ML17229A174

LER 96-016-00:on 961122,insufficient Testing & Maint Were Noted on 125 Vdc Bus cross-tie Breakers.Caused by Lack of Effective Maint & Testing.All Four 125 Vdc cross-tie Breakers Will Be refurbished.W/961220 Ltr

ML17229A174
Person / Time
Site:	Saint Lucie
Issue date:	12/20/1996
From:	Noble R, Stall J FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
L-96-338, LER-96-016, LER-96-16, NUDOCS 9612260079
Download: ML17229A174 (8)

Text

CATZGOHr Z REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

'ACCESSION NBR:9612260079 DOC.DATE: 96/12/20 NOTARIZED: NO DOCKET FACIL:50-335 St. Lucie Plant, Unit 1, Florida Power & Light Co. 05000335 AUTH. NAME AUTHOR AFFILIATION NOBLE,R.E. Florida Power & Light Co.

STALLgJ.A. Florida Power & Light Co.

RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 96-016-00:on 961122,insufficient testing & maint were noted on 125 vdc bus cross-tie breakers. Caused by lack of effective maint & testing.All four 125 vdc cross-tie breakers will be refurbished.W/961220 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR ENCL SIZE:

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

NOTES:

RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME ITTR ENCL ID CODE/NAME LTTR ENCL PD2-3 PD 1 1 WIENS, L. 1 1 INTERNAL: ACRS 1 1 AE~OD~D /NAB 2 2 AEOD/SPD/RRAB 2 2 gP'IL'E CENTER 1 1 NRR/DE/ECGB 1 1 NRR/DE/EELB 1 1 NRR/DE/EMEB 1 1 NRR/DRCH/HHFB 1 1 NRR/DRCH/HICB 1 1 NRR/DRCH/HOLB 1 1 NRR/DRCH/HQMB 1 1 NRR/DRPM/PECB 1 1 NRR/DSSA/SPLB 1 1 NRR/DSSA/SRXB 1 1 RES/DET/EIB 1 1 RGN2 FILE 01 1 1 D

EXTERNAL: L ST LOBBY WARD 1 1 LITCO BRYCE,J H 1 1 NOAC MURPHY,G.A 1 1 NOAC POORE,W. 1 1 NRC PDR 1 1 NUDOCS FULL TXT 1 1 E

N NOTE TO ALL "RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM OWFN SD-5(EXT. 415-2083) TO ELIMINATE YOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!

FULL TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES REQUIRED: LTTR 26 ENCL 26

Florida Power 5 Light Company, P.O. Box 128, Fort Pierce, FL 34954.0128 December 20, 1996 L-96-338 10CFR 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: 96-016 Date of Event: November 22, 1996 0

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, J. A. Stall Vice President St. Lucie Plant JAS/REN Attachment cc: Stewart D. Ebneter, Regional Administrator, USNRC Region II Senior Resident Inspector, USNRC, St, Lucie Plant 9612260079 961220 PDR ADOCK 05000335 8 PDR an FPL Group company

NRC FORM 366 U.S. NUCLEAR REOULATORY COMMISSION APPROVED SY OMS No. $ 160%104 SKFIRES oerso/$ $

(4-96)

ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH THIS MANOATO INFORMATION COLLECTION REQUEST: 60.0 HR* REPORTED LESSON LEARNED ARE INCORPORATED INTO THE UCENSIHO PROCESS AND F BACK To SIOUSIRY. FORWARD COMMENTS REGAROIHO BURDEN ESTIMAT LICENSEE EVENT REPORT (LER) TO THE INFORMATION ANO RECORDS MANAGEMENTBRANCH IM Fssl UW NUCLEAR REGIAATORY COMMISSION, WASHINOTOH, DC 20666O001 AND TO THE PAPERWORK REDUCTION PROJECT 1316001041, OFRCE 0 (See reverse for required number of MAHAOEMENTANO BUDOEl', WASHINOTOH, DC 2060%

digits/characters for each block)

FACIUTY NAME (1) DOCKET N UMSBl (E I PAOE IS I ST LUCIE UNIT 1 05000335 1 OF 6 TITLE Id)

Insufficient Testing and Maintenance on 125 VDC Bus Cross-tie Breakers FACIUTY NAME DOCKET NUMBER MONTH SEQUENTIAL REVISION DAY YEAR YEAR NUMBBI NUMBER MONTH OAY YEAR N/A FACIUTY NAME DOCKET NUMSER 11 22 98 96 016 00 12 20 96 N/A OPERATIN0 MoDE (9) 20.2201(b) 20.2203 (a)(2)(v) 50.73 (s) (2) 6) 50.73(s)(2)(viii)

POWER LEVEL (10) 20.2203(a)(2)(i) 20.2203 (s)(3) (ii) 50.73(s)(2)(iii) 73.71 OTHER

20. 2203(a) (2) (iii) 50.36(c) (1) 50.73(s) (2) (v) Specify In Abstract below or In NRC Form OSSA 20.2203(a)(2)(iv) 50.36(c)(2) 50.73(s) (2)(vii)

NAME TELEPHONE NUMBER Sndudo*oo Codol Richard E. Noble, Licensing Engineer (561) 467 - 7022 CAUSE SYSTEM MANUFACTURER REPORTABLE CAUSE SYSTEM MANUFACTURER REPORTABLE TO NPROS TO NPROS MONTH OAY YEAR EXPECTED YES SUBMISSION (If yes, complete EXPECTED SUBMISSION DATE). X No DATE (15)

ABSTRACT (Limit to 1400 spaces, l.e., approximately 15 single.spaced typewritten lines) (16)

On November 22, 1996, with St. Lucie Unit 1 operating in Mode 1 at 100 percent reactor power, a test of the 1AB-18 cross-tie breaker between the 1AB "swing" bus and the 1B 125 vdc bus was performed to confirm operability of the installed undervoltage release mechanism. Operability of the cross-tie breakers was questioned during a licensee initiated design review. The test resulted in a determination that the underyoltage release mechanism was inoperable as a result of age related degradation. The degraded condition of the tested breaker was evaluated as being applicable to the three other dc tie breakers based on their similar design and operating history. Based on the potential for common degraded condition of these breakers, the dc bus transfer function and, consequently, the "C" AFW pump were declared out of service. The appropriate technical specification limitinq condition for operation action was entered for the "C" AFW pump. The two breakers on the swing bus were removed. Maintenance and testing was performed and the breakers were returned to service within the time specified in the technical specifications. The transfer function has been restored and is currently in service.

Corrective actions include: 1)The two 125 vdc molded case breakers on the 1AB bus were removed, cleaned and exercised and then returned to service. 2)A review was performed for both units which determined that no other dc breakers utilized undervoltage release devices. 3)AII four cross-tie breakers on Unit 1 will be refurbished by the vendor during the next refueling outage. 4)A surveillance and maintenance schedule will be established for the cross-tie breakers. 5)A preventative maintenance schedule will be established to monitor molded case circuit breakers for age related degradation.

NRC FORM 386 (4 95)

NRC FORM 366A U.S. NUCLEAR REQULATORY COMMISSIO I4-96)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION YEAR SEQUENTIAL REVISION ST. LUCIE UNIT 1 05000335 2 OF 6 96 016 0.00 TEXT (ffmora specait required, use additional copies of JVRC Form 368AJ l17I During a licensee initiated design review, a condition was discovered which could potentially prevent a manual transfer of the dc power supply to the "C" turbine driven Auxiliary Feedwater (AFW) (EIIS:BA) pump. Manual transfer of the "C" AFW dc power supply is required to mitigate certain design basis events. Manual transfer is dependant on proper functioning of the undervoltage release mechanism of at least one of two molded case circuit breakers connected in series separating the 125 vdc 1AB "swing" bus (EIIS:EI) from a postulated safety bus (1A or 18) fault (refer to figure 1). It was determined that these undervoltage release mechanisms had not been tested for an extended period, possibly since initial plant startup.

On November 22, 1996, with St. Lucie Unit 1 operating in Mode 1 at 100 percent reactor power, a test of the lAB-18 breaker (one of the two cross tie breakers between the 1AB bus and the 18 125 vdc bus) was performed to confirm operability of the undervoltage release mechanism. The test determined that the undervoltage release mechanism was inoperable as a result of age related degradation. The degraded condition of the tested breaker was evaluated as being applicable to the three other dc tie breakers based on their similar design and operating history. The "C" AFW pump was declared out of service. The appropriate technical specification limiting condition for operation action was entered for the "C" AFW pump. The two breakers adjacent to the swing bus were removed. Maintenance and testing was performed and the breakers were returned to service within the time specified in the technical specifications. The transfer function has been restored and is currently in service.

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSIO I%86)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION YEAR SEQUENTIAL REVISION ST. LUCIE UNIT 1 05000335 3 OF 6 96 016 00 TEXT llfmore epece ie required, oee edditionel copiee of NRC Form 3MAJ I17I The event was discovered as a result of a detailed licensee design and UFSAR review. The primary cause for the common failure condition of the undervoltage release devices on the 125 vdc cross-tie breakers was lack of effective maintenance and testing. Movement of the strike pin which trips the breaker when activated by the undervoltage device was inhibited due to lubricant degradation or dust accumulation or a combination of these age related factors. Although proper breaker operation has been observed on an ongoing basis during routine swing bus transfer operations, the undervoltage release function is not exercised during normal bus transfer.

The critical role of the undervoltage release in the performance of AFW for certain design basis scenarios (i.e., scenarios requiring manual transfer of the swing 1AB 125 vdc bus to repower the "C" AFW pump) was not recognized and consequently not properly translated in maintenance and testing intervals. The installation of an integral undervoltage device into molded case circuit breakers is a unique application for the St Lucie plants and is used only in these dc cross-tie breakers.

This event was determined to be reportable under 50.72 (b)(2)(iii)(D) and 50.73(a)(2)(v) as "any event or condition that alone could have prevented '..".e fulfillment of the safety function of structures or systems that are needed to: mitigate the consequences of an accident." The condition of the 125 vdc cross-tie breakers resulted in a determination that the AFW system may not have performed as required during certain specific design basis events.

The AFW system consists of three trains. The "A" and "B" train consist of independent and redundant flow paths and 100'/ ac motor driven pumps. Electrical power is supplied from the respective "A" and "B" safety trains. The "C" AFW train utilizes redundant flow paths and a greater capacity steam turbine driven turbine pump. Control power for the turbine throttle valve and associated motor operated valves is supplied from the 1AB 125 vdc swing bus which can be powered from either the safety related 1A or 1B 125 vdc busses. Transfer of the 1AB bus is accomplished manually via switches in the control room when the swing bus is aligned to the bus that experienced the single failure.

NRC FOAM 388A H-06)

NRC FORM 366A U.S. NUCtSAR REGULATORY COMMNSIO 4-86 I LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION YEAR SEQUENTIAL REVISION S j. LUCIE UNIT 1 05000335 016 4 OF 6 96 00 (lfmore space & required, use additional copies of NRC Form 866AJ I17)

The degraded condition of the breaker udervoltage mechanisms on the 125 vdc cross-tie breakers could have prevented successful manual 1AB bus transfer during specific design basis events. Only one of two breakers operated in series would have been required to function to meet the specific design scenarios. Although only one of the two breakers was determined to be inoperable by direct testing, the degraded condition of the undervoltage device was considered applicable to all four cross-tie breakers.

The specific design basis events that require manual transfer of the 1AB bus are associated with restoring the "C" AFW pump in a loss of main feedwater scenario. The two specific scenarios are: (1)

Loss of offsite power, coincident with a main feedwater line break resulting in a faulted steam generator, with a dc bus failure on the train opposite the faulted generator and the 1AB "swing" bus aligned to the bus that experienced the single failure. (2) Loss of offsite power, coincident with a high energy line break on the discharge of one motor driven AFW pump, with a dc bus failure on the train opposite the faulted generator and the 1AB "swing" bus aligned to the bus that experienced the single failure. Both of these events are very specific low probability scenarios. Based on event frequencies from the Probablistic Safety Assessment (PSA), the frequency of the above described events is on the order of 1E-10. If manual 1AB bus transfer from the control room could not be accomplished due to the condition of the undervoltage release devices on the tie breakers, additional manual actions outside the control room would be required to restore AF'.".' If steam generator cooling could not be restored, the emergency operating procedures require the establishment of feed and bleed to maintain core cooling.

Based on the above, the protection of the health and safety of the public was not adversely affected by the event.

NRC FORM 386A I4-96)

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSIO I4-9SI LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION YEAR SEQUENTIAL REVISION ST. LUCIE UNIT 1 05000335 5 OF 6 96 016 00 TEXT iif'more speceis required, use eddittonel copies of NRC Farm 366AJ Ill)

The two 125 vdc molded case breakers on the 1AB bus were removed, cleaned and exercised and returned to service.

2. A review was performed for both units which determined that no other dc breakers utilized undervoltage release devices.

3. All four 125 vdc cross-tie breakers will be refurbished by the vendor during the next refueling outage.

4, A surveillance and maintenance schedule will be established for all four 125 vdc cross-tie breakers.

5. A preventative maintenance schedule will be established to monitor molded case circuit breakers for age related degradation.

6. There are several ongoing efforts to assure that design basis requirements have been adequately incorporated into applicable plant procedures. These efforts include: (1) Reviews are being conducted in accordance with Generic Letter 96-01, "Testing of Safety-Related Logic Circuits". The purpose of these reviews is to identify any internal circuit components in the reactor protection system or engineered safety features actuation system that are not currently directly tested by technical specification surveillance. (2) Ongoing reviews of the UFSAR and plant procedures by a dedicated group of engineers and plant operators to identify and correct discrepancies between these documents.

Component: Molded Case Circuit Breaker Manufacturer: ITE Model'TJL 350 None IIRC FORM 388A I4 9S)

NRC FORM 38SA U.S. NUCLFAR REOULATORY CCNMISSI i4-06)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION YEAR SEauENTIAI. REViSiON ST. LUCIE UNIT 1 05000335 6 OF 6 96 016 00 TEXT fSmoro tpocoit roqcirud, uto adoftenof copiot of JVRC ponn DM4J I17)

FlGURE 1 DC PO%ER SUPPLIES CHARGER CHARGER CHARGER 1A 1AB 1B BUS 1A BUS 1AB BUS 18

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TESTED BATTERY BREAKER BATTERY 1A 1B NRC FORll 386A H-06)