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At 1000 EDT on May 1 2020, Operations commenced a shutdown of DC Cook Unit 2 to comply with LCO 3.4.13, Condition B Reactor Coolant System (RCS) pressure boundary leakage. At 0354 EDT on May 1, 2020, Operations detected an estimated 8 gpm Reactor Coolant System leak. The source of the leak could not be identified and Tech Spec 3.4.13, Condition A was entered for unidentified RCS leakage in excess of the 0.8 gpm limit. At 0745 EDT on May 1, 2020, Unit 2 entered LCO 3.4.13, Condition B when the 4-hour limit to complete the required actions of Condition A could not be met. At 0945 EDT on May 1, 2020, Unit 2 entered LCO 3.4.13, Condition B when the 4-hour limit to complete the required actions of Condition A could not be met. At 0945 EDT on May 1, 2020, inspections inside containment identified the leak as pressure boundary leakage from a pressurizer spray line which also requires entry into LCO 3.4.13, Condition B. At 1059 EDT on May 1, Unit 2 was tripped from 15 percent power. All systems functioned normally. This event is reportable under 10 CFR 50.72(b)(2)(i), the initiation of any nuclear plant shutdown required by the plant's Technical Specifications as a 4-hour report and under 10 CFR 50.72 (b)(3)(ii)(A), degraded condition, as an 8-hour report. The NRC Resident Inspector has been notified.

• * * PARTIAL RETRACTION ON 5/15/2020 AT 1442 EDT FROM BUD HINCKLEY TO THOMAS HERRITY * * *

The condition identified in EN #54687, pursuant to 10 CFR 50.72 (b)(3)(ii)(a) has been evaluated, and has been determined not to be RCS pressure boundary leakage. As such, the 8-hour report is being retracted, as it is not an event or condition that results in, 'the condition of the nuclear power plant, including its principal safety barriers, being seriously degraded.' The leakage was subsequently determined to be from the tell-tale nipple of a pressurizer spray valve, not from the pressurizer spray line piping as previously reported. The Reactor Coolant Pressure Boundary (RCPB) is formed by the valve body, plug, seat, body to bonnet extension, and bonnet of the pressurizer spray valve. Therefore, the leakage is not RCPB leakage. There is no change to the 4-hour report made under 10 CFR 50.72(b)(2)(i), the initiation of any nuclear plant shutdown required by the plant's Technical Specifications. The NRC Resident Inspector was notified of this retraction. Notified R3DO (Stone).

On July 28, 2013, at 1018 EDT, DC Cook Unit 2 Reactor was manually tripped due to lowering steam generator level caused by an automatic trip of the west main feed pump. The west main feed pump tripped on low suction pressure resulting from a secondary plant transient. The cause of the secondary transient is still under investigation. This event is reportable under 10 CFR 50.72(b)(2)(iv)(B), Reactor Protection System (RPS) actuation, as a four (4) hour report, and under 10 CFR 50.72(b)(3)(iv)(A), specified system actuation of the Auxiliary Feedwater System, as an (8) hour report. The DC Cook Sr. Resident NRC Inspector has been notified. The electrical grid is stable and Unit 2 is being supplied by offsite power. All control rods fully inserted. Decay heat is being removed via steam dumps to the main condenser. Preliminary evaluation indicates all plant systems functioned normally following the Reactor Trip. DC Cook Unit 2 remains stable in Mode 3 while conducting the post trip review. No radioactive release is in progress as a result of this event. There was no affect on Unit 1.

• * * UPDATE FROM DEAN BRUCK TO DONALD NORWOOD AT 1753 EDT ON 7/29/13 * * *

Additional information received determined the Turbine Driven Auxiliary Feedwater Pump discharge valve to Steam Generator #2 did not position, as required, following the reactor trip. The affected discharge valve opened as expected during pump start. The valve closed instead of throttling to the intermediate position upon subsequent high flow demand. Feedwater flow to Steam Generator #2 was maintained by the East Motor Driven Auxiliary Feedwater Pump. The NRC Resident Inspector has been notified of this update. Notified R3DO (Orth).

D.C. Cook Unit 1 declared an Unusual Event (EAL H4 & H5) due to a fire in the Main Turbine. The reactor was manually tripped from 100 percent. The fire occurred at the upper level of the turbine building (Level 633), and was extinguished by the fire suppression system and local fire brigade. Three fire pumps are running at this time. No injuries were reported. All rods fully inserted, auxiliary feed water initiated and decay heat is being removed via atmospheric relief valves. Unit 1 is currently shutdown and stable in Mode 3, Hot Standby. Main steam stop valves are closed. Main condenser vacuum was broke. Unit 2 was not affected. All Unit 1 safety-related equipment is in-service and available. The licensee is currently assessing the extent of damage. The licensee will inform the NRC Resident Inspector. Notified DOE (Morrone), USDA (Shaf) and HHS (Mammarelli) that the NRC entered Monitoring Mode at 2045 EDT.

• * * UPDATE AT 0005 EDT ON 09/21/08 FROM BRADDOCK LEWIS TO V. KLCO * * *

On September 20, 2008 at 20:05 the DC Cook Unit 1 Reactor was manually tripped after a malfunction occurred on the main turbine generator causing high vibration. A fire in the Unit 1 Main Generator resulted from this malfunction. A Notification of Unusual Event was declared September 20, 2008 at 20:18 due to Event classifications H-4, Fire within the protected area not extinguished within 15 minutes and H-5, Toxic or Flammable gas release affecting plant operation. The Unit 1 Main Generator Fire was reported extinguished at September 20, 2008 at 20:28. The Unit 1 plant trip was uncomplicated and all Automatic Control systems functioned as expected. All control rods inserted on the Reactor trip. The Turbine and both Motor Driven Auxiliary Feedwater pumps automatically started and fed all four Steam Generators as designed. The Steam Generator Stop Valves were manually closed to arrest plant cooldown. The cause of the Main Generator fire has not yet been determined, but the investigation is ongoing. No radiological release resulted from this event. This event is being reported as a four hour report required by 10CFR50.72(b)(2)(iv)(B) due to the Reactor Protection System automatic actuation and as an eight hour report required by 10CFR50.72(b)(3)(iv)(A) for the automatic actuation of the Auxiliary Feedwater system. The Notification of Unusual Event was reported separately. Unit 1 is stable in Mode 3. Shutdown Margin was satisfactorily verified. The main condenser was isolated as the primary heat sink. Steam Generator Power Operated Relief Valves are removing core decay heat in automatic control due to breaking main condenser vacuum. Main condenser vacuum was broken to stop the Unit 1 main turbine generator due to high vibration. Preparations are in progress to cooldown Unit 1 to Mode 5, Cold Shutdown. The Fire Suppression Water System was actuated and one of two 565,000 gallon tanks was drained. The second 565,000 gallon Fire Suppression Water tank was placed in service to restore the Fire Suppression Water system function. The licensee notified the NRC Resident Inspector, local and state authorities. The licensee will likely make a press release. Notified R3RA (Caldwell), R3DO (Stone), NRR (Leeds and Galloway) IRD (McDermott), DHS (Gomez) and FEMA (Kuzia).

• * * UPDATE PROVIDED BY PAUL LEONARD TO JASON KOZAL AT 0414 ON 09/21/08 * * *

At 0409 the licensee terminated from the Notice of Unusual Event. The licensee has established the forced outage recovery team. No fires exist and no conditions conducive to fires exist due to the event. The licensee has established the integrity of the fire protection system. Notified R3RA (Caldwell), R3DO (Stone), NRR (Galloway), IRD (Grant), DHS (Jason), DOE (Maroni), FEMA (Sweetser), USDA (Phillip), and HHS (Nathan).