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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 48325 | 20 September 2012 18:16:00 | 10 CFR 50.72(b)(2)(xi), Notification to Government Agency or News Release 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation | Automatic Reactor Trip Due to Reactor Protection System Actuation | On 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. | Steam Generator Feedwater Reactor Protection System Main Condenser Control Rod | |
| ENS 48221 | 22 August 2012 12:01:00 | 10 CFR 50.72(b)(2)(xi), Notification to Government Agency or News Release 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Automatic Reactor Trip Due to High Reactor Coolant System Pressure | On 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. | Steam Generator Reactor Coolant System Feedwater Reactor Protection System Main Condenser Control Rod Emergency Feedwater System | 05000289/LER-2012-004 |
| ENS 43050 | 13 December 2006 22:48:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation | Unit Reactor Trip Due to Grid Disturbance | While 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. | Feedwater Reactor Protection System Main Condenser Control Rod | 05000289/LER-2006-003 |
| ENS 42957 | 2 November 2006 18:34:00 | 10 CFR 50.72(b)(2)(xi), Notification to Government Agency or News Release 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation | Automatic Turbine Trip/ Reactor Trip Due to Invalid Low Condenser Vacuum Signal | 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.
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. | Steam Generator Emergency Diesel Generator Main Steam Safety Valve Emergency Core Cooling System Safety Relief Valve | 05000289/LER-2006-002 |