ML20108E908

Presentation Slides for Sequoyah Nuclear Plant, Unit 2 - Exigent License Amendment Request TS 4.2.2, Control Rod Assemblies, Pre-Submittal Conference Call - April 16, 2020

ML20108E908
Person / Time
Site:	Sequoyah
Issue date:	04/16/2020
From:	Tennessee Valley Authority
To:	Office of Nuclear Reactor Regulation
Buckberg P
References
Download: ML20108E908 (13)

Text

Sequoyah Nuclear Plant Unit 2 TS 4.2.2 Control Rod Assemblies Exigent LAR Pre-Submittal Conference Call April 16, 2020

Objectives

• Provide a description of the SQN Unit 2 H-08 Control Rod issue

• Provide overview of planned implementation actions

• Provide overview of expected License Amendment Request (LAR) content

• Discuss planned submittal date and need date

• Answer NRC questions l 2

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Background===

• Sequoyah Units 1 & 2 are Westinghouse 4-loop 3455MWt ice condenser plant designs

- Framatome HTP 17x17 fuel

- 193 Fuel assemblies, 53 control rods

• Unit 2 is currently shut down for the U2R23 refueling outage l 3

Background - H-08

• During U2R23, excessive wear was identified on the faces of the stationary grippers along with wear marks along the interior walls of the control rod drive mechanism.

• The wear is similar to the wear identified on Unit 1 during U1R23 in November 2019.

• Unit 2 has not experienced the same dropped rod events as Unit 1.

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Background - Control Rod Configuration

• Total of 53 Rod Control Cluster Assemblies (RCCA)

• RCCAs are grouped into Banks:

- Four Shutdown Banks

- Four Control banks

• Rod H-08 is part of Control Bank D and located in the center of the core l 5

Background - H-08 Repairs

• Replacement of the Control Rod Drive Mechanism (CRDM) grippers is a long lead activity with first-of-a-kind elements (custom tooling, processes, crew qual. on mockups, etc.)

• Temporary modifications to utilize the H-08 movable gripper to hold the rod withdrawn were investigated during U1R23 but were not viable.

• Design change package being prepared for physical removal of the H-08 rod for the upcoming cycle.

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Plant Changes Required

• Remove RCCA and associated drive shaft at core location H-08

• Install control rod guide tube flow restrictor on the upper internals

• Remove H-08 inputs to Rod Position Indication (RPI) system

• Remove power fuses for H-08 CRDM from the Rod Control system

• Revise Reload Safety Evaluation to include impact of control rod removal on nuclear design and safety analyses

• Revise affected procedures and design documents l 7

Planned LAR Content

• Evaluated Rod H-08 removal impacts on:

- Shutdown Margin

- Boron Concentration and Boron Worth

- Moderator Temperature Coefficient

• UFSAR Chapter 15 parameters were analyzed using the NRC-approved methods described in TS 5.6.3 and showed that limits assumed in safety analysis remain bounding.

• The Reload Safety Evaluation for the removal of H-08 validated all cycle-specific Reload Design Safety Analysis Review Checklist limits.

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Overview of Proposed Change

• Requesting proposed amendment to allow Unit 2 to operate with 52 full-length control rod assemblies for one cycle

• No methodology changes

• Proposed change to TS 4.2.2 (change bar on right):

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Planned LAR Content

• Current COLR limits remain unchanged.

• No new operator actions are expected.

• No impact on the functionality, structural integrity, or thermal hydraulic configuration of the reactor vessel upper internals

- Flow restrictor installed in place of the control rod drive shaft l 10

Precedence LARs

• TVA (Sequoyah Unit 1) - Exigent LAR to Revise TS 4.2.2 Control Rod Assemblies (LAR - 11/16/19, SE 11/21/19)

• Duke (McGuire) - Exigent LAR to Revise TS 4.2.2 Control Rod Assemblies (LAR - 9/7/18, Withdrawn 9/28/18)

- LAR was to remove Rod H-08 from the core.

- LAR was submitted as a contingency if a repair to a thermal sleeve could not be performed. Repairs were successful

• South Texas Project - Emergency LAR to Revise TS 5.3.2 to Allow Operation with 56 Full-Length Rod Assemblies for Unit 1 Cycle 20 (LAR -12/3/15, SE 12/11/15) l 11

Proposed Schedule for Submittal and Requested Approval

• Sequoyah plans to submit the exigent LAR on April 17

• Plant is currently in Mode 6, progressing into Core Empty (No Mode) and continuing with refueling outage activities

• Plant will return to Mode 6 and remain in Mode 6 pending LAR approval and implementation of the design change

• Request NRC review 7 days after submittal l 12

Closing and Questions l 13