Semantic search
| Entered date | Event description | |
|---|---|---|
| ENS 52187 | 17 August 2016 17:46:00 | At 1722 (EDT) on 8/17/16, a Past Operability Evaluation (POE) determined the configuration of the Emergency Gas Treatment System (EGTS) flow controllers that existed prior to 0420 on 8/6/16 constituted an Unanalyzed Condition due to not meeting single failure criteria. This POE examined the condition where EGTS may auto-swap from the flow control path in A-Auto to the Standby flow control path upon the start of a Design Basis Event (DBE). The intended design of the EGTS swap over flow control path in Auto to Standby was to detect and respond to an actual failure of the A-Auto flow control path. The unnecessary auto-swap to Standby could prevent the EGTS train configured in Auto from performing its required safety function during a DBE. The POE performed a detailed calculation to determine the release effects due to the failure of the redundant trains of EGTS controllers. These calculations concluded that failure of both trains of EGTS controllers would not result in exceeding the 10CFR100 limits, however this condition was unanalyzed and failed to meet single failure criteria. This condition is reportable under 10CFR50.72(b)(3)(ii)(B), Unanalyzed Condition due to a system required to meet the single failure criterion does not do so. This condition had no impact to the health and safety of the public. The NRC Resident Inspector has been notified. |
| ENS 51994 | 8 June 2016 17:10:00 | At 1526 Eastern Daylight Time on 6/8/2016, a determination was made involving the potential impact of a tornado on the Emergency Diesel Generators (EDGs). The EDGs are required to be operable to provide power to ensure that acceptable fuel design limits, reactor coolant system pressure boundary limits, and containment integrity are not exceeded during abnormal transients. Further, the EDGs are designed with a crankcase pressure trip (setpoint = 1 inch water), which is bypassed during an emergency start. Engineering has determined that a tornado could potentially cause actuation of the crankcase pressure trip due to a low barometric condition. If an emergency start signal has NOT previously occurred, then during a tornado, actuation of the crankcase pressure trip would energize the shutdown relay causing an EDG lockout condition. The EDG lockout condition prevents subsequent EDG starts (normal or emergency) until operators manually reset the lockout condition locally at the EDG. This condition could potentially affect all four EDGs simultaneously. The EDGs are operable but degraded. All EDGs have successfully passed their required surveillances within the appropriate frequency. No severe weather warnings or watches are forecast in the local areas, which could challenge the crankcase pressure trip. This condition places both units in an unanalyzed condition that potentially significantly degrades plant safety, 10 CFR 50.72 (b)(3)(ii)(B). A compensatory measure has been established, that upon notification of a Tornado Warning, the EDGs would be 'emergency started' and run during the time the Tornado Warning was in effect. This action bypasses the crankcase pressure trip function and allows the EDGs to perform their required safety function. The NRC Senior Resident Inspector has been notified. |
| ENS 51935 | 16 May 2016 21:17:00 | On May 16, 2016 at 2105, Sequoyah Nuclear Power Plant identified a nonconforming condition involving the Emergency Diesel Generator (EDG) fire dampers installed in Units 1 and 2. Specifically, it has been identified that if a tornado causes a differential pressure across the east and west sides of the EDG Building, this could create a high airflow rate through the EDG Building ventilation path. The fire dampers for each EDG bay (required to isolate the space for CO2 fire suppression per SQN Fire Protection Report) have not been analyzed to withstand high air flows resulting from a tornado and could possibly fail in a way that impedes airflow for EDG cooling. This is an unanalyzed condition that could prevent all EDGs from supplying electrical power as designed during a tornado or other similar weather events. All 4 EDGs are required to be operable by both units' Technical Specifications to provide electrical power to safe shutdown/safety related equipment following accident conditions coincident with a loss of offsite power. The Current Licensing Basis (CLB) requires that tornado effects be considered in the design of safety related SSCs (Systems, Structures, and Components), and it cannot be demonstrated at this time that the described SSCs will withstand the design basis tornado. It has been determined that the CLB may not adequately address possible design basis tornado scenarios. The EDGs are located inside the power plant structure and are currently capable of performing their safety function. The occurrence of such an event is highly unlikely and there is no imminent concern regarding severe weather involving tornadoes. Compensatory measures have been developed to address the associated nonconformance. The condition described above is being reported as an unanalyzed condition that significantly degrades plant safety per 10 CFR 50.72(b)(3)(ii)(B). The NRC Resident Inspector has been notified. |
| ENS 51900 | 3 May 2016 15:13:00 | At 0833 (EDT) on May 3, 2016, security received an alarm on a Main Control Room (MCR) door. At 0847 (EDT), security notified the MCR staff of the door alarm and that the door was incapable of closure. At this time, both control room ventilation filtration trains (CREVS) were declared inoperable in accordance with Technical Specification 3.7.10, Condition B, due to the inoperability of the Control Room Envelope (CRE). Attempts to close the door were made, and it was identified that a screw had become wedged at the base of the door preventing it from latching. At 0855 (EDT), the screw was removed and the door verified to close as designed. CREVS was determined to be operable and LCO 3.7.10, Condition B was exited. The safety function of the CRE boundary is to ensure the in-leakage of unfiltered air into the CRE will not exceed the in-leakage assumed in the licensing basis analysis of Design Basis Accident (DBA) consequences to CRE occupants. In addition to an intact CRE boundary maintaining CRE occupant dose from a large radioactive release below the calculated dose in the licensing basis consequence analysis for DBAs, it also ensures the occupants are protected from hazardous chemicals and smoke. This condition had no impact to the health and safety of the public. The NRC Resident Inspector has been notified. |