05000369/LER-1982-052, Forwards LER 82-052/03L-0.Detailed Event Analysis Encl

Forwards LER 82-052/03L-0.Detailed Event Analysis Encl

ML20055B937
Person / Time
Site:	McGuire
Issue date:	07/13/1982
From:	Parker W DUKE POWER CO.
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20055B938	List: 05000369/LER-1982-052, Forwards LER 82-052/03L-0.Detailed Event Analysis Encl
References
82-52, NUDOCS 8207230605
Download: ML20055B937 (3)

LER-2082-052, Forwards LER 82-052/03L-0.Detailed Event Analysis Encl

Event date:
Report date:
3692082052R00 - NRC Website

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Mr. James P. O'Reilly, Regional Administrator U. S. Nuclear Regulatory Commission Region II 101 Marietta Street, Suite 3100 Atlanta, Georgia 30303 Re

McGuire Nuclear Station Unit 1 Docket No. 50-369

Dear Mr. O'Reilly:

Please find attached Reportable Occurrence Report R0-369/82-52. This report concerns T.S.3.8.2.1, "The following A.C. electrical busses and inverters shall be operable and energized.. 120 volt A.C. vital bus #1 EKVA energized from inverter #1 EVIA connected to D.C. channel 1...". This incident was considered to be of no significance with respect to the health and safety of the public.

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Ve truly yours, b Y

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William O. Parker, Jr.

PBN/j fw Attachment t

I cc: Director Records Center Office of Management and Program Analysis Institute of Nuclear Power Operations U. S.' Nuclear Regulatory Commission 1820 Water Place l Washington, D. C. 20555 Atlanta, Georgia 30339 l

l Mr. P. R. Bemis Senior Resident Inspector-NRC McGuire Nuclear Station i

L OFFICIAL CO e

8207230605 920713 PDh ADOCK 05000369 0 Ab S ,

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DUKE POWER COMPANY McGUIRE NUCLEAR STATION REPORTABLE OCCURRENCE REPORT NO. 82-52 REPORT DATE: July 13, 1982 FACILITY: McGuire Unit 1, Cornelius, NC IDENTIFICATION: A tb1 functioning Vital Static Inverter Contributed to an Inadvertant Reactor Trip DESCRIPTION: On June 13, 1982, while Unit I was operating at 75% reactor power, a momentary loss of power was experienced on the Vital Instrumentation and Control Power System, bus IEKVA, causing a failure of Channel 1 of the reactor protection and instrument systems and engineered safety systems. This, concurrent with an already-tripped Channel III of Reactor Coolant System (NC) loop C flow instrumentation (reference RO 369/82-49), resulted in a 2 out of 3 coincidence reactor trip on low loop flow.

A.C. Vital bus power supply, inverter IEVIA, was subsequently declared inoperable.

lEKVA was supplied by its alternate source, 120 VAC Regulated Power Distribution Center KRP.

During the transient ensuing from the reactor trip and subsequent turbine trip, the Condensate-Feedwater System was overpressurized causing the lifting of various reheater relief valves and a rupture on reheater D-1 relief line piping. Through operator action these adverse effects were soon controlled and a stable hot stand-by condition was then maintained.

On June 15, af ter performing maintenance on the power supply (a 120 VAC Vital Instrumentation and Control Power System (15 KVA static inverter) and verifying the inverter's proper operation, the reactor was returned to power operation.

The failure of Channel 1 is attributed to Component Failure / Malfunction of the Solidstate Controls, Inc. static inverter.

EVALUATION: In general, reactor protection and process control systems are battery powered for reliability purposes. The AC power required by these systems is obtained by DC to AC conversion through static inverters. Each year several reactor trips occur because of static inverter failures. Susceptibility is generic, and although some configurations have proven to be more sensitive to the problem than others, no design seems to be exempt.

l The June 13 reactor trip was the first vital inverter related incident to occur at the McGuire Nuclear Station. The possibility of an inverter failure causing a reactor trip at McGuire is remote because of the coincidence features of the Reactor Protection System. The only exceptions to the coincidence arrangement are in the source range and intermediate range nuclear instrumentation reactor trip subsystems, which are bypassed during power operation. The McGuire trip occurred at 75% reactor power as a result of a dual failure.

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Report No. 82-52 Page 2 SAFETY ANALYSIS: The reactor trip was the result of a dual failure event in which the Reactor Protection System functioned as designed. Neither malfunction in itself could have caused the trip.

Prior to the reactor trip, plant parameters were within normal limits; and, the incident was considered to be of no significance to the health and safety of the public.

CORRECTIVE ACTION: Discussion with the inverter manufacturer verified that either the silicon controlled rectifier (SCR) shorting printed circuit board or a constant voltage transformer (CVT) capacitor were the most probable failed components in the malfunctioning inverter. During corrective maintenance no symptoms of malfunction were presented. Output voltage waveforms appeared normal and compared favorably to those of a similar Unit 2 inverter. The SCR shorting circuit board was replaced as a precautionary measure, and the CVT capacitors (12) were visually inspected (deformation of the capacitor casing sometimes accompanies failure).

EVIA was placed in service on June 13 after observing proper operation of the inverter. Unit I was taken critical and returned to power operation on June 15. (

Secondary system overpressurization resulted from the reactor and turbine trips from a high power level. Secondary systems recovery from such a transient is dependent on a complex set of timed and sensor controlled iunctions which alter flows in response to the changing conditions. Station personnel are continuing to improve the coordination of these functions through timing and setpoint adjust-ments.