05000346/LER-1977-088-03, /03L-0:on 771027,source Range Detector NI-1 Indication Failed Low.Cause Unknown.Updated Rept Forthcoming

/03L-0:on 771027,source Range Detector NI-1 Indication Failed Low.Cause Unknown.Updated Rept Forthcoming

ML19329B301
Person / Time
Site:	Davis Besse
Issue date:	12/01/1977
From:	Karoly D TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19329B297	List: 05000346/LER-1977-088, Forwards LER 77-088/03L-0 05000346/LER-1977-088-03, /03L-0:on 771027,source Range Detector NI-1 Indication Failed Low.Cause Unknown.Updated Rept Forthcoming
References
LER-77-088-03L, LER-77-88-3L, NUDOCS 8002040722
Download: ML19329B301 (2)

LER-1977-088, /03L-0:on 771027,source Range Detector NI-1 Indication Failed Low.Cause Unknown.Updated Rept Forthcoming

Event date:
Report date:
3461977088R03 - NRC Website

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{ol2l lon October 27, 1977, at 1515 hours0.0175 days <br />0.421 hours <br />0.0025 weeks <br />5.764575e-4 months <br />, Source Range Detector NI-1 indication failed I

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This occurrence placed the station in the Action Statement No. 5 of Technical Io64l l Specification 3.3.1.1.

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l I o i sj i The redundant Source Range Detector, NI-2 was in service and operational.

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DAVIS-BESSE L~ NIT ONE NUCLEAR POWER STATION SUPPLEMEYrAL INFORMATION FOR LER NP-33-77-88 4

DATE OF EVENT: October 27, 1977 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE: Source Range Neutron Detector NI-1 failed.

Conditions Prior to Occurrence: 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.

1 Description of Occurrence:

On October 27, 1977, at 1515 hours0.0175 days <br />0.421 hours <br />0.0025 weeks <br />5.764575e-4 months <br />, Source Range Detec-i tor NI-l indication failed low. This occurrence placed the station in the Action Statement 5 of Technical Specification 3.3.1.1.

NI-l returned to normal operation /

indication by itself.

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

operational.

h Designation of Apparent Cause of Occurrence: The exact cause of this occurrence

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is unknown, but it is apparently due to an undetermined type of component failure.

Analysis of Occurrence: There was no danger to the health 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. The redundant Source Range Detector NI-2 was in service.

Corrective Action

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

The intermittent nature of the failure makes trouble-shooting extremely difficult. The return of Source Range Detector NI-l to normal operation removed the station from Action Statement 5 of Technical Specification 3.3.1.1.

The failures of NI-l seem to have no fixed frequency.

These detectors are used only during near zero power le.vels in the core and are de-energized during power operation. When the cause is determined, an additional report will be submitted which will include any further failures and the corrective action.

Failure Data: These short duration failures of NI-l are repetitive, but the cause is yet unknown. The previous failures of NI-1 occurred on October 11, 1977.

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