ML20127E111

Special Rept:On 850419,seismic Instrumentation Sys Began Alarming Continuously.Troubleshooting Indicated 120 Mv Peak to Peak 60 Cycle Signal on Sys Fire Sensor Signal Cables. Problem Under Investigation

ML20127E111
Person / Time
Site:	Byron
Issue date:	05/23/1985
From:	Querio R COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
BYRON-85-0780, BYRON-85-780, NUDOCS 8506240439
Download: ML20127E111 (2)

Text

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t Commonwealth Edison

. ./*x\ Byron NuclearSt' tion h/

( _ ) 4450 North Germ:n Church R:ad Byron, Illinois 61010 PRICRITY ROUTING rk fl GA.<A m u2b

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May 23,1985 LTR: BYRON 85-0780 Mr. James G. Keppler Regional Administrator Region Ill U.S. Nuclear Regulatory Commission ,

799 Roosevelt Road Glen Ellyn, IL 60137 j

Dear Sir:

This special report is submitted in accordance with Byron Station, Unit 1 Operating License NPF-23, Appendix A, Technical Specification 3.3.3.3, Action Statement a, 4

reporting of seismic monitoring instrumentation failures.

4 4

On April 19,1985 the Seismic Instrumentation System began alarming continuously.

4 Troubleshooting by the station Instrument Maintenance Department indicated

, a 120 millivolt peak to peak 60 cycle signal on one of the system's fire sensor

signal cables. This signal cable is for the fire field sensor. The noise signal j was discovered with the system cable lifted at both the cabinet and the sensor.

Assisted by Commonwealth Edison Technical Center Operational Analysis Department, the station Technical Staff walked down the cable to check for sources of induced noise. Upon investigation it was discovered that the cable

' runs within 2 feet of a Unit Auxiliary Transformer feed to a Train A 4KV non-safety  :

bus, and in close proximity to several other 4KV feeds. With Unit I shut down for a planned outage, the signal cat >1e was again checked. Only a small noise '

signal (approximately 10 millivolts peak to peali) was found on the cable.

Continuing the investigation, Byron Station will vary the electrical lineups between the Unit Auxiliary Transformer and the System Auxiliary Transformer to locate the source of the noise. Upon determining the noise source Byron Station will analyze the situation to resolve the problem.

Possible solutions are: 1) rerouting the signal cable away from the noise source;

2) providing magnetic shielding in the problem area; or 3) providing noise filtering at the cabinet.

This problem is under investigation and is being tracked by Limiting Condition 3 for Operation Action Requirement (LCOAR) IBOS 3.3.3-la.

DOC [ N MAY 2 819851 0,

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- BYRON 85-0780 Page. 2 This report was prepared by the Compliance Department with information supplied by the Technical Staff.

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- R.E. Querio Station Superintendent Byron Nuclear Power Station

~ REQ /WDP/gt cc: J. Ilinds, NRC Resident Inspector US NRC Document Control Desk, Washington, D.C.

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