05000346/LER-1978-121-03, /03L-0 on 781210:borated Water Storage Tank Level in Safety Features Actuation Sys Channel 3 Failed.Caused by Open Circuit in the Thermocouple for a Heat Trace Controller

/03L-0 on 781210:borated Water Storage Tank Level in Safety Features Actuation Sys Channel 3 Failed.Caused by Open Circuit in the Thermocouple for a Heat Trace Controller

ML19274D124
Person / Time
Site:	Davis Besse
Issue date:	01/05/1979
From:	Naylor R TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19274D121	List: 05000346/LER-1978-121, Forwards LER 78-121/03L-0 05000346/LER-1978-121-03, /03L-0 on 781210:borated Water Storage Tank Level in Safety Features Actuation Sys Channel 3 Failed.Caused by Open Circuit in the Thermocouple for a Heat Trace Controller ML19274D120
References
LER-78-121-03L, LER-78-121-3L, NUDOCS 7901120178
Download: ML19274D124 (2)

LER-1978-121, /03L-0 on 781210:borated Water Storage Tank Level in Safety Features Actuation Sys Channel 3 Failed.Caused by Open Circuit in the Thermocouple for a Heat Trace Controller

Event date:
Report date:
3461978121R03 - NRC Website

text

U. S. NUCLEAR REGULATORY COMMISSloN NRC FORM 36G (7 77)

LICENSEE EVENT REPORT

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TOLEDO EDISON CO:IPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-33-78-142 DATE OF EVENT: December 10, 1978 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE:

Safety Features Actuation System (SFAS) Channel 3 Borated Water Storage Tank (BWST) Level Transmitter Inoperable Conditions Prior to Occurrence:

The unit was in Mode 1, with Power (MWT) = 1330, and Load (Gross MWE) = 412.

Description of Occurrence:

On December 10, 1978, at 0547 hours0.00633 days <br />0.152 hours <br />9.044312e-4 weeks <br />2.081335e-4 months <br />, a high level fail alarm was received for the BWST level on SFAS Channel 3.

This placed the unit in the Action Statement (9) of Technical Specification 3.3.2.1.b which requires the inope.rable functional unit be placed in the tripped condition within one hour.

BWST Channel 3 level transmitter was placed in the tripped condition at 0609 hours0.00705 days <br />0.169 hours <br />0.00101 weeks <br />2.317245e-4 months <br /> on December 10, 1978.

Designation of Apparent Cause of Occurrence: The apparent cause of this occurrence was an open circuit in the thermocouple for the local controller of the heat trace.

The heat trace provides freeze protection for the level indication system. The freezing condition which r.bsequently occurred resulted in the inoperability of SFAS Channel 3 BUST levex indication and the high level fail alarm.

Analysis of Occurrence: There was no danger to the health and safety of the public or to unit personnel. The remaining three SFAS BUST level channels were operating properly and would 1. ave transferred the decay heat and containment spray suction to the emergency sump if a loss of coolant accident had occurred.

Corrective Action

The thermocouple for the local controller was replaced under Maintenance Work Order (MWO) 78-2871 and circuit operation was checked and found to be satisfactory.

The transmitter sas returned to operability at 1455 hours0.0168 days <br />0.404 hours <br />0.00241 weeks <br />5.536275e-4 months <br /> on December 10, 1978.

Failure Data: There have been previously reported occurrences of freezing of the BWST level transmitters sensing lines but none due to temperature controller difficulties.

LER #78-121