Semantic search
| Entered date | Event description | |
|---|---|---|
| ENS 53801 | 21 December 2018 00:02:00 | At 1642 Eastern Standard Time (EST) on December 20, 2018, it was determined that both trains of Containment Air Return Fan (CARF) were simultaneously INOPERABLE from 0817 (EST) to 1129 (EST) on November 20, 2018. This condition is not bounded by existing design and licensing documents; however, it poses no impact to the health and safety of the public or plant personnel. Therefore, this event is being reported as an eight-hour, non-emergency notification per 10 CFR 50.72(b)(3)(ii)(B). The NRC Resident Inspector has been notified. |
| ENS 53349 | 20 April 2018 00:55:00 | On April 19, 2018 at 1944 EDT, Watts Bar Nuclear Plant (WBN) determined that a preliminary analysis shows current acceptance criteria for gas accumulation in the WBN Unit 1 and Unit 2 Safety Injection System (SIS) and Residual Heat Removal System (RHRS) discharge piping may be non-conservative. The surveillances that check void values and allow venting of the systems are to be performed utilizing conservative criteria at more frequent intervals to ensure gas void volumes remain under acceptable limits. Additional analysis is being performed to determine final actions. The NRC Resident Inspector has been notified. |
| ENS 53291 | 26 March 2018 20:07:00 | At 1839 Eastern Daylight Time (EDT) on March 26, 2018, a Main Control Room (MCR) alarm was received for low control room positive pressure. At 1840 EDT, a Control Room Envelope (CRE) door was found ajar and immediately closed. Technical Specification 3.7.10, Control Room Emergency Ventilation System (CREVS), was declared not met for both trains and Condition B entered. At 1840 EDT on March 26, 2018, the alarm cleared, CREVS was declared operable and LCO (Limiting Condition for Operation) 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. From 1839 EDT to 1840 EDT, WBN (Watts Bar Nuclear) was unable to validate that CREVS could fulfill its required Safety Function. This event is being reported pursuant to 10 CFR 50.72(b)(3)(v)(D). A watch has been posted at the door to prevent recurrence. The NRC Resident Inspector has been notified. |
| ENS 52669 | 6 April 2017 22:40:00 | At 1620 EDT on April 6, 2017, a Main Control Room (MCR) door was found ajar. At that time, both control room ventilation filtrations 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). At 1623 EDT, the door was closed, CREVS was declared 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. Additionally, it ensures that the occupants are protected from hazardous chemicals and smoke. This event is being reported pursuant to 10 CFR 50.72(b)(3)(v)(D). NRC Resident Inspector has been notified.
Event Notification EN 52669, made on 4/06/2017, is being retracted because additional reviews have been performed supporting that a loss of safety function did not occur. Watts Bar Unit 2 has concluded that there was no loss of safety function, because when the door was found open it was capable of being closed and able to support the control room envelope function. A simulation performed on 04/07/17 also showed that with the door in question opened 1-2 inches that the control room pressure would have remained above the TS required positive pressure of 0.125 inches of water. The control room envelope is designed such that the door is expected to be opened to allow personnel entry and exit, and thus positive pressures in the control room will fluctuate. The event that occurred is similar to a number of individuals entering and exiting the control room in series. Since the control room envelope function was not lost, this event is not reportable and NRC Event Number 52669 is being retracted. The basis for this conclusion will be provided to the NRC Resident Inspector." The licensee informed the NRC Resident Inspector. Notified R2DO (Blamey). |
| ENS 52210 | 30 August 2016 21:49:00 | A fault occurred on the unit 2 "B" main bank transformer resulting in an oil fire. The main turbine tripped resulting in a reactor trip. All control rods fully inserted and no safety or relief valves lifted. Decay heat is being removed via steam dumps to the main condenser and feeding steam generators with auxiliary feedwater. Electrical power is through the normal shutdown electrical lineup. Offsite assistance was requested from the county and off duty fire brigade members. At 2228, the fire was reported as out. Spray is continuing and a reflash watch is being set. Unit 1 continued to operate at 100% power throughout the event. Notified the DHS SWO, FEMA Ops Center, DHS NICC, FEMA National Watch Center (E-mail) and Nuclear SSA (E-mail).
On August 30, 2016, at 2110 EDT, Watts Bar Nuclear Plant Unit 2 reactor tripped due to an electrical fault affecting the 2B Main Bank Transformer, resulting in a fire in the transformer. Concurrent with the reactor trip, the Auxiliary Feedwater system actuated as designed. All Control and Shutdown rods fully inserted. All safety systems responded as designed. The unit is currently stable in Mode 3, with decay heat removal via Auxiliary Feedwater and main steam dump systems. Unit 2 is in a normal shutdown electrical alignment. The fire was out at 2230 EDT. The cause of the fire is currently under investigation. The fire was reported at 2149 EDT. Local Fire Departments responded to the site as requested. The reactor trip and system actuation is being reported under 10CFR50.72(b)(3)(iv)(A) and 10CFR50.72 (b)(2)(iv)(B). There was no effect on WBN Unit 1. The NOUE was exited at 2342. The NRC Senior Resident Inspector has been notified. The Licensee notified the State of Tennessee. Notified the R2DO (Bartley), IRD MOC (Stapleton), NRR EO (Miller), DHS SWO, FEMA Ops Center, DHS NICC, FEMA National Watch Center (E-mail) and Nuclear SSA (E-mail). |
| ENS 49541 | 14 November 2013 20:35:00 | During analysis of Watts Bar Nuclear (WBN) Unit 2 fire protection features, it was revealed that a potential fire induced failure of centrifugal charging pumps could occur in Unit 1. Specifically, a potential fire induced failure of both Unit 1 Chemical and Volume Control System centrifugal charging pumps (CCPs) (1-PMP-62-108-A and 1-PMP-62-104-B) could occur due a fire in either auxiliary building room 737.0-A1 (general area for elevation 737.0) or 757.0-A2 (6.9 kV and Shutdown Board Room A). It is postulated that a fire in these rooms could cause a spurious closure of the CCP suction valve (1-LCV-62-133-B) from the volume control tank (VCT) (1-TANK-62-129) and could disable the control circuit which opens the flow from the refueling water storage tank (RWST) suction valve (1-LCV-62-135-A). The fire safe shutdown analysis (Fire Protection Report, Part VI) currently addresses this occurrence via the performance of a prompt main control room operator action to open the RWST suction path. However, this procedurally directed action may require several minutes to complete and due to the potentially short duration (possibly as short as a few seconds) for CCP survivability without suction flow, the action has now been determined to be unacceptable. As a result, the loss of charging flow could result in a loss of injection to the reactor coolant pump (RCP) seals which could subsequently lead to a RCP seal failure and a small break loss of coolant event. WBN engineering is continuing to validate whether the CCP minimum flow recirculation would protect the pumps with both suction paths (VCT and RWST) isolated and with the reactor at normal operating pressure. WBN has established compensatory measures to ensure that a fire in affected rooms will not cause a spurious closure of the CCP suctions valves. The licensee has notified the NRC Resident Inspector. |
| ENS 48056 | 29 June 2012 13:04:00 | On June 29, 2012, TVA issued an updated calculation titled 'PMF Determination for Tennessee River Watershed' The calculation resulted in an increase in the Watts Bar Nuclear (WBN) probable maximum flood (PMF) level from Elevation 734.9 to Elevation 739.2. All flood sensitive safety related systems, structures, and components have been reviewed and been determined to remain unaffected by the revised PMF surge elevation, with the exception of the Thermal Barrier Booster Pump Motors and Essential Raw Cooling Water (ERCW) equipment required for flood mode operation located on Elevation 722 of the Intake Pumping Station (IPS). The updated PMF of Elevation 739.2 could impact the ability of the thermal barrier booster pumps and the Elevation 722 IPS ERCW equipment to perform their design accident protection function. Because of the unanalyzed condition. the potential existed for WBN to exceed its PMF design basis and adversely affect plant safety. This notification is being made pursuant to 10 CFR 50.72(b)(3)(ii)(B). Compensatory measures have been prepared to install a temporary flood protection barrier around the thermal barrier booster pumps and provide additional protection of Elevation 722 of the IPS in the event of a flood alert. The potential for the increased PMF level and the associated compensatory measures were previously discussed in a public meeting between TVA and the NRC on May 31, 2012 and in correspondence between TVA and the NRC dated June 13, 2012 and June 25, 2012. All safety related equipment is currently operable. There are no indications of conditions that might result in a flood in the near term. The licensee notified the NRC Resident Inspector of this condition.
Based upon continuing engineering reviews, the chilled water circulating pump motors for the Train A and B Main Control Room and 6.9kV Shutdown Board Room, including various sub-components, would be partially submerged during a Probable Maximum Flood (PMF) event. These components were not previously considered as affected by the PMF. The affected components are located on floor elevation 737.0 of the auxiliary building. This notification is being made pursuant to 10 CFR 50.72(b)(3)(ii)(B). Compensatory measures have been prepared to install temporary flood protection barrier around the chilled water circulating pump motors and provide additional protection of Elevation 722 of the IPS in the event of a flood. All safety related equipment is currently operable. There are no indications of conditions that might result in a flood in the near term. The licensee notified the NRC Resident Inspector of this condition. Licensee Event Report 50-390/2012-002-00 will be supplemented to include a description of the potential PMF affects on the chilled water circulating pump motors. Notified the R2DO (Ernstes). |