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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 55866 | 29 April 2022 03:55:00 | 10 CFR 50.72(a)(1)(i), Emergency Class Declaration | Notice of Unusual Event | The following is a summary of information provided by the licensee via telephone: On 04/28/22, at 2355 EDT, with both Sequoyah Unit 1 and 2 in Mode-1, 100 percent, a Notice of Unusual Event was declared due to receiving two seismic alarms and security feeling ground movement. Additionally, security in a tower heard an explosion. Both units remain in Mode-1, 100 percent and they are investigating the validity of the seismic alarms before proceeding with the Abnormal Operating Procedure required shutdown. The following additional information was obtained from the licensee in accordance with Headquarters Operations Officers Report Guidance: The licensee will notify the NRC Resident Inspector. The state of Tennessee and the Tennessee Valley Authority were notified. Notified DHS SWO, FEMA Operations Center, CISA Central, FEMA NWC (email), DHS NRCC THD Desk(email), and DHS Nuclear SSA (email).
The following is a summary of information provided by the licensee via telephone: On 4/29/22, at 0406 EDT, Sequoyah Unit 1 and Unit 2 terminated the Notice of Unusual Event. The Civil Engineers determined that the alarms were due to a failed seismic indicator channel. Through interviews, only one security officer felt ground movement for a couple of seconds and heard a faint rumbling sound. The following additional information was obtained from the licensee in accordance with Headquarters Operations Officers Report Guidance: The licensee will notify the NRC Resident Inspector. The state of Tennessee and the Tennessee Valley Authority were notified. Notified R2DO (Miller), NRR EO (Miller), and IR MOC (Gott) via email. Additionally, notified DHS SWO, FEMA Operations Center, CISA Central, FEMA NWC (email), DHS NRCC THD Desk(email), and DHS Nuclear SSA (email).
The following information was provided by the licensee via email: SQN (Sequoyah Nuclear Plant) is retracting the previous NOUE (Notice of Unusual Event) declaration made on 4/28/22 at 2355 (EDT) based on Emergency Action Level HU2 for a seismic event greater than Operating Basis Earthquake levels. Following the declaration of the NOUE, the station reviewed all available indications and determined that a seismic event had not occurred. The instrumentation failure was documented under Event Notification #55867. Notified R2DO (Miller), and IR MOC (Gott), NRR EO (Miller) via email. | ||
| ENS 53754 | 26 November 2018 05:00:00 | 10 CFR 50.72(b)(2)(xi), Notification to Government Agency or News Release 10 CFR 50.72(a)(1)(i), Emergency Class Declaration | Unusual Event Declared for Excessive Smoke in Containment | At 0816 EST, a Notification of Unusual Event was declared for Unit 2 under Emergency Action Level H.U.4 for excessive smoke in the lower level of containment with a heat signal. Onsite fire brigade is responding to the event. A command post is established. Offsite support is requested by the fire brigade. No flames have been observed as of this report. The NRC Resident Inspector and State and Local government agencies will be notified. Notified DHS SWO, FEMA Operations Center, DHS NICC, FEMA NWC (email), DHS Nuclear SSA (email), and FEMA NRCC SASC (email).
At 1036 EST, Sequoyah Nuclear Station Unit 2 terminated the Notice of Unusual Event. The licensee determined that the source of the smoke in containment was oil on the pressurizer beneath the insulation, that heated up during plant heatup. The licensee did not see visible flame during the event. The licensee is still working to determine if there was any damage to the pressurizer. The licensee will notify the NRC Resident Inspector. Notified R2DO (Rose), R2RA (Haney), NRR (Nieh), IRD MOC (Gott), DHS SWO, FEMA Operations Center, DHS NICC, FEMA NWC (email), DHS Nuclear SSA (email), and FEMA NRCC SASC (email).
Following declaration of the Notification of Unusual Event, TVA media relations communicated with the local media regarding the event. The licensee has notified the NRC Resident Inspector. Notified R2DO (Rose).
At 1036 EDT, Sequoyah Nuclear Plant (SQN) terminated the Notification Of Unusual Event (NOUE) due to initial report of heat and smoke in Unit 2 Lower Containment. At 1000 EDT, it was determined that no fire had occurred. Due to difficulty of access to some of the areas being searched, the source could not be identified prior to 1000 EDT. No visible flame (heat or light) was observed. The source of the smoke was determined to be residual oil from a hydraulic tool oil in contact with pressurizer piping. The pressurizer piping was being heated up to support Unit 2 start-up following U2R22 refueling outage. Once the residual oil dissipated, the smoke stopped. It has been concluded that no fire or emergency condition existed. Unit 2 is currently in Mode 5, maintaining reactor coolant temperature 160F-170F and pressure 325psig-350psig with 2A Residual Heat Removal (RHR) system in service in accordance with U2R22 refueling outage plan. The licensee has notified the NRC Resident Inspector. Notified R2DO (Rose).
Sequoyah Nuclear Plant (SQN) is retracting this notification based on the following additional information not available at the time of the notification: Following a full Reactor Building inspection, it was concluded that a fire did not exist. The source of the smoke originally reported was later determined to be residual oil from a hydraulic tool in contact with pressurizer piping. Once the residual oil dissipated, the smoke stopped. The source of heat originally reported was normal heated conditions associated with the pressurizer commensurate with plant conditions. SQN reported initially based on the available information at the time and to ensure timeliness with emergency declaration and reporting notification requirements. The licensee has notified the NRC Resident Inspector. Notified R2DO (Shaeffer). | Residual Heat Removal | |
| ENS 47660 | 12 February 2012 13:34:00 | 10 CFR 50.72(a)(1)(i), Emergency Class Declaration | Unusual Event Due to Electrical Fault in 161 Kv Switchyard | At 0756 (EST) on 2/12/12, an electrical event occurred in the 161 kV switchyard that resulted in bus differential relay operating, and opening all PCBs (Protective Circuit Breakers) within 161 kV bus 2-2. Shortly after, a call was received from site security regarding an explosion in the switchyard. At 0820, a report was received that visible damage was present on an insulator between a PCB and a Motor Operated Disconnect (MOD) in the 161 kV switchyard, which is where the fault occurred. Follow up reports indicated an oil leak from a current transformer. Two other PCBs were identified to have visible damage. After the event, while opening MODS for PCBs that tripped open, the 'A' phase for one MOD did not open. No safety related equipment required to establish or maintain safe shutdown was affected. All the Diesel Generators remain in operable standby conditions. Unit 1 remained steady at 100% with no transients. Unit 2 had a 2B Condenser Circ Water pump trip off. Crew responded to the pump trip and Unit 2 remains at 100%. One offsite power source is inoperable and second offsite power source has been verified operable. Grid status is Yellow. There were no personnel injuries reported due to the fault and resulting explosion. The loss of the offsite power source resulted in the licensee entering a 72-hr. LCO. The licensee is investigating both the cause of loss of offsite power and the circulating water pump trip. The licensee has notified the State of Tennessee and the NRC Resident Inspector.
At 1019 EST, the licensee terminated their Notification of Unusual Event. The basis for termination was that the fault was cleared and the conditions for EAL entry no longer exists. The licensee has made state and local notifications and has notified the NRC Resident Inspector. Notified R2DO (Calle), IRD (Kozal), NRR (Evans), DHS (Beach), FEMA (Fuller), and NICC (Berger) | ||
| ENS 46270 | 23 September 2010 01:54:00 | 10 CFR 50.72(a)(1)(i), Emergency Class Declaration | Notification of Unusual Event Due to a Transformer Fire | At 2132 (EDT) on 9/22/2010, (the licensee) received a breaker tripout associated with the intertie transformer. Switching was ongoing in the switchyard at the time. At 2135 (EDT), the MCR (Main Control Room) was notified that flames were present on the A intertie transformer. NOUE was declared at 2154 (EDT). The state of Tennessee was notified at 2200 (EDT). There have been no observable effects on other plant equipment or structures at this time. This occurrence does not affect safety related equipment. Flames were extinguished at 2154" (EDT). The intertie transformer converts power between the 500 kV and 161 kV power lines. The transformer spilled an unknown quantity of oil into the gravel sump surrounding the transformer. The fire was extinguished by the onsite fire brigade and no offsite assistance was required. The licensee notified the NRC Resident Inspector.
The licensee terminated the Unusual Event based on the fire being extinguished and no further action is needed. The licensee is in the process of tagging out the failed transformer. Notified the R2DO (Hopper), NRR EO (Lee), IRD (Marshall), DHS (Kettleson) and FEMA (O'Connell).
The licensee plans to issue a media / press release concerning this event. Notified the R2DO (Hopper). | ||
| ENS 40113 | 28 August 2003 20:04:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(a)(1)(i), Emergency Class Declaration 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Alert Declared Due to Reactor Protection System Failure | At 1618 EDT on 08/28/03, an Alert was declared at Sequoyah Unit 1 due to a failure of the Reactor Protection System (RPS) to auto-trip the reactor following a turbine trip. Turbine oil trip testing was in progress when at 1604, the main turbine tripped. The reactor trip breakers were opened by manual operator action approximately 20 seconds after the valid reactor trip signal. Following the trip, all systems operated as required. The main steam isolation valves were manually closed based on indication of steam flow and a throttled steam dump valve. No primary system or steam generator safety valves opened. The unit is currently stable with temperature controlled using atmospheric relief valves. The Auxiliary Feedwater System received an auto-start signal and successfully operated. All control rods were fully inserted into the core. There was no release of radioactive material. The licensee has initiated an investigation into the cause of the incident. The NRC Resident Inspector and the State of Tennessee were notified by the licensee. The NRC notified FEMA (Steiner), DOE (Morroni), USDA (Beers-Block), HHS (Williams), DHS (Glick), and DOT/EPA/NRC (Threatt). The NRC entered monitoring phase of normal mode with Region 2 in the lead at 1735 EDT.
At 2030 EDT on 08/28/03, the licensee terminated the Alert at Sequoyah Unit 1. The reactor is stable and in Mode 3, Hot Standby. This termination is based upon containment integrity, Emergency Core Cooling System and Engineered Safety Features operability, availability of heat sink, onsite and offsite electrical system and Emergency Diesel Generator operability, radiation monitor operability, availability of technical support personnel, and activation of a forced outage recovery team. Reactor coolant samples were taken, which showed no increase in activity. The NRC notified FEMA (Austin), DOE (Morroni), USDA (Beers-Block), HHS (Hogan), DHS (Van Buskirk), and DOT/EPA/NRC (White). The NRC exited monitoring phase of normal mode at 2045 EDT. | Steam Generator Reactor Protection System Emergency Diesel Generator Main Steam Isolation Valve Auxiliary Feedwater Main Turbine Control Rod |