ML20135G150

Ro:On 850912,turbine Generator Tripped Out of Svc,Causing Loss of Power to Auxiliary Transformer.Caused by Reactor Protection Sys Core Protection Calculators Sensing Imminent Loss of Forced Coolant Circulation

ML20135G150
Person / Time
Site:	Palo Verde
Issue date:	09/13/1985
From:	Van Brunt E ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR
To:	NRC OFFICE OF ADMINISTRATION (ADM)
References
ANPP-33454-EEVB, NUDOCS 8509180209
Download: ML20135G150 (2)

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Arizona Nuclear Power Project P.O. box $2034 e PHOENIX. ARIZONA 85072-2034 U. S. Nuclear Regulatory Commission September 13, 1985 Document Control Desk ANPP-33454-EEVB/GEC Washington, D. C. 20555

Subject:

Palo Verde Nuclear Generating Station (PVNGS)

Unit 1 Docket No. STN 50-528, License No. NPF-41 Report of Notification of Unusual Event - Reactor Trip File: 85-056-026; G.I.01.10 Gentlemen:

Attached please find a report describing a Notification of Unusual Event at the Palo Verde Nuclear Generating Station. This report addresses a reactor trip.

This report is prepared and submitted pursuant to Table 5.1-1 of the PVNGS Emergency Plan. By copy of this letter we are also forwarding a copy of the report to the Regional Administrator of the Region V Office and other offsite authorities.

If you have any questions or concerns, please contact me.

Very truly yours, 2EL%d/g E. E. Van Brunt, Jr.

Executive Vice President Project Director EEVB/GEC/sih Attachment cc: J. B. Martin R. P. Zimmerman R. F. Fish, Jr.

E. A. Licitra R. A. Colson, ADES C. E. Tedford, ARRA R. E. Bluhm, FCDCD&ES R. G. Godbehere, MCSO R. T. Milstead, DPS INPO Records Center 8509180209 850913 PDR ADOCK 05000528 S PDR f f*

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- PALO VERDE NUCLEAR GENERATING STATION UNIT 1 NOTIFICATION OF UNUSUAL EVENT ON SEPTEMBER 12, 1985 Docket No. STN 50-528 Licensee No. NPF-41 At 2250 on September 12, 1985, the NRC Operations Center was notified, via the Emergency Notification System, of the declaration of a NOTIFICATION OF UNUSUAL EVENT for Unit 1 of the Palo Verde Nuclear Generating Station. The NOTIFICATION OF UNUSUAL EVENT was declared pursuant to Emergency Plan Implementing Procedure

- 02, which requires the reporting of a reactor trip which is complicated by concurrent or subsequent events or conditions.

At approximately 2208, the plant was at 53% power when a load rejection test was initiated by opening the high voltage output breakers from the turbine generator to the offsite distribution grid. The plant is designed to accept this transient and, as aligned during this test, should have run the turbine generator back to a low power level to support in-house power requirements and concurrently actuated the turbine bypass valves dumping excess steam to the condensor. As a result of an unidentified occurrence within the turbine generator control system, the turbine generator tripped out of service. Due to the system configuration during this event, this trip caused a loss of power to the plant auxiliary transformer which was supplying the in-house non-safety related equipment. (Normal plant configuration would have resulted in a fast transfer of these loads to offsite power supplies.) The reactor coolant pumps are supplied with power from this transformer and, as a result of the loss of the turbine generator, also lost power. As the reactor coolant pump speed decreased, the reactor protection system core protection calculators sensed an immenent loss of forced coolant circulation and initiated a reactor trip. The reactor trip occurred at approximately 2210.

Following the trip, the reactor operators stabilized the plant at approximately 2000 psia in the reactor coolant system and initiated manual control of the steam generator level with the "B" Train safety grade auxiliary feedwater pump. Initial flow of the relatively cold feedwater, as well as an extremely low decay heat load in the core, caused an overcooling of the reactor coolant system. At approximately 2220 the pressurizer pressure decayed to less than the Safety Injection System eetpoint of 1837 psia and an injection signal was generated.

The loss of pressurizer pressure to a level below 1837 psia caused a Containment Isolation Actuation Signal to be generated (this actuation signal is in accordance with system design).

The primary system pressure decreased to a low of approximately 1819 psia before recovery within approximately two minutes. The total volume of safety injection was approximately 300 gallons.

The plant was stabilized using natural circulation to carry decay heat to the steam generators for transfer via the steam bypass control system to the condensor.

Forced cooling of the primary system was restored at about 0029 on September 13, 1985, and the NOTIFICATION OF UNUSUAL EVENT was terminated at approximately 0102.

The event did not result in the release of any radioactive materials or challenge any fission product barriers. A Licensee Event Report will be submitted within 30 days to further describe the occurrence.

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