L-92-340, Special Rept:On 921127,PORV PCV-3-456 Opened Due to High Pressure in Rcs.Initial Temps of Shell Side Water in SG Found to Be Approx 145 F.Caused by Lack of Pressure Absorbing Bubble in Pressurizer.Procedure Revised
| ML17349A559 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 12/18/1992 |
| From: | Plunkett T FLORIDA POWER & LIGHT CO. |
| To: | NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| L-92-340, NUDOCS 9212280157 | |
| Download: ML17349A559 (7) | |
Text
ACCEI.ERAT "
DOCUMENT DIST UTION SYSTEM REGULAT INFORMATION DISTRIBUTIO SYSTEM (RIDS)'CCESSION.NBR:9212280157 DOC.DATE: 92/12/18 NOTARIZED: NO DOCKET FACIL:50-250 Turkey Point Plant, Unit 3, Florida Power and Light C 05000250 AUTH.NAME AUTHOR AFFILIATION PLUNKETT T.F.
Florida Power 6 Li ht'Co.
I g
RECIP.NAME RECIPIENT AFFILIATION Region 2 (Post 820201)
SUBJECT:
Special rept:on 921127,PORV PCV-3-456 opened due to high pressure in RCS.Initial temps of shell side water in SG found to be approx 145 F.Caused by lack of pressure absorbing bubble in pressurizer. Procedure revised.
DISTRIBUTION CODE:
IE22D COPIES'ECEIVED:LTR ENCL SIZE:
TITLE: 50.73/50.9 Licensee Event Report (LER), Incident Rpt, etc.
NOTES:NRR RAGHAVANiL 05000250 RECIPIENT ID CODE/NAME PD2-2 LA AULUCKiR INTERNAL: ACNW AEOD/DSP/TPAB NRR/DET/EMEB 7E NRR/DLPQ/LPEB10 NRR/DREP/PRPB11 NRR/DST/SICB8H3 NRR/DST/SRXB 8E RES/DSIR/EIB EXTERNAL: EGGG BRYCEiJ.H NRC PDR NSIC POOREiW.
NOTES:
COPIES LTTR ENCL 1
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1 RECIPIENT ID CODE/NAME PD2-2 PD AEOD/DOA AEOD/ROAB/DSP NRR/DLPQ/LHFB10 NRR/DOEA/OEAB NRR/DST/SELB 8D NRR/DST/SPLB8D1 02 RGN2 FILE 01 L ST LOBBY WARD NSIC MURPHYiG.A NUDOCS FULL TXT COPIES LTTR ENCL 1
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1 NOTE TO ALL"RIDS" RECIPIENTS PLEASE HELP US TO REDUCE WASTE! CONTACT THE DOCUMENT CONTROL DESV.
ROOM Pl-37 (EXT. 504-2065) TO ELIMINATEYOUR NAME FROM DISTRII3UTION
. LISTS FOR DOCUMENTS YOU DON'T NEED!
TOTAL NUMBER OF COPIES REQUIRED:
LTTR 30 ENCL 30
P.O. Box 0, Miami, Fi, 33102-9i00 FPL DEC 15 59i.
L&2-340 10 CFR 50.36 Stewart D. Ebneter Regional Administrator, Region II U.
S. Nuclear Regulatory Commission 101 Marietta St.,
N.W., Suite 2900
- Atlanta, GA 30323 Mr. Stewart D. Ebneter:
Re:
Turkey Point Unit 3 Docket No. 50-250 S ecial Re ort Over ressure Miti atin S stem In accordance with Technical Specifications 3.4.9.3 and 6.9.2, the attached Special Report details the cycling of pressure control valve 3-456.
Should there be any questions on this information please contact us.
Very truly yours, gP/~Id.c+ b~
T. F. Plunkett Vice President Turkey Point Nuclear TFP/JEK/jk Attachment cc:
- USNRC, Document Control Desk, Washington D.C.
Ross C. Butcher, Senior Resident Inspector, USNRC, Turkey Point Plant
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L-92-340 Page 2 of 4
SPECIAL REPORT PORV PCV-3-456 USED TO MITIGATE AN RCS PRESSURE TRANSIENT PURPOSE:
Technical Specifications (TS) 3.4.9.3 Action 3, requires the submission of a special report to the NRC in the event that a
power operated relief valve is used to mitigate a reactor coolant system pressure transient.
The TS,requires the report to describe the circumstances initiating the transient, the effect of the PORV on the transient, and any corrective action necessary to prevent recurrence.
BACKGROUND:
Turkey Point has an overpressure mitigating system which is designed to protect the reactor coolant system from pressure transients which could exceed the limits of Appendix G to 10 CFR Part 50 when one or more of the reactor coolant system cold legs is less than or equal to 275 'F.
During the last week of November
- 1992, Turkey Point Unit 3 was in the process of filling and venting the reactor coolant system.
Plant procedures specify 375 psig for filling and venting to allow for operating
- margin, since the Westinghouse technical manual identifies a
minimum loop pressure of 325 psig for filling and venting operations.
This pressure is to be maintained so that the starting pressure of the coolant loop does not fall below the 200 psid required across the number one seal of the reactor coolant pump.
The setpoint for the overpressure mitigating system is 415 psig plus or minus 15 psig.
TRANSIENT DESCRIPTION:
On November 27,
- 1992, at approximately 0255 ESTI the 3C reactor coolant pump was started during the fill and vent process.
Soon thereafter, the Unit 3 pressurizer power operated relief valve PCV-3-455B opened due to high pressure in the reactor coolant system.
At the time of the event, the reactor coolant system was water solid with no bubble in the pressurizer.
Reactor coolant system pressure was 375 psig prior to the pump start and the temperature of the reactor coolant system was 127 F.
Operations Procedure 3-OP-41.1, Reactor Coolant Pump, limits a reactor coolant pump start to times when the temperature of the steam generator is no more than 10 'F greater than that of the reactor coolant system.
This temperature limitation is required to be maintained to minimize the
L-92-340 Page 3 of 4
potential for a temperature induced pressure increase during the start of a reactor coolant pump.
Temperature measurements of blowdown from the steam generator were monitored starting at 2330 EST on November 26, 1992, in accordance with 3-0P-41.1.
The initial temperatures of the shell side water in the steam generators were found to be approximately 145 'F.
Feed and bleed of the steam generator shell side volume was begun and monitored until the blowdown temperature reached 128 'F.
Soon after reaching this temperature the 3C reactor coolant pump was started.
The control operator conducting the start of the reactor coolant pump also started opening pressure control valve PCV-145 to help control a possible pressure increase due to a temperature differential between the reactor coolant system and the steam generator.
PCV-145 is the outlet valve from the reactor coolant system letdown orifices.
None the less, after the start of the 3C reactor coolant
- pump, PCV-3-455B opened relieving pressure in the reactor coolant system.
The following factors are believed to have contributed to the lift of PCV-3-455B:
Starting a reactor coolant pump with a solid reactor coolant
- system, because no pressure absorbing bubble in the pressurizer was available to mitigate a pressure
- increase, A differential temperature between the reactor coolant system and the steam generator, resulted in an increase in pressure as an increase in the temperature in the bulk reactor coolant system occurred, A slow acting (by design) letdown outlet pressure control valve reduced the ability to quickly control pressure by use of the letdown system, Based upon the mass of the reactor head and its location outside the bulk residual heat removal cooling flow path, a potential thermal gradient could have existed which contributed to the pressure rise in the reactor coolant system after starting the reactor coolant pump.
Reactor coolant system pressure indications observed in the control room during the event, according to pressure indicator PI-3-402, never exceeded 400 psig.
Graphs of pressure versus time, generated from the plant computer
- system, substantiate this finding.
L-92-340 Page 4 of 4
EFFECTS OF PORV ACTUATION:
The opening of the pressurizer power operated relief valve was successful in reducing the pressure to less than the setpoint for its opening.
Continued operation of the letdown system at approximately 130 gpm returned the pressure to the normal operating band.
CORRECTIVE ACTIONS:
In accordance with the recommendation contained in the Westinghouse technical manual designated minimum pressure for a reactor coolant pump start, operating procedure 3/4-0P-41.1 has been revised to include a pressure for filland vent operations of greater than 325 psig.
A caution will be included to maintain the reactor coolant system pressure between 325 and 330 psig to allow margin to the overpressure mitigating system setpoint.