ML20028H043

LER 90-011-00:on 900830,RWCU Sys G31 Received Leak Hi & RWCU Leak Hi Hi Annunciators Although Actual Leak Had Not Occurred.Caused by Air in Instrument 2-G31-FT-N012 Sensing Lines.Investigation to Be conducted.W/900928 Ltr

ML20028H043
Person / Time
Site:	Brunswick
Issue date:	09/28/1990
From:	Foss M, Harness J CAROLINA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
BSEP-90-0666, BSEP-90-666, LER-90-011-02, LER-90-11-2, NUDOCS 9010050282
Download: ML20028H043 (6)

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Carolina Power & Light Company Brunswick Nuclear Project P. O. Box 10429 Southport, N.C.- 28461-0429 September 28, 1990 t

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B09-13510C 10CFR50.73 FILE:=

G SERIAL: BSEP/90 0666 U.S. Nuclear Regulatory Commission

-ATTN: Document Control Desk Washington, D. C. 20555 BRUNSWICK STEAM ELECTRIC PLANT UNIT 2 DOCKET NO. 50-325 LICENSE NO. DPR 62 LICENSEE EVENT REPORr 2-90-011 Centlemen:

. In- accordance with Title 10 of the Code of Federal Regulations, the enclosed Licensee Event Report is submitted. This report fulfills - the requirement for a written, report within thirty .(30) days of a reportable occurrence and is-submitted in accordance with the format set forth in NUREC-1022, September 1983.

very truly youu ht4v4V J. L. Harness, General Manager Brunswick Nuclear Project P

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Enclosure

.cc: Mr. S. D. Ebneter Mr. N. B. Le BSEP NRC Resident Office n .,

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'BSEP/90-0666- 2- f bec: Mr. R. M. Coats. Mr. L. I . Loflin Ms. T. A. Ward  ;

_Mr. C. W.-Crawford Mr. A. M. Lucas INPO- 1

-Mr. A. B. Cutter Mr. L. H. Martin Nuclear Licensing.

• Mr. W. J. Dorman Mr. R. E. Morgan File:-BC/A 4 Ms. R. S..Gatewood Mr. - H. A. - Follock- -SHEEC Training-Mr. W. P. Guarino Mr W. W. Simpson- Ref. Library -

Mr. M. D. Hill Mr. R. B, Starkey, Jr. S. H. Callis Mr. M. A. Jones Mr. C. E.'Vaughn Mr. B.'P. Leonard Mr. L. V. Vagoner

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On 8/30/90 at 0204 the Reactor Water Cleanup (RWCU) system (G31) was manually isolated following the receipt of the "RWCU Leak H1' and "RWCU Leak Hi Hi" annuncistors. An automatic isolation signal was received following the operators action to close the G31-F001 and G31-F004 valves prior to the valves reaching the full closed

, position. Af ter verifying that an actual leak had not occurred the 1

RWCU system was placed in service. Small reject flow oscillations were observed with the RWCU leak differential flow instrumentation showing downscale. The RWCU differential flow instrumentation was then declared inoperable r.nd the RWCU system isolated.

Suosequent maintenance included filling and venting the 3 delta flow instrument transmitters. Technicians identified air in the sensing lines of the 2-G31-FT-N012 instrument. The RWCU system was returned to servico and the RWCU delta flow instrumentation was '

declared operable. The safety significance of this event was minimal. An investigation into the air intrusion will be conducted and the results will be reported in a supplement to this LER dated 12/05/90.

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1 Event:

Manual RWCU Group 3 isolation s

Initial conditions 1 Unit 2 was in Startup (Mode 2) at approximately 1% power.

Emergency Core Cooling Systems (ECCS) were operable and RWCU was in service with the "A" filter device on line rejecting to the main i condenser to aid in reactor water level control. Reactor pressure was appr3ximately 30 lbs. and preparations were being made to i t establish condenser vacuum. ,

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Description:

On 8/30/90 at 0203 the Unit 2 Control Operator (CO) noted RWCU reject flow oscillating and intermittent "RWCU Leak Hi" and "RWCU Leak Hi Hi" annunciators. After both annunciators sealed in the -

operator decreased RWCU reject flow in an attempt to clear the annunciators. Approximately 30 seconds after the annunciators had sealed in the Senior control Operator (SCO) order the 2-G31-F001 and 2-G31-F004 valves closed. The CO manually initiated closure of ,

the 2-G31-F001 and 2-G31-F004 valves (PCIS group 3) at 0204. Prior  !

to the valves reaching the fully closed pasition a PCIS group J

. isolation . signal was received. An RWCG leak detection sy;;; tem isolation signal is generated upon a cleanup Leak Hi Hi following an approximate 40 second time delay. The CO then dispatched an Auxiliary Operator (AO) to investigate for leaks in the RWCU i system. Following the RWCU isolation the CO had to insert control -

rods to reduce heat-up rate and stop the reactor water- level increase. After verifying that no actual leak had occurred, the '

RWCU system was placed back in service. Small reject flow ,

oscillations were observed with the RWCU leak differential flow instrumentation showing downscale. The RWCU leak dif farential flow instrumentation was then declared inoperable al.d the RWCU ,,ystem isolated.  ;

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Event Investication:

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!. This event resulted from air entrapment in the instrument sensing  ;

j lines of the RWCU re-)ect flow transmitter 2-G31-FT-N012. FT-N012, ,

along with the RWCU outlet flow (~eturn to the reactor) transmitter  ;

2-G31-FT-041 and the RWCU system inlet flow transmitter 2-G31-FT- ,

NO36, provide input to the RWCU system summing circuit which feeds  :

I differential flow switches which in t'.'rn generates appropriate -

i alarms and icelations. Air in the instrum'e nt lines of the FT-N012 instrument sensing lines caused a ulse high RWCU differential flow (

indication. Instrument and Control (I&C) technicians filled and [

vented the above listed instruments under WR/JO 90-ANHPl.

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Event Cause:

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The cause of the air int: in the sensing lines could not be  !

l determined. It is believe .lome r,ir bubbles could have formed ,

in the instrument lines duril., ..e RWCU system shutdowns on 8/28/90 t and 8/29/90 for surveillance tests 2MST-RWCU-21M and 2MST-RWCU-22M. Subs 6quently, on establishing condenser vacuum nn tb. RWCU reject 2ine, the sAze of these bubbles increased enough +,t cause l

the observed flow oscillations. The potential presence of air in ,

L the RWCU flow transmitters following system maintenance is '

recognized in the system operating procedure (0P-14) and steps to fill and vent the instruments as necessary are & ' ded. Prior to _ .

this event there was no maintenance performed en the RWCU system.

L Corrective Actions: l The RWCU differential flow instruments were filled and vented under WR/JO 90-ANHP1 and the RWCU system returned to service at 0615 on i 8/30/90.

Event Assessnorttu.

The safety significance of this event is considered minimal. The CO manually initiated closure of the RWCU isolation valves upon  !

indichtion of a system leak. The isolation signal was generated by the Ir.alfunctioning of a RWCU flow transmitter, not from an actual  ;

brer.k. An investigation into the air intrusion will be conducted .

and the results will be reported in a supplement to this LER dated ,

10/05/90. A similar event was reported in LER 2-88-003. l

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