ML20024D211

Pre-Submittal Meeting for License Amendment Request (LAR) Revised Steam Generator (SG) Inspection Intervals - January 27, 2020

ML20024D211
Person / Time
Site:	Sequoyah
Issue date:	01/27/2020
From:	Tennessee Valley Authority
To:	Perry Buckberg Plant Licensing Branch II
Buckberg P
References
Download: ML20024D211 (25)

Text

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

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

Agenda

• 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 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).

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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.

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Proposed TS Change (Markups)

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

Proposed TS Change (Markups)

SQN Unit 1 - TS 5.5.7 d. 2. b, c, and d l 9

Proposed TS Change (Markups)

SQN Unit 1 - TS 5.6.6.i, Steam Generator Tube Inspection Report l 10

Proposed TS Change (Clean)

SQN Unit 1 - TS 5.5.7 d. 2 l 11

Proposed TS Change (Clean)

SQN Unit 1 - TS 5.5.7 d. 2. a and b l 12

Proposed TS Change (Clean)

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.

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.

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

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.

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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.

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%

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

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.

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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.

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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).

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Trending of Existing Degradation Mechanisms 1

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 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

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.

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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.

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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.

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