ML19325D493

LER 89-033-00:on 890916,electrical Power Lost to Div II 120 Volt Ac Distribution Panel,Resulting in auto-start of Div II Standby Gas Treatment & Annulus Mixing Sys.Caused by Failure of Elgar Power Line Conditioning transformer.W/891016 Ltr

ML19325D493
Person / Time
Site:	River Bend
Issue date:	10/16/1989
From:	Booker J, England L GULF STATES UTILITIES CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-033, LER-89-33, RBG-31628, NUDOCS 8910240256
Download: ML19325D493 (6)

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• ( A f.(IDL edd ()$ hD14 $ (H (,1 9 October 16 e 1989 RBG- ?.1678 File Nos. G9.5, G9.25.1.3 U.S. Nuclear Regolatory Commission Document Control Deck Washington, D.C. 20555 Gentlemen:  !

River Bend Station - Unit 1 I Docket No. 50-458 Please find enclosed Licensee Event Report No.89-033 for i River Bend Station - Unit 1. This report is being submitted pursuant to 10CFR50.73.

Sincerely,  ;

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J. E. Booker t Manager-River Bend Oversight JEB/T P/ G fEC/ch cc 'J . S . Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 1000 Arlingcon, TX 76011 ,.

NRC Res!. dent Inspector  !

P.O. Box 1053  :

St. Francisville, LA 70775  :

INPO Records Center 7 1100 circle 75 Parkway t Atlanta, GA 30339-3064 ,

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o. eve, b~o Ol2 01 2 9 10 At approximately 0900 on 9/16/89 with the unit in Operational Condition 1 at 100 percent power, electrical power was lost to l Division II 120VAC distribution panel ISCM*PNLO18. Loss of power to l

this panel resulted in the auto-start of the Division II standby gas treatment and annulus mixing systems and the Division II fuel building filter train. Additionally, the reactor building floor and equipment dtain isolation valves isolated, inboard (Division II) reactor water cleanup isolation valves isolated, reactor water sampling system l

isolation valve clcsed, auxiliary building equipment drains isolated and instrument air to the containment air locks isolated. A half isolation signal of the main steam isolation valves occurred and several Division II systems were declared inoperable for various reasons. Several Division II status lights and annunciators were also inoperable.

The cause of the power loss w6s determined to be the failure of an Elgar power line conditioning transformer ISCM*XRC14hl. The root cause of the failure is indeterminate at this time, however, GSU's investigation is continuing. Upon completion of this investigation, a supplemental report will be provided.

Since all plant systems were verified to have performed as designed, there was no impact on the health and safety of the public as a result of this event.

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vant gggamwi At approximately 0900 on 9/16/89 with the unit in Operational  :

Condition 1 at 100 percent power, electrical power was lost to 120VAC ,

distribution (*ED*) panel (*PL*) ISCM*PNLO1B. This is a Division II electrical distribution panel which distributes power to numerous ,

Division II loads from power line conditioning transformer (*XPT*) ,

ISCM*XRC14Bl. This transformer is in turn supplied by 480 var Division L II motor control center (*MCC*) 1EHS*MCC14B.- t Loss of the 120VAC power from panel ISCM*PNLO1B resulted in the following system responses: '

1) Division II annulus mixing system auto-started due to los air flow in the annulus pressure control system (*VC*). This  !

actuation was the result of several air-operated dampers (*DMP*)

actuating to their fail closed positien upon Inss of power to ,

their respective solenoid operated valves (*ISV*) (SOVs) .

2) Division II standby gas treatment system (*BH*) alro auto-started as a result of the low air flow condition of the annulus pressure control system.

3) Division II fuel building filter train (*BH*) auto-started due to low air flow in the normal fuel building ventilation system

(*VG*). This actuation was also the result of dampers actuating to their fail closed position upon loss of power to their respective SOVs.

4) Thereactorbuildingf$oordrains (DFR) and equipment drains (DER) (*WK*) isolated. These actuations were also as a result l of air operated valves (*ISV*) ( AOV) 1DFR*AOV101 and IDER*AOV126 actuating to their fail safe (closed) position upon loss of power to their respective SOVs. ,

5) The reactor water sample line air operated valve (*ISV*) (AOV) 1833*AOVF019 isolated as a result of loss of power to its respective SOV.

6) Inboard (Division II) reactor water cleanup (*CE*) (RWCU) isolation valves (*ISV*) (1G33*MOVF040, F001, F028, F053) isolated. This isolation was initiated by the nuclear steam supply shutoff system (*JE*) (NSSSS) due to the loss of power to the leak detection system portion of the circuit.

7) Division II standby service water (*Bl*) vacuum release (*BI*)

valves (*VTV*) (solenoid operated valves ISWP*SOV522B, ISWP*SCV522D, ISWP*SOVS23B, ISWP*SOV523D, and ISWP*SOV552B) isolated as a result of loss of power. This resulted in Division II standby service water being declared inoperable,

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8) Instrument air supply (*LD*) for the containment air locks

(*AL*) isolated due to a loss of power to solenoid operated valves (

• ISV* ) IJRB*SOV15 and IJRB*SOV25,

9) Power to the main steam safety relief valve (

• RV * ) (SRV) acoustic monitoring system (*IJ*) was lost.

10) Solenoid operated sample valves (*SMV*) ICMS*SOV33D, 33D, 33F, 33H, 33K, 33T, 33V, 33X, 33Z, 33BB, 34B, 34D) isolated and loss of power to recorder (*AR*) ICMS*AR25B occurred due to the loss of power. As a result, the primary containment hydrogen monitoring system (*IK*) (CMS) was declared inoperable.

11) The relay logic for the Division II main steam positive leakage control system (*BD*) (PLCS) / penetration valvo leakage control system (PVLCS) lost power causing these systems to be declared inoperable.

12) The auxiliary building crescent area floor drain (*WK*) air operated valves (*ISV*) 1DFR*AOV144,and 145 isolated due to the loss of power to their respective SOVs (*ISV*).

13) One-half isolation signal occurred for the main steam isolation valves (*JE*) due to the loss of power to a portion of the NSSSS logic.

14) In addition to the above, power was lost to several Division II status lights (* ANN *) and r.larms (uALM*).

This event is being reported as an engineered safety feature (ESP) l actuation pursuant 10CFR50. 73 (a) (2) (iv) .

l INVESTIGATION I

Investigation into this event revealed that the loss of power to distribution panel ISCM*PNLO1B was due to the failure of an Elgar Model No. PLC 503-1-1 power line conditioning transformer ISCM*XRC14Bl. This transformer is supplied 480VAC power from safety related motor control center 3EHS*MCC14B. Transformer 1SCM*XRC14B1 then steps the voltage down through one main step-down isolation '

transformer and regulates the output to obtain 120VAC plus or minus 3 percent by means of two Elgar buck / boost multi-tapped auto-transformers. Visual inspection revealed that one of the two buck / boost regulating transformers had failed.

A review of the plant response revealed that all systems responded as' designed for this loss of powe* event. The root cause of the failure of transforner ISCM*XRC14B1 has not yet been determined. However, an investigation into the cause of the failure is on gol..g. A revision m.... _. ... _ ........ ...

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This investigation is expected to be completed by 2/2/90.

A scarch of similar events at River Bend Station revealed that four earlier LERs have been submitted dercribing high voltage transformer failures, but GSU determined these were not comparable with this low ,

voltage power line conditioning transformer failure. There have been no other low voltage transformer failures which have resulted in a safety system initiation. However, there have been other instances where a blown fuse in an Elgar controlled regulating 480/120 VAC transformer caused ESP isolations, e.g., the reactor water cleanup system and a loss of shutdown cooling. That resultant reactor protection system (RPS) actuation was reported in LER 86-027.

Corrective actions taken in the above cases could not have been expected to have prevented this event. Based on the results of further root cause analysis, additional similarity review will be performed and reported in the supplement.

IMMEDIATE CORRECTIVE ACTION Prompt Maintenance Work Orders (MWOs) were issued to provide direction for overiding the following isolations.

1. 1 DER *AOV126

2. IDFR*AOV101

3. IB33*AOVF019

4. IJRB*SOV15 and IJRB*SOV25

5. IDFR*AOV144 and IDFR*AOV145 These MWOs provided directior for installing jumpers to allow the above listed valves to be opened intermittently under administrative control as allowed by Technica) Spec 3fication 3.6.4, " Primary Containment and Drywell Isolation Vaives." This allok+d interim control of drain sump levels, taking periodic reactor water samples, and maintaining access to primary containment by restering air to the primary containment air locks. The remaining system responses were not restored until completion of the troubleshooting because they did not immediately impact continued safe plant operation.

Meanwhile, actions were immediately undertaken to restore power to power line conditioner ISCM*PNLO1B within eight (8) hours as required <

by Technical Specification Section 3.8.3.1, Action a.2. A review of .

the plant Technical Specifications and the River Bend Station Updated Gafety Analysis Report (USAR) revealed that power line conditioning transformer 1RPS*XRC10B1 is not required by Technical Specifications or by any accident analysis. This transformer provides an alternate source of power (*ED*) to the reactor protection system (*JC*) (RPS)

'B' distribution panel (*PL*) (IC71-P301B) and is identical to ISCM*XRC14Bl. Power to 1RPS*XRC10B1 is also supplied from 1EHS*MCC14B. Additionally, the secondary conductors from IRPS*XRC10B1 .

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"a M o E d EEEeStYy*II$ove the location of ISCM*XRC14Bl. Prompt Modification Request (PMR) 89-25 was processed to allow rerouting of the conductors from 1RPS*XRC10B1 to restore power to ISCM*PNLO1B; to restore compliance with Technical Specification 3.8.3.1 and to reidentify IRPS*XRC10B1 as ISCM*XRC14Bl.

At 1652 on 9/16/89, preparations for a reactor power decrease were initiated because the eight hour time limit for restoration of power was nearing expiration. At 2045 on 9/16/89, power was restored to ISCM*PNLO1B through implementation of the PMR 89-25 changes described above. At 2057, the DTR system, the DER system, and the auxiliary building and fuel building ventilation systems were restored to normal operation. Standby gas treatment and annulus mixing were secured; CMS and PLCS/PVLCS were restored to operability. At 2147 RWCU isolation valves were opened. At 2250 full compliance with Technical Specification 3.8.3.1 was restored and the shutdown preparations were terminated. At 2301 RWCU pump (*P*) "A" was started.

_FURTHER CORRECTIVE ACTION Power was restored to RPS 'B' alternate supply at 0330 on 9/25/89 through implementation of PMR 89-26. Surveillance Test Procedure (STP)-303-1609 was completed at 1109 on 9/26/89 and the system was -

declared operable. A spare transformer was installed in the location of the failed transformer ISCM*XRC14B1 and it was wired to the RPS 'B' bus via PMR 89-26. Since this modification has resulted in the original locations of 1RPS*XRC10B1 and ISCM*XRC1481 being swapped, Modification Request (MR) 89-0195 has been initiated to return the wiring configuration te normal when plant conditions allow. In this way, power will not be removed from ISCM*PNLO1B during plant operation.

Any further corrective actions identified as a result of the failure analysis of ISCM*XRC14B1 will be provided in the supplemental report. ,

SAFETY ASSESSMENT All plant systems were verified to have operated as designed in response to the loss of power to ISCM*PNLO1B. Most of the systems were designed to fail to the safe condition by causing actuations of the various Division II systems or hy closing th' primary containment isolation valves. For those systems which were declared inoperable as -

a result of this event, the Division I systems t'ere not impacted and were capable of responding if required to mitigate the consequences of an event. All required Technical Specification Action statements were satisfied. Therefore, there was no impact on the health and safety of the public as a result of this event.

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

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