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Revised Steam Generator (SG) Inspection Intervals January 27, 2020
Revised Steam Generator (SG) Inspection Intervals January 27, 2020


Agenda
Opening Remarks
* Opening Remarks
 
* Background
===Background===
* SQN Unit 1 Replacement Steam Generators (RSGs)
SQN Unit 1 Replacement Steam Generators (RSGs)
* Current Technical Specification (TS) SG Requirements
Current Technical Specification (TS) SG Requirements Proposed TS Changes RSG Inspection History RSG Secondary Side Operational Assessments LAR Schedule Milestones Closing Remarks Agenda l 2
* Proposed TS Changes
* RSG Inspection History
* RSG Secondary Side
* Operational Assessments
* LAR Schedule Milestones
* Closing Remarks l 2


Opening Remarks
Opening Remarks Purpose of the meeting is to discuss a proposed LAR for a revision to the SQN Unit 1 TS for the SG inspection intervals for the life of the plant.
* Purpose of the meeting is to discuss a proposed LAR for a revision to the SQN Unit 1 TS for the SG inspection intervals for the life of the plant.
TVA is scheduled to perform the next SQN Unit 1 SG tube inspection during the SQN Unit 1 Cycle 24 Refueling Outage (U1R24), scheduled to commence on April 10, 2021.
* TVA is scheduled to perform the next SQN Unit 1 SG tube inspection during the SQN Unit 1 Cycle 24 Refueling Outage (U1R24), scheduled to commence on April 10, 2021.
Tennessee Valley Authority (TVA) has been involved in the development of Technical Specification Task Force (TSTF)-577, Performance Based Frequencies for Steam Generator Tube Inspections, along with meeting between the industry and the Nuclear Regulatory Commission (NRC).
* Tennessee Valley Authority (TVA) has been involved in the development of Technical Specification Task Force (TSTF)-577, Performance Based Frequencies for Steam Generator Tube Inspections, along with meeting between the industry and the Nuclear Regulatory Commission (NRC).
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Opening Remarks
Opening Remarks The operational experience of the SQN RSGs, as described in this presentation, demonstrate that the proposed change to the schedule for the SG inspections is appropriate and will result in a reduction of person-hours, dose to personnel, and risk to the plant.
* The operational experience of the SQN RSGs, as described in this presentation, demonstrate that the proposed change to the schedule for the SG inspections is appropriate and will result in a reduction of person-hours, dose to personnel, and risk to the plant.
TVA plans to follow the guidance in TSTF-577 for future similar LARs.
* TVA plans to follow the guidance in TSTF-577 for future similar LARs.
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===Background===
===
Background===
* SG TS are based on performance of the tube material.
* SG TS are based on performance of the tube material.
* Current TS inspection intervals developed under TSTF-449 and TSTF-510 with some uncertainty around Alloy 690TT tubing performance.
* Current TS inspection intervals developed under TSTF-449 and TSTF-510 with some uncertainty around Alloy 690TT tubing performance.
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Sequoyah Unit 1 RSGs
Sequoyah Unit 1 RSGs Four RSGs per unit Replaced U1R12 (spring of 2003)
- Four RSGs per unit
Westinghouse Model 57AG Recirculating SG design 4,983 Alloy 690TT tubes in triangular pitch Advanced tube support grid (ATSG) straight leg tube supports Ventilated flat bar U-bend tube supports Feedring with spray nozzles Two stage moisture separator design Similar to Unit 2 l 6
- Replaced U1R12 (spring of 2003)
- Westinghouse Model 57AG
- Recirculating SG design
- 4,983 Alloy 690TT tubes in triangular pitch
- Advanced tube support grid (ATSG) straight leg tube supports
- Ventilated flat bar U-bend tube supports
- Feedring with spray nozzles
- Two stage moisture separator design
- Similar to Unit 2                       l 6


Current SQN Unit 1 SG TS
Current SQN Unit 1 SG TS Maximum interval of 72 effective full power months (EFPM) or three refueling outages.
* Maximum interval of 72 effective full power months (EFPM) or three refueling outages.
After the first refueling outage following SG installation, inspect 100% of the tubes during the next 144 EFPM. This constitutes the first inspection period (completed Fall 2016).
* After the first refueling outage following SG installation, inspect 100% of the tubes during the next 144 EFPM. This constitutes the first inspection period (completed Fall 2016).
100% inspection during the next 120 EFPM (second inspection period).
* 100% inspection during the next 120 EFPM (second inspection period).
SQN Unit 1 is currently in the 120 EFPM sequential period.
    -    SQN Unit 1 is currently in the 120 EFPM sequential period.
Two scheduled inspections within period (1R24, 1R27) 100% inspection within the next 96 EFPM (third inspection period) and 72 EFPM thereafter.
    -    Two scheduled inspections within period (1R24, 1R27)
* 100% inspection within the next 96 EFPM (third inspection period) and 72 EFPM thereafter.
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Proposed TS Change (Markups)
Proposed TS Change (Markups) l 8 SQN Unit 1 - TS 5.5.7 d. 2, Steam Generator (SG) Program
SQN Unit 1 - TS 5.5.7 d. 2, Steam Generator (SG) Program l 8


Proposed TS Change (Markups)
Proposed TS Change (Markups) l 9 SQN Unit 1 - TS 5.5.7 d. 2. b, c, and d
SQN Unit 1 - TS 5.5.7 d. 2. b, c, and d l 9


Proposed TS Change (Markups)
Proposed TS Change (Markups) l 10 SQN Unit 1 - TS 5.6.6.i, Steam Generator Tube Inspection Report
SQN Unit 1 - TS 5.6.6.i, Steam Generator Tube Inspection Report l 10


Proposed TS Change (Clean)
Proposed TS Change (Clean) l 11 SQN Unit 1 - TS 5.5.7 d. 2
SQN Unit 1 - TS 5.5.7 d. 2 l 11


Proposed TS Change (Clean)
Proposed TS Change (Clean) l 12 SQN Unit 1 - TS 5.5.7 d. 2. a and b
SQN Unit 1 - TS 5.5.7 d. 2. a and b l 12


Proposed TS Change (Clean)
Proposed TS Change (Clean) l 13 SQN Unit 1 - TS 5.6.6.i
SQN Unit 1 - TS 5.6.6.i l 13


Current and Proposed SQN Unit 1 RSG Sequential Periods SGs Replaced 1R13     1R14  1R15    1R16      1R17      1R18      1R19  1R20      1R21            1R22 1R23      1R24      1R25      1R26      1R27      1R28      1R29 1R12 F-04     S-06   F-07   S-09       F-10     S-12       S-13 S-15     F-16           S-18 F-19     S-21       F-22     S-24       F-25     S-27       F-28 S-03 SG EFPY 1.3       2.7   4.1     5.4       6.8       8         9.5   11       12.4           13.7 14.9   16.3 est. 17.7 est 19.1 est. 20.5 est 21.9 est. 23.3 est.
Current and Proposed SQN Unit 1 RSG Sequential Periods l 14 Notes 1.
Cumulative                                                                                          End of                                                                              End of EFPM Within                                                                                           1st                                                                                2nd 0       16.8   33.6   49.2       66     80.4       98.4 116.4     133.2             4.8 19.2     36 est. 52.3 est. 69.1 est. 85.9 est 102.7 est. 119.5 est.
The schedule under the proposed amendment revise the allowable inspection interval for each SG to at least every 96 EFPM.
Sequential Period                                                                                     Period                                                                              Period TS Sequential 1st ISI                       144 EFPM Sequential Period                                                      120 EFPM Sequential Period Period Bobbin         100%       No     54%     No       No       46%         No   No     100%             No   No       50%       No         No       50%       No         No Base Scope      All SGs    ECT   All SGs  ECT       ECT     All SGs      ECT   ECT     All SGs3         ECT   ECT     All SGs2    ECT      ECT      All SGs2  ECT        ECT Inspection Schedule under   No  No        No        No      100%        No        No        No Proposed Amendment1 ->   ECT  ECT      ECT        ECT    All SGs3    ECT      ECT        ECT Notes
2.
: 1. The schedule under the proposed amendment revise the allowable inspection interval for each SG to at least every 96 EFPM.
50% is the TS minimum required inspection scope determined by dividing 100% by the number of scheduled inspections within the period.
: 2. 50% is the TS minimum required inspection scope determined by dividing 100% by the number of scheduled inspections within the period.
3.
: 3. The SQN U1R21 inspection consisted of a 100% combination bobbin and array coil inspection of all tubes full length with the exception of the U-bend sections of tube Rows 1 through 4, which were inspected with a singular bobbin probe due to dimensional constraints. This is the planned scope for all scheduled inspections under the proposed amendment.
The SQN U1R21 inspection consisted of a 100% combination bobbin and array coil inspection of all tubes full length with the exception of the U-bend sections of tube Rows 1 through 4, which were inspected with a singular bobbin probe due to dimensional constraints. This is the planned scope for all scheduled inspections under the proposed amendment.
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SGs Replaced 1R12 S-03 1R13 F-04 1R14 S-06 1R15 F-07 1R16 S-09 1R17 F-10 1R18 S-12 1R19 S-13 1R20 S-15 1R21 F-16 1R22 S-18 1R23 F-19 1R24 S-21 1R25 F-22 1R26 S-24 1R27 F-25 1R28 S-27 1R29 F-28 SG EFPY Cumulative 1.3 2.7 4.1 5.4 6.8 8
9.5 11 12.4 13.7 14.9 16.3 est.
17.7 est 19.1 est.
20.5 est 21.9 est.
23.3 est.
EFPM Within Sequential Period 0
16.8 33.6 49.2 66 80.4 98.4 116.4 133.2 4.8 19.2 36 est.
52.3 est.
69.1 est.
85.9 est 102.7 est. 119.5 est.
TS Sequential Period 1st ISI Bobbin Base Scope 100%
All SGs No ECT 54%
All SGs No ECT No ECT 46%
All SGs No ECT No ECT 100%
All SGs3 No ECT No ECT 50%
All SGs2 No ECT No ECT 50%
All SGs2 No ECT No ECT No ECT No ECT No ECT No ECT 100%
All SGs3 No ECT No ECT No ECT End of 1st Period 144 EFPM Sequential Period 120 EFPM Sequential Period Inspection Schedule under Proposed Amendment1 ->
End of 2nd Period


Current and Proposed SQN Unit 1 RSG Sequential Periods 1R30       1R31      1R32      1R33      1R34                1R35        1R36      1R37      1R38      1R39 S-30       F-31     S-33       F-34     S-36               F-37       S-39       F-40       S-42       F-43 SG EFPY 24.7 est. 26.1 est. 27.5 est. 28.9 est. 30.3 est.             31.7 est. 33.1 est. 34.5 est. 35.9 est. 37.3 est.
Current and Proposed SQN Unit 1 RSG Sequential Periods l 15 Notes 1.
Cumulative End of                                                        End of                                                          End of EFPM Within 2nd      16.3 est. 33.1 est. 49.9 est. 66.7 est. 83.5 est.     3rd    4.3 est. 21.1 est. 37.9 est. 54.7 est. 71.5 est. 4th Sequential Period Period                                                        Period                                                          Period TS Sequential 96 EFPM Sequential Period                                      72 EFPM Sequential Period Period Bobbin                         50%       No       No         50%       No                 No         50%       No         No       50%
The schedule under the proposed amendment revise the allowable inspection interval for each SG to at least every 96 EFPM.
2                              2                                          2                                2 Base Scope                    All SGs      ECT      ECT      All SGs    ECT                  ECT      All SGs    ECT        ECT      All SGs Inspection Schedule under                 No      100%      No        No        No                  No        100%        No        No        No Proposed Amendment1 ->                   ECT     All SGs3   ECT       ECT       ECT                 ECT       All SGs3   ECT       ECT       ECT Notes
2.
: 1. The schedule under the proposed amendment revise the allowable inspection interval for each SG to at least every 96 EFPM.
50% is the TS minimum required inspection scope determined by dividing 100% by the number of scheduled inspections within the period.
: 2. 50% is the TS minimum required inspection scope determined by dividing 100% by the number of scheduled inspections within the period.
3.
: 3. The SQN U1R21 inspection consisted of a 100% combination bobbin and array coil inspection of all tubes full length with the exception of the U-bend sections of tube Rows 1 through 4, which were inspected with a singular bobbin probe due to dimensional constraints. This is the planned scope for all scheduled inspections under the proposed amendment.
The SQN U1R21 inspection consisted of a 100% combination bobbin and array coil inspection of all tubes full length with the exception of the U-bend sections of tube Rows 1 through 4, which were inspected with a singular bobbin probe due to dimensional constraints. This is the planned scope for all scheduled inspections under the proposed amendment.
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1R30 S-30 1R31 F-31 1R32 S-33 1R33 F-34 1R34 S-36 1R35 F-37 1R36 S-39 1R37 F-40 1R38 S-42 1R39 F-43 SG EFPY Cumulative 24.7 est.
26.1 est.
27.5 est.
28.9 est.
30.3 est.
31.7 est.
33.1 est.
34.5 est.
35.9 est.
37.3 est.
EFPM Within Sequential Period 16.3 est.
33.1 est.
49.9 est.
66.7 est.
83.5 est.
4.3 est.
21.1 est.
37.9 est.
54.7 est.
71.5 est.
TS Sequential Period Bobbin Base Scope 50%
All SGs2 No ECT No ECT 50%
All SGs2 No ECT No ECT 50%
All SGs2 No ECT No ECT 50%
All SGs2 Inspection Schedule under Proposed Amendment1 ->
No ECT 100%
All SGs3 No ECT No ECT No ECT No ECT 100%
All SGs3 No ECT No ECT No ECT 96 EFPM Sequential Period 72 EFPM Sequential Period End of 2nd Period End of 3rd Period End of 4th Period


Benefits of the LAR
Benefits of the LAR
* The proposed TS changes will result in:
* The proposed TS changes will result in:
  - Reduced overall outage dose
Reduced overall outage dose Reduced number of person-hours Improved focus on essential work Eliminate nuclear plant risk l 16
  - Reduced number of person-hours
  - Improved focus on essential work
  - Eliminate nuclear plant risk l 16


Inspection History
Inspection History
* SQN1 RSGs
* SQN1 RSGs 100% pre-service inspection Four in-service inspections (1R13, 1R15, 1R18, 1R21)
  - 100% pre-service inspection
Historical inspections applied bobbin and rotating pancake coil (RPC) probe inspection strategies Most recent inspection was 100% full length combination bobbin and array probe
  - Four in-service inspections (1R13, 1R15, 1R18, 1R21)
  - Historical inspections applied bobbin and rotating pancake coil (RPC) probe inspection strategies
  - Most recent inspection was 100% full length combination bobbin and array probe
* Every tube in the SQN1 RSGs has been tested in-service at least three times in 16 years of operation.
* Every tube in the SQN1 RSGs has been tested in-service at least three times in 16 years of operation.
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RSG Degradation Experience
RSG Degradation Experience
* Two existing tube degradation mechanisms.
* Two existing tube degradation mechanisms.
  - Mechanical wear at U-bend supports
Mechanical wear at U-bend supports Mechanical wear at horizontal ATSGs
  - Mechanical wear at horizontal ATSGs
* Tube plugging to date: 0.17% (34 tubes) 20 tubes plugged pre-service 14 tubes preventively plugged for wear at U-bend supports No tubes plugged for wear at horizontal ATSGs
* Tube plugging to date: 0.17% (34 tubes)
  - 20 tubes plugged pre-service
  - 14 tubes preventively plugged for wear at U-bend supports
  - No tubes plugged for wear at horizontal ATSGs
* No indication has exceeded TS plugging limit of 40% through-wall (TW).
* No indication has exceeded TS plugging limit of 40% through-wall (TW).
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Trending of Existing Degradation Mechanisms 1
Trending of Existing Degradation Mechanisms l 19 SQN Unit 1 RSG Distribution of U-bend Support Wear Depths 0
0.95 0.9 0.85 U1R21 0.8 U1R18 0.75                                                  U1R15 0.7                                                  U1R13 Cumulative Density Function (CDF) 0.65                                                  Plugged Tubes 0.6 0.55 0.5                                                                       40%TW TS 0.45                                                                      Plugging Limit 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0
0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1
0   5     10     15     20         25           30         35     40       45   50 U-Bend Support %TW in (all SGs) l 19 SQN Unit 1 RSG Distribution of U-bend Support Wear Depths
0 5
10 15 20 25 30 35 40 45 50 Cumulative Density Function (CDF)
U-Bend Support %TW in (all SGs)
U1R21 U1R18 U1R15 U1R13 Plugged Tubes 40%TW TS Plugging Limit


SG Secondary Side
SG Secondary Side
* Tubesheet cleaned every SG inspection since RSG install.
* Tubesheet cleaned every SG inspection since RSG install.
  - Removes secondary deposit buildup and foreign objects
Removes secondary deposit buildup and foreign objects
* Foreign object search and retrieval (FOSAR) performed every SG inspection since RSG install.
* Foreign object search and retrieval (FOSAR) performed every SG inspection since RSG install.
  - Manual retrieval of identified foreign objects
Manual retrieval of identified foreign objects Inspect possible loose part indications from eddy current
  - Inspect possible loose part indications from eddy current
* Performed upper internals inspection of all four RSGs at U1R18.
* Performed upper internals inspection of all four RSGs at U1R18.
  - Feedring spray can nozzles trap foreign objects l 20
Feedring spray can nozzles trap foreign objects l 20


Operational Assessments
Operational Assessments
* Following U1R21 100% inspection
* Following U1R21 100% inspection Largest U-bend support wear left in-service is 28%TW Largest ATSG wear left in-service is 22%TW 95th percentile growth rate of 3.7%TW/EFP Years (EFPY)
  -  Largest U-bend support wear left in-service is 28%TW
  -  Largest ATSG wear left in-service is 22%TW
  -  95th percentile growth rate of 3.7%TW/EFP Years (EFPY)
* OA supports operation for at least 7.5 EFPY (five cycles) while maintaining tube integrity.
* OA supports operation for at least 7.5 EFPY (five cycles) while maintaining tube integrity.
* All SQN as-found inspection results have shown margin of >15%TW compared to three cycle OA worst case projected %TW.
* All SQN as-found inspection results have shown margin of >15%TW compared to three cycle OA worst case projected %TW.
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Operational Assessments (contd)
Operational Assessments (contd)
Examples of conservatism applied in the SQN Unit 1 OAs:
Examples of conservatism applied in the SQN Unit 1 OAs:
* Tube wear degradation lengths are assumed to be the full length of the tube support intersections.
Tube wear degradation lengths are assumed to be the full length of the tube support intersections.
* Each SQN Unit 1 operating cycle is assumed to be 1.5 EFPY.
Each SQN Unit 1 operating cycle is assumed to be 1.5 EFPY.
* Structural Integrity Performance Criteria (SIPC) of three times normal operating pressure differential is conservatively determined.
Structural Integrity Performance Criteria (SIPC) of three times normal operating pressure differential is conservatively determined.
    - The value applied does not include pressure drops within the system between the measurement point and the secondary side of the tubing.
The value applied does not include pressure drops within the system between the measurement point and the secondary side of the tubing.
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LAR Schedule Milestones
LAR Schedule Milestones January 27, 2020 - LAR pre-submittal meeting with NRC March 10, 2020 - LAR submittal - Request NRC approval within 12 months of submittal April 2020 - Teleconference or meeting to discuss any NRC questions March 10, 2021 - NRC approval of LAR (Requested). 30-day implementation period April 10, 2021 - Scheduled start of SQN U1R24 outage l 23
* January 27, 2020 - LAR pre-submittal meeting with NRC
* March 10, 2020 - LAR submittal - Request NRC approval within 12 months of submittal
* April 2020 - Teleconference or meeting to discuss any NRC questions
* March 10, 2021 - NRC approval of LAR (Requested). 30-day implementation period
* April 10, 2021 - Scheduled start of SQN U1R24 outage l 23


Summary
Summary Positive SQN operational performance of Alloy 690TT.
* Positive SQN operational performance of Alloy 690TT.
SQN performs comprehensive RSG inspections.
* SQN performs comprehensive RSG inspections.
Existing SQN1 RSG degradation mechanisms are understood and exhibit predictable behavior.
* Existing SQN1 RSG degradation mechanisms are understood and exhibit predictable behavior.
Operational assessments accurate and appropriately conservative.
* Operational assessments accurate and appropriately conservative.
Proposed TS changes are consistent with performance of Alloy 690TT tube material.
* Proposed TS changes are consistent with performance of Alloy 690TT tube material.
Degradation trending will be provided to NRC through enhanced reporting.
* Degradation trending will be provided to NRC through enhanced reporting.
Proposed TS changes are intended to be consistent with the proposed TSTF-577.
* Proposed TS changes are intended to be consistent with the proposed TSTF-577.
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Latest revision as of 23:46, 20 December 2024

Pre-Submittal Meeting for License Amendment Request (LAR) Revised Steam Generator (SG) Inspection Intervals - January 27, 2020
ML20024D211
Person / Time
Site: Sequoyah Tennessee Valley Authority icon.png
Issue date: 01/27/2020
From:
Tennessee Valley Authority
To: Perry Buckberg
Plant Licensing Branch II
Buckberg P
References
Download: ML20024D211 (25)
v • d • e


Text

Sequoyah Nuclear Plant (SQN) Unit 1 Pre-Submittal Meeting for License Amendment Request (LAR)

Revised Steam Generator (SG) Inspection Intervals January 27, 2020

Opening Remarks

Background

SQN Unit 1 Replacement Steam Generators (RSGs)

Current Technical Specification (TS) SG Requirements Proposed TS Changes RSG Inspection History RSG Secondary Side Operational Assessments LAR Schedule Milestones Closing Remarks Agenda l 2

Opening Remarks Purpose of the meeting is to discuss a proposed LAR for a revision to the SQN Unit 1 TS for the SG inspection intervals for the life of the plant.

TVA is scheduled to perform the next SQN Unit 1 SG tube inspection during the SQN Unit 1 Cycle 24 Refueling Outage (U1R24), scheduled to commence on April 10, 2021.

Tennessee Valley Authority (TVA) has been involved in the development of Technical Specification Task Force (TSTF)-577, Performance Based Frequencies for Steam Generator Tube Inspections, along with meeting between the industry and the Nuclear Regulatory Commission (NRC).

l 3

Opening Remarks The operational experience of the SQN RSGs, as described in this presentation, demonstrate that the proposed change to the schedule for the SG inspections is appropriate and will result in a reduction of person-hours, dose to personnel, and risk to the plant.

TVA plans to follow the guidance in TSTF-577 for future similar LARs.

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=

Background===

  • SG TS are based on performance of the tube material.
  • Current TS inspection intervals developed under TSTF-449 and TSTF-510 with some uncertainty around Alloy 690TT tubing performance.
  • Significant experience gained over the course of 15 years of additional Alloy 690TT service.
  • TS inspection intervals need to incorporate operating experiences.

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Sequoyah Unit 1 RSGs Four RSGs per unit Replaced U1R12 (spring of 2003)

Westinghouse Model 57AG Recirculating SG design 4,983 Alloy 690TT tubes in triangular pitch Advanced tube support grid (ATSG) straight leg tube supports Ventilated flat bar U-bend tube supports Feedring with spray nozzles Two stage moisture separator design Similar to Unit 2 l 6

Current SQN Unit 1 SG TS Maximum interval of 72 effective full power months (EFPM) or three refueling outages.

After the first refueling outage following SG installation, inspect 100% of the tubes during the next 144 EFPM. This constitutes the first inspection period (completed Fall 2016).

100% inspection during the next 120 EFPM (second inspection period).

SQN Unit 1 is currently in the 120 EFPM sequential period.

Two scheduled inspections within period (1R24, 1R27) 100% inspection within the next 96 EFPM (third inspection period) and 72 EFPM thereafter.

l 7

Proposed TS Change (Markups) l 8 SQN Unit 1 - TS 5.5.7 d. 2, Steam Generator (SG) Program

Proposed TS Change (Markups) l 9 SQN Unit 1 - TS 5.5.7 d. 2. b, c, and d

Proposed TS Change (Markups) l 10 SQN Unit 1 - TS 5.6.6.i, Steam Generator Tube Inspection Report

Proposed TS Change (Clean) l 11 SQN Unit 1 - TS 5.5.7 d. 2

Proposed TS Change (Clean) l 12 SQN Unit 1 - TS 5.5.7 d. 2. a and b

Proposed TS Change (Clean) l 13 SQN Unit 1 - TS 5.6.6.i

Current and Proposed SQN Unit 1 RSG Sequential Periods l 14 Notes 1.

The schedule under the proposed amendment revise the allowable inspection interval for each SG to at least every 96 EFPM.

2.

50% is the TS minimum required inspection scope determined by dividing 100% by the number of scheduled inspections within the period.

3.

The SQN U1R21 inspection consisted of a 100% combination bobbin and array coil inspection of all tubes full length with the exception of the U-bend sections of tube Rows 1 through 4, which were inspected with a singular bobbin probe due to dimensional constraints. This is the planned scope for all scheduled inspections under the proposed amendment.

SGs Replaced 1R12 S-03 1R13 F-04 1R14 S-06 1R15 F-07 1R16 S-09 1R17 F-10 1R18 S-12 1R19 S-13 1R20 S-15 1R21 F-16 1R22 S-18 1R23 F-19 1R24 S-21 1R25 F-22 1R26 S-24 1R27 F-25 1R28 S-27 1R29 F-28 SG EFPY Cumulative 1.3 2.7 4.1 5.4 6.8 8

9.5 11 12.4 13.7 14.9 16.3 est.

17.7 est 19.1 est.

20.5 est 21.9 est.

23.3 est.

EFPM Within Sequential Period 0

16.8 33.6 49.2 66 80.4 98.4 116.4 133.2 4.8 19.2 36 est.

52.3 est.

69.1 est.

85.9 est 102.7 est. 119.5 est.

TS Sequential Period 1st ISI Bobbin Base Scope 100%

All SGs No ECT 54%

All SGs No ECT No ECT 46%

All SGs No ECT No ECT 100%

All SGs3 No ECT No ECT 50%

All SGs2 No ECT No ECT 50%

All SGs2 No ECT No ECT No ECT No ECT No ECT No ECT 100%

All SGs3 No ECT No ECT No ECT End of 1st Period 144 EFPM Sequential Period 120 EFPM Sequential Period Inspection Schedule under Proposed Amendment1 ->

End of 2nd Period

Current and Proposed SQN Unit 1 RSG Sequential Periods l 15 Notes 1.

The schedule under the proposed amendment revise the allowable inspection interval for each SG to at least every 96 EFPM.

2.

50% is the TS minimum required inspection scope determined by dividing 100% by the number of scheduled inspections within the period.

3.

The SQN U1R21 inspection consisted of a 100% combination bobbin and array coil inspection of all tubes full length with the exception of the U-bend sections of tube Rows 1 through 4, which were inspected with a singular bobbin probe due to dimensional constraints. This is the planned scope for all scheduled inspections under the proposed amendment.

1R30 S-30 1R31 F-31 1R32 S-33 1R33 F-34 1R34 S-36 1R35 F-37 1R36 S-39 1R37 F-40 1R38 S-42 1R39 F-43 SG EFPY Cumulative 24.7 est.

26.1 est.

27.5 est.

28.9 est.

30.3 est.

31.7 est.

33.1 est.

34.5 est.

35.9 est.

37.3 est.

EFPM Within Sequential Period 16.3 est.

33.1 est.

49.9 est.

66.7 est.

83.5 est.

4.3 est.

21.1 est.

37.9 est.

54.7 est.

71.5 est.

TS Sequential Period Bobbin Base Scope 50%

All SGs2 No ECT No ECT 50%

All SGs2 No ECT No ECT 50%

All SGs2 No ECT No ECT 50%

All SGs2 Inspection Schedule under Proposed Amendment1 ->

No ECT 100%

All SGs3 No ECT No ECT No ECT No ECT 100%

All SGs3 No ECT No ECT No ECT 96 EFPM Sequential Period 72 EFPM Sequential Period End of 2nd Period End of 3rd Period End of 4th Period

Benefits of the LAR

  • The proposed TS changes will result in:

Reduced overall outage dose Reduced number of person-hours Improved focus on essential work Eliminate nuclear plant risk l 16

Inspection History

  • SQN1 RSGs 100% pre-service inspection Four in-service inspections (1R13, 1R15, 1R18, 1R21)

Historical inspections applied bobbin and rotating pancake coil (RPC) probe inspection strategies Most recent inspection was 100% full length combination bobbin and array probe

  • Every tube in the SQN1 RSGs has been tested in-service at least three times in 16 years of operation.

l 17

RSG Degradation Experience

  • Two existing tube degradation mechanisms.

Mechanical wear at U-bend supports Mechanical wear at horizontal ATSGs

  • Tube plugging to date: 0.17% (34 tubes) 20 tubes plugged pre-service 14 tubes preventively plugged for wear at U-bend supports No tubes plugged for wear at horizontal ATSGs
  • No indication has exceeded TS plugging limit of 40% through-wall (TW).

l 18

Trending of Existing Degradation Mechanisms l 19 SQN Unit 1 RSG Distribution of U-bend Support Wear Depths 0

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1

0 5

10 15 20 25 30 35 40 45 50 Cumulative Density Function (CDF)

U-Bend Support %TW in (all SGs)

U1R21 U1R18 U1R15 U1R13 Plugged Tubes 40%TW TS Plugging Limit

SG Secondary Side

  • Tubesheet cleaned every SG inspection since RSG install.

Removes secondary deposit buildup and foreign objects

  • Foreign object search and retrieval (FOSAR) performed every SG inspection since RSG install.

Manual retrieval of identified foreign objects Inspect possible loose part indications from eddy current

  • Performed upper internals inspection of all four RSGs at U1R18.

Feedring spray can nozzles trap foreign objects l 20

Operational Assessments

  • Following U1R21 100% inspection Largest U-bend support wear left in-service is 28%TW Largest ATSG wear left in-service is 22%TW 95th percentile growth rate of 3.7%TW/EFP Years (EFPY)
  • OA supports operation for at least 7.5 EFPY (five cycles) while maintaining tube integrity.
  • All SQN as-found inspection results have shown margin of >15%TW compared to three cycle OA worst case projected %TW.

l 21

Operational Assessments (contd)

Examples of conservatism applied in the SQN Unit 1 OAs:

Tube wear degradation lengths are assumed to be the full length of the tube support intersections.

Each SQN Unit 1 operating cycle is assumed to be 1.5 EFPY.

Structural Integrity Performance Criteria (SIPC) of three times normal operating pressure differential is conservatively determined.

The value applied does not include pressure drops within the system between the measurement point and the secondary side of the tubing.

l 22

LAR Schedule Milestones January 27, 2020 - LAR pre-submittal meeting with NRC March 10, 2020 - LAR submittal - Request NRC approval within 12 months of submittal April 2020 - Teleconference or meeting to discuss any NRC questions March 10, 2021 - NRC approval of LAR (Requested). 30-day implementation period April 10, 2021 - Scheduled start of SQN U1R24 outage l 23

Summary Positive SQN operational performance of Alloy 690TT.

SQN performs comprehensive RSG inspections.

Existing SQN1 RSG degradation mechanisms are understood and exhibit predictable behavior.

Operational assessments accurate and appropriately conservative.

Proposed TS changes are consistent with performance of Alloy 690TT tube material.

Degradation trending will be provided to NRC through enhanced reporting.

Proposed TS changes are intended to be consistent with the proposed TSTF-577.

l 24

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