05000346/LER-1979-079-03, /03L-0 on 790712:while Repositioning Group 8, Absolute Position Indication for Rod 4 Shifted from 25% to 0% Position.Caused by Oxide Film Buildup on Reed Switch Contacts.Corrective Maint Performed

/03L-0 on 790712:while Repositioning Group 8, Absolute Position Indication for Rod 4 Shifted from 25% to 0% Position.Caused by Oxide Film Buildup on Reed Switch Contacts.Corrective Maint Performed

ML19242D300
Person / Time
Site:	Davis Besse
Issue date:	08/09/1979
From:	Naylor R TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19242D286	List: 05000346/LER-1979-079, Forwards LER 79-079/03L-0 05000346/LER-1979-079-03, /03L-0 on 790712:while Repositioning Group 8, Absolute Position Indication for Rod 4 Shifted from 25% to 0% Position.Caused by Oxide Film Buildup on Reed Switch Contacts.Corrective Maint Performed
References
LER-79-079-03L, LER-79-79-3L, NUDOCS 7908140797
Download: ML19242D300 (2)

LER-1979-079, /03L-0 on 790712:while Repositioning Group 8, Absolute Position Indication for Rod 4 Shifted from 25% to 0% Position.Caused by Oxide Film Buildup on Reed Switch Contacts.Corrective Maint Performed

Event date:
Report date:
3461979079R03 - NRC Website

text

U. S. NUCLE AR REGULATOR NRC FORM 366 (7-7 7 )

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8 60 61 DOC A E T NUY6ER EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h On 7/12/79 at 0415 hours0.0048 days <br />0.115 hours <br />6.861772e-4 weeks <br />1.579075e-4 months <br /> while repositioning Group 8, the absolute position indica-l lo l2l l for Rod 4 of Group 8 shifted from the ?5% withdrawn position to the 0%

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DVR 79-121 Richard W. Naylor PHONE:

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TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION U'RT ONE SUPPLEMENTAL INFORMATION FOR LER NP-33-79-100 DATE OF EVENT: July 12, 1979 FACILITY:

Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE:

Faulty absolute position indication (API) reed switch for Rod 4 of Group 8 Conditions Prior to Occurrence: The unit was in Mode 1, with Power (>r,U) = 580, and Load (Gross MWE) = 200 Description of Occurrence: On July 12, 1979, at 0415 hours0.0048 days <br />0.115 hours <br />6.861772e-4 weeks <br />1.579075e-4 months <br /> while repositioning Group 8, Rod 4 of Group 8 absolute position indication (API) shifted from the 26% withdrawn to 0% actuating the asymmetric rod alarm.

This placed the unit in the Action Statement of Technical Specification 3.1.3.3.

The Technical Specifi-cation requires all abEolute position indication channels to be operable and capable of determining the rod group position within 6.5% when the unit is in Modes 1 and 2.

As the rod withdrawal continued, the API indication returned to normal removing the unit from the Action Statement of Technical Specification 3.1.3.3.

Designation of Anparent Cause of Occurrence: The cause of this occurrence has been determined to be a component failure in the position indicator tube reed switch.

An oxide film is believed to have built up on the reed switch contacts which interferes with the conduction across the switch contacts.

Analysis of Occurrence:

There was no danger to the health and safety of the public or to station personnel. The relative position indication and the group position channels were operating and once the rod was withdrawn past the faulty reed switch, the API indication returned to cperabic status.

Corrective Action

Under Maintenance Work Order (MWO) 79-2499, aaintenance personnel with Diamond Power (the position indicator manufacturer) performed corrective mainten-ance on the reed switch with a position indicator reed switch rejuvenator. This in-strument places a higher than normal operation voltage across the reed switch while the rod is run past the switch causing the switch to actuate.

The higher voltage removes the oxide film which returns the switch to operability.

On July 13, 1979, the switch was retested Ed declared operable.

Failure Data: Although there have been numerous previously reported occurrences of API failures, only two have been identified as oxide buildup in reed switch contacts; see Licensee Event Reports NP-33-79-90 and NP-33-79-97.

LER #79-079 69

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