ML20084H728

AO BFAO-7431W:on 740514,15 Pipe Hangers on Torus Spray Header Found Failed,Allowing Header to Drop & Rest on Several Drywell Vents.Caused by Deficient Design of Hanger Assembly.Larger Hangers Installed

ML20084H728
Person / Time
Site:	Browns Ferry
Issue date:	05/24/1974
From:	Eric Thomas TENNESSEE VALLEY AUTHORITY
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084H730	List: ML20084H728 ML20084H736 ML20084H740
References
A-740524, AO-BFAO-7431W, BFAO-7431W, NUDOCS 8305040792
Download: ML20084H728 (3)

Text

{C -

~

_9 p

.. TENNESS$E VhLLEVAUTHC! MTV r""]n 77.rT CHATTANOCGA, TENNESSEE =

3 74Q1 L -

m

{ 2 ,.' ,l,,'l.

- j q*

OW7$8MM May 24, 1974 "^"[ #! *g'" -

).Q ( %.(

n;:* ? L Y, fA p24 '/

f%jA Mr. John F. O' Leary, Director Directorate of Licensing Office of Regulation U.S. Atomic Energy Cc= mission Washington, DC 20545

Dear Mr. O' Leary:

TENNESSEE VALI2Y AUTHORITY - BRCh'NS FERRY KUCLEAR PIAIff UNIT 1 -

DOCKET No. 50-259 - FACILITY OPERATING LICEUSE DPR ABNORI'AL OCCURREHCE REPORT EFAO-7431W The enclosed report is to provide details concerning 15 of the 16 pipe hangers on the torus spray header which failed and allowed the header to drop and rest en several of the drywell vents and is submitted in accordance with Appendix A to Regulatory Guide 1.16, Revision 1, .

October 1973 ,

This event occurred on Browns Ferry Nuclear Plant u n 1T, .t. on e.ay .t.4, Ayt* (alscovery untej.

. Very truly yours, TENNESSEE VAL EY AUTHORITY

^

d E. F. Thomas Director of Power Production Enclosure CC (Enclomire): 9 Mr. Norman C. Moseley, Director oT' Region II Regulatory operations Off1ce, USAEC 7, L8f';h.,

E-230 Peachtree Street, IM., Suite 818 Atlanta, Georgia 30303 _

f>

g b. -< fJ C\

p I'AY291974 s O

.n, C5 Iyh; _

l gA t 1. :., ,/

{l,6 ,

(.J m .J.

O - .

ft S b)

COPY SDff REGION # _

L ..m ._

r

. p

~1

. U Corrective Action (continued) the exception of one-half of a It-inch pipe cic=p, spacer for the clerp, and a 2-foot-long hanger bar. A review by TVA Decica, the Plant Operations Review Co=mittee, and the Safety Review Board van conducted; and approval to operate the unit with those three unaccounted-for parts was obtained. ,

Following the installation of approved larger hangers, functional tests of the sprcy system veve satisfactorily conducted. Visual inspections of the piping, spreys, and henger system following the spray test were conducted. All components were found in good serviceable condition.

4 The spray header penetrations through the torus shell were dye penetrant checked. l No indications of distress were revealed. All structural components and support featurcs within the torus chove end below the waterlevel were inspected. On one t of the four 30-inch ring header suction strainers a nut had worked loose en a I!

bolt in the three independent hold-down dogs, permitting the strainer to become [

dislocated. The three independent hold-down doss were replaced by one continuous hold-down ring and the nuts were staked to prevent loosening. A sindlar modification was made to the other three suction strainers.

A piece of walkway grating approximately 30 inches by 30 inches had beco=c  ;

dislodged from the catwalk within the torus and had fallen into the torus water.

It was retrieved from a location innediately adjacent to the point of dislodccrent. '

This grating was returned to its original position and welded in place. All other grating was checked end confirmed to be held securely by tack welds or cle ps or was made secure b'/ weldinn.

Some of the catwalk support structure bolts were found loose. Corrections were cade by tightening the nuts end staking in place. Remaining components were found in good condition.

i Failure Data i No previous failures of the torus containment sprey header hangers have been experienced. The torus sprey header van designed end fabricated by Pittsburg Des Moines Steel Co=pany. i i

i t

6

. e e

9 g e a

(

• U

- (_)

si i AB!iORI&L OCCURICCE REPORT Report lio: BFAO-7431W Report Date: Pay 24,11974 Occurrence Date: May 14,1774 (disecvery date)

Facility: Browns Ferry Ih.tclear Plant unit 1-Identification of Occurrence Fifteen (15) of the sixteen (16) pipe hangers on the torus spray header failed and allowed the header to drop and rest on several of the drywell vents.

d Conditions Prior to Occurrence '

The unit was in cold shutdown condition when the occurrence was discovered.

The unit had been operated in the startup test program up to rated power before i this outage.

l Descrintion of Occurrence t

Follouing repairs to a torus sprey supp4 valvo (FCV 74-58), leakage tests l were conducted on the valvo. Visual observation of leakege through the valve a was possible by inspecting lechage from the spray nozzles in the torus. The torus was entered; and, upon viewing the torus sprcy header, it was discovered  !

that the pipe hengers had failed. ,

i Designation of Ance. rent Cause of Occurrence -

The single apparent cause of the occurrence was deficient design of the henger assembly. The henger support bolts were 1/4" dic=eter ASTM A193, Grade B7 bolts. '

Movement of the suspended header during extensive relief valve actuation for  ;

torus vibration tests was a probable cause of failure of the 1/4" bolts with subsequent failure of the hanger system.

AncJy' sis of Occurrence l

1 Torus spray header integrity ras not violated by the henger failures, and it may have been operable if called upon. The torus sprey system has not been operated since precperational testing.

The torus spray ecy be used following an accident to cool gases collected in  ;

the free volune above the suppression pool. Its use is not mandatory however, since the hot gases would under pressure pass to the drywell through the vacuum i breakers a".d be cooled by the containment cooling spray.  :

i i

Corrective Action J

The original haag;crs were removed, 'and larger hangers approved by General Electric '

Company and TVA Design were instelled. Divers were utilized in recovering hanger '.

material which fell into the torus water pool. All parts were accounted for with [

. L i

. L