ML20012C074

LER 90-004-00:on 900211,Div II Emergency 125-volt Dc Bus Experienced Voltage Spike,Causing Topaz Inverter to Trip & Resulting in Loss of Power to Control Room Panel.Cause Unknown.Setpoint Changes Being evaluated.W/900312 Ltr

ML20012C074
Person / Time
Site:	River Bend
Issue date:	03/12/1990
From:	England L, Odell W GULF STATES UTILITIES CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-004, LER-90-4, RBG-32480, NUDOCS 9003200043
Download: ML20012C074 (6)

Text

y - -

- 4 g

r V:

[ .

GULF STATES ' UTELETIES C'OMPANY  :

E n vt R BEND STAh0N - PDST OmCE P0x MD - St THANDSma toutstANA 70n$

A44 A 003E $04 6.% 609J 346 B6f,1 3

March 12 ,1990 RBG- 32480 File Nos G9.5, G9.25.1.3 1 U.S; Nuclear Regulatory Commission i .

Document Control Desk l Washington, D.C. 20555

^

l Gentlemen:

L River Bend Station - Unit.1 Docket No. 50-458 Please ' find ~ enclosed ^ Licensee Event Report No.90-004'for River Bend Station Unit 1. ,This report is being submitted-pursuant to 10CFR50.73.

Sincerely, f

1

-W. H. dell Manager-River Bend Oversight River Bend Nuclear Group' =!

, N0c)WefF/CLM/pg tb h WH0/PDG RGW/ A

-cc: U.S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 1000 Arlington, TX 76011

• NRC Resident Inspector

~

P.O. Box 1051 St.'Francisville, LA 70775 INP0 Records Center-1100 Circle 75 Parkway Atlanta, GA 30339-3064 l

l 6

S-

. . . _ _ ~ _ _ _ _ _ .

k perm att U.S. NUCLEAfi G.E!ULC.Tuv COesMieSIOce APPROVED OMS EO 3166 9104 ,

. , LICENSEE EVENT REPORT (LER) naEs si'a PACILITY 88AME 04 DOctLEY NUMSER Ul PAGE .J')

RIVER BEND STATION '

oisJoloIol4l518 1loFl 0l 5 flTLE e4) '

Engineered Safety Future Actuations due to Tripping of a Ibpaz Inverter Unit Evf NT DATE 168 LE R NumeE R I.) REPORT DATE 17) OTHER F ACILITIEs INVOLVED 181 MONTH DAY VEAR vtAR ,0M '*' , @y*,$ MONTH DAY vtAR ' AC' LIT v e.awas DOCKEY NuveEntsi o15l0lo10 1 l 1 0l2 1 l1 90 9 l0

, 0 l0 l4 0l0 0l3 l 9l0 o is to lo t oi i i

,,,,,,,,,a inis REPORT is sveMirTEo PURSUANT To THE RLouiREMENT: Or to C#R i ,Ca.ca eae e< ,'emr e ia ,eue-mes uti "00E 'E' 1 ao nomi to aosm y so.73i.H H.i 73.rumi g _

n .a.i.in Ha so ni.Hu eeni.iGH.i run.i

- noi 1 t0 #0 n oii. Hum so.m m m unmOH..a

_ gaE , gsg,,j., Age,y, ,

to sotteH1HnD lo.73talGHil to 73ie>QHvHHAl 76 sal to 40Etsin Hivl So.?31alGHill to 73 eH2HvedH81 2J4CHeH1Hva Do.73(aH2 Hull So.73lalGHal LICENSEE CONTACT FOR THi$ LER n2)

NAME TELE *MONE NUMSER E44 CODE Le A. England, Director-Nuclear Licensin9 51014 318111 -14111 al 5 COMPLETE ONE LINE FOR E ACH COMPONENT F AILURE DESCRISED IN THIS REPORT (13)

CAust SYSTEM COMPONENT MA AC-RtE *],' ,Ajp t CAUSE system COMPONENT OmfA E b MA%AC- g pp I I I I I I I I I I I l l t i I I I I l l I i l l l I f SUPPLEMENT AL REPORT EXPECTED nel l MONTH OAV vtAR

~9b Es o,,.. a.,n a. ruccreo svowssoON net ') NO , 0; 5 ol1 9l 0 tu TuCT a-,,, ,e , w . . . . o,, . . u,. ,,, , , n .i At 1009 on 02/11/90, with the plant at 100 percent power (Operational Condition 1), the Division II emergency 125 VDC bus experienced a voltage spike which caused a Topaz inverter unit (IE12A-PSI) to trip, resulting in a loss of power to specific instrumentation on control room panel H13-P618 (Division II). This event occurred coincident.

with a scheduled preventive maintenance task (PM) on Division II battery- charger (ENB*CHGRIB) when the' float / equalize switch on the charger was moved from the float position'to the equalize position.

Upon restoration of the inverters, multiple Division II Engineered Safety Feature (ESF) actuations occurred. Therefore, this event is i reportable pursuant to_100FR50.73(a)(2)(iv).

l Corrective actions include revising the preventive maintenance tasks, I developing new preventive maintenance tasks to include checking of the inverter trip setpoints, troubleshooting of the battery charger, evaluation of modifications to address automatic restart events, and development of load lists for the Topaz inverters. ,

Operations personnel properly responded to this event by limiting the number of ESF system actuations. Those ESF systems which did actuate responded per design. Therefore, this event did not adversely affect l

the health and safety of the public.

1

1 anc emna assa ut osuctsu t_soutatomy consucesses:

• * * ' ** LICENSEE EVENT REPORT (LER) TEXT CONTINUATION ***aono one e.o mo-cio.

seines. w m FAseUTV santIB 11 Doometosvassa ei Lee eeundetA tel **es tal n== " 2 ."

t' "*2n RIVER BLND STATION ol5lcl0lo141518 d0 --

O 10 14 010 012 0F 0 15

_UEYOY_T_EY___C3__NE___I__O_

(

At 1009 on-02/11/90, with the plant at 100 percent power (Operational Condition 1), the Division II emergency 125 VDC bus (*BU*) experienced a voltage spike which caused a Topaz- inverter (*INVT*) unit (IE12A-PSI) to trip, resulting in a loss of power to specific '

instrumentation on control room panel (*PL*) H13-P618 (Division II).

This event occurred coincident with a scheduled preventive maintenance task (PM) on Division II battery charger (*BYC*). (IENB*CHGR1B) when the float / equalize switch on the charger was moved from the float position to the equalize position.

Upon loss of power to control room panel H13-P618, the appropriate Technical Specification action statements were implemented. At 1111 on 02/11/90, the inverter was reset and power was restored to the control room panel. Upon restoration, multiple Division II Engineered r Safety reature (ESF) actuations occurred. Therefore, this event is -

reportable pursuant to 10CFR50.73(a)(2)(iv).

INVESTIGATION At 1009 on 02/11/90, with the plant at 100 percent power (Operational Condition 1), the Division II emergency 125 VDC bus experienced a voltage spike which caused a Topaz inverter unit (IE12A-PSI) to trip, resulting in a loss of power to specific instrumentation on control room panel H13-P618 (Division II). This event occurred coincident with a scheduled preventive maintenance task (PM) on a Division II battery charger (IENB*CHGRIB) when the float / equalize switch on the charger was moved from the float position to the equalize position.

Upon loss of power to control room panel H13-P618, the Division II reactor core. isolation cooling (RCIC) containment isolation valves (E51*M0VF076, F063, F064, and F031) were verified to be closed per Technical Specification 3.3.?. Prior to resetting the Topaz inverter unit, Operations personnel took the following actions:

. The Division II residual heat removal (RHR) pump breakers were racked out.

. The Division II automatic depressurization system (ADS) was placed in inhibit.

. The reactor core isolation cooling (RCIC) system trip and throttle valve were closed.

. The "B" safety relief valve (SRV) solenoids were placed in the "off" position.

These actions were taken to prevent actuation of the above systems and components upon resetting of the Topaz inverter unit.

geoa= == .u s os o isemwA

u2 oetu. ...uw , ~----. 1

• II UCENSEE EVENT REPORT (LER) TEXT CONTINUATION waoveo oue no siso-co. -

BM,I.08: o/Si/W :

,asam mass m acaat avuna m te. num . m am ,

'na .

tfr."' "'J.17:

. RIVER BEND STATION o l5 lo lo lo 14 l 518 91 0 --

01d 4 --

O lo 0 13 0 ' 0 15 _

""UpoE"*EYItoration of the Topaz inverter unit (E12A-PSI), the following t a Engineered. Safety Feature (ESF) actuations automatically initiated:

. The Division.II emergency diesel generator (*EK*) started.

. -The control building ventilation (*VI*) filter (*FLT*) unit (HVC*FLT18) started.

. The containment building unit cooler (*VA*) (*CLR*) HVR-UCIC tripped, while containment building unit cooler HVR-VCIB .

started and the associated service water (*Bl*) valves (*V*)-

(SWP*502B and 5038) opened.

. Reactor ' core isolation cooling (RCIC) system (*BN*)

initiation signal sealed in.

. The Division Il residual heat removal (RHR) initiation signal

(*B0*) sealed in and residual heat removal (RHR) ' containment isolation valves (*ISV*) (1E12*M0VF042B and 42C) opened.

An extensive evaluation of these ESF actuations was performed by Engineering personnel. This evaluation determined that all systems operated per their design and no other actuations should have.

L occurred.

The results of the investigation that followed the event were

. presented to an NRC augmented inspection team (AIT). This investigation revealed that the loss of 125 VDC power to specific instrumentation on control room panel P-618 occurred when the

! ~ float / equalize switch on-the battery charger IENB*CHGRIB was moved from the float position to the equalize position. At that time,.a

! . voltage spike.was induced into the 125 VDC battery bus that was of l sufficient magnitude to cause the Topaz. inverter unit (two inverters in a master-slave arrangement) to trip off line. The data obtained from the emergency response information system (ERIS) showed that a  !

l maximum voltage cf 146.3 volts was received from battery bus l 1ENB*BATDIB. This was above the 140 volt specification trip setting l for the Topaz inverter . Based on this evaluation, the Topaz inverter L unit appears to have operated per design and the problem is suspected to be associated with the battery charger.

An investigation and analysis of previous corrective and preventive l maintenance tasks (PM) revealed that no similar problems have occurred I during maintenance activities or in the performance of this quarterly L PM task. Additionally, a search of previous condition reports was L conducted to identify related deficiencies or events but none were l found.

GSU's investigation included an analysis of the opening of the RHR injection valves. This analysis identified three conditions that rist I. C Fonu assa e u o OPO t 946+024-634/446 1

,-w--- -

p .. .m...m,_ : o 1

9'

• UCENSEE EVENT REPORT (LER) TEXT CONTINUATION ***aovio o=e no neo-oies EKptROS 6/31/W PA88W7V NAIER til 00Catt Nuesta tal Lam Nuessen 40e Paet tal vsa. .

ageg,a6 ygam RIVER BEND STATION olsl0lolo14l518 91 0 -

ddA -

0 10 014 OP 015 7 e~sYt'iY iT O 7 YhYs*e"" valves to stroke open. First, power must be available to the RHR pump bus. Second, an RHR initiation signal must be provided either on reactor low water level, drywell high pressure or manual initiation. Third, the low reactor pressure vessel (RPV) pressure interlock permissive signal must be provided- to the trip. <

units. The first condition was satisfied throughout the event as power was always available to the pump bus. The second and third conditions were satisfied upon re-energization of the the Topaz .

inverter unit. At this time, the reactor low water level and RPV pressure interlock permissive trip signals were received momentarily which resulted in the valves opening.

Previous LERs have been reviewed to identify similar events. This review identified no other cases in which Topaz inverters have tripped resulting in ESF actuations. LER 89-038 reported the loss of the 125 VDC bus during maintenance on a battery charger, resulting in numerous ESFs. The ESF actuations were due to momentary signals being provided to trip units. However, this event bears only superficial similarity to the Topaz inverter event since the root causes are different.

CORRECTIVE ACTION GSU continues to evaluate the root cause of the voltage spike on the 125 VDC bus.- The results of this evaluation will be provided in a supplemental report by May 1, 1990. Based or, the investigation and engineering analysis to date, the following corrective actions are being implemented as a result of this event:

. Battery charger PMs, Division I and Division II, will not be performed again prior to the mid-cycle outage in March, 1990.

GSU will evaluate potential revisions to the PMs to minimize i

transients when switching from float to equalize. .This evaluation will be completed by May 1, 1990.

. Troubleshooting of the battery charger will be performed I during the mid-cycle outage in March, 1990. In the interim,_

the charger is being checked weekly for proper outputs.

. PMs will be developed for the 3 Topaz inverters which will include checking trip setpoints. The Division II PM will be performed during the mid-cycle outage and Division I PMs will be performed during the third refueling outage, currently scheduled to start in September, 1990.

go ~ m- ...oeo see.ouwss5

C v.

NRC % WBA US couCLS 2 EleULitOn7 COnissemeOle .

UCENSEE EVENT REPORT (LER) TEXT CONTINUATION maoveo ous no sie-em ames; wsum

-ii FABILITV GIAAR til Docutt fautSSR W gge seyngga gee PASG tal .

...a syg,46 m t; RIVER BTND STATION O 1510 l0 l0 l415 l A 01 0 -

010l4 -

0 10 015 OP 0lF venn- . anc a msawnn

. GSU will address the issue of automatic restart events by  :

evaluating the following: 1 1

- manual reset of the inverter unit l

- setpoint changes for the inverter and/or charger 1

- changing to a different type of inverter  ;

- addition of time delays q In addition-to the above actions, GSU is developing load lists for the two Division I Topaz inverters and the one Division II Topaz inverter.

These will be incorporated into the applicable procedures with i outlines for specific actions for loss and restoration. ' Applicable 1 personnel will be trained on these procedures and hardware. These actions will be completed prior to start-up from the third refueling outage.

S_AFETY_ ASSESSMENT Operations personnel properly responded to this event by limiting- the -

number of ESF' system actuations. Those ESF systems which did actuate responded per design. Therefore, this event'did not adversely affect the health and safety of the public.

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

80 888 3864 ou 8 GPO 10M+424 634/466

. -_ -. -. . - . _