ML19209B983

LER 79-092/03L-0:on 790908,source Range Neutron Detector NI-1 & Intermediate Range Neutron Detector NI-3 Failed Low During Reactor Shutdown.Caused by Signal Return Cable & Associated Connectors.Cables Cleaned

ML19209B983
Person / Time
Site:	Davis Besse
Issue date:	10/05/1979
From:	Deakyne K TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19209B981	List: ML19209B980 ML19209B983
References
LER-79-092-03L, LER-79-92-3L, NUDOCS 7910110354
Download: ML19209B983 (3)

Text

U. S. NUCL A .

NRC FORM 366 (7 77) .

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? 8 60 61 DOCKET NUYSE R EVENT DESCRIPTION AND PROSABLE CONSEQUENCES h o y l On September 8,1979 at 0220 hours0.00255 days <br />0.0611 hours <br />3.637566e-4 weeks <br />8.371e-5 months <br /> during a reactor shutdown, source rance neutron I l detector NI-l and intermediate range neutron detect or NI-3 f ailed low. This placed I o 3 o 1] l the unit in the Action Statement 6 of Technical Specification 3.3.1.1. The shutdown I o s I margin was calculated within one hotir and once per every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> thereaf ter. There [

O u l was no danger to the health.and safety of the public or station personnel. The redun-l o 7 l dant source range (NI-2) and intermediate range (NI-4) neutron detectors were operablei 1

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33 CAUSE DESCRIPTION AND CCRRECTIVE ACTIONS i p lThe caur has been attributed to the signal return cable and its associated connectors l l i l i l l Under MWO-IC-422-79 and IC-425-79, the cables associated with NI-l and NI-3 were dis- I gil7i l connected from the Reactor Protection System cabinet, cleaned, inspected, and recon-i 3 lnected. ST 5091.01 proved NI-l operable at 0130 hours0.0015 days <br />0.0361 hours <br />2.149471e-4 weeks <br />4.9465e-5 months <br /> on September 9, 1979. l i 4 l ST SC .17 proved NI-3 operable at 0920 hours0.0106 days <br />0.256 hours <br />0.00152 weeks <br />3.5006e-4 months <br /> on September 9, 1979 l 80 7 8 9 STA S  % POWER oTHER STATUS SCO RY DISCOVERY DESCRIPTION NA Operator observation l li l 5 l l D l@ l 0l 0l Cl@l l l Al@l ACTivlTY CONTENT AELEASED OF RELE ASE AMOUNT OF ACTIVITY LOCATION OF RELE ASE NA l l NA l l1 l 68 ]9 l Z l @ 10l Zl@l11 7 44 45 80 PERSONNEL EXPOSURES NUYBER TYPE NA l lil7110101 O l@l Z Ql DESCRIPTION PERSONNEL INJURIES NLYRER DESCRIPTION I

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INR 79-134 NAME OF PREPARER en NaDe PHONE:

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TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-33-79-107 ,

DATE OF EVENT: September 8, 1979 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE: Source Range Neutron Flux Instrument (NI-1) and Inter-mediate Range Neutron Flux Instrument (NI-3) f ailed low.

Conditions Prior to Occurrence: The unit was in Mode 3, with Power (MWT) = 0, and

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Load (Gross MWE) = 0.

Description of Occurrence: On September 8, 1979 at 0220 hours0.00255 days <br />0.0611 hours <br />3.637566e-4 weeks <br />8.371e-5 months <br /> during a reactor shut-down, source range neutron detector NI-l and internediate range neutron detector HI-3 failed low. The unit was placed into Action Statement 6 of Technical Specification 3.3.1.1. Shutdown margin was calculated within one hour and once per every 12 hcurs thereafter until the source range was declared operable.

Designation of Apparent Cause of Occurrence: Station personnel feel the problem lies in the signal return cable and its associated connectors. Previous similar failures have been corrected by cleaning the (".ble leads and connectors, and this same action corrected the present problem. Westinghouse field engineers will be on site October 3, 1979, to aid in further investigation of the problems.

Analysis of Occurrence: There was no danger to the health and safety of the public or to station personnel. The redundant source range and intermediate range were in service and operational.

Corrective Action: The corrective action was performed under Maintenance Work Order IC-422-79 (source range) and Maintenance Work Order IC-425-79 (intermediate range) .

The cabler asso _iated with NI-l were disconnected frem the Reactor Protection System (RPS) cabinet, cleaned and inspected. After the cables were reconnected, the source range was energized. The counts per second indicated by NI-l corresponded to those indicated by NI-2. Source Range Functional Test ST 5091.01 was performed and NI-1 was declared operable at 0130 hours0.0015 days <br />0.0361 hours <br />2.149471e-4 weeks <br />4.9465e-5 months <br /> on September 9, 1979.

The intermediate range test module was placed in the test mode nd a simulated signal was applied to check the operability of the intermediate range moiules. The modules responded properly to the simulated signal. The associated cables were then removed f rom the RPS cabinet for cleaning and inspection. After the cables were reconnected compensating voltage to the detector was de-energized. The intermediate range responded to the gamma background. This was done to ensure that the detector and its related cabling would respond to an actual signal. Intermediate Range Pre-Startup Functional Test ST 5030.17 was then perforned and NI-3 was declared operable at 0920 hours0.0106 days <br />0.256 hours <br />0.00152 weeks <br />3.5006e-4 months <br /> on September 9,1979, and recoved the station from the action statement.

LER #79-092 1129 289

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TOLED0 EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE PAGE 2 SUPPLEMENTAL INFORMATION FOR LER NP-33-79-107 An extensive troubleshooting program is under ' development to solve problems hampering the operation of the nuclear instrumentation. Westinghouse field engineers will check out the connectors and cable runs associated with the NI's using a time domain reflecto-meter in an effort to isolate the problem. Further corrective action will be based on this inspection.

Failure Data: There have been repetitive failures associated with Source Range Detector NI-1. These were reported in Licensee Event Reports NP-33-77-79, NP-33-77-88, NP-33-77-100, NP-33-78-110 and NP-33-79-87.

There have been no reportable occurrences of this nature related to NI-3.

LER #79-092 -

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