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 Entered dateSiteScramRegionReactor typeEvent description
ENS 5417621 July 2019 12:08:00CookManual ScramNRC Region 3On July 19, 2019, DC Cook Unit 2 started experiencing degraded performance on the Unit 2 Non-Essential Service Water System (NESW) which affected one (1) NESW pump. On July 21, 2019, a second NESW pump on Unit 2 experienced degradation. On July 21, 2019, DC Cook Unit 2 elected to do a rapid downpower over approximately 40 minutes and perform a Manual Reactor Trip from 17 percent (rated thermal power) to repair the condition before any threshold was exceeded. The manual reactor trip was completed at 0826 EDT on July 21, 2019. This notification is being made in accordance with 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), Reactor Protection System (RPS), as an eight (8) hour report. The DC Cook NRC Resident Inspector has been notified. Unit 2 is being supplied by offsite power. All control rods fully inserted. Aux Feedwater pumps were started as required and are operating properly. Decay heat is being removed via the Steam Generator Power Operated Relief Valves following breaking Main Condenser Vacuum for expedited cooldown of the Main Turbine. Preliminary evaluation indicates all plant systems functioned normally following the reactor trip. DC Cook Unit 2 remains stable in Mode 3. No radioactive release is in progress as a result of this event. Unit 1 was not affected.
ENS 533877 May 2018 06:42:00CookManual ScramNRC Region 3Westinghouse PWR 4-LoopOn May 7, 2018 at 0336 (EDT), DC Cook Unit 2 Reactor was manually tripped due to a high-high level experienced in the East Moisture Separator Drain Tank (MSDT) of the Moisture Separator Reheater (MSR). This notification is being made in accordance with 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 eight (8) hour report. The NRC Resident Inspector has been notified. Unit 2 is being supplied by offsite power. All control rods fully inserted. All Aux Feedwater Pumps started properly. Decay heat is being removed via the Steam Generator Power Operated Relief Valves following Main Steam Stop Valve closure at 0431 due to a slow RCS (Reactor Coolant System) cooldown. 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.
ENS 520656 July 2016 01:02:00CookManual ScramNRC Region 3Westinghouse PWR 4-LoopOn July 6, 2016, at 0038 (EDT), DC Cook Unit 2 Reactor was manually tripped and at 0050 (EDT) an Unusual Event (N-7 'Unanticipated Explosion') Emergency Declaration was made due to steam leak and associated damage to the turbine building. In accordance with Emergency Plan procedures, notifications of Berrien County and State of Michigan were completed. The licensee has notified the NRC Senior Resident Inspector. The Unusual Event was terminated at 0207 (EDT). This notification is being made in accordance with 10 CFR 50.72 (a)(1)(i) due to declaration of an emergency class. Original notification to NRC made at 0100 EDT via ENS. This event is reportable under 10 CFR 50.72(b)(2)(iv)(B), Reactor Protection System (RPS) actuation and 10 CFR 50.72(b)(2)(xi) Offsite Notification, 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 eight (8) hour report. The DC Cook NRC Resident Inspector has been notified. A press release is planned. Unit 2 is being supplied by offsite power. All control rods fully inserted. Decay heat is being removed via Steam Generator PORVs (Power Operated Relief Valve). 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. Notified DHS SWO, FEMA Ops Center, DHS NICC. Notified FEMA National Watch and Nuclear SSA via email.
ENS 5100423 April 2015 05:25:00CookManual ScramNRC Region 3Westinghouse PWR 4-LoopOn 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.
ENS 505871 November 2014 05:03:00CookManual ScramNRC Region 3Westinghouse PWR 4-Loop

On November 1, 2014, at 0249 (EDT), DC Cook Unit 1 reactor was manually tripped and at 0248 (EDT) DC Cook Unit 2 was manually tripped due lowering condenser vacuum caused by degraded forebay conditions (observed thick grass and sand). U-1 and U-2 entered Abnormal Operating Procedure for Degraded Forebay on November 1, 2014 at 0153 (EDT). Conditions degraded in U-1 and U-2 until all but 2 screens in each unit were tripped on overload and main condenser vacuum was lowering. U-1 and U-2 met criteria in the Degraded Forebay procedure to remove the units from service and remove all circulating water pumps from service. 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 eight (8) hour report. The electrical grid is stable. Unit 1 and Unit 2 are being supplied by offsite power. All control rods fully inserted in both units. Decay heat is being removed by steam generator PORVs. Preliminary evaluation indicates all plant systems functioned normally following the reactor trip with the exception of U-1 turbine driven auxiliary feed pump. DC Cook Unit 1 and Unit 2 remain stable in Mode 3 while conducting the post trip review. No radioactive release is in progress as a result of this event. Additional information received determined the Unit 1 turbine driven auxiliary feedwater pump tripped for unknown reasons. Feedwater flow to all steam generators was maintained by the U-1 east and west motor driven auxiliary feedwater pumps. U-2 reactor power was lowered from 100 percent to 50 percent over the hour prior to the trip in accordance with the Degraded Forebay Procedure. The DC Cook NRC Resident Inspector has been notified.

  • * * UPDATE PROVIDED BY RICHARD HARRIS TO JEFF ROTTON AT 0945 EDT ON 11/01/2014 * * *

At 0921 EDT, DC Cook issued a press release regarding the event described earlier. The licensee notified the NRC Resident Inspector. Notified R3DO (Lipa)

ENS 4922028 July 2013 13:43:00CookManual Scram
Automatic Scram
NRC Region 3Westinghouse PWR 4-Loop

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).

ENS 478811 May 2012 02:34:00CookAutomatic ScramNRC Region 3Westinghouse PWR 4-LoopOn 30 April, 2012, at 2328 (EDT), DC Cook Unit 2 Reactor automatically tripped due to a trip of the main turbine. The cause of the main turbine trip is still under investigation. 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 Generator PORVs to atmosphere. 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 releases were experienced as a result of this event. 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 eight (8) hour report. The DC Cook Resident NRC Inspector has been notified. The licensee stated that the trip was uncomplicated and the reactor is stable in mode 3 at no load temperature and pressure. The unit is on steam generator atmospheric relief valves because the secondary steam load on the plant was causing too much of a cool down. There is no primary to secondary steam generator leakage for the unit. The trip had no impact on Unit 1 which continues to operate at full power.
ENS 4747725 November 2011 06:32:00CookManual ScramNRC Region 3Westinghouse PWR 4-LoopAt 0522 EST on November 25, 2011, operators manually started all Auxiliary Feedwater (AFW) pumps in response to a manual trip of the Unit 1 East Main Feedwater Pump due to bearing failure. Operators were responding to increasing vibrations on the East Main Feedwater Pump and reducing turbine load when the East Main Feedwater Pump was manually tripped (at approximately 90% power) due to high vibrations. Operators entered the abnormal operating procedure for Loss of One Main Feedwater Pump, which directs starting all three AFW pumps. Plant power was stabilized at approximately 58%. The licensee has notified the NRC Senior Resident Inspector. This notification is being made in accordance with 10CFR50.72(b)(3)(iv)(A) due to the valid actuation of the AFW system in response to equipment failure.
ENS 472477 September 2011 12:14:00CookAutomatic ScramNRC Region 3Westinghouse PWR 4-LoopOn Sept 7, 2011, at 0854, DC Cook Unit 1 reactor automatically tripped due to a trip of the main turbine. The cause of the main turbine trip 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 eight (8) hour report. The DC Cook Sr. Resident NRC Inspector has been notified. The electrical grid is stable and Unit 1 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 1 remains stable in Mode 3 while conducting the post trip review.
ENS 4522826 July 2009 18:44:00CookManual ScramNRC Region 3Westinghouse PWR 4-LoopAt 1506 on Sunday, July 26, 2009, the Cook Nuclear Plant (CNP) Unit 2 reactor was manually tripped after the control room staff concluded that the #22 Reactor Coolant Pump (RCP) needed to be promptly secured due to a RCP seal malfunction as indicated by lowering #1 seal leakoff flows and rising #1 seal return and pump radial bearing temperature. This requires a 4-hour report under 10CFR50.72(b)(2)(iv)(B). Both motor-driven Auxiliary Feedwater pumps automatically started due to the reactor trip and trip of both Main Feedwater Pumps. The Turbine-Driven Auxiliary Feedwater Pump (TDAFP) started automatically due to low-low water levels in at least two steam generators, which is expected for a reactor trip from approximately full power. The automatic actuation of the reactor protection system and the TDAFP require an 8-hour report under 10CFR50.72(b)(3)(iv)(A). All systems functioned as expected after the trip, and no major components were out of service at the time except for the Moisture Separator Reheaters which were not in service since the beginning of the current power cycle. The licensee has notified the NRC Senior Resident Inspector. All control rods fully inserted as required. Electrical system is in normal post-trip lineup. Plant cooldown is via Condenser Steam Dumps using Auxiliary Feedwater pumps. Plant cooldown will continue to Mode 5 (cold shutdown).
ENS 4450720 September 2008 20:31:00CookManual ScramNRC Region 3Westinghouse PWR 4-Loop

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).

ENS 439562 February 2008 07:44:00CookManual ScramNRC Region 3Westinghouse PWR 4-LoopThe DC Cook Unit 1 Reactor was manually tripped from 93% power due to high vibrations on main turbine bearings #5 and 6. This event is reportable under 10CFR50.72(b)(2)(iv)(B), RPS actuation, as a four (4) hour report and under 10CFR50.72(b)(3)(iv)(A), specified system actuation of the Auxiliary Feedwater System, as an eight (8) hour report. Preliminary evaluation indicates all plant systems functioned normally following the Reactor Trip. DC Cook Unit 1 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 was notified 02/02/08 at approximately 0535 EST. The electrical grid is stable and Unit 1 is being supplied by offsite power. Unit 2 is not affected. All control rods fully inserted. Decay heat is being removed via steam dumps to the main condenser.
ENS 4360528 August 2007 15:17:00CookAutomatic ScramNRC Region 3Westinghouse PWR 4-LoopAt 13:54 on 8/28/07, DC Cook Unit 1 experienced an automatic reactor trip due to low steam generator water level coincident with low feedwater flow on #11 steam generator. The cause was a malfunction of the Main Feedwater Pump Digital Control System, which remains under investigation. This requires a 4-hour report under 10CFR50.72(b)(2)(iv)(B). Both Motor-Driven Auxiliary Feedwater Pumps automatically started due to the reactor trip. The Turbine-Driven Auxiliary Feedwater Pump (TDAFP) started automatically due to low-low water levels in at least two steam generators, which is expected for a reactor trip from 100% power. The automatic actuation of the reactor protection system and the TDAFP start require an 8-hour report under 10CFR50.72(b)(3)(iv)(A). All systems functioned as expected after the trip, and no major components were out of service at the time of the trip. This is a non-complicated trip. The NRC resident has been notified. The reactor tripped at 15% steam generator level and then level went off scale low as expected. All control rods fully inserted. No primary or secondary safeties or relief valves lifted with the exception of a feed heater relief valve. The plant is feeding steam generators with the motor driven auxiliary feed water pumps and dumping decay heat to the main condenser. The plant is in the normal shutdown electrical lineup.
ENS 4273930 July 2006 11:15:00CookManual ScramNRC Region 3Westinghouse PWR 4-LoopOn 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.
ENS 4163926 April 2005 02:12:00CookAutomatic ScramNRC Region 3Westinghouse PWR 4-LoopThe DC Cook Unit 1 Reactor automatically tripped during normal plant startup preparations to synchronize the Main Generator with the offsite electrical GRID. Indicated Reactor power at the time of trip was 8 % power and stable. Preliminary review indicates the trip was caused by an Intermediate Range high flux reactor trip signal. The Intermediate Range High Flux Reactor trip occurred below the Reactor Protection System actuation setpoint. This is a one-out-of-two logic and the trip is active below interlock Permissive P-10 (10% reactor power). The cause of the Reactor Trip is under investigation. This event is reportable under 10CFR50.72(b)(2)(iv)(B), RPS actuation, as a four (4) hour report and under 10CFR50,72(b)(3)(iv)(A), Specified system actuation of the Auxiliary Feedwater System, as an eight (8) hour report. Preliminary evaluation indicates all plant systems functioned normally following the Reactor Trip. DC Cook Unit 1 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 Senior Resident NRC Inspector was notified 04/26/05 at approximately 00:30 (hrs. EDT). The electrical grid is stable and Unit 1 is being supplied by offsite power. Unit 2 is not affected. All control rods fully inserted. Decay heat is being removed via steam dumps to the main condenser.
ENS 406609 April 2004 01:47:00CookManual Scram
Automatic Scram
NRC Region 3Westinghouse PWR 4-LoopOn April 8, 2004, at about 2215, Cook Unit 2 experienced a feedwater flow transient resulting in oscillating flows to Nr. 22, 23, & 24 steam generators. At 2216, the high level turbine trip setpoint was reached in Nr. 24 steam generator resulting in (a) main turbine trip signal. The main turbine trip signal caused a turbine trip resulting in an RPS (Reactor Protection System) actuation (reactor trip). At the time of the RPS actuation, Cook Unit 2 was at about 50 percent power and lowering power to facilitate turbine control maintenance. The cause of (the) feedwater transient is unknown and under investigation at this time. Following the RPS actuation, the Auxiliary Feedwater System automatically started on low-low Steam Generator levels. This constituted a valid unplanned actuation of the Engineered Safeguards Feature (ESF). Operators stabilized the Plant using Condenser Steam Dumps and Auxiliary Feedwater. Unit 2 is currently in Mode 3 with Reactor Coolant System conditions stable at normal operating temperature and pressure. No other ESF systems actuated. During the response to the RPS actuation by the operating crew, it was noted that the Main generator output breaker remained closed requiring a manual trip signal to open the output breakers. Another condition identified was a leak from a crack in the side of the 'C' South condenser near the condensate booster pumps' recirculation line inlet. The operating crew removed the condensate booster pumps from service to stop condenser hotwell outleakage; the main condenser remains in service. The causes for the above items are unknown and (are) under investigation at this time. All control rods fully inserted into the core in response to the automatic reactor trip and heat sink is currently been maintained using Auxiliary Feedwater Pumps and the Main Steam Dumps. Except as noted, all other systems functioned as required. The licensee notified the NRC Resident Inspector.
ENS 4062229 March 2004 17:17:00CookAutomatic ScramNRC Region 3Westinghouse PWR 4-LoopOn March 29, 2004 at 1404 hours (EST), Unit 2 received an automatic actuation of the Reactor Protection (RPS). The RPS actuation occurred when the train B Reactor Trip Bypass Breaker was manipulated during the conduct of the Solid State Protection System (SSPS). Testing the Bypass Breaker had been racked in and closed, but correct indication was not received earlier during the test. The decision was made to restore from the testing and the Bypass Breaker was being racked out when the actuation occurred. The Unit was at full power with all system in normal alignment. Initial indication is that the actuation signal was a Power Range Rate Trip. The RPS actuation is believed to be related to the manipulation of the Bypass Breaker. Cause is under investigation. Following the RPS actuation, the Auxiliary Feedwater System automatically started on low-low Steam Generator levels. This constituted a valid unplanned actuation of the Engineered Safeguards Feature (ESF). Operators stabilized the Plant using Condenser Steam Dumps and Auxiliary Feedwater. No other ESF systems actuated. All other Plant systems responded normally. All control rods fully inserted into the core. The Plant is currently stable in Mode 3, and Steam Generator levels are being maintained using the Auxiliary Feedwater System. The Licensee notified the NRC Resident Inspector.
ENS 4041930 December 2003 15:01:00CookManual ScramNRC Region 3Westinghouse PWR 4-LoopCook unit 2 automatically tripped from 100% power due to low steam generator level coincident with feed flow less than steam flow. The cause of this condition is under investigation, but it is suspected that unplanned closure of the steam generator 2 & 3 feedwater isolation valves led to the initiating signal. It is believed that the feedwater isolation valve closure originated from an abnormality in the Control Room Instrument Distribution(CRID) 120VAC power system. Technicians were landing leads on a Residual Heat Removal (RHR) System flow transmitter which was fed from the suspected CRID supply at the time of the event. An arc was observed during the lead landing procedure. The main generator also required a manual trip signal by control room operators due to sticking of the main stop valve which is also being investigated. All other systems responded as expected. All rods fully inserted, no ECCS actuation occurred, and no relief valves lifted. The unit is stable in mode 3 with aux feedwater providing heat sink supply. The NRC Resident Inspector has been informed.