ML19211A275

LER 79-109/03L-0:on 791113,discovered Couch (Deutsch) Relay Contacts Were Driving High Inductive Loads in 26 Nuclear safety-related Circuits.Caused by Inductive Surge When Contacts Open.Arc Suppression Diodes Added to Circuits

ML19211A275
Person / Time
Site:	Davis Besse
Issue date:	12/11/1979
From:	Beeler T TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19211A273	List: ML19211A272 ML19211A275
References
LER-79-109-03L, LER-79-109-3L, NUDOCS 7912170303
Download: ML19211A275 (2)

Text

U.S. NUCLEAR REGULATORY COMMISSION NRC F ORM 36G (770 LICENSEE EVENT REPORT (PLEASE PRINT OR TYPE alt REQUIRED INFORMATION)

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[ l o l 2 ] lDuring work on Facility Change Request (FCR)79-378, which added arc suppression diodet l o l a i tI o all non-saf ety related reactor coolant pump auxiliary relay interlock circuits, it l jol4) lvas found that Couch (Deutsch) relay contacts were driving high inductive loads in 26 l lol3l lnucicar safety related circuits. Although there has been no failures of these relays l There vad lOlcl l ni the Class IE circuits, this finding is being reported under T.S. 6.9.1.9.

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TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POUER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-33-79-126 DATE OF EVENT: November 13, 1979 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE: Couch (Deutsch) relays were driving high inductive surge levcis in certain nuclear safety related circuits Conditions Prior to Occurrence: The unit was in Mode 5, with Power (MRT) = 0, and Load (Gross MWE) = 0.

Description of Occurrence: During work on Facility Change Request (FCR)79-378, which added arc suppression diodes to nll non-safety related reactor coolant pump auxiliary relay interlock circuits, it was found that Couch (Deutsch) relay contacts were driving high inductive loads in twenty-six (26) nuclear safety related circuits. Although there have been no failures of these relays in the Class IE circuits, this finding is being reported under Technical Specification 6.9.1.9.

Designation of Apparent Cause of Occurrence: The cause of the potential Couch (Deutsch) relay failures has been determined to be an unexpected inductive surge in the circuit when the contacts open which may cause a shorting of the relay contacts to ground.

The initial design did not anticipate the surge in the Class IE circuits.

Analysis of Occurrence: There was no danger to the health and safety of the public or to station personnel. There has been no relay failures in the nuclear safety related circuits.

Corrective Action: As a preventative measure, FCR 79-378 Supplement 1 added arc sup-pression diodes to all twenty-six (26) Class IE circuits. This further assures the operability of the circuits by providing a path for the discharge of the energy in the coil through the diode rather than through the contacts of the interrupting relay.

Failure Data: There have been no previous relay failures in Class IE circuits due to an inductive surge in the circuits. However, in the non-safety related reactor coolant pump auxiliary relay circuit, there has been a failure; refer to Licensee Event Report NP-33-79-121.

LER #79-109 i592 219 e