05000414/LER-1995-001, Forwards LER 95-001-01,concerning Reactor Trip Due to Closure of Msiv.Rept Revised to Reflect Change to Corrective Actions Implemented

Forwards LER 95-001-01,concerning Reactor Trip Due to Closure of Msiv.Rept Revised to Reflect Change to Corrective Actions Implemented

ML20212A563
Person / Time
Site:	Catawba
Issue date:	10/16/1997
From:	Gordon Peterson DUKE POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20212A567	List: 05000414/LER-1995-001, Forwards LER 95-001-01,concerning Reactor Trip Due to Closure of Msiv.Rept Revised to Reflect Change to Corrective Actions Implemented
References
NUDOCS 9710240042
Download: ML20212A563 (2)

LER-2095-001, Forwards LER 95-001-01,concerning Reactor Trip Due to Closure of Msiv.Rept Revised to Reflect Change to Corrective Actions Implemented

Event date:
Report date:
4142095001R00 - NRC Website

text

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." Duke Power Company A tur twp umm m a.5, % Cateuse Nmirar Station 4800 Concord Road York, $C 2974%

Gary K. Fneteen (803) 831425! orin

\ke braidens t803) 8313426IM October 16, 1997 U.S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555

Subject:

Catawba Nuclear Station Docket No. 50-414 LER 414/95-001, Revision 1 Gentlement

-Attached is Licensee Event Report 414/95-001, Revision 1, concerning Remotor Trip Due to Closure of a Main Steam Isolation Valve.

This licensee event _ report has been revised to reflect a change to the corrective actions that have been implemented. Planned corrective _ action 2 in Revision 0 stated that a periodic maintenance program would be implemented to periodically monitor E-max model number 175C156 and 175C157 energized optical isolators in critical applications. Subsequent analysis of the failed component concluded the failure mechanism internal to the digital optical isolator was associated with a capacitor. Digital optical isolators were replaced with ones containing a more reliable capacitor. Analysis has determined that the_ service life of the -

more reliable capacitors is greater than 20 years Methods to accomplish periodic monitoring of digital optical isolators were evaluated. The result of-this evaluation was that periodic replacement of digital optical isolators that perform control functions and trending of failures to identify any new, generic failure modes would be the best option for ensuring digital optical isolator reliability. This action has been implemented. There have been no failures in critical control applications due to capacitor failures.following the extensive digital-optical isolator replacement: project.

However, two manual reactor trips have occurred on Unit 2 during the third quarter of 1997 which were attributed to failures of digital optical isolators in Main Steam Isolation Valve (MSIV) control circuitry._ Failure analysis has identified that resistors i:.ternal to-the digital optical isolators had degraded. These events are detailed in LER 414/97-006 which was transmitted by f letter to the NRC on August 25, 1997

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The periodic testing proposed in LER 414/95-001, Revision 0, would

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, not have identified the degrading digital optical isolators which resulted in the 1997 manual reactor trips. The periodic testing developed and evaluated by Engineering would have monitored the digital optical isolators in the MSIV contvol circuitry during refueling outage periods. During refueling outages the digital optical isolators are normally de-energized and would be energized by procedure immediately prior to testing. Subsequent to the events detailed in LER 414/97-006, Engineering and Maintenance personnel identified that degrading resistors cause the digital optical isolator to exhibit momentary output fluctuations when energized for a longer period of time (1 to 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />) and monitored for a longer period of time (approximately 15 minutes). This information has been used to develop enhanced procedures to periodically monitor digital optical isolators in MSIV applications on-line to identify degradation.

All corrective actions noted in LER 414/95-001, Revision 1, have been fully implemented. Revision 1 to the LER was written in the same tense as the original LER in order to provide a suitable comparison in the two versions and to cicarly denote the change in commitment. Thus, the committed corrective action which was revised continues to be under the heading of " Planned Corrective Actions" within the LER body.

This event is considered to be of no significance with respect to the health and safety of the public.

Very truly yourar A l -

Gary R. Peterson Site Vice-President Attachment cc: Mr. L.A. Reyes INPO Records Center Administratcr, Region II 700 Galleria Place U.S. Nuclear Regulatory Commission Atlanta, GA 30339-5957 61 Forsyth Street, S.W., Suite 23T85 Atlanta, GA 30323 Mr. P.S. Tam Mr. John Hoffman U.S. Nuclear Regulatory Commission Marsh & McLennan Inc.

Office of Nuclen7 Reactor Regulation 301 Tresser Blvd.

Rockville, MD 20852-2738 Stamford, CT 06904 Mr. D. Roberta NRC Resident Znspector Catawba Nuclear Station

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