05000374/LER-2008-001

LER-2008-001, High Pressure Core Spray System Declared Inoperable Due to Failed Room Ventilation Supply Fan

Docket Number
Event date:	06-11-2008
Report date:	08-08-2008
Reporting criterion:	10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
Initial Reporting
3742008001R00 - 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 : June 11, 2008 Event Time : 0545 CDT Reactor Mode (s) : 1� Power Level(s) : 100 percent Mode(s)Name :Run

B. DESCRIPTION OF EVENT:

On June 11, 2008, at 0545 CDT, the supply fan for the Division 3 Switchgear Room ventilation system (VD) [VJ] tripped unexpectedly. Division 3 AC power supports the High Pressure Core Spray System (HPCS) [BG]. HPCS remained functional and capable of vessel injection following the loss of ventilation to the Division 3 Switchgear Room; however, HPCS was declared inoperable based on long­ term temperature considerations associated with potential heat up concerns of the areas served by the failed ventilation system. The circuit breaker for the HPCS injection valve, which is a primary containment isolation valve, was opened at 1703 CDT on June 11, 2008, and the valve de-energized in the closed position to comply with Technical Specification (TS) 3.6.1.3 Required Action C.1. Disabling the injection valve affected the function, but not the availability of HPCS.

Troubleshooting identified the cause of the supply fan trip as an age-related failure of the fan motor winding. The fan motor was replaced, and the HPCS system was declared operable at 0608 on June 12, 2008. HPCS was inoperable for approximately 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and 23 minutes.

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 at 1748 CDT on June 11, 2008.

C. CAUSE OF EVENT:

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.

D. SAFETY ANALYSIS

The safety significance of this event was minimal. HPCS remained available and capable of vessel injection if required to mitigate the consequences of an accident. Additionally, the 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.

� This event constitutes a safety system functional failure.

E. CORRECTIVE ACTIONS

• The supply fan motor was replaced.

• A Service Request will be submitted to perform 20-year replacement/refurbishments of the motors identified in the extent of condition investigation.

• Duty cycle classifications for all 480-volt motors will be reviewed and a periodic 480-volt motor time­ based refurbishment/replacement will be implemented.

F. PREVIOUS OCCURENCES

On May 16, 2007, the Unit 2 Rounds Equipment Operator reported an unusually high d/p across the Division 3 Switchgear Room door, making it hard to close. Subsequent investigation found the Division 3 Switchgear Supply Fan not running, while the other Division 3 ventilation fans were running. The fan was successfully re-started per station procedure. No cause could be identified, and the trip was considered spurious.

G. COMPONENT FAILURE DATA

Reliance Nuclear Service 15HP, 1770RPM, 460VAC, 3PH, 1.0SF, 21AMPS Motor Model Number: 254TCZ Type: P Insulation Class: H Insulation Type: RH Serial Number: 1YF882360A3 SC �