ML20210V220

Special Rept 1-SR-86-042:on 860428,nonvalid Emergency Diesel Generator Tripped During Troubleshooting.Caused by Improper Temporary Clamp Reducing Cable Length.Clamp Removed

ML20210V220
Person / Time
Site:	Palo Verde
Issue date:	05/27/1986
From:	Van Brunt E ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR
To:	Martin J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V)
References
1-SR-86-042, 1-SR-86-42, ANPP-36688-EEVB, NUDOCS 8606100270
Download: ML20210V220 (3)

Text

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Arizona Nuclear Power Project P O DOX $2034

• PHOENIX AAl20NA 85072 2034 l .i Kiy 27. 1986 &

ANPP-36688-EEVB/PGN/98.05 2

. - > y ";j Mr. John B. Martin, Regional Administrator Office of Inspection and Enforcement

., 3'-

U.S. Nuclear Regulatory Commission ", ;

Region V .

1450 Maria Iane, Suite 210 '

Walnut Creek, CA 94596-5368 Subjects Palo Verde Nuclear Generating Station (PVNCS)

Unit 1 Docket No. STN 50-528 (Ilcense NPF-41)

Special Report - Nonvalid Diesel Generator Failure File 86-020-404 Dear Mr. Martin Attached please find a Special Report (1-SR-86-042) prepared and submitted pursuant to Technical Specifiestions 4.8.1.1.3 and 6.9.2. This report discusses a nonvalid diesel generator failure during troubleshooting.

If you have any questions, please contact me.

Very truly yours,

{ 'Cd CLLC ALd m E. E. Van Brunt, Jr.

Executive Vice President Project Director EEVS/lVN/dtm Attachment ces R. P. Zimmerman (all w/a)

A. L. Ilon E. A. 1.icitra A. C. Gehr INPO Records Center 0606100270 060527 l PDH O

ADOCK 00000520 PDH

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PAID VERDE NUCLEAR GENERATING STATION UNIT 1 Special Report 1-SR-86-042 Nonvalid Diesel Generator Failure During Troubleshooting Docket No. 50-528 License No. NPF-41 This Special Report describes an event involving a nonvalid testing failure of an emergency diesel generator during troubleshooting. he re port is provided pursuant to Technical Specifications 6.9.2 and 4.8.1.1.3, and contains the information recommended in Regulatory position C.3.b of Regulatory Guide 1.108, Revision 1. August 1977.

At 0637 on April 28, 1986, Palo Verde Unit 1 was in Mode 5 (COLD SHUTDOWN) when the train "A" emergency diesel generator started and tripped on an apparent overspeed condition prior to loading, at approximately 400 R1L he start attempt was a troubleshooting test which was being conducted on the cylinder heads and fuel lines, in ordsr to detect fuel leaks and jacket cooling water leaks.

We train "A" diesel generator was satisfactorily tested at 1952 on May 3, 1986. The elapsed period for which the diesel generator was unavailable after the trip was 5 days and 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br />. During this time all applicable Technical Specifications, as related to the diesel generators, were complied with. As a result, the unavailability of the train "A" diesel generator following the trip did not advarsely affect the safe operation of the plant.

Following the trip, investigation into the event determined that the trip was not caused by an actual overspeed condition. Examinatten of the overspeed governor, which initiates the overspeed trip when an actual overspeed condition exists, indicated that the governor was still in the  ;

normal, pre-trip position. When the overspeed governor trips, it assumes a post-trip position and must be manually reset. %erefore, since the overspeed governor was not found in the post-trip positten, the diesel  !

generator could not have tripped by an actual overspeed condition. <

When an engine oversloed condition exists, the overspeed governor trips, and initiates a diesel generator overspeed trip by closing the engine air intake butterfly valve. To close the air intake valve, the overspeed governor pushes on a sheathed steel cable, which unlatches the pawl that holds the valve open. %en, elsetrical limit switches on the air intake valve, which are actuated when the valve closes, complete the engine overspeed trip by isolating the fuel supply to the engine.

Further investigation into the cause of the event discovered a clamp which had been temporarily installed on the sheathed steel cable. It is believed that the clamp was installed by maintenance workers who had recently installed scaffolding in the immediate vicinity, in order to prevent the cable from being damaged during the reinstallation of j

insulation on the diesel generator exhaust pipe.

-,--..n---.--m- --,-~.,----e-- ,.-wn.e., .,,m,, --,,_.r,.y.-n, .,.,-,- -

,--- , ~, -.,v,, , , - , , , , . - -- - - - - - . - .

Clamping the cable caused a decreased bend radius in the cable. As a result of the decreased bend radius, the effective length of the cable, relative to the length of the sheath, was altered. This resulted in the unexpected unistching and closing of the air intake valve, and the subsequent trip of the diesel generator. As a corrective action, the clasp was removed, and the diesel generator was subsequently tested satisfactorily.

Prior to this event, there had been three valid diesel generator failures in the previous one hundred valid tests. As a result of this event, the number of valid diesel generator failures in the previous one hundred valid tests remains unchanged at three, and a test interval of not greater than seven days remains in effect, in accordance with Regulatory Guide C.2.d.