ML18036A312

LER 91-014-00:on 910629,manual Reactor Scram Occurred Due to Bulk Suppression Pool Water Temp Exceeding Tech Spec Limits. Procedure for Operating Rcic,Noting Potential for Thermal Stratification of Suppression pool,revised.W/910729 Ltr

ML18036A312
Person / Time
Site:	Browns Ferry
Issue date:	07/29/1991
From:	Austin S, Zeringue O TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-014-01, LER-91-14-1, NUDOCS 9108060263
Download: ML18036A312 (14)

Text

ACCELERATED DISTRIBUTION DEMONSTPTION SYSTEM REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9108060263 DOC.DATE: 91/07/29 NOTARIZED: NO DOCKET FACIL:50-260 Browns Ferry Nuclear Power Station, Unit 2, Tennessee 05000260 AUTH. NAME AUTHOR AFFILIATION AUSTIN,S. Tennessee Valley Authority ZERINGUE,O.J. Tennessee Valley Authority RECIP.NAME RECIPIENT AFFIL1ATION

SUBJECT:

LER 91-014-00:on 910629,manual reactor scram occurred due to bulk suppression pool water temp exceeding Tech Spec limits.

Revised procedure for operating RCIC to note potential for D thermal stratification of suppression pool.W/910729 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR t ENCL TITLE: 50.73/50;9 Licensee Event Report (LER), Tncident Rpt, etc. 2 SIZE:

NOTES RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID D CODE/NAME LTTR ENCL KREBS,M. 1 1 HEBDON,F 1 1 ROSS,T. 1 1 D INTERNAL: ACNW 2 2 ACRS 2 ~

2 AEOD/DOA 1 1 AEOD/DSP/TPAB 1 1 AEOD/ROAB/DSP 2 2 NRR/DET/ECMB 9H 1 1 NRR/DET/EMEB 7E 1' NRR/DLPQ/LHFB10 1 1 NRR/DLPQ/LPEB10 1 1 NRR/DOEA/OEAB 1 1

'NRR/DREP/PRPB11 2 2 NRR/DST/SELB SD 1 1 NRR/DST/SICBSH3 1 1 NRR/DST SPLBSD1 1 1 NRR/DST/SRXB SE 1 1 RE 1 1 RES/DSIR/EIB 1 1 RGN2 IEE 1 1 EXTERNAL EG&G BRYCE g Z ~ H 3 3 L ST LOBBY WARD 1 1 NRC PDR 1 1 NSIC MURPHY,G.A 1 1 NSIC POORE,W. 1 1 NUDOCS FULL TXT 1 1 D

D D

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PLEASE HEI.P US TO REDUCE IVASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOi~l Pl-37 (EXT. 20079) TO EL!iiIINATEYOUR NAME FROivl DISTRIBUTION LISTS FOR DOCUi i'IENTS YOU DON'T NEED!

FULL TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES REQUIRED: LTTR 33 ENCL 33

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Tennessee Valley Authority. Post Office sox 2000, Decatur. Alabama 35609 O.J. 'Ike'eringue Vice President. Browns Feny Operations JUL 29 1991 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555

Dear Sir:

TVA BROWNS FERRY NUCLEAR PLANT (BFN) UNIT 1 DOCKET NO. 50-260 FACILITY OPERATING LICENSE DPR-52 LICENSEE EVENT REPORT LER-50-260/91014 The enclosed report provides details concerning a manual reactor scram required because the suppression bulk water temperature exceeded technical specification limit. This report is submitted in accordance with 10 CFR 50.73(a)(2)(i).

Very truly yours, TENNESSEE VALLEY AUTHORITY Enclosure cc: see page 2 9 1 080(~t.) ~ 6~> ~p g 072'y PDR AD) )CK 0=-000260 PDR

4k 0 U.S. Nuclear Regulatory Commission JUL P.9 1991 cc (Enclosure):

INPO Records Center Suite 1500 1100 Circle 75 Parkway Atlanta, Georgia 30339 NRC Resident Inspector, BFN Regional Administrator U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, Suite 2900 Atlanta, Georgia 30323 Thierry M. Ross

'U.S. Nuclear Regulatory. Commission One White Flint, North 11555 .Rockville Pike Rockville, Maryland 20852

4i NRC Form 3 U.S. LEAR REGULATORY COltlISSION Approved OMB No. 3150-0104 (6-89) Expires 4/30/92 LICENSEE EVENT REPORT (LER)

FACILITY NAME (1)

F IDOCKET 'NUMBER (2) I~~Q- 4 TITLE (4) Hanual Reactor Scram Required Due to Bulk Suppression Pool Mater Temperature V NT DAY E 8 P T A I I i SEQUENTIAL i t REVISIONS

~ i.', J f FACILITY NAMES ,'IDOCKET NUMBER(S)

N Y N H A I I I I I 1 4 I I 072 99 1 OPERATING I ITHIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR g:

MODE I I m N [20.402(b) F20.405(c) )50.73(a)(2)(iv) i73.71(b)

'POWER f f (20.405(a)( 1)('i) [50.36(c)(,1) l50.73(a)(2)(v) i73.71(c),

LEVEL ) ) (20.405(a)( l)(ii) [50;36(c)(2) (50.73(a)(2)(vii) ]OTHER (Specify in

)20;405(a)( l)(iii) f~(50.73(a)(2)(i) [50.73(a)(2)(viii)(A) ( Abstract below and in

)20.405(a)( l)(iv) f ]50.73(a)(2)(ii) '[50.73(a)(2)(viii)(B) Text, NRC Form 366A)

NAME I AREA CODE I I I IREPORTABLEI I I I IREPORTABLEI A YTM NNT NF T N

.I I I .I.

I I I I PP NT P T I / SUBMISSION I X m 1 TED B I 0 T D ABSTRACT (Limit to 1400 spaces, i.e., approximately fifteen single-space typewritten lines) (16)

On June .29, 1991, during performance of power ascension testing activities following a six-year outage, the Unit 2 reactor "was manually scrammed at 0248 hours0.00287 days <br />0.0689 hours <br />4.100529e-4 weeks <br />9.4364e-5 months <br /> from approximately 25 megawatts thermal power due to .the bulk suppression pool water temperature exceeding the Technical Specification limit of 110'F. This occurred as a result of operating 'the Reactor Core Isolation Cooling (RCIC) system without suppression pool cooling, which caused thermal stratification of the suppression pool water.

TVA is currently performing a.root cause evaluation of this event. TVA will report the results in a supplement to this licensee event report. The expected submission date of this supplement is August 30, 1991.

To date, TVA has taken or initiated the following corrective actions. TVA revised the procedure for operating RCIC to note the potential for thermal stratification of the suppression pool, and to require evaluation of the necessity to initiate suppression pool cooling. Other plant procedures will be revised as necessary to add this information. TVA also issued an Operations Standing Order which specifies the expected rate of suppression pool heatup during operation of RCIC and the High Pressure Coolant Injection system, and when suppression pool cooling should be initiated. Operating crews will be trained on this order and the details of this event.

NRC Form 366(6-89)

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NRC Form 366A "U.S. N MR REGULATORY COHHISSION Approved OHB No. 3150-0104 (6-89) Expires 4/30/92 LICENSEE EVENT REPORT,(LER)

TEXT CONTINUATION FACILITY NAHE (1) IDOCKET NUHBER (2)

I ,I I I SEQUENTIAL I IREVISIONI I I I I Browns Ferry Uni t 2 I

'I' I' 4

TEXT.(If more space is required, use additional NRC Form 366A's) (17) v t On June '29, 1991, during performance of power ascension testing act'ivities following a six-year outage,, the Unit 2 reactor was. manually scrammed at 0248 hours0.00287 days <br />0.0689 hours <br />4.100529e-4 weeks <br />9.4364e-5 months <br /> due to the suppression .pool [BT] bulk water temperatuie exceeding the technical specification (TS) limit of 110'F. .At the time the reactor was scrammed Unit 2 was in the startup/hot standby mode with reactor power at approximately 25 megawatts thermal, a reactor pressure of 845 psig and reactor moderator temperature of 508'F.

On June 28, 1991 at 0644 hours0.00745 days <br />0.179 hours <br />0.00106 weeks <br />2.45042e-4 months <br /> the Unit 2 main turbine-generator '[TA] was,manually tripped due to high vibration. Following the turbine trip the reactor was placed in the startup/hot standby mode. To maintain reactor pressure, at 1605 hours0.0186 days <br />0.446 hours <br />0.00265 weeks <br />6.107025e-4 months <br /> on June 28, 1991 the Reactor Core Isolation Cooling (RCIC) [BN] system was placed in service and aligned in the condensate storage tank (CST) to CST flow path.

Operations personnel elected to place RCIC in service without establishing suppression pool cooling. This decision was made because Operations was monitoring suppression pool water temperature at, five minute 'intervals. They considered that

'this monitoring would provid'e timely indication of an increase in suppressi:on pool water, temperature, thus allowing ample time to .place suppression pool cooling in service.

At 0236 hours0.00273 days <br />0.0656 hours <br />3.902116e-4 weeks <br />8.9798e-5 months <br /> on June 29, 1991 a quarterly surveillance was,performed which required aligning Residual Heat Removal (RHR) system [BO] pump 2A for suppression pool cooling. At 'the time the surveillance was ini.tiated suppression pool water temperature was stable at 87'F. Mhen the RHR pump was placed in service the suppression pool temperature increased and at 0240 hours0.00278 days <br />0.0667 hours <br />3.968254e-4 weeks <br />9.132e-5 months <br /> had reached 98'F. At 0248

'ours 'the suppression pool water temperature exceeded the TS limit of 110'F and the reactor was manually scrammed.

At 0320 hours0.0037 days <br />0.0889 hours <br />5.291005e-4 weeks <br />1.2176e-4 months <br />, to stop further heat additi'on to the suppression pool, Operations personnel returned the RCIC system to standby readiness. At 0358 hours0.00414 days <br />0.0994 hours <br />5.919312e-4 weeks <br />1.36219e-4 months <br /> the suppression pool water temperature had decreased to 103'F.

In accordance with 10 CFR 50.73(a)(2)(i)(A), TVA reports this completion of,a plant shutdown required by the TS..

1 v nt The major systems involved in this event were: RHR, RCIC, primary containment system temperature elements located in the suppression pool and the suppression chamber atmospheric pressure and temperature recorder [IK].

The RHR system is designed to restore and maintain coolant inventory in the reactor vessel .so the core can be adequately cooled after a .loss of coolant accident (LOCA). RHR also provides containment cooling so that condensation of steam resulting from blowdown of a design 'basis LOCA is assured. During this event the ~

RHR system was operated in the, suppression pool cooling mode to maintain suppression pool water temperature below 90'F.

NRC Form 366(6-89)

NRC Form 366A U.S. N R REGULATORY CONNISSION Approved OMB No. 3150-0104 (6-09) Expires 4/30/92 LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NANE (1) [DOCKET NUNBER (2)

I i SE()VENT IAL / ) REVISION J Ferry Uni t 'rowns 2 I I I I I TEXT (If more space is required, use additional NRC Form 366A's) (17)

The purpose of the RCIC system is to provide a source of hi.gh pressure coolant makeup to the reactor vessel in case of a loss of feedwater flow. RCIC can also be used to maintain the reactor in hot standby condition. In this event the RCIC system was utilized to maintain the reactor in the hot standby mode. Reactor pressure was maintained by operating the RCIC turbine utilizing the steam generated to power it, and exhausting thi.s steam to the suppression pool. The RCIC turbine exhausts below the top of the water in the suppression pool.

Bulk suppression pool water temperature is monitored by 16 temperature elements located near the bottom of the torus vessel. As part of the NUREG-0661 long-term torus upgrade program, these temperature el'ements were located near the bottom of the suppression pool close to the exhaust of the main steam relief valves (MSRVs).

This modification was performed to ensure that the suppression pool temperature monitoring system accomplished its main function: to detect local suppression pool water temperature following MSRV discharge.

The 16 temperature elements are grouped into two divisions of eight elements. The torus is divided into 16 "bays," and'ne element from each division is located in every other bay. The bulk suppression pool water temperature is the average of the eight elements in a division. Bulk suppression pool water temperature from each division is charted on separate recorders. Each recorder also has provisions to record the temperature of one of the eight individual elements. During the time the RCIC system was operating each recorder was charting bulk suppression pool water temperature, and one of the recorders was charting the temperature of the element located in the bay into which the RCIC system exhausted. However, due to stratification of the hot water from the RCIC exhaust in the suppression pool, actual suppression pool water temperature was masked from these temperature elements.

.The suppression chamber atmosphere temperature is charted by the suppression chamber atmospheric pressure and temperature recorder. The temperature element utilized by this recorder is located in the suppression chamber directly above the RCIC During the ten ho'urs RCIC was operated this recorder indicated a constant turbine'xhaust.

temperature of 94'F. After the operators determined that the suppression pool water temperature had increased, this recorder was checked and found to be mechanically binding. The recorder's operation was corrected and the temperature immediately jumped to 155'F.

When the first RHR pump was started, it mixed the water and the actual bulk water temperature increased above the TS limit of 110'F to a maximum of 118'F. As required by TSs, Operations initiated the required manual reactor scram.

Although the suppression pool. water temperature surpassed the TS limit, the event did not negate the ability of plant systems to mitigate postulated accidents. At a reactor pressure of 1100 psig the maximum bulk suppression pool water temperature for stable steam condensation is 180'F. During this event the maximum bulk suppression pool water temperature attained was 118'F. Accordingly, TVA concludes that there were no safety consequences associated with this event.

NRC Form 366(6-B9)

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NRC Form 366A U.S. N AR REGULATORY COHHISSION Approved OHB No. 3150-0104 6-89) xpires LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION ACILITY NAHE (1) iOOCKET NUHBER (2)

I /SE()UENTIAL J )REVISION/ / f (

rowns Ferry Unit 2 I I I I I EXT (If more space is, required, use additiona1 NRC Form 366A's) (17)

TVA is currently performing a root cause evaluation of this event. TVA will report the results in a supplement to this licensee event report. The expected submission date of this supplement is August 30, 1991.

t'v t To date, TVA has taken or initiated the following corrective actions. TVA'as revised =the operating instruction for RCIC to note the potential for thermal stratification of the suppression pool water, and to require evaluation of the necessity for initiating suppression pool cooling. 'TVA will also revise other 'plant procedures as necessary to note the potential for thermal stratification of, the suppression pool and to add requirements to initiate suppression pool water cooling when activ'ities are in progress which have the potential to increase the suppression pool temperature.

TVA issued an Operations Standing Order which provides specific details regarding the potential for thermal stratification of the suppression pool when heat is being added to it. This Standing Order specifies the expected rate of suppression pool heatup during RCIC and HPCI operation. The Standing Order also specifies that suppression pool cooling is required whenever there exists a possibility that suppression pool water temperature could exceed 95'F. TVA will provide training to Operations personnel on this Standing Order and the specifics of, this event.

v v t None.

mm'tm t

l. TVA will train Operations personnel on the specific of this event and the Standing Order issued as a result of the event. This will be completed by September 16, 1991.

2. Plant procedures will be revised as necessary to note the potential for thermal stratification of the suppression pool water, and to include requirements to initiate suppression pool cooling when activities are in progress which have the potential to raise the suppression pool water temperature. This will be completed by September 16, 1991.

NRC Form 366(6-89)

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