ML19354E107

LER 89-016-00:on 891215 & 16,erratic Level Transmitter Behavior Caused Steam Generator B hi-hi Level Feedwater Isolation.Caused by Inner Plugs Remaining Partially Inserted After Valves Opened.Plugs Freed from seats.W/900116 Ltr

ML19354E107
Person / Time
Site:	Beaver Valley
Issue date:	01/16/1990
From:	Noonan T DUQUESNE LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-016-01, LER-89-16-1, ND3MNO:2012, NUDOCS 9001250390
Download: ML19354E107 (7)

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'Af Telephone (41't, 303 6000 01 a Shippmgport PA 15077 0004 i January 16, 1990 {

ND3MNO:2012 Beaver Valley Power Station, Unit No. 1 Docket No. 50-334, License No. DPR-66  ;

LER 89-016-00 ._,

United States Nuclear Regulatory Commission Document Control Desk '

Washington, DC 20555 l Gentlemen:

In accordance with Appendix A, Beaver Valley Technical specifications, the following Licensee Event Report is submitted:

i j LER 89-016-00, 10 CFR 50.73.a.2.iv, "Feedwater Isolation Due to Erratic Steam Generator Level Transmitter i  :

Behavior".

i l Very truly yours, ,

M T. P. Noonan General' Manager

' Nuclear' Operations-  ;

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JCnunry.16, 1990 ND3MNO:2012 l Page two cc: Mr. William T. Russell Regional Administrator United States Nuclear Regulatory Commission i Region 1 .

l 475 Allendale Road >

l King of Prussia, PA 19406  ;

C. A. Roteck, Ohio Edison ,

Mr. Peter Tam, BVPS Licensing Project Manager l United States Nuclear Regulatory Commission Washington, DC 20555 r J. Beall, Nuclear Regulatory Commission, BVPS Senior Resident Inspector Dave Amerine Centerior Energy 6200 Oak Tree Blvd.

Independence, Ohio 44101 INPO Records Center Suite 1500 1100 Circle 75 Parkway  :

At3anta, GA 30339 G. E. Muckle, Factory Mutual Engineering, Pittsburgh Mr. J. N. Steinmetz, Operating Plant Projects Manager Mid Atlantic Area Westinghouse Electric Corporation i Energy Systems Service Division-

, Box 355 i Pittsburgh, PA 15230 t American Nuclear Insurers c/o Dottie Sherman, ANI Library i The Exchange Suite 245 270 Farmington Avenue Farmington, CT 06032

'Mr. Richard Janati Department of Environmental Resources l P. O. Box 2063 16th Floor, Fulton Building Harrisburg, PA 17120 Director, Safety Evaluation & Control Virginia Electric & Power Co. . l l P.O. Box 26666 l One James River Plaza Richmond, VA 23261

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Feedwater Isolation Due to Erratic Steam Generator Level Transmitter Behavior _

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l On 12/15/89, the unit was in Mode 4 (Hot Shutdown) preparing to startup following completion of its seventh refueling outage.

Following the fill of the "B" Steam Generator, erratic level transmitter behavior caused a "B" Steam Generator Hi-Hi level l Feedwater Isolation. The Instrumentation and Control (I&C)

! department was requested to investigate and repair this l

malfunction. On 12/16/89, while troubleshooting these instruments, two channels indicated a Hi-Hi level, causing a second Feedwater Isolation. Investigation determined that this erratic behavior was caused by the level transmitters' Kerotest root stop valves' inner plugs remaining partially inserted after the valves were opened. After I&C freed the plugs, allowing the i valves to fully open, the transmitters functioned properly. The I

plugs apparently became bound to the seats when the valves were closed during the refueling outage while replacing the transmitters for Environmental Qualification concerns. There were no safety implications due to this event. Feedwater Isolations caused by Hi-Hi Steam Generator Levels are analyzed in Beaver Valley Unit 1 UFSAR section 14.1.9, " Excessive Heat Removal Due to Feedwater System Malfunctions."

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On 12/15/89, the unit was in Operational Mode 4 (Hot Shutdown) starting up from its seventh refueling outage. To support the required testing, operators filled the "B" Steam Generator to 60%

Narrow Range level using the 3A Auxiliary Feedwater Pump. After the fill was completed, the operators shutdown the Auxiliary  ;

Feedwater pump. At this time, "B" Steam Generator indicated level l began to behave erratically and exhibited a gradual increase. ,

Over a 14 minute time period, indicated level increased from 60% ,

to 75% on the Narrow Range level instruments, although no feedwater pumps were running and the Wide Range level channels indicated the level was not increasing. When indicated levels reached 75% on 2 of the 3 three Narrow Range channels, a Steam Generator Hi-Hi Level Feedwater Isolation signal was generated, as per design. The only components affected by this signal were the Steam Generator Feedwater inlet valves MOV-FW-156A, MOV-FW-156B and MOV-FW-156C. These valves closed in response to the Feedwater Isolation signal. These valves, due to the check valve nature of their design, prevent reverse flow in the normal Feedwater flowpath to the Steam Generators. The Auxiliary Feedwater flowpath was still available.

On 12/16/89, Instrumentation and Control (I&C) personnel were investigating the "B" Steam Generator Level indication problem.

I&C entered containment and varified that correct reference leg level for the "B" Steam Generator transmitters. The transmitters where then calibrated and verified to be operating properly. At I this time, I&C began to suspect that the transmitters root stop valves may not be fully open. Inspection of valve handwheels verified that the valves were in their full open position. A work i request was initiated to investigate the possibility that the transmitters' root stop valves plugs may not have come fully off

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1 their seats. One channel (LT-FW-486) was still being calibrated when maintenance began the stuck plug investigation on a second channel (LT-FW-485). Although redundant channels are not permitted to be worked simultaneously during power operations, ,

station procedures do permit working redundant channels, providing j operations superviory notification and approval is obtained, when the unit is in a mode where the instruments are not required to be operable. As these channels are not required while in mode 4, the work request for the second channel was approved.

Maintenance mechanically agitated the valves for LT-FW-485 to see ,

if the plugs would come free. During these attempts, the channel I spiked, indicating that its root stop valve plug had been sticking j and had come free. This spike caused the channel to indicate Hi-Hi level momentarily. This Hi-Hi level spike, combined with

'the Hi-Hi level bistable being tripped on the other channel being calibrated, completed the required 2/3 logic and caused a Feedwater Isolation signal. As with the first Feedwater Isolation signal, the only components affected were the three Steam Generator Feedwater inlet valves which again closed as designed.

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Cause of Event 1

This event was caused by the "B" Steam Generator Narrow Range Level Transmitters' root stop valves not being fully open. I&C had suspected after initial investigation / troubleshooting, that the valves might be partially closed based on the indicated levels i response. Examination determined that the root stop valve's ,

handles were in the full open position and that the valve stems were fully out (the full open position). However, these valves j are Kerotest zero-leakage valves. . The valve stems are not  !

directly. attached to the valve plugs, but push the valve plugs against the seats via an interposing diaphragm. When the valve ,

stems are screwed out, they release pressure-from the diaphragm on i top of the plugs and allow the plugs to be pushed off the valve l seats via an internal spring (see Figure 1). 3 A review of in-house experience with these valves was conducted to determined possible cause for the condition identified. This review showed that there was a potential for the plugs to stick if .

the valves were shut for extended periods of time. A review of industry experience (NPRDS) for failures of these valves, showed that the failures experienced were failures of the valves leaking by and not failures due to the plugs sticking in mid position. i These valves are normally maintained open, daring both outage and  ;

power operation conditions. However, during the refueling outage, these valves had been closed to isolate the level transmitters for replacement. When the valves were reopened, the plugs failed to fully come off the valve seats, partially restricting flow from ,

the steam Generator to the transmitters. This caused the transmitters to be sensitive to Steam Generator pressure fluctuation, causing the crratic indication, corrective Actions j The valve plugs were freed from the valve seats by I&c. '

Operations ramped the "B" Steam Generator level up and down several times while I&C observed transmitter response to ensure  ;

correct operation. The levels in the remaining steam generators 1 were ramped up and down to observe proper transmitter response in '

these steam generators.

Previous Occurrences There have been no previous similar events at Beaver Valley Unit .

1. There was one previous event (LER 89-022-00) at Unit 2 that involved a Kerotest valve whose plug became stuck to the seat. ,

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J Safety Analysis There were no safety implications due to this event. The failures I were detectable via transmitter response, once the instruments i were returned to service. At this time, the only components to be actuated by the Feedwater Isolations were three Feedwater inlet isolation valves to the Steam Generators, which responded properly  ;

(stroked closed) to the Feedwater Isolation signals. However, as verified by the Feedwater Flow recorder traces, there was no flow l through the valves prior to their closure, so their actuations had no affect on other plant parameters. The Feedwater Isolations only affected the Normal Feedwater flowpath. Auxiliary Feedwater ,

was always available. . Feedwatter Isolations due to Hi-Hi Steam  :

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