05000374/LER-2010-001

LER-2010-001, High Pressure Core Spray System Declared Inoperable Due to Failed Room Ventilation Control Relay

Docket Number
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
Initial Reporting
3742010001R00 - NRC Website

LaSalle County Station Unit 2 is a General Electric Company Boiling Water Reactor with 3489 Megawatts Thermal Rated Core Power.

A. CONDITION PRIOR TO EVENT:

Unit(s): 2 Event Date: September 25, 2010 Event Time: 0210 CDT Reactor Mode(s): 1 Mode(s) Name: Power Operation Power Level: 100 percent

B. DESCRIPTION OF EVENT:

On September 25, 2010, at 0210 hours0.00243 days <br />0.0583 hours <br />3.472222e-4 weeks <br />7.9905e-5 months <br /> CDT, the Unit 2 Rounds Equipment Operator reported that the Division 3 High Pressure Core Spray (HPCS)[BG] switchgear room supply fan 2VDO5C and the electrically interlocked exhaust fan 2VDO7C (VD)[VJ] were not running. The fans were noted to run when the control switch was placed in the start position, but when the control switch was released, the fans immediately shutdown.

All Unit 2 Division 3 equipment was declared inoperable and unavailable. Because HPCS is a single train system, this occurrence is reportable under 10 CFR 50.72(b)(3)(v)(D) and 10 CFR 50.73(a)(2)(v)(D) as an event or condition that alone could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident. The NRC was notified of this occurrence via ENS 46279, at 0924 hours0.0107 days <br />0.257 hours <br />0.00153 weeks <br />3.51582e-4 months <br /> CDT on September 25, 2010.

Troubleshooting identified that the switchgear cubicle control relay had failed. The relay was replaced, and post maintenance testing was completed satisfactorily. The HPCS system was declared operable at 1230 hours0.0142 days <br />0.342 hours <br />0.00203 weeks <br />4.68015e-4 months <br /> on September 25, 2010.

C. CAUSE OF EVENT:

Troubleshooting identified the Division 3, 480V Motor Control Center (MCC) 243-1 switchgear 2AP79E, cubicle 6A, control relay had failed. The Electrical Maintenance Department replaced the relay and post maintenance testing was completed satisfactorily. Failure analysis determined that the probable failure mode of the relay was age-related degradation.

The cause of the age-related degradation was determined to be improper classification of the relay as a low duty cycle component. As such, the relay did not have any periodic replacement requirements. Based on this failure after ten years of service and the 100% duty cycle of the component, the classification was changed to high duty cycle, and appropriate time-based replacements were established.

D. SAFETY ANALYSIS:

The safety significance of this event was minimal. Reactor Core Isolation Cooling System (RCIC) [BN], Automatic Depressurization System (ADS) [SB], and the Low Pressure Emergency Core Cooling Systems (Residual Heat Removal (RH) [BO] and Low Pressure Core Spray (LP) [BM]) were operable throughout the event.

E. CORRECTIVE ACTIONS:

o The failed relay was replaced, and post maintenance testing was completed satisfactorily.

• The classification of the relay was changed to high duty cycle, and appropriate time-based replacements were established.

F. PREVIOUS OCCURRENCES:

On June 11, 2008, at 0545 CDT, the supply fan for the Unit 2 Division 3 Switchgear Room ventilation system tripped unexpectedly. The direct cause of the supply fan trip was a failure of the fan motor stator winding. The apparent root cause was a failure to implement a time-based refurbishment program, which allowed the motor to be in-service beyond the expected lifetime of 20 years. Corrective actions included replacing the fan motor, and updating the preventative maintenance database to require replacement and/or refurbishment of these motors on a 20-year periodicity (LER 374/2008-001-00).

G. COMPONENT FAILURE DATA:

Potter and Brumfield, CS Series Sensors, CSJ-38-70010