05000353/LER-2005-002
| Docket Number | |
| Event date: | 03-28-2005 |
|---|---|
| Report date: | 05-26-2005 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 3532005002R00 - NRC Website | |
Unit Conditions Prior to the Event Unit 2 was in Operational Condition (OPCON) 1 (Power Operation) at approximately 100% power. There were no structures, systems or components out of service that contributed to this event.
Description of the Event
On Monday March 28, 2005, at 17:38 hours, while Unit 2 was operating at approximately 100% power, the Main Control Room position indication on the High Pressure Coolant Injection (HPCI) [EIIS: BJ] system outboard suppression pool suction motor operated valve (MOV) HV 055-2F041 was lost and the HPCI out-of-service alarm annunciated. HPCI was declared inoperable and Technical Specification 3.5.1 Action c.1 was entered, which requires system restoration to operable status within 14 days.
An investigation determined that the condition was caused by a loose control power fuse clip [El IS: FUB] located on the 250 VDC circuit breaker, which resulted in loss of control power to the MOV. The degraded fuse clip was replaced and the MOV was successfully stroked. The Unit 2 HPCI system was restored to operability at 21:30 hours.
The Reactor Core Isolation Cooling (RCIC) [EllS: BN] system remained operable during the entire period from when the loss of control power to the HPCI MOV occurred until the HPCI system was restored to operability at 21:30 hours.
This event involved the potential loss of safety function of the Unit 2 HPCI system for 3.9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br /> from March 28, 2005 17:38 to March 28, 2005 21:30. The 8-hour ENS notification required by 10CFR50.72(b)(3)(v)(D), was completed on March 28, 2005 at 23:56 EDT hours (Event# 41540).
This event involved a condition that could have prevented the fulfillment of the safety function of the HPCI system to mitigate the consequences of an accident; therefore, this LER is being submitted pursuant to the requirements of 10CFR50.73(a)(2)(v)(D).
Analysis of the Event
There were no actual safety consequences associated with this event. The potential safety consequences of this event were also minimal. HPCI suction was aligned to the condensate storage tank (CST) at the time of the failure; therefore, the initial system response to a loss of coolant accident was unaffected. The HPCI pump suction would not have automatically transferred from the CST to the suppression pool on a CST low level condition or a suppression pool high level condition. The CST has the capacity to provide full flow HPCI injection for approximately 15 minutes before needing to transfer to suction from the suppression pool. The HPCI response to a station black out (SBO) accident was potentially adversely affected since the follow-up operator actions require transferring the HPCI suction to the suppression pool. The reactor core isolation cooling (RCIC) system was operable during the period when HPCI was adversely affected by the fuse clip failure.
The terminal block, fuse clip, and rivets are part of a single assembly supplied by Westinghouse with Eaton Electric as the dedicated supplier (part number TBAF3).
These terminal blocks/ fuse clips are utilized in safeguard DC Motor Control Center applications for both the Limerick Unit 1 and Unit 2 HPCI and RCIC.
The laboratory analysis of the failure of the fuse clip determined that the loss of continuity was due to a loose rivet on the fuse clip that was not properly swagged during manufacturing.
The preventive maintenance (PM) procedures in place include inspection of the terminal block and fuse clips for loose connection, cracks, and other visible damage. The terminal block is not removed during the PM inspection. It was determined that the PM procedure should be enhanced to include inspection of the fuse block rivets for complete roll and tightness.
Cause of the Event
The cause of the event was a loss of control power to the HPCI pump suction outboard motor operated valve as a result of a manufacturing defect in the control power fuse clip.
Corrective Action Completed The degraded fuse clip was replaced. Storeroom inventories of replacement parts for the fuse clips were visually inspected and no deficiencies were identified.
Corrective Action Planned The procedure for periodic maintenance of Westinghouse 250 VDC magnetic starters will be revised to include a closer examination of the fuse block rivets by July 29, 2005.
Previous Similar Occurrences There were no previous occurrences of a loss of MOV control power rendering HPCI inoperable.
Component data:
Cause:� B� (Design, Manufacturing, Construction/Installation) System:� BJ� (High Pressure Coolant Injection System) Component:� FUB (Fuse Block) Manufacturer:� W120 (Westinghouse) Part Number� TBAF3