ML19325E819

LER 88-035-01:on 881113,momentary Loss of Power to Radiation Monitor 1RE-12116 Resulted in Control Room Isolation Actuation.Setpoint Will Be Raised During Next Refueling outage.W/891031 Ltr

ML19325E819
Person / Time
Site:	Vogtle
Issue date:	10/31/1989
From:	Hairston W, Odom R GEORGIA POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
0064, 64, ELV-00989, ELV-989, LER-88-035, LER-88-35, NUDOCS 8911090066
Download: ML19325E819 (5)

Text

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Docket No. 50-424  !

i U. S. Nuclear Regulatory Commission ATTN: Document Control Desk  :

Washington, D. C. 20555 Gentlemen:

V0GTLE ELECTRIC GENERATING PLANT ,

L LICENSEE EVENT REPORT CONTROL ROOM ISOLATION OCCURS DURING SURVElllANCE TESTING  :

In accordance with 10 CFR 50.73, Georgia Power Com)any hereby submits the  !

enclosed report revision relating to an event whic) occurred on November 13, 1988. This revision updates the cause and corrective action as a result of further investigation.

Sincerely, f lk.h.f W. G. Hairston, III t i

WGH,III/NJS/gm

Enclosure:

LER 50-424/1988-035-01 xc: Georaia Power Company Mr. C. K. McCoy Mr. G. Bockhold, Jr.  ;

! Mr. R. M. Odom .

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Mr. P. D. Rushton NORMS  ;

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U. S. Nuclear Reaulatory Commission L Mr. S. D. Ebneter, Regional Administrator

Mr. J. B. Hopkins, Licensing Project Manager, NRR >

l Mr. J. F. Rogge, Senior Resident Inspector, Vogtle L ,

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On 11/13/88, plant personnel were conducting Technical Specification (T. S.)

surveillance testing per Procedure 14710-1,

• Remote Shutdown Panel Transfer Switch and Control Circuit 18 Month Surveillance Test". While resetting the Train A load sequencer, a momentary loss of power to radiation monitor 1RE-12116 resulted in a Control Room Isolation (CRI) actuation at 1230 CST. The Train B ESF Chiller and Control Room HVAC Filter Fan actuated but Train A ESF components were out of service for the test and did not actuate. Control room operators verified that no abnormal radiation existed and reset the CRI signal at 1435 CST.

Investigation indicates the cause of the CRI was loss of power to radiation monitor 1RE-12116. The loss of power occurred while resetting the sequencer.

Resetting the sequencer caused a momentary, large current inrush. The current inrush activated a "zia" circuit in an inverter which shut down the inverter and interrupted power to tie distribution panel that supplies the sequencer and the radiation monitor. Corrective action includes raising the setpoint which activates the zip circuit during the next refueling outage and performing surveillance testing of the sequencer which will confirm proper system operation.

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l A. REQUIREMENT FOR REPORT This report is required per 10 CFR 50.73(a)(2)(iv) because an unplanned  !

Engineered Safety feature (ESF) actuat)0n occurred.

l B. UNIT STATUS AT TIME OF EVENT ,

At the time of the event on 11/13/88, Unit I was in Mode 5 (Cold Shutdown) at 0% rated thermal power. There was no inoperable equipment which contributed to the occurrence of this event. ,

C. DESCRIPTION OF EVENT  ;

On 11/13/88, plant personnel were conduct;ng Technical Specification (T. S.)

surveillance testing per Procedure 14710-1, " Remote Shutdown Panel Transfer Switch and Control Circuit 18 Month Surveillance Test". While resetting the -

Train A load sequencer, a momentary loss of power to radiation monitor

• 1RE-12116 resulted in a Control Room Isolation (CRI) actuation at 1230 CST.

The Train B ESF Chiller and Control Room HVAC Filter Fan actuated but Train A ESF components were out of service for the test and did not actuate.

Control room operators verified that no abnormal radiation condition existed and reset the CRI signal at 1435 CST.

i D. CAUSE OF EVENT l

Although the cause of the CRI cannot definitely be determined, investigation indicates the cause of the CRI was loss of power to radiation monitor 1RE-12116. This loss of power occurred while resetting sequencer l

1-1821-03-001. The sequencer and radiation monitor receive power from distribution panel 1AY2A, which is powered from inverter IADllll. A review of the design indicates that the " zip" circuit internal to the inverter shut down the inverter when the sequencer was reenergized, resulting in a loss of power to LAY 2A. The zip circuit is internal overcurrent protection in the 1ADllll inverter. This protection circuit is activated on overcurrent and on a rate of change of current. After the circuit shuts down the inverter, the inverter is energizcd by ramping the inverter output from zero to full voltage. The sequencer load is a capacitive load which draws a large inrush

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The corrective action initially identified for this event was to proceed '

with the installation of static transfer switches for distribution panel '

1AY2A. The present transfer mechanism requires operator action for '

repositioning the distribution panel input breakers and is a break-before-make type of transfer. The proposed static transfer switches would provide automatic transfer capability to an alternate power supply in  :

case of inverter failure. Further study of this proposed modification i indicates that this may not resolve this problem due to the short response ,

time which would be required of the static transfer switches. Raising the setpoint of the zip circuit should help prevent a momentary loss of power to the radiation monitor during the sequencer power up evolution. Current data does not provide positive indication that installation of the static transfer switches would have prevented this event. ,

E. ANALYSIS OF EVENT .

The proper equipment actuated in the appropriate manner. Additionally, plant personnel verified that no high radiation condition existed. Based on these considerations, it is concluded that there was no adverse effect on '

plant safety or public health and safety as a result of this event.

F. CORRECTIVE AC110N During the Spring 1990 refueling outage, the setpoint of the zip circuits '

will be raised to a higher setting. Eighteen month surveillance testing for the sequencers will also be performed at that time. Should other ESF actuations occur as a result of this testing, further evaluation will be .

performed.

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G. ADDITIONAL INFORMATION  !

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1. Failed Components  ;

None ,

2. Previous Similar Events i

LER 50-424/1987-005-05, dated'4-7-88,' discussed a similar CRI event. At -

that time, a work order was written and varying loads placed on the +

inverter including cycling the sequencer on and off without a repeat of [

the loss of voltage. The corrective action to install a static transfer  ;

switch has not yet been implemented and is no longer considered i necessary.  :

3. Energy Industry identification System Code:

Radiation Monitoring Systeu - IL Control Building Environmental Control System - VI q t

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