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| Entered date | Event description | |
|---|---|---|
| ENS 51720 | 9 February 2016 17:25:00 | At 1415 EST on 02/09/2016, Sequoyah Unit 1 was at 0 percent power (mode 3, 526F, 2235 psig) when a low steam line pressure Safety Injection actuated from Loop 2 Steam Generator. Prior to this event, the Loop 2 Main Steam Isolation Valve bypass was opened at 1413 EST for main steam line warm up in preparation for unit startup. Loop 2 Main Steam Isolation Valve bypass closed automatically following low steam line pressure Safety Injection. Following the Safety Injection, all safety-related equipment operated as designed. Current Reactor Coolant System temperature and pressure - Unit 1 is currently being maintained in Mode 3 at approximately 517 F and 2235 psig, with auxiliary feedwater supplying the steam generators and decay heat removal via steam generator atmospheric relief valves. There is no indication of any primary to secondary leakage. The electrical alignment is normal with shutdown power supplied from off-site power. There is no operational impact to Unit 2. The cause of the Safety Injection actuation is under investigation. This event had no impact on the health and/or safety of the public. The NRC Resident Inspector has been notified. Due to RCS pressure, the only system that injected into the RCS was the charging system. The AFW system initiated to feed the steam generators and the Emergency Diesel Generators started but did not load. |
| ENS 46195 | 21 August 2010 15:47:00 | At 1509 on 08/21/2010, a notification to outside state agencies, Tennessee Department of Environment and Conservation (TDEC) and Tennessee Emergency Management Agency (TEMA), was made due to a Towerbrom 960 (a microbiocide) chemical leak that developed at the Essential Raw Cooling Water (ERCW) intake station. The leak occurred during scheduled chemical treatment of the ERCW system. The leak was identified at 1850 EDT on 08/20/2010 and terminated at 1955 EDT on 08/20/2010. Chemically treated ERCW containing 55 ppm total residual chlorine reached the waters of the US which is above the 0.1 ppm allowed by the plant's National Pollutant Discharge Elimination System (NPDES) permit. There have been no observable adverse effects to the environment at this time. This occurrence does not affect safety related or other plant equipment. The licensee notified the NRC Resident Inspector. |
| ENS 45097 | 27 May 2009 22:12:00 | At approximately 1904 on 05/27/09, Sequoyah Unit 2 received an Automatic Reactor trip on Power Range High Neutron Rate Reactor Trip. The automatic trip occurred during severe weather and lightning onsite. ESF functions initiated as designed including Aux Feed Water auto-start and automatic Feedwater isolation. All control rods fully inserted. The plant is currently being maintained in Mode 3 at approximately 547 degrees F 2235 PSIG. Decay heat is being removed by the Auxiliary Feedwater system and Steam Dump valves. The cause of the Power Range Neutron Flux High Rate Reactor Trip is not known at this time and investigation is ongoing. Unit 1 remains at 100% power". No relief or safety valves lifted. The electrical lineup is normal and the 2B Diesel Generator is tagged out for maintenance. The licensee has contacted the NRC Resident Inspector. |
| ENS 44934 | 26 March 2009 08:29:00 | At approximately 0452 on 03/26/09, Sequoyah Unit 1 received an Automatic Reactor trip on Reactor Coolant Pump Busses Undervoltage. A loss of Common Service Station Transformer C caused a loss of power to the 1B and 1D Unit Boards. The 1B and 1D unit boards are the 6.9Kv electrical feeds to the 1-2 and 1-4 RCPs, respectively. RCPs 1-1 and 1-3 are running. ESF functions initiated as designed including Aux Feed Water auto-start, automatic Feedwater isolation, and auto-start of all four EDGs. The 1A Shutdown Board is being powered from the 1A EDG. The plant is currently being maintained in Mode 3 at approximately 547 degrees F /2235 PSIG. Decay heat is being removed by the auxiliary feedwater system and Steam Generator Atmospheric Relief valves. The cause of the loss of Common Service Station Transformer C is not known at this time and investigation is ongoing. All rods inserted as expected. No safety related equipment is out of service. Unit 1 has no known Steam Generator Tube leaks. The licensee notified the NRC Resident Inspector. |
| ENS 44935 | 26 March 2009 08:29:00 | At approximately 0452 on 03/26/09, Sequoyah Unit 2 received an Automatic Reactor trip on Reactor Coolant Pump Busses Undervoltage. A loss of Common Service Station Transformer C caused a loss of power to the 2B and 2D Unit Boards. The 2B and 2D unit boards are the 6.9Kv electrical feeds to the 2-2 and 2-4 RCPs, respectively. RCPs 2-1 and 2-3 are running. ESF functions initiated as designed including Aux Feed Water auto-start, automatic Feedwater isolation, and auto-start of all four EDGs. The 2A Shutdown Board is being powered from the 2A EDG. The plant is currently being maintained in Mode 3 at approximately 547 degrees F /2235 PSIG. Decay heat is being removed by the auxiliary feedwater system and Steam Generator Atmospheric Relief valves. The cause of the loss of Common Service Station Transformer C is not known at this time and investigation is ongoing. All rods inserted as expected. No safety related equipment is out of service. Unit 2 has no known Steam Generator Tube leaks. The licensee notified the NRC Resident Inspector. |