05000373/LER-2013-006
| Lasalle County Station, Unit 1 | |
| Event date: | 08-13-2013 |
|---|---|
| Report date: | 10-14-2013 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(B), System Actuation 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| Initial Reporting | |
| 3732013006R00 - 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 Event Date: August 13, 2013 Event Time: 1007 CDT Reactor Mode(s): 1 Mode(s) Name: Power Operation Power Level: 100%
B. DESCRIPTION OF EVENT:
On August 13, 2013, technicians were performing a circuit breaker cubicle inspection for the 1C Residual Heat Removal (RHR)[B0] pump. At approximately 1007 hours0.0117 days <br />0.28 hours <br />0.00167 weeks <br />3.831635e-4 months <br /> CDT, while the technicians were cleaning the lower cubicle, the 1A Diesel Generator (DG)[EK] cooling water pump [BI] automatically started. Operators were dispatched to verify that the pump was running normally, and once it was verified that there were no current plant conditions that would have required the 1A DG cooling water pump to start, the pump was secured.
This event is reportable under 10 CFR 50.73(a)(2)(iv)(A) as an event that resulted in the automatic actuation of a system listed in 10 CFR 50.73(a)(2)(iv)(B)(9). An ENS report was not required for this event.
C. CAUSE OF EVENT:
Investigation determined that the mechanically operated contact (MOC) switch in the bottom of the circuit breaker cubicle had been inadvertently bumped and the contacts made up during the cubicle cleaning. Closing the contacts caused the RHR Pump B/C Cubicle Cooler Fan 1VY03C (VY)[VF] fan to start, which in turn completed the start logic for the 1 A DG cooling water pump. Further investigation found that the MOC switch linkages were maladjusted, which allowed the contacts of the MOC switch to close from very light casual contact of the switch linkage. The maladjustment of the switch was due to the lack of adjustment guidance under previous revisions of the maintenance procedures.
D. SAFETY ANALYSIS:
The safety significance of this event was minimal. The 1A DG cooling water pump started and ran with no abnormalities noted. The unexpected start did not result in any other system actuations or plant transients.
E. CORRECTIVE ACTIONS:
- Procedure LES-GM-103, "Inspection of 4.16kV and 6.9 kV ITE Circuit Breakers" will be revised to provide guidance to verify correct actuation and ensure correct adjustment of MOC switch contacts.
- Procedure LES-GM-103 will also be revised to provide guidance to lift leads or install jumpers as needed prior to cleaning and inspecting breaker cubicles, in order to preclude inadvertent actuations.
F. PREVIOUS OCCURRENCES:
On July 26, 2010, at 1819 CDST, with Unit 1 in Mode 1 (Power Operation), the Division 1 Diesel Generator cooling water pump unexpectedly restarted after being secured.
The Division 1 DG cooling water pump was being shutdown following completion of required surveillances on related supported systems. The DG cooling water pump was secured using the main control room pump control switch. When the switch was returned to the standby position, the DG cooling water pump breaker received an automatic lock-out. The automatic lock-out occurred as a result of the circuit being designed to preclude continuous breaker cycling (anti-pumping). When the operator reset the breaker by placing the control switch momentarily to stop and back to standby, the DG cooling water pump automatically restarted. This was because the LPCS/Reactor Core Isolation Cooling (RCIC) corner room cooling fan was still running following the completed surveillances, and when the fan is running, an automatic start signal is provided to the DG cooling water pump. The operator was unaware that the LPCS/RCIC corner room cooling fan was still running.
The cause of the July 2010 event was a latent procedure error in that the steps being performed failed to require verification that all of the remote components that send start signals to the DG cooling water pump were secured. Procedure revisions have been initiated for procedures that direct securing DG cooling water pumps to ensure that all remote components that provide an automatic start signal have been secured. The corrective actions from this previous event would not have prevented the August 2013 occurrence.
G. COMPONENT FAILURE DATA:
There were no component failures associated with this event.