05000346/LER-1977-079-03, /03L-0:on 771011,source Range Defector NI-1 Indication Failed Low Twice,Then Returned to Normal Operation by Itself.Cause Unknown

/03L-0:on 771011,source Range Defector NI-1 Indication Failed Low Twice,Then Returned to Normal Operation by Itself.Cause Unknown

ML19329A819
Person / Time
Site:	Davis Besse
Issue date:	11/08/1977
From:	Hitchens D TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19329A814	List: 05000346/LER-1977-079, Forwards LER 77-079/03L-0 05000346/LER-1977-079-03, /03L-0:on 771011,source Range Defector NI-1 Indication Failed Low Twice,Then Returned to Normal Operation by Itself.Cause Unknown
References
LER-77-079-03L, LER-77-79-3L, NUDOCS 8001150714
Download: ML19329A819 (2)

LER-1977-079, /03L-0:on 771011,source Range Defector NI-1 Indication Failed Low Twice,Then Returned to Normal Operation by Itself.Cause Unknown

Event date:
Report date:
3461977079R03 - NRC Website

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8 60 61 QoCKET NUMBER 6d 69 EVENT DATE 24 7s REPORT DATE 80 source EVENT DESCRIPTION AND PROSA8LE CONSEQUENCES h I o 12 l l On October ll, 1977, Source R;. age Detector NI-l's indication failed los.

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occurred twice, once at 1208 hours0.014 days <br />0.336 hours <br />0.002 weeks <br />4.59644e-4 months <br /> and once at 1755 hours0.0203 days <br />0.488 hours <br />0.0029 weeks <br />6.677775e-4 months <br />. This occurrence placed I

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SUPPLEMENTAL INFORMATION FOR LER NP-33-77-79 DATE OF EVENT: October 11, 1977 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE: Source Range Neutron Detector, NI-1 failed.

Conditions Prior to occurredce: The plant was in Mode 3, with Power (MWT) = 0, and Load (MWE) = 0.

Technical Specification 3.3.1.1 was applicable as the Control Rod Drive Trip Breakers were closed and the Control Rod Drive System was capable of rod withdrawal.

Description of Occurrence: On October 11, 1977, Source Range Detector NI-l's indication failed low.

This occurred twice, once at 1208 hours0.014 days <br />0.336 hours <br />0.002 weeks <br />4.59644e-4 months <br /> and once at 1755 hours0.0203 days <br />0.488 hours <br />0.0029 weeks <br />6.677775e-4 months <br />. This occurrence placed the station in Action Statement No. 5 of Technical Specification 3.3.1.1.

On each occasion, NI-l returned to normal operation /indi-cation by itself. The first time at 1222 hours0.0141 days <br />0.339 hours <br />0.00202 weeks <br />4.64971e-4 months <br /> and the second at 1812 hours0.021 days <br />0.503 hours <br />0.003 weeks <br />6.89466e-4 months <br />.

The redundant Source Range Detector, NI-2 was in service and operational.

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Designation of Apparent Cause of Occurrence: The exact cause of this occurrence is unknown, but it is apparently due to an undetermined type of component failure.

Analysis of Occurrence: There was no danger to the hen?th and safety of the public or to station personnel. The thermal power level was maintained at less than 10-10 amps on the Intermediate Range Flux Instrumentation.

Corrective Action

NI-l had occasionally failed during the past outage, but no cause has yet been determined.

It has been determined that the signal coming to the Reactor Protection System cabinets from the preamplifier was lost, although j

the preamplifier had been replaced prior to this occurrence.

The instrumentation string returning to normal by itself 14 and 17 minutes af ter the beginning of occurrence respectively, makes trouble-shooting extremely diffi-cult. The return-of Source Range Detector NI-l to normal operation removed the station from Action Statement No. 5 of Technical Specification 3.3.1.1.

Failure Data:. These short duration failures of NI-l are repetitive, but the cause is yet unknown.

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