ML19274D166

LER 78-068/03L-0 on 781213:noted That Absolute Position Indication for Rod 5,Group 6 Was Fluctuating 10 to 15% Caused by Several Sticking Reed Switches

ML19274D166
Person / Time
Site:	Crystal River
Issue date:	01/05/1979
From:	Cooper J FLORIDA POWER CORP.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19274D162	List: ML19274D161 ML19274D166
References
LER-78-068-03L, LER-78-68-3L, NUDOCS 7901150114
Download: ML19274D166 (2)

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SUPPLEMENTARY INFORMATION Report No.: 50-302/ 78-068 /03L-0 Facility: Crystal River Unit #3 Report Date: 5 January 1979 Occurrence Date: 13 December 1978 Identification of Occurrence:

Inoperable absolute position indication for rod 5 group 6 contrary to Technical Specification 3.1.3.3.

Conditions Prior to Occurrence:

Mode 1 power operation (98%)

Description of Occurrence:

At 0900 and again at 1645, during normal plant operation, it was observed that the absolute position indication for Rod 5, group 6 was fluctuating 10 to 15%. These fluctuations caused numerous asymmetric faults as well as inhibiting rod withdrawal.

Reactor power was reduced and rod 5's position was verified per action statement 3.1.3.3. Operability was restored within two and one half hours in each case following maintenaace.

Designation of Apparent Cause:

The cause of these events can be attributed to several stuck reed switches. Mag-netization eminating from spurious magnetic fields generated during control rod operation, caused the reed switches to stick.

Analysis of Occurrence:

There was no hazard to plant personnel or general public as rod position indication was available and operable via relative position indications.

Corrective Action:

The application of a variable A.C. frequency to the affected reed switch circuit, different in each event, eliminates the magnetic field. Normal switch operability is then restored.

Failure Data:

Six previously reported occurrences, but first occurrence of this type for Rod 5, group 6.

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