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Carolina Power & Light Company

Brunswick Nucicar Project {P. O. Box 10429

Southport, NC 28461-0429January 24, 1990 ;

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FILE: B09-13510C 100FR50.73SERIAL: BSEP/90 0061

U.S. Nuclear Regulatory CommissionATTN: Document Control Desk i

Washington, DC 20555'

BRUNSWICK STEAM ELECTRIC PLANT UNIT 2DOCKET NO. 50-324LICENSE NO. DPR-62

LICENSEE EVENT REPORT 2-89-021!

Gentlemen:

In accordance with Title 10 to the Code of Federal Regulations, the enclosedLicensco Event Report is submitted. This report fulfills the requirement fora written report within thirty (30) days of a reportable occurrence and is inaccordance with the format set forth in NUREG-1022, September 1983.

Very truly yours,

gtJ. L. llarness, General ManagerBrunswick Nuclear Project

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|Enclosure !

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On December 25, 1989, the Unit 2 reactor was defueled with the fuel pool gatesinstalled during a scheduled refueling outage. At 1103 the ElectricalProtection Assembly (EPA) output. breakers associated with the A bus of theReactor Protection System (RPS) tripped open. The expected isolations andactuations occurred. The reason for the trip is unknown because the tripindicating lights on the breakers do not seal in. The load at the time of theevent was low; therefore, the cause for the trip is not thought to have been amagnetic or thermal trip. The voltage and frequency output of the A RPS!

| motor generator set was monitored and no problems were found. The overvoltage, under voltage and under frequency trip function setpoints werei

| calibrated and the results did not reveal a cause for the event. A| modification kit is available from General Electric which includes a provision

for seal in trip indications but it has been determined not to be costjustified. The RPS bus and EPA breakers are functioning normally. No furtheractions are planned.-

This event had no safety significance as the system functioned as designed..

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Event

A trip of the A Reactor Protection Systeru (RPS) Electrical. ProtectionAssembly (EPA) (EIIS/JC/BKR) I and 2 output breakers resulting in automaticEngineered Safety Feature actuations.

Initial Conditions

Unit 2 reactor was Jefueled and the fuel pool gates were installed during ascheduled refuel and maintenance outage. RPS A and B buses were being poweredfrom their associated motor-generator (M-G) (EIIS/JC/MG) sets.

Event Description

On December 25, 1989, at 1103, the Unit 2, numbers 1 and 2. EPA breakersassociated with RPS bus A (Ells /JC/BU) tripped open. The control operator (CO)verified that expected automatic actions occurred. A Primary ContainmentIsolation System (PCIS) (Ells /BD) Group 6 [ Containment Atmosphere Control (CAC)(Ells /DB) system] isolation occurred, the A and B Standby Gas Treatment (Ells /VA/Bll) systems automatically started and a half SCRAM signal was received whenthe A RPS logic tripped. At the time of the event, Group 2 isolation valves .

were mechanically blocked open, the Reactor B:111 ding was under clearanceisolated, drywell purge was secured and Group 3 and 8 valves were doenergized cfor outage activities; therefore, the involved valves and dampers did notisolate. An obvious cause for the breaker trips was not apparent. Per arecomn.endation f rom the Instrumentation and Control (ISC) group EPA breaker 1 ,

and 2 were closed. Indications were normal. At 1210 the trips were reset andsystems were returned to normal service. Work Request / Job Order (WR/J0)*

89-BBYK1 was initiated to investigate this event. At 2247, RPS bus A wastransferred to the alternate power source to allow for testing of the 1 and 2 ,

EPA breakers. '

Event Investigation

The EPA breakers are designed to trip whenever an under frequency, under ;'

voltage or over voltage condition exists at the output of their associatedRPS M-G set. The breakers will also trip on magnetics or thermal overload.It is not possible to determine which trip opened the involved breakers becausethe trip indications are for calibration purposes and are not provided with ascal-in function. This lack of a scal-in function prevents the determinationof what tripped the breaker and which breaker tripped first. Since the breakersare in series, if EPA 1 tripped then EPA 2 would trip on under voltage'.Theoretically, if EPA 2 tripped EPA 1 would not. However, it is possible thata resulting voltage regulator spike due to sudden unloading could trip EPA 1.At the time of the event, the bus load was low; therefore, it is assumed that .,

the trip was not the result of a thermal or magnetic overload. To deterpine if

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a problem existed with the remaining EPA breaker trip setpoints a maintenancesurveillance test (MST) was performed. 2MST-RPS21SA, RPS ElectricalProtection Assembly Channel Calibration, was performed on EPA breakers 1 and2. The test results did not indicate a problem which is thought to havetripped the breakers. The test did reveal that the under frequency time delaytrip varied from 0.5 to 1.0 seconds. The trip is required by the test to beset at a time delay of 0.9 seconds plus or minus 0.1. In addition to thetest, the output frequency and voltage of the RPS M G set was monitored. Noproblems were found. The most probabic cause of the variable time delay isdefective components on the printed circuit (PC) board. The PC board wasreplaced and the new PC was satisfactorily calibrated in accordance with2MST-RPS21SA on January 2, 1990. RPS A was transferred from the alternatepower supply to its M G set on January 8, 1990. No further problems have beenindicated.

Service Information Letter (SIL) 496, " Electrical I'retection Assembly Per-formance," dated August 23, 1989, addressed a number of performance problemsidentified by BWR owners. The SIL discussed and recommended methods forresolving the problems. CP&L reviewed the SIL and incorporated the recommen-dations which were applicable and beneficial to the Brunswick site. A modifi-cation kit was recommended by the SIL which provides for seal in trip indica-,,

tions and an associated reset switch. The modification kit was dc.termined not3 to be cost justified.

Past similar occurrences involving EPA breaker trips have been reported inLER 1-86 018, 1-86-030, 1-87-009 and 2-88-013. LER 1-86-018 reported threeEPA trips which occurred on July 11 and 12, 1986, and on August 2, 1986. The

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July trips were attributed to failure of the primary coil in the breakertransformer, T1, which was replaced. The cause of the August trip was notdetermined. LER 1-86-030 reported two EPA trips; one on Unit 2 on November -

20, 1986, and the other on Unit 1 on December 4, 1986. The cause of the twoevents was attributed to loose connections where sensor leads attac.h to the i

breakers. The connections are now verified at six month intervals. LER1 87-009 reported four EPA trips in March 1987. The cause was attributed to adefective underfrequency card and the card was replaced. LER 2-88-013reported four EPA trips while on the alternate power supply on August 2,1988. The cause was attributed to swings in the alternato power supplyvoltage. Voltage regulator transformers were installed to prevent this eventin the future.

Root Cause and Corrective Actions,

The cause of the event cannot be identified. No further corrective actionsare planned.

Event Assessment

This event had no safety significance as the system functioned as designed.,

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NRC Perm 306A (649)

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