ML20005F160

LER 89-040-00:on 891208,emergency Diesel Generators a & B Actuated Due to Degraded Voltage When Condensate Pump Started.Operator Guidelines & Procedures for Starting Condensate Pumps Being revised.W/900108 Ltr

ML20005F160
Person / Time
Site:	Crystal River
Issue date:	01/08/1990
From:	Beard P, Moffatt L FLORIDA POWER CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
3F0190-05, 3F190-5, LER-89-040, LER-89-40, NUDOCS 9001120369
Download: ML20005F160 (5)

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f. . e C ORPOR ATION January 8, 1990 3F0190-05 l

U. S. Nuclear Regulatory h imaion Attantion: Document Control Desk Washington, D. C. 20555

Subject:

Crystal River Unit 3 Docket No. 50-302 Operating License No. DPR-72 Licensee Event Report No.89-040

Dear Sir:

Enclosed is Licensee Event Report (IER)89-040 whid is submitted in accordance with 10 CFR 50.73.

'-' Should there be any questions, please contact this office.

Very truly yours,

[.M. Beard,Jr.

r- Senior Vice President Nuclear Operations WIR: mag Enclosure

!. xc: Regional Administrator, Region II L

Senior Resident Inspector i

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GENERAL OFFICE: 3201 Thirty fourth Street South

• P.o. Sox 14042

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A Florida Progress Company

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Florida Power Corporation is evaluatirg additional lorg tem actions to prevent unnecessary E DG starts when starting large loads such as the condensate punps, i

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On nar,amhar 8, 1989, Crystal River Unit 3 (CR-3) was in WDE: 3 (WP STAWBY) for replacement of a contml md drive stator (AA,M]. Wree mactor coolant punps (AB,P] were operating and the Reactor Coolant System [AB] pmssure and tenperature was 2155 psig and 545 degrees F. We CR-3 plant and Engineered Safeguards (ES) loads, 6900 V and 4160 V inclusive, were being supplied by the G-3 Startup Transformer (EA,XFMR), see the attached figure. At 0206 the voltage of the ES 4160 V bus (EB,HJ) degraded to the actuation setpoint of the Second IEvel Undervoltage Relays Systan [EB,2) (SWRS) and the time delay associated with these relays actuated. When the time delay was satisfied (5 seconds) and the voltage had not recovered above the SWPS setpoint, the A and .

B Emergency Diesel Generators [EK,D3] (D3M) started. W e voltage did not stay degraded larg enough, 18 seconds, to cause the ES buses to strip and reload onto the D3DG's. Control Rocxn operators verified the automatic start of the D3DG's and verified the recovery of the ES Bus voltage. We EGD3's were then returned to normal staMby condition.

A four hour report was made to the NRC Operations Center per 10CFR50.72(b) (2) (ii) . mis event is being reported per 10CFR50.73(a)(2)(iv) since it is considered an unplanned actuation of an ES system.

CAUSE:

l 2e cause of the DGDG actuation was a degraded voltage on the ES 4160 V buses for greater than 5 seconds. We degraded voltage occurred when CR-3 operators started the A Condensate pump (SD,P], which has a large starting current and a long start time. We condensate punps are powered by the 4160 V Unit bus l [EA,HJ). Contributors to this actuation include the SWRS setpoint, which is set very close to the normal operating range, and the low pre-event ES bus '

voltage, 4150 volts. In October 1989, the SWRS setpoint was changed from 3780 volts to 3864 volts due to concerna about nonconservative design ammptions, see IER 89-033. Prior to this setpoint change, sufficient margin existed such that starting the condensate punps would not cause an D3D3 actuation.

When the SWRS setpoint was changed in October, instructions were issued to operators to consider raising the grid voltage or redistributirg loads when starting a condensate punp. We licensed operator had recently started the condensate punps with the grid voltage at approximately the same level as the level for this event without causing an D3DG actuation. Werefore, the grid voltage appeared to be high enough to avoid an DGD3 actuation.

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EVENT ANMA' SIS:

We purpose of the SIURS is to prevent a sustained degraded voltage frm damaging Es equipment. Specifically, the SIURS is designed to prevent a deg A i voltage of less than 95% for longer than 18 secords at the erd devices. %e SIURS includes time delayed relays for starting the D3D3's and for stripping and loading the 4160 V ES buses. %e time delay relay's function is to allow same slight and tarporary voltage fluctuations without innediately starting the Ir.D3's a4/or stripping and reloading the Es buses onto the D3DG's. A degraded voltage must remain below the setpoint, 3864 volts on the 4160 V ES buses, for 5 seconds before startirg an D3D3. W e degraded voltage uust exist for a total of 18 seconds before the 4160 V bus loads are stripped and loaded onto the IGDG's. We degraded voltage appears to have lasted just slightly longer than the 5 second time delay required to start the diesel generators.

Power to the ES buses was always available. Were was no decrease in the margin of safety for the public. None of the safety functions of plant equignent were ocmprunised. All in-plant equipnent functioned as designed and plant response procedures were adequate for the situation. Actions by the operators in response to this event were timely and appropriate.

l CmRBCTIVE ACI'ICNS:

Operator guidelines and procedures for start 11g the Cordensate puraps are being revised to provide more specific re-endations for raising the bus voltage and/or realigning the ES buses prior to starting the CR-3 Condensate pumps.

1 Florida Power Corporation is evaluating additional long term actions to prevent unr==y D3D3 starts when starting large loads such as the Condensate pumps.

PRINIOUS SDGIAR EVENTS:

Unplanned D3D3 starts have previously occurred eleven times. Wis event was i the secord D3DG actuation due to an actual degraded voltage event. The prior event, IER 89-013, occurred khen Crystal River Unit 1/2 started a large load while the CR-3 ES buses were aligned to the CR-1/2 Startup Transforner.

Actions taken for IER 89-013 khich addressed actions to take khen aligned to i the CR-1/2 Startup Tnnsformer, were neither intended nor expected to prevent the actuation described by this report.

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