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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 54687 | 1 May 2020 07:54:00 | 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown | Technical Specification Required Shutdown Due to Reactor Coolant System Pressure Boundary Leakage | 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.
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). | Reactor Coolant System | |
| ENS 51106 | 31 May 2015 20:00:00 | 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown | Technical Specification Required Shutdown Due to Failure of an Emergency Diesel Generator | At 1600 (EDT) on May 31, 2015, (DC Cook) operations commenced a shutdown of DC Cook Unit 1 to comply with LCO 3.8.1 Condition G, when the 14 day limit to complete Condition B Required Action could not be met. At 0010 (EDT) on May 18, 2015, Unit 1 AB Emergency Diesel Generator was removed from service for planned maintenance. LCO 3.8.1 Condition B was entered which allows 14 days to restore diesel to operable. At 1049 (EDT) on May 21, 2015, Unit 1 AB Emergency Diesel Generator tripped during post maintenance testing due to high bearing temperatures. Subsequent actions to repair and restore the diesel to operable status have been unsuccessful. 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 four (4) hour report. The DC Cook Sr. Resident NRC Inspector has been notified. Unit 1 is expected to be in Mode 5 by 2030 EDT on June 1, 2015. There is no impact on Unit 2.
This update is to correct the information contained in the block titled 'Power/Mode After'. The power and mode after the event requiring notification (TECHNICAL SPECIFICATION REQUIRED SHUTDOWN DUE TO INABILITY TO RESTORE UNIT 1 AB EDG WITHIN THE COMPLETION TIME PRESCRIBED IN LCO 3.8.1 CONDITION B) was 99% power and mode 1. The licensee has notified the NRC Resident Inspector. D.C. Cook Unit 1 is currently in Mode 3 and conducting a normal cooldown to Mode 4. Notified R3DO (Passehl).
DC Cook Unit 1 reactor was shut down (Mode 3) at 0231 hours (EDT) June 01, 2015 and achieved Mode 5 at 0410 hours (EDT) June 02, 2015 to comply with LCO 3.8.1 Condition G with all systems operating normally. The licensee has notified the NRC Resident Inspector. Notified R3DO (Passehl). | Emergency Diesel Generator | 05000315/LER-2015-001 |
| ENS 51004 | 23 April 2015 06:10:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(b)(3)(iv)(A), System Actuation 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown | Manual Reactor Trip Due to a Secondary Plant Transient | On April 23, 2015 DC Cook Unit 2 Reactor was manually tripped due to an uncontrolled cooldown due to two (2) failed open steam dump valves. The cause of the failure is still under investigation. This event is reportable under 10 CFR 50.72(b)(2)(i) Tech Spec Required Shutdown, as a four (4) hour report; 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 Reactor Protection System (RPS), as an eight (8) hour report. The electrical grid is stable and Unit 2 continues to be supplied by offsite power. All control rods fully inserted. Decay heat is being removed via steam generator Power Operated Relief Valves due to steam dump valves being manually isolated. 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. The DC Cook Resident NRC Inspector has been notified. There is no indication of primary to secondary leakage and there is no impact on Unit 1. | Steam Generator Reactor Protection System Control Rod | 05000316/LER-2015-001 |
| ENS 48868 | 31 March 2013 08:14:00 | 10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded | Rcs Flow Instrument Line Through Wall Weld Defect | On 3/31/13 at 0414 EDT, dye penetrant testing identified a 10mm long relevant linear indication on a 3/4 inch RCS flow instrument line weld, between the RCS loop piping and the instrument isolation valve. This constitutes a weld defect in the primary coolant system that cannot be found acceptable per ASME Section XI. This section of piping is unisolable from the Reactor Coolant System. There is no evidence of active leakage currently or during the previous operating cycle, however, based on the dye penetrant testing this is considered a through wall leak. This event notification is being made in accordance with 10CFR50.72(b)(3)(ii)(A), as a condition that results in the condition of the nuclear power plant, including its principal safety barriers, being seriously degraded. Unit 1 is currently in a scheduled refueling outage in Mode 5 making preparations to transition to Mode 6. The plant is evaluating the appropriate repair method for this condition. The condition will be corrected during the current refueling outage. Unit 2 is in Mode 1 at 100% power and is unaffected by this condition. The NRC Resident Inspector has been notified. | Reactor Coolant System | |
| ENS 48120 | 19 July 2012 19:30:00 | 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown | Tech Spec Required Shutdown Due to Inability to Restore Main Steam Isolation Automatic Actuation Logic and Actuation Relays within the Required Time | At 1530 on July 19, 2012, operators commenced shutdown of DC Cook Unit 1 to comply with LCO 3.3.2, Condition I when the 6 hour time limit to complete Condition C Required Action could not be completed. At 0734 on July 19, 2012, operators identified that power had been lost to two of four Steam Generator Stop Valve Dump Valves (Dump Valves) on one of the two trains. DC Cook entered LCO 3.3.2 Condition B for Function 4a, manual initiation: 'restore required channel or train to operable within 48 hours.' DC Cook also entered LCO 3.3.2 Condition C for Function 4b, automatic actuation logic and actuation relays: 'restore required channel or train to operable within 6 hours.' Power was restored to one Dump Valve which was then declared operable at 1030. Efforts continue to restore power to the remaining Dump Valve. Enforcement Discretion was verbally granted by the Nuclear Regulatory Commission at 1736 on July 19, 2012 to begin at 1934 and end at 1934 on July 20, 2012. Upon receiving the Enforcement Discretion, the power reduction was stopped at 1738 at 50% power. This event is reportable under 10CFR50.72(b)(2)(i), 'The initiation of any nuclear plant shutdown required by the plant's Technical Specifications,' as a four (4) hour report. The DC Cook Sr. Resident NRC Inspector has been notified. | Steam Generator Main Steam | |
| ENS 44171 | 26 April 2008 02:10:00 | 10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded | Non-Isolable Rcs Boundary Leakage from Instrument Line | On April 25, 2008, DC Cook Unit 1 was in Mode 4 heating up the RCS after a refueling outage. Personnel were performing a containment walkdown, with the RCS at 1000 psig, looking for leakage. Wisps of steam were seen coming from a 3/4 inch RCS flow instrument line weld, between the RCS loop piping and the instrument isolation valve. The leakage is less than 0.1 gpm. The leakage can not be isolated from the RCS and has been declared to be RCS Pressure Boundary Leakage. Entry into the RCS Operational Leakage Technical Specification, 3.4.13, was made at 2210 on April 25, 2008. This Technical Specification requires being in Mode 5 within 36 hours. The plant is cooling down and depressurizing as required by Technical Specifications. The plant is currently evaluating the appropriate repair method for this condition. The licensee notified the NRC Resident Inspector. | 05000315/LER-2008-004 | |
| ENS 42739 | 30 July 2006 11:30:00 | 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown | Technical Specification Shutdown for High Containment Air Temperature | On July 30, 2006, at 0730, a plant shutdown was initiated in accordance with Technical Specification (TS) Action 3.6.5.B.1. This action requires that the unit be placed in Mode 3 within six hours if containment air temperature is not restored to within limits during the previous eight hours. On July 29, 2006, at 2026 TS Action 3.6.5.A was entered due to containment lower compartment average air temperature exceeding the TS Limiting Condition for Operation 3.6.5.B limit of 120 degrees Fahrenheit. Efforts to reduce the containment temperature during the eight hour completion time of Action 3.6.5.A were unsuccessful. In accordance with normal plant operating procedures, the unit shutdown was completed by initiating a manual reactor trip from 16.5% Reactor Power following a controlled plant shutdown on July 20, 2006, at 1014. All safety systems and plant equipment used in the shutdown functioned as designed. All rods inserted fully without incident. No PORV/safety valves lifted. Decay heat is being removed with AFW. Unit 2 containment air temperature is 117 degrees Fahrenheit. The licensee notified the NRC Resident Inspector. |