05000373/LER-2012-001
| Lasalle County Station | |
| Event date: | 09-18-2012 |
|---|---|
| Report date: | 11-09-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material |
| Initial Reporting | |
| 3732012001R00 - NRC Website | |
LaSalle County Station Units 1 and 2 are General Electric Company Boiling Water Reactors with 3546 Megawatts Rated Core Thermal Power.
A. CONDITION PRIOR TO EVENT:
Unit(s): 1 / 2� Event Date: September 18, 2012� Event Time: 0115 CDT Reactor Mode(s): 1 / 1 Mode(s) Name: Power Operation / Power Operation Power Level: 100% / 100%
B. DESCRIPTION OF EVENT:
On September 18, 2012, Units 1 and 2 were in Mode 1 at 100% power. At 0115 hours0.00133 days <br />0.0319 hours <br />1.901455e-4 weeks <br />4.37575e-5 months <br /> CDT, an Equipment Operator (EO) reported that the Unit 2 Reactor Building 761' Interlock Doors 424/314 were both open at the same time for approximately 10 seconds. The control room supervisor instructed the EO to remain in the interlock to ensure one door remained closed at all times. During the time that both interlock doors were open, Technical Specification (TS) Surveillance Requirement (SR) 3.6.4.1.2 ("Verify one secondary containment access door in each access opening is closed") was not met. The Secondary Containment (CS) [NG] was declared INOPERABLE for the period of time both interlock doors were open and until administrative controls (posting the operator at the door) were established to verify one door remained closed at all times. LaSalle Station entered and exited TS 3.6.4.1 Required Action A.1 for both Unit 1 and 2 to restore Secondary Containment to OPERABLE status within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.
This occurrence is reportable under 10 CFR 50.73(a)(2)(v)(C) and (D) as an event or condition that could have prevented the fulfillment of the safety function of the structures or systems that are needed to control the release of radioactive material and to mitigate the consequences of an accident.
An ENS report was made to the NRC (EN# 48317) at 0459 CDT on 9/18/12 pursuant to 10CFR50.72(b)(3)(v)(C), Event or Condition that could have prevented the fulfillment of a Safety Function needed to Control the Release of Radioactive Material.
This event constitutes a safety system functional failure.
C. CAUSE OF EVENT:
The two loose screws on the locking solenoid bracket caused the electric lock assembly to become misaligned.
The misalignment of the electric lock assembly prohibited the locking solenoid plunger from being fully engaged with the door catch. This condition prevented door 424 from locking when opening paired interlock door 314.
This malfunction resulted in the capability to open both interlock doors at the same time.
The loosening of the screws was determined to be due to repeated stressing from repeated challenging of the interlock function.
D. SAFETY ANALYSIS:
The safety significance of this event was minimal. The Reactor Building-to-outside differential pressure remained negative throughout the period that the Secondary Containment was inoperable. The Secondary Containment was inoperable for a brief period (i.e. approximately 10 seconds), TS 3.6.4.1 entered and exited at 0115 CDT, which was significantly less than the four-hour Completion Time to restore the secondary containment to operable status allowed by TS 3.6.4.1 Required Action A.1
E. CORRECTIVE ACTIONS:
- The interlock door limit switch has been replaced
- The solenoid mounting bracket was removed, tightened, and re-installed.
F. PREVIOUS OCCURRENCES:
On March 2, 2011, Unit 1 was in Mode 1 at 100% power and Unit 2 was in Mode 5 in a refueling outage, with fuel moves in progress. At 0928 hours0.0107 days <br />0.258 hours <br />0.00153 weeks <br />3.53104e-4 months <br /> CST, the Unit 1 Reactor Operator reported that the control room indication for secondary containment [NG] vacuum was 0.17 inch of vacuum water gauge.
The cause of the event could not be determined; however, it is suspected that both Unit 2 steam tunnel airlock doors were simultaneously opened and held open to transport material during outage demobilization activities.
G. COMPONENT FAILURE DATA:
Locknetics/SDC style lock