ML17227A792

LER 92-008-01:on 921105,discovered Digital Data Process Sys Calorimetric Error Due to Calibration Error.Operations Reduced Power to Less That 100%,RTDs Examined by Labs & I&C Personnel Reviewed tests.W/930331 Ltr

ML17227A792
Person / Time
Site:	Saint Lucie
Issue date:	03/31/1993
From:	Sager D, Young R FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
L-93-052, L-93-52, LER-92-008, LER-92-8, NUDOCS 9304050241
Download: ML17227A792 (6)

Text

ACCELERAT9 DOCUMENT DISTF+BUTION SYSTEM l~

REGULATORY "INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9304050241 DOC.DATE: 93/03/31 NOTARIZED: NO DOCKET FAClL:50-389 St. Lucie Plant, Unit 2, Florida Power & Light Co. 05000389 AUTH. NAME AUTHOR AFFILIATION YOUNG,R.J. Florida Power & Light Co.

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

RECIP.NAME RECIPIENT, AFFILIATION

SUBJECT:

LER 92-008-01:on 921105,discovered-digital data process sys calorimetric error due to calibration error. Operations redused unit power less than 100%,RTDs were examined by laboratories & I&C personnel reviewed test.W/930331 ltr.

DISTRIBUTION CODE: ZE22T COPIES RECEIVED LTR L TlTLE: 50..73/50.9 Licensee'Event Report (LER), Incident Rpt, etc.

ENCL L SIZE:

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 NORRIS,J 1 1 INTERNAL: ACNW 2 2 ACRS 2 2 AEOD/DOA 1 1 AEOD/DSP/TPAB 1 1 AEOD/ROAB/DSP 2 2 NRR/DE/EELB 1 1 NRR/DE/EMEB 1 1 NRR/DORS/OEAB 1 1 NRR/DRCH/HHFBHE 1 1 NRR/DRCH/HICB 1 1 NRR/DRCH/HOLB 1 NRR/DRIL/RPEB 1 1 NRR/DRSS/PRPB 2 2 NRR- DSSA/SPLB 1 1 NRR/DSSA/SRXB 1 1 'REG F E 02 1 1 RES/DSIR/EIB 1 1 ILE 01 1 1 EXTERNAL EG&G BRYCE i J ~ H 2 2 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 NOTE TO ALL"RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 504-2065) TO ELIMINATEYOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!

FULL TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES REQUIRED: LTTR 32 ENCL 32

P.O. Box 120, Ft. Prerce, FL 34954-0129 March 31, 1993 FPL L-93-052 U. S. Nuclear Regulatory 'Commission Attn: Document Control Desk Washington, D. C..20555 Re: St. Lucie Unit 2 Docket No. 50-389 Event: 92-008 Date of Event: November 5, 1992 DDPS Calorimetric Error due to Instrument Calibration Error The attached supplemental Licensee Event Report is being submitted voluntarily to provide additional information on the subject event.

Very truly yours, D. A. ager Vice P esident St. L cie Plant DAS/JWH/kw Attachment cc: 'Stewart D. Ebneter, Regional Administrator, USNRC Region II Senior Resident Inspector, USNRC, St. Lucie Plant DAS/PSL 5866-93 At A eww 9304050241 93033i PDR ADOCK 05000389 S PDR an FPL Group company

FPL Fa~rmlffof U.S. NUCLEAR REGULATORY COMMISSION AfffETTTOOAATHCT 0T 00.0TOH NRC Form SQI E rrHTEC'000 0

+89)

LICENSEE EVENT REPORT (LER)

CCTATASAIOfAWACfTHC TOT, OC TC 00h, fflO 'TO THE PAPE ffffoflA000UC TfCH PfrOJE CT Of 000frHA Of0 fCE Of TTAHACEAEfrfATAT TTAXXT,Wk+OTOTOAOC 00r00 FACILITYNAME (1) DOCKET NUMBER (2) PAGE 3 St. Lucie Unit 2

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050003891 0 4 (4) Digital Data Process System Calorimetric Error due to Instrument Calibration Error.

EVENT DATE (5) LER NUMBER (6) REPORT DATE (7) OTHER FACILITIES INVOLVED(8)

MONTH DAY YEAR YEAR S IAL DAY YEAR FACILITYNAMES DOCKET NUMBER(S)

N/A 05 000 1 1 059 2 9 2 0 0 8 0 1 0 3 3 1 9 3 N/A 05000 OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR:

Checlr one or more of the followin (11)

MODE (9) 20.402(b) 20.405(c) 50.73(a)(2)(iv) 73.71(b)

POWER LEVEL 20.405(a)(1)(i) 50.36(c)(1) 50.73(a)(2)(v) 73.71(c)

(1) 1 0 0 20.405(a)(1)(ii) 50.36(c)(2) 50.73(a) (2)(vii) OTHER (Specify in Abstract 20.405(a)(1)(iii) 50.73(a)(2)(i) 50.73(a)(2)(viii)(A) below andin Text 20.405(a)(1)(iv) 50.73(a) (2)(ii) 50.73(a)(2)(viii)(B) NRC Form 366A) 20.405(a)(1)(v) 50.73(a) (2) (iii) 50.73(a)(2)(x)

LICENSEE CONTACT FOR THIS LER 12 TELEP ONE NUMBER AREA CODE Robert J. Young, Shift Technical Advisor, 4 0 7 465 -3550 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT 13 CAUSE SYSTEM COMPONENT MANUFAC- REPORTABLE CAUSE SYSTEM COMPONENT MANUFAC- REPORTABLE TURER TO NPRDS  :

TURER TO NPRDS X I 0 R T D R135Y I I I SUPPLEMENTAL REPORT EXPECTED 14 EXPECTEP MONTH DAY YEAR SUBMISSION YES (Ifyes, complete EXPECTED SUBMISSION DATE) NO DATE (15)

ABSTRACT (Limit to 1400 spaces.i.e. approximately fifteen single-space typewritten lines) (16)

On 5 November1992, St. Lucie Unit 2 was in mode 1 operating at 100% steady state power. Utility Instrumentation and Control (I&C) personnel were implementing a plant modification to replace six resistance temperature detectors (RTDs) for the main feedwater system. These RTDs provide inputs to the digital data process system (DDPS) and are used in the calorimetric power calculation. Upon installation of the new RTDs the DDPS indicated a power level slightly greater than 100%. Operators reduced power until DDPS indicated less than 100%. It was noted that lower feedwater temperature readings were being obtained from the new RTDs. The original RTDs were subsequently determined to be incorrectly reading main feedwater temperatures.

The root cause of this event was RTD instrument error. Investigations of the failed RTDs by the AMS Corp.

revealed that cold working of the platinum sensing element did not cause the calibration shift because annealing processes did not restore the RTDs to calibration. Continued investigations were conducted independently by the RTD Manufacturer (RdF Corp.) and the Florida Power & Light Metallurgical Laboratory. The result of the examination by RdF concluded that a resistance shift occurred internal to the sensing element, in the platinum sensing coil. Examinations conducted by the FPL Lab have not revealed any additional information.

Corrective actions taken were: 1) Operations reduced unit power to less than 100%, 2) IBC personnel determined that the new RTDs were functioning correctly, 3) A review of historical data for St. Lucie Unit 1 from 1982 to present verified that there were no similar instrument errors, 4) At plant management's request FPL Nuclear Engineering performed an evaluation and concluded that St. Lucie Unit 2 was operating within its safety analysis, 5) l8 C personnel verified that all other calorimetric DDPS inputs were correct and only the main feedwater RTDs were in error, 6) The failed RTDs were examined by independent laboratories.

This Licensee Event Report is being submitted voluntarily.

FPL Facsimile of NRC Form 366 (6-89)

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FPL Faoflrriro ol U.S. NUCLEAR REGULATORY COMMISSION APIWOTLO OLO IALLAF04 IDI NRC Form 366 DF5KR ACCT t LICENSEE EVENT REPORT (LER) LCTIAATTOTLAACLUPL II IKSK7CKTO CTAPLTPA TII TIPS PPCIUIATTTW CCLLLCTTIPI ICOLC CT'44 IITLFOFIWAAO COUULUT4 ArCAIIOPAT OATX8 LCTIUATT TO TIC IC CCPTCS AUC ICPIATTC UFI4AOEAC UT CIUFFCUIP4TILLLC IAICLLUTICOAATOTT TEXTCONTINUAZON WAOUICTIPI,OC TC04A FKI TOTIC P TFFFFCPU FCOVCTCW PIC\CCT TIII44IAILOFFICC Cf IAFFUCLICNlAFO IAICCT.WAOUFCTCALCC lÃCL FACILITYNAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3)

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YEAR EQUENTIAL REVISION St. LUCie Unit 2 NUMBER NUMBER 0 500 0389 9 2 0 0 8 0 1 0 2 0 4 TEXT (Ifmore spaceis required, use additional NRC Form 366A's) (17)

On 5 November 1992, St. Lucie Unit 2 was in mode 1 operating at 100% steady state power.

Utility Instrumentation and Control (l8C) personnel were replacing six resistance temperature detectors (RTDs) that are inputs to the digital data process system (DDPS) (EIIS:IO) for temperature of the main feedwater system (EIIS:SJ). These inputs are used by the DDPS in the calculation of calorimetric power. Upon installation of the new RTDs the DDPS power indicated approximately 1%

greater than 100% power. Utility operators reduced the Unit power level until a DDPS indicated power level less than 100% was obtained.

Plant personnel determined that temperature differences existed between the feedwater temperature inputs to the DDPS before and after the installation of new RTDs. I8 C personnel performed a calibration test on the original RTDs and found that five of the six RTDs read high by an average of 5.5 degrees Fahrenheit (One RTD was damaged during removal). The Instrument error resulted in a DDPS reactor power calculation that was lower than actual power. I8 C compared the calibration data of the new RTDs with the vendor data and concluded that the new RTDs were reading correctly.

The root cause of this event was main feedwater temperature instrument error. A review of historical data for unit 2 since 1984 showed that the feedwater temperature inputs from these RTDs had been slowly increasing but at a very slow rate. Investigations by the AMS Corporation revealed that the most probable cause for error in these RTDs, cold working of the platinum wire, did not occur since normal annealing processes did not restore the RTDs to calibration. Continued investigations were conducted independently by the RTD Manufacturer (RdF Corporation) and the Florida Power 8 Light Metallurgical Laboratory. Examinations by RdF included a baseline examination (visual, calibration and radiographic) and a teardown analysis. Baseline examinations revealed that a calibration shift (error) had taken place in each sensor. The teardown analysis revealed that the platinum lead wires were almost separated in two places and the cross section was flattened and feathered at the edges, causes unknown. However calibration checks determined that these conditions did not contribute to the calibration shift and that the cause for the RTD error lay in the platinum sensor. Examinations conducted at the Florida Power 8 Light Metallurgical Laboratory have not revealed any additional information.

Contributing factors to this event included: 1) DDPS instrument limits (deadband or acceptance limits), which are a part of the software package, force the DDPS to accept only those inputs that are within set limits. If the inputs are within these limits then the DDPS considers them believable. The DDPS limits were set at a 10 degrees Fahrenheit input comparison which allowed all of the feedwater temperature inputs to be used for the DDPS calculations even though the RTD inputs had drifted high. 2) The main feedwater temperature instrument loops are periodically calibrated, but their RTDs are not routinely calibrated. This is due to the risk of damaging the RTDs when removing them from their thermowells. These two factors contributed to the inability to detect the slowly increasing instrument error.

FPL Facsimile of NRC Form 366 (6-89)

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~ LICENSEE EVENT REPORT (LER) ICOISST:0001015 fONWNOCONNCNTSICCNICNOOAOTNTSTTAATCTOTIC ICCOAOS If Nf> ISIONI0 NANACS IC NT WIANCN 000A IAS IAOASANICOtAATCTIT TEXT CONTINUATlON f WAStDICTCW,DC TOMC NO TO TIO 0 AITIIACTWICOUCTC7I IITCkSCT 001 I001 WI Cf ICE Of QANAOTICNTAIITSADIST,WADNICTONDCSCCA FACILITYNAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3)

YEAR EQUENTIAL REVISION NUMBER NUMBER St. Lucie Unit 2 0 500 0389 9 2 0 0 8 0 1 0 3 0 4 TEXT (Ifmore spaceis required, use additional NRC Form 366A's) (17)

This event is being reported voluntarily for informational purposes.

A representative sample of manual calorimetrics performed as per OP 2-3200020, Qjm;~

', were reviewed. All manual calorimetrics were found to be within the 2%

procedural limit when compared with the DDPS calorimetric power. Manual calorimetrics are an independent check of DDPS calorimetric power and are performed using instrument readings on the Reactor Turbine Generator Boards (RTGBs) (EIIS:IU) and use a different style of feedwater temperature instruments than the RTDs used to provide input to the DDPS.

FPL Nuclear Engineering evaluated this event using a conservative approach. Calculations performed show that with the observed feedwater RTD error the actual nominal unit power was 101.04% with an additional instrument uncertainty of up to +0.95%. This power level is the worst case since a review of historical data revealed that the RTD error had been increasing at a very slow rate since 1984. From the evaluation it is concluded that St. Lucie Unit 2 was operating within the bounds of its FSAR Chapter 15 safety analysis which assumes a maximum power level of 102%

(100% nominal power level plus 2'/o due to calibration and instrument errors). The Bases for the Technical Specifications also take into account variations due to calibration and instrument error for the Variable High Power Trip.

The health and safety of the public were unaffected by this event.

1. Operations reduced Unit 2 power to maintain DDPS indicated power below 100%.

2. I&C sent the failed RTDs to the AMS Corporation for analysis. Analysis did not reveal the cause of the calibration error but were able to determine that the normal reason for RTD error, cold working of the platinum element, did not happen in this instance.

3. I&C sent two RTDs to the RdF Corporation and the Florida Power 8 Light Metallurgical Laboratoty for further analysis. Results of the RdF examination revealed that the calibration shift took place in the platinum sensing element. Examinations conducted at the FPL Metallurgical Laboratory did not reveal any additional information.

4. I&C personnel reviewed the calibration test data and determined that the newly installed main feedwater RTDs were functioning correctly (the new RTDs are made by a different manufacturer than the original RTDs).

FPL Facsimile of NRC Form 366 (6-89)

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YEAR EQUENTIAL REVISION NUMBER NUMBER St. Lucie Unit 2 0500038992 0 0 8 0 1 0 4 0 4 TEXT (Ifmore spaceis required, use additional NRC Form 366A's) (17)

5. Plant performance, MWs generated, and MWs expected were examined for St. Lucie Unit 1 to determine if a similar problem existed for that unit. No adverse trends were noted.

6. A historical review of the St. Lucie Unit 1 DDPS feedwater temperature inputs from 1982 to the present verified that no inconsistencies existed to give an erroneous DDPS calorimetric power.

7. An I&C generated calibration curve for the newly installed RTDs was compared to a vendor supplied calibration curve with minimal differences detected. This allows a high degree of confidence in the new RTD curves.

8. At the request of plant management, Nuclear Engineering performed an evaluation, JPN-PSL-SEIS-92-018, and determined that St. Lucie Unit 2 did not operate outside of its FSAR Chapter 15 safety analysis.

9. I8 C determined that a tighter instrument deadband of a nominal 5 degrees Fahrenheit should be maintained in the DDPS software for RTD instrument input comparisons and has made the change.

10. I&C determined that RTDs of the same model are not installed in other Unit 1 or Unit 2 systems

11. I&C determined only the Unit 2 main feedwater RTDs provided erroneous input to the DDPS.

12. I&C has added an additional high feedwater temperature alarm to the DDPS. This alarm will preclude similar drift events from being undetected.

nn il RDF Corporation RTD part number 21453 iilr n No other LERs pertaining to inaccurrate RTDs were identified.

FPL Facsimile of NRC Form 366 (6-89)