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On 02/13/2016 at 0206 CST, an unexpected trip of a Fuel Building ventilation exhaust fan occurred and secondary containment differential pressure became positive. Secondary containment was declared INOPERABLE when Technical Specification-required differential pressure was not being maintained and entered LCO 3.6.4.1 Action A.1

At 0256 (CST), the standby gas treatment system was started and secondary containment differential pressure was restored to Technical Specification requirements at 0257 CST. This loss of secondary containment is reportable under 10 CFR 50.72(b)(3)(v)(C) as an event or condition that could have prevented fulfillment of a safety function needed to control the release of radioactive material. The cause of the fuel building exhaust fan trip is unknown at this time. The NRC Resident Inspector has been notified.

At 22:04 CDT on 9/02/2012, the Emergency Reserve Auxiliary Transformer (ERAT) transferred unexpectedly to the Reserve Auxiliary Transformer (RAT). During this transfer, the Fuel Pool Cooling and Cleanup (FC) system pump 'A' tripped and the Fuel Building Ventilation (VF) system isolated. Upper containment pool level dropped below the minimum required level per Technical Specifications (TS) 3.6.2.4 and Secondary Containment differential pressure increased above 0.25 inches vacuum per TS 3.6.4.1. Upper Containment Pool level was restored above the minimum level at 01:27 CDT on 9/3/2012 within the 4 hour completion time. The Upper Containment Pool is a part of the suppression pool makeup system used to ensure the Primary Containment function. Secondary Containment differential pressure was restored at 22:19 on 9/2/2012 when the Standby Gas Treatment System was started. Maintaining secondary containment differential pressure helps to control the release of radioactive material. This event is being reported as a condition that could have prevented the fulfillment of a safety function per 10 CFR 50.72(b)(3)(v)(B) and 10 CFR 50.72(b)(3)(v)(C). The station is currently in a 72-hour action to restore the ERAT to an operable status per TS LCO 3.8.1 Required Action A.2. Plant conditions are stable and actions are underway to repair the ERAT. The NRC Resident (Inspector) has been notified.

• * * RETRACTION ON 10/26/12 AT 1322 EDT FROM KEN LEFFEL TO DONG PARK * * *

Upper Containment Pool level dropped below the normal pool level of 827 feet-3 inches when the Fuel Pool Cooling and Cleanup system pump 'A' tripped, and was initially reported as dropping below the minimum level (825 feet-6 inches) required by Technical Specification (TS) 3.6.2.4. However, subsequent reports from the field confirmed that the lowest level reached was 827 feet 0 inches, which is greater than the minimum required TS level. Therefore, no loss of safety function occurred for the Upper Containment Pool level as a result of this event, and the event is not reportable under 50.72 (b)(3)(v)(B). The NRC Resident (Inspector) has been notified." Notified R3DO (Pelke).

During the performance of operator rounds in the Lake Screenhouse Safe Shutdown System (SX) pump rooms, two water tight doors were left opened simultaneously during the room checks. These two doors opened simultaneously (which) allowed for communication between the Division 1 SX room and Division 2 SX pump room. The operator was in constant attendance in the Division 2 SX pump room during the performance of the equipment checks. During site review, it was determined that a flood in either the Division 1 or Division 2 SX pump rooms would not be isolated to the initiating room, but potentially affect both trains of SX. This could result in a loss of cooling for both Residual Heat Removal systems, therefore, a condition that could have prevented fulfillment of a safety function under 10CFR50.72(b)(3)(v)(B). The NRC Senior Resident has been notified. Offsite power is normal and emergency diesel generators are operable and available.

* * * RETRACTION FROM ED TIEDEMANN TO PETE SNYDER ON 6/8/11 AT 1141 EDT * * * 

A subsequent plant barrier impairment evaluation consistent with Exelon Procedure CC-AA-201, 'Plant Barrier Control Program' has determined that no loss of safety funct ion would have occurred. Each of the following door functions and related postulated events were reviewed for impact: ventilation; flooding, internal and external; high energy line breaks; missiles; radiation protection; and fires. For the condition with the SX pump room water tight doors being open with an operator in the area, the conclusion is an SX division remains protected to ensure that in any of the evaluated events the safety function of SX has been maintained. The licensee has notified the NRC Resident Inspector.

The Division 3 Emergency Diesel Generator (EDG) was declared INOPERABLE following a trip during a routine monthly surveillance run. As soon as the Division 3 EDG was at full load it tripped off line (output breaker tripped). The Division 3 EDG supplies electrical power to the High Pressure Core Spray System in the event of a loss of offsite power. No problems occurred on the Division 3, 4160 volt, safety related bus. This event is being reported in accordance with 10CFR50.72(b)(3)(v)(B), Event or Condition That Could Have Prevented Fulfillment of a Safety Function for a single-train system failure. The NRC Resident inspector has been notified.

• * * THIS EVENT IS BEING RETRACTED ON 12/20/05 AT 1557 * * *

Subsequent trouble-shooting and testing determined that the cause of the engine trip on 11/21/05 was an invalid high coolant temperature trip signal. This trip is bypassed during a Loss of Coolant (LOCA) initiation of the system, therefore, it was determined that the EDG would have been able to perform its safety function during a LOCA. Following a Loss of Offsite Power (LOOP), reactor water level is expected to reach Reactor Pressure Vessel (RPV) Water Level Low Low (Level 2) within 30 seconds of the initiating signal. Once Level 2 is reached, both the EDG and the LOCA Trip bypass signals are actuated. It was determined that the bypass would have occurred prior to the high coolant temperature trip. Based on the above, it was determined that the Division 3 EDG would have been fully capable of performing its safety function under both LOCA and LOOP. The Division 3 EDG was restored to an operable condition at 0214 on 11/22/05. The NRC Senior Resident Inspector has been notified. Notified R3DO (H. Peterson).