ML20028G917

LER 90-021-00:on 900829,inadvertent Reactor Protective Sys Actuation Occurred While Operator Changed Power Source. Caused by Operator Not Following Proper Procedures.Operator counseled.W/900928 Ltr

ML20028G917
Person / Time
Site:	Fort Calhoun
Issue date:	09/28/1990
From:	Gates W, Voss K OMAHA PUBLIC POWER DISTRICT
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-021, LER-90-21, LIC-90-0731, LIC-90-731, NUDOCS 9010030223
Download: ML20028G917 (5)

Text

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Omaha Public Power District I 444 South 16th Street Mall )

Omaha, Nebraska 68102-2247 -)

402/636-2000 1 1

September 28, 1990 1 l10 90-0731 I

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U. S. Nuclear Regulatory Commission I Attn Document Control Desk Mail Station P1-137 Washington, DC 20555 ReTerence: Docket No. 50-285 l Gentlemen: I

Subject:

Licensee Event Report 90-21 for the Fort Calhoun Station )

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, j PleasefindattachedLicenseeEventReport90-21datedSeptember28}(iv).

1990. Thisreportisbeingsubmittedpursuantto10CFR50.73(a)(2 1

If you should have any questions, please contact me.  :

Sincerely,

)

i W. G. Gates J Division Manager i Nuclear Operations ,

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. Attachment c: .R. D. Martin, NRC Regional Administrator I A. Bournia, NRC Project Manager R. P. Mullikin, NRC Senior Resident Inspector 1 INP0 Records Center American Nuclear Insurers

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On August 29, 1990, with the plant in cold shutdown, the Reactor Protection System at Fort Calhoun Station was inadvertently actuated. The actuation occurred while an operator was changing the power source for control rod clutch power supplies in preparation for electrical maintenance on an instrument bus '

transformer. Prior to this incident, all control rods were fully inserted in the core. Therefore, no actual rod movement occurred.

The cause of this event was failure by the operator involved to follow procedure. A contributing factor was the failure to notify the Shift Supervisor when unexpected results were obtained during the performance of this activity. Corrective actions inchWe individual counseling of the operator involved, and additional instruct % n tc < arations personnel that a questioning attitude must be maintained at all timo <id unanticipated results reported to supervision.

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010 0l2 0F 0l4 rixm - . .e, . - nn At Fort Calhoun Station, the Reactot ProtectiveSystem(RPS)controlspowerto-theControlElementDriveMechanisms(CEDM's). The CEDM magnetic clutch power

. supplies (PS1, PS2, PS3, and PS4) are fed from the 125 VDC busses (DC bus #1 or

1. 2)throughfour120VAC!instrumentinverters(refertoattachedfiure). ,

Inverters 'A' and 'C' are fed from DC bus #1 and Inverters 'B' and D' are fed  !

from DC bus #2, psi and PS3 are fed from Inverters 'A' or 'B' through the l supply breaker CB-AB, W b PS2 and PS4 are fed from Inverters 'C' or 'D' through the supply bre m .'B-CD. Each of the four inverters is supplied with a bypass transformer whict c.an supply power to the associated instrument bus in the event of inverter failure. PS1 and PS3 are redundant to PS2 and PS4 with respect to their ability to maintain the clutch power sup) lies energized.

,_ Breskers CB-AB and CB-CD are undervoltage type breakers w1ich are designed to open if their source of power is de-energized. A loss of all four clutch power supplies will cause a reactor trip. A trip will not occur if only half of the

)ower supplies are lost..The transfer switches for breakers CB-AB and CB-CD i

lave a break-before-make feature which can momentarily interrupt power to the undervoltage circuit, causing this bresker to open. If a transfer switch is

. operated quickly enough to minimize the power interruption, the associated breaker will not trip.

On August 29, 1990, while the plant was in cold shutdown for replacement of a .

reactor coolant pump seal, the bypass transformer for Inverter D was scheduled ,

to be replaced. The clutch power supplies were being fed from Inverters 'A' and 'D' at this time. The prerequisites for the Maintenance Work Order stated "if inverter D is supplying power to the clutch power.su) plies, shift the feed

, from Instrument D to Instrument Bus C...". To accomplis 1 this the Shift Supervisor decided to transfer the clutch power supplies to 'B' and 'C'. This would assure the power to the clutch power supplies were not being fed from the same 125 VDC bus, which is considered good practice. A licensed operator was assigned to perform this task.

The operator transferred PSI and PS3 from 'A' to 'B' first. At this. time CB-AB l tripped, the amn.eter readings on PSI and PS3 went to zero, and the ammeter readings on PS2 and PS4 doubled. This trip was due to a momentary undervoltage condition during operation of the transfer switch. The operator and the electricians noticed the ammeter change; they were not n : what caused the change, but decided to continue with the transfer as pl.. ad without discussing '

the unexpected results with the shift supervisor. The relevant procedure, 01-EE-4, provides guidance to assure the transfer is completed properly. It requires, verification that the clutch power supply breaker is closed and all four clutch power supply ammeters read upscale. Both. steps were missed by the operator and the tripped breaker was not noticed at this time.

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L At 2102, the operator then transferred the power supplies from 'O' to 'C' and immediately the red trip lights on the clutch power supply breaker panel came on due to a momentary loss of power to PS2 and PS4 during the transfer. All power to the clutches was lost at this point and the Reactor Trip annunciator actuated. . The operator then noticed breaker CB-AB was in the trip position and reset it at that time. The RPS was then reset.

The NRC was notified at 0029 on August 30, 1990 pursuant te requirements of 10CFR50.72(b)(2)(ii)duetoaninadvertentactuationofthencactorProtective System. Thiseventisalsoreportablepursuantto10CFR50.73(a)(2)(iv).

1 The cause of this event was failure by the' operator involved to follow

procedure.. Because the transferring of clutch power su) plies is an infrequent '

operation, the operator was not thoroughly familiar wit 1 the meaning of the indications he received. Another contributing factor was the failure of the .'

personnel involved to report the unexpected results to the Shift Supervisor.

The corrective actions for this event are:

1. The operator involved was counselled on his failure to follow the procedure and the need to notify his supervisor when unexpected results r,ccur.

2. Operations personnel will be given further instruction via memorandum concerning the need for notification of supervision when unexpected results or abNeinal indications are received. This will be completed by Octobe. ' ,

3. This even* wi.' be discussed during Licensed Operator requalification i training This will ' a completed by December 31, 1990. '

This event occurr. >h*- in Mode 4 (Cold Shutdown) with all control rods inserted in -r -

mntrol rod movement took place and all equipment respon ~, .& Nuclear safety was not adversely affected by this event. If h- J.t hh ecurred with the plant at power, it would have resulted in a rea t,a ip.

There have been other reparted inadvertent actuations durirg shutdowns of Engineered Safeguards Feats ces/ Reactor Protective System; however, there have been no other LER's due to the inadvertent loss of power to the control rod clutch power supplies.

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