ML20085E963

AO BFAO-50-260/759W:on 750322,during Second Stage Relief Valve Testing & Refurbishing,Piston & Stem Locknut Found Loose in Air Actuator Chamber on Valve 2 PCV-1-31.Stem & Nut Drilled Twice.New second-stage Stem Installed

ML20085E963
Person / Time
Site:	Browns Ferry
Issue date:	07/18/1975
From:	Eric Thomas TENNESSEE VALLEY AUTHORITY
To:	Rusche B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE)
References
NUDOCS 8308170184
Download: ML20085E963 (3)

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$ g July 18, 1975 - dl -. . b f :,l JUL22B75 :

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s,; n ', lm Mr. Benard C. Rusche \

Director of Nuclear Reactor Regulation' \ -

U.S. Nuclear Regulatory Commission s l Waahington, DC 20$55

Dear Mr. Rusche:

TENNESSEE VALLEY AUTHORITY - BROWNS FERRY NUCLEAR PLANT UffIT 2 -

DOCKET NO. 50-260 - FACILITY OPERATING LICEIGE DPR ABNORMAL OCCURRENCE REPORT BFA0-50-260/759W The enclosed report is to provide details concerning the broken accond-atage atem in main steam relief valves. This report is submitted in accordance with Appendix A to Regulatory Guide 1.16, Revision 1, October 1973 This event occurred on Browns Ferry Nuclear Plant unit 2.

Very truly youra, TENNESSEE VALLEY AUTHORITY

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\ - ic 7 7ts o E. F. Thomaa Director of Power Production Enclosure CC (Enclosure):

Mr. Norman C. Moseley, Director U.S. Nuclear Regulatory Commincion Regional Office 230 Peachtree Street, NW., Suite 818 Atlanta, Georgia 30303 l

l 8300170104 0 PDR ADOCK 0 PDR 6

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tortam W An Equal Opportunity Employer 77S1

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ABNORMAL OCCURRE'!CE REPORT Report No.: BFAO-50-260-759W Report Date: July 18, 1975 .

Occurrence Date: March 22, 1975 Facility: Browns Ferry nuclear Plant unit 2 Identification of Occurrence Main steam relief valves'- broken second-stage stem lConditionsPriortoOccurrence ,

De unit was scrammed on 1/ arch 22,1975, due to fire in the unit 1 area.

During the subsequent unit cooldown, the relief valves were operated to relieve and control reactor pressure.

Description of Occurrence During subsequent relief valve testing and refurbishing, the second-stage piston and stem locknut were found loose in the air actuator chamber on valve 2 PCV-1-31, serial !!o. 65 The threaded portion of the second-stage stem was still in the locknut. The unit has been in the cold shutdown condition since March 22, 1975 Designation of Apparent Cause of Occurrence A close exanination of the locknut on the second-stage stem revealed that the stem and nut had been drilled and pinned twice. Although the complete fracture did not occur until the valve operated, the apparent cause of the stem failure was overstress when the locknut was removed after the initial locking pin had been drilled out. Removal of a locknut, after the drilling and pinning technique of securing the locknut has been applied, is a difficult task. The pin must be drilled out and the nut removed. The surface condition of the drilled threads readily creates a galling situation which opposes nut removal.

Analysis of Occurrence The second-stage stem broke during a valve actuation. Although the valve opened when required, failure of this nature could adversely affect its ability to operate. Ho radioactive materials were released to the environment nor was there any danger to the public health and safety as a result of this occurrence.

Corrective Action

The valve will have a new second-stage stem installed with a new-type l locking device. Also, all the valves for units 1, 2, and 3 will be l

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BFAO-50-250/759W l

evamined and all the valves with the drill-and-pin-type stem locknut will be removed and the second-stage stems will be replaced with new ones with the new-type locking device.

Failure Data Target Rock safety reliel' valve ,

Model 67F, Serial No. 65 l Valve position 2 PCV-1-31 e

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