ML20169A522
| ML20169A522 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 06/25/2020 |
| From: | Kimberly Green Plant Licensing Branch II |
| To: | Jim Barstow Tennessee Valley Authority |
| Green K | |
| References | |
| Download: ML20169A522 (33) | |
Text
Watts Bar Nuclear Plant (WBN) Unit 1 Pre-Submittal Meeting for License Amendment Request (LAR)
Revised Steam Generator (SG) Inspection Intervals and TSTF-510 June 25, 2020
Agenda
- Opening Remarks
- Background
- WBN Unit 1 Replacement Steam Generators (RSGs)
- Current Technical Specification (TS) SG Requirements
- Proposed TS SG Requirements
- RSG Inspection History
- RSG Secondary Side
- Operational Assessments
- LAR Layout
- TSTF-510 Variations
- Proposed TS Changes
- LAR Schedule Milestones
- Closing Remarks l 2
Opening Remarks
- Purpose of the meeting is to discuss a proposed LAR for a revision to the WBN Unit 1 TS for the SG inspection intervals for the life of the plant and to adopt Technical Specification Task Force (TSTF)-
510, "Revision to Steam Generator Program Inspection Frequencies and Tube Sample Selection."
- Tennessee Valley Authority (TVA) is scheduled to perform the next WBN Unit 1 SG tube inspection during the WBN Unit 1 Cycle 17 Refueling Outage (U1R17), scheduled to commence in October 2021.
- TVA has been involved in the development of Technical Specification Task Force (TSTF)-577, Performance Based Frequencies for Steam Generator Tube Inspections, along with meetings between the industry and the Nuclear Regulatory Commission (NRC).
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Opening Remarks
- The operational experience of the WBN 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.
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Background
- SG TS are based on performance of the tube material.
- Current TS inspection intervals developed under TSTF-449 with some uncertainty around Alloy 690TT tubing performance. Proposed TS changes include TS-510.
- 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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- Four RSGs per unit
- Replaced U1R7 (Fall 2006)
- Westinghouse Model 68AXP
- Recirculating SG design
- 5,128 Alloy 690TT tubes in triangular pitch
- Advanced tube support grid (ATSG) straight leg tube supports
- Ventilated flat bar U-bend tube supports
- Axial flow preheater
- Two stage moisture separators l 6
- 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.
- WBN Unit 1 is currently in the 144 EFPM sequential period.
- Completion scheduled for Fall 2021 just prior to U1R17 outage.
- Inspection outages were U1R8, U1R11 and U1R14.
- 100% inspection during the next 108 EFPM (second inspection period).
- 100% inspection within the next 72 EFPM (third inspection period) and 60 EFPM thereafter.
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- 100% inspection within the next 96 EFPM (second and subsequent inspection periods).
- Revise TS on the Steam Generator Tube Inspection Report to require discussion of trending of tube degradation over the inspection interval and provide comparison of the prior operational assessment degradation projections to the as-found condition.
- Proposed TS changes are consistent with similar LAR for Sequoyah Unit 1, submitted to NRC on February 24, 2020 (ML20056C857).
- TS markups (including those for TSTF-510) are provided later in the presentation.
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Current and Proposed WBN Unit 1 RSG Sequential Periods SGs Replaced 1R8 1R9 1R10 1R11 1R12 1R13 1R14 1R15 1R16 1R17 1R18 1R19 1R20 1R21 1R22 1R23 1R24 1R25 1R26 1R7 S-08 F-09 S-11 F-12 S-14 F-15 S-17 F-18 S-20 F-21 S-23 F-24 S-26 F-27 S-29 F-30 S-32 F-33 S-35 F-06 SG EFPY 1.2 2.6 4 5.3 6.6 8 9.3 10.6 12 13.4 est. 14.8 est. 16.2 est. 17.6 est 19.0 est. 20.4 est 21.8 est. 23.2 est. 24.6 est. 26.0 est.
Cumulative EFPM Within 0 16.8 33.6 49.2 64.8 81.6 97.2 112.8 129.6 2.4 est. 19.2 est. 36 est. 52.8 est. 69.6 est. 86.4 est. 103.2 est. 12 est. 28.8 est. 45.6 est.
Sequential Period TS Sequential End of 1st ISI 144 EFPM Sequential Period 108 EFPM Sequential Period 72 EFPM Sequential Period WBN Period Unit 1 Bobbin 100% No No 57.8% No No 100% No No 33.3% No No 33.3% No No 33.3% No No 50%
License Base Scope1 All SGs ECT ECT All SGs ECT ECT All SGs3 ECT ECT All SGs2 ECT ECT All SGs2 ECT ECT All SGs2 ECT ECT All SGs2 EFPM Within Proposed 15.6 32.4 49.2 est 66 est. 82.8 est. 3.6 est. 20.4 est. 37.2 est. 54 est. 70.8 est. 87.6 est. 8.4 est.
Sequential Period Proposed TS 3rd 96 1st 96 EFPM Sequential Period 2nd 96 EFPM Sequential Period Sequential Period EFPM Bobbin Base Scope Under No No No No 100% No No No No 100% No No 4
Proposed Amendment -> ECT ECT ECT ECT All SGs3 ECT ECT ECT ECT All SGs3 ECT ECT Notes
- 1. The bobbin base scope is accompanied by additional special interest and diagnostic exams using RPC and Array probes.
- 2. The TS minimum required inspection scope determined by dividing 100% by the number of scheduled inspections within the period.
- 3. The WBN U1R14 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.
- 4. The schedule under the proposed amendment revises the allowable inspection interval for each SG to at least every 96 EFPM.
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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 10
Inspection History
- WBN1 RSGs
- 100% pre-service inspection
- Three in-service inspections (1R8, 1R11, and 1R14)
- 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 WBN1 RSGs has been tested in-service at least two times in 14 years of operation.
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RSG Degradation Experience
- Two existing tube degradation mechanisms.
- Mechanical wear at horizontal ATSGs
- Mechanical wear at U-bend supports
- Tube plugging to date: 0.14% (29 tubes)
- 2 tubes plugged pre-service
- 21 tubes plugged for wear at horizontal ATSGs
- No tubes plugged for wear at U-bend supports
- 6 tubes preventively plugged to address foreign object
- No indication has exceeded TS plugging limit of 40% through-wall (TW). l 12
Trending of Existing Degradation Mechanisms WBN Unit 1 RSG Distribution of ATSG Support Wear Depths l 13
SG Secondary Side
- Removes secondary deposit buildup and foreign objects
- Manual retrieval of identified foreign objects
- Inspect possible loose part indications from eddy current
- Performed upper internals inspection of two RSGs at U1R11 and U1R14.
- Preheater water box design traps foreign objects l 14
Operational Assessments
- Following U1R14 100% inspection
- Largest U-bend support wear left in-service is 27%TW
- Largest ATSG wear left in-service is 37%TW
- 95th percentile growth rate of 5.4%TW/EFP Years (EFPY)
- OA supports operation for at least 7.5 EFPY (five cycles) while maintaining tube integrity.
- All WBN as-found inspection results have shown margin compared to three cycle OA worst case projected %TW.
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Operational Assessments (contd)
Examples of conservatism applied in the WBN Unit 1 OAs:
- Tube wear degradation lengths are assumed to be the full length of the tube support intersections.
- 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 Layout
- Enclosure 1 provides a description and technical evaluation of the proposed change, a regulatory evaluation, and a discussion of environmental considerations for the proposed change to the required SG tube inspection frequency
- Enclosure 2 provides a description and assessment of the proposed changes, the requested confirmation of applicability, and plant-specific verifications associated with TSTF-510.
- Enclosure 3 provides the existing WBN Unit 1 TS pages marked up to show the proposed changes.
- Enclosure 4 provides the existing WBN Unit 1 TS pages retyped to show the proposed changes.
- Enclosure 5 provides the existing WBN Unit 1 TS Bases pages marked-up to show the proposed changes to meet TSTF-510 (no TS Bases changes are required for the SG tube inspection frequency).
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TSTF-510 Variations
- The WBN Unit 1 TS utilize different numbering than the Standard Technical Specifications (STSs) on which TSTF-510 was based.
- STS 5.5.9, "Steam Generator (SG) Program," is numbered as TS 5.7.2.12 in the WBN Unit 1 TS and STS 5.6.7, Steam Generator Tube Inspection Report, is numbered as TS 5.9.9 in the WBN Unit 1 TS. These differences are administrative and do not affect the applicability of TSTF-510 to the WBN Unit 1 TS.
- Current verbiage: For design basis accidents that have a faulted steam generator, accident induced leakage is not to exceed 1.0 gallon per minute (gpm) for the faulted steam generator and 150 gallons per day (gpd) for the non-faulted steam generators. For design basis accidents that do not have a faulted steam generator, accident induced leakage is not to exceed 150 gpd per steam generator. This verbiage originated in WBN 1 License Amendment 65 (ML062910090), which implemented TSTF-449.
- Revised verbiage: Leakage for all degradation mechanisms is not to exceed 150 gpd for each unfaulted SG. Leakage for all degradation mechanisms is not to exceed 1 gpm in the faulted SG. The proposed verbiage is consistent with the WBN Unit 2 TS per License Amendment 28 (ML19063B721) and WBN dual unit Updated Final Safety Analysis Report (UFSAR)
Section 15.5.4.
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Proposed TS Changes (Markups)
Yellow - TSTF 510 Blue - SG Inspection Frequency l 19
Proposed TS Changes (Markups)
Yellow - TSTF 510 Blue - SG Inspection Frequency l 20
Proposed TS Changes (Markups)
Yellow - TSTF 510 Blue - SG Inspection Frequency l 21
Proposed TS Changes (Markups)
Yellow - TSTF 510 Blue - SG Inspection Frequency WBN Unit 1 - TS 5.7.2.12 l 22
Proposed TS Changes (Markups)
Yellow - TSTF 510 Blue - SG Inspection Frequency l 23
Proposed TS Changes (Markups)
Yellow - TSTF 510 Blue - SG Inspection Frequency l 24
Proposed TS Changes (Clean) l 25
Proposed TS Change (Clean) l 26
Proposed TS Change (Clean) l 27
Proposed TS Change (Clean) l 28
Proposed TS Change (Clean) l 29
Proposed TS Change (Clean) l 30
LAR Schedule Milestones
- June 25, 2020 - LAR pre-submittal meeting with NRC
- August 30, 2020 - LAR submittal - Request NRC approval within 12 months of submittal (this is a no later than date)
- NRC approval of LAR within one year from the date of the submittal (Requested). 30-day implementation period
- October 2021 - Scheduled start of WBN U1R17 outage l 31
Summary
- Positive WBN operational performance of Alloy 690TT.
- Existing WBN1 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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