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| Start date | Title | Description | Topic | |
|---|---|---|---|---|
| ENS 55866 | 29 April 2022 03:55:00 | 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. | Operating Basis Earthquake |
| ENS 55421 | 20 August 2021 13:05:00 | Auxiliary Building Gas Treatment Systems Inoperable | At 0905 EDT, it was discovered both trains of Auxiliary Building Gas Treatment System (ABGTS) were simultaneously INOPERABLE due to the auxiliary building secondary containment enclosure (ABSCE) being inoperable; therefore, this condition is being reported as an eight-hour, non-emergency notification per 10 CFR 50.72(b)(3)(v). There was no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified. ABSCE and ABGTS were returned to operable.
This is a retraction of the 8-hour Immediate notification (EN55421) made to the NRC by Sequoyah Nuclear Plant on August 20, 2021. Sequoyah is retracting this event notification based on the following: Regulatory Guidance in NUREG-1022, Revision 3, 'Event Reporting Guidelines 10 CFR 50.72 and 50.73', Sections 2.8 'Retraction and Cancellation of Event Reporting', and 4.2.3 'ENS Notification Retraction'. On August 20, 2021 personnel found door A-118 open. This door is part of the ABSCE. During the initial investigation, it was found that other personnel had the door open using Precaution A of 0-TI-SXX-000-016.0 which allows material access through ABSCE doors if the door is closed within three minutes. It was found that A-118 door had been open for greater than three minutes. With this door open the ABSCE was beyond its capability for ABGTS fan to maintain the required pressure during an Aux. Building Isolation. Thus, the site declared the ABSCE and both Trains of ABGTS inoperable per LCO 3.7.12 Conditions A, B and E. With the ABSCE being a single train system, this caused a condition that "could have prevented the fulfillment of the safety function" which requires an Immediate Notification to the NRC within eight hours under 10 CFR 50.72 (b)(3)(v)(C) and 10 CFR 50.72 (b)(3)(v)(D). This Immediate Notification was reported on August 20, 2021 at 1600 EDT. It was later determined that at 'Time of Discovery', although Door A-118 was open, it was not obstructed, the door was open by normal means, was capable of being closed and was now attended. The time requirement per 0-TI-SXX-000-016.0 for closure of an open ABSCE door is within three minutes of notification. Although the individual found holding the door was unaware of the requirement of 0-TI-SXX-000-016.0 to close the door, communications were established and the Main Control Room (MCR), upon discovery of the 'Open Door', could have directed closure starting at the Time of Discovery if required. Since the MCR was aware the door was open, had communications established with personnel at the door, the door was capable of closure and not restricted, the three minute closure requirement of 0-TI-SXX-000-016.0 was met. Subsequently, the door was closed within approximately two minutes of notification to close. The closure of the door with these procedural measures met confirmed the integrity of the ABSCE and therefore Operability of ABGTS. Based on the above critical thinking, entry into LCO 3.7.12 Condition A, B, and E was retracted on August 22, 2021 at 2044 EDT. With the LCO conditions retracted and the above determination that at the Time of Discovery safety function was maintained, the Immediate Notification per 10 CFR 50.72 (b)(3)(v)(C) and 10 CFR 50.72 (b)(3)(v)(D) was not required. The issue of Past Operability remains for instances in time that the door did not have appropriate compensatory measures in place. Any further notification required for this event will be submitted as a Licensee Event Report. Notified R2DO (Miller) | Time of Discovery Past operability |
| ENS 53754 | 26 November 2018 05:00:00 | 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). | |
| ENS 50244 | 1 July 2014 02:46:00 | Unanalyzed Condition That Could Have Resulted in an Increased Maximum Flood Level | On June 27, 2014, TVA identified in a reanalyzed hydrologic analysis for Sequoyah Nuclear Plant (SQN) a deviation from the current hydrologic analysis. The flooding analysis in Section 2.4.3 of the SQN UFSAR assumes that the Watts Bar West Saddle Dike fails completely and instantaneously at approximately 1.5 feet of overtopping during a Peak Maximum Flood (PMF). This assumption exists in the original design basis analysis and the revised analysis which supports SQN-TS-12-02, "Application to Revise Sequoyah Nuclear Plant Units 1 and 2 Updated Final Safety Analysis Report Regarding Changes to Hydrologic Analysis". The results of recent studies of the West Saddle Dike, conducted as part of the Fukushima Order 2.1 flooding review, indicate that the complete and instantaneous failure of the Watts Bar West Saddle Dike may not be a valid assumption. If the dike does not fail, analyses performed using the codes and methods consistent with those used in original plant design show that the east floodwall of the Watts Bar Dam would overtop. As a result of this overtopping, the east floodwall is assumed to fail. Based on this assumption and analysis, failure of the east floodwall of the Watts Bar Dam would result in an increase in the flood level at the SQN Plant Site. The current licensing basis PMF level for SQN is 719.6 feet as stated in Section 2.4.2.2 of the SQN UFSAR. In addition, it should be noted that by letter dated August 10, 2012, as supplemented by letters dated April 5, 2013 and January 16, 2014, TVA proposed a revised PMF level of 722.0 feet. Introducing non failure of the Watts Bar West Saddle Dike indicated a potential increase of approximately 1.5 feet over the revised PMF level. TVA performed additional analysis using current industry standard for flooding analysis. Specifically, TVA modeled the condition using the United States Army Corps of Engineers Hydrologic Engineering Center River Analysis System (HEC-RAS) tool. TVA's analysis of the condition using HEC-RAS determined that all required safety equipment for SQN would not be impacted and are considered operable based on a Prompt Determination of Operability completed on June 30, 2014. This report addresses a condition as described in 10 CFR 50.72 (b)(3)(ii)(B). TVA is making this report consistent with the guidance of NUREG-1022 regarding the application of engineering judgment to the evaluation of reportability of an unanalyzed condition. The NRC Resident Inspector has been notified of this condition.
On June 30, 2014, SQN reported (Event 50244) that during a re-analysis conducted as part of the Fukushima Order 2.1 flooding review, a probable maximum flood (PMF) design assumption that the Watts Bar Dam west saddle dike fails completely and instantaneously at approximately 1.5 feet of overtopping, was determined to be a non-conservative flood model assumption (i.e., invalid). As a result, TVA postulated that Watts Bar Dam's east floodwall would fail, increasing the site flood level at Sequoyah Nuclear Plant (SQN) by 1.5 feet; a condition that was beyond the current licensing basis. Through subsequent analysis, TVA has demonstrated that although the west saddle dike may not completely and instantaneously fail during a PMF (as previously assumed), the consequential increase in reservoir levels does not result in a failure of the Watts Bar Dam east floodwall and would not result in an increase in the flood level at SQN. Therefore, the previously reported 10 CFR 50.72(b)(3)(ii)(B) event is being retracted. The NRC Resident Inspector has been informed of this event retraction. Notified the R2DO (Hickey). | Unanalyzed Condition |
| ENS 49690 | 3 January 2014 20:00:00 | Abgts Potentially Inoperable for Both Units Under Worst-Case Conditions | At 1500 EST on 01/03/2014, TVA determined that during certain conditions, Service Air usage (air used for non-safety related tools/equipment) could result in introducing air into the Auxiliary Building Secondary Containment Enclosure that could, in worst-case conditions, exceed the margin required to maintain the Auxiliary Building Gas Treatment System (ABGTS) operable for Sequoyah Units 1 and 2. ABGTS is required to be operable for both units by Technical Specifications. This is an unanalyzed condition that could prevent both trains of ABGTS from performing (their) safety function(s). Service air has been isolated to the Auxiliary Building and is under administrative controls until further analysis (is) complete. This is additional information discovered during follow-up evaluation regarding the issue identified in LER 50-327/2013-004. Further analysis will be performed to determine safety significance. There is 1600 scfm margin in the ABSGTS. The Service Air compressors have an 1850 scfm capacity. The licensee informed the NRC Resident Inspector.
Sequoyah Nuclear Plant, Units 1 and 2, are retracting the 8 hour non-emergency notification January 3, 2014 at 2207 EST (EN# 49690). The notification on January 3, 2014, reported under certain conditions, service air usage could result in the Auxiliary Building Secondary Containment Enclosure (ABSCE), in worst case conditions, exceeding the margin required to maintain the Auxiliary Building Gas Treatment System (ABGTS) operable and prevent both trains of ABGTS from performing its safety function(s). Subsequent engineering analysis concluded acceptable margin was available. Both trains of ABGTS would have remained operable and capable of performing its design function(s) at all times. The engineering analysis results are captured in the licensee's corrective action program. Based on the new analysis, the condition reported in EN #49690 did not result in an unanalyzed condition that significantly degraded plant safety. This event report is being retracted. The NRC Resident Inspector has been briefed on the analysis results and informed of this retraction. Notified R2DO (McCoy). | Unanalyzed Condition |
| ENS 49476 | 27 October 2013 21:30:00 | Auxiliary Building Gas Treatment System Inoperable | At 1730 EDT on 10/27/2013, SQN (Sequoyah Nuclear) discovered that Unit 1 containment penetration X-108 had a maintenance flange installed with a service air connection attached. The service air connection was connected to a temporary air compressor supplying air to maintenance loads inside Unit 1 containment. Contrary to the requirements of the breaching permit, personnel were not stationed at the penetration to isolate the service air connection in the event of the air line rupturing inside Unit 1 containment or upon initiation of an auxiliary building isolation signal. Since the Unit 1 containment is open to the auxiliary building as part of outage activities, if the service air line had ruptured, the additional air into the Unit 1 containment could have exceeded the capacity of the Auxiliary Building Gas Treatment System (ABGTS) and potentially have impacted the ability of the ABGTS to perform its design safety function. This resulted in both trains of the ABGTS being declared inoperable requiring Unit 2 to enter the action of LCO 3.0.3. The service air line was isolated immediately and Unit 2 exited the action of LCO 3.0.3 at 1732 EDT. At the time of the event, Unit 1 was defueled and did not require ABGTS to be operable. Unit 1 subsequently entered Mode 6 at 1904 EDT on 10/27/2013 and is currently conducting refueling operations. Unit 2 remains in Mode 1, 100% power and stable. There were no actual operational impacts to either unit. The licensee has notified the NRC Resident Inspector.
Sequoyah Nuclear Plant, Units 1 and 2, are retracting the 8 hour non-emergency notification made on October 27, 2013 at 2229 EDT (EN# 49476). The notification on October 27, 2013, reported that if the service air line (associated with penetration X-108) had ruptured, the additional air into the Unit 1 containment could have exceeded the capacity of the Auxiliary Building Gas Treatment System (ABGTS) and potentially have impacted both trains of ABGTS from performing its safety function(s). Subsequent engineering analysis concluded acceptable margin was available. Both trains of ABGTS would have remained operable and capable of performing its design function(s) at all times. The engineering analysis results are captured in the licensee's corrective action program. Based on the new analysis, the condition reported in EN #49476 did not result in a potential uncontrolled radioactive release. This event report is being retracted. The NRC Resident Inspector has been briefed on the analysis results and informed of this retraction. Notified R2DO (McCoy). | |
| ENS 40305 | 10 November 2003 04:15:00 | Sequoyah Unit 2 Auxiliary Feedwater Actuation During Outage | On 11/9/03 at 2315 (EST), with Unit 2 in Mode 3 in preparation for a Refueling Outage, an unanticipated ESF actuation occurred. With one Main Feedwater Pump (MFP) reset and one MFP tripped per the General Operating Procedures, Main Condenser Vacuum was being broken. Low Condenser vacuum caused the trip of the reset MFP. The signal for trip of two MFPs caused an Aux Feedwater (AFW) start. AFW was in service in manual control per procedure when the start signal was received; however, the start signal caused the Level Control Valves (LCVs) to reposition to their accident position. The licensee notified the NRC Resident Inspector.
On November 9, 2003, after the planned Unit 2 reactor shutdown for refueling outage number 12, an auxiliary feedwater system start signal was initiated. During the shutdown, the auxiliary feedwater pumps (AFW) were started and both main feedwater pumps (MFP) had been tripped. Following transition from emergency operating procedure to the normal plant shutdown procedure, the feedwater isolation signal and one MFP trip were reset to allow shutdown of the turbine-driven pump, in accordance with plant procedures. As a result of the reactor coolant temperature decreasing below 540 degrees Fahrenheit, emergency boration was performed, and subsequently, control room personnel closed the main steam isolation valves (MSIVs) to limit cooldown of the RCS. After closure of the MSIVs, Operations personnel broke main condenser vacuum in accordance with plant procedures. The operators knew by their procedure that this would result in a low-condenser vacuum trip signal to the reset MFP trip bus and, with both MFPs trip bus tripped, the logic would be completed for initiation of an AFW start signal. The procedure states 'Breaking main condenser vacuum will cause loss of main feed pump turbine condenser vacuum to both MFPs resulting in an ESF actuation.' On November 10, 2003, at 0039 Eastern standard time, NRC was notified in accordance with 10 CFR 50.72 (b)(3)(iv)(A) of the ESF actuation (event notification No. 40305). 10 CFR 50.72 and 50.73 requires reporting of any event or condition that results in valid actuation of any of the systems listed in paragraph (b)(3)(iv)(B) except when the actuation results from and is part of a pre-planned sequence during testing or reactor operation. NUREG 1022 states that the intent is to require reporting of actuations of systems that mitigate the consequences of significant events. The breaking of the condenser vacuum was driven by plant conditions. However, the start signal to the AFW system was not to mitigate an event for the condition the plant was in (i.e., both MFPs had been secured and decay heat was being controlled by AFW in accordance with normal operating procedures) and is therefore considered a preplanned event. Based on the above information, the initiation of the AFW start signal is not reportable and the notification is being withdrawn. The licensee has notified the NRC Resident Inspector. Notified R2DO(Ayres) |