ML21217A287

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TVA Slides - Pre-Submittal Meeting for Proposed License Amendment Request Re Application to Modify Technical Specification 3.7.8 Essential Raw Cooling Water (ERCW) System, to Support Permanent Shutdown Board
ML21217A287
Person / Time
Site: Watts Bar  Tennessee Valley Authority icon.png
Issue date: 08/19/2021
From:
Tennessee Valley Authority
To: Kimberly Green
Plant Licensing Branch II
Green K
References
Download: ML21217A287 (28)
v • d • e


Text

Watts Bar Nuclear Plant Watts Bar Nuclear Plant (WBN)

Pre-Submittal Meeting for Proposed License Amendment Request Regarding Application to Modify Watts Bar Nuclear Plant Units 1 and 2 Technical Specifications (TS) 3.7.8, Essential Raw Cooling Water (ERCW) System, to Support Permanent Shutdown Board Cleaning August 19, 2021

Agenda

  • Opening Remarks
  • Background
  • System Overview
  • Overview of the 6.9 kilovolt (kV) Shutdown Board (SDBD)

Maintenance Activities

  • Basis for Change
  • Technical Evaluation
  • Regulatory Precedent
  • Schedule for Submittal
  • Closing Remarks 2

Opening Remarks

  • This license amendment request (LAR) proposes a permanent extension of the WBN Units 1 and 2 Technical Specification (TS) 3.7.8 Essential Raw Cooling Water (ERCW) System completion time from 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to 7 days to perform scheduled maintenance activities on a 6.9kV SDBD and associated 480V boards and motor control centers (MCC) when a WBN unit is in a outage and is defueled.
  • Due to the commonality of the WBN 6.9kV SDBD loads, performing maintenance on a 6.9kV SDBD during a WBN refueling outage affects the ERCW system on the operating unit.
  • With regard to the ERCW system currently, WBN TS require two ERCW pumps aligned to separate 6.9kV SDBDs to be operable per train, with two trains required for each unit.

Consequently, this requires all four 6.9 kV SDBDs to be operable to support the ERCW pump TS requirement.

  • This change is needed to support the shutdown board cleaning planned for the WBN Unit 1 Cycle 18 refueling outage (U1R18) scheduled for spring 2023.

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Background

  • WBN Unit 2 License Amendment 35 dated February 24, 2020 (ML20024F835),

revised WBN Unit 2, Technical Specification 3.7.8 to extend the allowed Completion Time to restore one ERCW System train to operable status from 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to seven days, on a one-time basis.

  • The revision to WBN Unit 2 TS 3.7.8 was contingent on the following:

Only applicable during the Unit 1 spring 2020 outage but no later than May 31, 2020.

Only applicable when Unit 1 is defueled.

Only applicable during planned maintenance on 6.9 kV SDBD 1 A-A and associated 480 V boards and MCC.

UHS Temperature of 71°F.

  • Similar changes are needed to the Unit 1 and 2 TS 3.7.8 to support future and ongoing maintenance of the 6.9 kV SDBDs and associated 480 V boards and MCCs for both units.

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System Overview

  • The ERCW System is a common two-train system with each train having the capability to provide the required cooling water for both units under any credible plant condition.
  • These ERCW System trains are independent and redundant.
  • Each train of the ERCW system has four pumps total. As noted in the bases of WBN TS 3.7.8, for operating modes 1-4, two ERCW pumps aligned to separate 6.9kV SDBDs are required to be operable per train, with two trains required for each unit.
  • The ERCW system has been analyzed for "worst case" heat loads under combinations of maximum river water temperature, design basis accident conditions, normal cooldown requirements, power train failures, for both units.
  • The ERCW system has sufficient pump capacity for cooling water flows under all conditions and the system is arranged in such a way that even a complete header loss can be isolated in a manner that does not jeopardize plant safety.

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System Overview (contd) l 6

System Overview (contd)

ERCW Pump Motor Electrical Board Alignment l 7

Overview of 6.9kV SDBD Maintenance

  • Maintenance activities performed during a 6.9kV SDBD board outage include:

Breaker compartment inspections

  • Indicating light resistor replacements
  • Fuse blocks
  • Relays and instruments Circuit breaker interface inspections and adjustments
  • Primary/Secondary disconnects
  • Shutter inspection
  • Breaker position and interface measurements and adjustments Bus inspections and tests
  • As-found and as-left insulation resistance (megger) testing

Overview of 6.9kV SDBD Maintenance (contd)

Shutdown Board Maintenance Timeline Activity Duration 1 Install Clearance 6 Hours 2 Ground Installation 4.5 Hours 3 Breaker Compartment Inspections 42 Hours 4 Circuit Breaker Interface Inspections 34 Hours and Adjustments 5 Bus Inspections and Tests 8 Hours 6 Ground Removal 4.5 Hours 7 Release Clearance 6 Hours Total 105 Hours

  • 105 Hours are needed to support the SDBD board outage activities.
  • Remaining duration of the TS change allows for a contingency should the maintenance activities identify the need for an unexpected repair.

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Proposed Technical Specification Changes for WBN Unit 2

- TS 3.7.8 Condition A is modified as follows:

> Delete current Note 1 which states: Only applicable during the Unit 1 spring 2020 outage (U1R16), but no later than May 31, 2020.

> Note 2 is re-sequenced to Note 1: Only applicable when Unit 1 is defueled.

> Note 3 is re-sequenced as Note 2 and is revised to state: Only applicable during planned maintenance of a Unit 1 6.9kV SDBD and the associated 480V boards and motor control centers.

> Revise the UHS temperature in the Completion Time for Required Action A.1 and for Required Action A.2 from 71ºF to 78ºF.

> Minor correction to Condition C to note that it applies to all of Condition A .

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Proposed Technical Specification Changes for WBN Unit 2 l 11

Proposed Technical Specification Changes for WBN Unit 2 l 12

Proposed Technical Specification Changes for WBN Unit 1

- Similar to the changes to the WBN Unit 2 TS

- New WBN Unit 1 TS 3.7.8 Condition A to increase the completion time for an inoperable ERCW Train from 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to 7 days with the following Notes:

1. Only applicable when WBN 2 unit is defueled.
2. Only applicable during planned maintenance of a Unit 2 6.9kV SDBD and the associated 480V boards and MCC.

- Both Notes are required to be met in order to use Condition A .

- The Required Actions and Completion Times of WBN Unit 1 TS 3.7.8 Condition A are modified to be consistent with the WBN Unit 2 TS.

- WBN Unit 1 TS 3.7.8 Conditions B and C are modified identical to the WBN Unit 2 TS changes.

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Proposed Technical Specification Changes for WBN Unit 1 l 14

Proposed Technical Specification Changes for WBN Unit 1 l 15

Proposed WBN UFSAR Change (for NRC Information Only)

WBN UFSAR Section 9.2.1.3 will be revised to reflect the new ERCW system alignments needed to support SDBD maintenance (as indicated in the revised TS 3.7.8 Bases) l 16

Proposed WBN UFSAR Change (for NRC Information Only)

WBN UFSAR Section 9.2.1.3 will be revised to reflect the new ERCW system alignments needed to support SDBD maintenance (as indicated in the revised TS 3.7.8 Bases) l 17

Basis for Proposed TS Changes

  • TVA employs a graded approach to defense in depth (DID) and protected equipment strategies when equipment is removed from service

> NPG-SPP-07.0 Work Management

>> This program incorporates risk assessment methodologies and contingency processes to maximize personnel safety, plant safety, plant reliability, and worker productivity during plant modifications, maintenance, and testing.

> Includes both Online Work Management and Outage Management

>> NPG-SPP-07.1 On Line Work Management provides the guidance for the implementing work management process that promotes personnel/nuclear safety, access plant risk, maximize plant reliability, and improve schedule credibility/stability.

>> NPG-SPP-07.2 Outage Management provides guidance for the development and risk assessment of the outage schedule

> NPG-SPP-07.3.4 Protected Equipment

>> Provides guidance for protecting plant equipment in order to minimize the potential for adverse operational events.

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Basis for Proposed Change (contd)

- Engineering analyses have been performed with a single ERCW pump powered from the 6.9kV SDBD in operation under the following bases:

>> Design basis accident on the WBN operating unit

>> Loss of offsite power

>> WBN Unit in a outage with 100 hour0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> limit prior to irradiated fuel movement (WBN TS 3.9.10)

>> WBN outage unit is defueled

>> Unnecessary ERCW cooling loads isolated on the WBN outage Unit .

>> A 6.9kV SDBD and associated 480V boards are out of service

>> The ERCW train not impacted by the maintenance activities assumed failed

>> UHS temperature of 78°F

- Each SDBD outage scenario is evaluated

- This analyses conclude that a single ERCW pump powered from the available 6.9kV SDBD can supply sufficient heat removal, while maintaining the outlet piping l 19 thermal stress temperature limits

Technical Evaluation

  • Hydraulic Proto-Flo model is used for the ERCW analyses

- Proto-Flo model was modified to reflect the ERCW one pump configuration powered from the available 6.9kV SDBD

- Reconfigured flow rates were compared to the analyzed flow rates for required equipment

> For components where flow rates are less than analyzed;

>> ERCW temperature versus ERCW flow curves were developed to determine the maximum allowable temperature for the one pump ERCW operation.

o PROTO-HX was used to determine the ERCW temperature required for available flow rate for heat exchangers and discharge piping temperature limits o Heat transfer analyses were used for the shutdown board room and electric board room chiller performance

- The UHS temperature of 78°F ensures the required ERCW loads have sufficient cooling, while maintaining the outlet piping thermal stress temperature limits.

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Technical Evaluation (contd)

  • Conservatism in the analyses include

- ERCW minimum pump performance curve by specifying a lower bounding head versus flow curve relative to the vendor pump curves.

- Predicted flow rates for a single ERCW pump performance are reduced by 5% in the ERCW hydraulic analyses to account for analysis uncertainties

- 100 gallon per minute (gpm) system leakage loss is assumed in the analyses. This accounts for any unidentified system leakage which is in excess of typical system leakage under normal operating conditions.

  • Hardware change supporting/credited in the ERCW analyses

- To improve ERCW flow margin, the component cooling system (CCS) train B heat exchanger post accident flow control valve will being replaced and relocated to improve flow balance between the two ERCW discharge headers

- This new valve installation is scheduled for implementation in U1R17 (Fall 2021) l 21

A review of Technical Evaluation (contd) the past six years of plant data has shown that the ERCW spring and fall seasonal maximum temperatures remain below the proposed limit of 78ºF.

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Technical Evaluation (contd)

Further review of the histogram for WBN spring outage timeframes show the spring seasonal temperature history relative to the proposed SDBD cleaning maximum ERCW temperature analytical limit of 78°F. Spring outages are typically in the March to May timeframe l 23

Technical Evaluation (contd)

Further review of the histogram for WBN fall outage timeframes show the fall seasonal temperature history relative to the proposed SDBD cleaning ERCW temperature limit of 78°F.

Fall outages typically begin in the late September-early October timeframe l 24

Precedent

  • As previously noted, this LAR is similar in nature to the NRC-approved one-time revision to WBN Unit 2, TS 3.7.8 to extend the allowed Completion Time to restore one ERCW System train to operable status from 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to seven days to support maintenance on the WBN Unit 1 6.9 kV SDBD 1A-A and associated 480 V boards and MCCs (ML20024F835).
  • The proposed LAR is also consistent with the license amendment approved by the NRC for the Sequoyah Nuclear Plant (SQN), that also made a change to TS 3.7.8 for SQN Units 1 and 2 (ML16225A276), which added a new Condition A to TS 3.7.8 with a completion time of seven days and a limiting UHS temperature of 79°F.

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Schedule Milestones

  • August 19, 2021 - Pre-submittal meeting with NRC
  • September 30, 2021 - LAR Submittal - Request NRC approval within 12 months of submittal with 30-day implementation
  • September 30, 2022 - NRC Approval of LAR (Requested)
  • WBN Unit 1 Cycle 18 refueling outage (U1R18) scheduled for spring 2023 l 26

Closing Remarks Proposed WBN TS change is needed to support scheduled maintenance activities of the 6.9kV SDBDs during refueling outages at WBN.

Due to the commonality of the 6.9kV SDBDs, performing maintenance on a 6.9kV SDBD during a WBN Unit refueling outage affects operability of the ERCW system for the operating WBN Unit .

The change will extend the WBN TS 3.7.8 completion time from 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to 7 days to support maintenance activities on a SDBD when the other WBN Unit is in operation provided UHS temperature is 78°F.

This change is needed to support the U1R18 outage scheduled for Spring 2023.

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