Semantic search
| Start date | Title | Description | Topic | |
|---|---|---|---|---|
| ENS 56970 | 16 February 2024 03:24:00 | Actuation of Emergency Diesel Generator System | The following information was provided by the licensee via email: At 2224 EST on February 15, 2024, with both units 1 and 2 in mode 1 at 100 percent power, an actuation of the emergency diesel generator (EDG) system on 1A-A, 1B-B, and 2B-B EDGs occurred while removing clearances. The 2A-A EDG did not start because it was still under a clearance. The reason for the emergency diesel generator system auto-start was clearance removal sequencing errors. The emergency diesel generator system automatically started as designed when the common emergency start signal was received. This event is being reported in accordance with 10 CFR 50.72(b)(3)(iv)(A) as an event that results in a valid actuation of the emergency diesel generator system. There was no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified.
The following information was provided by the licensee via email: In accordance with NUREG-1022, Section 2.8 and Section 4.2.3, Watts Barr is retracting the previous report EN 56970 pursuant to 10 CFR 50.72(b)(3)(iv)(A). The start signal for the 1A-A, 1B-B, and 2B-B emergency diesel generators (EDG)s was from activation of the common emergency start of the 2A-A EDG. The actuation was not from a loss of offsite power (LOOP) to any shutdown board or from any parameters that would initiate a safety injection (SI) signal, for which the EDG is designed to provide a design basis safety function. Also, the starts were not from intentional manual actuation. Starting the EDGs did not make them inoperable and each EDG was able to perform its design safety function. The common emergency start relay for each diesel is not safety related. It is an anticipatory and redundant circuit to start other EDGs in the event of a LOOP or SI related to the specific EDG. With the 2A-A EDG out of service, the associated common emergency circuit would not be required to perform any function. The starts were not initiated in response to actual plant conditions or parameters satisfying the requirements for initiation of the system. Since the starts were not initiated via an automatic signal from a LOOP, SI, or traditional operator action, the signal is not a valid actuation in accordance with 10 CFR 50.72(b)(3)(iv)(A). Therefore, EN 56970 is being retracted. The NRC Resident Inspector has been notified of this retraction. Notified R2DO (Miller) | |
| ENS 56809 | 21 October 2023 13:07:00 | Notification of Unusual Event Declared | The following information was provided by the licensee via fax and email: Fire potentially degrading the level of safety of the plant. The following additional information was obtained from the licensee in accordance with Headquarters Operations Officers Report Guidance: At 0907 EST, the licensee declared a notification of unusual event, under emergency action level HU.4, due to multiple fire alarms and CO2 discharge in the emergency diesel building. When the plant fire brigade entered the building, there was no indication of fire or damage to any plant equipment. The cause of the multiple alarms is under investigation. State and local authorities were notified and no offsite assistance was requested. Both units remain at 100 percent power. The NRC Resident Inspector has been notified. Notified DHS SWO, FEMA Operations Center, CISA Central, FEMA NWC (email), CWMD Watch Desk (email), DHS NRCC THD Desk (email), and DHS Nuclear SSA (email).
At 1007 EDT, Watts Bar terminated the notification of unusual event. The basis for termination was that no fire or damaged plant equipment was found. The NRC Resident Inspector has been notified. Notified R2DO (Miller), IR-MOC (Crouch), NRR-EO (Felts), DHS-SWO, FEMA Ops Center, CISA Central, FEMA NWC (email), CWMD Watch Desk (email), DHS NRCC THD Desk (email), and DHS Nuclear SSA (email).
Watts Bar Nuclear Plant (WBN) is retracting Event Notice 56809, Notice of Unusual Event, based on the following additional information, not available at the time of the initial notification. Specifically, in accordance with the emergency preparedness implementing procedures, WBN reported a condition that was determined to meet emergency action level (EAL) HU4, Initiating criteria number 1, receipt of multiple (more than 1) fire alarms or indicators and the fire was within any Table H2 plant area, which includes the diesel generator building. It was further determined that multiple fire detection zones actuated (spurious and invalid) enabling the discharge of installed fire suppression (CO2) into the space. Upon entry by the site fire brigade, it was determined that no smoke or fire existed and reported to the Shift Manager at 0930 EDT. All fire alarms were reset. Troubleshooting activities are in progress to determine the cause. A fire watch has been established and CO2 has been isolated. The required compensatory measures for the affected areas will remain in place until completion of the investigation, and CO2 suppression is restored to functional. Notified R2DO (Miller), IR-MOC (Crouch), NRR-EO (Felts), DHS-SWO (email), FEMA Ops Center (email), CISA Central (email), FEMA NWC (email), CWMD Watch Desk (email), DHS NRCC THD Desk (email), and DHS Nuclear SSA (email). | Fire Watch |
| ENS 54531 | 19 February 2020 14:57:00 | EN Revision Imported Date : 2/21/2020 NOTIFICATION OF UNUSUAL EVENT DUE TO FIRE IN CONTROL BUILDING At 0957 EST on February 19, 2020, a Notification of Unusual Event (NOUE) has been determined to be present at the Watts Bar plant Unit 1 under criteria HU4 for a fire potentially degrading the safety of the plant (fire for more than 15 minutes). The NRC Senior Resident Inspector has been notified for this event. Notified DHS SWO, FEMA Operations Center, CISA IOCC, FEMA NWC (email), DHS Nuclear SSA (email), and FEMA NRCC SASC (email).
The fire was declared extinguished at 1033 EST. The NOUE was terminated at 1126 EST. The investigation into the cause of the fire is in progress. Notified R2DO (Musser), NRR EO (Miller), and IRD MOC (Kennedy). Additionally, notified DHS SWO, FEMA Operations Center, CISA IOCC, FEMA NWC (email), DHS Nuclear SSA (email), and FEMA NRCC SASC (email).
Watts Bar Nuclear Plant (WBN) is retracting Event Notice 54531 (NOUE notification) based on the following additional information. WBN reported a condition that was determined to meet the definition of a FIRE in the plant Emergency Preparedness Implementing Procedures (EPIP) based on indications available to the decision-maker at the time the declaration was made. A fire, without observation of flame, is considered present if large quantities of smoke and heat are observed. Moderate quantities of smoke were observed coming from an electrical cabinet not required to support safe plant operation. Once Fire Brigade personnel were able to access the affected room, no evidence of flame or significant heat was observed. Plant personnel ultimately determined that an overheated electrical component (transformer) resulted in the smoke. As such, the actual conditions did not meet the EPIP definition of a fire. The NRC Resident Inspector has been notified of this retraction. Notified R2DO (Musser), NRR EO (Miller), and IRD MOC (Kennedy). | ||
| ENS 53356 | 22 April 2018 06:22:00 | Both Trains of Residual Heat Removal Inoperable | On April 22, 2018 at 0222 EDT, Watts Bar Nuclear Plant (WBN) Unit 2 entered TS (Technical Specifications) LCO (Limiting Condition for Operation) 3.0.3 due to both trains of the Residual Heat Removal System (RHRS) becoming inoperable. During surveillance testing, the gas void values on Emergency Core Cooling System (ECCS) piping common to both trains did not meet acceptance criteria. This caused both RHRS trains to become inoperable. Operations subsequently vented the RHRS to meet the acceptance criteria and exited TS LCO 3.0.3 at 0227 EDT. More frequent surveillances will be conducted to monitor gas void volumes while additional analysis is being performed to determine corrective actions. The NRC Resident Inspector has been notified.
This event is being retracted. The initial report was based on a conservative acceptance criteria for gas accumulation adopted on April 19, 2018 when it was determined that the previously used acceptance criteria for gas accumulation in the ECCS was non-conservative. Additional analysis has subsequently been performed and determined that a higher gas accumulation acceptance criteria does not challenge operability. With a void of less than the acceptance criteria, in the event of ECCS actuation, the system piping support loads will remain within structural limits and the piping system will remain operable. Therefore, both trains of Unit 2 RHRS were operable and the previously reported 10 CFR 50.72(b)(3)(v)(B) event is being retracted. The NRC Resident Inspector staff has been informed of this event retraction. Notified R2DO (Desai) of this retraction. | |
| ENS 53355 | 22 April 2018 01:52:00 | Both Trains of Residual Heat Removal Inoperable | On April 21, 2018 at 2152 EDT, Watts Bar Nuclear Plant (WBN) Unit 1 entered TS (Technical Specifications) LCO (Limiting Condition for Operation) 3.0.3 due to both trains of the Residual Heat Removal System (RHRS) becoming inoperable. During surveillance testing, the gas void values on Emergency Core Cooling System (ECCS) piping common to both trains did not meet acceptance criteria. This caused both RHRS trains to become inoperable. Operations subsequently vented the RHRS to meet the acceptance criteria and exited TS LCO 3.0.3 at 2222 EDT. More frequent surveillances will be conducted to monitor gas void volumes while additional analysis is being performed to determine corrective actions. The NRC Resident Inspector has been notified.
This event is being retracted. The initial report was based on a conservative acceptance criteria for gas accumulation adopted on April 19, 2018 when it was determined that the previously used acceptance criteria for gas accumulation in the ECCS was non-conservative. Additional analysis has subsequently been performed and determined that a higher gas accumulation acceptance criteria does not challenge operability. With a void of less than the acceptance criteria, in the event of ECCS actuation, the system piping support loads will remain within structural limits and the piping system will remain operable. Therefore, both trains of Unit 1 RHRS were operable and the previously reported 10 CFR 50.72(b)(3)(v)(B) event is being retracted. The NRC Resident Inspector has been informed of this event retraction. Notified R2DO (Ehrhardt). | |
| ENS 53196 | 4 February 2018 09:45:00 | Failure of Containment Penetration Thermal Relief Check Valves to Meet Surveillance Acceptance Criteria | At 0445 (EST) on February 4, 2018, Watts Bar Unit 1 entered Technical Specification 3.6.1 condition A and 3.6.3 condition A.1 and A.2 due to inoperable containment penetration thermal relief check valves 1-CKV-31-3407 and 1-CKV-31-3421 associated with one train of the Containment Incore Instrument Room Chiller system. During surveillance testing, the thermal relief check valves failed to open and pass flow as required by acceptance criteria. The two penetrations were subsequently drained and isolated in accordance with the surveillance procedure to remove any thermal expansion concerns. Technical Specification 3.6.1 was exited February 4, 2018 at 0512 once the two penetrations were drained and isolated. The purpose of the thermal relief check valves is to allow flow from an isolated penetration back into the upstream containment piping to prevent over-pressurization due to thermal expansion. Over-pressurization of an isolated containment penetration could potentially cause the penetration or both of the isolation valves to fail and provide a direct flow path to the environment from the potentially contaminated containment atmosphere under certain Design Basis Accidents. Therefore, failure of the thermal relief check valves to open could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material. This event is being reported pursuant to 10 CFR 50.72(b)(3)(v)(C). NRC Resident Inspector has been notified.
The purpose of this notification is to retract ENS notification 53196 made on 2/4/2018 for Watts Bar Nuclear Plant. The previous notification reported a surveillance failure of two containment penetration thermal relief check valves that, at the time of discovery, could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material. After Engineering evaluation, it has been determined there is reasonable assurance the two thermal relief check valves (1-CKV-31-3407 and 1-CKV-31-3421) were capable of performing their specified safety function to isolate containment and act as a thermal relief device during a design basis accident. The basis of the evaluation included: 1. No maintenance activities or interactions with the check valves had occurred since last tested. 2. All surveillance testing for the valves was within required frequency. 3. The opening force for a new check valve of the same size and similar to 1-CKV-31-3407 and 1-CKV-31-3421 is 0.38 pounds. Engineering analysis has determined the minimum failure pressure of the piping systems associated with the containment penetration in question is 450 psig. If it is assumed the force applied on the check valve seat reaches 450 psig, the force applied on the seat would reach 111 pounds or 300 times the force required to open a new, clean check valve. Based on engineering judgement of previous operating experience where the pressure required to open the same stuck check valve was within a safety factor of 6 to potential equipment damage, the thermal relief check valves would have opened prior to equipment damage and thus the identified condition would not have resulted in adversely affecting the containment isolation boundary. Entry into Technical Specification (TS) 3.6.1 condition A on 2/4/2018 at 0445 has been retracted. Although not a loss of safety function, the containment penetrations associated with 1-CKV-31-3407 and 1-CKV-31-3421 remain inoperable and are being tracked by TS 3.6.3 condition A.1 and A.2. The NRC Resident Inspector has been notified. Notified the R2DO (Rose). | Time of Discovery |
| ENS 52669 | 6 April 2017 20:20:00 | Temporary Loss of Control Room Envelope Boundary | 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 51795 | 17 March 2016 05:15:00 | 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 50245 | 1 July 2014 02:46:00 | Unanalyzed Condition That Could Have Resulted in an Increased Maximum Flood Level | On June 27, 2014, TVA identified in a reanalyzed hydrologic analysis for Watts Bar Nuclear Plant (WBN) a deviation from the current hydrologic analysis. The flooding analysis in Section 2.4.3 of the WBN UFSAR assumes that the Watts Bar West Saddle Dike fails completely and instantaneously at approximately 1.5 feet of overtopping during a Peak Maximum Flood (PMF). This assumption exists in the original design basis analysis and the revised analysis which supports WBN-UFSAR-12-01 (Application to Revise Watts Bar Nuclear Plant Unit 1 Updated Final Safety Analysis Report Regarding Changes to Hydrologic Analysis). The results of recent studies of the West Saddle Dike, conducted as part of the Fukushima Order 2.1 flooding review, indicate that the complete and instantaneous failure of the Watts Bar West Saddle Dike may not be a valid assumption. If the dike does not fail, analyses performed using the codes and methods consistent with those used in original plant design show that the east floodwall of the Watts Bar Dam would overtop. As a result of this overtopping, the east floodwall is assumed to fail. Based on this assumption and analysis, failure of the east floodwall of the Watts Bar Dam would result in an increase in the flood level at the WBN Plant Site. The current licensing basis PMF level for WBN is 734.9 feet as stated in Section 2.4.3.5 of the WBN UFSAR. In addition, it should be noted that by letter dated July 19, 2012, TVA proposed a revised PMF level of 739.2 feet. Introducing non failure of the Watts Bar West Saddle Dike indicated a potential increase of approximately 1.7 feet over the revised PMF level. TVA performed additional analysis using current industry standard for flooding analysis. Specifically, TVA modeled the condition using the United States Army Corps of Engineers Hydrologic Engineering Center River Analysis System (HEC-RAS) tool. TVA's analysis of the condition using HEC-RAS determined that all required safety equipment for WBN would not be impacted and are considered operable based on a Prompt Determination of Operability completed on June 30, 2014. This report addresses a condition as described in 10 CFR 50.72 (b)(3)(ii)(B). TVA is making this report consistent with the guidance of NUREG-1022 regarding the application of engineering judgment to the evaluation of reportability of an unanalyzed condition. The NRC Resident Inspector has been notified of this condition.
On June 30, 2014, TVA reported (Event 50245) that during a re-analysis conducted as part of the Fukushima Order 2.1 flooding review, a probable maximum flood (PMF) design assumption that the Watts Bar Dam west saddle dike fails completely and instantaneously at approximately 1.5 feet of overtopping, was determined to be a non-conservative flood model assumption (i.e., invalid). As a result, TVA postulated that Watts Bar Dam's east floodwall would fail, increasing the site flood level at Watts Bar Nuclear Plant (WBN) by 1.7 feet; a condition that was beyond the current licensing basis. Through subsequent analysis, TVA has demonstrated that although the west saddle dike may not completely and instantaneously fail during a PMF (as previously assumed), the consequential increase in reservoir levels does not result in a failure of the Watts Bar Dam east floodwall and would not result in an increase in the flood level at WBN. Therefore, the previously reported 10 CFR 50.72(b)(3)(ii)(B) event is being retracted. The NRC resident Inspector has been informed of this event retraction. Notified the R2DO (Hickey). | Unanalyzed Condition |
| ENS 49389 | 27 September 2013 16:45:00 | Calculation Error Resulted in Unanalyzed Condition for Appendix R Event | On July 18, 2012, TVA identified that a calculation error resulted in the inability to establish Essential Raw Cooling Water (ERCW) supply to the Component Cooling System (CCS) heat exchanger within the required time to ensure cooling is available to Reactor Coolant System (RCS) seal injection water during an Appendix R event. TVA promptly established fire watches as a compensatory measure to prevent initiation of fires in the areas of concern. Subsequently, abnormal operating instructions were revised to take action to ensure that adequate time is available to establish ERCW cooling to CCS, and ensure cooling to (Reactor Coolant Pump) RCP seal injection water. The calculation error was identified on July 18, 2012, however, it was not recognized at the time that an unanalyzed condition existed that was reportable under 10 CFR 50.72(b)(3)(ii)(B). This report documents that the condition that existed until fire watches were established is reportable under 10 CFR 50.72(b)(3)(ii)(B). The NRC Resident Inspector has been notified of this condition.
Watts Bar Nuclear Plant Unit 1 is retracting this 8 hour non-emergency notification made on September 27, 2013, at 1335 EDT (EN #49389). The notification on September 27, 2013, reported a calculation error which resulted in the inability to establish Essential Raw Cooling Water (ERCW) to supply the Component Cooing System (CCS) heat exchanger within the required time to ensure cooling is available to Reactor Coolant System (RCS) seal injection water during an Appendix R event. Subsequent analysis of actual plant data concluded that TVA could have established cooling to RCS seal injection during the subject Appendix R event, and achieved and maintained fire safe shutdown. Therefore, this event was not reportable under 10 CFR 50.72(b)(3)(ii)(B). The NRC Resident Inspector has been notified. R2DO (Bartley) notified. | Safe Shutdown Unanalyzed Condition |
| ENS 45827 | 8 April 2010 04:00:00 | Diesel Generators Wired Incorrectly | Action F of LCO 3.8.1, 'AC Sources - Operating,' was entered at 20:57 EDT April 7, 2010 for the 2A-A and the 2B-B diesel generators (DGs) being inoperable. Action F has a two hour allowed outage time (AOT). The DGs were determined to be inoperable due to incorrectly implemented wiring changes made by personnel performing construction work on Watts Bar Unit 2. The impact of the change is that during (an) actual or simulated ESF actuation signal, if the diesel is in test mode, and the output breaker is closed in parallel with the board supply breakers, the DG would not return to a 'ready to load' state meaning the output breaker would not have opened as designed for this condition. This function is tested as required on an 18 month frequency as a part of Surveillance Requirement (SR) 3.8.1.17. The wiring changes which affected the DGs were made in accordance with Unit 2 Work Order (WO) 09-954447 and 09-954448. The WOs as developed would not have an impact on Unit 1 operations. A review of the Unit 1 Operator Logs from January 1, 2010 to present, did not find any entries establishing the Unit 2 work had been authorized by Unit 1. The proper technical specification entry would have been Action 8 of LCO 3.8.1 for this activity. Entry into Action B of LCO 3.8.1 requires the implementation of several actions including a verification of the operability of the offsite circuits. Since these Technical Specification required actions were not complied with, WBN is providing this 24-hour notification in accordance with Section 2.G of the Watts Bar Unit 1 Facility Operating License. During the review of work performed by Unit 2 it was identified that the wiring was initially lifted on January 6. 2010. At the time of this report, actions have been taken to restore the wiring to its appropriate configuration on both of the DG circuits. 2B-B DG wiring was restored at 22:18 on April 7, 2010 and the 2B-B DG was declared operable. Action F of LCO 3.8.1 was exited at this time and Action B was entered for the 2A-A DG (14 day AOT). 2A-A DG circuitry was restored at 00:37 on April 8, 2010, and all LCO actions were exited. This event has been entered into TVA's corrective action program and actions are being initiated to establish the reason the leads were incorrectly lifted and to verify that no other similar wiring issues exist. The licensee notified the NRC Resident Inspector. * * * RETRACTION FROM WES DANIEL TO PETE SNYDER AT 1646 ON 5/10/10 * * * The Watts Bar Nuclear Plant (WBN) Unit 2 diesel generators (DGs) were not inoperable. The Unit 2 DGs were initially declared inoperable because of an inappropriate wiring change that disabled a DG output breaker trip in the event of an actual or simulated ESF actuation signal while the DG is in test mode and the output breaker is closed in parallel with the board supply breakers. Because Surveillance Requirement (SR) 3-8.1.17 required verification of this function for the Unit 1 DGs, and TVA was uncertain of the impact of the loss of this function to the Unit 2 DGs, TVA conservatively declared the Unit 2 DGs inoperable because they would not be able to meet this SR. Upon review TVA determined that it was proper to exclude this surveillance requirement for the Unit 2 DGs. Since SR 3.8.1.17 only applies to Unit 1 DGs, inability of Unit 2 DGs to meet this requirement is not a basis for inoperability. TVA has concluded that the Unit 2 DGs and offsite power sources were operable, and WBN was in compliance with its Technical Specifications throughout the period that the wiring change was installed. Therefore, this event was not reportable under WBN License (NPF-90) Condition 2.G, 10 CFR 50.72, or 10 CFR 50.73. The licensee notified the NRC Resident Inspector. Notified R2DO (O'Donohue). | Offsite Circuit |
| ENS 45331 | 8 September 2009 01:20:00 | Discovery of After-The-Fact Emergency Condition Unusual Event | This report documents a condition in which WBN (Watts Bar Nuclear) Unit 1 met the criteria to declare a NOUE (Notification of Unusual Event) based on RCS (Reactor Coolant System) unidentified leakage. Prior to declaration, the event was terminated thus no declaration was made. This event is reportable within one hour as an acceptable alternative to reporting in accordance with 10CFR50.72(a)(1)(i) - declaration of any of the emergency classes specified in the licensees approved emergency plan. During tagout installation in support of planned maintenance on the cation bed flush valve (1-FLV-62-921) in the CVCS/Letdown system, isolation boundary valve leakage of approximately 80 gpm was present for approximately three minutes. The leakage was terminated by reclosing opened vent (1-VTV-62-917) and drain valves (1-DRV-62-920). Cation Bed Inlet (l-ISV-62-915) and Outlet (1-ISV-62-916) and all other boundary valve isolations were verified to be in the correct, closed position per the tagout instructions. This RCS leakage was directed to the Tritiated Drain Collector Tank, thus all leakage was contained within plant systems and no radiological releases resulted. A work order will be initiated to troubleshoot and repair the faulty isolation valve. This amount of leakage is in excess of the amount specified in WBN Emergency Plans for declaration of an NOUE based on >10 gpm unidentified leakage per EAL 2.5. Prior to declaration, the event was terminated, thus no declaration was made. The State of Tennessee and the NRC Resident Inspector has been notified.
Event Notice 45331 reported a condition in which WBN Unit 1 conservatively determined it met the criteria to declare a NOUE based on RCS unidentified leakage. Prior to declaration, the event was terminated thus no declaration was made. Based upon further review and discussion with others in the industry, the NOUE criterion cited, EAL 2.5, applies to specific sources of excessive RCS leakage. The source of the leakage discussed in the event has been confirmed as CVCS leakage, not RCS leakage. An action to clarify the basis and scope of this EAL is being pursued within TVA's Corrective Action Program. Therefore, Event Notice 45331 is being retracted. The NRC resident has been notified. Notified the R2DO (Blamey). | |
| ENS 43894 | 11 January 2008 20:10:00 | Discovery of an After the Fact Unusual Event | At 1510, "(Watts Bar Nuclear (WBN)) had identified RCS leakage in excess of 25 gallons per minute (gpm). The leakage was estimated at 105 gpm. This is a report notification only and not a declaration. The EAL that was exceeded was 2.6, RCS identified leakage. While placing a mixed bed demineralizer in service VCT level was observed to have dropped 10%. The demineralizer was immediately removed from service. This terminated the drop in VCT level. In accordance with WBN EPIP-1 Emergency Classification Flowchart, section 3.0 step 3.3.7, if an EAL was exceeded but the emergency has been totally resolved (prior to declaration), the emergency condition that was appropriate shall not be declared but reported only. The duration of the leakage was approximately 15 minutes. The unit remains at mode 1 and 100% power. The cause for the unexpected level decrease is under investigation at this time. There were no radiological releases associated. The licensee will notify the NRC Resident Inspector.
The original report contains a typographical error. The leak duration was reported as 15 minutes. The correct time period is 1.5 minutes. Notified R2DO(Moorman)
On January 11, 2008, TVA notified the NRC of the discovery of an after the fact unusual event. The reported event described potential RCS leakage in excess of 25 GPM that was approximately 1 and 1/2 minutes in duration. The estimated magnitude of this leak was based on a step change in Volume Control Tank (VCT) level that occurred when placing the 1A Mixed Bed Demineralizer in service. TVA's post-event investigation concluded the cause of the VCT level change was the filling of a void in the 1A Mixed Bed Demineralizer. The cause of the void was a procedural deficiency in the flush methodology used when returning the demineralizer to service. Based on the evaluation of this event, TVA has concluded that no actual RCS leakage occurred. The RCS pressure boundary remained intact throughout this evolution. Based on the result of this evaluation and the subsequent successful alignment of the demineralizer without incident, TVA is retracting this event. The licensee has notified the NRC Resident of this retraction. Notified the R2DO (Munday) and NRR EO (Brown). |