ML20329A372
| ML20329A372 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 11/24/2020 |
| From: | Tennessee Valley Authority |
| To: | Plant Licensing Branch II |
| Green K, NRR/DORL, LPL2-2, 415-1627 | |
| References | |
| EPID L-2020-LRM-0107 | |
| Download: ML20329A372 (19) | |
Text
Watts Bar Nuclear Plant Unit 2 Pre-Submittal Teleconference for Proposed License Amendment Request Regarding Technical Specification 5.9.9, Steam Generator Tube Inspection Report, to use POPCD Methodology
Agenda Opening Remarks and Purpose of the Proposed LAR Proposed Technical Specification 5.9.9 Changes Introduction Existing SG Tube Degradation Mechanisms post U2R3 Inspection Preliminary GL95-05 Operational Assessment (OA) Predictions Probability of Detection (POD)
Purpose of WBN 2 POPCD Regulatory Precedent Schedule for Submittal Summary and Closing Remarks l 2
Opening Remarks and Purpose of the Proposed LAR The proposed Technical Specification (TS) amendment revises the Watts Bar Nuclear Plant (WBN) Units 2 TS 5.9.9, Steam Generator Tube Inspection Report to add reporting requirement for the Probability of Prior Cycle Detection (POPCD) methodology.
Use of POPCD requires NRC approval.
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Proposed WBN 2 TS 5.9.9 Change l 4
Introduction
- Significant Inspection scope was performed.
- SG-3 did not pass GL95-05 criteria for conditional probability of burst.
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Existing SG Tube Degradation Mechanisms post U2R3 Inspection Volumetric Indications due to Tube Fabrication and Installation Mechanical Wear at Anti-Vibration Bars Mechanical Wear at Tube Support Plates Circumferential ODSCC at the Hot Leg Top of Tubesheet Axial ODSCC at the Hot Leg Top of Tubesheet (New)
Axial PWSCC at the Hot Leg Top of Tubesheet (New)
Circumferential ODSCC at Freespan Dings (New)
Axial ODSCC at Freespan Dings (New)
Axial ODSCC at TSPs - GL 95-05 Axial ODSCC at the FDB - GL 95-05 (New)
Condition Monitoring requirements met for all degradation mechanisms except for GL 95-05 conditional burst probability in SG3 (WBN 2 TS 5.9.9 Item 5) l 6
U2R3 SG Bobbin DSI Voltage CDF l 7
Probability of Detection (POD)
GL95-05 Section 2.b.1 Requires BOC distribution of bobbin DSIs to be scaled upward by factor of 1/POD Conservatively accounts for non-detected crack indications that are assumed to be returned to service.
POD should be assumed to have a value of 0.6, or as an alternative, an NRC approved POD function can be used, if such a function becomes available.
Substantial industry data shows a POD of 1.0 in the range of 3-4 volts.
No undetected indication has exceeded 3.2v (EPRI NP-7490, Add 7) l 8
Preliminary GL95-05 Operational Assessment (OA) Predictions
- Short Term-POD of 1.0 is used to support operation for select flaws.
- Longer Term-POPCD
- POPCD precedent - Sequoyah Nuclear Plant (SQN) Unit 2, Diablo Canyon Units 1 and 2.
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Preliminary GL95-05 Operational Assessment (OA) Predictions l 10 Effective Full Power Days (EFPD)
POD SG 1 503.9 0.6 SG 2 503.9 0.6 up to 3.2v 1.03.2v SG 3 270 POPCD Preliminary 240 0.6 up to 3.2v 1.03.2v 180 0.6 up to 8v 1.08v SG 4 503.9 0.6 up to 3.2v 1.03.2v
Purpose of WBN 2 POPCD
- POPCD will allow a more realistic POD.
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POPCD Definition
- POPCD is calculated as the ratio of indications reported at the prior inspection to the total indications found at the subsequent inspection.
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POPCD Definition
- Premise-all indications that can contribute significantly to burst and leakage for GL95-05 can be confirmed with RPC or equivalent.
- Treats all new indications at an inspection as having been undetected at the prior inspection.
- Supported by industry POPCD database of 42 inspections.
- Industry data includes 9 inspections of high noise plant data. No undetected indications exceeded 3.2 volts.
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Voltage Bin Example from SQN 2 (Cycle
- 12) Reference ML070250031, Table 4
- Voltage Bins Range for each 0.1v
- Voltage Bin (0.91v-1.00v)
Determine the total for Detection at EOCn-These are from previous cycle. (58 indications)
Determine at No Detection at EOCn (New Indications)-
These are from the subsequent cycle. (9)
POPCD for Voltage Bin 0.866.
- Build table for each voltage bin using number of indications for each category and calculate POPCD.
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Noise Considerations
- Preliminary POPCD indicated potential improved detection of axial ODSCC at TSP center for large voltage indications.
- Noise Monitoring performed during U2R3.
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Conclusion
- Short term use of 1.0 POD factor for DSIs > 8 Volts
- Short term use of 1.0 POD factor for DSIs > 3.2 Volts
- LAR for application of POPCD method
Regulatory Precedent On March 24, 2008, NRC issued a license amendment for SQN Unit 2, which revised approved the use of the POPCD methodology and revised the SG TS reporting requirement to reflect the use of POPCD (ML080710575).
On October 28, 2004, NRC issued a license amendment for Diablo Canyon Power Plant (DCPP), Unit Nos. 1 and 2, which also approved the use of the POPCD methodology and revised the SG TS reporting requirement to reflect the use of POPCD (ML043140456).
The proposed LAR mimics the TS changes for the SQN Unit 2 and DCCP LARs.
TVA has reviewed the LARs and RAI responses for each of the below precedents and have addressed them, as applicable, in this enclosure.
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Schedule for Submittal November 17, 2020 - Pre-submittal teleconference with NRC December 18, 2020 - Submit LAR to NRC (attempting to improve this date)
Request NRC approval by February 8, 2021 with implementation by February 14, 2021 (i.e., 90 days from WBN 2 entering Mode 4 on November 16, 2020) to comply with the proposed 90-day reporting requirement for POPCD.
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