ML20198Q326

Special Rept 1-SR-86-033:on 860417,during Surveillance Testing,Emergency Diesel Generator Train a Tripped on Overspeed Condition.Caused by Deflection of Air Intake Overspeed Butterfly Valve Disk to Fully Open Position

ML20198Q326
Person / Time
Site:	Palo Verde
Issue date:	05/19/1986
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-86-033, 1-SR-86-33, ANPP-36639-EEVB, NUDOCS 8606090133
Download: ML20198Q326 (3)

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Arizona Nuclear Power Project g ,,,,,. 2 2 :' D 0 1 P O. BOX 52034 e PHOENIX, ARIZONA 85072-2034 May 19,1986 ANPP-36639-EEVB/PGN/98.05 Mr. John B. Martin, Regional Administrator Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission Region V 1450 Maria Iane, Suite 210 Walnut Creek, CA 94596-5368 Sub ject: Palo Verde Nuclear Generating Station (PVNGS)

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

Special Report - Valid Diesel Generator Failure File: 86-020-404

Dear Mr. Martin:

Attached please find a Special Report (1-SR-86-033) prepared and submitted pursuant to Technical Specifications 4.8.1.1.3 and 6.9.2. This report discusses a valid diesel generator failure due to malfunction of the intake air damper.

If you have any questions, please contact me.

Very truly yours, c _

h O CR ~

E. E. Van Brunt, Jr.

Executive Vice President Project Director EEVB/PGN/ dim Attachment cc: R. P. Zimmerman (all w/a)

A. L. Hon s E. A. Licitra A. C. Gehr INPO Records Center 8606090133 DR 860D19 ADOCK 0D000520 PDR ff$$ l W'

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PALO VERDE NUCLEAR GENERATING STATION UNIT 1 Special Report 1-SR-86-033 Valid Diesel Generator Failure Due to Malfunction of the Inte.ke Air Damper Docket No. 50-528 I

License No. NPF-41 l This Special Report describes an event involving the valid failure of an emergency diesel generator. The report 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 1042 MST on April 17, 1986, Palo Verde Unit 1 was in Mode 5 (COLD SHUTDOWN) when the train "A" emergency diesel generator tripped on an indicated overspeed condition during Technical Specification required surveillance testing. At the time of the trip, the diesel generator was being manually loaded from the control room to 6050 KW by a licensed utility operator, in order to perform an operability demonstration at 110% of rated diesel generator load.

The diesel generator trip resulted from the air intake overspeed butterfly valve disk deflecting from the normal partially closed position to the fully open position. The disk deflection resulted in the operation of the overspeed trip limit switches, which are directly actuated by a change in butterfly valve disk position, and caused a subsequent overspeed trip initiation. The air intake overspeed butterfly valve is located in _ the engine air inlet piping, and assists in terminating diesel generator operation when an overspeed condition is detected, by isolating the turbocharger intake air supply, in addition to actuating the overspeed trip limit switches. .

An overspeed trip on the diesel generator is typically initiated by the diesel generator governor, and is indicated by the closing of the air intake

overspeed butterfly valve. However, an actual overspeed condition did not exist at the time of the trip. Determination that an overspeed condition did not exist was made based on the fact that the diesel generator was aligned with the offsite power grid at all times during the event, and could not have been rotating at a speed greater than that which coincided with the grid frequency. Also, after the overspeed trip, the butterfly valve disk was not found in the closed position, but rather in an open position, deflected in a direction which was counter to the normal post-trip rotation direction.

The root cause of this event was an equipment malfunction. Investigation into the cause of this event identified that the spring which assists in the closing of the overspeed butterfly valve, when an overspeed trip is received, had experienced some loss of tension. Although the cause of the detensioning ,

of the spring has not been identified, it is assumed that it was due to normal '

aging. i i

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In addition to assisting valve closure when an overspeed trip is received, the spring assists in holding the butterfly valve latched in the partially closed, normal operating position when an overspeed trip is not active, by applying force to a lever which keeps the valve latched in position. The partial loss of spring tension resulted in an unanticipated valve disk deflection in the opening direction, because of the greater than normal intake air flow which existed at the time of the trip (the. diesel generator was operating at approximately 110% of rated output), and caused the disk on the overspeed butterfly valve to fully open.

As a corrective action, the spring tension was adjusted on the train "A" diesel generator. Additionally, new springs have been ordered and will be installed upon receipt, and an engineering evaluation will be initiated to evaluate the need for periodic replacement of the springs.

Prior to the trip, the train "A" diesel generator had been declared INOPERABLE '

at 1600 on April 16, 1986, as a result of the train "A" Balance of Plant Engineered Safety Features Actuation System (BOP-ESFAS) being removed from service. The diesel generator was satisfactorily tested at 1952 on May 3, 1986, but has not been returned to an OPERABLE status because of the I unavailability of the train "A" BOP-ESFAS.

The elapsed period of time during which the availability of the train "A" diesel generator was indeterminate (from time ~ of failure, until successful testing) was 16 days and 9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br />. During this time, all applicable Technical Specifications related to the diesel generator were complied with. As a result, the unavailability of the train "A" diesel generator did not adversely ,

affect the safe operation of the plant.  ;

Prior to this event, there had been three valid diesel generator failures in the last one-hundred valid tests. As a result of this event, the number of valid diesel generator failures in the last one-hundred valid tests increased to fo ir, and a test interval of not greater than three days was implemented in accordance with Regulatory Position C.2.d.

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