05000373/LER-2013-003
| Lasalle County Station, Unit 1 | |
| Event date: | 04-18-2013 |
|---|---|
| Report date: | 06-17-2013 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| Initial Reporting | |
| 3732013003R00 - NRC Website | |
LaSalle County Station Units 1 is a General Electric Company Boiling Water Reactor with 3546 Megawatts Rated Core Thermal Power.
A. CONDITION PRIOR TO EVENT:
Unit(s): 1 Reactor Mode(s): 3 Event Date: April 18, 2013 Event Time: 1325 CDT Mode(s) Name: Hot Shutdown Power Level: 0%
B. DESCRIPTION OF EVENT:
On April 18, 2013, at approximately 1325 hours0.0153 days <br />0.368 hours <br />0.00219 weeks <br />5.041625e-4 months <br /> CDT, Unit 1 was in Mode 3 following a loss of offsite power event and dual unit scram the previous day. While attempting to raise Unit 1 reactor water level with the Low Pressure Core Spray (LPCS)[BM] system, LPCS injection motor-operated valve 1E21-F005 failed to open when the control switch (1E21A-S002) was held in the "OPEN" position.
The LPCS system was declared inoperable but available, with an Equipment Operator briefed and ready to manually open the injection valve if required. Technical Specification (TS) 3.5.1 Required Action A.1 was entered, requiring that LPCS be restored to operable status within seven days. The 1C Residual Heat Removal (RHR)[BO] system was started and lined up as a standby injection source.
Initial review of the failure determined that the event was not reportable; however, subsequent review determined that because LPCS is a single train system, the event was reportable under 10 CFR 50.73(a)(2)(v)(D) as an event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident. An ENS report was made (EN-48966) pursuant to 50.72(b)(3)(v)(D) at 1123 CDT on April 25, 2013.
This event constitutes a safety system functional failure.
C. CAUSE OF EVENT:
Troubleshooting identified that the problem was with control switch 1E21A-5002, which is a General Electric single block module (Type SBM) switch. The switch was tested following replacement, and it was determined that the direct cause of the event was the failure of the 1 & 1T contact set. The most probable cause of the contact set failure was electrical erosion of the contact surface, which allowed the buildup of oxidation that prevented 1E21-F005 valve operation. Electrical contact erosion is caused by arcing inherent in the cycling of the switch. All other contacts in the switch were found to be working normally.
D. SAFETY ANALYSIS:
The safety significance of this event was minimal. Troubleshooting of the switch and review of the control circuit wiring found that the failure of contacts 1 & 1T would not have prevented 1E21-F005 from automatically opening upon an actuation signal.
LaSalle County Station, Unit 1 05000373
E. CORRECTIVE ACTIONS:
- Control switch 1E21A-S002 was replaced, and the new switch was tested satisfactorily.
- A sample of SBM switches will be tested to determine if electrical contact erosion is starting to occur on other switches with similar in-service life installed in similar electrical circuits.
F. PREVIOUS OCCURRENCES:
A review found no previous occurrence of a system rendered inoperable due to failure of a control switch in the past ten years.
G. COMPONENT FAILURE DATA:
General Electric Type SBM Switch