the evaluation of the steam generators with respect to meeting the performance criteria for structural integrity, operating leakage and accident condition leakage prior to the current shut down, in light of the inspection results. This is a summary of the two previous SG inspections, 2RF16 and 2RF17, and does not change any CM conclusions. This section is provided to summarize the prior CM evaluations and to demonstrate that CM has been met by standard methods for all indications detected during recent inspections for CPNPP Unit 2. It was demonstrated at the 2RF16 and 2RF17 outages that in each case the prior OA methodologies provided conservative results with respect to the detected degradation.

3.1 Existing Degradation Mechanisms The tube existing degradation mechanisms in the Comanche Peak Unit 2 SGs reported through 2RF17 include:

Wear at AVB supports Wear at Preheater Baffle Plates Wear at Quatrefoil Tube Support Plates Wear due to foreign objects Circumferential PWSCC at bulges/overexpansions with the hot leg tubesheet Circumferential PWSCC at hot leg tubesheet expansion transitions The following sections provide the CM assessment for the existing degradation mechanisms reported during the prior and current inspection outages.

3.1.1 Tube Wear at AVBs AVB wear has been reported at Comanche Peak Unit 2 SGs in prior inspections. A total of 331 AVB wear indications were reported in the SGs during 2RF16. The scope of 2RF17 SG eddy current testing did not include bobbin testing, so there was no reported AVB wear. Table 3-1 provides a summary of the AVB wear indications reported in each SG during prior inspections.

No tubes were plugged due to AVB wear during the prior 2RF16 outage. The maximum depth of all AVB wear indications reported during 2RF16 was 39% TW. The CM limit for this degradation mechanism at 2RF16 was 67% TW per the 2RF16 180 day report (Reference 5). Therefore, the SG performance criteria for structural and leakage integrity were demonstrated.

SG-CDMP-20-13 Revision 0 Page 23 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 25 of 57 Westinghouse Non-Proprietary Class 3 Table 3-1. Historical AVB Wear at CPNPP Unit 2 All 4 SGs 2RF10 2RF12 2RF14 2RF16 Total No. Ind 274 286 329 331

<20% TW 182 206 230 240 20-29% TW 75 63 80 78 30-39% TW 17 15 18 13

>=40% TW 0 2 1 0 Maximum %TW 34 44 40 39 Average %TW 18.0 17.4 16.9 16.1 Depth Growth per EFPY Maximum - 6.62 7.15 2.14 Average - -0.16 0.295 -0.18 95th Percentile - 1.3 2.16 0.95 3.1.2 Tube Wear at Tube Support Plates During 2RF16 four wear indications were reported: three at preheater baffle plate supports, and one newly discovered indication in a quatrefoil tube support plate. Table 3-2 provides a listing of preheater baffle plate and quatrefoil TSP wear indications reported through 2RF16. The largest indication reported during the prior 2RF16 inspection was 16% TW for the quatrefoil TSP and 7%

for the PBP. The CM limit for tube wear at support structures at 2RF16 was 51% per the 2RF16 180 day report (Reference 5). Therefore, the SG performance criteria for structural and leakage integrity were demonstrated.

Table 3-2. Summary of Tube Support Plate Wear Indications in 2RF16 2RF12 2RF14 2RF16 Inch1 Depth Depth Depth Support Plate SG Row Col Locn. (in) Volts (% TW) (% TW) (% TW) Type Preheater 2-01(1) 48(1) 38(1) C2 0.4 0.30 -- 4 6 Baffle(1) 2-01 49 56 C5 -0.4 0.18 7 3 4 Preheater Baffle 2-01 49 67 C7 0.41 0.54 -- -- 16 Quatrefoil TSP 2-03 45 55 C2 0.06 0.33 6 7 7 Preheater Baffle (1) This indication was listed as foreign object wear in 2RF14 and 2RF16 tube integrity reports. It was recharacterized and sized as a PBP wear indication.

3.1.3 Tube Wear Due to Foreign Objects For the remaining foreign object wear indications in Table 3-3 that were not inspected during 2RF17, no foreign objects remain adjacent to the affected tube locations, thereby removing the condition for continued wear progression. The largest of these flaw indications left in service during the prior 2RF16 inspection was 28% TW. This is less than the 55% TW CM limit for SG-CDMP-20-13 Revision 0 Page 24 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 26 of 57 Westinghouse Non-Proprietary Class 3 foreign object wear bound by an axial length of 0.3 inch per the 2RF16 180 day report (Reference 5). NDE measurement uncertainties used in calculating this limit are associated with the ETSS 21998.1 +POINT probe sizing technique. Therefore, the SG performance criteria for structural and leakage integrity were demonstrated.

Table 3-3. Summary of Foreign Object Wear Indications Reported in 2RF16 and 2RF17 2RF14 2RF16 2RF17 Axial TSP Circ SG OUTAGE Row Col Volts Ind Inch Depth Depth Depth Length Locn Extent

(%TW) (%TW) (%TW) (inch)

(inch) 2-01 2RF16 48 38 0.3 PCT C2 0 4(1) 6(1) - - -

2-02 2RF16 3 114 0.26 PCT C4 0.4 24 24 - 0.21 0.44 2-02 2RF16 4 114 0.17 PCT C4 0.42 17 17 - 0.17 0.46 2-02 2RF16 6 1 0.17 PCT C1 0.51 17 17 - 0.18 0.41 2-02 2RF16 6 2 0.33 PCT C1 0.49 28 28 - 0.21 0.44 2-02 2RF16 6 2 0.16 PCT C1 0.87 16 16 - 0.21 0.40 2-03 2RF16 21 50 0.11 PCT C2 0.66 -- 12 - 0.18 0.37 2-04 2RF16 26 69 0.17 PCT C2 1.29 19 18 - 0.33 0.42 2-04 2RF16 32 71 0.27 PCT C2 0.64 25 25 - 0.22 0.38 2-04 2RF16 34 77 0.15 PCT C2 0.53 16 17 - 0.29 0.40 2-04 2RF17 12 91 0.09 PCT C6 0.50 -- --(3) 6(2) 0.21 0.46 (2) (2) (2) 2-04 2RF17 13 92 0.40 PCT C6 0.42 7 14 17 0.32 0.56 (1) This was listed as foreign object wear in 2RF14 and 2RF16 tube integrity reports. This indication is a PBP wear indication and historically has been correctly sized as a PBP wear indication.

(2) Depth sizing of indication is based on ETSS 96911.1.

(3) No degradation was reported during 2RF16. Historical data review in 2RF17 showed a precursor signal present at 2RF16 with little to no change.

3.1.4 Circumferential PWSCC within Tubesheet and at Expansion Transitions Circumferential PWSCC was first detected at CPNPP Unit 2 during 2RF16. Four indications of circumferential PWSCC were found in three tubes during the 2RF16 inspection. Three indications were found within the hot leg tubesheet below the top of tubesheet at identified BLG/OXP locations. One indication was found within the top of the hot leg tubesheet expansion transition.

All of the indications were located within SG 2-03. Table 3-4 provides the location and sizing information related to each flaw detected during the prior 2RF16 inspection.

As a result of the 2RF16 inspection findings for circumferential PWSCC at hot leg tubesheet locations, inspections for this degradation mechanism were required to be performed during 2RF17. No indications of circumferential PWSCC were reported during the 2RF17 inspections.

SG-CDMP-20-13 Revision 0 Page 25 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 27 of 57 Westinghouse Non-Proprietary Class 3 Table 3-4. Summary of Historical Circumferential PWSCC Axial Circ.

Inch1 Depth PDA SG Row Col Ind. Volts Location Extent Extent (in) (%TW) (%)

(in) (deg) 2RF16 Inspection Results 2-03 5 79 SCI 0.71 TSH -1.11 48 0.29 31 4.1 2-03 48 86 SCI 0.55 TSH 0 69 0.22 60 11.5 SCI 0.92 TSH -2.03 46 0.26 32 4.1 2-03 1 94 SCI 0.80 TSH -2.02 43 0.22 35 4.2 2RF17 Inspection Results No circumferential PWSCC indications reported during 2RF17.

Flaw profiling was not required to demonstrate CM for the PWSCC indications detected during 2RF16. The PDA values reported in Table 3-4 are based on the simple PDA (i.e., maximum depth applied to the entire circumferential extent of the flaw) which is very conservative. Still the simple PDA for the detected flaws easily meet the CM criteria of a critical PDA of 74.2 or circumferential length of 267 degrees.

3.2 Channel Head Indications A channel head cladding anomaly has been reported within SG 2-01 and within SG 2-02, as discussed in Section 2.5. Images from the 2RF17 visual inspection and historical visual inspections of these flaws are shown in Figure 2-1 and Figure 2-2.

The cladding anomaly contained in the cold leg of SG 2-01 was previously estimated to be approximately 5/8-inch in length and half as wide. Evidence of this cladding anomaly has been present as early as 2003. It is evident through comparison of the images shown in Figure 2-1 that there has been no apparent change in the anomaly character from 2RF14 through 2RF17.

Therefore, the conclusion of the engineering evaluation performed in previous assessments (Reference 9 and Reference 10) remains valid and applicable to the condition found in 2RF17.

There is significant margin between the estimated flaw depth and the American Society of Mechanical Engineers (ASME) Code allowable and no repairs were required.

Figure 2-2 provides the 2RF17 and 2RF16 visual inspection images of the tubesheet cladding anomaly near Tube R1C109 in SG 2-02 hot leg. This shows a small pit-like anomaly that is approximately 1/16-inch in diameter. Comparison of the 2RF16 and 2RF17 visual inspection results shows no apparent change in the character of the anomaly. The flaw is shallow and smaller than the larger SG 2-01 anomaly, and therefore is enveloped by the conclusion to be acceptable with significant margin.

SG-CDMP-20-13 Revision 0 Page 26 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 28 of 57 Westinghouse Non-Proprietary Class 3 3.3 Tube Plug Visual Examinations During both 2RF16 and 2RF17 SG inspections, visual examinations were performed on previously installed tube plugs in accordance with the requirements in Section 6.10 of the EPRI SG Examinations Guidelines (Reference 2). No anomalous conditions, such as plug degradation or leakage, were reported from the examinations.

The tube plug visual examinations shall be conducted again during the next time SG inspections are performed. Should the 2RF18 inspections be deferred, then these visual examinations would next occur during 2RF19.

3.4 Secondary Side Integrity Secondary side maintenance performed during 2RF16 included sludge lancing, tubesheet and upper tube bundle visual inspections and FOSAR. There was no sludge lancing, FOSAR, and upper tube bundle inspection activities performed during 2RF17. There were no anomalies or degradation of secondary side components reported in the secondary side SG inspections.

The 2RF16 FOSAR operation was performed over the tubesheet and over Preheater Baffle Plate B. All of the PLP indications reported in the eddy current inspection over the tubesheet and Preheater Baffle Plate B were subjected to FOSAR with the exception of the areas of Preheater Baffle Plate B that are not accessible by FOSAR. Objects identified during the visual inspection were retrieved where possible.

Upper steam drum visual inspections were performed in all four SGs during 2RF17. Components inspected included all accessible steam drum components such as primary and secondary moisture separator components, drains, steam vents, deck plates, support gussets, shell, and auxiliary nozzle.

The steam drum inspections did not find any indications of rapidly progressing erosion, cracking, material loss or other forms of degradation. Small amounts of incipient erosion were observed in various components. However, this amount of degradation is judged to be quite small in comparison to the expected structural margin of the component and is consistent with the condition found during the previous inspections in 2RF08.

As a result of the data obtained during the steam drum inspection, there were no immediate recommendations made regarding any actions that should be taken prior to restart of Comanche Peak Unit 2.

3.5 Condition Monitoring Conclusion The SG inspections performed during 2RF16 and 2RF17 were appropriate for detection of both existing and potential degradation mechanisms for CPNPP Unit 2. For detected degradation, all indications met the defined CM limits for the SG performance criteria demonstrating structural and leakage integrity over the past operating interval. Flaw profiling was not required for any indications detected during 2RF16 or 2RF17 to meet CM. No tubes required in situ pressure testing during 2RF16 or 2RF17 to meet CM.

SG-CDMP-20-13 Revision 0 Page 27 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 29 of 57 Westinghouse Non-Proprietary Class 3 During plant operation in Cycles 16, 17 and 18, no primary-to-secondary leakage was detected based on N-16 monitors, condenser off gas monitors, or grab sample measurements. This further confirms that leakage integrity was maintained during Cycles 16, 17 and 18.

SG-CDMP-20-13 Revision 0 Page 28 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 30 of 57 Westinghouse Non-Proprietary Class 3 4 Operational Assessment The Operational Assessment (OA) is the forward-looking evaluation to assess if the steam generators will meet the structural, operating leakage, and accident condition leakage performance criteria until the next scheduled inspection.

The fundamental objective of an OA is to ensure that the structural integrity performance criteria (SIPC) and accident induced leakage performance criteria (AILPC) for the SG tubing will be satisfied over the operating interval to the next SG inspection. The OA process involves projecting the condition of tubes that contain or potentially could contain degradation mechanisms that have been experienced within the SGs to the end of the next inspection interval. For degradation mechanisms that are repaired based on flaw sizing (i.e. wear mechanisms), the OA process involves projecting the largest flaw left in service to the end of the inspection interval. For repair on detection mechanisms, such as stress corrosion cracking (SCC), this involves the projection of undetected flaws that may be present but not identified by nondestructive examination (NDE) techniques. Both methods address tubes not inspected in the current inspection and flaws that may remain undetected. The SIPC and AILPC must be satisfied at a probability of 0.95 probability at 50% confidence (95/50). For fully probabilistic OA methods, the probability of burst (POB) and probability of leakage (POL) each must be 5% or less. The projected leakage at the most limiting accident conditions, typical steam line break (SLB) conditions, must be less than the leakage assumed in the plant accident analyses.

The OA for CPNPP Unit 2 uses both simplified and fully probabilistic methodologies. The methodologies follow the guidance of the EPRI SG Integrity Assessment Guidelines (Reference 3) and the EPRI Degradation Specific Management Flaw Handbook (Reference 4).

The simplified OA method involves a single tube analysis to provide a conservative estimate of the projected end-of-cycle (EOC) condition considering all uncertainties at 0.95 probability and 50% confidence. The applicable uncertainties are for burst relation, material strength, and NDE flaw sizing. The single tube methods are referred to as worst-case degraded tube methods as the most severely flawed tube is selected for evaluation. The worst-case degraded tube OA methods involve determining the most limiting flaw at the beginning-of- cycle (BOC) and applying conservative flaw growth over the intended inspection interval to arrive at the EOC flaw condition.

The simplified OA method is used for tube wear mechanisms, such as wear at support structures.

Burst pressures for wear mechanisms were derived from the calculational methodology of Reference 4. The Westinghouse proprietary Single Flaw Model computer code (Reference 14) was used to perform these calculations.

Fully probabilistic OA analysis methods model the entire tube bundle and a distribution of the flaw for a given degradation mechanism to determine a distribution of structural and leakage integrity parameters at the end of the inspection interval. The term full bundle analysis is often used to describe this method. The fully probabilistic analysis is considered to provide the most accurate and realistic projection of the SG condition to demonstrate satisfaction of the SIPC and AILPC.

In a fully probabilistic analysis, distributions defining the flaw size, growth rate, probability of detection (POD), burst relation, material property, uncertainties and other relevant inputs are randomly sampled for a simulation to determine burst and leakage parameters and each simulation SG-CDMP-20-13 Revision 0 Page 29 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 31 of 57 Westinghouse Non-Proprietary Class 3 is repeated many times to generate the EOC structural and leakage parameters for comparison to the SIPC and AILPC. The Westinghouse proprietary Full Bundle Model (FBM) computer code (Reference 15) was used to perform the fully probabilistic analyses.

The EPRI PWR SG Integrity Assessment Guidelines (Reference 3) classify degradation mechanisms as Existing and Potential. The interpretation of these categorizations is literal:

Existing degradation mechanisms are those that have been observed in the SGs, Potential degradation mechanisms are those that may be expected in the SGs based on industry operating experience or other (i.e., laboratory) experience.

The following sections will provide the OA of the existing and potential degradation mechanisms at CPNPP Unit 2 to demonstrate that there is sufficient margin against structural and leakage integrity limits for the steam generators to continue operation until 2RF19.

4.1 Existing Degradation Mechanisms 4.1.1 Tube Wear at AVBs During 2RF16, no tubes were plugged due to anti-vibration bar (AVB) wear. The number of AVB indications in all SGs was a total of 331, compared to 329 indications reported in 2RF14 and 286 reported in 2RF12 (Table 2-3). The maximum wear depth reported during the most recent inspection for AVB wear during 2RF16 was 39% TW.

Inspections for this degradation mechanism were not required during 2RF17. For existing AVB wear flaws, a three-cycle assessment was performed since all previously identified flaws were inspected during 2RF16 and will be inspected again in 2RF19. With the current sampling strategy for AVB wear, a small number of tubes with undetected flaws could grow for up to seven cycles between inspections (i.e., from 2RF12 to 2RF19) for a small number of tubes since the bobbin inspection scope for 2RF14 was limited to 34% of tubes and 50% at 2RF16.

The AVB wear growth distributions were re-assessed using the industry standard methodology of the Benards approximation method described in Reference 3. AVB wear data obtained during the 2RF10 through 2RF16 inspections were evaluated to develop the growth rate distributions over the last three inspection intervals. Figure 4-1 shows the resultant growth rate distribution. The 95th percentile of the growth rate curve that bounds the 2RF12, 2RF14 and 2RF16 growth data is 2.16% through-wall per effective full power years (TW/EFPY).

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      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 32 of 57 Westinghouse Non-Proprietary Class 3 Figure 4-1: CNPP Unit 2 AVB Wear Historical Growth Rate Distribution 4.1.1.1 Prediction of AVB Wear at 2RF19 The largest AVB wear flaw left in service during 2RF16 was 39% TW. The length of the largest indication left in service is assumed to be 0.5 inch based on the size of the AVBs. To predict the maximum wear depth at 2RF19 the following parameters were considered:

The estimated durations for inspection intervals are based on Table 2-1 cycle durations.

The 95th percentile growth rate for 2RF19 that bounds the 2RF12, 2RF14 and 2RF16 data is 2.16% TW/EFPY.

CPNPP Unit 2 tubing material properties from the EPRI Flaw Handbook (Reference 4) and NDE uncertainties from Examination Technique Specification Sheet (ETSS) 96004.3.

The maximum measured depth at 2RF19 is predicted deterministically and the burst pressure is determined by performing a statistical Monte Carlo simulation using the Westinghouse proprietary Single Flaw Model software (Reference 14) for the deterministically determined depth and maximum AVB wear length.

The 2RF19 flaw depth for the largest flaw returned to service (39% TW) can be calculated deterministically using NDE uncertainties from ETSS 96004.3 at 95% probability 50% confidence levels by applying the 95th percentile growth rate. The 1.12 factor accounts for the square root sum of squares (SRSS) of the technique standard error and the analyst error.

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      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 33 of 57 Westinghouse Non-Proprietary Class 3 219 0.97 39% 2.50% 1.645 3.10% 1.12 2.16% 4.3 55.3%

This result is a worst-case projected AVB wear flaw with a burst pressure of 5075 psi at 95%

probability and 50% confidence levels. These results compare favorably to the bounding 3PNO loading limit of 3909 psi for structural burst and the structural limit of 69.4% TW. For pressure-only loading of volumetric flaws, satisfaction of structural integrity implies satisfaction of leakage integrity at accident conditions since steam line break (SLB) accident condition pressure differential for pop-through is much smaller than 3PNO.

The largest undetected flaw depth was determined through a probability of detection (POD) curve generated from the industry recommended Model Assisted Probability of Detection (MAPOD) methodology (Reference 16). The noise-based POD curve was developed using the EPRI ETSS I96041.1 data set and the generic noise distribution provided in the ETSS. The noise distribution was the ETSS default noise distribution which is from a higher noise level plant. The resultant POD curve produced a 95th percentile value of 17% TW. Therefore, the maximum depth of an undetected flaw is assumed to be 17% TW.

Using the same growth rate to project the maximum undetected flaw size over 7 cycles results in a bounded depth of 38.4% at 2RF19. NDE uncertainty is not considered for undetected flaw projection since it is not a measured flaw.

219 17% 2.16% 9.9 38.4%

This result is a projected worst-case undetected AVB wear flaw with a burst pressure of 6438 psi at 95% probability and 50% confidence levels. These results compare favorably to the bounding 3PNO loading limit of 3909 psi for structural burst and the structural limit of 69.4% TW.

This OA evaluates the growth rate of AVB wear indications on a per EFPY basis, considers both detected and undetected flaws, and shows margin from the requirements for structural and leakage integrity over the upcoming inspection interval. Therefore, the OA projects that AVB wear degradation will not violate the SG tube integrity performance criteria if the next SG inspection is in 2RF19 with appropriate regulatory approval.

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      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 34 of 57 Westinghouse Non-Proprietary Class 3 4.1.2 Tube Wear at Tube Support Plates During 2RF16 four tube support wear indications were reported: three at preheater baffle plate supports, and one newly discovered indication in a quatrefoil tube support plate. The indications exhibit negligible growth rates, except for the indication which was discovered during 2RF16 and does not have historical flaw depths to compare. The maximum depth PBP indication is 7% TW and the tube support plate flaw depth is 16% TW.

Inspections for this degradation mechanism were not required during 2RF17. For existing TSP wear flaws, a three-cycle assessment is performed since all previously identified flaws were inspected during 2RF16 and will be inspected again in 2RF19. With the current sampling strategy for TSP wear, tubes with undetected flaws could grow for up to seven cycles between inspections (i.e., from 2RF12 to 2RF19) for a small number of tubes since the bobbin inspection scope for 2RF14 was limited to 34% of tubes and to 50% of tubes in 2RF16.

Since there are only four PBP and TSP wear indications reported through 2RF16 and these four indications have shown little to no growth, it is not possible to obtain reliable growth rates from site-specific data to support the OA. TSP wear growth from similar plants shows that using a PBP/TSP wear growth rate of 4.5% TW/EFPY is conservative since bounding growth rate for TSP and PBP wear from three other plants with Westinghouse Model D5 SGs selected for comparison was 4.38% TW/EFPY.

4.1.2.1 Prediction of PBP/FDB Wear at 2RF19 The maximum measured wear indication at a PBP that was left in service was 7% TW. The length of the largest indication left in service is assumed to be 0.75 inch, which is the bounding length based on the plate thickness. The wall thinning with limited axial extent (less than 135 degrees) is applied for PBP wear.

To predict the maximum wear depth at PBP intersections at 2RF19 the following parameters were considered:

The estimated durations for inspection intervals are based on Table 2-1 cycle durations.

The growth rate is conservatively assumed to be 4.5% TW/EFPY (see Section 4.1.2)

CPNPP Unit 2 tubing material properties from the EPRI Flaw Handbook (Reference 4) and NDE uncertainties from ETSS 96910.1.

The maximum measured depth at 2RF19 is predicted deterministically and the burst pressure is determined by performing a statistical Monte Carlo simulation using the Westinghouse proprietary Single Flaw Model software (Reference 14) for the deterministically determined depth and maximum PBP wear length.

The largest undetected flaw depth was determined through a POD curve generated from the industry recommended MAPOD methodology (Reference 16). The noise-based POD curve was developed using the EPRI ETSS I96042.1 data set and the generic noise distribution provided in the ETSS. The noise distribution was the ETSS default noise distribution which is from a higher SG-CDMP-20-13 Revision 0 Page 33 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 35 of 57 Westinghouse Non-Proprietary Class 3 noise level plant. The resultant POD curve produced a 95th percentile value of 9% TW. Therefore, the maximum depth of an undetected flaw is assumed to be 9% TW for PBP wear.

The 2RF19 flaw depth for the largest flaw returned to service (7%) can be calculated deterministically using NDE uncertainties from ETSS 96910.1 at 95% probability 50% confidence levels by applying the 4.5% growth rate. The 1.12 factor accounts for the square root sum of squares of the technique standard error and the analyst error.

219 0.95 7% 6.70% 1.645 5.36% 1.12 4.5% 4.3 42.6%

This results in a worst-case projected PBP wear flaw with a burst pressure of 5938 psi at 95%

probability and 50% confidence levels. These results compare favorably to the bounding 3PNO loading limit of 3909 psi for structural burst and the structural limit of 65.9% TW, which considers burst relation and material uncertainties. For pressure-only loading of volumetric flaws, satisfaction of structural integrity implies satisfaction of leakage integrity at accident conditions since steam line break accident condition pressure differential for pop-through is much smaller than 3PNO.

Using the same growth rate to project the maximum undetected flaw size of 9% TW over 7 cycles results in a bounded depth of 53.6% TW at 2RF19. NDE uncertainty is not considered for undetected flaw projection since it is not a measured flaw.

219 9% 4.5% 9.9 53.6%

This result is a worst-case projected undetected PBP wear flaw with a burst pressure of 4981 psi at 95% probability and 50% confidence levels. These results compare favorably to the bounding 3PNO loading limit of 3909 psi for structural burst and the structural limit of 65.9% TW, which considers burst relation and material uncertainties.

Hence, the PBP wear meets the burst pressure criteria until the next inspection. For pressure-only loading of volumetric flaws, satisfaction of the condition monitoring limit at 3PNO also satisfies the leakage criterion since the pop-through pressure differential of PSLB is smaller than 3PNO.

Therefore, they meet the primary-to-secondary leakage criterion at accident conditions. Thus, the structural and leakage integrity will be met for the baffle plate wear mechanism during the next operating cycle.

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      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 36 of 57 Westinghouse Non-Proprietary Class 3 4.1.2.2 Prediction of Tube Support Wear at 2RF19 The maximum measured wear indication at a TSP that was left in service was sized at 16% TW.

The length of the largest indication left in service is assumed to be 1.12 inch, which is the bounding length based on the plate thickness. The wall thinning with limited axial extent (less than 135 degrees) is applied for TSP wear.

To predict the maximum wear depth at TSP intersections at 2RF19, the following parameters were considered:

The estimated durations for inspection intervals are based on Table 2-1 cycle durations.

The growth rate is conservatively assumed to be 4.5% TW/EFPY (see Section 4.1.2)

CPNPP Unit 2 tubing material properties from the EPRI Flaw Handbook (Reference 4) and NDE uncertainties from ETSS 96910.1 +POINT probe sizing technique.

The maximum measured depth at 2RF19 is predicted deterministically and the burst pressure is determined by performing a statistical Monte Carlo simulation using the Westinghouse proprietary Single Flaw Model software (Reference 14) for the deterministically determined depth and maximum TSP wear length.

The largest undetected flaw depth was determined through a POD curve generated from the industry recommended MAPOD methodology (Reference 14). The noise-based POD curve was developed using the EPRI bobbin coil detection technique ETSS I96043.1 data set and the generic noise distribution provided in the ETSS. The noise distribution was the ETSS default noise distribution which is from a higher noise level plant. The resultant POD curve produced a 95th percentile value of 13% TW. Therefore, the maximum depth of an undetected flaw is assumed to be 13% TW.

The 2RF19 flaw depth for the largest flaw returned to service (7%) can be calculated deterministically using NDE uncertainties from ETSS 96910.1 at 95% probability 50% confidence levels by applying the 5% growth rate:

219 0.95 16% 6.70% 1.645 5.36% 1.12 4.5% 4.3 51.1%

This result is a worst-case projected TSP wear flaw with a burst pressure of 5063 psi at 95%

probability and 50% confidence levels. These results compare favorably to the bounding 3PNO loading limit of 3909 psi for structural burst and the structural limit of 63.7% TW, which considers burst relation and material uncertainties. For pressure-only loading of volumetric flaws, satisfaction of structural integrity implies satisfaction of leakage integrity at accident conditions since steam line break accident condition pressure differential for pop-through is much smaller than 3PNO.

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      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 37 of 57 Westinghouse Non-Proprietary Class 3 Using the same growth rate to project the maximum undetected flaw size over 7 cycles results in a bounded depth of 57.6% TW at 2RF19. NDE uncertainty is not considered for undetected flaw projection since it is not a measured flaw.

219 13% 4.5% 9.9 57.6%

This results in a worst-case projected TSP wear flaw with a burst pressure of 4465 psi at 95%

probability and 50% confidence levels. These results compare favorably to the bounding 3PNO loading limit of 3909 psi for structural burst and the end-of-cycle condition monitoring limit of 63.7% TW, which considers burst relation and material uncertainties.

Hence, the wear meets the burst pressure criteria until the next inspection. For pressure-only loading of volumetric flaws, satisfaction of the condition monitoring limit at 3PNO also satisfies the leakage criterion since the pop-through pressure differential of PSLB is smaller than 3PNO.

Therefore, they meet the primary-to-secondary leakage criterion at accident conditions. Thus, the structural and leakage integrity will be met for the baffle plate wear mechanism during the next operating cycle.

4.1.3 Tube Wear Due to Foreign Objects Through the previous SG inspection during 2RF17 (2018), twelve indications of volumetric tube wear from foreign object interaction remain in service. The measured flaw depths range from 6% TW to 28% TW and the measured flaw lengths range are bounded by 0.33 inch. The largest flaw, 28% TW, satisfies the condition monitoring limit of 55.8% TW for volumetric indications with 0.5 inch axial extents. The CM limit contains all uncertainties, including NDE flaw measurement, at 0.95 probability and 50% confidence so that NDE measured flaw depth can be compared directly to this limit. These indications have experienced no growth since their initial reporting or through review of historical data. No foreign objects remain within the vicinity of the affected tubes as confirmed through secondary side visual inspections and eddy current examinations. Therefore, there is no mechanism to produced further flaw progression during future operations. With no mechanism present for further flaw growth and all wear flaws satisfy condition monitoring limits, all SG performance criteria for structural and leakage integrity will be satisfied during the next operating cycle to 2RF19.

4.1.4 Circumferential PWSCC Indications During 2RF16, three indications in two tubes were detected within the hot leg tubesheet at identified BLG/OXP locations. In addition, one indication was found within a hot leg top of tubesheet expansion transition. These four indications represent the first instance of SCC in the Comanche Peak Unit 2 SGs. Tubesheet inspections were performed again in 2RF17 with no further instances of SCC being detected. Circumferential PWSCC at expansion transitions and at BLG/OXP locations within the tubesheet are two separate, but similar, degradation mechanisms.

A bounding approach was applied in this OA to evaluate both mechanisms with one combined SG-CDMP-20-13 Revision 0 Page 36 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 38 of 57 Westinghouse Non-Proprietary Class 3 evaluation, as both are circumferential PWSCC at areas of higher residual stress due to tube deformation at or within the tubesheet.

The detection technique for both flaw types is the same and +POINT technique ETSS 20510.1 is utilized. The site-specific POD curve was developed in 2RF16 based on Ahat data from ETSS 20510.1 and 180-degree tubesheet noise measurements recorded during 2RF16. The 180-degree noise measurements are appropriate for use because the circumferential extent of all four indications are relatively small, which is consistent with industry circumferential PWSCC indications. This POD, which has a 0.95 detection capability at 76% TW depth, was applied again in 2RF17 for a two-cycle OA. Dating back to 2RF16, all tubes at the top of the tubesheet have been inspected at least once. Therefore, to technically justify deferral of SG inspections to 2RF19, a three-cycle OA must be documented to account for undetected flaws that were undetected at 2RF16.

The major inputs for performing a fully probabilistic full bundle OA for SCC are the POD, the undetected flaw population and the flaw growth rates. As discussed above, a site-specific POD was developed during 2RF16 and re-applied during OA calculations for 2RF17. This same POD will apply for OA calculations to defer inspections to 2RF19. The undetected flaw population for maximum depth is determined by processing a uniform distribution from 0 to 100% TW through the site-specific POD (maximum depth) function. In doing this, an undetected flaw distribution was developed that has a 95th percentile maximum depth of approximately 58% TW. A conservative shape factor based on flaw sizes in the re-analyzed Alloy 600TT industry circumferential SCC flaw population was applied to select a distribution function for undetected flaw PDA sizes. The resultant distribution, including considerations for NDE measurement uncertainties, has a 95th percentile PDA of approximately 21 PDA for the undetected flaw population. The distribution for undetected flaw length was also based on the re-analyzed Alloy 600TT industry circumferential SCC flaw population data and resulted in a function with a 0.95 flaw length at approximately 135 degrees, including considerations for NDE measurement uncertainties. This significantly bounds the circumferential extent of the detected flaws from 2RF16 which were 60 degrees at the expansion transition and between 31 and 35 degrees at the BLG/OXP locations. Two undetected flaws from a single SG will be conservatively used as the base case for this OA based on Weibull failure projection data for circumferential flaw initiates of industry A600TT experiences and applied to CPNPP Unit 2 at 2RF19 (~25.5 EFPY for CPNPP Unit 2 SGs).

Plant-specific growth rates are not available for this mechanism. Therefore, the EPRI default growth rates for SCC, adjusted for the Comanche Peak Unit 2 hot leg temperature of 618°F, were used for the OA. Recent industry work has shown that lower growth rates are justifiable based on re-analyzed Alloy 600TT industry SCC flaw population data, therefore, considerable margin exists beyond that identified in the results of this OA.

The results for the three-cycle OA for this mechanism are summarized below in Table 4-1.

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      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 39 of 57 Westinghouse Non-Proprietary Class 3 Table 4-1. Circumferential PWSCC at Tubesheet Locations Fully Probabilistic OA Results 2RF19 Projection SG Performance Parameter (2 Flaws, 3-Cycles) Criteria Probability of Burst 1.67% 5%

Probability of Leak 2.72% 5%

Burst Pressure 4604 psi 3909 psi Accident Induced Leak Rate 0.146 gpm 0.35 gpm 4.2 Potential Degradation Mechanisms Prior to each SG inspection a Degradation Assessment is performed to identify the type and location of flaws to which the tubes may be susceptible. This review is required by the plant Technical Specifications (Reference 18). The assessment is based on operating experience at CPNPP and plants within the industry that contain similar SG design and tubing material, as well as laboratory data. Existing degradation mechanisms are flaw types that have been reported at CPNPP Unit 2 and are described in Section 3.1. Potential degradation mechanisms are those flaw types that have not occurred at CPNPP Unit 2 but could occur in the future based on industry experience and laboratory data. The following potential degradation mechanisms were identified to be applicable to the CPNPP Unit 2 SG tubing as potential degradation mechanisms.

Axial ODSCC at tube support plates Axial ODSCC at dents/dings Axial and Circumferential ODSCC in dents/dings at and below drill hole baffle plate Axial and Circumferential ODSCC at top of HL tubesheet Axial PWSCC at BLG/OXP locations within HL tubesheet Axial PWSCC at HL tubesheet expansion transition Axial and Circumferential PWSCC at Row 1 and 2 U-bends Axial and Circumferential ODSCC/PWSCC in tubes hydraulically expanded at preheater baffle plates The following potential degradation mechanisms evaluated for this report were selected based on the frequency of their historical occurrence in the Alloy 600TT fleet, as shown in Table 4-2.

Axial ODSCC at tube support plates for high stress tubes Circumferential ODSCC at top of tubesheet expansion transitions Axial PWSCC at top of tubesheet expansion transitions Axial ODSCC at the top of tubesheet expansion transitions and sludge pile SG-CDMP-20-13 Revision 0 Page 38 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 40 of 57 Westinghouse Non-Proprietary Class 3 Table 4-2. Industry SCC Experience in A600TT Tubing Number of Mechanism Location Affected Tubes Axial ODSCC TTS Expansion Transition 7 Axial PWSCC TTS Expansion Transition 4 Circ. ODSCC TTS Expansion Transition 63 Circ. PWSCC TTS Expansion Transition 2 Circ. PWSCC Tubesheet 16 Bulge/Overexpansion Axial ODSCC Dent/Ding 2 Axial PWSCC Low Row U-Bend 2 Axial ODSCC Freespan near TSP 2 Axial ODSCC TSP (High Stress Tubes) 27 Total 125 4.2.1 Axial ODSCC at Tube Support Plates for High Stress Tubes Axial ODSCC at TSP locations has not been detected at Comanche Peak Unit 2 but has been detected in other Alloy 600TT SGs. These have almost exclusively been observed in tubes designated as 2-sigma with possible higher residual stresses. Therefore, the occurrence of this degradation mechanism at Comanche Peak Unit 2 is considered for extending the OA to 2RF19.

Axial ODSCC at TSP locations are detected from bobbin, though at Comanche Peak Unit 2 the high stress tubes are inspected with +POINT probe at the hot leg (HL) and cold leg (CL) TSP locations as part of the standard inspection program. This inspection was last performed during 2RF16 during which 100% of the high stress tubes were inspected at all TSP intersections with

+POINT probe. Therefore, a three-cycle OA is performed from 2RF16 to 2RF19 for this mechanism. The bobbin probe ETSS specified for detection of axial ODSCC at TSP locations is I28413, and the +POINT probe technique for this mechanism is I28425.

Evaluations have been performed for other plants that implement this inspection method for the 2-sigma tube population and in these cases the OA utilizes a double POD method. That is, the probability of detection is based on the capability of the bobbin technique supplemented by the capability of the +POINT probe technique. Separately, the bobbin detection capability at 0.95 is nearly 100% TW by some POD models, and the +POINT probe detection capability at 0.95 is approximately 64% TW. When processing a uniform flaw distribution through the supplemented POD, the undetected flaw distribution has a 0.95 depth of approximately 34% TW.

The major inputs for performing a fully probabilistic full bundle OA for SCC are the POD, the undetected flaw population and the flaw growth rates. As discussed above, the POD is based on the bobbin inspection as supplemented by a +POINT probe inspection. This method has been performed for other Alloy 600TT plants where axial ODSCC at TSP locations is an active degradation mechanism. The undetected flaw population is determined by processing a uniform distribution from 0 to 100% TW through the POD function. The median undetected flaw length is approximately 0.53 inch, with a 95th percentile at approximately 0.8 inch, which is judged to be conservative from a review of flaw sizes in the re-analyzed Alloy 600TT industry circumferential SG-CDMP-20-13 Revision 0 Page 39 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 41 of 57 Westinghouse Non-Proprietary Class 3 SCC flaw population data. Two undetected flaws from a single SG will be conservatively used as the base case for this OA based on the Weibull failure projection data for flaw initiates at 2RF19

(~25.5 EFPY for Comanche Peak 2 SGs).

Form factors used to convert the individual flaw parameters to terms of structural equivalent depth and structural equivalent length for compatibility with the burst regression are applied in the evaluation model. For this evaluation, the length form factor is represented based on a uniform distribution from 1 to 3 while the depth form factor is represented based on a normal distribution with a mean value of 1.25 and standard deviation of 0.08.

Plant-specific growth rates are not available for this mechanism. Therefore, the EPRI default growth rates for SCC, adjusted for the Comanche Peak Unit 2 hot leg temperature of 618°F, were used for the OA. Recent industry work has shown that lower growth rates are justifiable based on re-analyzed Alloy 600TT industry SCC flaw population data, so in reality considerable additional margin exists beyond that identified in the results of this OA.

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      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 42 of 57 Westinghouse Non-Proprietary Class 3 The results for the three-cycle OA for this mechanism are summarized below in Table 4-3.

Table 4-3. Axial ODSCC at TSP (2-Sigma Tubes) Fully Probabilistic OA Results 2RF19 Projection SG Performance Parameter (2 Flaws, 3-Cycles) Criteria Probability of Burst 0.617% 5%

Probability of Leak 0.847% 5%

Burst Pressure 5291 psi 3909 psi Accident Induced Leak Rate 0 gpm 0.35 gpm 4.2.2 Circumferential ODSCC at Top of Tubesheet Circumferential ODSCC at the TTS has not been detected at Comanche Peak Unit 2 but has been detected in other plants with Alloy 600TT SG tubing material. Therefore, the occurrence of this degradation mechanism at Comanche Peak Unit 2 is considered for extending the OA to 2RF19.

Circumferential ODSCC indications at the TTS are detected from +POINT probe using ETSS technique 21410.1. The TTS was last inspected during 2RF17 where 50% of the TTS of SGs 1, 2 and 4 were inspected along with 100% of SG 3. Dating back to 2RF16, 100% of tubes at the TTS were inspected with +POINT probe. Therefore, a three-cycle OA is performed from 2RF16 to 2RF19 for this mechanism.

The major inputs for performing a fully probabilistic full bundle OA for SCC are the POD, the undetected flaw population and the flaw growth rates. A site-specific POD function was developed by using Ahat data from the ETSS 21410.1 along with 360-degree tubesheet noise measurements collected during 2RF16. The POD function has a 95th percentile maximum depth of 58% TW. A uniform distribution of flaws from 1% TW to 99% TW was then processed through this POD function resulting in an undetected flaw distribution with a 95th percentile maximum depth of approximately 46% TW. A conservative shape factor was applied based on flaw sizes in the re-analyzed Alloy 600TT industry SCC flaw population to select a distribution function for PDA.

The resultant flaw distribution, including considerations for NDE measurement uncertainties, has a 95th percentile PDA of approximately 18 PDA. The distribution for flaw length was also based on the re-analyzed Alloy 600TT industry SCC flaw population data and resulted in a distribution, including considerations for NDE measurement uncertainties, with a 95th percentile flaw length at approximately 135 degrees. Two undetected flaws from a single SG will be conservatively used as the base case for this OA based on Weibull failure projection data for flaw initiates at 2RF19

(~25.5 EFPY for Comanche Peak Unit 2 SGs).

Plant-specific growth rates are not available for this mechanism. Therefore, the EPRI default growth rates for SCC, adjusted for the Comanche Peak Unit 2 hot leg temperature of 618°F, were used for the OA. Recent industry work has shown that lower growth rates are justifiable based on re-analyzed Alloy 600TT industry SCC flaw population data, so in reality considerable additional margin exists beyond that identified in the results of this OA.

SG-CDMP-20-13 Revision 0 Page 41 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 43 of 57 Westinghouse Non-Proprietary Class 3 The results for the three-cycle OA for this mechanism are summarized below in Table 4-4.

Table 4-4. Circumferential ODSCC at TTS Fully Probabilistic OA Results 2RF19 Projection SG Performance Parameter (2 Flaws, 3-Cycles) Criteria Probability of Burst 0.63% 5%

Probability of Leak 2.14% 5%

Burst Pressure 5584 psi 3909 psi Accident Induced Leak Rate 0.05 gpm 0.35 gpm 4.2.3 Axial PWSCC at Top of Tubesheet CPNPP Unit 2 has not experienced axial PWSCC at the top of tubesheet expansion transitions or within the hydraulically expanded region within the tubesheet above the tube end weld joint. Axial PWSCC at these locations have been experienced within the industry in SGs containing A600TT tubing; the same tubing material type as the CPNPP Unit 2 SGs. This mechanism is classified as a potential degradation mechanism for the CPNPP Unit 2 SGs. Tube inspection programs have been implemented for detection of axial PWSCC at expansion transitions and within the tubesheet expanded region below the top of tubesheet. These inspection programs were completed in accordance with the sampling and frequency requirements specified in the plant Technical Specifications (Reference 18). The inspection technique used for detection of axial PWSCC at expansion transitions was qualified in accordance with Appendix H of Reference 2 and validated to site-specific conditions. The EPRI +POINT probe technique ETSS 20511.1 was used for detection of axial PWSCC at CPNPP Unit 2.

During 2RF16 (2017), the tubesheet +POINT probe inspection scope was 100% for SG 3 and 50%

in SGs 1, 2 and 4. The extent of the inspection was from 3 inches above the top of the tubesheet to the H* depth below the top of tubesheet. These inspection scopes were in response to detection of circumferential PWSCC at tubesheet bulges/overexpansions and at the expansion transition (see Section 2.3). During 2RF17 (2018), tubesheet +POINT probe inspections were performed on 100% of the tubes in SG 3 and 50% of the tubes in SGs 1, 2, and 4 which included all tubes which were not inspected in 2FR16. Therefore, a three-cycle inspection interval was used for the OA duration to account for assumed undetected flaws at 2RF16 that may be present until the next inspection at 2RF19.

A fully probabilistic full bundle OA was performed to evaluate potential axial PWSCC flaws over a three-cycle operating period through the proposed inspection deferral operating period to 2RF19.

The primary inputs to the fully probabilistic model are flaw detection POD, undetected flaw size and population, flaw growth rates, and site-specific parameters such as tubing size and material properties, differential pressure, and allowable accident induced leak rate.

A site-specific noise-based POD curve for flaw depth was developed using the industry recommended MAPOD methodology. MAPOD generates a POD curve through probabilistic SG-CDMP-20-13 Revision 0 Page 42 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 44 of 57 Westinghouse Non-Proprietary Class 3 simulations using a tube noise distribution and a flaw voltage-to-flaw depth correlation (i.e., Ahat function). The noise distribution applied was developed from +POINT probe data collected during the 2RF16 inspection of top of tubesheet expansion transitions. The Ahat function was derived from re-analysis of the ETSS 20511.1 data that provides metallurgical flaw depths from destructive examination of actual pulled tube and laboratory produced flaw samples. The resultant POD curve was input to the fully probabilistic full bundle model. The 95th percentile from this POD curve is 71% TW.

The postulated undetected flaw size population for maximum depth was derived from simulations using the site-specific POD curve, discussed above. The postulated undetected flaw length distribution was derived from re-analysis of the eddy current data of all axial SCC flaws, including historical data review of reported flaws that have been experienced at other industry plants that contain A600TT SG tubing material. The 95th percentile from this postulated undetected length distribution, including considerations for NDE measurement uncertainties, is 0.33 inch.

The number of undetected flaws, which represents the number of flaws at the beginning of the OA inspection interval, was determined through Weibull failure projections using axial SCC initiation experiences from all industry plants containing A600TT SG tubing. The Weibull failure projection was applied to the CPNPP Unit 2 SGs to estimate the number of flaws to evaluate by the fully probabilistic OA model. The number of flaws that were evaluated within the OA model is conservatively bound by two flaws. The Weibull failure projection function was also used within the OA model to address flaws that may initiate during the three-cycle OA duration.

Form factors used to convert the individual flaw parameters to terms of structural equivalent depth and structural equivalent length for compatibility with the burst regression are applied in the evaluation model. For this evaluation, the length form factor is represented based on a uniform distribution from 1 to 3 while the depth form factor is represented based on a normal distribution with a mean value of 1.25 and standard deviation of 0.08 As no indications of axial PWSCC have been observed at CPNPP Unit 2, site-specific growth rates cannot be determined. The industry default growth rates for SCC mechanism recommended in Reference 3 were applied for flaw maximum depth and total length growth progression. The growth rates were adjusted to the CPNPP Unit 2 operating temperature using the Arrhenius temperature correction method described in Reference 3.

The results of the fully probabilistic projections over the three cycle OA evaluation period for axial PWSCC at expansion transitions are provided in Table 4-5. All results are well within the applicable SG performance criteria. The probability of burst and probability of leak for axial PWSCC at expansion transitions are 1.29% and 0.64%, respectively, and satisfy the performance criteria of 5% for each parameter. The projected lower 5% percentile burst pressure and accident induced leak rate at steam line break conditions are 4767 psi and 0 gpm, respectively. These satisfy the minimum burst pressure requirement of 3909 psi and the site accident induced leak rate limit of 0.35 gpm.

Therefore, if the potential axial PWSCC at expansion transition degradation mechanism were to occur at CPNPP Unit 2, all SG performance criteria for structural and leakage integrity have been SG-CDMP-20-13 Revision 0 Page 43 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 45 of 57 Westinghouse Non-Proprietary Class 3 demonstrated to be maintained for at least three operating cycles encompassing the period of inspection deferral through to 2RF19.

Table 4-5. Axial PWSCC at Expansion Transition Fully Probabilistic OA Results 2RF19 Projection SG Performance Parameter (2 Flaws, 3-Cycles) Criteria Probability of Burst 1.29% 5%

Probability of Leak 0.64% 5%

Burst Pressure 4767 psi 3909 psi Accident Induced Leak Rate 0 gpm 0.35 gpm 4.2.4 Axial ODSCC at Top of Tubesheet CPNPP Unit 2 has not experienced axial ODSCC at the top of tubesheet expansion transitions or within the sludge pile. Axial ODSCC at these locations have been experienced within the industry in SGs containing A600TT tubing; the same tubing material type as the CPNPP Unit 2 SGs. This mechanism is classified as a potential degradation mechanism for the CPNPP Unit 2 SGs. Tube inspection programs have been implemented for detection of axial ODSCC at expansion transitions and within the tubesheet expanded region below the top of tubesheet. These inspection programs were completed in accordance with the sampling and frequency requirements specified in the plant Technical Specifications (Reference 18). The inspection technique used for detection of axial ODSCC at expansion transitions was qualified in accordance with Appendix I of Reference 2 and validated to site-specific conditions. The EPRI +POINT probe technique ETSS I28424 was used for detection of axial ODSCC at CPNPP Unit 2.

During 2RF16 (2017), the tubesheet +POINT probe inspection scope was 100% for SG 3 and 50%

in SGs 1, 2 and 4. The extent of the inspection was from 3 inches above the top of the tubesheet to the H* depth below the top of the tubesheet. During 2RF17 (2018), tubesheet +POINT probe inspections were performed on 100% of the tubes in SG 3 and 50% of the tubes in SGs 1, 2, and 4 which included all tubes which were not inspected in 2RF16. Therefore, a three-cycle inspection interval was used for the OA duration to account for assumed undetected flaws at 2RF16 that may be present until the next inspection at 2RF19.

A fully probabilistic full bundle OA was performed to evaluate potential axial ODSCC flaws over a three-cycle operating period through the proposed inspection deferral operating period to 2RF19.

The primary inputs to the fully probabilistic model are flaw detection POD, undetected flaw size and population, flaw growth rates, and site-specific parameters such as tubing size and material properties, differential pressure, and allowable accident induced leak rate.

A site-specific noise-based POD curve for flaw depth was developed using the industry recommended MAPOD methodology. MAPOD generates a POD curve through probabilistic simulations using a tube noise distribution and a flaw voltage-to-flaw depth correlation (i.e., Ahat function). The noise distribution applied was developed from +POINT probe data collected during the 2RF16 inspection of top of tubesheet expansion transitions. The Ahat function was derived from re-analysis of the ETSS I28424 data that provides metallurgical flaw depths from destructive SG-CDMP-20-13 Revision 0 Page 44 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 46 of 57 Westinghouse Non-Proprietary Class 3 examination of actual pulled tube and laboratory produced flaw samples. The resultant POD curve was input to the fully probabilistic full bundle model. The 95th percentile from this POD curve is 87% TW.

The postulated undetected flaw size population for maximum depth was derived from simulations using the site-specific POD curve, discussed above. The postulated undetected flaw length distribution was derived from re-analysis of the eddy current data of all axial SCC flaws, including historical data review of reported flaws, that have been experienced at other industry plants that contain A600TT SG tubing material. The 95th percentile from this postulated undetected length distribution, including considerations for NDE measurement uncertainties, is 0.33 inch.

The number of undetected flaws, which represents the number of flaws at the beginning of the OA inspection interval, was determined through Weibull failure projections using axial SCC initiation experiences from all industry plants containing A600TT SG tubing. The Weibull failure projection was applied to the CPNPP Unit 2 SGs to estimate the number of flaws to evaluate by the fully probabilistic OA model. The number of flaws that were evaluated within the OA model is conservatively bound by two flaws. The Weibull failure projection function was also used within the OA model to address flaws that may initiate during the three-cycle OA duration.

Form factors used to convert the individual flaw parameters to terms of structural equivalent depth and structural equivalent length for compatibility with the burst regression are applied in the evaluation model. For this evaluation, the length form factor is represented based on a uniform distribution from 1 to 3 while the depth form factor is represented based on a normal distribution with a mean value of 1.25 and standard deviation of 0.08.

As no indications of axial ODSCC have been observed at CPNPP Unit 2, site-specific growth rates cannot be determined. The industry default growth rates for SCC mechanism recommended in Reference 3 were applied for flaw maximum depth and total length growth progression. The growth rates were adjusted to the CPNPP Unit 2 operating temperature using the Arrhenius temperature correction method described in Reference 3.

The results of the fully probabilistic projections over the three-cycle OA evaluation period for axial ODSCC at expansion transitions are provided in Table 4-6. All results are well within the applicable SG performance criteria. The probability of burst and probability of leak for axial ODSCC at expansion transitions are 1.17% and 0.42%, respectively, and satisfy the performance criteria of 5% for each parameter. The projected lower 5% percentile burst pressure and accident induced leak rate at steam line break conditions are 4757 psi and 0.0014 gpm, respectively. These satisfy the minimum burst pressure requirement of 3909 psi and the site accident induced leak rate limit of 0.35 gpm.

Therefore, if the potential axial ODSCC at expansion transition degradation mechanism were to occur at CPNPP Unit 2, all SG performance criteria for structural and leakage integrity have been demonstrated to be maintained for at least three operating cycles encompassing the period of inspection deferral through to 2RF19.

SG-CDMP-20-13 Revision 0 Page 45 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 47 of 57 Westinghouse Non-Proprietary Class 3 Table 4-6. Axial ODSCC at Expansion Transition Fully Probabilistic OA Results 2RF19 Projection SG Performance Parameter (2 Flaws, 3 Cycles) Criteria Probability of Burst 1.17% 5%

Probability of Leak 0.42% 5%

Burst Pressure 4757 psi 3909 psi Accident Induced Leak Rate 0.0014 gpm 0.35 gpm 4.3 Leakage Integrity The OA results in Section 4.1 and Section 4.2 demonstrate that that the SG performance criteria for leakage integrity were satisfied by the POL calculated probabilistically for each existing and potential SCC mechanism being less than the 5% acceptance criteria. Section 8.3.3 of the SG IAGL (Reference 3) requires that the total cumulative leakage be determined for all existing mechanisms where an OA is performed probabilistically. For CPNPP Unit 2, there is only one SCC mechanism that requires a probabilistic OA per the EPRI guidelines (Reference 3) since it is an existing mechanism in the SGs having last been detected during 2RF16. However, to provide further technical justification for deferral of SG inspections from 2RF18 to 2RF19, OA for the most-likely potential mechanisms were performed and therefore will be considered for combined probability of leakage. This includes the following potential degradation mechanisms:

- Axial ODSCC at TTS expansion transitions

- Axial PWSCC at TTS expansion transitions

- Circumferential ODSCC at TTS expansion transitions

- Axial ODSCC at TSP locations in 2-sigma tubes It is overly conservative to consider that all four of these potential mechanisms would occur within this past inspection interval with none of them having been detected at CPNPP Unit 2 to date.

However, a practical approach is to combine the POL from the most limiting potential mechanism with the POL from the existing mechanism of Circumferential PWSCC at TTS locations.

Table 4-7 displays the POL that were calculated for each of the SCC mechanisms evaluated in this report.

Table 4-7. OA Calculated POL by SCC Mechanism SCC Mechanism POL %

Circ OD TTS 2.14 Circ ID TTS 2.62 Ax OD TTS 0.42 Ax ID TTS 0.64 Ax OD TSP 0.85 SG-CDMP-20-13 Revision 0 Page 46 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 48 of 57 Westinghouse Non-Proprietary Class 3 When combining the POL from the circumferential PWSCC at TTS and circumferential ODSCC at TTS mechanisms using the method from the EPRI SG IAGL, the result is a cumulative POL of 4.7%, which is less than the acceptance criteria of 5.0%

In addition, the CPNPP Unit 2 licensing commitment associated with the implementation of the H* alternate repair criteria (ARC) requires that the OA compute the difference between the allowable accident induced leakage (0.3472 gpm) and the accident induced leakage from sources other than the tubesheet expansion region, divided by a H* leak rate factor (which is 3.16 for CPNPP Unit 2), and compare it to the observed operational leakage. Practically, this is a check to determine if an administrative leakage limit needs to be applied that is more restrictive than the permitted operational leakage of 150 gpd per plant Technical Specifications.

The predicted leakage (at 0.95 probability) is calculated probabilistically for each SCC mechanism evaluated in this OA. The summary of the predicted leakages, and calculation of the allowable H*

leak rate, are provided in Table 4-8 below.

Table 4-8. OA Predicted Leakages by SCC Mechanism SCC Mechanism 0.95 LR (gpm)

Circ OD TTS 0.05 Circ ID TTS 0.146 Ax OD TTS 0 Ax ID TTS 0 Ax OD TSP 0.0014 Total 0.1974 Allowable H* Leak Rate = (0.3472 gpm - 0.1974 gpm) / 3.16 = 0.0474 gpm or 68.3 gpd The leak rate of 68.3 gpd is less than the permitted operational leakage of 150 gpd per plant Technical Specifications and is also less than the EPRI recommended administrative limit of 75 gpd. Therefore, a new administrative limit will need to be established for allowable primary-to-secondary operational leakage for CPNPP Unit 2 during Cycle 19. This calculation and administrative limit can be revisited during the OA performed following SG inspections at 2RF19.

4.4 Channel Head Indications As described in Section 2.3, indications were observed in the cladding of the channel head in SG 1 and SG 2. Luminant performed a cursory review of historical inspections for both indications and has determined that the discoloration was visible in 2003 for the indication in SG 2-01 and no precursor was visible in SG 2-02. Since the SG 2-01 indication was observed as early as 2003, it was judged that the condition would have no impact on the operation of the steam generators. An assessment of the condition starting from the beginning of plant operation in Cycle 1 was made.

Based on the corrosion rate progression during outages (aerated condition in the channel head) and during plant operation (deaerated condition in the channel head), it was determined that the combined aerated and deaerated corrosion rate is 0.00087 inch per cycle (Reference 9). Operation SG-CDMP-20-13 Revision 0 Page 47 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 49 of 57 Westinghouse Non-Proprietary Class 3 through 2RF18 results in a total wall loss of 0.0157 inch. Projecting the corrosion for an additional cycle through 2RF19 results in a total wall loss of 0.0166 inch.

The acceptability of the indication for continued operation was evaluated by comparison to the allowable planar flaws for ferritic steel in Table IWB-3510-1 of Reference 11. The reported indication was estimated to be approximately 5/8-inch long and approximately half as wide. The allowable surface flaw depth of 1.9% of the bowl thickness is taken from Table IWB-3510-1 for the conservative flaw depth to the length ratio of zero. The steam generator bowl thickness is approximately 5.3 inches, giving an allowable surface flaw depth of 0.10 inch. Since the estimated depth of the flaw, projected to the end of Cycle 19, is significantly less than the allowable depth, the indication is acceptable for continued operation through to 2RF19, when the next inspection is recommended. The indication in SG 2-02 is enveloped by the analysis above and is therefore acceptable for continued operation through to 2RF19 (Reference 10).

Based on the conclusion from the aforementioned assessments that the anomalies did not represent a structural integrity concern, no action was required during 2RF17. Inspection and recharacterization for both indications are recommended during the next inspection outage of the SGs in 2RF19.

4.5 Foreign Object Evaluation Foreign Object Search and Retrieval (FOSAR) of the SG tubesheet was last performed at CPNPP Unit 2 during 2RF16. For foreign objects that were not able to be removed from the SGs, an evaluation was performed to determine the acceptable duration of continued operation with the objects remaining in the SG. In many cases, the foreign objects were small or are in a region of the tube bundle where little or no tube degradation would be expected to occur over multiple cycles of operation. Evaluation and acceptability of a foreign object remaining in the SG is dependent on various factors, such as size and type of foreign object, material properties of the object, fluid flow characteristics at the location of the object, fixity of the object, the operating duration between inspections, and the objects propensity for causing tube wear (i.e., flaw detected by eddy current examination). The amount of tube wear a particular foreign object can cause is dependent on many factors as described.

Westinghouse uses a proprietary computer code (WEART) to determine wear times for a given foreign object. It uses Archards theory of wear to determine the volume of metal removed for a given force and sliding distance. Tube vibration parameters (such as natural frequency and associated displacements) are used to obtain the distance and the force is supplied by the local fluid flow conditions. In general, it is assumed the foreign object is in the worst location at or near the periphery of the tube bundle. The evaluation of the potential for fretting and impact/sliding wear caused by the presence of loose objects remaining in the secondary side of steam generators involves postulating scenarios in which the loose objects contact vibrating tubes and wear into the tubes over significant periods of time. The objective is to estimate the time each loose object would require to wear into a tube until the tube wall no longer meets the minimum wall thickness requirements pertaining to the maintenance of tube integrity.

SG-CDMP-20-13 Revision 0 Page 48 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 50 of 57 Westinghouse Non-Proprietary Class 3 For the foreign objects inventory at Comanche Peak Unit 2, results were considered from 2RF16, which was the last outage where tubesheet FOSAR and primary tube inspections were performed (Reference 12). The inspections performed during these outages provide information on the current foreign objects inventory at Comanche Peak Unit 2. This inventory consists of 46 metallic foreign objects and includes wires, bristles, gaskets, metal strips, and shims. Non-metallic parts, such as scale or sludge rocks, were not included in this count because they do not pose a potential for tube wear.

FOSAR and tube inspections were planned for the upcoming spring 2020 (2RF18) outage, therefore, the existing loose parts evaluations (Reference 12) were only completed with an acceptable duration up to this point. In order to allow a deferral of steam generator activities from the perspective of foreign objects, the list of parts identified during these two outages must be shown to have acceptability with respect to wear time for an additional 1.5 EFPY, or until fall 2021 (2RF19).

There are two categories of parts that warranted additional evaluation in order to show that the foreign objects remaining in the Comanche Peak Unit 2 SGs would not wear into a tube beyond the minimum wall thickness requirements after an additional 1.5 EFPY.

Forty-one (41) of the 46 foreign objects in the inventory were smaller parts and were acceptable for an operating period of three EFPY by comparison to a bounding evaluation performed in Reference 3. Five separate categories of parts were evaluated: wires, metal objects, gasket material, machine remnants, and slag, and bounding dimensions for the parts were determined in order to show acceptability for three EFPY or two cycles of operation. Therefore, during outage FOSAR activities, if the part was smaller than the bounding part dimensions, it was acceptable for 3 EFPY. This was a conservative method of dispositioning a large majority of the smaller parts.

In order to show acceptability for a longer period of time (i.e., 4.5 EFPY), the WEART calculations were re-run with smaller part dimensions based on the actual part sizes identified in the 2RF16 outage. All of these parts were smaller than the original bounding calculation part dimensions and were acceptable for greater than 4.5 EFPY.

The remaining five foreign objects identified that were not dispositioned by bounding calculations either had dimensions that were too large or they did not fit into the typical standard Westinghouse foreign object methodology. During the 2RF16 outage, it was recognized that an outage would be performed after one cycle. Therefore, these parts were shown to be acceptable for a wear time of 1.5 EFPY, after which they would be inspected and re-evaluated. It is noted that during the 2RF16 outage, no wear was detected on tubes that were adjacent to these parts. During the follow-up outage in Fall 2018 (2RF17), the same tubes were inspected again and shown to have no indications of wear. Therefore, Westinghouse concludes that based on the presence of no wear over one cycle of operation, it is expected that no wear would be seen for an additional cycle of operation from 2RF18 to 2RF19. In order to provide a defense in depth evaluation, the Westinghouse foreign object wear calculations (that initially provided an allowance for 1.5 EFPY of wear time) were investigated for conservatism. All parts would need to be acceptable for greater than three years of operation, which would be satisfactory when projecting wear for these parts from fall 2018 (2RF17, with no wear detected on adjacent tubes) until fall 2021 (2RF19).

Conservatism was removed from the calculations and wear times were shown to be in excess of SG-CDMP-20-13 Revision 0 Page 49 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 51 of 57 Westinghouse Non-Proprietary Class 3 three EFPY. The conservatisms that were removed include substituting the local flow velocities instead of bounding flow velocities and using the actual instead of a bounding loose part geometry.

To conclude, all parts identified in the steam generators of Comanche Peak Unit 2 during 2RF16, which comprise the current foreign objects inventory in all four SGs, are shown to have wear time results that can be extended by 1.5 EFPY when eliminating excess conservatism in the analysis. Therefore, these objects will not reach minimum tube wall thickness requirements pertaining to the maintenance of tube integrity until after an additional 1.5 EFPY until Fall 2021 (2RF19).

4.6 Secondary Side Integrity No anomalous conditions adverse to structural integrity were reported from the 2RF16 visual inspection. The FOSAR operation was performed over the tubesheet and over Baffle Plate B. The objects reported during the visual inspection and the possible loose parts from the eddy current inspection were evaluated to conclude there would be no adverse effect on SG tube integrity for the next operating interval for objects that remained in the SGs. Most of the objects were retrieved during FOSAR.

Upper steam drum visual inspections were performed in all four SGs during 2RF17. The steam drum inspections did not find any significant signs of progressing erosion, cracking, material loss or other forms of degradation. Small amounts of incipient erosion have been observed in various components. However, this amount of degradation is judged to be quite small in comparison to the expected structural margin of the component and have been evaluated as acceptable. The steam drum component condition in 2RF17 was similar to the condition at the previous steam drum inspection during 2RF08 with no evidence of progressing degradation.

The current steam drum inspection interval was set at 12 years from 2RF08 to 2RF17; while this showed no issues, extended operation of the steam drum components as the steam generators age increases the risk of encountering issues or anomalies that could affect moisture separation and general steam drum component function.

4.7 High Stress Tubes 4.7.1 Potential for Unidentified High Stress Tubes The first report of SCC of any type in Alloy 600TT SG tubing material occurred in a Model F plant in 2002. Fifteen tubes were reported to contain multiple axial ODSCC within TSP intersection. Root cause investigations, which included laboratory examination of two tubes removed from the affected SGs, concluded that the main contributor to the early onset of SCC was an elevated level of residual stress in the affected tubes. The source of the elevated residual stress was believed to be related to straightening operations (i.e., cold working) during the tubing manufacturing process that may have occurred after tube heat treating with no subsequent heat treatment. This condition was limited to a small number of tubes. Tubes affected by this condition are herein referred to as high stress tubes.

SG-CDMP-20-13 Revision 0 Page 50 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 52 of 57 Westinghouse Non-Proprietary Class 3 Following this event, the industry, through EPRI, developed an eddy current screening technique to identify tubes that potentially could contain high residual stress. One screening technique relies upon the raw eddy current results for tubes in shorter U-bend radiused rows. This method provides a more definitive screening result. The other technique for longer radiused tubes relies upon a statistical method and therefore, only provides a possibility that a tube could contain high residual stress. The eddy current screening for CPNPP Unit 2 was completed in 2003. A total of 73 tubes were initially identified as tubes that potentially could contain residual stress. Nine of these tubes were subsequently removed from service as a preventative measure or for other reasons.

Therefore, 64 tubes that potentially contain high residual stress remain in service.

4.7.2 Inspections Performed to Address Potentially Missed High Stress Tubes It is known that the initial screening for high stress tubes at other plants with Alloy 600TT SG tubing did not completely identify all high stress tubes in some plants. This condition was observed during apparent cause reviews following detection of SCC. A causal factor leading to not identifying all high stress tubes was related to a database inaccuracy for the affected tubes.

The high stress tube screening database for CPNPP Unit 2 was reviewed in light of this event and it was concluded that no high stress tubes were mis-identified, thus providing additional assurance that the original screening for high stress tubes remains accurate.

A robust inspection program for high stress tubes had previously been implemented at CPNPP Unit 2. This includes full-length bobbin coil inspections and targets +POINT probe inspections of areas more susceptible to degradation. Tubes not identified with high residual stress are inspected in accordance with the requirements of the Plant Technical Specifications (Reference 18), NEI 97-06 (Reference 1) and its mandatory industry guidance (Reference 2).

4.7.3 High Stress Tube Cracking at Comanche Peak Unit 2 One high stress tube at CPNPP Unit 2 was reported to contain an axial PWSCC indication at the tubesheet expansion transition during the 2RF16 SG inspection in 2017. However, SCC initiation at this location is driven by the stresses caused by the hydraulic expansion tube deformation rather than by the residual stresses imparted by cold working during tubing manufacturing. The residual stresses from tubing manufacturing are replaced with the higher stresses caused by tube deformation from expanding the tube into the tubesheet. No other indications of SCC have been observed at CPNPP Unit 2.

4.7.4 Inspection Strategy (Prior and Future)

The prior and future inspection plans for CPNPP Unit 2 include inspections of all high stress tubes with the bobbin coil probe from tube end to tube end. Additionally, each hot leg and cold leg TSP location is inspected with the +POINT probe in all high stress tubes. The hot leg and cold leg tubesheet region from 3 inches above the tubesheet to the H* distance below the top of the tubesheet are also inspected with the +POINT probe in all high stress tubes. This inspection plan was implemented in all prior SG inspections with the exception of 2RF17. The 2RF17 inspection scope targeted the top of the tubesheet and the tubesheet expansion zone inspections in accordance SG-CDMP-20-13 Revision 0 Page 51 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 53 of 57 Westinghouse Non-Proprietary Class 3 with the Plant Technical Specifications for required inspections in the refueling outage following crack detection during 2RF16.

4.8 Final Operational Assessment Conclusion A comprehensive Operational Assessment has been performed for the CPNPP Unit 2 SGs to demonstrate SG performance criteria for structural and leakage integrity is expected to be maintained at least to 2RF19 planned for Fall 2021, which would be the next planned SG inspections should the 2RF18 inspection deferred.

The OA is performed for all existing degradation mechanisms that have been detected at CPNPP Unit 2 as of the last SG inspections during 2RF17. The OA for each degradation mechanism includes evaluation of both detected and undetected flaws, which are assumed based on the inspection frequency and POD of inspection techniques. In addition to existing mechanisms, OA evaluations are performed for potential mechanisms in this report. OA evaluations for potential degradation mechanisms are beyond what is required per the EPRI SG IAGL but are performed to provide further technical justification for deferral of SG inspections from 2RF18 to 2RF19. This essentially assumes that these types of degradation have occurred and went undetected through the operating duration to the next inspections at 2RF19.

The Operational Assessment for tube wear mechanisms was performed using conservative methods to project EOC flaw depths for each active mechanism. For detected wear, this includes burst relation, material property and NDE measurement uncertainties. For undetected wear, this includes burst relation and material property uncertainties. It was concluded that in the case for each mechanism the projected EOC depth of the largest flaw returned to service in 2RF17 and the assumed largest flaw that escaped detection will remain below the calculated structural limits with sufficient margin at 2RF19. This demonstrates that structural integrity is expected to be maintained to at least 2RF19. For volumetric flaws ligament tearing is coincident to burst.

Therefore since structural integrity against tube burst at 3PNO was demonstrated, leakage integrity is expected to be maintained to at least 2RF19 as well. OA results for wear mechanisms with margin against the acceptance criteria are provided in Table 4-9.

The Operational Assessment for SCC mechanisms was performed with assumed undetected flaws for each existing and potential degradation mechanism. Probabilistic methods were used for the OA calculations with an acceptance criterion of 5.0% for POB, POL, minimum burst pressure requirement and the plants accident induced leak rate limit. The evaluations include uncertainties associated with burst relation and tube material properties. Each evaluation was performed for 3 cycles assuming undetected flaws at 2RF16. Accepted industry methods were used to develop the POD functions, undetected flaw populations and growth rates for each SCC mechanism evaluated.

For each SCC mechanism, the POB and POL were calculated to be below the 5.0% criterion which demonstrates structural and leakage integrity to at least to 2RF19. OA results for SCC mechanisms with margin against the acceptance criteria are provided in Table 4-10.

When combining predicted leakages from the OA calculations, and in considering CPNPP Unit 2 requirements associated with the H* alternate repair criteria, it was determined that an SG-CDMP-20-13 Revision 0 Page 52 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 54 of 57 Westinghouse Non-Proprietary Class 3 administrative leakage limit would need to be applied for Cycle 19. The calculated administrative leakage limit was 68 gpd, though the plant could elect to implement a more conservative limit.

Two SG channel head cladding anomalies are being tracked at CPNPP Unit 2 and were last visually observed during 2RF17. The anomalies did not appear to change from the prior inspection. A corrosion rate evaluation has been performed for the larger of the two flaws, which was last updated at 2RF17. For this OA, the projected wall loss per plant cycle was projected for another cycle to 2RF19. Considerable margin exists in this calculation when projected to 2RF19, at which point the next planned visual inspections of the anomalies would be performed.

A total of 46 metallic foreign objects remained in secondary side of the SGs following 2RF17.

The vast majority of these objects were small parts and demonstrated by bounding calculations through tube wear projections to not adversely affect tube integrity at least to 2RF19. Five larger parts that were initially observed in 2RF16 did not fit within the bounding analysis models.

Adjacent tubes to these objects were inspected with +POINT probe during 2RF17 inspections and no tube wear was detected indicating that the objects did not adversely affect the tube over the past cycle of operation. For this OA, a two-cycle foreign object evaluation was performed for these objects which concluded that they are not expected to adversely affect tube integrity to at least 2RF19, at which point the next planned primary and secondary SG inspections would be performed.

Upper steam drum visual inspections were last performed in all four SGs during 2RF17. The steam drum inspections did not find any significant signs of progressing erosion, cracking, material loss or other forms of degradation. Small amounts of incipient erosion have been observed in various components. However, this amount of degradation is judged to be quite small in comparison to the expected structural margin of the component and have been evaluated as acceptable. The steam drum component condition in 2RF17 was similar to the condition at the previous steam drum inspection during 2RF08 with no evidence of progressing degradation.

Table 4-9. OA Results Summary Table for Tube Wear Mechanisms OA Projection at SG Performance 2RF19 Criterion Projected Burst Mechanism Type Projected Depth Burst Pressure Depth Criterion Pressure Requirement

(%TW) (%TW)

(psi) (psi)

AVB Wear Existing 55.3 5075 69.4 3909 Undetected 38.4 6438 69.4 3909 Quatrefoil TSP Existing 51.1 5063 63.7 3909 Wear Undetected 57.6 4465 63.7 3909 Baffle Plate Existing 42.6 5938 65.9 3909 Wear Undetected 53.6 4981 65.9 3909 FO Wear Existing 28 (NDE) 6314 55.8 (CM) 3909 SG-CDMP-20-13 Revision 0 Page 53 of 56

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(%) (%) (psi) (gpm)

Circ PWSCC TTS Existing 1.67 2.72 4604 0.146 Circ ODSCC TTS Potential 0.63 2.14 5584 0.05 Axial PWSCC Potential 1.29 0.64 4767 0 TTS Axial ODSCC Potential 1.17 0.42 4757 0.0014 TTS Axial ODSCC Potential 0.617 0.847 5291 0 TSP SG Performance Criterion 5% 5% 3909 0.3472 SG-CDMP-20-13 Revision 0 Page 54 of 56

      • This record was final approved on 4/10/2020 12:26:39 PM. (This statement was added by the PRIME system upon its validation) to TXX-20025 Page 56 of 57 Westinghouse Non-Proprietary Class 3 5 References
1. Steam Generator Program Guidelines, NEI 97-06 Revision 3, January 2011.
2. Steam Generator Management Program: Pressurized Water Reactor Steam Generator Examination Guidelines: Revision 8, EPRI, Palo Alto, CA: 2016. 3002007572.
3. Steam Generator Management Program: Steam Generator Integrity Assessment Guidelines, Revision 4. EPRI, Palo Alto, CA: 2016. 3002007571.
4. Steam Generator Management Program: Steam Generator Degradation Specific Management Flaw Handbook, Revision 2. EPRI, Palo Alto, CA: October 2015.

3002005426.

5. Vistra Energy Report, TXX-17083, Comanche Peak Nuclear Power Plant Unit 2 Sixteenth Refueling Outage (2RF16) Steam Generator 180 Day Report, October 2017.
6. Vistra Energy Report, TXX-19063, Unit 2 Seventeenth Refueling Outage (2RF17) Steam Generator 180 Day Report, June 2019.
7. Email from Ashley Birdett (Luminant) to Westinghouse (EFPY), Burnup Estimate for U2C17-19, dated April 6, 2020. (Attached in EDMS)
8. Email from Ashley Birdett (Luminant) to Westinghouse, Comanche Peak 2RF18 Degradation Assessment Inputs, dated March 3, 2020. (Attached in EDMS)
9. Westinghouse Letter WPT-17797, Revision 0, Comanche Peak Nuclear Power Plant Unit 2 Steam Generator 1 Channel Head Cladding Flaw, April 2014. (Westinghouse Proprietary Class 2)
10. Westinghouse Letter, WPT-18035, Revision 0, Comanche Peak Nuclear Power Plant Unit 2 Steam Generator 2 Channel Head Cladding Anomaly, April 2017. (Westinghouse Proprietary Class 2)
11. American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, 2007 Edition through 2008 Addenda.
12. Westinghouse Letter WPT-18036, Revision 1, Comanche Peak Nuclear Power Plant Unit 2 Evaluation of Steam Generator Secondary Side Foreign Objects at Comanche Peak Unit 2 during Spring 2017 Outage 2RF16, April 2017. (Westinghouse Proprietary Class 2)
13. Westinghouse Calculation Note, CN-SGDA-06-81, Revision 0, Effect of 3628 MWt NSSS Uprate on Steam Generator Foreign Objects Analysis for Comanche Peak Unit 2, December 2006. (Westinghouse Proprietary Class 2)
14. Westinghouse Letter, LTR-CDMP-19-38, Revision 0, Software Release Letter for Single Flaw Model, Version 2.4, September 2019.
15. Westinghouse Letter LTR-CDMP-19-37, Revision 0, Software Release Letter for Full Bundle Model, Version 2.2, September 2019.
16. EPRI Computer Software Product 30020010334, Steam Generator Management Program:

Model Assisted Probability of Detection Using R (MAPOD-R) Version 2.1, 2017.

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17. NRC Safety Evaluation Report, Comanche Peak Nuclear Power Plant, Units 1 and 2 -

Issuance of Amendments RE: License Amendment Request for Changes to Technical Specifications 5.5.9 and 5.6.9 Regarding Alternate Steam Generator Repair Criteria (TAC Nos. ME8374 and ME8375), dated October 18, 2012. ADAMS Accession No. ML12263A036.

18. Comanche Peak Unit 2 Plant Technical Specification 5.5.9.
19. Westinghouse Report, WPT-18228, Revision 0, Comanche Peak 2RF18 Steam Generator Degradation Assessment, April 2020. (Westinghouse Proprietary Class 2)
20. NEI TSTF-510, Revision 2, Revision to Steam Generator Program Inspection Frequencies and Tube Sample Inspection, April 2012.

SG-CDMP-20-13 Revision 0 Page 56 of 56

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