ML18100B298

LER 94-014-00:on 940426,SG 1-2 Automatically Started When Two Indicating Light Sockets Shorted Together Due to Personnel Error.Description of Event & Lessons Learned Will Be Published in Operations Incident Summary.W/940524 Ltr

ML18100B298
Person / Time
Site:	Diablo Canyon
Issue date:	05/24/1994
From:	RUEGER G M, SISK D P PACIFIC GAS & ELECTRIC CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
DCL-94-116, LER-94-014, LER-94-14, NUDOCS 9406010063
Download: ML18100B298 (7)

Text

... Pacific Gas am! Electric Gompany May* 24, 19-94 PG&E Letter DCL-94-11 6 77 Beale Strfft 1451 P.O.

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CA 9417' 41 :J/973-4684 Fax 415/973-2313 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Docket No. 50-275, OL-DPR-80 Diablo Canyon, Unit 1 Licensee Event Report 1-94-014-00 Gregory M. Rueger Senior Vice President and General Manager Power Generation Unplanned Diesel Generator Start (ESF Actuation)

When Two Indicating Light Sockets Shorted Together Due to Personnel Error Gentlemen:

Pursuant to 1 0 CFR 50. 73 (a)(2)(iv), PG&E is submitting the enclosed Licensee Event Report regarding an unplanned diesel generator start (ESF actuation) when, due to a personnel error during startup bus potential circuit indicating lamp replacement, two indicating light sockets shorted together, causing the circuit's protective fuse to open resulting in a loss of potential sensing voltage. Sincerely, cc: L. J. Callan Mary H. Miller Kenneth E. Perkins Sheri R. Peterson Diablo Distribution INPO Enclosure DC 1-94-0P-N026 64 7 2S/KWR/2246 9406010063 940524 PDR ADDCK 05000275 S PDR I ! ! i ii -I {I f l LICENSEE EVENT REPORT (LE-FACILITY NAME (11 I DOCKET NUMBER (21 I PAGE (31 Diablo Canyon, Unit 1 lo 5IOIOIOl217l5lll°F 6

Unplanned Diesel Generator Start (ESF Actuation)

When Two Indicating Light Sockets Shorted Together Due to Personnel.Error EVENT DATE (61 LER NUMBER !Bl REPORT DATE (71 OTHER FACILITIES INVOLVED (8) MON YR DAY YR SEQUENTIAL REVISION MON DAY YR NUMBER DOCKET NUMBER !SI FACILITY NAMES NUMBER 04 26 94 94 -0 I 1 I 4 -0 I 0 05 24 94 OPERATING MODE (9) 5 POWER I LEVEL <10 i o I o I o ....... ( . ..** ., ..............

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THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR: (11) ---'x"'--10 CFR 50.73Ca)(2)(iv)

___ OTHER ---------(Specify in Abstract below and in text,* NRC Form 366A) LICENSEE CONTACT FOR THIS LER (121 TELEPHONE NUMBER AREA CODE David P. Sisk; Senior Regulatory Compliance Engineer 805 545-4420 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (131 CAUSE SYSTEM COMPONENT MANUFAC-REPORTABLE

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CAUSE SYSTEM COMPONENT MANUFAC-REPORTABLE

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TURER TO NPRDS : : ) :: TURER I I I I I I I I* SUPPLEMENTAL REPORT EXPECTED (141

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• ... : .*.***** YEAR I I YES (if yes, complete EXPECTED SUBMISSION DATE) *1 X I NO EXPECTED SUBMISSION DATE (15) ABSTRACT (16) . 6472S On April 26, 1994, at 1332 PDT, with Unit 1 in Mode 5 (Cold Shutdown), Diesel Generator (DG) 1-2 automatically started from an apparent loss of the startup power source when the "C-phase" and "B-phase" potential transformer sensing circuits were inadvertently shorted together while an operator was replacing an indicating light bulb. This event constitutes an engineered safety feature (ESF) actuation.

The contra l room operators verified that auxiliary power was available and returned all equipment to normal status. A non-emergency report was made to the NRC in accordance with 10 CFR 50.72(b)(2)(ii) on April 26, 1994, at 1136 PDT. The root cause of this event is personnel error (noncognitive), due to a lack of knowledge concerning the task at hand, in that the operator was not aware that the ac potential circuits could be inadvertently shorted together while attempting to replace an indicating light bulb. This inadvertent short between the C-phase and the adjacent B-phase socket resulted in the C-phase secondary potential fuse opening. This caused the DG 1-2 circuitry to sense startup bus undervoltage (U/V), resulting in an inadvertent automatic start of the DG. The DG did not load onto the bus since auxiliary power to the vital 4160-volt bus was not interrupted and, therefore, no 4160-volt U/V was sensed. A description of the event and lessons learned will be published in an Operations Incident Summary and distributed to personnel involved in minor maintenance activities, such as replacement indicating bulb .

I --., LICENSEE EVENT REPORT (LER) TEXT cor9NuATION FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) TEXT (17) 6472S YEAR SEQUENTIAL . . REVISION NUMBER ,::*' NUMBER Diablo Canyon, Unit 1 o Is I o I o I o I 2 I 7 I s 94 -o I 114 -o Io 2 I OF I 6 I. Plant Conditions Unit 1 was in Mode 5 (Cold Shutdown) with an average reactor coolant system temperature less than 200 degrees Fahrenheit.

II. Description of Problem A. Summary On April 26, 1994, at 1332 PDT, with Unit 1 in Mode 5 (Cold Shutdown), Diesel Generator (DG) [EB][DG] 1-2 automatically started from an apparent loss of the startup power [EA] source when the 11 C-phase 11 and 11 B-phase 11 potential transformer

[EC][XPT]

sensing circuits [EC][CBL4]

were inadvertently shorted together, resulting in the C-phase secondary potential fuse [EC][FU] opening, while an operator was replacing an indicating light bulb [EC][IL].

This caused the DG 1-2 circuitry to sense startup bus undervoltage (U/V) [EA][27], resulting in an inadvertent automatic start of the DG. The DG did not load onto the bus since auxiliary power to the vital 4160-volt bus [EA][BU] was not interrupted.

This event constitutes an engineered safety feature (ESF) actuation.

The control room operators verified that auxiliary power [EA] was available and returned all actuated equipment to normal status. A four-hour, non-emergency report was made to the NRC in accordance with 10 CFR 50.72(b)(2)(ii) on April 26, 1994, at 1136 PDT: B. Background None. C. Event Description On April 26, 1994, by routine observation, a non-licensed electrical watch operator found the C-phase potential indicating light burned out on the 4160-volt breaker [EA][52] for the startup power source feeder to vital Bus G. In attempting to replace the indicating light bulb, the operator found it necessary to remove the retaining ring for the indicating light socket. While removing the retaining ring, the entire indicating light socket was rotated resulting in an inadvertent short of the C-phase socket to the adjacent B-phase socket. The C-phase secondary potential fuse opened as a result of the short. On April 26, 1994, at 0834 PDT, DG 1-2 sensed an apparent startup power source U/V and DG 1-2 cranking alarms annunciated in the main control room. Control room operators observed DG 1-2 start and achieve rated speed and voltage.

l -

LICENSEE cVENT REPORT {LER) TEXT CO-NUATION FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) TEXT (17) 6472S YEAR * .. :*. SEQUENTLAL j :<:::::::

REVISION I:::',:* NUMBER :/:\: NUMBER Diablo Canyon, Unit 1 On April 26, 1994, at 0905 PDT, control room operators placed DG 1-2 in manua 1 , defeated the automatic start .feature at the startup feeder breaker cubicle per the annunciator response procedure guidance, _and . DG 1-2 was shutdown and the control switch [EA][HS] returned to the "auto" position.

The safety injection and 4160-volt bus U/V starts are still enabled in this configuration.

Electrical maintenance investigation determined that the C-phase potential transformer fuse in the 4160-volt Bus G secondary potential sensing circuitry had opened. The opened fuse caused a loss of sensed potential on the startup power source, initiating a DG automatic start. The DG did not load onto the vital 4160-volt bus since the auxiliary power source was available and aligned to the vital 4160-volt Bus G for the duration of the event. The fuse was replaced and the startup feeder circuit DG 1-2 automatic start feature was returned to service. On April 26, 1994, at 1136 PDT, a four-hour, non-emergency report was made pursuant to 10 CFR 50.72(b)(2)(ii).

D. Inoperable Structures, Components, or Systems that Contributed to the Event None. E. Dates and Approximate Times for Major Occurrences

1. April 26, 1994, at 0834 PDT: Event Date/Discovery Date: Inadvertent start of DG 1-2 during indicating light bulb replacement.

2. April 26, 1994, at 1136 PDT: A four-hour, non-emergency report was made to the NRC in accordance with 10 CFR 50.72 (b)(2)(ii).

F. Other Systems or Secondary Functions Affected None. G. Method of Discovery The event was immediately apparent to plant* operators due to alarms and indications received in the control room. i 'i LICENSE VENT REPORT_ (LER) TEXT co91NUATION

'., FACILITY NAME (1) DDCKET NUMBER (2) LER NUMBER (6) PAGE (3) TEXT (17) 6472S YEAR SEQUENTlAL REVISKlN NUMBER I::{::\: NUMBER Diablo Canyon, Unit 1 H. Operator Actions DG 1-2 was placed in manual, the automatic start feature at the startup feeder breaker cubicle was defeated in accordance with the annunciator response procedure guidance, and DG 1-2 wis shutdown and the control switch returned to the "auto" position.

I. Safety System Responses DG 1-2 started but did not load onto.its associated 4160-volt bus since auxiliary power was available.

III. Cause of the Problem A. Immediate Cause The opened fuse caused a loss of sensed potential on the startup power source, initiating a DG automatic start. B. Root Cause The root cause of this event is personnel error (noncognitive), due to a lack of knowledge concerning the task at hand, in that the operator was not aware that the ac potential circuits could be inadvertently shorted together while attempting to replace an indicating light bulb. This inadvertent short between the C-phase and the adjacent B-phase socket resulted in the C-phase secondary potential fuse opening. This caused the DG 1-2 circuitry to sense startup bus U/V, resulting in an inadvertent automatic start of the DG. The DG did not load onto the bus since auxiliary power to the vital 4160-volt bus was not interrupted and, therefore, no 4160-volt U/V was sensed. C. Contributing Cause None. IV. Analysis of the Event Since all equipment performed as designed during this event, the inadvertent actuation of the DG ESF component did not adversely affect the health and safety of the public. V. Corrective Actions A. Immediate Corrective Actions The fuse was replaced.

LICENSE .::VENT REPORT (LER} TEXT coi9NUATION FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) TEXT (H) 64725 Diablo Canyon, Unit 1 o Is I o I o I o I 2 I 1 I s 94 -o I 114 -o Io

• s I OF I 6 B. Corrective Actions to Prevent Recurrence A description of the event and lessons learned was published in an Operations Incident Summary and distributed to personnel involved in minor maintenance activities, such as replacement of an indicating bulb. The summary described how much action an operator should take with regard to repair of a problem-indicating light and when to request Electrical Maintenance personnel involvement in the repair. VI. Additional Information A. Failed Components None. B. Previous LERs on Similar Problems LER 1-94-007, dated April 28, 1994, and LER 1-94-011, dated May 11, 1994, describe two events regarding a short-to-ground on the second level U/V sensing circuit for 4160-volt Bus H. This short-to-ground resulted in opening the potential transformer sensing circuit fuse, which started and *loaded the associated DG. The corrective actions for these LERs are related to preventing the short-to-ground and were under investigating at the *time of this event. Therefore, these corrective could not have prevented the current event. LER 2-91-001-00, dated July 15, 1991, describes an Instrumentation and Controls (I&C) technician inadvertently dropping a screw on the power switch for power supply NM51 while performing maintenance.

This resulted in a voltage transient to the output relays of radiation protection monitors RM-11 and RM-12, which caused a solid state protection system Train B CVI actuation.

The corrective actions to prevent recurrence included (1) counseling the technician regarding the necessity for establishing a temporary electrical . barrier when working around energized equipment, when practical, and (2) issuance of a maintenance bulletin that describes the event and discusses current policies and procedures applicable to performing work on energized equipment.

These corrective actions could not have prevented the current event since the maintenance bulletin was issued for I&C personnel only. The cause of the current event was a lack of knowledge concerning the task at hand, 1n that the operator was not aware that the ac.potential circuits could be inadvertently shorted together while attempting to replace an indicating light bulb.

LICENSEE EVENT REPORT (LER) TEXT CO-NUATION FACILITY NAME (l) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) VEAR L::::::: SEQUENTIAL 1:::::::::::

REVISION -r/{-NUMBER F:::::? NUMBER Diablo Canyon, Unit 1 o Is.I o I o I o I 2 I 7 I s 94 -o I 114 -o Io 6 I OF I 6 TEXT (17) 6472S LER 1-90-019-00, dated December 27, 1990, describes how a contract electrician was performing design modifications in an energized radiation monitor cabinet. As the electrician removed the pliers the cabinet, the pliers came in contact with the terminals on a fuse block, causing a voltage transient on an inverter, and ultimately resulting in a CVI. The root cause was determined to be personnel error in that if the electrician had taped the tool in accordance with standard work practices for in energized cabinets, electrical contact w.ith the fuse block may not have occurred.

A contributory cause was determined to be a previously issued maintenance bulletin regarding work on energized equipment, which recommends taping tools, had not been reviewed with *the technician.

Corrective actions included distributing and training on relevant maintenance bulletins to the general construction crews who also perform work on energized equipment within the plant. The corrective actions from this event concentrated on the use of tools within energized cabinets or in the vicinity of energized equipment.