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| Entered date | Event description | |
|---|---|---|
| ENS 51725 | 11 February 2016 01:20:00 | This report is being made pursuant to 10CFR50.72(b)(3)(v)(C), event or condition that could have prevented fulfillment of a safety function needed to control the release of radioactive material and 10CFR50.72(b)(3)(v)(D), event or condition that could have prevented fulfillment of a safety function needed to mitigate the consequences of an accident. LaSalle Station's Unit 1 and Unit 2 were in Mode 1. At 2207 (CST) (on 2/10/16), Secondary Containment Differential Pressure dropped below the Technical Specification (TS) 3.6.4.1 minimum of 0.25 inches water vacuum. The initial indications are a failure of one Unit 1 Reactor Building Exhaust Isolation Damper, which resulted in a trip of the Unit 1 Reactor Building Exhaust Fans. At 2245, Secondary Containment Differential Pressure was restored to within the TS 3.6.4.1 limits by securing and isolating the Unit 1 Reactor Building Ventilation System. Troubleshooting plans are being developed to determine cause of the damper failure and to correct the deficient condition. The licensee has notified the NRC Resident Inspector. |
| ENS 46372 | 28 October 2010 15:21:00 | This report is being made pursuant to 10CFR50.72(b)(3)(v), Event or Condition that could have prevented fulfillment of a Safety Function. As part of a recent NRC Component Design Basis Inspection (CDBI), the seismic analysis of the Unit One and Unit Two Standby Liquid Control (SBLC) system test tanks was questioned. During the formal operability determination process initiated on 10/27/10, Engineering was verifying design data and calculations. During this review, on 10/28/10, Engineering determined that the historical calculation used the wrong formula in determining the test tank's natural frequency. The consequence is that if the test tank is filled with water, the possibility exists that the test tank could fall over or collapse during a seismic event and adversely affect adjacent safety-related items (i.e. SBLC). Calculations confirm that empty test tanks are seismically qualified. The SBLC test tanks on both units had been drained of water on 10/27/10 and thus both Unit One and Unit Two SBLC systems are fully operable at this time. The licensee has notified the NRC Resident Inspector. |