ML20024H238

LER 91-003-01:on 910322,Div II Control Power Circuit Deenergized,Resulting in Deenergization of Charcoal Filter Train Suction Dampers.Caused by Inadequate Work Plan.Plan Revised to Document Restoration of wiring.W/910521 Ltr

ML20024H238
Person / Time
Site:	River Bend
Issue date:	05/21/1991
From:	England L, Odell W GULF STATES UTILITIES CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-003, LER-91-3, RBG-35-031, RBG-35-31, NUDOCS 9105300329
Download: ML20024H238 (4)

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May 21,1991 RIG. 35,031 Pile Nos. G9.5, G9.25.1.3 U. S. Nuclear Regulatory Cconission Docment Control Desk Washington, D.C. 20555 Centlenen:

River Bend Station - Unit 1 Docket No. 50-458 Please find enclosed Revision 1 to Licensee Pvent Report No.91-003 for River Bend Station - Unit 1. This revision is sulnitted because the Modification Request (MR) nunter provided in the orginal report, MR 90-0007, is incorrect. The correct designation is MR 90-0071.

Sincerely, gfbJt;J b~s s~r g;,. W. H. Odell Manager - Oversight River Bend Nuclear Group 76E/M fdl kgL UE/PDG/D?al/DCH/pj cc: U.S. Nuclear Regulatory Camtission 611 Ryan Plaza Drive, Suite 1000 Arlington, 'IX 76011 NRC Posident Insp3ctor P.O. Box 1051 St. Francisville, IA 70775 INPO Pacords Center 1100 Circle 75 Parkway Atlanta, CA 30339-3064 Mr. C.R. Oberg Public Utility Ccrmission of Texas 7800 Shoal Creek Blvd., suite 400 North Austin, TX 78757

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At 1055 on 3/22/91, during maintenance on the Division II control building local air intake radiation monitor 1RMS*RE13B, the Division II control power circuit was de-energized. This resulted j. the de-energization of the Division II charcoal filter train suction dampers lifVC* AOD19D and 111VC* AOD19F, and isolation of the air operated dampers (AODs) to the Division II air handling units, 1HVC*AOD6B and 1HVC*AOD8B. Note that dampers 19D and 19F were closed at the time of the event. The isolations resulted in a trip of the Division II control building ventilation system / chiller and automatic swap to the Division I ventilation system / chiller. This report is submitted pursuant to 10CFR50.73 to document the engineered safety feature (ESP) actuations described above. The event occurred during the implementation of Modification Recluest (MR) 90-0071. This MR specified l that the RM-80 mother board was to be removed from 1RMS*RE138. The root cause of this event is that the maintenance planner overlooked the 115VAC control power to the RM-80 mother board and thus, the potential for the ESF actuations.

' This event concerned the engineering / maintenance planning interface and responsibility. As previously reported in LER 90-033, Revision 2, a task force evaluation of this issue was performed and the task force recommendations are undergoing management evaluation. Following management review, LER 90-033 will again be revised to provide GSU's final disposition of this issue.

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0 l1 Ol 2 0F 0 l3 raren - . e m..,on REPORTED CONDITION At 1055 on 3/22/91, during maintenance on the Division II control building local air intake radiation monitor 1RMS*REl3D (

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, Division II control power circuit was de-energized. This resulted in the de-energization of the Division II charcoal filter train suction dampers (*DMP*) IHVC*AOD19D and JHVC*AOD19F, and isolation of the air operated dampers (*DMP*) (AODs) to the Division II air handling units, 1HVC*AOD6B and 1HVC*AOD88. Note that dampers 19D and 19F were closed at the time of the event. The isolations resulted in a trip of the Division II control building ventilation ( *VI * ) system / chiller and automatic swap to the Division I ventilation (*VI*) system / chiller.

This report is submitted pursuant to 10CFR50.73 to document the engineered safety feature (ESP) actuations described above.

INVESTIGATION The event occurred during the implementation of Modification Requent

(.M R) 90-0071. This modification was written to swap electronic l components between radiation monitors (

• RA * ) 1RMS*RE13B and 1RMS*RC14B in an effort to mitigate noise problems. This MR specified that the RM-80 mother board was to be removed from 1RNS*RE13B, The design ESF actuation of the unit had been disabled by disconnecting the vendor wiring from the neutral side connection on the control interface junction box. However, the 115 VAC control power supplied by circuit 1HVCB14 was left connected. The circuit overload apparently resulted from the removal of the RM-80 mother board while the control power was still connected. Fuse (*FU*) 1HVCD14-F2 failed, resulting in a loss of power to the components supplied by the control circuit and thus, the ESF actuations described above.

The root cause of this event is that the maintenance planner overlooked the 115VAC control power to the RM-80 mother board and thus, the potential for the ESF actuations. During the development of the work plan, lifting of the neutral lead was specified to defeat the design ESF actuation of 1RMS*RE13B. This is a standard practice when performing routine maintenance on the radiation monitors, and was a correct step in_this case. However, the removal of the RM-80 mother board is non-routine maintenance and required the additional step of

-isolating the control power. A contributing factor to the event was that voltage monitoring was not performed to ensure that the mother-board was not powered prior to removal.

A review of previous reports has identified three similar events. LER 90-033 identified an isolation of the reactor water cleanup (RWCU) system during modifications to power supply wiring in a control room panel. .LER 89-016 reported isolations of valves (*ISV*) 1 DER *AOV126 and 3DPR*AOV101 during a modification in panel (*PL*) IH13*P852. An engineering analysis completed prior to the implementation of the modification (to install an emergency operating procedure actuation swi+ch) did not rovnal tho nntoneial for ralnv 39-?-1790904 to renct

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0] q 3 0 l1 0l3 or 0 l3 rext . , . ..e , ms. .om before relay 3D-IISCB04 when the AC daisy chain neutral for the Division II BOP loss of coolant accident (LOCA) initiation circuit was reestablished. LER 90-035 reported a loss of shutdown cooling when a cable (*CBL3*) was disconnected from control room panel (*PL*)

1H13-P692. The system angineer prepared a cable-effects liet for a modification. This was caused by the system engineer not recognizing that the removal of the cable would result in the isolation of valve 1E12*MOVF009.

Each of these events concerned the engineering / maintenance planning interface and responsibility. As previously reported in LER 90-033, Revision 2, a task force evaluation of this issue was performed and the task force recommendations are undergoing management evaluation.

Following management review, LER 90-033 will again be revised to provide GSU's final disposition of this issue.

CORRECTIVE ACTION The immediate corrective action was the lifting of the vendor wiring to the hot side of circuit lHVCB1.. The work plan was revised to document correct removal and restoration of both the hot and neutral wiring.

Fuse 1HVCB14-F2 was replaced. The control building ventilation system was restored to its pre-event line-up by operations personnel.

All instrumentation and controls (I&C) personnel will be instructed on the actuation interfaces which are typical of the ESF digital radiation monitoring system (DRMS) units, and emphasis will be placed on the fact that lifting the neutral lead alone is not sufficient for non-routine maintenance such as mother board removal, ln addition, the associated condition report will be added to required reading for all I&C personnel and I&C planners. These corrective actions will be completed by 5/3/91.

In addition, the maintenance planning department has an ongoing enhancement program which will strengthen the planning process. A lead planner position has been created with the responsibility to review every package after it has been planned and b' fore it is incued to the field. This review is to ensure that the job plans are technically correct and that necessary precautions are in the package 7.

SAFETY ASSESSMENT The ESF actuations all occurred per design. The control room ventilation system automatically shifted to its redundant standby train, as designed. Therefore, this event did not adversely a f fect the health and safety of the public.

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