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Crystal River Unit 3Docket No. 50-302

May 10, 19933F0593-04

U. S. Nuclear Regulatory CommissionAttention: Document Control DeskWashington, D. C. 20555

Subject: Licensee Event Report (LER) 93-04

Dear Sir:

Enclosed is Licensee Event Report (LER) 93-04 which is submitted inaccordance with 10 CFR 50.73.

Sincerely,

G. L. oldtVice PresidentNuclear Production

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Enclosure

xc: Regional Administrator, Region 11Project Manager, NRRSenior Resident Inspector

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PE F4E I N C 1 De FOF MANAGEMENT AND BUD 3ET, WASHINGTON DC 20603.

F AcilTV NAME (1) DOOTT NUMBER (2) PAGE (3)

CRYSTAL RIVER UNIT 3 (CR-3) o | 5 | 0 | 0 | 01310 | 2 1 |OF| o | 4TITti (4)

Inappropriate Personnel Action Resulted in Degraded Class 1E Bus Voltage and Actuation of Ernergency Diesel Generatori

EVENT DATE(6) LER NUMBER (6) EPORT DATE (7) OTHER FActuTIES INVOLVED (a)

SEQUENTIAL REVISION FACIUTY NAMES DOCKET NUMBEF(S)

o|5|o|0|0| | |MONTH DAY YEAR YEAR NUMBER - NUMBER MONTH DAY YEAR N/A

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MODE (9) 520 402(b) 20.405(c) X 60.73(aK2Xw) 73.71(b)

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UCENSEE CONT ACT FOR TH&S LER (12)

NAME TELEPHONE NUMBERAREA CODE

W. A. Stephenson, Nuclear Safety Supervisor9|o|4 7] 9 | 51- | 6| 4 | 8 | 6

COMPLETE ONE LINE FOR EAOt COMPONENT FAILURE IN THIS FEPORY (13)

CAUSE SYST EM COMPONENT MANUF AC- REPORTABLE CAUSE SYSTEM COMPONENT MANUFAC- REPORTABLETUFtER TO NPRDS TURER TO NPRDS

I I I I I I I I I I I i ! |

1 I I I I I I i I i l i I IEXPECTED MONTH DAY YEARSUFMIMENTAL FEPORT EXPECTEDO4)

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On April 8,1993, Crystal River Unit 3 (CR-3) was in MODE 5 (COLD SHUTDOWN) for aplanned maintenance outage. Electrical power was being supplied via backfeed fromthe 500 kilovolt (KV) switchyard. One of the two Class lE electrical systems was outof service. At 1803 the 500KV breakers opened, interrupting the power backfeed. Thein-service Class 1E 4160 Volt (V) bus deenergized. The "B" Emergency DieselGenerator started automatically and reenergized the bus. This report is submitted inaccordance with 10CFR50.73(a)(2)(iv).

Decay heat removal flow was stopped for approximately three minutes during thetransition of loads to the Emergency Diesel Generator. Reactor Coolant Systemtemperature, initially 89 degrees Fahrenheit, increased approximately 4.5 degreesFahrenheit during this period.

The event occurred when personnel followed an incorrect sequence for removing DCpower to the 500KV breaker protective relays as a result of inadequate Workinstructions being used to replace a battery cell in one of the switchyard battery 1banks. Additional administrative controls have been established to reduce the riskof interruption of offsite power and decay heat removal. Additional corrective !actions, based on the results of a Human Perfcrmance Enhancement System (HPES) ianalysis, will be addressed. |

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OF MANAGEMENT AND BUDGET, WASHINGTON DC 20603.

F AC1RV NAME (1) DOGIT NUUBER(4 LER NUMBER (8) PAGE (3) >i stoutwimL - REVISION

" " " '" " " E"CRYSTAL RIVER UNIT 3 (CR-3)

0| 5| 0| 0| 0| 3| 0| 2 9|3 - 0|0|4 - 0|0 0 | 2 |OF| 0 | 4itxi e m m e m u .ae.w unc e , mu . sm

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EVENT DESCRIPTION :

On April 8,1993, Crystal River Unit 3 (CR-3) was in MODE 5 (COLD SHUTDOWN) for a |"

planned maintenance outage. The reactor [AC, RCT] was being cooled by the "B" iDecay Heat (DH) Removal [BP] system. Reactor Coolant System (RCS)[AB] temperaturewas 89 degrees Fahrenheit (F). RCS pressure was being maintained at 58 pounds per !square inch gauge (psig). The startup transformer [E, XFMR] and the "A" EngineeredSafeguards (ES) electrical busses [EB, BU] were out of service due to maintenanceand modification activities. The offsite power transformer [EB, XFMR] powered fromthe 230KV switchyard was available as a backup, but not in service. All plantelectrical power was supplied via backfeed from the 500 kilovolt (KV) switchyard 1[FK]. Under this arrangement, power was supplied through the main generator outputbreakers [EL, BKR), stepup (output) transformers [EL, XFMR], and the auxiliarytransformer [EL, XFMR].

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Power for operating the 500KV switchyard breakers and protective relay [FK, RLY]circuits is provided by two battery banks located in the switchyard. Battery

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'voltage is maintained by local battery chargers [FK, BYC). At the time of theevent, electrical technicians were preparing to replace an individual cell in oneof the switchyard battery banks.

At 1803 technicians opened the battery disconnect switch [FK, DISC] to isolate thebattery from its load as part of the replacement work. This action caused batterycharger output voltage to oscillate, leading to actuation of protective relayingand opening of breakers in the 500KV switchyard, resulting in loss of the powerbackfeed. The "B" ES bus [EB, BU] deenergized when the backfeed was lost. Whenthe "B" ES bus deenergized, the "B" DH Pump [BP, P] tripped, resulting in atemporary loss of DH removal flow. Relays which monitor "B" ES 4160 volt (V) bus !voltage sensed the loss of power and initiated the starting sequence for the "B"

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Emergency Diesel Generator (EDG)[EL DG). The EDG started md automaticallyreenergized the bus. Operators then restarted the "B" DH pump and restored decayheat removal. This report is submitted in accordance with 10CFR 50.73(a)(2)(iv).

At 2019, operators aligned the "B" ES busses to the offsite power transformer. ;

EVENT ANALYSIS L

The "B" EDG functioned as designed. The EDG automatically started and reenergizedthe 4160V "B" ES bus. Operator actions were timely, appropriate and in accordancewith plant procedures.

The core was without cooling for approximately three minutes. RCS temperatureincreased approximately 4.5 degrees F during this period. The core was adequatelysubcooled at all times.

NHC Form 306A (6-49)

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MMn"2"Mu"8"aMTenML"M"EOF M ANAGE MENT AND BUDGET, WASHINGTON DC 70503.

F AC3JTY NAME (1) DOOK.ET NUMBER (2) LEH NUMBER (6) PAGE (3)atoutwTen . htV@ON

YEAR NUMBEN . NUMBERCRYSTAL RIVER UNIT 3 (CR-3)

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CAUSli

The "B" EDG started following loss of the 500KV backfeed, and "B" ES bus voltage.A Human Performance Enhancement System (HPES) root cause analysis is beingperformed. The apparent cause is personnel action resulting from inadequate workinstructions being used to replace a battery cell in the switchyard battery bank.

An incorrect sequence of steps was used during the replacement. The techniciansintended to isolate the battery and allow the charger to power the DC bus. Toproperly secure switchyard DC power, technicians should have first deenergized thebattery charger, and then opened the battery disconnect switch. Although thesesteps were not included in the written work instructions, appropriate day shiftworkers, including engineering department personnel, were aware of the required

j action sequence. Work plans called for the job to be performed on the day shiftdue to the availability of these personnel and their contact with the vendor ontechnical issues.

Due to miscommunication between shifts, night shift personnel thought that theywere supposed to complete the battery cell replacement. Unaware of the requiredaction sequence, technicians opened the battery disconnect switch beforedeenergizing the charger. Based on their experience with plant battery chargers,night shift technicians believed that this was acceptable.

The switchyard battery chargers and batteries are arranged such that opening thebattery disconnect switch causes the chargers to carry the loads. However, due totheir design, the switchyard battery chargers are not satisfactory power suppliesby themselves. The technicians had experience working with plant battery chargerswhich are capable of supplying DC loads without the batteries attached to the bus.When technicians opened the battery disconnect switch, lack of output filtering ofthe switchyard battery charger output imposed an AC signal on the DC busses. TheDC busses also experienced a rapid rise in DC voltage. The imposed AC signalcaused many DC solid state protective relays to fail, and caused the 500KV breakersto open. This resulted in an interruption of offsite power to the plant.

CORRECTIVE ACTION

The affected relays were tested and the failed relays were repaired or replaced.

Florida Power Corporation has established additional administrative controls onswitchyard activities. These controls will reduce the risk of interruptions of

t offsite power by avoiding any type of work within the switchyard providing powerto shutdown cooling. This would not include " foot patrols" but would includevehicular traffic and maintenance, modification, or testing activities. Anyexceptions would require approval of senior plant management prior to initiation.

| Additional corrective actions, based on the results of the HPES evaluation, willbe developed.

N8C Form 366A (6-89)

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FACERY NAME (1) DomET NUMBmG3 LER NUMBER (6) PAGE(3. stoutwr.at . nevia.oi.

YEAR NWBER : NWBERCRYSTAL RIVER UNIT 3 (CR-3)

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PREVIOUS SIMILAR EVENTS

There have been thirteen previous events where either one or both EDGs haveautomatically started due to a sensed undervoltage condition on the ES busses.This was the second event which resulted from loss of the backfeed from the 500KVswitchyard.

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NHC Form 306A(6 49)1

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