ML20085G889

AO BFAO-50-260/7419W:on 741015,2-inch Schedule 80 Stainless Steel Equalizing Line Appurtenant to 22-inch Crosstie Piping Between Two Reactor Coolant Recirculation Pump Loops Suffered Fatigue Failure.Caused by Excessive Vibration

ML20085G889
Person / Time
Site:	Browns Ferry
Issue date:	10/25/1974
From:	Eric Thomas TENNESSEE VALLEY AUTHORITY
To:	Case E US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20085G893	List: ML20085G889 ML20085G900
References
NUDOCS 8308290498
Download: ML20085G889 (3)

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• Aruxwm an-October 25, 1974 SfrIZi9 "#J A . . t _,

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Fr. Edcon G. Case /b,-'-

Acting Director of Licensing Office of Regulation U.S. Atcmic Energy Cer:missien Washingtcn, DC 20545 .

Dear P.r. Case; i

TEITIiESSEE VALLEY AUIHORITY - ERGINS FFIdlY L'JCIFJd1 PIAITT UNE' 2 -

i DOCKET IIO. 50-260 - FACILITY OPERATIIIG LICENSE DPR ABNORI/AL I

OCCURRE"CE FSPORT EFAC-50-260/7h19'i The enclosed repcrt is to provide details concerning fatigue failure of a 2-inch schedulo 80 stainless-steel equa.lizing line appurtenant to the 22-inch cresstie piping between the two reactor coolant recir-culation pur:p locps and in submitted in accordance with Appendix A -

to Regulatcry Guide 1.16, Revision 1, October 1973. This event occurred en Browns Ferry Nuclear Plant unit 2 on October 15, 1974.  ;

Very truly yourc, TEIINESSEE VALLEY AUTHORITY ~ G~I/' '"$ x  !

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PE. F. Thc :as

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F' Director of Power Production -

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Enclosure .

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Mr. Norman C. P.oscley, Director p -

Region II Regulatory Operatiens Office, USAEC 230 Peachtree Street, N!f., Suite 818 Atlanta, Georgia 30303 E

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AEHORI'AL OCCUICC.CE REPORI Report Uurber: BI'AO- 50-060/7h19'd

' Report Date: October 25, 1974 Occurrence Date: October 15, 197h Facil'.ty: brc. ins Ferry nuclear Plant unit 2 t

Identification of Cecurrence Fatigue failure of a 2-inch schedule 80 stainless-steel equalizing line appurtenent to the 22-inch crosstie piping between the two reactor coolant recirculation punp loops.

Conditions Prior to Occurrence The reacter was in a cold chutdown conditien in an outage initiated by a failure of a rain power transforcer on October 7, 1974. The unit had been placcd in the shut-down cooling node of operation on October 11, 1974.

Description of Occurrence A prograr_ was under uay to inspect for prcper support and restraint of all instruuant censing lines, drains, vents, and sample lines 1 inch and smaller und the b-inch recirculation pa p discharce valve bypasses within the drywell. During the inspection,1:ater was noted leaking frca cracks in the pipe surface at the toe of the fillet ucld '.;here the ,cqualizing line nas attached to the rain valve bcdy.

Eccause of the arcunt of verk in progress in this inmediate area, the leak would have been discovered if it had existed for any appreciable time. Incediate acbion was taken to succescfully isolate the failed piping by valve closure.

Designaticn of Apnarent Cause of Occurrence Extensive testing derenstrated that the 2-inch recirculation valve bypass line experienced excessive vicration during cperation of the RIiR system at a shute.oun cooling flou of approxinately 9,000 cpr. Testing also demonstrated that normal recirculatica patp operation does not induce sinilar vibration. Examination of the failed section of piping by a consultant confirms that the failure is due to fatigue rhich propagated frca the outside to the inside of the 2-inch line.

Isnalysis of Occurrence The cause of the failure was fatigue of the 2-inch equalizing line st the toe of a fillet veld where the line was joined to the valve body. The fatigue failure resulted from vibraticn of the 2-inch equalizinr; line vile operatinft in the shutdoun cooling mode with approxinateg 9,000-gpn cooling flow. There were no adverse effects to the public health ani safety as a result of this occurrence.

Corrective Action Plant design has been modified to remove the equalizing valves across cach of the 22-inch crosctie valves. The crenstie valves FCV-68-33 and FCV-68-35 have been electrically de-energized and plant instructions changed to require one of tha valves shut and the other open. The 2-inch equalizing valves, FCV-68-36 and FCV-68-3',, and portions of the 2-inch schedule 80 stainless-steel lines were recoved. The retainin;; stubs cf the 2-inch equalizing' lines vere corrected as follows:

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1. The two 2-inch schedule 80 stainless..cteel linec that could be icolated were renovel and replaecd with neu P-inch .;cneaulo 80 stai.nlecc-stcel pipe uith a

. 3,000-pound cocket .. eld pipe cap welded on the end.

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2. The tuo 2-inch schedule 80 stainlesc-cteel linec uhich could not be isol ted i from the re tetnr veccel by valving were plugged and welded using a freeze plug technique. Also, a cloce-fittirq cleeve fabricated frca 304 ctainleca j cteel with an 0 306 inch vall vac inctalled over the 2-inch stubs and plu26ed i

on one end and the other end uelded to the valve bodies of F0V 68-35 anl  ;

FCV-68-33 The cleeve was drilled and tapped with 1/h-inch UP2 to detect l failure of the inner 2-inch line.

j Baced on vibration data taken on unit 2 and subsequent analyces, there is no

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reason to expect that continued normal power operation of unit 1 vill aggravate j any enterial fatigue problem the 2-inch recirculation valve-bypacc line ray have j 3 custained because of excescive vibration during prior operation of the PFn sycten i or from vibration inacced by the recirculation purps. There is no evidence to indicate that there is coincidcnce between the vibrational modes in the 2-inch e

bypacc lines in unit: 1 and 2 as a function of EHR flow. However, we vill nake I vibration neacurer.ents of the unit 1 bypaca line the next time the RHR systen is placed in service. Subseauent action vill be based upon the results of thic l tecting. , ,

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