ML19351A676

LER 89-038-00:on 891113,unplanned Loss of Div I 125 Volt Dc Bus Occurred.Caused by Failure to Adequately Verify Clearance Boundaries.Power Restored to Bus & Isolations reset.W/891213 Ltr

ML19351A676
Person / Time
Site:	River Bend
Issue date:	12/13/1989
From:	Booker J, England L GULF STATES UTILITIES CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-038, LER-89-38, RBG-31941, NUDOCS 8912200435
Download: ML19351A676 (4)

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!? U.S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555 h Gentlemen: ,

', River Bend Station - Unit 1-Docket No. 50-458 h Please find- enclosed , Licensee Event Report. No.89-038,

" Unplanned-Loss of the Division I 125.VDC Bus" for River Bend Station - Unit 1. - This report is being submitted pursuant to 10CFR50.73.  ;

l-Sincerely,

. ( h<bb a J. E. Booker Manager-River Bend Oversight River Bond Nuclear Group n *) 01 ha, Cib JEB/TFP/RGW/DCH/RLR/ch cc U.S. Nuclear Regulatory Commission 611-Ryan Plaza Drive, Suite 1000 Arlington, TX 76011 i

NRC Resident Inspector P.O Box 1051=

St. Francisville, LA 70775 INPO Records' Center 1100 Circle 75 Parkway Atlanta, GA 30339-3064 6

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At 2236 on 11/13/89 with the plant in Operational Condition 1, at 96 percent power, an unplanned losn of ENB*SWG01 A, Division I 125 VDC bus occurred. Power was restored to the bus in three minutes.

Appropriate engineered safety feature systems responded to the de-energization and re-energization of the bus.

The investigation that followed this event revealed that personnel failed to adequately verify clearance boundaries and correctly l implement the applicable procedure. Corrective actions have been implemented to address this matter. Since the safety systems properly responded to the electrical transient and operations personnel restored the bus in a timely manner, this event had no impact on the health and safety of the public.

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0D 0 12 OF 0D RIPOR E [O $ TiO Y At 2236 on 11/13/89 with the plant in Operational Condition 1, at 96 percent power, an unplanned loss of ENB*SWG01A, Division I 125 VDC bus occurred. Power was restored to the bus in three minutes. The loss of the bus actuated the logics for the following isolations and initiations:

I -* Balance-of-plant (BOP) Division I isolation Reactor water cleanup (RWCU) system Division I loslation

• Reactor core isolation cooling (RCIC) syctem Division I isolation Auto-start of Division I containment monitoring system The isolations indicated above created low flow conditions which caused auto-starts of the following systems:

• Fuel building filter trains A and B

• Division II stand-by gas treatment (59GT) and annulus mixing systems

. The re-energization of the bus re-energized RCIC instrumentation. The re-energization of the instrumentation provided initiation signals which caused the following:

• RCIC auto-start The Division I SBGT and annulus mixing system did not start when the

' bus was de-energized due to a loss of control power. When the bus was re-energized, these Division I systems did not start due to the other train already running.

The loss of ENB*SWG01A, Division I 125 VDC bus (*BU*), occurred during a planned Division I diesel generator (*DG*) outage. Electrical Maintenance was preparing to perform maintenance on battery charger

(*BYC*) ENB*CHGRIA which required it to be electrically tagged out of l service. The tag out of the charger caused the loss of the bus when both the 480V supply breaker (*BKR*) to the charger, EJS*SWG1A-ACB010 l and the Division I battery output breaker ENB*SWGIA-ACB561 were racked out at the same time.

This event resulted in the actuation of engineered safety features (ESFs). Therefore, this report is hereby submitted pursuant to 10CFR50.73 (a) (2) (iv' .,

l-INVESTIGATION Preventive Maintenance Work Order (PMWO) P53214 authorized preventive' maintenance on ENB*CHGRIA that was scheduled by Electrical Maintenance for the night shift on 11/13/89. The electrical foreman responsible for the work filled out a clearance after reviewing the prints for l

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O 10 0 13 0F 0 13 fintn . =ac - m m on personnel safety. The operator attempted to de-energize the charger by implementing the clearance. However, the clearance boundaries were not adequately verified. The operator also failed to correctly implement the operating procedure for removing the charger from service or transferring the switchgear to an alternate charger (SOP-0049). Correctly using SOP-0049 for removing the charger from service or transferring the switchgear to an alternate charger would have alerted the operator to open ACB560 instead of ACB561. Opening ACB560 would have isolated the charger only, whereas ACB561 isolated the batteries from the bus. A meeting was held in the control room to discuss the events and both the operator and the electrical foreman admitted they had looked over the prints and had missed the fact that this clearance would isolate the entire bus instead of just the charger.

A review of previously submitted LERs found that a similar_ event was reported in LER 89-012 submitted June 30, 1989. In this event, RHR shutdown cooling was lost while the plant was in a shutdown condition.

The ESF actuation was due to a loss of power to the Division II isolation logic when an operator opened the breaker supplying the logic system. The operator was hanging a clearance tag for maintenance and the documents he was using failed to identify the isolation of RHR shutdown cooling.

CORRECTIVE ACTION Corrective action to restore the bus took three minutes. Following restoration of the bus, all isolations and actuations were reset and all systems were returned to a standby lineup. A caution statement has been added to Preventive Maintenance Procedure, (PMP)-1045, i

" Quarterly Maintenance on Battery Chargers", to state " ensure tagout of the charger does not isolate the bus." Additionally, all Category I charger preventive maintenance tasks have had the breakers added which need to be tagged for maintenance. A near miss investigation was held to discuss this error. The major contributing factors to this event were human error and failure to follow the procedure. All tagging requestors and officials shall receive additional training on this event by February 13, 1990.

SAFETY ASSESSMENT The actuations of the safety systems occurred as a result of de-energizing and re-energizing the Division I 125 VDC bus. Since the safety systems properly responded to this electrical transient and control room personnel restored the plant in a timely manner, there was no impact on the health and safety of the public. ,

NOTE: Energy Industry Identification System Codes are identified in the text as (*XX*).

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