ML17250B182

Special Rept:On 900430,RCS Pressure Transient Occurred Due to Excess Letdown Being Ineffective at Lower Pressures. Operating Procedures Revised to Alert Operators on Effective Methods of Pressure Control Under Conditions

ML17250B182
Person / Time
Site:	Ginna
Issue date:	05/30/1990
From:	MECREDY R C ROCHESTER GAS & ELECTRIC CORP.
To:	MARTIN T T NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9006110327
Download: ML17250B182 (4)

Text

ACCELERATED DI UTION DEMONS ATION SYSTEM REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)ACCESSION NBR:9006110327 DOC.DATE: 90/05/30 NOTARIZED:

NO FACIL:50-244 Robert Emmet Ginna Nuclear.Plant, Unit 1, Rochester G AUTH.NAME AUTHOR AFFILIATION MECREDY,R.C.

Rochester Gas&Electric Corp.RECIP.NAME RECIPIENT AFFILIATION MARTIN,T.T.

Document Control Branch (Document Control Desk)

SUBJECT:

Special rept:on 900430,use of overpressure protection sys to mitigate RCS pressure transient.

DISTRIBUTION CODE: IE22D COPIES RECEIVED:LTR ENCL 0 SIZE: TITLE: 50.73/50.9 Licensee Event Report (LER), ncident Rpt, etc.DOCKET 05000244 NOTES:License Exp date in accordance with 10CFR2,2.109(9/19/72).

05000244 RECIPIENT ID CODE/NAME PD1-3 LA JOHNSON,A INTERNAL: ACNW AEOD/DS P/TPAB DEDRO NRR/DET/EMEB9H3

~NRR/DLPQ/LPEB10 NRR/DREP/PRPB11 NRR/DST/SICB 7E NRR/DST/SRXB 8E RES/DSIR/EIB EXTERNAL: EG&G STUART,V.A LPDR NSIC MAYS,G NUDOCS FULL TXT COPIES LTTR ENCL 1 1 RECIPIENT ID CODE/NAME PD1-3 PD AEOD/DOA AEOD/ROAB/DS P NRR/DET/ECMB 9H NRR/DLPQ/LHFB11 NRR/DOEA/OEABll NRR/DST/SELB 8D RBj~PLB8D1 EG 02 RGN1 FILE 01 L ST LOBBY WARD NRC PDR NSIC MURPHY,G.A COPIES LTTR EN 1 CL NOTE TO ALL"RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTE!CONI'ACT THE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT.20079)TO ELIMINATE YOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!TOTAL NUMBER OF COPIES REQUIRED: LTTR 34 ENCL C~

ROCHESTER GAS AND ELECTRIC CORPORATION

~e9 EAST AVENUE, ROCHESTER, N.Y.I~6~9-000>

/May 30, 1990 Mr.Thomas T.Martin, Regional Administrator U.S.Nuclear Regulatory Commission 475 Allendale Road King of Prussia, PA 19406

Subject:

Thirty (30)Day Special Report Use of the Overpressure Protection System to Mitigate an RCS Pressure Transient R.E.Ginna Nuclear Power Plant Docket No.50-244

Dear Mr.Martin:

In accordance with Technical Specification 3.15.1.3, this thirty day special report on Use of the Overpressure Protection System to Mitigate an RCS Pressure Transient, is hereby submitted.

On April 30, 1990, at 0810 EDST, the Reactor Coolant System (RCS).was in a'olid condition with pressure and temperature at 325 psig and 340 F respe'ctively with the"B" Reactor Coolant Pump operating.

Decay heat removal was via the steam generators with RHR still lined up to the RCS.The letdown pressure control valve, PCV-135, was in automatic controlling RCS pressure at 325 psig.Periodic test procedure PT-7 (Hydro Test of Reactor Coolant System)was in progress for the required RCS hydro subsequent to the annual refueling and maintenance outage.The reactor vessel overpressure protection system was in service as required until the RHR system is taken out of service and isolated from the RCS.Isolation of the RHR system was being performed when the over-pressure protection system activated at approximately 400 psig RCS pressure.The two pressurizer power operated relief valves (PORVs)operated as designed to mitigate the slow pressure transient and stabilized RCS pressure at approximately 360 psig.The pressurizer PORVs were open for approximately four seconds.900gg i0~27 900~F DR ADOCK 0.000244 PDC~+2.2.Ii0 The apparent causes of the event are as follows: o Excess letdown, which is normally used to control RCS pressure by varying charging flow with excess letdown flow during the performance of the RCS hydro, was ineffective at the lower pressures so the Control Room Operators were using normal letdown to supplement excess letdown for RCS pressure control.Also, with the RHR system still open to the RCS, some letdown was still being accomplished through its letdown path.0" During the above evolution, RCS pressure was being controlled by the letdown pressure control valve, PCV-135, from the letdown orifices and RHR system.Excess letdown was in service, but ineffective in controlling RCS pressure.When the RHR system was isolated from the RCS, letdown from the RHR path was terminated and all normal letdown now to PCV-135 was through ,letdown orifices.With PCV-135 set in automatic, letdown pressure was being controlled at approxi-mately 325 psig.With charging flow at a minimum, RCS pressure slowly increased to the overpressure protection actuation setpoint due to an approximate 80 psig system differential between letdown and the operating coolant pump discharge pressure, before Control Room Operators could intervene manually to control it.Immediate corrective action was taken to ensure that the pres-surizer PORVs opened to mitigate the RCS pressure transient and then closed.Subsequently, the Control Room Operators placed PCV-135 in manual and adjusted it to control RCS pressure at approximately 340 psig.Corrective action to prevent recurrence will be as follows: Continued evaluation of the events initiating the RCS pressure transient.

Checkout of the proper operation of the excess letdown system during these conditions.

Revision of operating procedures to alert operators on effective methods of pressure control under these conditions.

Ve truly yours, Robert C.M cre Division Manager Nuclear Production RCM/eeh xc: U.S.Nuclear Regulatory Commission (Original)

Document Control Desk Washington, DC 20555 Ginna USNRC Senior Resident Inspector