ML20012A173

LER-89-023-00:on 891209,four Out of Six Condenser Low Vacuum Setpoints Found at Values Less Conservative than Tech Spec Limit.Caused by Sensing Element Drift & Lack of Margin for Drift in Calibr Procedure.Setpoint changed.W/900227 Ltr

ML20012A173
Person / Time
Site:	Oyster Creek
Issue date:	02/27/1990
From:	Fitzpatrick E, Rogers J GENERAL PUBLIC UTILITIES CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-023, LER-89-23, NUDOCS 9003080442
Download: ML20012A173 (5)

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a GPU Nuolear Corporstion ~

gggf_ Post Office Box 388 Route 9 South c~ , ,t. Forked River,New Jersey 087310386 609 971 4000

,L Writer's Direct Dial Number:

February 27,'1990 1

4J U.S.-Nuclear Regulatory Commission

_ Document-Control Desk Washington, DC 20555 Dear Sir

Subject:

Oyster Creek Nuclear; Generating Station-Docket No.' 50-219

[L Voluntary Licensee. Event Report l

This letter forwards'one (1) copy of. Voluntary Report No.89-023. This' \

event has been: determined to be not reportable as defined in USNRC '!

regulations.

Very truly yours, gc -

E. E.-Fitzp rick Vice President-and Director Oyster Creek EEF:JRadmd

'Encs.

cc Mr. William T. Russell, Administrator Region I

.U.S. Nuclear Regulatory Commission l

" 475 Allendale Road ~j King of Prussia, PA 19406 l l .- . . . .

'l 1- NRC Resident Inspectors ,

Oyster Creek Nuclear Generating Station I

'Mr.'Alex Dromerick L U.S.' Nuclear Regulatory Commission l

-Washington, DC 20555  ;

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9003080442 900227 DR ADOCK0500g9 y]

y l GPU Nuclear Corporation is a subsidiary of the General Public Utilities Corporation

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Oyster Creek, Unit 1 o is I o I o I o 1211 19 1 IOFl 014 I b' FOUR OUT OF SIX LOW VACUUM SCRAM SElPOINTS FOUND OUT OF SPECIFICATION DUE TO SENSING ELEMENT DRIFT veut OAn mi un muu . mi 4 0.TOATi m OTnen e Aciutin i=v0Lv 0 as>

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NA%4 TELEPHONE 8evMgtR Al 1A CODE John Rogers, Licensing Department 6 0 t9 91711 1 -1418 I 91 3 COMPLETE ONE LINE FOR E ACM CORAPO.stNT # AILunt OtacRet0 88 TMS A0 PORT (13b CAv84 Sv5 TEM COMPONENT "'"N[ " h'O PR DS CAvst sytTEM COMPONENT "h"NNO "h "$' -

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' $~ g#]w79: 7 l 1 l l l l t l l l l l l l suprLaMENTAL REPORT EXPECTRO n4l MONTH OAY Y5AD sueu ss ON Ytt lif v.s. e mos.. GK9fCTfD SU0e*IS$10N DA TED NO l l l Assu ACT <u,,,,, . ,= o. . .,.-., a, , . -e . , n ei on December 9, 1989, at approximately 0800 houre, during a surveillance test, four out of six condenser low vacuum scram setpoints were found at values less conservative than the Technical Specification lim.1t. The cause of this occurrence is attributed to sensing element drift, and lack of margin for drift in the "as left" setpoint in the calibration procedure. The surveillance test results demonstrated that the low vacuum scram function was operable, and would have responded as designed. Prior to this event, GPUN had initiated a program to review setpoints and instrument drift characteristics to determine if setpoint changes would be appropriate. The surveillance setpoint was changed and the setpoint review program will continue.

This condition is considered not reportable. This is a voluntary report.

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Q0 q2 or 0 l4 Date of Discovery The condition was discovered on December 9, 1989 at approximately 0800 hours0.00926 days <br />0.222 hours <br />0.00132 weeks <br />3.044e-4 months <br />.

t Identification of Discovery During a surveillance test, four of six condenser low vacuum scram setpoints

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were found at values less conservativ6 than the Technical Specification limit.

Although this condition is not considered reportable, a voluntary report is being submitted to provide information to the USNRC and the industry.

Conditions Prior to Discovery On December 7, 1989, the plant was operating at full power when a vacuum transient was experienced in the main condenser during a backwashing evolution. The indicated vacuum in one of the three sections of the main condenser (CFI-COND) decreased below the scram setpoint. The other two sections of the main condenser indicated that vacuum remained above the scram setpoint by a considerable margin. The reactor protection instrumentation is independent of.these' indicators, and is comprised of switch input only (CFI-33), with no control room indication. As a precaution the plant was shutdown to test the low vacuum scram setpoints.

Desch16 tion of Occurrence on December 9, A989, Instrument Technicians performed a test on the main condenser low vacuum scram sensors (CFI-PE). The results of the "as found" setpoints (in inchas Hg vacuum) are summarimd below:

SWITCH "A" CONDENSER "B" CONDENSER "C" CONDENSER TRIP SYS 1 SENSOR 1 SENSOR 2 SENSOR 3 RSCS-ll *22.8- *22.9 23.35 RSCS-12 *22.8 *22.9 23.36 s

TRIP SYS 2 SENSOR 4 SENSOR 5 SENSOR 6 '

RSCS-21 *22.88 *21.65 23.07 RSCS-22 *22.88 *21.65 23.07 Indicates Setpoint below Tech Spec limit of 23 inches Hg vacuum, i

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1 The cause of this occurrence is attributed to sensing element drift, and the-I lack of margin for drift in the acceptable "as left" setpoint in the c calibration procedure. The acceptable "as left" setpoint in the calibration -

L procedure was 23 + .5 -0 inches Hg vacuum. The Technical Specification limit I is greater than or equal to 23 inches Hg vacuum.

Analysis of Occurrence and Safety Assessment i

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The purpose of the low condenser vacuum scram is to protect the main condenser l in the event that vacuum is lost. A decrease in condenser vacuum (22 inches l Hg) will cause the turbine stop valves to close resulting in a turbine trip.

The closure of the stop valves will cause a reactor scram signal independent of the low vacuum scram. The low condenser vacuum scram anticipates this transient and trips the reactor protection system at 23 inches Hg for additional conservatism.

The protective functions are provided by two redundant cam operated vacuum trip systems. Each of these trip systems (VT-1 and VT-2)(EIIS Code - IT) has three

. bellows, one for each condenser section (A,B, and C) which operate independently. A low vacuum condition in any condenser section will cause cam rotation. The reactor protection system (RPS) monitors main condenser vacuum by four switches identified as RSCS-ll, 12, 21 and 22. These switches are operated by VT-1 and VT-2. VT-1 operates vacuum switches RSCS-ll and 12 and VT-2 operates RSCS-21.and 22.

RSCS-11 and 21 input to RPS I and RSCS-12 and 22 input to RPS II. Therefore, each mechanical trip system actuates both RPS channels and both trip systems, L any one of which would cause a reactor scram. Technical Specification Table

!. 3.1.1 reflects this arrangement and requires operability of both RPS channels in both RPS trip systems. The operability of both RPS channels and both RPS trip systems was verified during the surveillance on December 9, 1989.

The Technical Specifications were not written to address the mechanical bellows

, assemblies which rotate.the cam shaft and operate the vacuum switches. The condenser arrangement is such that vacuum changes in one section are communicated to the other sections. Thus, a reactor scram will occur before the condenser overpressurizes provided that any one of the three bellows (in either assembly) operates properly. Therefore, a trip channel is operable if any one of the three associated bellows causes a trip signal within the acceptable setpoint range.

l The surveillance test resulto demonstrated that the low vacuum scram function was operable and would have responded as designed in the C Condenser section l, regardless of the slightly lower setpoints in the "A" and "B" condenser I sections.

Based upon the above, the safety significance of this event is considered to be minimal.

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i corrective Action  ;

The acceptable "as left" setpoint in the calibration procedure has been changed to 24 +.35 -0 inches Hg vacuum to allow for expected instrument drift.

Prior to this event, CPUN had initiated a program to review instrument setpoints and drift characteristics to determine if setpoint changes would be '

appropriate. The review is ongoing and any setpoint changes will be made as appropriate to prevent a similar event in the future.

l Additionally, a review has been initiated to determine the desirability of ,

l changing or eliminating the Low condenser Vacuum Scram setpoint. A Technical Specification Change Request will be submitted if a revision to the existing Technical Specifications is determined to be appropriate.

Similar Events r

LER 87-016 "Setpoints for three of eight isolation condenser pipe break sensors out of specification due to instrument drift" LER89-23

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