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| Discovered date | Reporting criterion | Title | Event description | |
|---|---|---|---|---|
| ENS 53398 | 11 May 2018 14:11:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | Containment Shield Building Inoperable | At 1011 EDT on May 11, 2018, Containment Shield Building Annulus differential pressure exceeded the required limit. The Shield Building was declared inoperable requiring entry into Technical Specification (TS) 3.6.15 Conditions A and B. The event was initiated by failure of the operating annulus vacuum fan. Main Control Room Operators manually started the stand-by annulus vacuum fan to recover pressure. Shield Building Annulus differential pressure was restored to the required value at 1016 EDT and TS 3.6.15 Condition A and B were exited on May 11, 2018 at 1016 EDT. The failure mechanism for the annulus vacuum fan is being investigated. The Containment Shield Building ensures the release of radioactive material from the containment atmosphere is restricted to those leakage paths and associated leakage rates assumed in the accident analysis during a Loss of Coolant Accident (LOCA). The Emergency Gas Treatment System (EGTS) would have automatically started and performed its design function to maintain the Shield Building Annulus differential pressure within required limits. The event is being reported pursuant to 10 CFR 50.72(b)(3)(v)(C) and 10 CFR 50.72(b)(3)(v)(D). The NRC Resident has been notified. |
| ENS 53173 | 18 January 2018 01:02:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Shield Building Inoperable | At 2002 EST on January 17, 2018, annulus differential pressure exceeded its pressure limit. At that time, the Shield Building was declared inoperable requiring entry into Technical Specification 3.6.15, Conditions A and B. Action was taken by field operators to swap annulus vacuum control dampers to restore annulus differential pressure. At 2024 EST, annulus differential pressure was restored to required limits, the Shield Building was declared operable, and LCO 3.6.15, Conditions A and B were exited. The temporary loss of the Shield Building resulted from a failure of the annulus vacuum control system to maintain the required differential pressure. Manual swap-over of pressure control to the backup damper restored differential pressure to required limits allowing exit from TS LCO 3.6.15 and restoration of the Shield Building safety function. The Shield Building ensures that the release of radioactive material from the containment atmosphere is restricted to those leakage paths and associated leakage rates assumed in the accident analysis during a Loss of Coolant Accident (LOCA). The Emergency Gas Treatment System (EGTS) would have automatically started and performed its design function to maintain annulus vacuum within required limits. This event is being reported pursuant to 10 CFR 50.72(b)(3)(v)(D). The NRC Resident Inspector has been notified. |
| ENS 52187 | 17 August 2016 21:22:00 | 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | Unanalyzed Condition Due to Not Meeting Single Failure Criteria | 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 51982 | 5 June 2016 16:27:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(b)(3)(iv)(A), System Actuation 10 CFR 50.72(b)(2)(iv)(A), System Actuation - ECCS Discharge | Reactor Trip and Eccs Actuation Caused by Turbine Governor Valve Failure | On June 5, 2016 at 1227 Eastern Daylight Time (EDT), Watts Bar Nuclear Plant (WBN) Unit 2 was in MODE 1 at approximately 12.5% power when a safety injection actuation occurred, followed by an automatic reactor protection system (RPS) trip. Preliminary data suggests that the #1 high pressure turbine governor valve failed open causing a steam header pressure rate of decrease safety injection (SI) actuation signal. As designed, the safety injection actuation caused both trains of the shared Emergency Gas Treatment System (EGTS) to align to Unit 2, requiring WBN Unit 1 to enter Technical Specification (TS) LCO 3.0.3 at 1227 (EDT). Also as designed, Unit 1 annulus pressure momentarily increased, causing operation personnel to enter LCO 3.6.15 Condition B at 1240 (EDT). At 1242 (EDT), after annulus pressure normalized, operations personnel exited LCO 3.6.15. At 1245 (EDT), Operations personnel secured safety injection and Unit 2 was stabilized in MODE 3 at normal operating pressure and temperature. By 1349 (EDT), Unit 1 Operations personnel had restored both trains of EGTS to standby readiness, and exited TS 3.0.3. No primary safety barriers (RCS, containment and fuel clad) were challenged and no primary or secondary safety or relief valves actuated during the event. The Unit 2 plant trip was uncomplicated and safety equipment operated as expected. Unit 2 is stable in Mode 3 at normal operating temperature and pressure, in normal shutdown power alignment. Unit 1 is stable in Mode 1 at 100% power. The Senior Resident Inspector has been notified of this event. The MSIVs are shut with the steam generators (SG) discharging steam using the atmospheric dump valves. There is no primary to secondary leakage. Motor driven AFW pumps are running to maintain SG levels. RCS pressure remained above ECCS (Emergency Core Cooling System) discharge pressure. |
| ENS 51795 | 17 March 2016 05:15:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | Loss of Emergency and Auxiliary Gas Treatment Systems | On March 17, 2016, at 0115 (EDT), Watts Bar Unit 1 (WBN1) entered Technical Specification Limiting Condition of Operation (TS LCO) 3.0.3 due to the inoperability of both trains of the Emergency Gas Treatment System (EGTS). TS LCO 3.7.12 Condition B was also entered at this time due to the inoperability of both trains of the Auxiliary Gas Treatment System (ABGTS). The train B EGTS and train B ABGTS had been removed from service for scheduled maintenance, when at 0115, the train A Auxiliary Air Compressor became inoperable. On March 17, 2016, at 0133, the train A Auxiliary Air Compressor was declared OPERABLE, and TS LCO 3.0.3 and 3.7.12 Condition B were exited. The auxiliary air system supports the EGTS by providing a safety grade air supply. When train A auxiliary air became inoperable, the supported train A EGTS and ABGTS became inoperable, creating a condition where both trains of EGTS and ABGTS were unavailable. In the event of an accident, the EGTS establishes a negative pressure in the annulus between the shield building and the steel containment vessel and the ABGTS establishes a negative pressure in the Auxiliary Building Secondary Containment Enclosure (ABSCE). Filters in these system mitigate the release of radioactive contaminants to the environment. WBN1 remained in Mode 1 at 100% power and no safety functions were required during the event. This event is reportable under 10 CFR 50.72(b)(3)(v)(C) and (D) as a condition that could have prevented the fulfillment of a safety function. The NRC Resident Inspector has been notified.
The purpose of this notification is to retract event report no. 51795 made on 3/17/16 at 0802 (EDT). Previously, Tennessee Valley Authority (TVA) reported a loss of the Emergency and Auxiliary Building Gas Treatment Systems (EGTS/ABGTS) at Watts Bar Nuclear Plant Unit 1 (WBN1). Both trains of EGTS and ABGTS were declared INOPERABLE when the train A auxiliary air system cooling water supply bypass valve was isolated, prior to completing the requisite post maintenance testing following repairs to the normal cooling water supply solenoid valve. Upon recognition, WBN1 operations personnel declared the train A auxiliary air system INOPERABLE, resulting in inoperability of Train A EGTS and ABGTS and forcing entry into TS LCO (Limiting Condition for Operation) 3.0.3 (from TS LCO 3.6.9 EGTS) and 3.7.12 Condition B for ABGTS. At the time the condition was recognized, train B EGTS and train B ABGTS were INOPERABLE for scheduled maintenance. Subsequently, TVA completed the post maintenance testing of the train A auxiliary air system ERCW (Emergency Raw Cooling Water) normal supply solenoid valve and determined that the valve, while not fully qualified at the time, was in fact operable and capable of performing its safety function. Therefore, entry into TS LCO 3.0.3 and 3.7.12 Condition B was not necessary and the event is no longer reportable under 10 CFR 50.72(b)(3)(v)(C) and (D) as a condition that could have prevented the fulfillment of a safety function. The NRC Resident Inspector has been notified. Notified the R2DO (McCoy). |
| ENS 51117 | 12 April 2015 17:20:00 | 10 CFR 50.73(a)(1), Submit an LER | 60-Day Optional Telephonic Notification for an Invalid Containment Isolation Activation. | This 60-day telephone notification is being submitted in accordance with 10 CFR 50.73(a)(1) and 10 CFR 50.73(a)(2)(iv)(A) to report an invalid actuation of the Train B Phase A Containment Isolation at Sequoyah Nuclear Plant. At 1320 EDT on April 12, 2015, during planned performance of the Containment Isolation Train-A, Phase A Isolation Testing and Emergency Gas Treatment System (EGTS) Cleanup System Test, the main control room received several Train-B annunciators. Upon investigation, it was determined that an invalid signal to the Train-B Solid State Protective System (SSPS) actuated the Train B, Phase A Containment Isolation. The invalid isolation signal was the result of a human performance error during the performance of the Phase A Isolation Test surveillance procedure. Operations personnel responded to the SSPS initiation, testing was aborted, ensured that all equipment operated as designed and restored affected systems in accordance with plant procedures. Approval to restart testing was obtained. All prerequisites were met and testing of the SSPS Train-A, Phase A Isolation was completed satisfactorily. As part of the prerequisite test alignment of the Train-A, Phase A, Unit 2 had entered a planned 7 day action for EGTS being inoperable. During the test when the Train-B of Phase A actuated, the suction dampers for Unit 1 supply to EGTS were closed per plant procedures. This prevented Train-B EGTS from aligning to Unit 1 and allowed Train-B of EGTS to remain operable for Unit 2. An SSPS Phase A signal can be generated automatically by a Safety Injection Signal (SIS) or manually. At the time of the event, plant conditions for an SIS did not exist; therefore, the Phase A actuation was invalid. The licensee notified the NRC Resident Inspector. |
| ENS 48995 | 3 May 2013 05:11:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | Temporary Loss of Both Trains of Emergency Gas Treatment System | On May 3, 2013, at 0111 (EDT), Technical Specification Limiting Condition of Operation (TS LCO) 3.0.3 was entered due to the loss of both trains of Emergency Gas Treatment System (EGTS). The Train B EGTS had been removed from service for scheduled maintenance and at 0111 the Train A auxiliary air dryer stopped functioning. On May 3, 2013, at 0155, Train B EGTS was restored to service and declared Operable, and TS LCO 3.0.3 was exited. The auxiliary air system is required to support multiple safety related systems. The auxiliary air system is the safety grade air supply for EGTS. As Train A auxiliary air was no longer Operable, and the B train EGTS system was inoperable, the safety function supported by EGTS was not available. The EGTS establishes a negative pressure in the annulus between the shield building and the steel containment vessel. Filters in the system then control the release of radioactive contaminants to the environment. Watts Bar Unit 1 remained in Mode 1 at 100% power. No reactivity was added to the plant. This event is reportable under 10 CFR 50.72(b)(3)(v)(C) and (D) as a condition that could have prevented the fulfillment of a safety function. The NRC Resident Inspector has been notified. |