Semantic search
| Entered date | Event description | |
|---|---|---|
| ENS 54242 | 27 August 2019 02:34:00 | At 0109 EDT, with Unit 1 in Mode 1 at 100 percent power, the reactor automatically tripped due to a dropped rod causing a negative rate trip. The trip was not complex, with all systems responding normally post-trip. Operations responded and stabilized the plant. Decay heat is being removed by the auxiliary feedwater (AFW) and steam dump systems. Unit 2 is not affected. Due to the reactor protection system actuation while critical, this event is being reported as a four-hour, non-emergency notification per 10 CFR 50.72(b)(2)(iv)(B) and in accordance with 10 CFR 50.72(b)(3)(iv)(A) as an event that results in a valid actuation of the AFW system. There was no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified. |
| ENS 52769 | 24 May 2017 04:10:00 | On May 23, 2017 at 2330, while transferring 2A-A 6.9 kV Shutdown Board from its alternate power source to its normal power source in support of outage testing, a failure occurred which resulted in the loss of the Shutdown Board, emergency start of all 4 Emergency Diesel Generators (EDGs), and required the manual emergency stop of 2A-A EDG. During transfer of the 2A-A 6.9kV Shutdown Board, the hand switch for the normal feeder breaker on the shutdown board was being maintained in the 'CLOSE' position while the alternate feeder breaker hand switch was placed in 'TRIP.' As expected, the alternate feeder breaker opened and the normal feeder breaker closed. However, the upstream supply breaker to the normal feeder breaker immediately tripped due to an overcurrent relay actuation on a single phase. As a result, the 2A-A 6.9 kV Shutdown Board deenergized, initiating a blackout signal which started all 4 of the station's EDGs. During board stripping (opening of all feeder and load breakers, to prepare the board for automatic reenergization from the EDG), the normal feeder breaker to the Shutdown Board failed to trip. This failure to trip prevented the emergency feeder breaker in the output of 2A-A EDG from closing, in accordance with interlock logic. As a result, 2A-A 6.9 kV Shutdown Board remained deenergized which prevented the cooling water supply valve for the EDG from opening due to loss of motive power. This lack of cooling caused operators to emergency stop the 2A-A EDG. Power was restored to the Shutdown Board on May 24, 2017 at 0037. Unit 1 is currently stable in Mode 1, at 100% power and Unit 2 is stable in Mode 5 with RCS at 164 F and 340 psig. The cause of the breaker trip on overcurrent and the failure of the normal feeder to trip on load shedding are under investigation. This event had no impact on the health and/or safety of the public. The NRC Resident Inspector has been notified. |
| ENS 49690 | 3 January 2014 22:07:00 | 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). |