ML20329A372

Pre-Submittal Teleconference for Proposed License Amendment Request Regarding Technical Specification 5.9.9, Steam Generator Tube Inspection Report, to Use Popcd Methodology

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.

l 3

Proposed WBN 2 TS 5.9.9 Change l 4

Introduction

• WBN U2R3 is the 3rd ISI for the Unit 2 Model D3 SGs (Alloy 600MA).

• This was the first outage to implement GL95-05 Voltage Based Repair Criteria (ARC).

• Significant Inspection scope was performed.

• SG-3 did not pass GL95-05 criteria for conditional probability of burst.

l 5

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

• Using the POD value of 0.6 is limiting for WBN 2.

• 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.

l 9

Preliminary GL95-05 Operational Assessment (OA) Predictions Effective Full Power Days POD (EFPD)

SG 1 503.9 0.6 SG 2 503.9 0.6 up to 3.2v 1.03.2v 270 POPCD Preliminary SG 3 240 0.6 up to 3.2v 1.03.2v 180 0.6 up to 8v 1.08v 0.6 up to 3.2v 1.03.2v SG 4 503.9 l 10

Purpose of WBN 2 POPCD

• WBN U2R3 inspection results didnt support a cycle length of 90 days due to POD of 0.6.

• POPCD will allow a more realistic POD.

l 11

POPCD Definition

• POPCD is calculated as the ratio of indications reported at the prior inspection to the total indications found at the subsequent inspection.

l 12

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.

l 13

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. l 14

Noise Considerations

• TSP ODSCC indications are dominantly located near the center of the TSP.

• WBN 2 has relatively low bobbin noise measurements at the TSP center.

• Preliminary POPCD indicated potential improved detection of axial ODSCC at TSP center for large voltage indications.

• Noise Monitoring performed during U2R3.

l 15

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

• Evaluating the use of WBN 1 data to support WBN 2 specific POPCD l 16

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. l 17

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.

l 18