05000219/LER-1990-008

LER 90-008-00:on 900625,reactor Scram Occurred on Low Condenser Vacuum.Caused by Failure of Backwash Outlet Valve to Open,Causing Loss of Circulating Water to Condenser A. Plant Stabilized & Taken to Cold shutdown.W/900723 Ltr

ML20055J242
Person / Time
Site:	Oyster Creek
Issue date:	07/23/1990
From:	Barnes D, Fitzpatrick E GENERAL PUBLIC UTILITIES CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-008, LER-90-8, NUDOCS 9008010237
Download: ML20055J242 (4)

LER-2090-008,

Event date:
Report date:
2192090008R00 - NRC Website

text

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= GPU Nuoleer Corporation .

."' g Post Office Box 388 Route 9 South g

Forked River, New Jersey 087310388 609 971 4000

~ Writer's Direct Dial Number:

July.23, 1990

.U.S. Nuclear Regulatory.Comnission

-ATTN Document Control Desk j

' washington, DC 20555- 1 Dear Sir Subjects Oyster Creek Nuclear. Generating Station' '

Docket No.-50-219 'j Licensee Event Report. , ,

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'This letter forwards one (1) copy of.. Licensee Event Report'(LER)-No.90-008.  !

Very truly yours,

. 1 k

E..E. Fit trick Vice President & Director ~!

Oyster Creek EEF:BDe (1er/Covltrasjc) j Enclosure '

-ces Mr. Thomas Martin, Administrator Region I :I U.S. Nuclear Regulatory Commission  !

475 Allendale Road King of Prussia,'PA 19406 Mr. Alexander W. Dromerick U.S. Nuclear Regulatory Commission Washington, DC 20555 NRC Resident Inspector.

Oyster. Creek Nuclear Generating Station Forked River, NJ 08731 9008010237 900723 PDR ADOCK 05000219 fl.j\

s PDC

• GPU Nuclear Corporation is a subsidiary of General Public Utihbes Corporation

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. . - .o n ei On June 25, 1990, at approximately 6:18 AM, a reactor scram occurred on low condenser vacuum. The scram occurred during initiation of backwashing of the A north main condenser. The scram was1 caused by the failure of the backwash outlet valve to open, causing a loss of circulating water to the A condenser.

The backwash outlet valve failed to open due to a breaker trip of the motor ,

operator. The plant was stabilized in a hot standby condition and subsequently I taken to cold shutdown. The motor operator, the breaker and the valve were all l l

inspected and tested satisfactorily. The auxiliary contacts on the motor close coil were replaced and auxiliary contacts on the motor open coil were realigned. The remaining 20 circulating water valves manipulated during backwashing evolutions were tested and verified to be operating. properly.

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DATE OF OCCURRENCE l 1

l The event occurred on June 25, 1990 at approximately 0618 hours0.00715 days <br />0.172 hours <br />0.00102 weeks <br />2.35149e-4 months <br />. l IDENTIFICATION OF OCCURRENCE  ;

i While initiating the daily backwash (EIIS-SI) or a main condenser (CIF-COND), l the backwash outlet valve, V-3-18, (CIF-20) failed to open. This , f ailure i resulted in a loss of circulating water.(EIIS-KE) to the A'condensor causing {

sufficient decrease in vacuum to' actuate 'the Reactor Protection System {

(EIIS-JC) low condenser vacuum' scram. This event is reportable under .!

10CrR50.73(a)(2)(iv), " Automatic Initiation of any Engineered Safety Feature,.

including the Reactor Protection System".

i CONDITIONS PRIOR TO OCCURRENCE '

The reactor was at 100 percent power in the RUN mode with a generator output of approximately 632 megawatts electric.

DESCRIPTION OF OCCURRENCE On June 25, 1990, the plant automatically. scrammed.on low condenser vacuum

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while backwashing the main condensers, Backwashing is rperformed daily to maintain condenser tube cleanliness. Oyster Creek has three parallel condenser sectiono and each section has north and south water boxes. Normal circulating weter flowpath is through all six water boxes. Backwashing A north condenser L' half allows normal flow through A south. The A south discharge is then routed to A north outlet for reverse flow to A north inlet and discharge through the  !

backwash outlet valve.

A control room operator initiated the backwash for.A north main condenser by ,

taking the backwash control switch to backwash. The three valves controlled by this switch (south outlet closes - south to north outlet crosstie opens - north 'j backwash outlet opens) started to stroke as observed by ' double position-indication. The A north circulating water inlet'and outlet valves were then given a close signal. The CRO then observed loss of position indication for.

the backwash outlet valve and realized its breaker (CIP-52) had tripped. All

• five valves have seal in circuits therefore the failure of the backwash-outlet valve to open caused a loss of circulating water to the A main condenser. An l electrician standing by near the motor control center reset the breaker and closed the opening contactor. As the backwash outlet valve was stroking open the Reactor' Protection System Low Vacuum Scram initiated.--Elapsed time from taking the switch to backwash to the reactor scram was just over one minute.

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The catse of this occurrence is the failure of the backwash outlet valve to open.

The breaker for the valves motor operator tripped on overcurrent. s Binding of the auxiliary contacts on the motor close coil and out of alignment contacts on the motor open coil were observed. It is postulated that only two phases made up causing an overcurrent condition.

ANALYSIS OF OCCURRENCE AND SAFETY SIGNIFICANCE The Reactor Protection System performed as intended-shutting down the reactor on low condenser vacuum. This scram protects the main condensers from overpressurization and minimizes the transient on the reactor vessel by shutting i down the reactor prior to the turbine trip (stop valve closure). No other safety' systems were initiated. This event would have been less significant at lower power levels. This event has minimal safety significance.

CORRECTIVE ACTION

1. The motor and associated cable for the backwash outlet valve (V-3-18) were meggared with acceptable results.

2. The breaker was inspected and its routine- prevontive maintenance check was .  ;

performed natisfactorily.

3. The auxiliary contacts on the motor closed coil were replacod and auxiliary contacts on the motor open coil were realigned.

4. V-3-18 was stroked while taking current = traces. Results were within nameplate i data.

5'. The remaining 20 circulating water valves manipulated during bachwashing were stroked.while taking current traces. 'All valveu stroked smoothly and current traces were less than nameplate data.

6. Procedure 323 was revised to include a 10 second time delay between placing the backwash control switch to backwash and isolating the circulating water inlet and outlet valves. '

SIMILAR EVENTS None. I l

EOUIPMENT FAILURE DATA Cause B Systems SI Component: 52 Component Manufacturer: General Electric Co.

Component Modelt TEF134036 Reportable to NPRDS: No j

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