ML19211B168

Day Special Report for One Train of Reactor Vessel Level Monitor Inoperable

ML19211B168
Person / Time
Site:	Millstone
Issue date:	07/24/2019
From:	Daugherty J Dominion Energy Nuclear Connecticut
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
19-317
Download: ML19211B168 (5)

Text

Dominion Energy Nuclear Connecticut, Inc.

• ~ Dominion Rt 156, Rope Ferry Road, Waterford, CT 06385 DominionEnergy.com JUL 2 4 Z81B ji,' Energy U. S. Nuclear Regulatory Commission Serial No.19-317 Attention: Document Control Desk NSS&L/LD RO Washington, DC 20555 Docket No. 50-423 License No. NPF-49 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 3 30-DAY SPECIAL REPORT FOR ONE TRAIN OF REACTOR VESSEL LEVEL MONITOR INOPERABLE In accordance with the Millstone Power Station Unit 3 (MPS3) Technical Specifications (TSs), Section 3.3.3.6.e, Dominion Energy Nuclear Connecticut, Inc., hereby submits this Special Report documenting conditions surrounding one train of the Reactor Vessel Level Monitor (RVLM) not being restored to an operable status within 7days.

MPS3 TS 3.3.3.6.e requires an inoperable channel of the RVLM to be restored to operable status within 7 days if repairs are feasible without shutting down, or prepare and submit a Special Report to the NRG within 30 days following the event. The report shall outline the action taken, the cause of the. inoperability, and the plans and schedule for restoring the channel to operable status. The 30 day Special Report for the Reactor Vessel Level Monitor (RVLM) event is contained in Attachment 1.

Should you have further questions please contact Mr. Jeffry Langan at (860) 444-5544.

Sincerely,

/7-z---_

J. r~augherty Site Vice President - Millstone 30-day Special Report - One Train Reactor Vessel Level Monitor Inoperable Commitments made in this letter: None

Serial No.19-317 Docket No. 50-423 30 day Special Report Page 2 of 2 cc: U.S. Nuclear Regulatory Commission Region I 2100 Renaissance Blvd. Suite 100 King of Prussia, PA 19406-2713 R. V. Guzman Senior Project Manager - Millstone Power Station U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 08 C2 11555 Rockville Pike Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station

Serial No.19-317 Docket No. 50-423 Attachment 1 ATTACHMENT 1 30-DAY SPECIAL REPORT Reactor Vessel Level Monitor DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 3

Serial No.19-317 Docket No. 50-423 Attachment 1 30-DA Y SPECIAL REPORT Reactor Vessel Level Monitor In accordance with the Millstone Power Station Unit 3 (MPS3) Technical Specifications (TSs), section 3.3.3.6.e, Dominion Energy Nuclear Connecticut, Inc., hereby submits this Special Report documenting conditions surrounding an inoperable train of the Reactor Vessel Level Monitor (RVLM) not being restored to operable status within 7 da%. *

Background:

At 08:44 on June 29, 2019, MPS3 *Operations received *alarms for Reactor Head* Level Low from 'A' train Reactor Vessel LeveC Monitor (RVLM). The RVLM indicated reactor vessel level fluctuating between 81 % and 100%. Plant Process Computer (PPC) trends during the event showed both. the Unheated Junction Thermocouple and Heated.

Junction. Thermocouple temperatures at the 19% plenum elevation fluctuating rapidly

. between approximately 100 degrees F and 1000 degrees F, causing the level alarm ..

After consulting with Maintenance, Operations determined the 'A' train RVLM to be inoperable due to the erratic indication. As a result, MPS3 Operatlons entered Tech Spec 3.3.3.6 Action Statement 'e' for the 'A' train RVLM inoperable at 11 :45 on June 29,

. 2019 .. Over the following 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, the erratic operation observed on the 19% plenum level indication was observed intermittently on several other sensors. * *

• Action Taken:

The* failed 'A' . train RVLM was entered irito the* Corrective Action Program on June 29, 2019, and a work order to restore the RVLM was created. On June 30, 2019, the 'A' train RVLM analog-to-digi(al conyerter card was identified as the most probable ,

cause of the erratic indication and was replaced. Following restoration, several thermocouples still showed erratic indication. Further 'troubleshooting determined the

. cause of the erratic indication was most likely being introduced downstream of the heater controller cabinet. Individual heaters were bypassed at each sensor to determine if a single heater at one elevation was the c~use of the erratic indication at all levels.

Troubleshooting conducted between June 29, 2019, and July 6, 2019, by Maintenance and Engineering was not successful in resolving the erratic indication. Further troubleshooting and repair requires work to be performed at the RVLM sensor connections located at the reactor head panel, which is inaccessible at power and access to the RVLM sensor probes within the reactor vessel. Therefore, additional troubleshooting and repair will not be feasible until the next refueling outage of MPS3.

Serial No.19-317 Docket No. 50-423 Attachment 1 Cause of lnoperability:

The cause of the inoperability of the 'A' train RVLM is noise in the thermocouple circuit causing erratic indication of head and plenum level. The cause of the noise cannot be determined at this time.

Corrective Action:

Millstone's efforts to restore the inoperable 'A' train of RVLM to operable status have not been successful. Due to the fact the RVLM connectors and sensors are inaccessible when the plant is online, additional troubleshooting and restoration of the inoperable 'A' train RVLM is not feasible. Millstone will perform additional troubleshooting and corrective maintenance to restore the 'A' Train RVLM during the next refueling outage in the fall of 2020.