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| Entered date | Site | Region | Scram | Reactor type | Event description | |
|---|---|---|---|---|---|---|
| ENS 47628 | 31 January 2012 22:58:00 | San Onofre | NRC Region 4 | Manual Scram | CE | At 1505 PST, Unit 3 entered Abnormal Operation Instruction S023-13-14 'Reactor Coolant Leak' for a steam generator leak exceeding 5 gallons per day. At 1549 PST, the leak rate was determined to be 82 gallons per day. At 1610 PST, a leak rate greater than 75 gallons per day with an increasing rate of leakage exceeding 30 gallons per hour was established and entry into S023-13-28 'Rapid Power Reduction' was performed. At 1630 PST, commenced rapid power reduction per S023-13-28 'Rapid Power Reduction'. At 1731 PST, with reactor power at 35% the Unit was manually tripped. At 1738 PST, Unit 3 entered Emergency Operation Instruction S023-12-4 'Steam Generator Tube Rupture'. At 1800 PST the affected steam generator was isolated. All control rods fully inserted on the trip. Decay heat is being removed thru the main steam bypass valves into the main condenser. Main feedwater is maintaining steam generator level. No relief valves lifted during the manual trip. The plant is in normal shutdown electrical lineup. Unit 2 is presently in a refueling outage and was not affected by this event. The licensee has notified the NRC Resident Inspector. The licensee has issued a press release. |
| ENS 47252 | 8 September 2011 19:08:00 | San Onofre | NRC Region 4 | Automatic Scram | CE | On September 8, 2011 at 1538 PDT, the San Onofre Units 2 and 3 reactors tripped due to a grid disturbance. All control rods fully inserted. The EFAS (Emergency Feed Actuation System) initiated as expected for a reactor trip. Steam generators are being fed by the main feedwater system and decay heat is being removed through the steam bypass system to the main condensers. There is no primary to secondary leakage and no safety relief valves lifted. Site electrical power sources are being fed from off-site power and both units are in a normal shutdown configuration. The emergency diesel-generators are in standby/operable status and were not required during the event. Both units are stable (NOT/NOP) and in Mode 3. The reactor trip response is considered uncomplicated. The licensee has notified the NRC Resident Inspector. |
| ENS 45347 | 13 September 2009 16:12:00 | San Onofre | NRC Region 4 | Automatic Scram | CE | The SONGS Unit 2 reactor automatically tripped from approximately 94% power at 1243 PDT due to loss of turbine load caused by lowering main condenser vacuum. Prior to the reactor trip, personnel were attempting to conduct a heat treat on Unit 2. During this evolution, Gate 5 in the main circulating water system was being repositioned when it stopped moving at 45 percent. This resulted in a recirculation and subsequent increase in circulating water temperature, a lowering main condenser vacuum, a loss of load on the main turbine, and an associated automatic reactor trip. All rods inserted on the automatic reactor trip and the electric grid is stable. This event report is being made under 10CFR50.72(b)(2)(iv)(B) as a valid Reactor Protection System actuation. Decay heat is being removed via normal feedwater to steam generators steaming through the condenser bypass valves to the main condenser. At the time of this event, SONGS Unit 3 was operating at approximately 99% power. The licensee notified the NRC Resident Inspector. |
| ENS 43435 | 21 June 2007 03:24:00 | San Onofre | NRC Region 4 | Manual Scram | CE | At 2250 on 6/20/07, "Instrument Air header pressure failed at a brazed joint. The loss of Instrument Air pressure caused the Steam Generator (S/G) Feedwater Regulating Valves to stop controlling and S/G level, E-088, to rise uncontrolled. Control Room Operators tripped the reactor manually. Main Feedwater Pumps were manually tripped to stop excess feedwater to the S/Gs. Loss of Instrument Air failed the normal cooling to Containment. Containment Emergency Cooling units were manually started to provide containment cooling. The standard post trip actions were carried out with all safety functions satisfied." The site is proceeding with post trip recovery. The Instrument Air leak was isolated at 2321 PDT. All control rods fully inserted on the manual trip. RCPs are in operation transferring decay heat to the S/Gs. Emergency feedwater is feeding the S/Gs with steam being discharged to the condenser via the steam dumps. Atmospheric relief valves were used to discharge steam to the atmosphere initially for approximately 20 minutes following the trip. There are no primary to secondary tube leaks. Containment isolation failed closed as expected following the loss of instrument air pressure to the containment. Normal offsite power is available and the emergency diesel generators are available if needed. The licensee notified the NRC Resident Inspector. |
| ENS 41368 | 3 February 2005 18:02:00 | San Onofre | NRC Region 4 | Automatic Scram | CE | On February 3, 2005, at about 1227 PST, SONGS Unit 2 tripped from about 100 percent power. Preliminary information indicates that the Unit 2 Unit Auxiliary Transformer tripped on high differential current, which caused the main generator to trip and caused the Reactor Protection System to automatically trip the reactor, as expected. Auxiliary Feedwater system actuated as designed and the Unit remains stable in Mode 3 on Main Feedwater. SCE's investigation is ongoing. SCE is reporting this occurrence in accordance with 10CFR50.72(b)(2)(iv)(B) and 10CFR50.72(b)(3)(iv). At the time of this event, SONGS Unit 3 was at about 100 percent power. The NRC resident inspectors are aware of this event and SCE will provide them with a copy of this report. All control rods fully inserted. Decay heat is being rejected to the main condenser. All ESF systems are available and the electrical grid is stable. |
| ENS 41209 | 19 November 2004 12:25:00 | San Onofre | NRC Region 4 | Automatic Scram | CE | The following information was obtained from the licensee via facsimile: 1. SYSTEMS AFFECTED: Reactor trip, Aux feed water actuation. 2. ACTUATIONS AND THEIR INITIATING SIGNALS: Reactor trip - Loss of Load Turbine Trip, Aux Feed Water (AFW) - 21% (on the narrow range indication) in Steam Generators. 3. CAUSES: Reactor tripped due to an undetermined cause in the main generator end of the secondary plant. AFW started as expected on EFAS (Emergency Feedwater Actuation Signal) at 21% from a trip at 100%. 4. EFFECT OF EVENT ON PLANT: Plant is stable at 545F (and) 2250 (psi) hot standby conditions and will remain here until cause determination made as to cause of trip. 5. ACTIONS TAKEN OR PLANNED: Maintain hot standby conditions for post trip review. CONTINUATION SHEET: 1) Remain in Mode 3 for cause determination post-trip review to provide actual mode required. 2) Estimate restart date pending cause determination and any repairs required. 3) All rods inserted, no primary or secondary reliefs lifted, electrical grid stable, all safety systems performed as expected, no effect on Unit 3. Electrical power supplied from offsite power. Decay heat removal is via steam dump to condenser. The licensee has notified the NRC Resident Inspector. |
| ENS 40791 | 4 June 2004 08:21:00 | San Onofre | NRC Region 4 | Manual Scram | CE | San Onofre Nuclear Generating Station (SONGS) experienced a large influx of seaweed that required securing one of the four running Circulating Water (CW) pumps. When conditions continued to degrade, the Operations Department decided to manually trip the unit. During the trip, all control rods inserted into the core. No manual or power-operated relief valves lifted during the transient. Decay heat is being removed via the atmospheric dump valves. There is no known primary-to-secondary leakage. The Operations staff is maintaining the unit at normal operating pressure and temperature. The electrical grid is stable. Currently, only one CW pump is running. Unit 2 is unaffected and is not experiencing a seaweed influx at this time. The licensee has informed the NRC Resident Inspector |
| ENS 40664 | 10 April 2004 16:54:00 | San Onofre | NRC Region 4 | Manual Scram | CE | San Onofre Unit 2 was manually tripped from 97% power due to the loss of feed water pumps. After both feedwater pumps tripped, the operators manually tripped the reactor. Both trains of the emergency feed water system actuated as expected due to the initial power level. The plant is stable at NOP/NOT. The cause of the feed water pump trips is being evaluated. All control rods fully inserted and all safety systems worked properly. The steam generators are discharging steam to the main condenser using the turbine bypass valves. AFW pumps are running to maintain steam generator water levels. The Licensee notified the NRC Resident Inspector. |