ML19242B948

LER 79-078/03L-0 on 790710:indication of Source Range Neutron Detector NI-1 Failed Low Twice.Cause Due to Undetermined Component Failure in Both Cases.Unit Tested to Verify Operability

ML19242B948
Person / Time
Site:	Davis Besse
Issue date:	08/06/1979
From:	Deakyne K TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19242B941	List: ML19242B940 ML19242B948
References
LER-79-078-03L, LER-79-78-3L, NUDOCS 7908090573
Download: ML19242B948 (2)

Text

.: F ORM :46 U. S. NUCLE AR REGULATORY COMMISSION 77)

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7 60 bl COC K ET f.u ?.* 3 E n EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h l o l 2 I [_On 7 /10/ 79 a t 0300 hours0.00347 days <br />0.0833 hours <br />4.960317e-4 weeks <br />1.1415e-4 months <br />, the indication of Source Rance Neutron Detector NI-1 failed 1 o i low. None of the Action Statements of Technical Specification 3.3.1.1 were applicabid o 4 as the Control Rod Drive System was not energized for rod withdrawal. NI-1 failed I lo Isl I low a second time at 2339 hours0.0271 days <br />0.65 hours <br />0.00387 weeks <br />8.899895e-4 months <br /> on 7/10/79, one minute af ter criticality during a readtor I o 16 i startup. This occurrence placed the unit in Action Statement 5 of Technical Snecifi-I o 7 cation 3.3.1.1. The startup was terminated and reculatinn rods were inserted. There o 8 l was no danger to the nublic or unit personn 31. The redundant detector NI-2 was opera le.

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44 47 CAUSE DESCRIPTION AND CORRECTIVE ALTIONS h lil0l The cause is apparently due to an undetermined conponent failure in both i i i i cases. After inspection, cleaning and tighteninn of the cable connectors at the cabi-l g,97; l net and preamplifier, the indication of NI-1 was consistent with that of NI-2. Followt-

, 3 l iag the corrective action for each f ailure, the operability of NI-1 was verified via l i 4 l surveillance testing. The unit was removed from the Action Statement at 0545 hours0.00631 days <br />0.151 hours <br />9.011243e-4 weeks <br />2.073725e-4 months <br /> onl 7 8 9 7 /11Y)7 9.

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TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-33-79-87 DATE OF EVENT: July 10, 1979 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE: Source Range Detector NI-l indication dropped to zero counts per second Conditions Prior to Occurrence: The unit was in Mode 3, with Power (MWT) = 0, and Load (Gross MWE) = 0.

Description of Occurrence: On July 10, 1979 at 0300 hours0.00347 days <br />0.0833 hours <br />4.960317e-4 weeks <br />1.1415e-4 months <br />, Source Range Neutron Detector NI-l indication dropped to zero counts per second (cps) . None of the action statenents of Technical Specification 3.3.1.1 were applicabla as the control rod drive trip breakers were open, and the Control Rod Drive System was not capable of rod with-drawal. At 2339 hours0.0271 days <br />0.65 hours <br />0.00387 weeks <br />8.899895e-4 months <br /> on the same day, an identical occurrence took place. The Source Range Detector NI-l had f ailed low one minute af ter criticality during a reac-tor startup. This occurrence placed the unit in Action Statement 5 of Technical Speci-fication 3.3.1.1 which requires both source range channels operable during a reactor startup with 610-10 amps on the intermediate range instrumentation. The startup was terminated and regulating rods were inserted.

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

Analysis of Occurrence: There was no danger to che health and safety of the public or to station personnel. The redundant Source Range Detector NI-2 was in service and opera tional.

Corrective Action: The corrective action was performed under Maintenance Work Orders IC-337-79 and IC-339-79. In both cases, the corrective action was basically the same.

The source range test module was placed in the test mode and a simulated signal was applied to check the operability of the source range modules. The source range modules responded properly to the simulated signal. Next, the preamplifier and detector were de-energized, and the cable connectors at the Reactor Protection System Cabinet and the Source Range Preamplifier were removed, inspected for internal damage, cleaned, and tightened. Source Range Detector NI-l was re-energized, and the counts per second indicated were consistent to that of Source Range Detector NI-2. Followine the cor-rective action for each failure, Source Range Functional Test ST 5091.01 was performed to verify operability. After the second failure, NI-l was declared operable at 0545 hours0.00631 days <br />0.151 hours <br />9.011243e-4 weeks <br />2.073725e-4 months <br /> on July 11, 1979, removing the unit from the Action Statenent of Technical Specification 3.3.1.1. An extensive troubleshooting program will be developed to be implemented during the refueling outage to determine the cause of the repetitive failures of NI-1.

Failure Data: There have been repetitive failures associated with Source Range De-tector NI-1. These were reported in Licensee Event Reports NP-33-77-79, NP-33-77-88, NP-33-77-100, and NP-33-78-110.

E'b aas 2 O f-LER #79-078