05000219/LER-2003-003

LER-2003-003,

Docket Number
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation
2192003003R00 - NRC Website

NAME

William Stewart TELEP/sONE NUMBER prelude Area Carlo) 609.971.4775 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE SYSTEM COMPONENT

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FACTUNER

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1 SUPPLEMENTAL REPORT EXPECTED (14) EXPECTED

SUBMISN

DATE (15) StO __

MONTH DAY YEAR

I YES (ti yes, complete EXPECTED sueurssioN DATE). I X I_NO _ ABSTRACT (Limit to 1400 moms. Le,. aporofdrnatelv 15 SITale-sPaced hiriewfflien Lies) (15) On August 14, 2003, an electrical disturbance In the oft-site electrical power grid caused an overexcitation condition in the main generator. This resulted In a main generator lockout, turbine trip, and reactor scram from 100% power. The reactor shut down as designed. Plant cooldown to cold shutdown was required due to the trip of all five recirculation pumps (three auto trip and two manual trip). Off-site power was available throughout the event.

The safety significance of this event is considered minimal. The plant responded as designed for this type of event. Technical Specification limits were maintained. There was no radioactive release. Off-site power was not lost. Operator response was appropriate.

DATE OF DISCOVERY

This event occurred on August 14, 2003.

IDENTIFICATION OF OCCURRENCE

Note: System Identification codes from IEEE 805-1984 are indicated with Si. Component Function Identifiers from ANSI/IEEE 803A-1983 are indicated by CFI.

An electrical disturbance In the off-site electrical power grid (St - FK) caused an overexcitation condition in the main generator (SI - TB, CFI - GEN & TG). In response to the overexcitation condition, protective relaying (CFI - 86) locked out the main generator which tripped the main turbine (SI - TA, CFI - TRB) and scrammed the reactor (SI - AC, CFI - RCT). Off-site power was not lost. Actuation of the Reactor Protection System Is reportable under 10 CFR 50.73(a)(2)(iv)(A).

CONDITIONS PRIOR TO DISCOVERY

The plant was operating at approximately 100% power with all reactor plant pressures and temperatures normal for full power operation. All safety-related equipment was operable.

DESCRIPTION OF OCCURRENCE

On August 14, 2003, at 1610 hours0.0186 days <br />0.447 hours <br />0.00266 weeks <br />6.12605e-4 months <br />, annunciators (CFI - ANN) in the Main Control Room indicated a voltage transient and Main Generator Overexcitation. The sequence of alarms (SI - IQ) shows that the initial condition was a low voltage and low VAR condition on the main generator. Within seconds, the low voltage alarm (CFI - EA) cleared and over-voltage and over excitation alarms (CFI - IA) were received. About nine seconds later protective relaying locked out the Main Generator which tripped the main turbine and resulted in a reactor scram.

4 NRC FORM WM (1.2001) Oyster Creek, Unit 1 05000 219 1-1 SEQUENTIAL REVISION FACILITY NAME (t) � DOCKET (2) LER NUMBER 46 The turbine trip caused a pressure Increase which caused one of five Electromatic Relief Valves (CFI - RV) to open momentarily, three of five Reactor Recirculation Pumps (SI - AD, CFI - P) to trip due to the pressure signal in the Anticipatory Trip Without Scram logic, and both Isolation Condensers (SI - BL) to actuate. The reactor scram shut down the reactor as designed. During scram follow-up actions, the locking feature of the Reactor Mode Switch prevented placing it in the Shutdown Position before reactor pressure decreased to 850 psig. As a result, the Main Steam isolation Valves (MSIVs) (SI - SB, CFI - ISV) automatically shut. Operators manually tripped the two operating Reactor Recirculation pumps, as required by procedure due to the auto trip of three of the recirculation pumps, and stabilized plant conditions. Off-site power was available throughout the event.

Although no Technical Specification required the plant to be placed In the Cold Shutdown condition, the trip of all reactor recirculation pumps required cooldown to cold shutdown to recover the plant. Plant cooldown was begun at 1902 hours0.022 days <br />0.528 hours <br />0.00314 weeks <br />7.23711e-4 months <br /> using the Isolation Condensers.

Shutdown Cooling (SI - BO) was placed in service at 0030 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> on August 15, 2003 and the cold shutdown condition was reached at 0236 hours0.00273 days <br />0.0656 hours <br />3.902116e-4 weeks <br />8.9798e-5 months <br />.

APPARENT CAUSE

Actuation of the Reactor Protection System was caused by closure of the turbine stop veil/es when the turbine tripped. The turbine trip was caused by the Main Generator Lockout, which was caused by protective relaying in response to an overexcitation condition on the main generator. The overexcitation condition was caused by a significant transient on the off-site power grid external to the station. Subsequently, it was recognized the transient on the power grid was related to a cascading blackout affecting a large part of the northeast United Sates and adjacent parts of Canada.

ANALYSIS OF OCCURRENCE AND SAFETY ASSESSMENT

The safety significance of this event is considered minimal. The plant is designed for this type of transient and responded as designed. Technical specification limits were maintained_ There was no radioactive release, nor any effect on the health and safety of the public. Off-site power was available throughout the event. Operator response was appropriate.

CORRECTIVE ACTIONS

Evaluated generator-related electrical components for damage from the transient and determined no repair was needed.

Investigated the problem with the reactor mode switch and determined the locking mechanism was operating properly and no repair was needed.

Training on Mode Switch operating technique will be provided to Operations personnel.