ML17228A158

LER 93-004-00:on 930409,typo Discovered in Rept Used to Determine RPS Low RCS Flow Trip Setpoint.Error Existed Since Aug 1988.Caused by Design Control Inadequacy.Engineering Package Developed to Correct calculations.W/930510 Ltr

ML17228A158
Person / Time
Site:	Saint Lucie
Issue date:	05/10/1993
From:	SAGER D A, YOUNG R J FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
L-93-129, LER-93-004-02, LER-93-4-2, NUDOCS 9305180328
Download: ML17228A158 (7)

Text

ACCELERANT DOCUMENT DISTRj: UTION SYSTEM REGULAT INFORMATION DISTRIBUTION STEM (RIDS)ACCESSION NBR:9305180328 DOC.DATE: 93/05/10 NOTARIZED:

NO FACIL:50-335 St.Lucie Plant, Unit 1, Florida Power&Light Co.AUTH.NAME AUTHOR AFFILIATION YOUNG,R.J.

Florida Power&Light Co.SAGER,D.A.

Florida Power&Light Co.RECIP.NAME RECIPIENT AFFILIATION DOCKET¹05000335

SUBJECT:

LER 93-004-00:on 930409,typo discovered in rept used to determine RPS low RCS flow trip setpoint.Error existed since Aug 1988.Caused by design control inadequacy.

Engineering package developed to correct calculations.W/930510 ltr.DZSTRZSUTZON CODE: IE22T COPIES RECEIVED:LTR I ENCL/SIZE: TITIE: 50.73/50.9 Licensee Event Report (LER), Incident Rpt, etc.NOTES: D RECIPIENT ID CODE/NAME PD2-2 LA NORRISgJ INTERNAL: ACNW AEOD/DOA AEOD/ROAB/DSP NRR/DE/EMEB NRR/DRCH/HHFB NRR/DRCH/HOLB NRR/DRSS/PRPB NRR/DSSA/SRXB RES/DSIR/EIB EXTERNAL: EG&G BRYCEPJ.H NRC PDR NSIC POOREPW.COPIES LTTR ENCL 1 1 1 1 2 2 1 1 2 2 1 1 1 1 1 1 2 2 1 1 1 1 2 2 1 1 1 1 RECIPIENT ID CODE/NAME PD2-2 PD ACRS AEOD/DSP/TPAB NRR/DE/EELB NRR/DORS/OEAB NRR/DRCH/HICB NRR/DRIL/RPEB NRR.DSSA/SPLB 02 RGN2 FILE 01 L ST LOBBY WARD NSIC MURPHY,G.A NUDOCS FULL TXT COPIES LTTR ENCL 1 1 2 2 1 1 1 1 1 1 1, 1 1 1 1 1 1 1 1 1 1 1 1.1 1 1 D D D D NOTE TO ALL"RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTE!CONTACT THE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT.504-2065)TO ELIMINATE YOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!D FULL TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES REQUIRED: LTTR 32 ENCL 32 PP'f May 10, 1993 L-93-129 10 CFR 50.73 U.S.Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C.20555 Re:.St.Lucie Unit 1 Docket No.50-335 Reportable Event: 93-004 Date of Event: April 9, 1993 Incorrect RCS Low Flow Trip Setpoint due to a Desi n Error The attached Licensee Event Report is being submitted pursuant to the requirements of 10 CFR 50.73 to provide notification of the subject event.Very truly yours, 4A8a~D.A.ger Vice r sident St.Lu e Plant DAS/JWH/kw Attachment cc: Stewart D.Ebneter, Regional Administrator, USNRC Region II Senior Resident Inspector, USNRC, St.Lucie Plant DAS/PSL 8917-93 170033 9305i80328 9305i0 PDR ADOCK 05000335 S PDR an FPL Group company PPP FPL FEOElmlo ol NRC Form K6 (M9)L.S.tEUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)APPROYOT ONE NCk 01 10 010I ENNPEE'NHNT EET PIATE 0 NAaE N PEN INEPCNTE TO CEPNCY WITH TI00 Nf OIEAATlON CCATEC STINT INCEEET.>>0 HTE SONWNa CONNENTE SNONEPNO TAfaENEETTwIE To THE INOCla0 ANT PE PONTE NANAK INNT EAANCH TPANIA IAN IANAE NI PE IANATCNY~WATPNarol.

OC IPHE Na To THE PPENWITTN SEOOC TON PNOECT o'110010PA Cf SCE Of NAMOEIENT PIEI OAXNT.WASPNeOTCPC OC ITNEL FACILITY NAME (1)St.Lucie Unit 1 DOCKET NUMBER (2)PAGE 3 050003351 0 4 (4)Incorrect Reactor Coolant System Low Flow Trip Setpoint results in a condition prohibited by Technical Specifications due to a Design Control Inadequacy.

EVENT DATE (5)LER NUMBER (6)REPORT DATE (7)OTHER FACILITIES INVOLVED (8)MOMlH DAY 0 4 09 OPERATING MODE (9)YEAR YEAR 9 3 9 3 S IAL 0 0 4 MONTH DAY YEAR 00051093 FACILITY NAMES N/A N/A 20.402(b)20.405(c)50.73(a)(2)(iv)

THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR: Check one or more of the followin (11)DOCKET NUMBER(S)05 000 05000 73.71(b)POWER LEVEL (10)20.405(a)(1

)(i)20.405(a)(1

)(ii)20.405(a)(1)(iii) 20.405(a)(1)(iv) 20.405(a)(1)(v) 50.36(c)(1) 50.36(c)(2) 50.73(a)(2)(i) 50.73(a)(2)(ii) 50.73(a)(2)(iii) 50.73(a)(2)(v) 50.73(a)(2)(vii) 50.73(a)(2)(viii)(A) 50.73(a)(2)(viii)(B) 50.73(a)(2)(x) 73.71(c)OTHER (Specify in Abstract below and in Text NRC Form 366A)NAME LICENSEE CONTACT FOR THIS LER 12 Robert J.Young, Shift Technical Advisor TELEP ONE NUMBER AREA CODE 4 0 7 465.3550 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT 13 CAUSE SYSTEM COMPONENT MANUFAG-REPORTABLE TURER TO NPRDS CAUSE SYSTEM COMPONENT MANUFAC-REPORTABLE lURER TO NPRDS SUPPLEMENTAL REPORT EXPECTED 14 I I I EXPECTED MONIH DAY YEAR SUBMISSION DATE (15)YES (If yes, complete EXPECTED SUBMISSION DATE)ABSTRACT (Limit to 1400 spaces.i e.approximately fifteen single-space typewritten lines)(1 6)On April 9, 1993, St.Lucie Unit 1 was in Mode 6 when a typographical error was discovered by FPL Nuclear Engineering in a report used to determine the Reactor Protection System (RPS)low Reactor Coolant System (RCS)flow trip setpoint.Technical Specification 2.2.1, Table 2.2-1 states that the trip setpoint will be greater than or equal to 95%of design reactor coolant flow.The FPL Nuclear Engineering report, which described the conversion of pressure drop across the steam generators to the RPS low RCS flow trip setpoint, contained an incorrect constant.The report was subsequently transmitted to the plant staff and the Instrument and Control Department adjusted the RCS low flow setpoint.This error caused the setting of the RCS low flow trip setpoint to a value approximately 3%below the minimum 95%of design flow.This setpoint error existed since August 1988.The root cause of this event was a design control inadequacy.

A typographical error was made in the report transmitted to the plant staff.The error would have been discovered if the review process for the transmitted report had undergone an independent review.The Nuclear Engineering process currently in place prevents a similar event from occurring by requiring independent review of transmitted setpoints.

Corrective actions for this event: An engineering evaluation was performed that concluded that the operation of Unit 1 during this time period was within the bounds of the safety analysis.A review of the procedure used to determine the Unit 2 low RCS flow setpoint verified that it did not contain a similar error.After a review of internal records, Nuclear Engineering verified that no other Unit 1 or 2 RPS setpoint changes were transmitted to the plant in error.An engineering package was developed to provide the corrected calculations for determination of the RPS reactor coolant system low flow trip setpoint.Instrumentation and Control personnel will revise appropriate procedures and install the correct trip setpoint in the Unit 1 RPS prior to entering mode 2.Prior to discovery of this event, Engineering adopted a process requiring independent review of setpoints before transmittal to the plant staff.FPL Facsimile of NRG Form 366 (6-89)

FPL Fsaslnilsof NRC Form SEI (&89)U.S.NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)TEXT CONTINUATION Asswosf 0 oe Ixs ss ss C I ss f xssus'ass s f STAIAT f 0 OATCE N sf il INSAONsf To COINET WITH siss Sf CWNATTCN Cas Ef COON IfoUECTI sfs Isxs ssxswNe coNNENTs IKOANowo Esses N fsoNATE To TIO INcsxsss Ne ISAONTS NANACE sf NT fssANCH TASTCE ua NXXENT IuauATEXTT

~wAEINe TON.Oo ssssf Ne To TIO SNEIIwow IsoucwoN Twof cs ETI sseIsss asrscf os swNACEISNT Ne Tseofs.WANNesfsf oc ssexs FACILITY NAME (1)St.Lucie Unit1 DOCKET NUMBER (2)YEAR LER NUMBER (6)g EQUENTIAL NUMBER REVISION NUMBER PAGE (3)0 500 0335 9 3 TEXT (lf more spaceis required, use additional NRC Form 366A's)(1/)0 0 4 0 0 0 2 0 4 On April 9, 1993, with Unit 1 in Mode 6, FPL Nuclear Engineering performed a review of the calculations that are contained in the St.Lucie Unit 1 Low Flow Trip Setpoint Calibration Guidelines.

The review was being performed to support a proposed change to the steam generator tube plugging criteria.During this review, a typographical error in a report that described conversion of pressure drop across the Steam Generators (EIIS:AB)to the Reactor Protection System (RPS)(EIIS: JC)Reactor Coolant System (RCS)low flow trip setpoint was found.The error resulted in the calculation of a non-conservative setpoint with which the RPS creates an automatic reactor trip to protect against a loss of RCS flow.This error caused the RPS low RCS flow trip setpoint to be approximately 3 percent below the Technical Specification minimum of 95 percent of design flow.In 1987 the report containing the incorrect information was sent to the plant staff to support a modification to the RPS.In August 1988, the report was referenced when the modification to the RPS was implemented and was used to modify plant procedures for the initial setting and subsequent monthly checks of this RPS low flow trip setpoint.This condition was discovered in April of 1993.The root cause of this event was a design control inadequacy.

A typographical error was made by FPL Nuclear Engineering in the transmittal of a calculated setpoint to the plant staff.During a transfer of information from an independently verified engineering calculation to a report, a transcription error caused a constant that converts pressure drop across the Steam Generators to the low RCS flow trip setpoint to be non-conservative.

The incorrect report would have been discovered and corrected had the transmitted report to the plant staff received the same independent review that the original calculation had received.Prior to the discovery of this event, FPL Nuclear Engineering adopted the process for requiring independent review of all setpoints before transmittal to the plant staff.This event is reportable under 10CFR50.73(a)(2)(i)(B), as"Any operation or condition prohibited by the plant's Technical Specifications." Technical Specification 2.2.1 requires that the RPS trip setpoint for RCS low flow be set at or above 95 percent of design flow (370,000 gpm).For cycles 9, 10 and 11 of Unit 1 operation, the RCS low flow trip was erroneously set at slightly higher than 92 percent of design flow.The RCS low flow trip setpoint ensures that for a degradation of RCS flow resulting from analyzed transients, a reactor trip occurs to prevent departure from nucleate boiling ratio (DNBR)safety limits.The process signal for this function is developed from four independent differential pressure channels which measure the pressure drop across the primary side of both Steam Generators.

The total Steam Generator pressure drop is compared with the low RCS flow trip setpoint.If two channels indicate a flow which is less than the trip setpoint, an RPS trip signal is initiated.

FPL Facsimile of NRC Form 366 (6-89)

FPL Facstmlo ol NRC Form S66 ($89)U.S.NUCLEAR REGULATORY COMMrSS ION UCENSEE EVENT REPORT (LER)TEXT CONTINUATION

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$$$oeror cofrfoa rrfoeo oe TAIAT To ofvcrN ITN Ioefcfoc To ccoe$v TATN ooo ofrfvAACON couococN Iacra cTl$0 4 Ieoa foNwrfo ccrrrNT o fccfrlooro IAATIEN oeoNATc To Tto Iocofoo wo$fafomo NANACT$C NT ONANCN reeTCA ua NOCIT AN IN$$AATON v~wANNIOTCN, oc$0$$a ANI To llo f ATNAwrovr IacucocN ffvoac I$$$Ioe ror$cff ICE of IIANAccoaNT Afo$$$$ccr,wANNrcrcfo oc Toooa FACILITY NAME (1)St.Lucie Unit 1 DOCKET NUMBER (2)YEAR LER NUMBER (6)EQUENTIAL-r REVISION NUMBER 4 NUMBER PAGE (3)0500033593 TEXT (If more spaceis required, use additional NRC Form 366A's)(17)0 0 4 0 0 0 3 0 4 An evaluation (JPN-PSL1-SEFJ-93-006) was performed by FPL Engineering to determine the available safety analysis margin for the most limiting transients (loss of offsite power and loss of RCS flow)for which protection is provided by the RCS low flow trip.The results show that the approximate 3 percent setpoint error is sufficiently offset by available flow margin.Thus, violation of the DNBR limit for a loss of offsite power or a loss of RCS flow event would not have occurred if there hadbeen a degradation of RCS flow event during the time period that the setpoint error was in place.(A review of Unit 1 reactor trips showed that the RCS low flow trip function was not challenged during cycles 9,10 and 11.An additional review of actual operating conditions during cycles 9, 10, and 11 was performed to ensure that no other condition existed that would further aggravate the condition described in this LER).The Reactor Coolant Pump (RCP)(EIIS:P) seized rotor event has been reanalyzed by the fuel vendor for a 4 percent reduction in design flow and the corresponding 4 percent reduction in the RCS low flow trip setpoint.The analysis shows that the acceptance criteria for the postulated RCP seized rotor event was not violated.Therefore, the health and safety of the public was not affected by this condition.

1.Prior to the discovery of this event, Nuclear Engineering proceduralized a review process to ensure the accuracy of setpoints and plant changes.This process requires an independent verification of setpoints and plant changes before transmittal to the plant staff, and would have detected the error described in this report.2.Nuclear Engineering prepared an engineering evaluation and determined that operation of Unit 1 was bounded by the safety analyses for Cycles 9, 10, and 11.3.Nuclear Engineering reviewed internal records and verified that no other Unit 1 or 2 RPS setpoint changes were transmitted to the plant staff in error.4.Nuclear Engineering reviewed the Unit 2 RCS Low Flow Trip Setpoint Determination procedure and verified that it did not use erroneous data.5.A FPL engineering package was developed to document and transmit the corrected calculation for the Unit 1 RPS Iow RCS flow trip setpoint.6.The I&C Department will revise procedures 1-0120050 and 1-1400050~to reflect the correct RCS low flow trip setpoints prior to Unit 1 entering Mode 2.7.The I&C Department will make the RPS low RCS flow trip setpoint changes prior to Unit 1 entering Mode 2.FPL Facsimile of NRC Form 366 (6-89)

FPL F55cslrrllo ol NRC Form S6B U.S.NUCLEAR REGULATORY COMMrSSION

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5 N05TOON AAIYNWCa<ISTACTTGNTNOXGTTITIOSTINTTYNCS TN INNAGSINNT AI05 TAOGCT, WAONKITTYA OO 5050$.FACILITY NAME (1)DOCKET NUMBER (2)LER NUMBER (6)PAGE (3)St.Lucie Unit 1 YEAR': 0 500 0335 9 3 EQUENTIAL NUMBER 0 0 4.REVISIO NUMBER 0 0 0 4 0 4 TEXT (If more spaceis required, use additional NRC Form 366A's)(1/)None A previous similar LER at St.Lucie involving a design error for the RPS was: LER 335-79-30 Steam Generator Low Level RPS trip setpoints less than Technical Specifications due to a design ermr.FPL Facsimile of NRC Form 366 (6-89)