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| Entered date | Event description | |
|---|---|---|
| ENS 49476 | 27 October 2013 22:29:00 | 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 48778 | 24 February 2013 15:20:00 | On February 24, 2013 at 1205 (EST) with reactor power at 25% and the turbine offline, a manual reactor trip for Sequoyah Unit 2 was initiated due to loss of condenser vacuum indication causing closure of condenser steam dumps, opening of the Steam Generator Atmospheric Relief Valves, and lowering hotwell level resulting in imminent loss of hotwell pumps. The cause of the event was determined to be a faulty test connection on B Condenser vacuum pressure switch. During the event, steam pressure rose to the setpoint for the first Steam Generator code safety valve (1064 psig). (The safety valve opened, then reseated). Following the reactor trip, all safety related equipment operated as designed. Auxiliary feedwater actuated as expected on loss of the operating main feedwater pumps. The reactor trip was uncomplicated. Unit 2 is currently being maintained in Mode 3 at NOP/NOT (Normal Pressure and Temperature), with auxiliary feedwater supplying the steam generators and maintaining level at approximately 33% narrow range. Method of decay heat removal is via atmospheric reliefs to the atmosphere. Current RCS conditions: temperature (is) 547 degrees F and stable. Pressure (is) 2235 psig and stable. (There is) no indication of any primary/secondary leakage. All rods are inserted. Electrical alignment is normal and supplied from offsite power. (There is) no impact to Unit 1. Unit 1 is operating at 100% power / Mode 1. There was no impact on public health and safety. Post-trip investigation is in progress and planned restart is 02/25/2013. (The licensee plans a press release.) The licensee notified the NRC Resident Inspector. |