ML20044H044

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LER 93-009-00:on 930504,circuit Breaker Did Not Close During Planned Bus Transfer Due to Loose Control Circuit Wire.Lug Replaced & Reterminated on 930505 & Post Work Testing Completed W/Satisfactory results.W/930602 Ltr
ML20044H044
Person / Time
Site: Pilgrim
Issue date: 06/02/1993
From: Boulette E, Ellis D
BOSTON EDISON CO.
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
BECO-93-071, BECO-93-71, LER-93-009, LER-93-9, NUDOCS 9306070280
Download: ML20044H044 (9)
v • d • e


Text

/, *A 8 10 CFR 50.73 BOSTON EDISON Pilgrim Nuclear Power Station Rocky Hil! Road Plymouth, Massachusetts 02360 E. T. Boulette, PhD senior Vice President-Nuclear

,r June 2, 1993 BEco Ltr.93-071 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555 Docket No. 50-293 License No. DPR-35 The enclosed Licensee Event Report (LER) 93-009-00, " Circuit Breaker Did Not Close During Planned Bus Transfer due to Loose Control Circuit Wire", is submitted in accordance with 10 CFR Part 50.73.

Please do not hesitate to contact me if there are any questions regarding this report.

O LLN C E. T. Boulette DWE/bal Enclosuro: LER 93-009-00 cc: Mr. Thomas T. Martin Regional Administrator, Region I U.S. Nuclear Regulatory Commission 475 Allendale Rd. ,

King of Prussia, PA 19406 Mr. R. B. Eaton Div. of Reactor Projects I/II  !

Office of NRR - USNRC  ;

One White Flint North - Mail Stop 14D1  !

11555 Rockville Pike Rockville, MD 20852 i

Sr. NRC Resident Inspector - Pilgrim Station l Standard BEco LER Distribution i

9306070$80935602 // I PDR ADOCK 05000293 /. i S PDR // I '

I NRC FORM,366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150-0104 (5-921 EXPIRES 5/31/95 EST: MATED BURDEN PER RESPONSE TO COMPT.Y W!TH THIS LICENSEE EVENT REPORT (LER) l"Su"#5b'n%"J%*0Jf0 T%rs%^2 AND RECORDS MANAGEMENT BRANCH (MNB8 7714), U.S. NUCLEAR FIEGULATORY COMMISSION, WASHINGTON, DC 20S55-0001, AND TO THE PAPERWORK REDUCTON PROJECT (3150-0104), OFFICE (See severse tof number of digfts/chareders for each W.u) OF MANAGEMENT AND BUDGET, WASHINGTON, DC 20501 FACILITY NAME (1) DOCKET NUMBER (2) PAGE (3)

PILGRIM NUCLEAR POWER STATION 05000 - 293 1 of 8 TITLE (4)

Circuit Breaker Did Not Close During Planned Bus Transfer due to Loose Control Circuit Wire EVENT DATE (5) LER NUMBER (6) REPORT DATE (7) OTHER FACILITIES INVOLVED (8)

SEQUENTIAL REVISION FACluTY NAME DOCKET NUMBER

.' MONTH DAV YEAR YEAR NUMBER NUMBER MONTH DAV YEAR N/A 05000 F ACluTY NAME DOCKET NUMBER 05 04 93 93 009 00 06 02 93 N/A 05000 OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR 6: (Check one or more)(11)

OI 20.402(b) 20.405(c) 50.73(a)(2)(iv) 73 71(b) 000 20.405(aH1W 50mW SoMaH2W 73 M e)

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_ 20.405(aH1)0i) 50.36(c)(2) X 50.73(a)(2)(vii) (D) OTHER 20.405(a)(1)(iii) 50.73(a)(2)(i) 50.73(a)(2)(viii)(A) 20.405(a)(1)(iv) 50.73fa)(210i) 50.73(a)(2)(viii)(B) Ac 20.405ta)(1)(v) 50.73(a)(2)(iii) 50.73(a)(2)(x) Form 3f4A)

LICENSEE CONTACT FOR THIS LER (12)

NAME TD.EPHONE NUMBER (Include Area Codel Douglas W. Ellis - Senior Compliance Engineer (508) 747-8160 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE SYSTEM COMPONENT MANUFACTURER S CAUSE SYSTE'M COMPONENT MANUFACTURER S X EC 52 G080 Y SUPPLEMENTAL REPORT EXPECTED (14) " "

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EXPECTED YES NO SUBMISSION (tf yes, comp 6m EXPECTED SUBMIS3ON DATE) x DATE (15)

ABSTRACT On May 4, 1993, at 0230 hours0.00266 days <br />0.0639 hours <br />3.80291e-4 weeks <br />8.7515e-5 months <br />, a safety-related 480 VAC load center bus that is part of a safety-related bus transfer scheme became de-energized during a planned bus transfer conducted while shut down. The related motor control centers became de-energized including the motor control center of the valves that are part of the Residual Heat Removal (RHR) System / Low Pressure Coolant Injection (LPCI) function. At the time of the event, the RHR/LPCI function was not required to be operable. The bus was re-energized at 0235 hours0.00272 days <br />0.0653 hours <br />3.885582e-4 weeks <br />8.94175e-5 months <br />.

The cause of the bus and related components becoming de-energized was circuit breaker 52-102, that is part of the transfer scheme, not closing during the transfer. The cause of breaker 52-102 not closing was a loose wire-to-lug connection in the automatic transfer portion of the circuitry that controls the breaker. Corrective action taken included replacement of the lug. The bus transfer function was subsequently tested with satisfactory results.

The event occurred while shut down in a refueling outage. The Reactor Vessel (RV) head was not installed. The reactor mode selector switch was in the REFUEL position. There was no movement of a fuel assembly or fuel cask at the time of the event. This report is submitted in accordance with 10 CFR 50.73(a)(2)(vii)(D). This event posed no threat to the public health and safety.

NHC F ORM :p%A @92;

NRO FORM 366A U.S. NUCLEAR REGULATORY COMMisslON APPRoVEo BY OMB NO. 3150-0104 u-9 n , EXPIRES 5/31/95 ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH THIS LICENSEE EVENT REPORT (LER) LTZEG'"JSERIMCJkZ*,~FOT2 TEXT CONTINUATION #$UEOYRCCESSEN R NGTON 5 A TO THE PAPERWORK REDUCTION PRC11ECT (315CHn04), OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON, DC 20503.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3)

YEAR R NM PILGRIM NUCLEAR POWER STATION 05000-293 93 009 00 TEXT (if more space is required, use additional copies of NRC Form 366A)(17)

BACKGROUND Safety-related load center Bus B6 is a 480 VAC swing type bus that can be powered by Bus B1 or B2. Bus B1 is the normal power source for Bus B6 with breakers52-102 and 52-601 in the CLOSED position and with breakers52-202 and 52-602 in the OPEN position. Circuit breakers 52-102/52-202 and 52-601/52-602 are interlocked to preclude Bus B6 from being simultaneously powered by Bus B1 and Bus 82. The interlocks of breakers 52-102/52-202 are independent of the interlocks of breakers 52-601/52-602. Located at the end of this report is a figure depicting a simplified single line diagram of the emergency service portion of the Auxiliary Power Distribution System including the Bus B6 transfer breakers.

The Bus B6 automatic transfer scheme is as follows:

  • If Bus B1 was powering Bus B6 and Bus B1 were to experience a loss of voltage for approximately one second and sufficient Bus B2 voltage is available, breaker 52-102 opens and 52-202 closes, and 52-601 opens and 52-602 closes.

Bus B6 would then be energized from Bus B2.

  • If Bus 82 was powering Bus B6 and Bus B2 were to experience a loss of voltage for approximately one second and sufficient Bus B1 voltage is available, breaker 52-202 opens and 52-102 closes, and 52-602 opens and 52-601 closes.

Bus B6 would then be energized from Bus Bl.

  • If both Bus 81 and Bus 82 were to experience a loss of voltage for approximately one second, the two breakers in the CLOSED position would open and all four transfer breakers would then be in the OPEN position. Depending upon which Bus (B1 or B2) subsequently becomes energized, the related breakers would close and Bus B6 would then be energized.

The source of control power for the four Bus B6 transfer circuit breakers is via 125 VDC Bus D6 that is supplied from 125 VDC Bus D16 or Bus D17 through an automatic transfer switch (Y10). This configuration makes the control power for the circuit breakers highly reliable and independent of the 480 VAC buses. ,

1 SYSTEMS CONFIGURATIONS PRIOR TO THE EVENT Just prior to the event, the following systems configurations existed:

  • The reactor mode selector switch was in the REFUEL position. Some fuel assemblies were not installed in the core. The control rods were fully '

inserted for the core locations where fuel was installed. The Reactor Vessel (RV) water temperature was approximately 75 degrees Fahrenheit. There was no movement of a fuel cask or irradiated fuel.

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NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150-0104 n-m EXPIRES 5/31/95 ESTlMATED BURDEN PER RESPONSE TO COMPLY WITH THIS LICENSEE EVENT REPORT (LER) 10^%T2 S L "EN% C # O Oi d TT%

TEXT CONTINUATION $"ETOYRC I[S5"EN S N O 0 A TO THE PAPERWORK REDUCTION PROJECT (3150-0104h OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON, DC 20503.

FACILITY N AME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3)

YEAR B N 3 0f 8 PILGRIM NUCLEAR POWER STATION 05000-293 93 009 00 TEXT (It more space is required, use additional copies of NRC form 366A)(17)

  • Safety-related 4160 VAC Buses A5 and A6 and 480 VAC Buses B1, B2, B6 and its related electrical system were energized. Bus B6 was being powered from Bus B2. The Emergency Diesel Generator 'B' was in standby service. EDG 'A' was not available for service because of maintenance activities.
  • The Salt Service Water (SSW) System Loop 'B' pump P-2080 was in service providing cooling water to the RBCCW Loop 'B' heat exchanger. The SSW Loop 'B' pump P-208E was in standby service. The SSW System Loop 'A' pumps were not in service because of Loop 'A' piping replacement. The Loop 'A'/'B' swing pump P-208C was in standby service and available for Loop 'B' service.
  • The 345 KV switchyard ring bus was energized via transmission lines 342 and 355. The air type circuit breakers 102, 103, 104 and 105 were closed. The 4160 VAC Buses that were in service were energized via the Startup Transformer.

The Unit Auxiliary and Shutdown Transformers were in standby service.

EVENT DESCRIPTION On May 4, 1993, at 0230 hours0.00266 days <br />0.0639 hours <br />3.80291e-4 weeks <br />8.7515e-5 months <br />, 480 VAC load center Bus B6 became de-energized. The bus became de-energized because circuit breaker 52-102 did not close automatically as designed during a planned transfer conducted while shut down. Circuit breaker 52-102 was manufactured by the General Electric Company, type AK-2A-50-1 modified with a Micro-Versa trip unit.

The transfer was being conducted in accordance with step 4 of procedure 3.M.3-35 (Rev. 14)

Attachment 24, " Automatic Dead Bus Transfer From B2 to 81 Supplying B6 - By Pulling B2 PT Fuses". For this step, the secondary fuses of the potential transformers for Bus 82 were ,

removed from their installed locations. The removal causes the control circuitry to sense  ;

a loss of voltage on Bus B2. The removal of the fuses should have resulted in the  !

automatic opening of breakers52-202 and 52-602 and the automatic closing of breakers j 52-102 and 52-601. Breaker 52-202 opened but its related transfer breaker (52-102) did >

not close. Meanwhile, breaker 52-602, in-series with breaker 52-202 from Bus B2 to Bus i B6, opened automatically and its related transfer breaker (52-601) closed automatically as l designed. This configuration resulted in safety-related Bus B6 becoming de-energized because the in-series feeder breakers from Bus B2 to Bus B6 were open and one in-series feeder breaker from Bus B1 to B6 was open.

The loss of power to 480 VAC Bus 86 resulted in a loss of power to the following:  !

  • 480 VAC MCC-810 that provides power to equipment including SSW pump P-208C.

. 480 VAC MCC-B20 that provides power to equipment including: i l

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i NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPRO'!ED BY OMB NO. 3150-0104 n-m EXPIRES 5/31/95 ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH THIS LICENSEE EVENT REPORT (LER) Clu%7'2"mGJ" G B Ro5 EAT O INF M TEXT CONTINUATION $$u" Ness"cISTE"[0A[s[$dN TO THE PAPERWORK REDUCTION PROJECT (31540104), OF FICE OF M ANAGEMENT AND BUDGET, WASHINGTON, DC 20503.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) vEAR SOEP "duS?%

4 of 8 PILGRIM NUCLEAR POWER STATION 05000-293 93 009 00 TEXT Of more space is required, use additional copies of NRC Form 366A)(17)

. RHR System Valves:

. Inboard injection valves M0-1001-29A/B (normally closed). This would cause the RHR loops ' A' and 'B' to be inoperable for the Low Pressure Coolant Injection (LPCI) mode.

  • Outboard injection valves M0-1001-28A/B (normally open).

. Recirculation System Loops ' A' and 'B' pump suction and discharge valves. This could also cause the RHR/LPCI function to be inoperable.

Breaker 52-102 was closed via its control switch at Bus 81 and Bus B6 was re-energized via Bus B1 at approximately 0235 hours0.00272 days <br />0.0653 hours <br />3.885582e-4 weeks <br />8.94175e-5 months <br />.

Problem Report 93.9215 was written to document the event.

CAUSE Bus B6 became de-energized because breaker 52-102 did not close during the transfer. The cause of breaker 52-102 not closing was a loose wire-to-lug connection in the breaker's control circuit. The wire is located in the time delay portion of the control circuit that permits breaker 52-102 to close automatically. The wire is connected in parallel with the control switch that permits breaker 52-102 to be closed manually. The wire is not lifted and the terminal is not jumpered for Bus B6 transfers.

CORRECTIVE ACTION The lug was replaced and reterminated on May 5,1993. Post work testing was completed with satisfactory results on May 5, 1993, at 0140 hours0.00162 days <br />0.0389 hours <br />2.314815e-4 weeks <br />5.327e-5 months <br />. The testing was conducted in accordance with procedure 3.M.3-35 (Rev. 14) Attachment 24.

The root cause analysis had not been completeo when this report was submitted. If the analysis identifies other corrective actions, the actions will be tracked via the Problem Report process.

SAFETY CONSE0VENCES The de-energizing of 480 VAC Bus 86 posed no threat to the public health and safety.

NRC FORM 366A {5 92)

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NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISslON APPROVEo BY OMB NO. 3150-0104 n-m , EXPIRES 5/31/95 EST1 MATED BURDEN PER RESPONSE TO COMPLY WITH THIS ]

LICENSEE EVENT REPORT (LER) 2""G*"EGOMTERc!M*LAT M RM T TEXT CONTINUATION S u" S

  • E E0EN S GT DC 0 1 TO THE PAPERWORK REDUCTON PROJECT (3150-0104), OFFCE OF MANAGEMENT AND BUDGET, WASHINGTON, DC 20503.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3)

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YEAR Ma PILGRIM NUCLEAR POWER STATION 05000-293 93 009 00 TEXT Cf more space is required, use additional copies of NRC Form 366A)(17)

The Core Standby Cooling Systems (CSCS) consist of the High Pressure Coolant Injection (HPCI) System, Automatic Depressurization System (ADS), Core Spray System, and the RHR System /LPCI mode. The HPCI System provides high pressure core cooling. The Core Spray System (Trains ' A' and 'B') and the RHR/LPCI mode are each capable of independently providing low pressure core cooling if necessary. In the event low pressure core cooling was necessary and Bus B6 was or were to become de-energized, the operability of the RHR/LPCI valves, powered by 480 VAC power from Bus B6, would be affected. However, the Core Spray System would be available to provide core cooling by each of the system's two 100 percent capacity Trains ('A' and 'B'). The Core Spray pumps 'A' and 'B' are powered by safety-related 4160 VAC Bus A5 and A6, respectively. The Core Spray Train 'A' suction and injection valves are powered from 480 VAC Bus B1 via MCC-B17. The Core Spray Train

'B' suction and injection valves are powered from 480 VAC Bus B2 via MCC-B18. The Core Spray channel ' A' circuitry is powered from 125 VDC control Bus ' A' via Distribution Panel

'A' (Bus D4). The Core Spray channel 'B' circuitry is powered from 125 VDC control Bus

'B' via Distribution Panel 'B' (Bus DS). This design ensures a failure of one 125 VDC supply would not affect the other power supply and, therefore, the failure would not cause the failure of both Core Spray Trains. Because no loads associated with the Core Spray '

System are connected to Bus B6 or to the 125 VDC Distribution Panel 'C' (Bus D6), a loss of power of Bus B6 or Bus D6 would not cause a failure of either Core Spray Train.

Overload protection is provided on both of the series connected Bus 86 tie breakers52-102 and 52-601 (52-202 and 52-602). Thus, a fault on Bus B1 would not cause the loss of Bus 82 or B6, or a fault on Bus 82 would not cause the loss of Bus 81 or B6. A loss of Bus B6 would not cause the loss of Bus B1 or B2.

This report is submitted in accordance with 10 CFR 50.73(a)(2)(vii)(D) because the normally-closed RHR/LPCI Loops ' A' and 'B' injection valves (MO-1001-29A/B) would not have opened for the RHR/LPCI function and because the normally-open Recirculation System Loops

' A' and 'B' suction and discharge valves would not have closed for the RHR/LPCI function.

For this event, the operability of the RHR/LPCI function was not required.

SIMILARITY TO PREVIOUS EVENTS A review was conducted of Pilgrim Station Licensee Event Reports (LERs). The review focused on LERs involving an instance of Bus B6 becoming similarly de-energimi, or involving a loose wire. The review identified related events reported in LERs 50-293/87-005-00, 90-005-01, and 91-019-00.

LER 87-005-00 involved breaker 52-102 not closing because a jumper was not installed while breaker 52-202 was removed from its cubicle for maintenance. LER 90-005-01 involved the failure of breaker 52-202 to open during a planned transfer of Bus 86. LER 92-019-00 involved the failure of breaker 52-602 to close during a planned transfer of Bus B6. No LERs submitted since 1984 involved a loose wire.

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EXPIRES 5/31/95 ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH THIS LICENSEE EVENT REPORT (LER) 1 "I 0s"R 2 'f i"Rc T s" M f0 0 N a u %

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FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3)

YEAR 6 Of 8 PILGRIM NUCLEAR POWER STATION 05000-293 93 009 00 TEXT (rf more space is required, use additional copies of NRC Form 366A)(17)

For LER 87-005-00, Bus B6 became de-energized while shut down on March 31, 1987 at 0845 hours0.00978 days <br />0.235 hours <br />0.0014 weeks <br />3.215225e-4 months <br /> due to a loss of preferred offsite power (345 KV) during a storm. At the time of the event, Bus B6 was energized from Bus B1 and breaker 52-202 was not installed in its cubicle because it was being overhauled. The EDG 'A' was in standby service and EDG 'B' had been removed from service for planned maintenance. The 345 KV preferred offsite power sources, transmission lines 342 and 355, were energized. The mechanical disconnects for the switchyard air circuit breaker ACB-102 were in the OPEN position because ACB-102 had ,

been removed from service for maintenance. The switchyard air circuit breakers ACB-103, and ACB-104, and ACB-105 were closed. The loss of preferred offsite power resulted in the automatic opening of ACBs 103 and 104 and a loss of voltage to the 4160 VAC Buses, including A5 and A6, and the 480 VAC Buses including B1, B2, and B6. The EDG 'A' started automatically and re-energized Bus A5 and related electrical system as designed approximately 10 seconds later. Meanwhile, the Bus B6 transfer control circuitry, sensing a loss of voltage on Bus B1 for greater than one second, caused breakers52-102 and 52-601 to open automatically. Breaker 52-601 reclosed automatically as a result of Bus B1 becoming re-energized. Concurrently, Bus A6 (and Bus B2) remained de-energized because EDG 'B' was not available for service. Bus B6 remained de-energized and breaker 52-102 did not reclose automatically because a jumper had not been installed in the control circuit when breaker 52-202 was removed from its cubicle for maintenance (overhaul).

After a jumper was installed, breaker 52-102 automatically closed and, with breaker 52-601 in the CLOSED position, Bus B6 was re-energized at 1027 hours0.0119 days <br />0.285 hours <br />0.0017 weeks <br />3.907735e-4 months <br />. The cause of the loss of preferred offsite power was a transmission line 342 fault that was due to the storm. The cause of breaker 52-102 not reclosing was that a detailed review of the control circuitry was not performed while preplanning the removal of breaker 52-202 for maintenance.

For LER 90-005-01, Bus B6 became de-energized during a planned Bus B6 transfer while shut .

down on March 20, 1990 at 1750 hours0.0203 days <br />0.486 hours <br />0.00289 weeks <br />6.65875e-4 months <br />. The transfer was being conducted in accordance with ,

step 4 of procedure 3.M.3-35 (Rev. 10) Attachment 24, " Automatic Dead Bus Transfer From B2 to B1 Supplying B6 - By Pulling B2 PT Fuses". Breaker 52-202 failed to open automatically as designed during the transfer and consequently its related transfer breaker (52-102) did not close. Meanwhile, breaker 52-602 opened as designed and its related transfer breaker (52-601) closed. Consequently, Bus B6 became de-energized because one in-series breaker in each of the two feeder circuits (from Bus B1 to Bus B6 and from Bus B2 to Bus B6) was in the OPEN position. The failure of breaker 52-202 to open resulted in the failure of its trip coil. Bus B2 was intentionally de-energized in response to the event and was re-energized at 1825 hours0.0211 days <br />0.507 hours <br />0.00302 weeks <br />6.944125e-4 months <br /> after breaker 52-202 was tripped and removed from its cubicle.

Breaker 52-202 failed to open because its latch prop, that is part of the breaker's trip mechanism, was misaligned due to the absence of a retainer ring. The cause of the missing retainer ring could not be determined with certainty. Corrective action taken included offsite inspection, overhaul, and testing of breaker 52-202 by the manufacturer, and onsite inspection, overhaul, and testing of similar breakers by manufacturer and utility personnel. Circuit breaker 52-202 was manufactured by the General Electric Company, type AK-2A-50-1 modified with a Micro-Versa trip unit, serial number 224All26-312-AE-1.

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q, f NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPRO'!ED BY OMB NO. 3150-0104 u-m EXPIRES 5/31/95 ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH THIS LICENSEE EVENT REPORT (LER) l%MMEs" RECT S L 1 $ LTMO O J Efe" TEXT CONTINUATION Eu"EORv OcEs's*fw"$S"oT7DC$sso"oN TO THE PAPERWORK REDUCTION PROJECT (3150 0104), OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON, DC 20503.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3)

YEAR M PILGRIM NUCLEAR POWER STATION 05000-293 93 009 00 TEXT pt more space is required, use additionat copies of NRC Form 366A)(17)

For LER 91-019-00, Bus B6 became de-energized during a planned Bus B6 transfer while shut down on May 25, 1991 at 0215 hours0.00249 days <br />0.0597 hours <br />3.554894e-4 weeks <br />8.18075e-5 months <br />. Breaker 52-602 did not close automatically as designed during the transfer. The transfer was being conducted in accordance with step 4 of procedure 3.M.3-35 (Rev. 12) Attachment 23, " Automatic Dead Bus Transfer From Bl to B2 Supplying B6 - By Pulling B1 PT Fuses". For the step, the secondary fuses of the potential transformers for Bus B1 were removed from their installed locations. The removal of the fuses should have resulted in the automatic opening of breakers52-102 and 52-601, and the automatic closing of breakers52-202 and 52-602. Breaker 52-601 opened -

automatically but breaker 52-602 did not close. Meanwhile, breaker 52-102 opened -

automatically and its related transfer breaker 52-202 closed automatically as designed.

This configuration resulted in Bus B6 becoming de-energized because breakers52-102 and 52-601 from Bus Bl to Bus B6 were open, and breaker 52-602 from Bus B2 to Bus B6 was open.

The cause of breaker 52-602 not closing was interference between the breaker trip latch roller assembly and clevis pin. The interference was similar to that documented in Service Advice Letter (SAL) 306.0, issued on May 1, 1991. A 10 CFR Part 21 report regarding the breaker was submitted to the NRC on July 26, 1991. Corrective action taken included breaker repair by General Electric personnel. The repair included machining the trip latch roller assembly and clevis pin to establish the clearance described in SAL 306.0. Circuit breaker 52-602 was manufactured by the General Electric Company, type AK-2A-50-1 modified with a Micro-Versa trip unit, serial number 0224A1126-310-AE-2.

ENERGY INDUSTRY IDENTIFICATION SYSTEM (Ells) CODES The Ells codes for this report are as follows:

COMPONENTS CODES Bus BU Circuit Breaker (52-102), AC 52 SYSTEMS Low-Voltage Power System EC Residual Heat Removal System (RHR/LPCI) B0 NAC FORM 304A (5 9?)

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i NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO,3150-0104 I t s-m EXPIRES 5/31/95

, j EST! MATED BURDEN PER HESPONSE TO COMPLY WTTH THIS INFORMATON COLLECTION REQUEST: 50.0 HRS. FORWARD LICENSEE EVENT REPORT (LER) COMMENT 3 REGARDING BURDEN EST! MATE TO THE INFORMATION AND RECORDS MANAGEMENT BRANCH (MN98 7714), U.S. NUCLEAR TEXT CONTINUATION REGULATORY COMMISSON, WASHINGTON, DC 20555-0001, AND TO THE PAPERWORK REDUCTON PRuJECT (3150-0104), OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON, DC 20503.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3)

SEQUENTIAL REVISION vEAR NuusER NuuseR PILGRIM NUCLEAR POWER STATION 05000-293 8d8 93 009 00 TEXT (tt more space is required, use additional copies of NRC Form 366A)(17) l STATICN ,

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