ML17348B306

LER 91-012-00:on 911007,delta-T Factor in Overpower Delta-T & Overtemp Delta-T Found Set at Design Value of 56.1 F Instead of TS Value.Caused by Procedure Error.Values Changed & Plant Procedures developed.W/911219 Ltr

ML17348B306
Person / Time
Site:	Turkey Point
Issue date:	12/19/1991
From:	Plunkett T, Dawn Powell FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
L-91-324, LER-91-012, LER-91-12, NUDOCS 9112300269
Download: ML17348B306 (9)

Text

ACCELERATED DISTPJBUTION DEMONSTRATlON 5Yh l'hM 0

REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9112300269 DOC ~ DATE: 91/12/19 NOTARIZED: NO DOCKET FACIL:50-250 Turkey Point Plant, Unit 3, Florida Power and Light C '05000250 AUTH. NAME AUTHOR AFFILIATION POWELL,D.R. Florida Power & Light Co.

PLUNKETT,T.F. Florida Power & Light Co.

RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 91-012-00:on 911007,delta-T factor in overpower Delta-T

& overtemp Delta-T found set at design value of 56.1 F D instead of TS value. Caused by procedure error. Values changed

& plant procedures developed.W/911219 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR ENCL SIZE:

TITLE: 50.73/50.9 Licensee Event Report (LER), Inciden Rpt, etc.

NOTES:

RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD2-2 LA 1 . 1 PD2-2 PD 1 1 D AULUCK,R 1 1 INTERNAL: ACNW 2 2 AEOD/DOA 1 1 AEOD/DS P/TPAB 1 1 AEOD/ROAB/DSP 2 2 NRR/DET/ECMB 9H 1 1 NRR/DET/EMEB 7E 1 1 NRR/DLPQ/LHFB10 1 .1 NRR/DLPQ/LPEB10 1 1 NRR/DOEA/OEAB 1 1 NRR/DREP/PRPB11 2 2 NRR/DST/SELB 8D 1 1 NRR/DST/SICB8H3 1 1 NRR/EST/~B.8 Dl FILE ~ 02I

-FILE' "01

'E 1

1 1

1 NRR/DST/SRXB 8E RES/DSIR/EIB 1

1 1

1 RGN2 1 1 EXTERNAL EG&G BRYCE I J ~ H 3 3 L ST LOBBY WARD 1 1 NRC PDR 1 1 NSIC MURPHY,G.A 1 '

NSIC POOREIW ~ 1 1 NUDOCS FULL TXT 1 1 D

NOTE TO ALL "RIDS" RECIPIEÃIS:

. PLEASE HELP US TO REDUCI'. iVASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOXI PI-37 (EXT. 20079) 1'0 ELllv!INATE YOUR NAiXIE FROM DISTRIBUTION LISTS FOR DOCUb IENTS YOU DON"T NEED!

1 FULL TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES REQUIRED: LTTR 31 ENCL 31

OgcE L-91-324 10 CFR 50.73 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Gentlemen:

Re: Turkey Point Units 3 and 4 Docket No. 50-250 Reportable Event: 91-012-00 Use of Design hT Rather Than Indicated hT for bT in OPBT and OTBT Setpoints as Required by Technical S ecifications for Units 3 and 4.

The attached Licensee Event Report 250-91-012-00 is being provided in accordance with 10 CFR 50.73 (a) (2) (i) (B) .

The event was determined to be reportable during a detailed review of a safety evaluation to be submitted to the Plant Nuclear Safety Committee on November 29, 1991.

If there are any questions please contact us.

Very truly yours, T. F. Plunkett

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Vice President Turkey Point Nuclear TFP/JEK/3k.

enclosures

-e cc: Stewart D. Ebneter, Regional Administrator, Region II, USNRC, Senior Resident Inspector, USNRC, Turkey Point Plant aA f0'Il .0 COl,"p4<<1

LICENSEE EVENT REPORT (LER)

FACILITY NAME (1) DOCKET NUMBER (2) PACE (3)

TURKEY POINT UNITS 3 AND 4 05000250 1 oF 4 TITLE (4)

Use of Design Delta-Temperature (Delta-T) Rather Than Indicated Delta-T for Delta-T, in Overpower Delta-T and Overtemperature Delta-T Setpoints as Re uired b Technical Specifications for Units 3 and 4.

EVENT DATE (5) LER NUMBER(6) RPT DATE (2) OTHER PACILITIES INV (8)

MON DAY SEQ 6 RP DAY YR DOCKET 4 (S)

FACILITY NAMES 10 07 91 91 012 00 12 19 91 TVRKEY POINT UNIT 4 05000251 OPERATINC MODE (()) I/5 10 CFR 50.73 a 2 i B POKER I,EVEI, (10) 50/0 LICENSEE CONTACT FOR THIS LER (12)

David R, Powell, Licensing Manager TELEPHONE NVMBER 305-246-6559 COMPLETE ONE LINE fOR EACH COMPONENT FAII.URE DESCRIBED IN THIS REPORT (13)

CAUSE SYSTEM COMPONENT WNUFACTVRER NPRDS2 CAUSE SYSTEM MANUFACTURER NPRDS2 COMPONENT SUPPLEMENTAL REPORT EXPECTED (14) NO tw YES 0 EXPECTED SUBMISSION DAY YEAR DATE (15)

(If yee, coetPlete EXPECTED SUBMISSION DATE)

ABSTRACT (16)

On October 7, 1991, with Unit 3 at 50% of rated power, during calibration of a new digital instrumentation rack, the Delta-T, factor in Overpower Delta-T and Overtemperature Delta-T setpoint formula was found to be set at the design value (56.1 F) instead of the indicated value as required by Technical Specifications.

A safety evaluation was performed to assess the effect of the higher Delta-T, factor.'he evaluation concluded that the plant had been operating within its design bases during all past cycles. Indicated Delta-T values at rated thermal power were obtained following calibration and inserted for the Delta-T,. factor in OP Delta-T and OT Delta-T setpoint formula.

The event was determined to be reportable, in accordance with 10 CFR 50.73 (a) (2) (i) (B), during a detailed review of a safety evaluation which was submitted to the Plant Nuclear Safety Committee for review on November 29, 1991.

LICENSEEIENT REPORT (LER) TEXT ONTINOATION FACILITY NAME DOCKET NUMBER LER NUMBER PAGE NO.

TURKEY POINT UNIT 3 05000250 91-012-00 02 OF 04 EVENT DESCRIPTION On October 7, 1991, during calibration of the Eagle-21 system (digital instrumentation rack) (EIIS-IG) (IEEE-CHA) 'at 50% reactor power for Turkey Point Unit 3, the hT, value used in the Overtemperature Delta-T (OTIT) and Overpower Delta-T (OPBT) setpoints was found to be 56.1 F (design hT, Ts < To yd at rated thermal power). Technical Specification 2.2.1 requires that indicated values of hT at rated thermal power be used for hT,. A review of operational history at Turkey Point Units 3 and 4 prior to the resistance temperature detector (RTD) bypass elimination modification revealed'that indicated hT at rated thermal power had been as low as 53.8'. This review also revealed that the design value of 56.1' had been used for all past cycles .for both Unit 3 and Unit 4 ~ At present, following the RTD bypass elimination modification this past summer, the indicated values of dT at rated thermal power are:

Loop BTo A B C Unit 3 51;87 51.98 52.38 Unit 4 52.52 53.22 52.73 At power levels less than 75% of rated thermal power, during startup testing, the power range high flux reactor trip setpoint is adjusted down and will trip the reactor prior to OPBT and OTET taking effect and tripping the plant. In addition, other reactor trip inputs exist that will trip the reactor upon receiving a valid signal.

During a subsequent evaluation of the dT, issue the determination was made that the setpoints for OPbT and OTBT had been non-conservative and therefore should have required the entry into an Action Statement in accordance with Technical Specification 2.2.1 b.

The event was determined to be reportable following a detailed review of a safety evaluation which was submitted to the Plant Nuclear Safety 'Committee on November 29, 1991 for final management approval. The event is considered to be reportable in accordance with 10 CFR 50.73 (a) (2) (i) (B), "Any operation or condition prohibited by the plant's Technical Specifications."

II. EVENT CAUSE The cause of this event was a procedure error. The calibration procedure installing hT, value in the OPET and OTBT setpoints used 56.1' until the setpoint methodology and the validity of the adjustable values in the new Eagle 21 digital instrumentation racks was reviewed and the error recognized.

Subsequently a safety evaluation determined that the dT, within the OPAT and OTBT equations, used to define the setpoints, was non-conservative. Surveillance procedures, although adequate in the identification of correct setpoints, did not verify the correctness of constants in the OPbT and OThT setpoints..

LICENSEEfZNT REPORT (LER) TEXT NTINUATION FACILITY NAME DOCKET NUMBER LER NUMBER PAGE NO.

TURKEY POINT UNIT 3 05000250 91-012-00 03 OF 04 III . EVLNT SAFETY ANALYSIS The OPBT and OTBT setpoints are designed to'provide protection against departure from nucleate boiling (DNB) and linear power

-density limits in the case of relevant transients, i.e.,

uncontrolled r'od withdrawal, uncontrolled bank withdrawal, core cooldown, boron dilution and loss of load events. A detailed safety analysis was performed by Florida Power and Light based upon work performed by Westinghouse to assess the safety significance of the use of the bT design value of 56.1 F's hT, in the reactor protection setpoints for OPBT and OTbT.

The transients that comprise the Turkey Point'licensing basis and require a dT reactor trip for accident "mitigation are the Uncontrolled Rod Cluster Control Assembly (RCCA) Withdrawal at Power (FSAR 14.1.2), Chemical and Volume Control Malfunction (Boron Dilution, (FSAR 14.1.5), and Loss of External Electrical Load (FSAR 14.1.10) events. These safety analyses use design hT for dT,. The hT was used to start operation since the actual indicated dT 'esign can not be determined until either operation has occurred at rated thermal power or a best fit curve of bTs at lower power levels can be extrapolated to estimate indicated dT at rated thermal power.

At power levels less than 75% rated thermal power, while calibration was in progress, the power range high flux reactor trip setpoint was

. lowered and would have tripped the reactor prior to OPbT and OTbT taking effect and tripping the plant. Other 'reactor'trip inputs exist that will trip the reactor upon receiving a valid trip signal.

If these trips do not occur, the effect of having the design bT for hT, rather than the indicated bT required by Technical Specifications is the same as increasing the trip setpoint, or more correctly increasing the time to a reactor trip. Analysis has shown that even if a delayed reactor trip would have occurred, the plant would have remained within its design.

The OTbT trip provides core protection for DNB for all combinations of pressure, power, coolant temperature and axial power distribution provided the transient is slow with respect to coolant transit delays from the core to the temperature detectors and pressure is within the range between the pressurizer high and low pressure trip setpoints.

The OPbT trip setpoint is automatically varied with (1) coolant temperature, and (2) rate of change of temperature. For instance, the faster the temperature changes in the upward direction the lower the trip setpoint.

Based upon the benefit from the increased actual core flow and the available margin in the setpoint.s, the design basis is met with the bT, factor set to the design value of 56.1 F.

IV. CORRECTIVE ACTIONS The hT, values for Units 3 and 4 have been changed to indicated hT values at rated thermal power, This process was completed using installation and startup procedures which meet the surveillance,reqgjrements of the Technical Specifications.

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LICENSEEENT REPORT (LER) TEXT Vl'INUATION FACILITY NAME DOCKET NUMBER LER NUMBER PAGE NO.

TURKEY POINT UNIT 3 05000250 91-012-00 04 OF 04

2. Plant procedures have been developed to calculate and implement indicated dT values at rated thermal power for hT, during power'scension and periodic calibration. Most values fo'r constants used in the Eagle 21 system are obtained from vendor design documentation for the system. However, hT for hT, and the G factor (scaling factor ex-core to in-core) were obtained by measurement of the appropriate parameters and supplied by memo for inclusion into the Eagle 21 system.

Formalization of the source of correct tuning constants will be complete by April 30, 1992 ADDITIONAL INFORMATION None.

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