ML17250B248

LER 91-007-00:on 910731,B Emergency Diesel Generator Started Automatically Due to Initiation Signal from Bus 16 & 17 Undervoltage Monitoring/Protection Sys.Caused by Temp Related Switch Failure.Switch replaced.W/910829 Ltr

ML17250B248
Person / Time
Site:	Ginna
Issue date:	08/29/1991
From:	Backus W, Mecredy R ROCHESTER GAS & ELECTRIC CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-007, LER-91-7, NUDOCS 9109130162
Download: ML17250B248 (26)

Text

ACCELERATED D+~RIBUTION DEMONS~TION SYSTEM REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9109130162 DOC.DATE: 91/08/29 NOTARIZED: NO DOCKET FACIL:50-244 Robert Emmet Ginna Nuclear Plant, Unit 1, Rochester G ,05000244 AUTH. NAME AUTHOR AFFILIATION BACKUS,W.H. Rochester Gas & Electric Corp.

MECREDY,R.C. Rochester Gas & Electric Corp.

RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 91-007-00:on 910731,"B" Emergency Diesel Generator started automatically due to initiation signal from Bus 16 &

17 Undervoltage monitoring/protection sys.Caused temp l

D failure. Replace solid state switch.W/910829 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR i ENCL SIZE:

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

NOTES:License .Exp date in accordance with 10CFR2,2.109(9/19/72). 05000244 A D

RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL D PDl-3 LA 1 1 PDl-3 PD 1 1 JOHNSON,A 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/PRPBll 2 2 NRR/DST/SELB 8D 1 1 NRR/DST/SICB8H3 1 1 1 1 NRR/DST/SRXB 8E 1 1 REG FIL 02 1 1 RES/DSIR/EIB 1 1 FILE 01 1 1 EXTERNAL EG&G BRYCE g J ~ H 3 3 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 D

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TO ALL "RIDS" RECIPIENTS PLEASE HELP US TO REDUCE KYASTE! CONTACT THE DOCUi~!ENT CONTROL DESK, ROOii1 Pl-37 (EXT. 2M79) TO ELIS!!NATE YOUR NAME FROiil DISTRIBUTION LISTS FOR DOCUiIEiNTS YOU DON'T NEED!

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

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srarc ROCHESTER GAS AND ELECTRIC CORPORATION 4 89 EAST AVENUE, ROCHESTER N. Y. 14S49.0001 ROBERT C MECREOY, TELEPHONE Vice Presideni AREA coDE 716 546 2700 Cinna Nuciear Producdon August 29, 1991 U.S. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555

Subject:

LER 91-007, Safeguards, Buses Undervoltage Relay Actuations Due to Failed Solid State Switches Causes Automatic Starts of the "B" Emergency Diesel Generator R.E. Ginna Nuclear Power Plant Docket No. 50-244 In accordance with 10 CFR 50.73, Licensee Event Report System, item (a)(2)(iv), which requires a report of, "any event or condition that resulted in manual or automatic actuation of any Engineered Safety Feature (ESF), including the Reactor Protection System (RPS)", the attached Event Report LER 91-007 is hereby submitted.

This event has in no way affected the public's health and safety.

Ver truly yours, Robert C. ecre y XCA U.S. Nuclear Regulatory Commission Region I 475 Allendale Road King of Prussia, PA 19406 Ginna USNRC Senior Resident Inspector trrrg't 9109l 30l b2 S05000244 10829 PDR @DOCH, S PDR

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SVS>>LtlstNTAL 1SSOAT ttrtCTSO IIsl SSOHTSS CAY YSA1 txrtctto SUSSS I STION OATS IISI Yt t litree, esrsees SAASCTSO SVSVISSIOH OA Tll HO estTAAOT ILssH s Iescl seers, lA, ee<<>>seers<<e Hrsees eever>>cere Iree>>rssee <<cess lltl On July 31, 1991 at 1746 EDST, with the reactor at approximately 984 full power and again on August 2, 1991 at. 1049 EDST, with the reactor at approximately 98> full power, the "B" Emergency Diesel Generator started automatically due to an initiation signal from the Bus 16 and Bus 17 Undervoltage Monitoring/Protection Systems.

The "B" Emergency Diesel Generator started normal for both events and attained proper voltage and frequency.

close into Bus 16 or Bus 17 because these buses were at their

'y design, it did not proper voltage fed from their normal power supply.

Immediate operator action was to verify that. Bus 16 and Bus 17 were energized and that the "B" Emergency Diesel Generator was operating properly.

The cause of the event was determined to be a temperature related failure of a solid state switch printed circuit board.

Corrective action taken was to replace the solid state switch printed circuit board with a qualified spare, followed. by a satisfactory test and return to service. Corrective actions to prevent recurrence are discussed in section (V)(B).

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IIC arm 344A V.5. NVCLEAII IIEOULATOIIYCOM51(54(ON (0431 LICENSEE EVENT REPORT ILER) TEXT CONTINUATION A55AOVEO OV4 NO 3(50&(04 E)IPIAES 413IIES I'ACILITYNASIE lll OOCKET NUMEEII 13l LEII NV154EII (Sl 5AOE (3I 55QVCNTIAL 5 5 V l5 K) H HUM 5A ~ yVM 5A R.E. Ginna Nuclear Power Plant 24 491 007 00 02 1 TEXT II(mew ~ N naca/. w5 aanaW HIIC fam ~ 3 I II Tl o s o o o 0F 1 PRE-EVENT PLANT CONDITIONS This LER covers two separate events, which had the same general cause and consequences, and occurred within a reasonably short length of time.

Prior to both events, the plant was at approximately 98%

steady state reactor power with no major activities, in progress.

II; DESCRIPTION OF EVENT A. DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES:

0 July 31, 1991, 1746 EDST: First event date and time 0 July 31, 1991, 1746 EDST: First event discovery date and time 0 July 31, 1991, 1843 EDST: Safeguards Bus 17 power supply manually transferred to "B" Emergency Diesel Generator to Safeguards 480 volt Bus 17 per T-27.4 (Diesel Generator Operation) 0 August 1, 1991, 0331 EDST: Safeguards 480 volt Bus 17 normal power power supply restored 0 August 1, 1991, 0331 EDST: Safeguards 480 volt Bus 17 "B" Emergency Diesel 'enerator power supply terminated and "B" Emergency Diesel Generator stopped and aligned for auto standby 0 August 2, 1991, 1049 EDST: Second event date and time 0 August 2, 1991, 1049 EDST: Second event discovery date and time

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NRC Sar~ 255A V.S. NUCLEAR REOULATORY COMMI55ION (042 I L'ICENSEE EVENT REPORT {LER) TEXT CONTINUATION ASSROVSO OMS NO, 2I 50&105 EXSIRES:5I2l/$ 5 SACILITY NAME III OOCKET NUINER l2I LER N~ER I5) ~ AOE ISI YEAR I. 55QVCNTIAL HUM 15VISION HVM 51 R.E. Ginna Nuclear Power Plant 0 TEXT Ilfaero Swee e ~. wr aASaonV HSIC Anti ~ 5 I I ITI 0 5 0 0 0 2 4 4 9 1 0 7 0 0 3 o August 2, 1991, 1321 EDST: Safeguards Bus 16 power supply manually transferred to "B" Emergency Diesel Generator per M-48.13 (Isolation of Bus 16 Undervoltage System For Maintenance, Tr'oubleshooting, Rework and Testing) 0 August 2, 1991, 1707 EDST: Safeguards 480 volt Bus -16 normal power supply=,restored. "B" Emergency Diesel Generator power supply terminated.

o August 2, 1991, 1725 EDST: "B" Emergency Diesel Generator stopped and aligned for auto standby B. EV1sNT:

On July 31, 1991 at 1746 EDST, with the reactor at approximately 984 full power, the Control Room received the following alarms: '-15 (Bus 17 Undervoltage Safeguards) and J-32 (Emergency Diesel Gen 1B Panel). The Control Room operators immediately verified proper voltage on Bus 17 and that the normal power supply breaker was closed. The Control Room operators also verified that the "B" Emergency Diesel Generator had started and displayed proper voltage and frequency. By design, the "B" Emergency Diesel Generator did not close into Bus 17, as the Bus voltage was normal and was still being supplied by its normal power supply.

Auxiliary operators were dispatched to check the Bus 17 Undervoltage Monitoring/Protection System cabinets and the operation of the "B" Emergency Diesel Generator. The operation of the "B" Emergency Diesel Generator was found to be normal and investigation of Bus 17 Undervoltage Monitoring/Protection System cabinets indicated an odor resembling that of burning elect;rical insulation and one red indication light and four amber indication lights were illuminated.

The red light indicates trouble in the system and the amber lights indicate auxiliary relays have actuated (i.e. Diesel start, Control Room Annunciator, etc.).

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MAC Stre 154A U.5. IIUCLTAIIlltOULATOIIYCOMMI5NOII I545 I LICENSEE EVENT REPORT (LER) TEXT CONTINUATION r APPIIOVEO OMI IIO 1150WIOt t)IPII155. 5151/55 PACILITY HAM% Ill OOCKET IIUMIEII111 LTII MUAIICII151 PAOT 111 55OIJCMTIAL i ~ PTVISIOrr

~ rVM A rrVM 5A R.E. Ginna Nuclear Power Plant TENT Irs rrrrrrP MrPct e o s o o o 2 491 0 0 7 0 0 0 40F trrrnrL rrtP AP5trPnsl IYAc srrrrrr ss5A'SI (111 Subsequently, at 1843 EDST, the power supply to Bus 17 was transferred from the normal supply to the "B" Emergency Diesel Generator per operating procedure, T-27.4 (Diesel Generator Operation). This was done at this time because the Shift Supervisor was unsure of how many channels of undervoltage protection were still operable for Bus 17 and to comply with Technical Specification Table 3.5.1, action statement 7, which states in part that, "any time the number of operable channels is less than the minimum operable channels, either a) be at hot shutdown within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and an RCS temperature less than 350 F= within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, or b) energize the affected bus with a diesel generator."

At 0331 EDST, August 1, 1991, subsequent to the repair, testing, and return to service of Bus 17 Undervoltage Monitoring/Protection System, Bus 17 normal power was restored and the Bus 17 "B" Emergency Diesel Generator power supply terminated. Following this, the "B" Emergency Diesel Generator was stopped and aligned for auto standby.

Again on August 2, 1991 at 1049 EDST, with the reactor at approximately 98l. full power, the Control Room received the following alarms: L-7 (Bus 16 Undervoltage Safeguards) and J-32 (Emergency Diesel Gen 1B Panel). The Control Room operators immediately verified proper voltage on Bus 16 and that the normal power supply breaker was closed. The Control Room operators also veiified that the "B" Emergency Diesel Generator had started and displayed proper voltage and frequency. By design, the "B" Emergency Diesel Generator did not close into Bus 16, as the bus voltage was normal and was its normal power supply.

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o s o o o 244 91 007 00 05 or-N>>c>>>> >>CcrncE ooo co>>error ~ rYAC focrrr BASSA'cl IITI Auxiliary operators were dispatched to check the Bus 16 Undervoltage Monitoring/Protection System cabinets and the operation of the "B" Emergency Diesel Generator. The operation of the "B" Emergency Diesel Generator was found to be normal and investigation of Bus 16 Undervoltage Monitoring/Protection System cabinets indicated one red indication light and four amber indications lights.

As this event occurred during normal working hours, Maintenance personnel were dispatched quickly to evaluate, the problem with the Bus 16 Undervoltage Monitoring/Protection System. They reported that only one of the Bus 16 Undervoltage Protection channels was affected, thus the Shift Supervisor was not required to load the "B" Emergency Diesel Generator onto Bus 16 per Technical Specifications.

Subsequently, at 1321 EDST, the power supply to Bus 16 was transferred from its normal supply to the "B" Emergency Diesel Generator per Maintenance procedure, M-48.13 (Isolation of Bus 16 undervoltage System For Maintenance, Troubleshooting, Rework and Testing).

This transfer was done so the Maintenance Department could repair, test, and return to service, the Bus 16 Undervoltage Monitoring/Protection System.

At 1707 EDST, August 2, 1991, subsequent to the repair, testing, and return to service of the Bus 16 Undervoltage Monitoring/Protection System, Bus 16 normal power supply was restored and the Bus 16 "B" Emergency Diesel Generator power supply terminated.

At 1725 EDST, August 2, 1991, the "B" Emergency Diesel Generator 'as stopped and aligned for auto standby.

C. INOPERABLE STRUCTURES, COMPONENTS, OR SYSTEMS THAT CONTRIBUTED TO THE 19719lT:

None.

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None.

E. METHOD OP DISCOVERY:

The event was immediately apparent due to alarms and indications in the Control Room and at the affected Safeguard Buses Undervoltage Monitoring/Protection System cabinets.

OPERATOR ACTION:

Following the Bus 17 undervoltage alarm and the "B" Emergency Diesel Generator automatic start, the Control Room operators immediately verified proper voltage on Bus 17 via its normal power supply and that the "B" Emergency Diesel Generator displayed proper voltage and frequency.

Subsequently, the Control Room operators transferred Bus 17 from its normal supply to the "B" Emergency Diesel Generator per T-27.4 to satisfy plant technical specifications and to facilitate troubleshooting, repairing, and testing of the Bus 17 Undervoltage Monitoring/Protection System.

Following the Bus 16 undervoltage alarm and the "B" Emergency Diesel Generator automatic start,'he Control Room operators immediately verified proper voltage on Bus 16 via its normal power supply and that the "B" Emergency Diesel Generator displayed proper voltage and frequency.

Subsequently, the Control Room operators transferred Bus 16 from its normal supply to the "B" Emergency Diesel Generator per M-48.13 to facilitate repairing and testing of the Bus 16 Undervoltage Monitoring/Protection System.

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G. SAFETY SYSTEM RESPONSES.

The "B" Emergency Diesel Generator automatically started and displayed proper voltage and frequency.

III. CAUSE OP EVENT A. IMMFJ)IATE CAUSE:

The automatic actuation of the "B" Emergency Diesel Generator was due to an undervoltage signal from the Bus 17 Undervoltage Monitoring/Protection System for the first event and an undervoltage signal from the Bus 16 Undervoltage Monitoring/Protection System for the second event.

B. INTERMEDIATE CAUSE:

The undervoltage signal from,the Bus 17 Undervoltage Monitoring/Protection System was due to the internal failure of the system's solid state switch printed circuit board number one (1).

The undervoltage signal from the Bus 16 Undervoltage Monitoring/Protection System was due to the internal failure of the system's solid state switch printed circuit board number two (2).

The above solid state switches are identical in design and provide the interface mechanism between the solid state undervoltage relays and the mechanical actuation relays.

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%%dna C ROOT CAUSE:

The underlying cause of the internal failure of the system's solid state switch was determined to be, that present circuit design results in fairly high

'emperatures at the circuit card. This fairly high temperature generally reduces the useful life of specific transistors and causes them to fail prematurely.

ANALYSIS OR KRTENT The events are reportable in accordance with 10 CFR 50.73, Licensee Event Report System, item (a)(2)(iv), which requires reporting of, "any event or condition that resulted in manual or automatic actuation of any Engineered Safety Feature (ESF). including the Reactor Protection System (RPS)". The starting of the "B" Emergency Diesel Generator was an automatic actuation of an ESF System.

An assessment was performed considering both the safety consequences and implications of this event with the following results and conclusions:

There were no operational or. safety consequences or implications. attributed to the starting of the "B" Emergency Diesel Generator because:

The "B" Emergency Diesel Generator operated as designed.

0 Both Bus 17 power supplies (i.e. normal and emergency) were either in use or available throughout the event.

Both Bus 16 power supplies (i.e. normal and emergency) were either in use or available throughout the event.

0 The Bus 16 and Bus 17 undervoltage Monitoring/Protec-tion System failure was in the conservative direction (i.e. the failure actuated the "B" Emergency Diesel Generator).

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the public's "V. CORRECTIVE ACTION A. ACTION TAKEN TO RETURN AFFECTED SYSTEMS TO PRE-EVENT NORMAL STATUS:

o The Maintenance Department, after troublesho'oting the Bus 16 and Bus 17 Undervoltage Monitoring/Pro-tection System, determined that the problem was a solid state switch printed circuit board in the system.

o The Maintenance Department replaced the affected solid state switch printed circuit boards with qualified spares, tested the systems satisfactorily and returned them to service.

o Operations, after the Bus 16 and Bus 17 Undervoltage Monitoring/Protection System was restored to service, returned Bus 16 and Bus 17 to their normal power supply and stopped the "B" Emergency Diesel Generator and aligned auto standby.

it for B. ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE:

The following is an outline of the corrective actions being taken or planned in response to the recent failures of the solid state switch circuit boards located inside the Undervoltage Monitoring/Protection System cabinet:

Short Term Response:

a) Auxiliary operators are checking each undervoltage cabinet for proper status light indication once per shift.

b) Each solid state switch circuit board was visually checked for signs of heat related degradation.

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L'ICENSEE EVENT REPORT ILER) TEXT CONTINUATION AFFIIOVEO OMS IIO SISOW104 ExFIAEs. SISlrss FACILITY IIAME III COCKET IIUMSEII (SI Lfll NUMSEII Itl ~ AQS ISI v t *II StQVt MTIAL AtVltrQH HUM 'to rrV M tA R.E. Ginna Nuclear Power Plant: o s o o o 244 9 1 007 00 10 DF TExT IIImore toeoe rt nous'. rrto ~ eeooror ivAC Fomr ~ sl IITl c) A voltage check of each train of Undervoltage Monitoring/Protection was conducted to verify the integrity of the diodes which have previously exhibited heat related degradation.

0 Intermediate Term Response:

a) Replacement of remaining solid state switch circuit boards which have been in service

'or an extended. time period (service life estimated at 4-5 years) was completed for Bus 16, and for the failed card on Bus 17.

In addition, boards were replaced on Bus 14.

b) The periodic test procedure for testing the undervoltage relays (PT-9.1) was enhanced to include periodic full end-to-end testing.

c) Full end-to-end testing was performed on Buses 14, 16, 17 and 18, including verification of trip functions that were previously tested annually.

0 Long Term Response:

a) The Undervoltage System will be modified to eliminate heat related degradation of the solid state switch circuit boards.

b) Remaining solid state switch circuit boards, which have been in service for an extended time period, will be replaced when parts are available. This includes one card on Bus 17 and two cards on Bus 18.

c) Other internal components that are affected by heat will be evaluated for periodic replacement.

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R.E. Ginna Nuclear Power Plant 0 5 0 0 0 2 4 4 9 0 0 7 0 0 1 1 oF1 1 TUB IifmeA <<M>> <<>>0used, v>> <<<<RAvvA'RC AvvA ~'el IITI ADDITIONAL INFORMATION A. FAILED COMPONENTS:

The failed solid state switch printed circuit boards were supplied by Electro-Mechanics, part number 33013-898 and 33013-899, assembly numbers 03021-287 and 03021-288.

PREVIOUS LERs ON SIMILAR EVENTS:

A similar LER event historical search was conducted with the following results: LER 88-008 Undervoltage Relay Actuation Due to a Failed (Safeguard'us Solid State Switch Caused Automatic Start of "B" Emergency Diesel Generator) was a similar event. The root cause of LER 88-008 was determined to be a random failure of an electronic component and no corrective action was deemed necessary to prevent recurrence. LER 90-015 (Safeguards Bus Undervoltage Relay Actuation Due to a Failed Solid State Switch Causes an Automatic Start of the "ALI Emergency Diesel Generator) was also a similar event. The root cause of LER 90-015 was determined to be a failure of an electronic component. Corrective action taken was to perform thermography on the failed solid state switch printed circuit board and then provide the results of this thermography to Electro-Mechanics, the system designer, for review. Based on the review of the thermography results by RG&E and Electro-Mechanics, modifications to the circuit design are being evaluated. Printed circuit card replacement intervals are also being evaluated.

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The above corrective action led to the root cause determination and corrective action for LER 91-007.

C. SPECIAL COMMENTS:

None.

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