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 Entered dateSiteScramRegionReactor typeEvent description
ENS 5332913 April 2018 06:07:00OconeeManual ScramNRC Region 2B&W-L-LPOn 4/13/2018 at 0227 (EDT), the Oconee Unit 1 Reactor was manually tripped from 24 percent power due to the inability to control main feedwater flow through the Main Feedwater Control Valves using the Integrated Control System. Due to the RPS actuation while critical, this event is being reported as a 4-hour Non-Emergency per 10 CFR 50.72(b)(2)(iv)(B). Following the reactor trip, multiple Main Steam Relief Valves failed to reseat at the expected pressure. Using procedure guidance, Main Steam Pressure was lowered by 115 psig, resulting in the closing of all Main Steam Relief Valves. All other post-trip conditions are normal and all other systems performed as expected. Unit 1 is currently in Mode 3 and stable. Decay heat is being removed by the steam generators discharging steam to the main condenser using the turbine bypass valves. Units 2 and 3 are not affected by the Unit 1 reactor trip. The licensee notified the NRC Resident Inspector.
ENS 5287024 July 2017 19:25:00OconeeAutomatic ScramNRC Region 2B&W-L-LPAt 1638 (EDT) on 7/24/2017, Oconee Unit 3 experienced an automatic reactor trip due to a load rejection when the generator output breakers both tripped open unexpectedly while 525kV switchyard maintenance was being performed. The trip was uncomplicated with all systems responding normally post-trip. Due to the RPS (Reactor Protection System) actuation while critical, this event is being reported as a 4-hour non-emergency notification per 10 CFR 50.72(b)(2)(iv)(B). The plant responded normally to the reactor trip, and there was no impact on the health and safety of the public or plant personnel. Operations responded using the Emergency Operating Procedure and stabilized Unit 3 in MODE 3. The NRC Senior Resident Inspector has been notified. Decay heat is removed by discharging steam to the main condenser using the turbine bypass valves. Unit 1 and 2 are not affected.
ENS 5271026 April 2017 14:49:00Arkansas NuclearAutomatic ScramNRC Region 4B&W-L-LP
CE
At 1004 CDT, Arkansas Nuclear One, Unit 1 (ANO-1) reactor automatically tripped due to the partial loss of offsite power. At the time of the trip, the site was in a Tornado Warning and a Severe Thunderstorm Warning. The Emergency Feedwater (EFW) system auto-actuated due to the loss of main feedwater pumps and the loss of the Reactor Coolant pumps. Both Emergency Diesel Generators started as expected with only one loading as expected. All control rods fully inserted. Currently, ANO-1 has stabilized in Hot Standby via natural circulation. ANO-1 also lost Spent Fuel Pool cooling for approximately 69 minutes. The temperature of the spent fuel pool at the beginning of the event was approximately 102 (degrees) F. The spent fuel pool saw a heatup of 1 (degree) F during the loss of spent fuel pool cooling. The Spent Fuel Pool cooling has been restored. ANO-2 is currently in a refueling outage with all fuel in the spent fuel pool. ANO-2 completed a full core off load to the spent fuel pool and this was completed on April 12, 2017. Spent Fuel Pool cooling was lost for approximately 10 minutes. The Spent Fuel Pool temperature was 91 (degrees) F prior to the event. No heat up of the pool was identified during the event. Cooling has subsequently been restored. The #1 Emergency Diesel Generator auto-started as designed but did not supply the safety bus due to availability of offsite power. No radiological releases have occurred from either unit due to this event. The licensee has notified the NRC Resident Inspector.
ENS 5160715 December 2015 10:24:00Arkansas NuclearManual ScramNRC Region 4B&W-L-LPThis is a 4-hour Non-Emergency 10 CFR 50.72(b)(2)(iv)(B) notification due to a Reactor Protection System (RPS) actuation. Arkansas Nuclear One, Unit 1, was manually tripped from 43 percent power at 0544 CST. The reactor was manually tripped due to operator judgement during control issues with the Integrated Control System (ICS) during a planned downpower for Electro-Hydraulic Control (EHC) system maintenance. CV-2672 B, low load control valve, failed to close. Subsequently, CV-2674 B, low load block valve, began to close and caused a loss of feed to E-24B Steam Generator. No additional equipment issues were noted. All control rods fully inserted. Emergency Feedwater (EFW) actuated and was utilized to maintain Steam Generator (SG) levels. This (EFW actuation) meets the 8 hour Non-Emergency Immediate Notification Criteria ((10CFR50.72(b)(3)(iv)(A)). No Primary safety valves lifted. Main Steam Safety Valves (MSSVs) did lift initially after the trip. The NRC Resident (Inspector) has been notified. Decay heat is being removed via the steam dump valves to the main condenser. Unit 1 is in a normal shutdown electrical lineup. Unit 2 was not affected by the transient on Unit 1. The licensee notified the State of Arkansas.
ENS 5078131 January 2015 18:00:00OconeeAutomatic Scram
Manual Scram
NRC Region 2B&W-L-LPAt 1431 EST on 1/31/15, Oconee Unit 3 was manually tripped due to oscillations in the feedwater system in anticipation of an automatic trip. At 1427 EST, Unit 3 began experiencing small feedwater oscillations. Specifically, 3FDW-32, the 3A main feedwater control valve, appeared to be oscillating with corresponding feedwater flow oscillation. Feedwater oscillations continued to grow in magnitude and at 1431 EST a manual trip was directed by the Unit 3 control room supervisor. The shutdown was orderly and the unit is currently stable and in Mode 3 (Hot Standby). Units 1 and 2 were unaffected by the trip and are currently 100% power (Mode 1). Due to the RPS actuation while critical, this event is being reported as a 4-hour non-emergency per 10CFR50.72(b)(2)(iv)(B). Following the reactor trip, a main steam relief valve (MSRV) failed to reseat as expected. Emergency Operating procedure guidance was utilized to reduce main steam system pressure by approximately 80 psig to reseat the valve (valve reseated at 1506 EST). All of the main steam relief valves are now seated. In addition, the 3B condensate booster pump experienced a mechanical seal leak (approximately 4-5 gpm). The pump was subsequently secured at 1447 EST. All other post trip conditions were normal and all other systems performed as expected. Unit 3 is currently in Mode 3 and stable. All rods fully inserted. Main Feedwater is feeding the steam generators and decay heat is being removed to the Main Condenser. The cause of the trip is under investigation. There is no known primary to secondary leakage. The NRC Resident Inspector has been informed.
ENS 4947124 October 2013 09:45:00OconeeManual Scram
Automatic Scram
NRC Region 2B&W-L-LP

At 0553 EDT on 10/24/2013, Oconee Unit 3 was manually tripped due to oscillations in the feedwater system in anticipation of an automatic reactor trip. At 0549 EDT, Unit 3 began experiencing small feedwater oscillations. The feedwater control system was placed in manual in an attempt to stabilize feedwater flows. Feedwater oscillations continued to grow in magnitude and at 0553 EDT, a manual trip was directed to prevent an automatic reactor trip. Due to an RPS actuation, this event is being reported as a 4 and 8 hour Non-Emergency per 10 CFR 50.72 (b)(2)(iv)(B) and 10 CFR 50.72 (b)(3) Following the reactor trip, four main steam relief valves failed to reseat. Procedure guidance was utilized to reduce main steam system pressure by approximately 30 psig to reseat the main steam relief valves. All main stream relief valves are now reseated. All other post trip conditions were normal and all other systems performed as expected. Unit 3 is currently in Mode 3 and stable. Operations have been stabilized on Unit 3. A post-trip investigation is in progress, per site procedures and directives. The licensee has notified the NRC Resident Inspector.

  • * * UPDATE FROM BOB MEIXELL TO DONALD NORWOOD AT 1439 ON 9/10/14 * * *

Duke Energy reviewed NRC Event Number 49471 against NUREG 1022, Rev 3, section 3.2.6, "System Actuation" and determined this event should have been reported only per 10 CFR 50.72 (b)(2)(iv)(B), RPS Actuation (while critical). Thus, Duke Energy is revising NRC Event Number 49471 to remove the 8-hour report criteria 10 CFR 50.72 (b)(2)(iv)(A). The NRC Resident Inspector was notified of this revised report. This update has no effect on safety significance. Notified R2DO (Shaeffer).

ENS 4832520 September 2012 16:15:00Three Mile IslandAutomatic ScramNRC Region 1B&W-L-LPOn September 20th at 1416 EDT, Three Mile Island automatically tripped due to a flux to flow imbalance as a result of a trip of the 'C' reactor coolant pump. The cause of the trip of the 'C' reactor coolant pump is still under investigation. The electrical grid is stable and unit 1 is being supplied by offsite power. All control rods have fully inserted. Decay heat is being removed by main feedwater flow to both steam generators that are exhausting via the normal main condenser cooling loop under manual control. Preliminary evaluation indicates that all plant systems functioned normally following the reactor trip, except for automatic operation of turbine bypass valve control due to failure of the automatic control function to control precisely at setpoint. Three Mile Island remains stable in hot shutdown mode 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, and under 10 CFR 50.72 (b)(2)(xi) due to an information release to local officials. Both are four hour reports. The licensee notified the NRC Resident Inspector." The licensee has notified the state and local governments, and will be making a media release.
ENS 4822122 August 2012 11:32:00Three Mile IslandAutomatic ScramNRC Region 1B&W-L-LPOn August 22, 2012, during a planned load reduction, Three Mile Island Unit 1 Reactor automatically tripped at 0801 EDT due to high reactor coolant system pressure as a result of a main feedwater transient. The cause of the main feedwater transient is still under investigation. The Emergency Feedwater System (EFW) actuated at 0801 EDT. 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 the Emergency Feedwater System (EFW) flow to both Steam Generators that are exhausting via the normal main condenser cooling loop under manual control. Preliminary evaluation indicates all plant systems functioned normally following the reactor trip and EFW actuation except for manual operation of Turbine Bypass Valve control due to failure of the automatic control function. Three Mile Island Unit 1 remains stable in Hot Shutdown mode 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, and under 10 CFR 50.72(b)(2)(xi), due to an information release to local officials, both are four (4) hour reports. This event is also reportable under 10 CFR 50.72(b)(3)(iv)(A) and 10 CFR 50.72(b)(3)(iv)(B), due to a valid actuation of the Emergency Feedwater System. The licensee notified the NRC Resident Inspector." Licensee notified the State, local and other Government agencies.
ENS 461597 August 2010 18:47:00OconeeManual ScramNRC Region 2B&W-L-LPAt 1451 on 8/7/2010, Oconee Unit 1 initiated a manual reactor trip from approximately 17% power due to indicated vibrations on 1A1 and 1A2 reactor coolant pumps (RCP) reaching the high vibration trip criteria. All systems responded normally following the reactor trip. Unit 1 is currently stable in MODE 3. An investigation is in progress to determine the cause of the elevated reactor coolant pump vibrations. All control rods fully inserted on the trip. Decay heat is being removed via the turbine bypass valves to the main condenser. Steam generator water level is being maintained with main feedwater. There is no evidence that the PORVs or safety valves lifted. The plant is in its normal shutdown electrical lineup. There were no indications on the loose parts monitor except for the RCP high vibration. There was no affect on units 2 or 3. The licensee notified the NRC Resident Inspector.
ENS 4587226 April 2010 01:35:00Arkansas NuclearAutomatic ScramNRC Region 4B&W-L-LPThis is a 4 hour Non-Emergency 10CFR 50.72(b)(2)(iv)(B) notification due to an Automatic Reactor Protection System (RPS) actuation (scram). At 2126 hours (CDT) on April 25, 2010, Unit 1 Reactor automatically tripped due to 2 of 4 Reactor Protection System (RPS) Channels tripped. At the time of the trip, reactor power, as indicated by heat balance, was ~20%, while excore Nuclear Instrumentation (NI) indicated ~30%. The RPS high reactor power trip setpoint was 50% power. An NI calibration initiated an automatic withdrawal command to the control rod drive system. The rod withdrawal, resulted in one RPS channel tripping on high reactor power and another RPS channel tripping on high reactor coolant system pressure. All control rods fully inserted into the core and no safety systems, other than RPS, actuated. Emergency feedwater did not actuate and was not needed. No primary safety valves lifted. Seven secondary safety valves lifted and subsequently reseated. The plant is currently stable in Mode 3. The NRC resident has been notified. The licensee also informed the State of Arkansas and does not plan a press release. The Unit 1 reactor trip was uncomplicated. Current means of decay heat removal is normal feedwater to the Steam Generators with steam discharge to the Main Condenser through Main Steam Bypass. The Main Generator was online at the time of the trip and the plant is currently in a normal post trip electrical line up. There is no indication of primary-secondary tube leakage. All systems functioned as required.
ENS 4585418 April 2010 18:04:00Arkansas NuclearManual ScramNRC Region 4B&W-L-LPThis is a 4-hour Non-Emergency, 10CFR 50.72(b)(2)(iv)(B) notification due to an RPS actuation (scram). Arkansas Nuclear One Unit 1 was manually tripped from 11% power at 1357 hrs. CDT. The cause of the trip was operator judgment due to a small fire reported in the high pressure turbine enclosure at governor valve number 3 by a fire watch stationed at that location and an unrelated failure of P-32C Reactor Coolant Pump 3rd stage seal (upper seal) occurring earlier that afternoon. No additional equipment issues were noted. An extinguishing agent (CO2) was applied within approximately 30 seconds. All control rods fully inserted. No primary safeties lifted. No secondary safeties lifted. Emergency feedwater did not actuate and was not needed. No safety systems actuated. The plant will be cooled down to repair the P-32C Reactor Coolant Pump Seal. The NRC Resident has been notified. There was no effect on Unit 2. The grid is stable with Unit 1 in a normal shutdown electrical lineup. Decay heat is being removed via the steam dumps to condenser using normal feed to the steam generators. The licensee will be notifying the Arkansas Department of Health.
ENS 4528624 August 2009 12:48:00Crystal RiverManual ScramNRC Region 2B&W-L-LPFollowing completion of surveillance testing for the electrical checks of the Control Rod Drive power train, the operating crew observed that Group 7 regulating control rods unexpectedly lost power and inserted into the core. The Operators manually tripped the reactor prior to exceeding any RPS trip set point. There were no other safety system actuations and the plant is stable at normal post-trip temperature and pressure. There are seven rods in Group 7. Operators tripped the unit within 7 seconds. All rods fully inserted on the trip. The plant is removing decay heat through the main condenser and feeding generators with auxiliary feed. The licensee notified the NRC Resident Inspector.
ENS 448377 February 2009 12:18:00Arkansas NuclearManual ScramNRC Region 4B&W-L-LP

Arkansas Nuclear One Unit 1 declared an Unusual Event per EAL 7.5 at 1059 CST based on a fire onsite. The fire occurred on the 354 foot elevation iso-phase bus deck of the turbine building. The fire was attributed to a failed bonnet on a manual valve which had unthreaded during operation releasing hydrogen in the vicinity of the hydrogen add station. The licensee extinguished the fire using water and posted a reflash watch. There were no reported personnel injuries. Offsite assistance was requested from the London Fire Department which arrived onsite after the fire had been extinguished. The reactor was manually tripped with all control rods fully inserting. The plant is currently stable with decay heat removal via the steam dumps to the main condenser. The licensee informed state/local agencies and the NRC Resident Inspector.

  • * * UPDATE AT 1338 EST ON 2/7/09 FROM JACKSON TO SANDIN * * *

The Unusual Event was terminated at 1338 CST after confirmation that the fire was extinguished and a review of the exit criteria as defined in plant procedures. The licensee is performing a damage assessment at this time. The licensee was in the process of informing state/local agencies and will inform the NRC Resident Inspector. Notified R4DO (Clark), NRR(Hiland), IRD (Grant), DHS (Banner) and FEMA (Canupp).

  • * * UPDATE AT 1508 EST ON 2/10/09 FROM SCHEIDE TO HUFFMAN * * *

The subject event notification erroneously reported that all control rods fully inserted following the manual reactor trip initiated in response to a fire on site. In actuality, the rod bottom light for Rod 6 in Rod Group 7 on the CRD Position Indication Panel did not illuminate following the reactor trip and it was verified by plant computer to have inserted to 2.3 percent withdrawn. The control board operator identified this condition quickly and reported it to the Control Room Supervisor in his immediate action response. This condition did not necessitate any additional operator actions and shutdown margin requirements were maintained. The licensee has informed the NRC Resident Inspector. R4DO (Miller) notified.

ENS 448315 February 2009 19:20:00Arkansas NuclearManual ScramNRC Region 4B&W-L-LPArkansas Nuclear One Unit 1 was manually tripped from 61% power due to Control Rod Drive motor (CRD) high temperatures due to a loss of cooling water flow from Non-Nuclear Intermediate Cooling Water (ICW). No significant equipment issues were observed. No primary safeties lifted. Secondary safeties lifted for ~18 seconds. Emergency feedwater did not actuate and was not needed. Post trip response was normal and the plant is stable in mode 3. Post transient review is in progress. All control rods fully inserted into the core. There is no known primary-secondary steam generator tube leakage. The offsite electrical grid is stable. The loss of ICW flow is attributed to the mechanical failure of service air compressor C-3A. Decay heat removal is via main feedwater to the steam generator and steam to the main condenser. The licensee informed state, other government agencies and the NRC Resident Inspector and will inform local government agencies. No press release is planned.
ENS 4480727 January 2009 12:41:00Crystal RiverManual ScramNRC Region 2B&W-L-LPCalibrations of the 'A' Unit 4160V Switchgear metering were in progress when the 'A' Unit 4160V Bus tripped. This resulted in the loss of the 'A' Feedwater Booster Pump (FWBP) and 'A' Condensate Pump (CDP). The Operating crew identified the loss of the 'A' FWBP with increasing RCS pressure and manually tripped the reactor. There were no other safety system actuations and the plant is stable at normal post-trip temperature and pressure. All rods inserted during the trip. Decay heat is being removed via steam dumps to the condenser. The electrical grid is stable with plant loads being supplied by offsite power via the startup transformer. Both vital busses are being powered from offsite. During the transient, main steam relief valves did lift but have been reseated. The NRC Resident Inspector has been notified.
ENS 4473620 December 2008 14:23:00Arkansas NuclearManual ScramNRC Region 4B&W-L-LPArkansas Nuclear one Unit 1 manually tripped from 100% power due to control rod mechanism group 7 unexpectedly dropping from 90% to 70%. No Primary safeties lifted. Secondary safeties lifted for approximately 1 minute. Emergency feedwater did not actuate and was not needed. Post trip response was normal and the plant is stable in mode 3. Post transient review is in progress. All control rods fully inserted on the trip. The plant is in its normal shutdown electrical lineup. Steam generator level is being maintained using aux feed and steam is being dumped to the main condenser through the turbine bypass valves. There is no primary to secondary leakage. The licensee notified the NRC Resident Inspector, the State of Arkansas, and the Arkansas Department of Health. See similar event number 44716.
ENS 4471612 December 2008 11:48:00Arkansas NuclearManual ScramNRC Region 4B&W-L-LPFollowing startup from refueling outage 1R21, Arkansas Nuclear One Unit 1 was holding stable at 32% reactor power in order to perform Nuclear Instrumentation (NI) calibration. Control Rod Drive Mechanism (CRDM) control was in automatic with the controlling group (Group 7) at approximately 75% withdrawn. Control room operators received an asymmetric rod alarm and noted abnormal rod pattern on Group 7 with reactor power lowering. At this point, operations manually scrammed the reactor. Post trip response was normal and the plant is stable in Mode 3. Reactor Coolant System pressure is approximately 2155 psig and temperature is approximately 550 degree F. Post Transient Review is in progress. Unit 1 is in a normal post trip electrical lineup. No primary or secondary reliefs lifted during the transient. Auxiliary feedwater was placed in service to supply the Steam Generators for decay heat removal via the Main Condenser. The licensee informed both the State and NRC Resident Inspector.
ENS 446387 November 2008 12:05:00OconeeAutomatic ScramNRC Region 2B&W-L-LPAt 0834 on 11-7-08, Oconee Nuclear Station (ONS) Unit 3 experienced an automatic reactor trip due to a reactor protective systems (RPS) actuation. ONS Unit 3 post trip parameters are normal. Main Feedwater remained in service following the event and Emergency Feedwater was not required and remained available. Electrical power automatically transferred to the Startup power source from the switchyard and emergency AC power sources were not required and remained available. The cause of the RPS actuation and automatic reactor trip are under investigation. ONS Unit 1 remained at 100% power with no issues following the ONS Unit 3 reactor trip. ONS Unit 2 remained in No-Mode. No other safety systems have actuated or exhibited abnormal behavior. Therefore, the safety significance of this condition is low. All control rods fully inserted during this event. The unit is removing decay heat to the main condenser. No primary relief valves lifted and Main Steam relief valves cycled following the trip. There are no Steam Generator tube leaks. The licensee notified the NRC Resident Inspector.
ENS 4443824 August 2008 18:03:00Crystal RiverManual ScramNRC Region 2B&W-L-LPThe 'A' Condensate Pump became uncoupled, lowering Condensate flow. Operators began to manually lower reactor power to maintain deaerator level. Reactor power was lowered to approximately 62 percent. At this power, (feedwater) flow oscillations began and were excessive. With these flow oscillations increasing the decision was made to manually trip the Reactor. The Reactor was manually tripped at 1557 hours. There were no safety system actuations other than RPS (Manual). The plant is stable in a normal post trip configuration. All control rods inserted into the core during the reactor trip. Offsite power is available and powering safety loads. The steam generator safeties lifted during the transient and reseated. There is no known primary to secondary leakage. Decay heat is being removed via steam dumps to the condenser using normal feedwater to the steam generator. The emergency feedwater system was not initiated during the reactor trip. The licensee notified the NRC Resident Inspector.
ENS 4410931 March 2008 17:11:00OconeeAutomatic ScramNRC Region 2B&W-L-LP

Event: At 1352 hours, Unit 2 experienced a Reactor Trip due to a turbine trip. The indicated cause was low condenser vacuum. The exact cause is still under investigation but is believed to be related to a maintenance procedure in progress on the condenser vacuum instrumentation. Post-trip response was normal. Auxiliary power transferred to the start-up source (switchyard) as expected. Main Feedwater was not affected so there was no demand for Emergency Feedwater. A second High Pressure Injection pump was manually started per procedure to maintain Pressurizer level indication on scale. This is a routine action to compensate for post-trip RCS temperature and volume changes. In an apparently unrelated event, Keowee Hydro Units (KHU) 1 and 2 were shutdown from commercial operation at approximately 1425 hours. During the shutdown, the KHU 1 output breaker failed to open as expected and KHU 1 was manually locked out. The lockout removed both the Overhead and Underground Power Paths from service, making on-site emergency power unavailable to all three Oconee units. Per Tech Specs, a gas turbine unit at Lee Steam Station was started and used to energize the Oconee Standby Bus at 1518 hours. Initial Safety Significance: There is little or no safety significance to the Unit trip. The subsequent KHU 1 lockout removed both the Overhead and Underground Power Paths from service, making on-site emergency power unavailable until the Lee gas turbine was aligned. There was no demand for the Keowee emergency power function during either event. Corrective Action(s): Investigations are in progress as to the cause of the Reactor Trip and the KHU 1 lock out. Alignment of KHU 2 to the underground is currently on hold, pending evaluation of the problem which led to the KHU 1 lockout. All control rods fully inserted with decay heat being removed via the turbine bypass valves. The licensee notified the NRC Resident Inspector.

  • * * UPDATE AT 1055 EDT ON 04/02/08 FROM COREY GRAY TO HOWIE CROUCH * * *

The licensee is retracting a portion of the original report identified under 10CFR50.72(b)(3)(v)(D) based on the following: Event: UPDATE: At 1352 hours, Unit 2 experienced a Reactor Trip due to a turbine trip. The indicated cause was low condenser vacuum. The exact cause is still under investigation but is believed to be related to a maintenance procedure in progress on the condenser vacuum instrumentation. Post-trip response was normal. Auxiliary power transferred to the start-up source (switchyard) as expected. Main Feedwater was not affected so there was no demand for Emergency Feedwater. A second High Pressure Injection pump was manually started per procedure to maintain Pressurizer level indication on scale. This is a routine action to compensate for post-trip RCS temperature and volume changes. In an unrelated event, Keowee Hydro Units (KHU) 1 and 2 were shutdown from commercial operation at approximately 1425 hours. During the shutdown, the KHU 1 output breaker, ACB-1, failed to open as expected and KHU 1 was manually locked out. The lockout removed KHU 1 and the Overhead Power Path from service due to the failed ACB. Because KHU 1 was the unit aligned to the Underground Power Path, Operations declared that path inoperable also. This condition was initially reported as making on-site emergency power unavailable to all three Oconee units. Per Tech Specs, a gas turbine unit at Lee Steam Station was started and used to energize the Oconee Standby Bus at 1518 hours. In this alignment, the Lee gas turbine provides the on-site emergency power function. A design feature allows a KHU to automatically align to the Underground Path when the unit originally aligned to that path has been locked out, the overhead path is locked out and an emergency start signal exists. Keowee Operations confirmed that during the lockout event the required lockout signals were present on KHU 1 such that KHU 2 would have aligned to the Underground Power Path if an emergency start demand had occurred. As a result, the Underground Power Path remained available during this event and there was no loss of safety function. Therefore the portion of the event related to 10CFR50.72(b)(3)(v)(D) is RETRACTED. The Underground Power Path was administratively inoperable because a surveillance (SR 3.8.1.3) to verify operability of KHU 2 to the underground path, required per TS 3.8.1 Condition C.1, could not be performed. The surveillance procedure utilizes a normal start signal, which was inhibited by the lockout on the overhead path. The surveillance procedure does not include provisions for using an emergency start signal. At 1906 hours, after the overhead lockout had been reset, KHU 2 successfully completed an Operability test aligned to the Underground Power Path. Investigation determined that the failure of ACB-1, the output breaker for KHU 1, was due to a terminal strip sliding link in the trip circuit being in an intermediate position. It was damaged during repair so the entire sliding link block was replaced. The unit was successfully tested connected to each power path and was declared Operable on 4-1-08 at approximately 0600 hours. At 0930 hours on 4-1-08 the standby bus was disconnected from Lee. Initial Safety Significance: There is little or no safety significance to the Unit trip. The subsequent KHU 1 lockout removed the Overhead Power Path from service. The Lee gas turbine was aligned to energize the standby bus. Operations and Engineering subsequently confirmed that on-site emergency power remained available via KHU 2 and the Underground Power Path. There was no demand for the Keowee emergency power function during either event. Corrective Action(s): Investigation as to the cause of the Reactor Trip continues. Unit 2 is now on-line at low power and is in the process of returning to full power. ACB-1, the output breaker for KHU 1, terminal strip sliding link has been repaired/replaced; both KHUs have been tested and declared operable; the Lee gas turbine has been secured. The licensee informed the NRC Resident Inspector. Notified R2DO (Evans).

ENS 4317921 February 2007 22:11:00Crystal RiverAutomatic ScramNRC Region 2B&W-L-LPAt 1915 on February 21, 2007, Crystal River Unit 3 was at reduced power (71%) for planned maintenance on one of four condenser waterboxes when the Integrated Control System (ICS) for Main Feedwater became erratic causing a feedwater transient that underfed the once thru steam generators. The reactor protection system (RPS) actuated on high Reactor Coolant System pressure causing a reactor trip. CR3 also received an Emergency Feedwater Actuation (EFIC) on low steam generator levels. This event is reportable as a 4-Hour Non-Emergency Notification per 10CFR50.72 (b)(2)(iv)(B) for Reactor Protection System Actuation and as an 8-Hour Non-Emergency Notification per 10CFR50.72 (b)(3)(iv)(A) for Emergency Feedwater Actuation and for Reactor Protection System actuation. All systems responded as designed and the plant remains stable with Emergency Feedwater in MODE 3. The licensee informed the NRC Resident Inspector.
ENS 4305013 December 2006 21:00:00Three Mile IslandAutomatic ScramNRC Region 1B&W-L-LPWhile operating at 100 % power the unit experienced an automatic Reactor trip from Reactor Protection System actuation at 17:48 on 12/13/06. At the time of the trip there was a grid disturbance followed by the unit tripping. The cause of the trip is under investigation. All plant systems functioned as designed. The unit is being maintained in Hot Shutdown conditions using applicable plant procedures. All control rods inserted fully after the reactor trip. S/G safety valves lifted and reset per design during the transient. The S/Gs are being supplied with normal feedwater and decay heat is being removed to the main condenser via the steam dump valves. The electric plant is in a normal shutdown lineup and the EDGs are available. The licensee notified the NRC Resident Inspector, PEMA, the Counties of Dauphin, Cumberland, Lancaster, York, and Lebanon.
ENS 429572 November 2006 14:53:00Three Mile IslandAutomatic ScramNRC Region 1B&W-L-LP

At 1334 on 11-2-06 an Automatic Reactor Trip occurred from 100% power. All systems functioned as required. One safety valve stuck open on both OTSGs. They subsequently re-seated. An employee working on the roof at the time of the trip fell off a ladder and injured his leg. Emergency medical was contacted to assist with the injured worker. Two fire trucks and an ambulance was dispatched to the site to remove the injured worker. The worker was not contaminated. There is no indication of any OTSG tube leaks. Initial investigation indicates the reactor tripped, due to a turbine trip due to an invalid low vacuum signal. State and local officials will be notified of this event by the licensee. I&C Techs were performing maintenance on one of the low pressure vacuum switches. An electrical fault fed to the other two low pressure vacuum switches causing a 2 out of 3 signal which resulted in a turbine trip followed by a reactor trip signal, as expected. All rods fully inserted into the core. One safety valve (9 safety valves on each OTSG) on each Once Through Steam Generator stuck open. OTSG "B" safety relief valve was open less than one minute. There are no leaking OTSG tubes. A condensate relief valve located in the turbine building opened/shut - nobody injured. The ICS (Integrated Control System) operated as expected. All emergency core cooling systems and the emergency diesel generators are fully operable plus the electrical grid is stable. A licensee working on the industrial coolers on top of the industrial building, standing on a ladder, fell off the ladder when OTSG relief valve opened. Licensee either broke or badly sprained his leg. The NRC Resident Inspector was informed of this event by the licensee.

  • * * UPDATE ON 11/03/06 AT 1607 EST FROM ADAM MILLER TO MACKINNON * * *

Post trip evaluation determined that the Main Steam safety valves were not stuck open. The safety valves were operating within their tolerance band. The "B" OTSG Main Steam safety valve reseated with no operator action as steam pressure decreased. The "A" Main Steam safety valve was reseated when operators lowered OTSG pressure in accordance with Plant Operating Procedures. TMI-1 issued a press release on this event at 15:13 on 11/2/06." R1DO (John White) notified. The NRC Resident Inspector was notified of this update by the licensee.

ENS 4249312 April 2006 14:48:00OconeeAutomatic ScramNRC Region 2B&W-L-LPAt 1335 EDT the Unit 2 Reactor tripped from 100% power on a Flux/Flow/Imbalance on two (2) RPS Channels "A" and "D." The initiating event was the trip of the "2B2" Reactor Coolant Pump (RCP) for unknown reasons. I & E Techs were working in the RCP Monitoring Cabinets at the time. Immediately following the RCP trip, Unit 2 commenced a runback as expected for approximately six (6) seconds before the RPS actuation occurred. All rods fully inserted with an anomaly noted for CRD (Control Rod Drive) Group 3 Rod 7 API (Absolute Position Indication) indicating approximately 21%, however, the PI (Position Indicating) Panel light was on. The licensee suspects that the problem is related to a reed switch for the API indication and not the actual rod position. Shutdown Margin has confirmed that the Reactor is subcritical. The Pressurizer Code Safeties and PORV did not lift during the transient. Unit 2 is currently stable in Mode 3 discharging steam to the Main Condenser via the Turbine Bypass Valves using Main Feedwater for steam generator level control. Offsite power is available and stable. This event did not impact Units 1 or 3. RCP "2B2" will remain secured until the cause of the trip is identified and corrected. There is no known primary to secondary leakage for Unit 2. The licensee has completed EOP (Emergency Operating Procedure) subsequent actions. The licensee informed the NRC Resident Inspector.
ENS 4222926 December 2005 15:35:00Arkansas NuclearAutomatic ScramNRC Region 4B&W-L-LPA reactor trip occurred due to a Reactor Protective System (RPS) actuation from probable Main Turbine problems. The Emergency Feedwater Initiation and Control System (EFIC) actuated on the 'A' Steam Generator only due to a momentary level spike post trip. The RPS and EFIC performed as designed. Unit 1 will remain in mode 3 for troubleshooting efforts. No significant equipment issues observed. This report is being made in compliance with the 4 hour and 8 hour non-emergency notifications required by 10CFR50.72(b)(2)(iv)(B) and 10CFR50.72(b)(3)(iv)(A), respectively. The licensee notified the NRC Resident Inspector and State authorities. All rods fully inserted. The trip was characterized as uncomplicated and all systems functioned as required. Electrical conditions are stable. The reactor is currently at no load temperature and pressure with decay heat being removed via the turbine bypass valves and cooling to the steam generators from the non-safety related auxiliary feedwater system. The trip had no impact on Unit 2. The licensee was in no significant LCO at the time of the trip. The licensee noted that one of the main steam code safeties did stick open for a short period of time but closed after secondary pressure was reduced without any overcooling. The cause of the turbine trip is under investigation.
ENS 4209429 October 2005 04:39:00Crystal RiverManual ScramNRC Region 2B&W-L-LPThis event is reportable under 10 CFR 50.72 (b)(2)(iv)(B) and 10 CFR 50.72 (b)(3)(iv)(B)(6). During a plant shutdown for a refueling outage at 0126 (EDT) on October 29, a manual reactor trip was initiated in anticipation of Critical Operation on Emergency Feedwater. CR3 (Crystal River Unit 3) experienced an automatic Emergency Feedwater Actuation based upon a loss of both Main Feedwater Pumps. Main Feedwater Pumps tripped on a loss of the running Main Feedwater Booster Pump, which was automatically tripped on low Feedwater De-aerator Tank level. The redundant Main Feedwater Booster Pump was shutdown as part of the plant shutdown sequence. The low Feedwater De-aerator Tank level occurred due to a loss of the operating Condensate Pump while the redundant Condensate Pump was tagged out of service for scheduled maintenance. The cause of the failed condensate pump that initiated the event sequence is still under investigation but the licensee indicated that it appears to be due to a mechanical failure. The licensee notified the NRC Resident Inspector.
ENS 4196631 August 2005 17:38:00OconeeAutomatic ScramNRC Region 2B&W-L-LP

Event: At 1428 hours on 8/31/2005, Oconee Unit 3 tripped. A routine test of the alternate power source for the Control Rod Drive System was in progress when power to the Control Rod Drive system was interrupted, which resulted in a reactor trip. AC power transferred to the Start-up source (switchyard). Normally the Main Steam Header pressure control setpoint is automatically increased for post-trip RCS temperature control. This did not occur. As a result the RCS cooled down to approximately 536F (versus a normal post-trip temperature of approximately 555F), reducing RCS pressure to the actuation setpoint for Engineered Safeguards Channels 1 and 2. This started the High Pressure Injection pumps in ECCS mode, caused partial containment isolation and initiated start-up of both Keowee Hydro Units (emergency power). Because Start-up power was available, Keowee did not supply power but remained in stand-by. At 1133 hours Operators terminated ECCS injection. Initial Safety Significance: Because RCS pressure decreased below normal post-trip levels which resulted in an ECCS actuation, this is considered an abnormal transient. Unit 3 has been stabilized and at this time the actual event is considered to have low safety significance. The exact cause of the loss of power to the Control Rod Drive system is unknown, but is under investigation. It is suspected that that loss also resulted in the failure of the Main Steam Header Pressure to shift to the post-trip Main Steam pressure control setpoint. Corrective Action(s): Operations stabilized Unit 3. A post-trip investigation is in progress, per site procedures and directives. All control rods fully inserted as a result of the reactor trip. No primary or secondary reliefs or PORVs lifted. Pressurizer level decreased off-scale low and was recovered prior to securing the High Pressure Injection pumps (the licensee estimates approximately 3000 gallons was injected). Current RCS temp is 542F (Tave) with RCS pressure in the normal post-trip band. Decay heat is being removed by the Steam Generators to Condenser through the Turbine Bypass Valves. Main Feedwater remained in service during the transient. The licensee informed the NRC Resident Inspector and does not plan a press release at this time.

  • * *UPDATE FROM LICENSEE (NIX) TO NRC (HUFFMAN) @ 2156 EDT ON 8/31/05 * * *

During this event, the Engineering Safeguards (ES) System was manually bypassed at 14:33 on 8-31-05 to restore both High Pressure Injection (HPI) System trains to a normal lineup following an ES-initiated safety injection. Manually bypassing ES for both trains of HPI required entry into Tech Spec 3.0.3 at 15:33 on 8-31-05. Tech Spec 3.0.3 requires shutdown of Unit 3 to Mode 3 by 03:33 on 9-1-05 and to Mode 4 by 09:33 on 9-1-05. This condition was discovered to apply at 21:15 on 8-31-05. Initial Safety Significance: Units 1 and 2 remain at 100% power with no issues following the Unit 3 ES Actuation and Keowee Hydro Unit emergency start. Unit 3 remains in Mode 3. No other safety systems have actuated or exhibited abnormal behavior. Therefore, the safety significance of this condition is LOW. Corrective Action(s): Restore ES System to Automatic for the HPI System. The licensee reported this under 10 CFR 50.72(b)(2) (i), Technical Specification Shutdown. The licensee will notify the NRC Resident Inspector. R2DO (Lesser) notified.

ENS 410236 September 2004 12:44:00Crystal RiverAutomatic ScramNRC Region 2B&W-L-LPAt approximately 1150 (EDT), CR3 Site experienced a 230KV 'B' Buss loss. The resultant loss of power was a loss of both non-vital 4160V busses. All RCPs tripped and a reactor trip occurred. The plant is stable on natural circulation cooling. This report is based on the Reactor Protection System Actuation and Specified System Actuation (Emergency Feedwater). The "B" ESF 4160KV Bus deenergized resulting in an autostart of the "B" EDG, as expected. Natural Circulation has been confirmed with both Steam Generators (SGs) receiving Emergency Feedwater (EFW) via both the Turbine-Driven and Diesel-Driven EFW Pumps. The SGs are using the Atmospheric Dumps to remove decay heat. There was no known SG tube leakage prior to the transient. The cause for the partial loss of offsite power is under investigation. The licensee informed the NRC Resident Inspector.
ENS 4060824 March 2004 04:39:00Crystal RiverAutomatic ScramNRC Region 2B&W-L-LPAt approximately 0331 EST the reactor tripped due to reactor protection system actuation. The Emergency Feedwater System actuated. It appears that a main feedwater perturbation (sensed low feedwater flow) occurred which actuated a main turbine trip. The main turbine trip actuated the reactor protection system which tripped the reactor. The reactor shutdown and all control rods fully inserted. Decay heat is being removed using the turbine bypass valves and emergency feedwater. The Licensee notified the NRC Resident Inspector.
ENS 402995 November 2003 19:31:00Crystal RiverAutomatic ScramNRC Region 2B&W-L-LPCrystal River Unit 3 was at 37 percent power starting up from a refueling outage. During troubleshooting of control problems with the B Main Feedwater Pump, a feedwater transient occurred which underfed the steam generators. This resulted in a reactor trip on high Reactor Coolant System pressure and Emergency Feedwater Actuation on low steam generator levels. This event is reportable as a 4-Hour Non-Emergency Notification per 10CFR50.72 (b)(2)(iv)(B) for Reactor Protection System Actuation and as an 8-Hour Non Emergency Notification per 10CFR50.72 (b)(3)(iv)(A) for Emergency Feedwater Actuation. The licensee reported that all control rods fully inserted on the trip and that steam generator safety valves lifted and reseated as expected. The primary system is currently at 2155 psi, 549 degrees F with steam generator feedwater being supplied by auxiliary feedwater. The main condenser is available and is being used for primary system heat removal via steam dump. The station electrical grid is stable and in normal configuration; the emergency diesel generators are operable and in standby. The licensee has notified the NRC Resident Inspector.
ENS 4011929 August 2003 21:59:00Arkansas NuclearAutomatic ScramNRC Region 4B&W-L-LP

Unit 1 experienced an automatic reactor trip at approximately 14:28 CDT as a result of a turbine trip. Initial indications are that the trip was associated with a lightning strike on site. Plant is stable in Mode 3. All control rods fully inserted and there are no offsite radiation releases. Anomalies noted are 'C' Main Phase Transformer Sudden Pressure Trip Alarm, Main Generator Output Breakers failed to automatically open and were subsequently manually opened, and 'B' Once Through Steam Generator (OTSG) main feedwater block valve failed to indicate closed which resulted in a low level condition on 'B' OTSG and subsequent automatic actuation of Emergency Feedwater (EFW). EFW is controlling both OTSG levels at low level limits. A normal fast transfer to the Startup Transformer occurred following the trip and offsite power remains available. All EDGs are in standby, if needed. There is no safety related equipment out of service at this time. Decay heat is currently being removed via the steam dumps to the main condenser. The licensee will conduct an investigation into the equipment failures and determine if any plant equipment was damaged by the lightning strike. The licensee informed the NRC Resident Inspector.

  • * * UPDATE AT 0144 EDT FROM HOGUE TO CROUCH * * *

This message is intended to provide clarifying information for Event Notification #40119. Unit 1 experienced an automatic reactor trip at approximately 14:28 CDT as a result of a turbine trip. Initial indications are that the trip was associated with a lightning strike on site. Plant is stable in Mode 3. All control rods fully inserted and there are no offsite radiation releases. The following anomalies were noted in conjunction with plant trip. A 'C' Main Phase Transformer Sudden Pressure Trip Alarm occurred as a result of an indication problem only. The Main Generator Output Breakers failed to automatically open and were subsequently manually opened. The 'B' Once Through Steam Generator (OTSG) main feedwater (MFW) block valve failed to fully close. Complications associated with manual control of feedwater flow when the MFW block valve failed to fully close resulted in a momentary low level in the 'B' OTSG and Emergency Feedwater (EFW) automatic actuation. EFW flow quickly restored the 'B' OTSG level to normal. Both MFW pumps remained operating throughout the transient, and MFW flow was never lost. The EFW System was allowed to recirc for approximately 2 hours. After the MFW block valve was manually closed, the auxiliary feedwater pump was placed in service and EFW and the MFW pumps were secured. The licensee will be notifying the NRC Resident Inspector.

  • * * UPDATE 2017 EDT ON 8/30/03 FROM RICHARD SCHEIDE TO S. SANDIN * * *

The following information was provided as an update: This message is intended to update the information provided in previous notifications concerning Event Notification #40119. Based on subsequent investigation the automatic reactor trip which occurred at approximately 14:28 CDT on August 29, 2003, was a result of high reactor coolant system (RCS) pressure. The high RCS pressure resulted from the inadvertent closure of the main turbine governor valves. Although not conclusively determined, the closure of these valves is most likely due to a lightning strike on site. This automatic reactor trip also resulted in a main turbine trip. Anomalies associated with this event remain as previously reported. The primary PORV (2450 psia) and Safeties (2500 psia) did not lift during the pressure excursion. The High RCS Pressure setpoint for RPS actuation is 2355 psia. The licensee informed the NRC Resident Inspector. Notified R4DO(Runyan).