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B ALTIMOREGAS ANO.

ELECTRIC.

CHARI.ES CENTER e P.O. BOX 141! * BALs|f. ORE. MARYLAND 21203 147S

R E DENTONGtNinAL uaNActa

(.ALVCPT SLIFF $

April 3, 1991

U.S. Nuclear Regulatory Commission <

Washington, D.C. 2G)55

ATTENTION: Document Control Desk

SUBJ EC1 : Calvert Cliffa Nuclear Power PlantUnit No. 1; Docket No. 50 317; 1.icense No. DPR 53Lisrtisee Fvent _ Report 90 023. Pavision Ol

Gentlemen:

The attached report ir, being sent to you as required under 10 CPR Sn.73guidelines, Should you have any ques tion , regarding this report , we vill bepleased to dis, cuss claem with you.

-Jfry truly yours,

[ _..

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l RED,/DWM/bj dI AttachmentI

| cc: D. A. Brune, Esquire

| J. E.-Silberg, EsquireR. A. Capra. NRCD. G. McDenal d, J r. , NRCT. T. Martin, NRCL. E. Nicholson, NRCR. I. McLean, DNRJ . 11. Val t e r , ~PSC

| Director, Offics of Management Informationand Program Control

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On Augus ?. , 1990, Unit 1 experienced an r.,tuation of wbsys'x i ZA of theEngineered Safety Features Actuation System (ESFAS). The actuation occurredwhile power was being restored to sdosystett ZA followjog maintenance and wascaused by the operat'.on of a fuse in the vital AC Distribution panel. Thefuse operated on over current but subsequent troubleshooting did not identify |tne cause. The system operated normally after the fuse was replaced.

August 7, 1990 prior to the restoration of ESFAS Subsystem ZA, Unit 1'"

, s'e. lanced a partial actuation of subsystem ZB of the ESFAS which was causedby t. degraded 15 VDC pcwer supply in the Actuation Logic Cabinet. The powers upply vas retur d to the ESFAS vendor for analysis. The vendor determinedthat th. power ply vo'itage regulator had failed,

In 'uoth cwer.n. plant systetts and corrponents perfortted as required by thedes!gn, consis st with plaat conditions and system lineups. Following the

g actuation on k2b 'st 7. Containment Integrity was established in accordancewith Technical Sp cifications because loss of the Undervoltage start signalassociated with ES'AS required that the Unit 1 Emergency Diesels be declaredicoperable.

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LICEtGEE EVi1T REPORT (LER) TEXT CONTINUATION'

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F AOILif f NAME DOCkti NUMD(R LfHNUMotR PAQt

Calvert Cliffs, Unit 1 05000317 90-023-01 0 2 0F 0 5

w m. .m. . - n. m me.>

I. DESCRIPTION OF EVENT

on August 2, 1990 at 0925 hours, Calvert Cliffs Unit 1 experienced an actuationof subsystem ZA of the Engineered Safety Features Actuation System (ESFAS). Theactuation occurred while power was being restored to subsystem ZA followingmaintenance and was caused by the failure of a fuse in the vital AC DistributionPanel (lY01) which protects the Actuation Logic Cabinet (IC67L).

The Actuation ingic Cabinet contains five 15 VDC power supplies providing powerfor tba ' ( _ssociated with the ESFrS and five 28 VDC power supplies providingpower for lights in the Actuation Cab. net and Relay Coil Power for the RelayCabinet which actuates plant components based on ESFAS signals. The fuse failurroccurred while switching on the third 28 VDC power supply which was beingperformed in accordance with Operating Instruction (01)-34, Engineered SafetyFeatures Actuation System. No injection of water into the Reactor Coolant Systemoccurred and Shutdown Cooling was not af fected because the Safety Injection pumpsassociated with ESFAS subsystem ZA were locked out and shutdown cooling wasprovided by the Low Pressu e Safety Injection Pump associated with the redundantESFAS subsystem (ZB).

Fcllowing the actuation which occurred immediately after switching on the 28 VDCpower supply, the operators stopped the procedure for energizing the cabinet. AControl Room Operator performed a panel check to identify plant status andcompleted the appropriate checklists in the Emergency Operating ProceduresAttachments to verify proper operation of the ESFAS. Subsequent review of thesechecklists indicated that all plant systems and cornponents performed as requiredby the design, consistent with plant conditions and system lineups. ESFAS

subsystem ZA was de energized and a trouble shooting plan was developed todetermine the cause of the fuse failure.

On August 7 1990 at 2130 hours, prior to the re.storation of ESFAS Subsystem ZA,Calvert Cliffs Unit 1 experienced a partial actuation of subsystem ZB of theESFAS. The actuation was limited to the ESFAS functions associated with one ofthe five 15 VDC power supplies. The affected power supply controlled theContainment Spcay Actuation Signal (CSAS); the Recirculation Actuation Signal(RAS); the Contait.sent Radtet ten cignal (CRS); and, the Steam Cenerator IsolationSignal (SCIS). There e no Energer cy Diesel Cenerator (EDC) start, injection ofwater into the Reactor Coolant S-ptem, initiation of Containment Spray or impacton Shutdowct Cooling.

Following the actuation, the Control Room Operator performed a panel check toidentify plant status and completed the appropriate checklists in the EmergencyOperating Procedures Attachments to verify proper operation of the ESFAS.Subsequent review of these checklists indicated that all plant systems andcomponents performed as required by the design, consistent with plant conditionsand system lineups. However, the Control Room Operators noted the Logic Trip

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LICENSEE EVENT REPORT (LER) TEXT CONTINUATibN,

F ACluiY hAME DOCKET NUMBER Lf R NUWBER P AC.(

Calvert Cliffs, Unit 1 05000317 90 023-01 0 3 0F 0 5im e w. .w. . .>,.a . mon. ..>

module lights associated with the second 15 VDC power supply (CSAS/ RAS /CRS/SCIS)were dimly lit and the indicated voltage was 12 VDC versus the required 15 VDC.ESFAS subsystem ZB was de energized and a trouble shooting plan was developed todetermine the cause of the degraded 15 VDC power supply.

At the time of each of the ESFAS actuations described above, the Reactor was inMODE 5 (Cold Shutdown) at approximately 200 psi and 120 Degrees Fahtenheit.Following the actuation of ESFAS subsystem ZB on August 7, both ESFAS Subsystems(ZA and ZB) were inoperable. The ESFAS system provides the undervoltage (UV)start signal for the EDGs. Therefore, the EDCs for Unit I were declaredinoperable and Containment Inte6rity was established in accordance with TechnicalSpecification 3.8.2.2, A.C. Distribution Shutdown.

Actuations of the ESFAS System are reportable in accordance with 10 CFR50.73(a)(2)(iv), "Any event or condition that resulted in manual or automaticactuation of any ESF."

II. CAUSE OF EVENT

The proximate cause cf the ESTAS Subsystem ZA actuation on August 2, 1990 was thefailure of a 12 amp fuse between the 120 VAC vital power supply (lYOl) and theESFAS Subsystem ZA Actuation Logic Cabinet (lC67 L) . An initial evaluationr'vealed that the fuse on tha line side failed but the fuse on the neutral didnot-fail. Therefore, it was suspected that a short or ground in the actuationlogic cabinet caused the fuse to operate. Systematic trouble shooting of thecabinet failed to reveal any faults which would result in over current.Therefore, it was concluded that the failure was due to the line fuse (lY01)opening at a lower value than its rated capacity of 12 amps. Failure analysis ofthe fuse indicated that it operated on over current but subsequenttroubleshooting did not identify the cause. The system operated normally afterthe fuse was replaced.

The proximate cause of the ESFAS Subsystem ZB partial actuation on August 7, 1990was a degraded 15 VDC power supply in the IC68L cabinet. A PreventiveMaintenance inspection completed on May 7, 1990 verified the power supply wasoperating properly at that time. Troubleshooting did not reveal the caur, of thefailure on August 7, 1990. A replacement was installed and the defective power

! supply was returned to the ESFAS veador for failure analysis. The ESFAS vendorl determined that the power supply voltage regulator had failed. Additional| troubleshooting to determine the cause of the voltage regulator failure was not

| performed since repetitive failures of this component have not been expertenesd.|

| III. ANALYSIS OF EVENT:

The ESFAS System initiates the start of equipment designed to mitigate andterminate a loss os coolant, a main steam line break or a loss of feedwater

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UCENSEE EVENT REPORT (LER) TEXT CONTINUATION,

raciuty naut oocaravunn un uvueen raai

Calvert Cliffs, Unit 1 05000317 90 023 01 0 4 0F 0 5 ;rncen,,w. w.o .m m

event. The ESFAS system, including both sensor and actuation systems, and theequipment it operates are divided into two independent and redundant subsystemsdesigned to ensure the system responds even in the event of a singic failure.The ESFAS system and the equipment it operates are subjected to comprehensivesurveillance test and Preventive Maintenance programs intended to ensure properequipment operation and detect degraded equipment before it prevents properoperation or causes unnecessary challenges to the systems. There was no waterinjected into the Reactor Coolant System and Containment Spray was not initiated.

A review of Licensee Event Reports back to 1984 indicates that the ESPASactuations described in this report were the first instances of inadvertentactuations due to equipment failure in Unit 1. The single inadvertent actuationdue to equipment failure in Unit 2 did not involve power supplies or an overload.

These challenges to the ESFAS system are not indicative of unreliability of theESFAS system in performing its design function; did not have an adverse impact onthe plant when they occurred; and, ere not expected to result in degradedperformance of ESFAS or the equipment ESFAS actuates. Therefore, these ESFASactuations r- not considered safety significant.

IV. CORRECTIVE ACTIONS

Following the actuation of ESFAS Subsystem ZA, trouble shooting failed to revealany conditions which may have caused the fuse to operate. The fuses werereplaced and checks were made at each major step of the procedure for restoringpower to the (.abinet. No discrepancies or faults were identified. ESFASSubsystem A was returned to service on August 15, 1990 at 0630 hours. The fuseoperated on over current while power was being restored to the system. No causefor the over current was identified and the system has operated normally sincethe fuse was replaced.

Following the actuation of ESFAS Subsystem ZB, trouble shooting revealed the 15VDC power supply would not maintain the required voltage. No cause for thedegraded performance was identified. The power supply was replaced and ESFASSubsystem ZB was returned to service on August 8, 1990 at 1705 hours. Themalfunctioning power supply was returned to the ESEAS vendor for evaluation andfailure analysis. The ESEAS vendor determined that the power supply voltageregulator had failed. Additional troubleshooting to determine the cause of thevoltage regulator failure was not performed since repetitive failures of thiscomponent have not been experienced.

V. ADDITIONAL INFORMATION

A review of Licensee Event Reports determined the unnecessary challenges to theESFAS system described in this report wers the first instances of inadvertentactuations due to equipment failure in Unit 1. The single inadvertent actuation

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LICENSEE EVENT REPORT (LER) TEXT CONTINUATION

F ACluTY kAWE DOCKET NUW6tR UM MVWBER PAQt

Calvert Cliffs Unit 1 05000317 90 023-01 0 5 0F 0 5ren a w. ua. ,m,.s . suam.,>

due to equipment failure in Unit 2 (LER 318/86 03) did not involve power suppliesor an overload.

A, Component Identification:

IEEE 803 IEEE 805EIIS Funct. System ID

Reactor Coolant System N/A AB

ens neered Safety Features N/A JEi

Safety Injection System N/A BP, BQ, CB

Low Pressure Safety Injection Pump P BP

t