05000346/LER-1978-093-03, /03L-0:on 780913,source Range Neutron Flux Instrument NI-1 Failed Low.Caused by Undetermined Component failure.NI-1 Power Source Replaced to Correct Faulty Computer Input signal.NI-1 Declared Operable on 780818

/03L-0:on 780913,source Range Neutron Flux Instrument NI-1 Failed Low.Caused by Undetermined Component failure.NI-1 Power Source Replaced to Correct Faulty Computer Input signal.NI-1 Declared Operable on 780818

ML20147A878
Person / Time
Site:	Davis Besse
Issue date:	09/13/1978
From:	Kovach S TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20147A874	List: 05000346/LER-1978-093, Forwards LER 78-093/03L-0 05000346/LER-1978-093-03, /03L-0:on 780913,source Range Neutron Flux Instrument NI-1 Failed Low.Caused by Undetermined Component failure.NI-1 Power Source Replaced to Correct Faulty Computer Input signal.NI-1 Declared Operable on 780818
References
LER-78-093-03L, LER-78-93-3L, NP-33-78-110, NUDOCS 7809220058
Download: ML20147A878 (2)

LER-1978-093, /03L-0:on 780913,source Range Neutron Flux Instrument NI-1 Failed Low.Caused by Undetermined Component failure.NI-1 Power Source Replaced to Correct Faulty Computer Input signal.NI-1 Declared Operable on 780818

Event date:
Report date:
3461978093R03 - NRC Website

text

9 U. S. NUCLE AR REGULATORY COMMISSION NRC FORM 366 (7 77)

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8 EVENT DESCRIPTION AND PROB ABLE CONSEQUENCES h The other sourcei [o g g l On 8/17/78, the source range neutron flux instrument NI-1 f ailed low.

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o TOLEDO EDISON COMPANY DAVIS-BESSE UNIT ONE NUCLEAR POWER STATION SUPPLEMENTAL INFORMATION FOR LER NP-33-78-110 DATE OF EVENT: August 17, 1978 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE:

Source Range Neutron Flux Instrument NI-1 f ailed low Conditions Prior to Occurrence: The unit was in Mode 5 with Power (MWT) = 0, and Load (MWE) = 0.

Description of Occurrence: On August 17, 1978 at 2205 hours0.0255 days <br />0.613 hours <br />0.00365 weeks <br />8.390025e-4 months <br />, the source range neutron flux instrument NI-1 failed low. The unit was not placed in Action Statement 6 of Technical Specification 3.3.1.1.

Action Statement 6 applies only if more than one source range channel is inoperable. The other source range neutron flux instrument, NI-2, was operable; no action was applicable. This report is being sub-mitted as documentation of a component f ailure.

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.

The intermittent nature of its f ailure makes troubleshooting extremely dif ficult.

These failures seem to have no fixed frequency. The detectors are used only during near zero power limits in the core and are de-energized during power operation.

Analysis of Occurrence: There was no danger to the health and safety of the public or to unit personnel. The redundant s,ource range detector, NI-2, was operable.

The unit was in Mode 5 at the time of the occurrence.

Corrective Action

Instrument and Control personnel placed the source range test module in the test operate position, then returned it to the operate position.

Although operability was restored at this time, personnel replaced NI-l's power supply in order to correct a f aulty computer input signal under !!aintenance Work Order IC-480-78. NI-1 was declared operable at 1415 hours0.0164 days <br />0.393 hours <br />0.00234 weeks <br />5.384075e-4 months <br /> on August 18, 1978 upon completion of Surveillance Test ST 5091.01, " Source Range Monitor Functional Test".

I Failure Data: Short duration failures of NI-1 are repetitive, but the cause is j

i yet unknown. Previous failures of NI-1 were reported in Licensee Event Reports NP-33-77-68, NP-33-77-79, and NP-33-77-100.

l LER #78-093