ML19329B301

LER 77-088/03L-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: ML19329B296 ML19329B301
References
LER-77-088-03L, LER-77-88-3L, NUDOCS 8002040722
Download: ML19329B301 (2)

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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 to13l l low. This occurrence placed the station in the Action Statement No. 5 of Technical  !

NI-1 returned to normal operation / indication bv itself. l Io64l l Specification 3.3.1.1.

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

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. TOLEDO EDISON COMPANY D 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

\ 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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