ML19323D888
| ML19323D888 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 11/15/2019 |
| From: | Tennessee Valley Authority |
| To: | Office of Nuclear Reactor Regulation |
| Buckberg P, NRR/DORL/LPL2-2, 415-1383 | |
| Shared Package | |
| ML19323D956 | List: |
| References | |
| EPID L-2019-LLA-0239 | |
| Download: ML19323D888 (15) | |
Text
Sequoyah Nuclear Plant Unit 1 TS 4.2.2 Control Rod Assemblies Exigent LAR Pre-Submittal Conference Call November 15, 2019
Objectives l 2 Provide a description of the SQN Unit 1 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
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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 1 is currently shut down for the U1R23 refueling outage l 3
Background - H-08 On August 27, 2019 SQN Unit 1 center control rod (core location H-8) dropped into the core while the reactor was at 100% power causing an automatic scram of the unit.
Troubleshooting completed at the time investigated the electronic control system and no deficiencies were identified.
The site initiated a root cause analysis which was indeterminate pending additional inspections during the fall refueling outage.
The reactor was returned to 100% power and a second set of grippers was used to assist the normal grippers in holding the H-8 rod in position. There were no issues for the remainder of the cycle.
l 4
Background - H-08 Troubleshooting During the refueling outage, remote inspections of the inside of the control rod drive mechanism were performed using robotic cameras and action was taken to replace the H-08 jack shaft.
The inspections performed identified excessive wear on the faces of the stationary grippers along with wear marks along the interior walls of the control rod drive mechanism.
Throughout the process, the OEM has been reviewing inspection data as well as third party reviews.
During pre-startup testing the H-8 rod dropped into the reactor multiple times at various positions both above and below the normal operating position. The degradation in operating characteristics of the H-8 control rod was not anticipated.
l 5
Background - Control Rod Configuration l 6 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
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 but were not viable.
Design change package being prepared for physical removal of the H-08 rod for the upcoming cycle.
l 7 Background - H-08 Repairs
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 8
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 bounded.
The Reload Safety Evaluation for the removal of H-08 validated all cycle-specific Reload Design Safety Analysis Review Checklist limits.
l 9
Overview of Proposed Change Requesting proposed amendment to allow Unit 1 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):
l 10
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 11
Precedence LAR 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)
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 l 12
Differences between SQN 1 and Precedence SQN Exigent LAR McGuire STP Not a contingency Contingency Not a contingency TS 4.2.2 note in accordance with ITS format TS 4.2.2 footnote TS 4.2.2. footnote Framatome analysis In-house analysis Westinghouse analysis No thimble plug Thimble plug Thimble plug Control bank RCCA Control bank RCCA Shutdown bank RCCA l 13
Proposed Schedule for Submittal and Requested Approval Sequoyah plans to submit the exigent LAR on November 16 Plant is currently progressing to Mode 6 to perform initial field work Plant is remaining in Mode 6 pending approval and implementation of the design change Request NRC review 7 days after submittal l 14
Closing and Questions l 15