ML20085G916

AO BFAO-733W:on 730703,refueling Bridge Interlock Switch Failed.Cause Could Not Be Determined.Switches Removed, Cleaned & Tested

ML20085G916
Person / Time
Site:	Browns Ferry
Issue date:	07/13/1973
From:	Eric Thomas TENNESSEE VALLEY AUTHORITY
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20085G919	List: ML20085G916 ML20085G933
References
BFAO-733W, NUDOCS 8308290514
Download: ML20085G916 (2)

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i TENNESSEE VALLEY AUTHO AITY L""E CHATTANOOGA, TENNESSEE I '

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July 13,1973 \* ff g/pgg Mr. John F. O' leary, Director Directorate of Licensing e

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l kh U. S. Atomic Energy Commissicn Washington, DC 20545 4h#hb k f Odf .."

Subject:

TENNESSEE VALLEY AUTHORITY - BROWS FERRY NUCLEAR FIAh"f UNIT 1 - DOCKET NO. 50-259 - FACILITY OPERATING LICENSE DPR ABNORMAL OCCURRENCE REPORT BFAO-733W The purpose of this report is to provide details concerning the failure of a refueling interlock at Browns Ferry Nuclear Plant

, at 5:30 a.m. CDT cn July 3, 1973 i '

Description of Incident During the weekly refueling interlock surveillance test en unit 1 refueling platform at.5:30 a.m. CDT on July 3, 1973, a refueling bridge interlock switch malfunctioned. The malfunction permitted refuel platform motion to continue past the_ block point toward the-core with the reactor mode switch in the startup position and all control rods fully inserted.

Investigation and Corrective Action After an extensive investigation, the exact cause of the limit-switch malfunction could not be determined. From all indications the limit switch had apparently passed over an obstruction, possibly the power supply cable; and sufficient force had been exerted to the switch actuating arm to cause it to slip on the' switch shaft.

Beth refueling platform bridge interlock switches were removed,1 disassembled, inspected, cleaned, lubricated, reassembled, and bench-tested. During the inspection, the switches operated

. satisfactorily; and there was no damage to the switch internals.

Subsequent bench checks of both switches were satisfactory when the.

actuating arm was displaced an adequate amount. ,

8308290514 730713 p.

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Mr. John F. O'Icary July 13,1973 TENNESSEE VALLEY AUTHORITY - BROWNS FERRY NUCLEAR PIANT UNIT 1 - DOCKET NO. 50-259 - FACILITY OPERATING LICENSE DPR ABNORMAL OCCURRENCE REPORT BFAO-733A l

The switches were reinstalled on the refueling platform bridge, and the motion of the actuating arms on .the cam plate located on the floor was carefully observed. Measurements were taken to assv 'Nat switch contacts were opened sufficiently to assure reliaols eperation when the_ actuating arm was in contact with the cam _'. ate. The switch arm actuation throughout the full travel of the platform was observed. These checks revealed that adequate motion was attained to produce confidence that the switches would perform their intended function. Previous plans to install la 1/4-inchshimonthecamplatewerecancelled.

Functional checks of the switches indicated proper operation. '

Applicable portions of surveillance instruction 4.10.A-1 which

! functionally tests the refueling interlocks were subsequently performed satisfactorily. '

The Plant Operations Review Com:nittee reviewed investigative findings and preposed corrective actions on July 4, 1973, at 9:00 a.m. CDT. The committee approved the corrective actions and recommended resumption of refueling activities upon satis-factory completion of the surveillance instruction.

Refueling activities were resumed' July 4,.1973,'at lo':oo p.m. CDT.

Very truly yours, TENNESSEE VALLEY AUTHORITY

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-( h / e7&v, E." F. Thomcs '

Director of Power Production CC: Mr. Norman C. Moseley, Director-

. Region _II Regulatory _ Operations Office, USAEC 230 Peachtree Street, nw.-

Atlanta, Georgia. 30303 '

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