ML20011E118

LER 89-033-01:on 890916,loss of Power to Div II 120-volt Ac Distribution Panel Caused auto-start of Standby Gas Treatment & Annulus Mixing Sys,Resulting in ESF Actuations. Caused by Transformer Failure.Valves opened.W/900130 Ltr

ML20011E118
Person / Time
Site:	River Bend
Issue date:	01/30/1990
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-32221, NUDOCS 9002080016
Download: ML20011E118 (7)

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GULF .1!i$TATES UTILITIES C'OMPANY Oh s  %,(P 0lND $1 A11DN PObfOSM tBDA??O $1 ikACSWLLI LO 8:Si AN A 7074 Af4 A (.Dbi bCJ (M (v.JM Sat, EMI I.

January 30, 1996 RBG- 32221 File Nos. G9.5, G9.25.1.3

-U.S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555- ,

Gentlemen:

River Bend Station - Unit 1 Docket No. 50-458 Please find enclosed Licensee Event Report No.89-033 Revision 1 "ESF Actuations as a Result of Power Line Conditioning Transformer Failure". This supplemental report is hereby submitted to' provide the results of GSU's evaluation of the failure of the power line conditioner.

Sincerely, jJ. E.F.

Booker L Ap Manager-River Bend Oversight p River Bend Nuclear Group JEB/TTP/RGW/DCH/JMH/pg cc: U.S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 1000 Arlington, TX 76011 x NRC Resident Inspector P.O. Box 1051 St. Francisville, LA 70775 INPO Records Center 1100 Circle 75 Parkway Atlanta, GA 30339-3064

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7,ti ,,, ,., ,- eurevio so.,,u,o= oe re, "y ~0 O 'I l l l aset a aet , .-, .e , - , e . ._, . e.,-. a a , n ti At approximately 0900 on 9/16/89 with the unit in Operational Condition 1 at 100 percent power, electrical power was lost to Division II 120VAC distribution panel ISCM*PNL018. Loss of power to I this panel resulted in the auto-start of the Division 11 standby gas I treatment and annulus mixing systems and the Division 11 fuel building l filter train. Additionally, the reactor building floor and equipment l

drain isolation valves isolated, inboard (Division II) reactor water cleanup isolation valves isolated, reactor water sampling system l isolation valve closed, auxiliary building equipment drains isolated I 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 11 status lights and annunciators were also \

inoperable.

The cause of the power loss was determined to be the failure of an Elgar power line conditioning transformer ISCM*XRC1481. A failure analysis has been performed on the power line conditioner (PLC). The inspection and test results indicate that this is a random f ailure.

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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011 0l2 OP 0 16 von. . ea senwim REPORTED CONDITION 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*PNLO10. This is a Division 11 electrical distribution panel which distributes power to numerous Division II loads from power line conditioning transformer (*XPT*)

ISCM*XRC1481. This transformer is in turn supplied by 480VAC Division  ;

II motor control center (*MCC*) 1EHS*MCC14B.

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 low 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 position upon loss of their respective solenoid operated valves (*ISV*) (SOVs) power to .

2) Division II standby gas treatment system (*BH*) also ,

auto-started as a result of the low air flow condition of the annulus pressure control system.

3) Division 11 fuel building filter train (*BH*) auto-started due

. to low air flow in the normal fuel building ventilation system t

(*VG*). This actuation was also the result of dampers actuating to their fail closed position upon loss of power to their respective S0Vs.

4) The reactor building floor drains (DFR) and equipment drains (DER) (*WK*) isolated. These actuations were also as a result of air operated valves (*ISV*) (A0V) 1DFR*A0V101 and IDER*A0V126 actuating to their fail safe (closed) position upon loss of power to their respective S0Vs.

5) The reactor water sample line air operated valve (*ISV*) (A0V)

IB33*A0VF019 isolated as a result of loss of power to its respective 50V..

6) Inboard (Division II) reactor water cleanup (*CE*) (RWCU) isolation valves (*ISV*) (1G33*MOVF040 F001, F028, F053) s 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*SOVS22D, ISWP*S0V523B, 1SWP*S0V523D, and 1SWP*SOV5528) 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*SOV33B, 33D, 33F, 33H, 33K, 33T, 33V, 33X, 332, 33BB, 34B 340) 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 valve leakage control system (PVLCS) lost power cousing these systems to be declared inoperable.

12) The auxiliary building crescent area floor drain (*WK*) air operated valves (*ISV*) 1DFR*A0V144 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 alarms (* ALM *).

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

INVESTIGATION 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*XRC14B1. This transformer is supplied 480VAC power from safety related motor control center 1EHS*MCC148. Transformer ISCM*XRC14B1 then steps the voltage down through one ma n 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 failure analysis on PLC 503-1-1 has been conducted by Wyle Laboratories. The test program included a detailed visual inspection, transformer testing, and testing of various PLC components,

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nh ol4 W ob i an n am e. . .mmm me == ma mm l Based on the inspection and test results it was concluded that the I burned PLC had current flow through the silicon controlled rectifiers  !

(SCRs) in excess of.500 amperes. This is unusual as the SCRs would be )

expected to fail in an "open" position and thus not allow the flow of I such high currents. Therefore, this failure is considered to be a I random failure.  !

A search of similar events at River Bend Station revealed that four earlier LERs have been submitted describing 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 l where a blown fuse in an Elgar controlled regulating 480/120 VAC i transformer caused ESF isolations, e.g., the reactor water cleanup 1 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 l expected to have prevented this event. Additional similarity review '

has revealed no other LERs on ESF actuations due to random failures in low voltage transformers.

IMMEDIATE CORRECTIVE ACTION

. Prompt Maintenance Work Orders (MW0s) were issued to provide direction  !

for overiding the following isolations.

1. 1 DER *A0V126

2. 1DFR*A0V101

3. IB33*A0VF019

4. 1JRB*S0V15 and IJRB*S0V25

5. 1DFR*A0V144 and IDFR*A0V145 These MW0s provided direction for installing jumpers to allow the above listed valves to be opened intermittently under administrative i control as allowed by Technical Specification 3.6.4, " Primary Containment- and Drywell Isolation Valves." This allowed interim control of drain sump. levels, taking periodic reactor water samples, and maintaining access to primary containment by restoring 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*PNL01B 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 Safety 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

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'B' distribution panel (*PL*) (IC71-P001B) and is identical to ISCM*XRC14Bl. Power to IRPS*XRC1081 is also supplied from 1EHS*MCC14B. Additionally, the secondary conductors from 1RPS*XRC1081 are routed above the location of ISCM*XRC14Bl. Prompt directly(PMR) 89-25 was processed to allow rerouting of Modification Request the conductors from 1RPS*XRC10B1 to restore power to ISCM*PNLO1B; to restore compliance with Technical Specification 3.8.3.1 and to reidentify 1RPS*XRC1081 as ISCM*XRC1481.

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*PNL018 through implementation of the PMR 89-25 changes described above. At 2057, the DFR 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 i 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*XRC1481 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 1SCM*XRC1481 being swapped, Modification Request (MR) 89-0195 has been initiated to return the wiring configuration to normal when plant conditions allow. In this ,

way, power will not be removed from ISCM*PNL018 during plant '

operation.

I SAFETY _ ASSESSMENT All plant systems were verified to have operated as designed in l response to the loss of power to ISCM*PNL01B. Most of the systems l

were designed to fail to the safe condition by causing actuations of ,

the various Division II systems or by closing the primary containment isolation valves. For those systems which were declared inoperable as a result of this event, the Division I systems were 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.

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