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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 52964 | 12 September 2017 16:31:00 | 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Standby Liquid Control System Piping Failure | On September 12, 2017 at 1131 CDT, both Unit 3 Standby Liquid Control system (SLC) subsystems were declared inoperable for a through wall leak on the common discharge piping. With both subsystems inoperable, the SLC system was unable to fulfill its safety function. This event is reportable under 10 CFR 50.72(b)(3)(v)(A) for an event or condition that could have prevented the fulfillment of a safety function of a system that is needed to shut down the reactor and maintain it in a safe shutdown condition and under 10 CFR 50.72(b)(3)(v)(D) for a system that was unavailable for accident mitigation. The NRC Resident Inspector has been notified. With both trains of SLC inoperable, the licensee entered an 8-hr. action statement to restore at least one train to operability. If unable to do so, then the plant will enter a 12-hr. shutdown action statement. | Standby Liquid Control | |
| ENS 46354 | 22 October 2010 22:51:00 | 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor | Potential Inoperability of Oscillation Power Range Monitors | |||
| ENS 44665 | 3 November 2008 16:42:00 | 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor | Control Rods Drift Out While Shutdown | On 11/03/2008, with Unit 3 shut down and all control rods in, an unexpected drift of three control rods out from their full-in position occurred. The immediate cause of this event was high control rod drive (CRD) cooling and exhaust water header pressures as the final group of hydraulic control unit (HCU) valves were being isolated. At the time, Operations personnel were in the process of completing the isolation of the CRD HCUs by closing the (101) Insert Riser Isolation Valve and (102) Withdraw Riser Isolation Valve on each HCU with a CRD pump in operation and the CRD charging water header isolated. A control rod drift alarm was received in the Unit 3 control room, followed by several rod position indication system (RPIS) indications that the associated control rods had drifted from position 00 (full-in) to their 'over travel-in' position. Later, all indications returned to the full-in position, with the exception of three CRDs. These three CRDs settled at final positions 06, 16, and 18, respectively. Immediate corrective actions were taken to re-open the 101 valve for each of the three CRDs, allowing the control rod to re-insert to full-in. The 101 valve was then re-closed. Calculations by nuclear engineering identified that the reactor remained subcritical for the actual plant conditions and that there was no risk of fuel damage. Initial review of the event by Exelon determined that it was not reportable. After additional review and evaluation, the decision was made to conservatively report the event pursuant to 10 CFR 50.72 (b)(3)(v), 'Event or Condition That Could Have Prevented Fulfillment of a Safety Function.' A root cause investigation is underway to determine the cause. The industry has been notified via the operating experience process on November 7, 2008. The licensee notified the NRC Resident Inspector. | Control Rod |