05000369/LER-1982-071, Forwards LER 82-071/03L-0.Detailed Event Analysis Encl

Forwards LER 82-071/03L-0.Detailed Event Analysis Encl

ML20027D331
Person / Time
Site:	McGuire
Issue date:	10/22/1982
From:	Tucker H DUKE POWER CO.
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20027D332	List: 05000369/LER-1982-071, Forwards LER 82-071/03L-0.Detailed Event Analysis Encl 05000369/LER-1982-071-03, /03L-0:on 820922,motor Control Ctr Lemxd Lost Power Causing Temporary Inoperability of Several Essential Sys/Components.Caused by Automatic Trip of Feeder Breaker. Breaker Reset & Closed.Power Restored
References
NUDOCS 8211040141
Download: ML20027D331 (3)

LER-1982-071, Forwards LER 82-071/03L-0.Detailed Event Analysis Encl

Event date:
Report date:
3691982071R00 - NRC Website

text

DUKE POWER GOMPAhT 4

P.O. Box 33180 CHARLOTrE. N.O. 28242 HAL H. Tl!GKEH TELEPHONE (704) 373-4531 vsom remasormt Nf?(.LEAM PRODUCTION October 22, 1982 cc N

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Mr. James P. O'Reilly, Regional Administrator a

U. S. Nuclear Regulatory Commission C

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Region 11 ro

- 4 0 101 Marietta Street, Suite 3100 Atlanta, Georgia 30303 3

6 El Re: McGuire Nuclear Station Unit 1

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..I' Docket No. 50-369 wc:

Dear Mr. O'Reilly:

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Please find attached Reportable Occurrence Report R0-369/82-71. This report concerns a loss of motor control center 1EMXD and resultant loss of various systems required by Technical Specifications 3.6.5.6, 3.6.4.2, 3.6.1.8, 3.3.3.9, 3.3.3.1, 3.4.5, and 3.6.4.3.

This incident was considered to be of no significance with respect to the health and safety of the public.

Very truly yours, J/ct/ B.'~Tiu k o Hal B. Tucker PBN:jfw Attachment cc: Director INPO Records Center Office of Management and Program Analysis 1100 Circle 75 Parkway, Suite 1500 U. S. Nuclear Regulatory Commission Atlanta, Georgia 30339 Washington, D. C.

20555 Mr. P. R. Bemis Senior Resident Inspector-NRC McGuire Nuclear Station L'isi'3N' B211040141 821022 d'

PDR ADOCK 05000369 bM

DUKE POWER COMPANY MCGUIRE NUCLEAR STATION REPORTABLE OCCURRENCE REPORT NO. 82-71 REPORT DATE: October 22, 1982 FACILITY: McGuire Unit 1, Cornelius, NC IDENTIFICATION: Loss of Motor Centrol Center (MCC) lEMXD and Resultant Loss of Various Required Systems

DESCRIPTION

On September 22, 1982, Unit 1 MCC lEMXD lost power due to an automatic overcurrent trip of its feeder breaker, lELXD Compartment 4C.

The unit was operating at 75% reactor power; however, the power loss did not affect operation of the unit.

The loss of IENXD resulted in the following essential systems / components being temporarily inoperable due to loss of power (applicable Technical Specifications are given): Containment Air Return Fan IB and Hydrogen Skimmer Fan IB (T.S.3.6.

5.6); Hydrogen Recombiner IB (T.S.3.6.4.2); Annulus Ventilation Fan IB (T.S.3.6.

1.8); Unit Vent Radiation Monitors (IEMF 35, 36, 37 - particulate, iodine, gaseous)

(T.S.3.3.3.9); Fuel Building Ventilation Rad. Monitor (IEMF 42)(T.S.3.3.3.1); Con-trol Room Air Intake B Rad. Monitor (IEMF 43B)(T.S.3.3.3.1); Pressurizer PORV Isolation Valves INC31B and INC35B (T.S.3.4.5); Hydrogen Distributed Ignition.'B' Train Circuits (T.S.3.6.4.3).

The feeder breaker was reset and closed within 8 minutes, restoring power to IEMXD. Subsequent measurements of the feeder breaker load currents revealed no cause for the overcurrent trip, and a spurious trip is suspected.

EVALUATION: MCC lEMXD is part of the 600 VAC Essential Auxiliary Power system and provides circuit protection to various 'B' train components.

Incoming power is obtained from distribution center IELXD compartment 4C.

Overcurrent protection for breaker 4C is provided by an I.T.E. Imperial Corporation " Power Shield" solid state trip device, model number SS4G. This device was set up to trip on either a short time current of 2400 amps or a long time current of 600 amps.

On September 22, 1982, investigation of "ELXD supply to lEMXD-open" and " Motor Control Center Bus IEMXD Voltage-Lo" alarms found the Power Shield trip device of IELXD breaker 4C tripped (AUTO TRIP indicator popped out). The breaker was reset and closed. Technicians measured currents of 255 amps on each phase of breaker 4C, well below the overcurrent trip setpoints. Discussions with the Operators on duty and a review of the Alarm Typer printout for the period revealed no equipment operation that could have caused the trip. The trip appears to have been spurious and may have been caused by voltage spikes affecting the solid state Power Shield.

Prior to Unit I startup, sporadic tripping problems had been identified on some breakers using I.T.E. Power Shields. Part of the problem was attributed by the manufacturer to defective silicon controlled rectifiers (SCR's) in the Power Shield. These SCR's were replaced on all Unit 1 devices prior to startup. Addi-tionally, the manufacturer has recommended adding a capacitor to the trip terminals of the Power Shield to protect the SCR from transients.

Report No. 82-71 Page 2 Although it is possible that a manufacturing deficiency contributed to this trip, this cannot be ascertained.

SAFETY ANALYSIS

The Containment Air Return Fan, Hydrogen Skimmer Fan, Hydrogen Recombiner, and Annulus Bentilation Fan are' redundant and all 'A' train components of these systems were operable. The Hydrogen Distributed Ignition cystem is also redundant in that at each strategic igniter location, two igniters are present -

one powered from 'A' train and one powered from 'B' train. Thus, the minimum requirements of Technical Specification 3.6.4.3 were met.

Power was restored to lEMXD and all systems were again operable before any other Tech. Spec. Actions were necessary. If the loss of power had been lengthy, Control Room Air Intake 'B' would have been closed and Air Intake

'A' used; alternate means of sampling the Unit Vent activity were also available.

The most significant aspect of the incident was the loss of control power to Pressurizer PORV Isolation valves INC31B and INC35B. The valves failed in the

'as is' position - open in this case (normal operation). Failure of the Isolation valves require unit shutdown if operability is not soon restored (T.S.3.4.5).

The purpose of the Power Operated Relief Valves is to minimize the undesirable opening of the spring loaded pressurizer code safety valves (code safety valves were never compromised during the incident) by relieving Reactor Coolant system pressure during all design transients. The PORV Isolation valves function to provide positive cutoff should a PORV become inoperable. Had the PORV's opened due to a high pressurizer pressure condition, all paths to the Pressurizer Relief Tank would have been available. Conversely, in the event of inadvertent automatic opening of the PORV's, no method of closing the PORV Isolation valves would have been readily available to terminate the release.

In this case the PORV's them-selves could have been closed from the Control Room, thus, terminating the unde-sirable release (PORV's fail closed). Therefore, safe operation of the pressurizer was assured during this incident.

The health and safety of the public were not affected by this incident.

CORRECTIVE ACTION

Immediately after receiving the "ELXD Supply to lEMXD - OPEN" and "MCC Bus IEMXD Voltage - Lo" alarms, a Nuclear Equipment Operator (NEO) was dispatched to reset the breaker. This action resulted in power being restored to lEMXD within 8 minutes. Technicians then verified that loading of the breaker circuit was normal. No problems were encountered when breaker 4C was reset.

A modification will be performed to install a capacitor to the trip terminals of the Power Shields on the 600 VAC Essential Auxiliary Power system, including IELXD breaker 4C.

This should protect the SCR from transients.

Unit 2 breakers that have had their Power Shields modified with the new SCR and the capacitor addition have experienced no sporadic trips.