ML20085M358

Final Deficiency Rept Re Failure of Operator for RHR Sys Valve FCV-74-73.Initially Reported on 731222.Operator Mechanism Reassembled.Limitorque Stem Locking Nut Exam Instituted

ML20085M358
Person / Time
Site:	Browns Ferry, 05000000
Issue date:	02/26/1974
From:	Gilleland J TENNESSEE VALLEY AUTHORITY
To:	Knuth D US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20085M352	List: ML20085M358 ML20085M363
References
10CFR-050.55E, 10CFR-50.55E, NUDOCS 8311080284
Download: ML20085M358 (4)

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TENNESSEE VALLEY AUTHOFilTV CHATTANOOGA, TENNESSEE 37401 -

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February 26, 1974 OTH ANNIVEASAAY OF PEOPLEIN PA ATNE ASHIP t

Mr. Donald F. Knuth, Director Directorate of Regulatory Operations -

U.S. Atomic Energy Commission Washington, DC 20545 -

Dear Mr. Knuth:

Initial report of a deficiency involving FCV-74-73 in Browns

,i Ferry Nuclear Plant unit 2 was made on December 22, 1973. An )

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f interim report, J. E. Gilleland to D. F. Knuth, was submitted -

on January 23, 1974. In summary, during Preoperational Test ~

g ao. G-31, the operator mechanism of FCV-74-73 in the Residual .-- g .. r Heat Removal System failed mechanically. The failure was BM  :

apparently caused by the lock nut's failure to secure the .i Q . q -

stem nut which allowed the stem nut to travel without actuating the valve. The lock nut should have been double-staked to the . " Mil.M drive sleeve at the factory, but on this particular valve the p p.[f.fl,? [(

double-staking apparently was not done adequately. We have j .y,'Op" . / ",;'j taken the corrective action described in the enclosure which 7' "

is submitted as the final deficiency report in accordance  !

with paragraph 50.55(e) of 10 CFR 50. ,

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• !ery truly yours,  :

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, .c J. E. Gilleland v Assistent to the Manager of Power b T.'hY j l$.g g ;if

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Enclosure -

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CC (Enclosure): , *D,G Mr. Norman C. Moseley, Director ({'*ggf2

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Directorate of Regulatory Operations U.S. Atomic Energy Commission j $U Region II - Suite 818 (?'?'1[.. .

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BROWNS FERRY NUCLEAR PLANT UNIT 2 FAILURE OF OPERATOR FOR VALVE FCV-74-73 IN ' DIE RilR SYSTEM FINAL REPORT On December 22, 1973, an initial report was made to AEC-DRO Inspector W. S.

Little of the failure of the operator for valve FCV-74-73 in tha Residual Heat Removal System (RHRS). This report was made via a telecon by C. S. Walker, D. R. Magnuson, A. L. Mazzetti, and L. D. Weber in compliance with paragraph 50.55(c) of 10CFR50. An interim report was submitted on January 23, 1974.

This is the final report for the occurrence.

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• Description of the Associated Plant Equipment The subject valve-operator assembly is located in the RHRS in unit 2 of the Browns Ferry Nuclear Plant. The assembly is situated in the 12-in. portion

- of the 18-in. Recirculation Loop II prior to the entry of this line into the suppression pool through penetration X-210B. The valve is a 12-in.

Walworth Elobe valve with a design pressure and temperature of 450-psis and j 350*F, respectively, and a flow rating of 20,000 gym. Its operator is a

, . . LimiTorque type SMB-2 valve control.

i Description and Cause of Occurrence During Preoperational Test No. G-31 in unit 2 of the Browns Ferry plhnt,'the operator mechanism of valve FCV-74-73 in the RilRS, failed mechanically. The failure was apparently caused by the locking nu't's failure to secure the stem nut which allowed the stem nut to rise up the threaded stem of-the valve without actuating -the valve. - The locking nut 'is screwed into the drive sleeve in the operator. assembly.above the stem nut and prevents the stem nut from rising when the valve is closed. The means of securing the stem nut against

!. rotation ,that had been used was double " staking".the threads on the drive

' sleeve that mate with the threads'of the locking nut. However, this means,.

as performed, was ineffective in preventing the locking nut from unscrew- .

ing from the drive ~siceva. y O

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2 Staking the threads on the drive sleeve is an operation requiring proper technique and judgment. If the staking or scoring of the threads in order to prevent further movement is performed too lightly, the locking nut will not be prevented from unscrewing. If, on the other hand, the staking is done too heavily. disassembling the operator mechanism will require destroy-ing the staked portions of the threads.

Corrective Measures The inmediate corrective measure taken to repair the operator mechanism was to reassemble the mechanism. During this work, special care was taken to adequately stake the threads on the drive sleeve to insure that the locking j nut was tightly held in the operator mechanism.

Staking of the threads of the drive sleeve was done as follows:

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1. The staking was performed through each of the two wrench holes of the locking nut.

2. The peaks of two adjacent threads and the valley in between were severely deformed by means of a center punch. If there was a doubt as to whether the staking was performed severely,enough, it was deemed better to err on the conservative side by carrying out the operation too heavily.since it is preferable to destroy the staked portions of. the threads when disassembling the operator than

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to risk autodisassembly. -

A Limitorque stem lock'ing nut examination was instituted to provide assurance that-the locking nut on each Limitorque operator will be securely crimped or staked in two places. This examination will be performed by a member of the engineering staff at the Browns Ferry site. Records for each individual valve will be kept. Exhibit 1,.antitled "Limitorque Stem Locknut Check," is a copy of these records for the examination performed on the Limitorque operators,of unit 2 on December 19, 1973.

Although..this deficiency is not considered.to be generic, a similar staking check will be performed on the Limitorque operators-for unit 3 before the respective valves'are installed. Such a staking check will also be made on m_. . . . _ . . . . . . ,. .

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o g 3 l every Limitorque operator that is reassembled in the future. We believe l l

that such examinations will prevent the recurrence of this problem in the ,

future.

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