ML20012E188

Special Rept:On 891227 & 900116,pressurizer Level Channel L-0466 Read Approx 10% Higher than Three Other Channels. Caused by Failure of Kerotest Valve to Fully Open,Preventing Steam from Entering Ref Leg.Ref Leg Filled

ML20012E188
Person / Time
Site:	South Texas
Issue date:	03/19/1990
From:	Vaughn G HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ST-HL-AE-3405, NUDOCS 9003300188
Download: ML20012E188 (4)

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COMtpting Houston Lig & PowerBBy South Temas Projnt Eintele P.O. Bos 249 ' Wadsworth. Generating Teams 77483 S '

March 19, 1990  !

ST-HL-AE-3405 Filo No.: G02 l

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f U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 South Texas Project Electric Generating Station Unit 2 i Docket No. STN 50-499 t Special Report Regarding An Inoperable Channel of Remote Shutdown Monitoring Instrumentation r

Pursuant to the South Texas Project Electric Generating Station ,

Technical Specifications 3.3.3.5, Houston Lighting & Power submits the l attached'Special Report regarding an inoperable channel of remote shutdown ,

monitoring instrumentation.

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If you should have any questions on this. matter, please contact .

Mr. C. A. Ayala at (512) 972-8628. -

G.E.V g 6 {

G. E. Vaughn l Vice President i

Nuclear Operations .

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Attachment Special Report Regarding An Inoperable Channel of Remote I

Shutdown Monitoring Instrumentation I

t 9003300188 900319 l PDR ADOCK 05000499 s PDC

/f A Subsidiary of Houston Industries incorporated

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Attachment t

ST-HL-AE-3405 l Page 1 of 2 ,

t South Texas Project Electric Generating Station  :

Unit 2 '

Docket No. STN 50-499

' Special Report Regarding An Inoperable Channel of Remote Shutdown Monitoring Inst rument at ion l

DESCRIPTION OF EVENT:

On December 27, 1989, Unit 2 pressuriter level channel L-0466 (see '

attached Figure 1) was determined to be reading approximately 10 percent '

higher than the other three channels.- At the time, Unit 2 was in Mode 5 ,

preparing to start up from a planned outage. Attempts to restore the channel l to the correct indication were initially unsuccessful however, the channel.

Indicated level' acceptably on January 13, 1990 when Unit 2 first entered  :

Mode 3 during startup. On January 16, 1990, during the performance of a channel check, channel L-0466 was again determined to be deviating excessively from the other channels and was declared inoperable. Further unsuccessful attempts have been made to restore channel L-0466. Technical Specification i 3.3.3.5 requires that a Special Report be written describing the corrective action to be'taken if one channel of remote shutdown instrumentation is  !

inoperable for more than 60 days.

CORRECTIVE ACTION:

Following the initial identification of this problem on December 27, 1989, corrective action was taken to fill the reference leg, recalibrate all level instrumentation channels, verify that there were no F

external leaks . verify instrument and tap locations, and verify instrument scaling nalculations. None of tho actions resulted in a reduction of the deviation between the level channels to less than 5 percent. [

Gnce Unit 2 was placed in Mode 1, further attempts were made to restore correct level indication. The level transmitter and associated instrument manifold for channel L-0466 were replaced to eliminate potential internal leak-paths. No improvement'in level deviation was noted.

i NL.90.074.01

4, e Attachment 7 ST-HL-AE-3405  ;

r Page 2 of 2 E  !

CORRECTIVE ACTION Cont'd.  !

Each pressurizer level reference leg has a pair of Kerotest diaphragm root valves. The high-side valve for channel L-0466 was closed in an attempt

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to perform a depressurized reference leg fills however, it failed to isolate e pressure. Radiographic examination of the valve following an attempt to  ;

reopen it indicates that it is not fully open. Subsequent attempts to fully i open the valve have been unsuccessful. Radiographic surveys of the condensate p p pots on various channels have indicated that channel L-0466 h.is less than a full reference leg. Attempts to fill this leg have not changed the indicated-

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deviation.

Independent of the above corrective actions, channel L-0466 drifted back to within 5 percent of the redundant channels however, HL&P conservatively chose to leave the channel in trip. During pressuriter pressure and level .

swing tests conducted on March 14, 1990, channel L-0466 behaved as expected {

and remained within 5 percent of the redundant channels. On March 16, 1990 channel L-0466 drifted back to 5 percent above one of the redundant channels and remains inoperable.

Based on the behavior of channel'L-0466, it is believed that the failure ,

e of the Kerotest valve to fully open has prevented a sufficient quantity of steam from entering the condensing pot and filling the reference leg. Further corrective maintenance to open the Kerotest valve and refill the reference leg  :

can only be performed in Modes 5 or 6. These activities are currently scheduled to be performed during the next refueling outage which is scheduled ,

to begin in October of 1990.  !

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NL.90.074.01.

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PRESSURIZER LEVEL INSTRUMENTATION CHANNEL L-0466 KER0 TEST VALVE

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