ML20029B075

LER 91-002-00:on 910129,startup Transformer Incapable of Maintaining Voltage Output Above Setpoint of Second Level Undervoltage Relays Under Es Actuation Conditions.New Offsite Power Supply installed.W/910228 Ltr

ML20029B075
Person / Time
Site:	Crystal River
Issue date:	02/28/1991
From:	Bandhauer W, Boldt G FLORIDA POWER CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
3F0291-14, 3F291-14, LER-91-002, LER-91-2, NUDOCS 9103050366
Download: ML20029B075 (4)

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00 coneomAtnow Crystal River Unit 3 Docket to. 50 302 i february 28, 1991 3F0291-14' V. S. Nuclear Regulatory Commission Attention: Document Control Desk .

Washington, D. C. . 20555  ;

Subject:

Licensee-Event-Report (LER) 91 002 l

Dear Sir:

L Enclosed is Licensee Event Report (LER): 91-002 which is submitted in accordance with 10 CFR 50.73.

Sincerely, l -

l G. L. Boldt

! -Vice' President' i

- Nuclear Production WLR

mag j- . Enclosure

.xt: Regional Administrator, Region II Project Manager, Region 11 Senior Resident Inspector 9103050366 910228 f I PDR ADOCK 05000302 I S PDR '

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On January 29, 1991, Crystal River Unit 3 was operating in MODE I (POWER 4

OPERATIONS) at 99% rated power. It was reported to plant management that the UNIT 3 STARTUP TRANSFORMER (SVX) is incapable of maintaining its voltage output above the setpoint of the Second Level Undervoltage Relays (SLURS) under certain Engineered Safeguards (ES) actuation conditions.

The SVX is the alternate offsite power source for the ES busses.

Calculations also show that the steady state loading on the 4160V winding of the SVX will exceed the forced Oil and Air (F0A) 65 degree Centigrade

rating of the winding during intermediate and large break Loss of Coolant Accident (LOCA) scenarios.

The cause of this inability to meet performance requirements is a failure to anticipate a specific combination of events and conditions in the initial design and subsequent plant modifications, immediate and permanent procedure changes were initiated to provide guidance to the licensed operators. A plant modification has been initiated to install a new alternate offsite power supply for the ES busses.

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0l0 0) 2 oF o l3 rext a mm em e me.m en mew vc rw 3,u v nn EVENT DESCRIPTION On January 29, 1991, Crystal River Unit 3 was operating in MODE I (p0WER OPERATIONS)at99%ratedpower. The continuing Design Basis review program identified to plant management that the UNIT 3 STARTUP TRANSFORMER (SVX)

[EB,XfMR) was not capable of maintaining its voltage output above the setpoint of the Second Level Undervoltage Relays (SLURS) (EB,PR) under certain Engineered Safeguards (ES) [EB BU] actuation conditions. The SVX .

is the alternate offsite power source for the ES busses. A specific combination of conditions is necessary before this problem exists. The ,

necessary combination is for the SUX to be carrying both of the 4160V Unit Busses [EA,BV) and either of the ES 4160V busses, and for an ES actuation to occur, and for the ES busses to be supplying those loads required by an intermediate or large break Loss of Coolant Accident (LOCA).

The function of the SLURS is to protect the ES 4160V busses from sustained periods of low voltage. Continued operation of safety related equipment in a degraded voltage condition could cause damage and loss of function for -

vital safety related end devices. The potential for degradation of the ES 4160V bus voltage below the SLUR setpoint results in the SVX (the alternate offsite power source) not meeting its design criteria. Calculations also

• indicate that the steady state loading on the 4160V winding of the SVX will exceed the forced Oil and Air (F0A) 65 degree Centigrade rating of the winding during the LOCA situations mentioned above.

CAI)SE OF EVENT The cause of this inability to meet performance requirements is a failure to anticipate a specific combination of events and conditions in the initial design and subsequent plant modifications. Neither the initial loading calculations nor those performed for the addition of the StVRs considered the magnitude of the voltage drop experienced with fully loaded ES and unit busses.

SAFETY CONSE0ViliGil .

- If the SUX were loaded with both Unit 4160V busses carrying normal loads and either ES 4160V busses carrying normal operating loads, and an ES actuation due to an intermediate or large break LOCA were to occur, the following would be the sequence of events:

1. Engineered Safeguards equipment would be loaded onto the ES 4160V ,

bus.

2. The SUX would not be able to keep the voltage of the ES 4160V bus above the setpoint of the SLURS.

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3. The SLURS, which are time delay devices, would separate the ES loads from the ES 4160V and de energize the 4160V bus.

4. When the ES busses experienced an undervoltage condition, the .

Emergency Diesel Generator (EDG) (EK,0G) would start.

5. ES loads would be picked up by the EDG and the plant would be protected as designed.

These actions would fully comply with the design objective of protecting the nuclear core and preventing the release of radioactive muedal. Therefore, the health and safety of the public would not be compromisod by the inability of the Unit 3 Startup Transformer to meet it: design objective.

CORRECTIVE ACJ1MJ

1. Guidance concerning acceptable electrical lineups for the Unit and ES 4160V busses was immediately provided to the licensed operators. The acceptable electrical lineups preclude the SUX from carrying the loads described above.

2. Immediate notification was made to the Nuclear Regulatory Commission by means of a one hour report.

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3. Procedure changes to Opratihg procedures are being implemented to guide the operatorr, in electrical lineups for the Unit and ES 4160V busses.

4. Florida Power Corporation (FPC) will install an additional transformer to be used as the alternate offsite power source for the ES 4160V busses.

5. The Design Basis review program, which led to identification of this inadequacy on the part of the SUX, will continue.

PREVIOUS SIMILAR l'VElill Several previous Licensee Event Report (LER) events caused by design or system ' inadequacies were discovered by the use of more stringent analysis methods than the original methods employed. Among the more recent LERs are 90 002 and 90 005. Neither of these LERs dealt with the SUX or the electrical system.

N3C Form 366A (14101

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