ML20085G551

Sixth Interim Deficiency Rept Re Potential Design Deficiency in Valve Yoke to Motor Mount Weld.Initially Reported on 740514.Engineering Change Notice L-1316 Issued to Add Support Hangers to motor-operated Valves in RHR Sys

ML20085G551
Person / Time
Site:	Browns Ferry
Issue date:	03/03/1975
From:	Gilleland J TENNESSEE VALLEY AUTHORITY
To:	Knuth D NRC OFFICE OF INSPECTION & ENFORCEMENT (IE)
Shared Package
ML20085G493	List: ML20085G489 ML20085G504 ML20085G551 ML20085G575
References
NUDOCS 8308290137
Download: ML20085G551 (3)

Text

-

_ _ ,, .q OwTroh

+

M O'g 5

s.

TENNESSEE VALLEY AUTHORITY i E 2 CHATTANOOGA. TENNESSEE 374o1

1. D6 19*

J March 3,1975 i

l Mr. Donald F. Knuth, Director 1

Office of Inspection and Enforcement U.S. Nucicar Regulatory Commission Washington, DC 20545 l

Dear Mr. Knuth:

{ BROWNS FERRY NUCLEAR PLANT UNITS 2 AND 3 - POTENTIAL DESIGN DEFICIENCY IN VALVE YOKE TO MOTOR MOUNT WELD Initial report of the subject potential deficiency was made 4

on May 14, 1974, and was followed by our June 14, July 15, August 12, September 13, 1974, and our January 15, 1975, letters, J. E. Gilleland to Donald F. Knuth. Because the yoke to motor base welds of FCV-74-58 in unit 1

, failed, similar valves (FCV's 74-58 and 74-72) in units 2 and 3 may be subject to the same type of failure.

Corrective action has been initiated as described in the enclosed sixth interim report on this problem. We are awaiting a forual reoort fiu.a Southwest K**aarch inarireta ta deta miaa j if additional corrective action is required. Their report' will be forwarded to -the Nuclear Regulatory Comission immediately -

9 after being received and reviewed by TVA.

Very truly yours, ,

i .

y I

J. E. Gilleland Assistant Manager of Power Enclosure

• j CC (Enclosure):

, Mr. Norman C. Moseley, Director i

Office of Inspection and Enforcement U.S. Nuclear Regulatory Comission i- Region.II - Suite 818

• 230 Peachtree Street, NW -

, Atlanta, Georgia 30303

' 0 96*

B308290137 761122 [?

~

PDR ADOCK 05000260i -

p ,)[<

i PDR S _

t An Equal Opportunity Employer m.____ e aw

L .)

~

o. . .

O -

\

l ENCLOSURE  !

BROWNS FERRY NUCLEAR PLANT UNITS 2 AND 3 FAILURE OF THE WELD BETWEEN THE YOKE AND MOTOR MOUNTING PL1TE FOR FLOW CONTROL VALVES (FCV'S) 74-58 AND 74-72 SIXTH INTERIM REPORT -

On May 14, 1974, an initial report regarding the subject deficiency was made by telecon to W. S. Little, AEC-DRO Inspector, Region II. The report was made by L. D. Weber and J. A. Raulston in compliance with paragraph 50.55(e) of 10CFR50. There have been five interim reports previous to this report. These were dated June 14, 1974; July 15, 1974; August 12, 1974; September 13, 1974; and January 15, 1975.

Description of Occurrence On May 12, 1974, the Unit i reactor at Browns Ferry was in the cold shutdown condition so that repairs on this unit could be made. While draining a section of the RHR line to permit repair work, torus spray valve FCV 74-58 tripped out e*Acetrically when an atte=pt was made to operate the valve. After some Investigation, it was discovered that the valve operator on FCV 74-58 had separated frn the valve stem. Because the veld betvcen the fokc and motor

,'uase of rCV /4-So failed in unit i, tne respective valves (FCV's 74-58 and 74-72) in Units 2 and 3 were assu=ed to be subject to a similar type of failure.

' Ca#us"e'of'Deficicncy

~

i Extensive vibrational testing has recently been completed at Browns Ferry.

It was determined that the deficiency was caused by both vibrations and an insufficient amount of weld. Overstressing caused by vibration of a weld of insufficient depth resulted in the subject deficiency. The cause of the vibrations was pinpointed by the vibrational tests. These tests indicated that excessive pressure drop across certain components in the RHR system caused the vibrations.

Safe'ty Implications

• The function of FCV 74-58 in the RHR system is to provide spray in the torus

.; ., after a loss of coolant accident. This spray condenses any stemn that may 4 thereby lowering containment pressure. The loss of one l l' l, exist in the torus.of these vnives due to the deficiency previously described would not I

the pressore in the containment to rise significantly because there are two spray vnives in the torus, and either one is capabic of accomplishing the pressure suppression function. 'the re fo re , loss of one spray valve would not -

incapacitate this subsystem of the RHR system, and the plant would remain controllable in any situation.

j p

i r f

n ._

) * . . . .

Description'of Corrective Action Engineering Change Notice (ECN) L-1316 has been issued to add support

. hangers to the motor-operated valves FCV 74-53 and FCV 74-72 located in g

- the RilR system. The additional actions needed to correct the vibration probicm are being proposed in a formal report which Southwest Research Institute is prepcring for TVA. This report will be forwarded to the NRC in:nediately after being received and reviewed by TVA.

Means Taken to Prevent a Recurrence All welds on the subject equipment have been inspected. In addition, support hangers have been added by ECN L-1316. Currently, we are awaiting the fonnal report from Southwest Research Institute. This report will indicate whether additional corrective action is required.

4 i

1 b

I e s

a e

4 f

4 6

6 e 9 e

O 5 ,

l -

l .

I .

l' i L -

i