ML17228A135

LER 93-005-00:on 930104,vibration Levels Increased on Reactor Coolant Pump 2A1 & Controlled Unit Shutdown Commenced on 930125.Caused by Pump Shaft Cracking.Motor Rotor & Radial Bearing Assembly replaced.W/930427 Ltr

ML17228A135
Person / Time
Site:	Saint Lucie
Issue date:	04/27/1993
From:	Sager D, Galen Smith FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
L-93-123, LER-93-005, LER-93-5, NUDOCS 9305030010
Download: ML17228A135 (6)

Text

ACCELERATED DOCUMENT DISTRIBUTION SYSTEM REGULAOZY INFORMATION DISTRIBUTI SYSTEM (RIDE)

ACCESSION NBR:9305030010 DOC.DATE: 93/04/27 NOTARIZED: NO DOCKET ¹ FACIL:50-389 St. Lucie Plant, Unit 2, Florida Power & Light Co. 05000389 AUTH. NAME AUTHOR AFFILIATION SMITH,G.D. Florida Power & Light Co.

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

RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 93-005-00:on 930104,vibration levels increased on reactor coolant pump 2Al & controlled unit shutdown commenced on 930125.Caused by pump shaft cracking. Motor rotor & radial bearing assembly replaced.W/930427 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR ! ENCL TITLE: 50.73/50.9 Licensee Event Report (LER),incident Rpt, etc. 3 SIZE:

NOTES:

RECIP1ENT 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/HHFB 1 1 NRR/DRCH/HICB 1 1 NRR/DRCH/HOLB 1 1 NRR/DRIL/RPEB 1- 1 NRR/DRSS/PRPB 2 2 NRRQJP~A/SPLB 1 1 NRR/DSSA/SRXB 1 1 REG FILE+ 02 1 1 RES/DSIR/EIB 1 1 RGN2~FTLE 01 1 1 S'XTERNAL:

EG&G BRYCE,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:

D PLEASE HELP VS 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 128, Ft. Pierce, FL 34954-012S April 27, 1993 L-93-123 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Re: St. Lucie Unit 2 Docket No. 50-389 Reportable Event: 93-005 Date of Event: January 4, 1993 High Reactor Coolant Pump Vibration Resulting in a Controlled Unit Shutdown due to a Cracked Shaft The attached Licensee Event Report is being submitted voluntarily to provide notification of the subject event.

Very truly yours, D. A. Sager Vice President St. Lucie Plant DAS/JWH/kw Attachment cc: Stewart D. Ebneter, Regional Administrator, USNRC Region Senior Resident Inspector, USNRC, St. Lucie Plant II DAS/PSL 8915-93 30005J'-

9305030010 93042?

PDR ADOCK 05000389 S PDR an FPL Group company

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050003891 0 4 High Reactor Coolant Pump vibration resulting in a controlled Unit shutdown due to a cracked shaft EVENT DATE (5) LER NUMBER (6) REPORT DATE (7) OTHER FACILITIES INVOLVED(8)

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

N/A 05 00 2 9 3 N/A 0 1 1 9 3 0 0 5 0 0 0 4 2 7 9 3 05 0 0 0 OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR:

Check one or more of the followin (11)

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

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

LEVEL (10) 1 0 0 20.405(a)(1)(ii) 50.36(c)(2) 50.73(a)(2)(vii) X 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) V01untar Re ort LICENSEE CONTACT FOR THIS LER 12 NAME TELEP ONE NUMBER AREA CODE Galen D. Smith, Shift Technical Advisor 4 0 7 465 -3550 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT 13 CAUSE SYSTEM COMPONENT REPORTABLE CAUSE SYSTEM COMPONENT MANUFAC- REPORTABLE TO NPRDS TURER TO NPRDS A B P B 5 8 0 I I I SUPPLEMENTAL REPORT EXPECTED 14 EXPECTED MONTH DAY YEAR SUBMISSION YES (Ifyes, complete EXPECTED SUBMISSION DATE) NO DATE(15) 0 4 P 7 9 4 ABSTRACT (Limit to 1400 spaces.i e. approximately fifteen single-space typewritten lines) (16)

On January 4, 1993, vibration levels began to increase on the 2A1 reactor coolant pump. The 1X (synchronous speed) and 2X (2 times synchronous speed) vibration levels increased at the upper motor, 1X and 2X phase angles wandered, and the orbit exhibited a non-uniform shaft rotation. Overall vibration levels continued to trend upwards. At 2315 on January 12th, a controlled plant shutdown was commenced at a vibration level of 15 mils and increasing. A root cause team was assembled and subsequently developed a detailed inspection plan.

Disassembly of the reactor coolant pump'and inspection of the pump shaft revealed two cracks just above the hydrostatic bearing. Upon replacement of the pump internals the 2A1 reactor coolant pump was restarted with satisfactory vibration readings. The unit was returned to Mode 1 on April 1, 1993.

The root cause of the pump shaft cracking is still under investigation. The corrective actions as a result of this event were: 1) Replaced the motor rotor assembly on the 2A1 reactor coolant pump. 2) Replaced the motor upper radial bearing assembly (shoes, adjusting bolts), upper and lower thrust bearing shoes, reset the upper and lower radial and thrust bearing clearances. 3) Installed a new pump rotating element and seal. 4) The defective pump rotating element was sent to an off-site examination facility for non-destructive examination and subsequent metallurgical examination of the crack area. This voluntary Licensee Event Report Is being submitted for industry informational purposes.

FPL Facsimile of NRC Form 366 (6-89)

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U.S. NUCLEAR REGULATORYCOMMlSSCN AffROIIDQIAS NO Sl lf0 I0I NRC Fam X6 ttfNNNIO00t LICENSEE EVENT REPORT (LER) 00TNIATTDSJTDTN ffIlINNI00IN'ODIANAT WllNTI00 00CINIATTCNCOULCDCN INC1NCT: NI0 IR0 IORWARS aSNNNT 0 INONIONC N/CNN TCTTNATC TO TIN INCCRS0 TEXT CONlNUAllON Wft INACITT0IIANNNINNTDRANCN If'SNLISO IANlTNT INCIAATCRT WANNATTDI.DC IOSS0 AN) TO TIN 0 NTRfRÃWINCOCTION fROCCT ISIS00IOIS Cf IICf Cf NANACCINNTANS NASOTT. WARDROOM DC ICNIA FACILITYNAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3)

YEAR EQUENTIAL 5 REVISIO St. Lucie Unit 2 NUMBER Ã NUMBER 0 500 0389 9 3 0 0 5 0' 0 3 0 4 TEXT (Ifmore spaceis required, use additional NRC Form 366A's) (17)

The accident analyses in the UFSAR do not specifically address shaft shearing scenarios. However, Section 15.3.5.1.5.2 of the UFSAR addresses the relationship between a sheared shaft and shaft seizure. A sheared shaft will offer less resistance to flow during the post-LOOP flow coast down phase than a shaft seizure since the shaft is still capable of rotating. During the long term portion of the event, the reverse flow through the affected RCP is greater during the shaft shear event than the shaft seizure event. However, the lower core flow experienced during long term portion of the event has no impact on the minimum Departure from Nucleate Boiling Ratio (DNBR) which has been proven to occur during the first two to four seconds of the transient. It is during this time frame that the shaft seizure event is most limiting due to the lower core flow. Therefore, the margin to design limits is smaller for a shaft seizure event and as a result the shaft shearing event is bounded by the shaft seizure accident analysis.

Based on actual plant conditions at the time of the unit shutdown, a more credible event would have been a loss of flow through one RCP. This event is considered an infrequent type with an insignificant approach to off-site dose limits. Although a partial loss of RCS flow event is not specifically analyzed in the UFSAR, the core and system performance is considered to be no more adverse than a total loss of RCS flow that would occur during a LOOP since, by design, a low RCS flow trip (93% core flow) would automatically initiate a plant trip. In this situation, the minimum DNBR would be higher, due to a hwer power to flow ratio, than for a total loss of core flow event. A partial loss of RCS flow through one RCP due to shaft shear is bounded well within the UFSAR accident analysis since 1) There was no existing steam generator tube leakage, 2) a shaft shear event is less limiting than a shaft seizure event, and 3) no LOOP occurred.

The health and safety of the public was not adversely affected by this event.

1) A new motor rotor assembly was installed on the 2A1 RCP.

2) The motor upper radial bearing assembly (shoes and adjusting bolts), lower thrust bearing shoes were replaced (housing was reused) and the motor upper and lower radial bearing and thrust bearing clearances were reset.

3) A new pump rotating element and seal were installed.

4) The existing pump rotating element was sent to an off-site contaminated material examination facility for dimensional measurements, nondestructive examination, and subsequent metallurgical examination of the crack area.

5) New vibration probes were mounted on the pump shaft. The output of these probes was directed to the control room instrumentation previously associated with the lower motor bearing.

Although the lower motor vibration probes no longer provide control room indication, they will remain on the pump motor as permanently installed test equipment.,

FPL Facsimile of NRC Form 366 (6-89)

FPL FOCSlnT'IOOI US. NUCLEAR REGULATORY COMMISION NRC Form S66 AAYROYTOOIO N(5 P 5001 05 E000%0 00005 UCENSEE EVENT REPORT (LER) TSTSAATTO 500IDCN 00 R ICS050OC TO COADTYISTN 5100 00CIYAAITDNCOIICCTION IC5CCST: 500 IRC ICSNINYICOINRNISICCARD005DSCNN TSINIATC TOTIC ICC50050 TEXT CONTINUATtON N05 ICYORT0 NANACCIC NT D RANCH P 550j, IAS. IAACATARICCIAATCRYIOMASDCIA WANNNITON.DC 505N5 NCI TO TIC 0AKRWI005 IC DVCDON IIY5CCT551 50 01055 Cf I ICE Cf NANAOIINNTANT IAOCCT. WADNATT505DC 50NO FACILIfY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3)

YEAR EQUENTIAL REVISlON

.'- 'UMBER St. Lucie Unit 2 NUMBER 0 500 0389 9 3 0 0 5 0 0 0 4 0 4 TEXT (Ifmore space is required, use additional NRC Form 366A's) (17)

Reactor Coolant Pump Rotating Assembly Byron Jackson Co.

¹ Serial 741-N-0001 Model 35x35x43 DFSS Unit 1 1A1 RCP failed due to a bent shaft in 1990.

FPL Facsimile of NRC Form 366 (6-89)