ML19329B518

RO NP-33-77-13-1:on 770607,seismic Trigger Failed to Operate During Surveillance Test.Caused by Fabrication Error.Component Omitted from Printed Circuit Board Assembly. New Omnitrigger Substituted for Defective One

ML19329B518
Person / Time
Site:	Davis Besse
Issue date:	08/17/1977
From:	Achie K, Lingenfelter J TOLEDO EDISON CO.
To:
Shared Package
ML19329B506	List: ML19329B505 ML19329B518
References
NUDOCS 8002050676
Download: ML19329B518 (2)

Text

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tytwi uc semiPriou g g At approximately 15,30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> on June 7, 1977, during Surveill'nce a Test, j r ao ,2 gl ST 5034.01, it was found that the seismic trigger was not operating a as w

[jEl properly. The trigger was firing spuriously (NP-33-77-13-1). The cause :

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@>esl This is a suoplemental report as reouested on NRC-0IE Exit' Interview .

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[ID' on July 21, 1977. - . . . . ~ . . - - - . . . . . .

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Jacque Lin;;cnfciter/ Ken Aebie (439) 259-5000 Eat. 5 3 8oo205Oh% . .. .,

. .. TOLEDO EDISON CONTAIR g DAVIS-BESSE NUCLEAR P0hTR ST.iTION UNIT ONE

/ SUPPLETENTAL REPORT ON CAUSE OF 0:CIITRIGGER FAILURE REQUESTED BY NRC-OIE EXIT INTERVIE.i ON JULY 21, 1977 SUPPLEMENTAL REPORT NP-33-77-13-1 On June 7,1977, the Seismic Monitoring System automatically actuated. Upon evaluation of the graphic record, it was found that there was no seismic event to trigger the system. It was also found that the PMT (playback) batteries had been discharged indicating that the PMT section had been main-tained in an activated state for some duration.

Troubleshooting of the system started immediately. It was determined that in order for the FMT section to have remained activated, the omnitrigger would have had to continuously actuated the system. Since there was no gra-phic record of a semismic event from any of the sensors, it was determined that the omnitrigger itself was at fault. On June 27, 1977, a new o=nitrigger was obtained and substituted for the one suspected of being defective.

The defective omnitrigger was returned to the vendor, Terra Technology, for repair and failure analysis. Terra Technology infor=ed Toledo Edison that several components were defective and one transistor was omitted during assembly. The missing transistor supplies actuation for the relay which causes system sctuation.

With the above transistor missing, the omnitrigger could perform as normal or actuate at any time on its own or in any on-off combination. This fabrication

\s, error has been determined to have caused the failure of the seismic trigger.

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