ML20133H294

Unusual Event:On 851003,reactor Tripped,Resulting from Loss of Power from Offsite Sources.Cause Under Investigation. Plant Stabilized by Natural Circulation to Remove Decay Heat Via Steam Generators.Offsite Power Restored

ML20133H294
Person / Time
Site:	Palo Verde
Issue date:	10/04/1985
From:	Van Brunt E ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR
To:	NRC OFFICE OF ADMINISTRATION (ADM)
References
ANPP-33665-EEVB, NUDOCS 8510170005
Download: ML20133H294 (2)

Text

Arizona Nuclear Power Project P O BOX 52034

• PHOENIX, ARIZONA 85072-2034 October 4, 1985 ANPP-33665-EEVB/GEC U. S. Nuclear Regulatory Commission Document Control Desk Washington, D. C. 20555

Subject:

Palo Verde Nuclear Generating Station (PVNGS)

Unit 1 Docket Nos. STN 50-528, License No. NPF-41 Report of Notification of Unusual Event - Reactor Trip File: 85-056-026; G.1.01.10 Gentlemen:

Attached please find a report describing a Notification of Unusual Event at the Palo x Verde Nuclear Generating Station on October 3, 1985. This report addresses a reactor trip resulting from a loss of power to the unit from offsite sources.

This report is prepared and submitted pursuant to Table 5.3-1 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, (

- . M (\ L L E. E. Van Brunt, Jr.

Executive Vice President Project Director EEVB/GEC/s1h Attachment cc: J. B. Martin (all w/a)

R. P. Zimmerman R. F. Fish, Jr.

E. A. Licitra R. A. Colson, ADES

'C. E. Tedford, ARRA R. E. Bluhm, MCDCD&ES R. G. Godbehere, MCSO R. T. Milstead, DPS INPO Records Center

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I PALO VERDE NUCLEAR GENERATING STATION UNIT 1 NOTIFICATION OF UNUSUAL EVENT OF OCTOBER 3, 1985 Docket No. 50-528 License No. NPF-41 At 1722 MST on October 3, 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 1644, the plant was at 52% power when a loss of power to the unit from offsite sources caused a reactor trip. All in-house loads were being supplied from offsite sources at the time of the transient, due to the system alignment for the performance of electrical system interaction testing with the offsite power supply grid. The exact cause of t; loss of power is under investigation at this time. The initial loss of power occurred on one-half of the supply system, and caused two of the reactor coolant pumps to lose power and begin to coast down in speed. The reactor protection system core protection calculators detected an imminent loss of forced circulation, and initiated a reactor trip. At approximately the same time, the other half of the offsite supply system experienced a loss of power, completing the loss of offsite power. The reactor coolant system was cooled via natural circulation following the loss of forced circulation. The trip of the reactor caused a turbine trip to occur, which caused the turbine generator control valves to close. The secondary system pressure increased to cause three main steam safety valves to lift momentarily.

In response to the loss of offsite power to the essential power buses, both diesel generators started and loaded as designed. The transient to the power system also caused the initiation of Control Room Essential Filtration, Fuel Building Essential Ventilation, and Containment Purge Isolation.

All safety systems performed as designed, and in a conservative manner.

At 1658, the Shift Supervisor declared a NOTIFICATION OF UNUSUAL EVENT and made the appropriate notifications.

The plant was stabilized using natural circulation to remove decay heat via the steam generators and the secondary system atmospheric dump valves. The transient did not result in any challenges to the fission product barriers, or result in any releases of radioactive materials.

Offsite power was restored to the unit at approximately 1710, and a reactor coolant pump was restored to service at about 2018, restoring forced circulation. The NOTIFICATION OF UNUSUAL EVENT was terminated at 2035. The event continues to be evaluated, and a Licensee Event Report will be submitted within 30 days to further describe this occurrence.