PNO-II-86-041, on 860613,25 Gpm Leak Discovered Inside Containment.Caused by 360-degree Crack in Socket Weld to Flange for Variable Orifice Control Valve Outlet Side.Weld Will Be Analyzed by Westinghouse for Metal Fatigue

PNO-II-86-041:on 860613,25 Gpm Leak Discovered Inside Containment.Caused by 360-degree Crack in Socket Weld to Flange for Variable Orifice Control Valve Outlet Side.Weld Will Be Analyzed by Westinghouse for Metal Fatigue

ML20206J625
Person / Time
Site:	Catawba
Issue date:	06/17/1986
From:	Brownlee V, Burger C NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
To:
References
PNO-II-86-041, PNO-II-86-41, NUDOCS 8606270219
Download: ML20206J625 (2)

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. k June 17, 1986 PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE PNO-II-86-41 This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or public interest significance. The information is as initially received without verifi-cation or evaluation, and is basically all that is known by the Region II staff on this date.

FACILITY: Duke Power Company Licensee Emergency Classification:

Catawba Unit 1 X Notificaticn of Unusual Event Docket No. 50-413 Alert Rock Hill, South Carolina Site Area Emergency General Emergency Not Applicable

SUBJECT:

LEAK INSIDE CONTAINMENT AND UNSCHEDULED SHUTDOWN Duke Power Company declared an unusual event at 3 p.m. (EDT) on Friday, June 13, in accordance with technical specification requirements --

an unidentified, 1.4-gallon-per-minute leak had existed for four hours.

At 3:42 p.m., a breaker short-circuit in a turbine building power panel disabled the main generator hydrogen cooling pump and cut off power to the control circuit of the variable letdown orifice control valve, which is located on the primary side of the plant.

Because main generator temperatures began increasing due to the loss of the hydrogen cooling pump, the plant operator began unloading the generator. In addition, loss of the control circuit caused the orifice control valve to fail full open, causing a letdown flow rate of about 110 gallons per minute (gpm).

The operator shifted the letdown to a 45-gpm orifice and innediately noted a high charging rate and a low letdown rate, indicating a possible primary system leak. These conditions were later determined to be due to cooldown caused by unloading of the generator, as well as by the leak.

After about 45 minutes, the leak was stopped when operators closed two letdown isolation valves. A controlled shutdown of the reactor was begun, and the generator was taken off line. Although the leak at first appeared to be 150 gpm, later calculations made before the isolation valves were closed determined that it was about 25 gpm. Workers who entered containment found a 360-degree crack in a one-inch socket weld to the flange for the variable orifice control valve outlet side.

The plant reached cold shutdown at 2:15 a.m. on June 14, and the unusual event was ended at 3 a.m. on June 15. Resident inspectors, who were on site, closely monitored the incident.

Duke has found that the control panel failure was caused by a vendor-installed metal nameplate, about one inch by 2.5 inches, which shorted two buses together. A preliminary evaluation by Duke design personnel indicates that the socket weld failure may have been caused by vibration induced metal fatigue. The weld will be analyzed by the Westinghouse laboratory in Pittsburgh, PA.

Region II entered the standby response mode and staffed its regional response center at 4:35 p.m. on June 13. This standby response ended at 10 p.m.

Duke announced the shutdown and primary system leak to newspapers and broadcast stations in the plant vicinity.

8606270219 860617 PDR I&E PNO-II-86-041 PDR

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,.s f.Y Tha State of South Carolina has b:en informed.

This infonnation is current as of 8 a.m. today. l

Contact:

C. Burger, 242-4198 V. L. Brownlee, 242-5583 DISTRIBUTION:

H. Street ll:35 MNBB/lMPhillips fi.d1E WIl 9 Willste 'p4 MAIL:

Chairman Palladino IDT NRR IE NMSS XDTiiDh8 Com. Roberts PA OIA RES .00T: Trans Only Com. Asselstine MPA AE00 Applicable State Com.~ Bernthal ELD Com. Zech Air Rights ll,*1 INPO - GFL-SECY SP NSAC o

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Regions: T At? / W V PDR 11 1 Licensee:

(ReactorLicensees)

Applicable Resident Site - IG55 m______