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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 49514 | 7 November 2013 18:33:00 | 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat 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 | Conduit Flood Seal Missing | On 11/7/13, it was identified that a missing conduit flood seal between an outside manhole and the West switchgear room compromised the flooding design of both the East and West switchgear rooms. Compensatory measures were implemented for the flood seal in accordance with the plant's barrier control process. Repair of the seal is in progress. The event is being reported under 10CFR 50.72(b)(3)(v) as internal flooding of both Switchgear Rooms could affect (a.) safe shutdown, (b.) removal of decay heat, (c.) control of release of radioactive material and (d.) mitigating an accident. The NRC Senior Resident Inspector has been notified of this condition. | ||
| ENS 49355 | 18 September 2013 16:59:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | High Pressure Coolant Injection System Declared Inoperable Due to Steam Leak | On 9/18/13, during performance of the High Pressure Coolant Injection (HPCI) pump operability surveillance, a minor steam leak was discovered on the governor valve inspection cover flange. Due to the leak, HPCI was declared inoperable. Actions taken: A 14-day LCO per TS 3.5.E.2 has been entered and corrective actions are in progress. The licensee has notified the NRC Resident Inspector.
After further evaluation, the gasket leak at the flange was determined to have no impact on the operability of the HPCI system, and therefore the HPCI system was able to perform all safety functions with the identified condition. The immediate determination, made on September 18, 2013, that the HPCI system was inoperable was revised based on the results of an analysis of the HPCI room heat up rate. The heat up rate was modeled using a calculated steam leak rate based on actual measurements of the damaged gasket after removal from the HPCI turbine flange. The time to heat up was based on the first set point at which isolation due to a temperature increase would occur. It was determined that the existing gap in the gasket represented approximately one-tenth of the approximate size of a steam leak that would be expected to result in an isolation, therefore the existing flange leak had no impact on operability of the HPCI system or its ability to mitigate the consequences of an accident. The licensee has notified the NRC site Resident Inspector. Notified R1DO (Krohn). | High Pressure Coolant Injection | |
| ENS 48847 | 24 March 2013 03:18:00 | 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat 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 | Switchgear Room Degraded Flood Seals | On 3/23/13 it was identified that a conduit flood seal between an outside manhole and the switchgear rooms is displaced. This degraded flood seal compromises the flooding design of both the East and West Switchgear Rooms. Compensatory measures were implemented for the flood seal in accordance with the plants barrier control process. Repairs of the seal are in progress. Per the licensee these switchgear rooms contain both normal and safety related 4kV and 480 V electrical boards. Compensatory measures implemented include: Plant Maintenance personnel will take actions to seal any leak within 24 hours of a flooding event and also provide sump pumps to remove any water that has leaked in. The licensee notified the NRC Resident Inspector and the Vermont State Liaison.
This is an update to NRC Event No. 48847 reported on 3/24/13 at 1316 (EDT). On 3/27/2013 the extent of condition review identified two additional possible water intrusion paths from the outside to the switchgear rooms. Compensatory measures were implemented for these paths in accordance with plant procedures. Efforts to seal these paths are in progress. This is an on-going extent of condition assessment. The licensee will inform the NRC Resident Inspector and the Vermont State Liaison. Notified R1DO (Krohn). | ||
| ENS 47962 | 24 May 2012 20:30:00 | 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat 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 | Missing Flooding Barrier Inside East Switchgear Room | On 5/24/12, it was identified that a conduit flood seal was missing between an outside manhole and the interior of the switchgear rooms. The missing flood seal compromised the interior flooding design for both East and West Switchgear Rooms. Repairs were made by procuring and installing a 4" flood seal so that the flood path has been plugged. The conduit plug seal is now functional. The event is being reported under 10CFR 50.72(b)(3)(v) as internal flooding of both Switchgear Rooms could possibly affect (a.)safe shutdown, (b.)removal of decay heat, (c.)control of release of radioactive material and (d.)mitigating an accident. The NRC Resident Inspector has been notified. | ||
| ENS 47495 | 2 December 2011 14:45:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Wrong Train Emergency Diesel Fuel Rack Trip | While hanging tags on the 'B' Diesel Generator, which was tagged out for maintenance, the operator mistakenly entered the 'A' Diesel Generator Room and tripped the 'A' Diesel Generator fuel rack, making it inoperable. At this time both diesels were inoperable placing the plant in a 24 Hour LCO. When the fuel rack was tripped alarms were received in the control room, the operator was immediately contacted and the problem was identified and corrected. Total LCO time was approximately 2 minutes. The licensee notified the NRC Resident Inspector. | ||
| ENS 46618 | 16 February 2011 16:25:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Steam Leak on High Pressure Coolant Injection System | During system startup of (High Pressure Coolant Injection) HPCI for quarterly surveillance, audible and visual indications of steam leakage were observed. The system was secured and subsequently isolated (with outboard valve de-energized for configuration control). As a result of the steam leakage, a local fire alarm was received in the Control Room. HPCI is currently isolated and will not perform its safety function. Operators were dispatched to the Reactor Building fire panel to verify that the fire alarm was due solely to the steam leak. As a precautionary measure, personnel were evacuated from the Reactor Building. Operators entered (Off Normal Procedure) ON 3158, Reactor Building High Area Temperature/Water Level, and verified that room temperatures were decreasing after the steam line was isolated. No EOP-4, Secondary Containment Control, entry conditions were exceeded. The steam leak was isolated when HPCI was secured. Associated fire alarms were verified to be caused by the steam leak. There was no impact on other plant equipment or personnel safety. The source of the steam leak is suspected to be from a steam trap but this has not been confirmed. The licensee notified the NRC Resident Inspector and the State of Vermont Department of Public Service Nuclear Engineer. Notified R1DO (Ferdas) | Secondary containment High Pressure Coolant Injection | |
| ENS 43413 | 8 June 2007 13:10:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | High Pressure Coolant Injection (Hpci) Declared Inoperable. | During the performance of quarterly HPCI valve testing in accordance with OP4120 one of the two injection valves, HPCI-19, did not stroke open as required. Prior to testing the HPCI system was in normal standby line up. HPCI-19 was stroke tested during the outage on 6-1-07 and operated normally. HPCI-19 was also tested and verified to open during the ECCS test on 6-1-07. HPCI was declared inoperable per Technical Specification 3.5.E.2 (14 day Limiting Condition of Operation). All other ECCS systems and the EDGs are fully operable and the electrical grid is stable. The licensee has initiated repair efforts. The NRC Resident Inspector was notified of this event by the licensee. | High Pressure Coolant Injection | 05000271/LER-2007-002 |
| ENS 43113 | 23 January 2007 00:00:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Hpci Declared Inoperable Due to Faulty Flow Indicator | The licensee discovered that the High Pressure Coolant Injection (HPCI) system flow control loop was degraded in such a manner that HPCI would not perform its safety function. The HPCI loop flow indicator indicated 200 GPM with no flow in the loop. The specification for that parameter is <100GPM. With the flow indicator in this condition the HPCI flow controller would perform non-conservatively (less flow into the system than was demanded), and would not perform its intended safety function therefore rendering HPCI inoperable. The licensee declared HPCI inoperable and in accordance with Technical Specification 3.5.E.2 entered a 14 day LCO. The licensee has commenced troubleshooting and will initiate repairs as necessary to return the system to operation. The licensee notified the NRC Resident Inspector.
BASIS FOR RETRACTION: NRC Event Notification 43113 was conservatively made to ensure that the Eight-Hour Non-Emergency reporting requirements of 10CFR50.73 were met pending the evaluation of an atypical condition observed with the High Pressure Coolant Injection (HPCI) Flow Indicator that was observed by Operators during routine monitoring of plant equipment. After comparing the observed flow indication to allowable values for meter uncertainties, it was determined that the initial NRC Notification was not required. The HPCI system was capable of fulfilling all design safety functions. Additional measures to ensure system reliability were completed that included removing and bench testing the recently refurbished 'square root converter' and calibration verification of involved components. No degraded conditions were discovered. ENS Event Number 43113, made on 01/22/07, is being retracted. R1DO (Neil Perry) notified. The NRC Resident Inspector was notified of this retraction by the licensee. | High Pressure Coolant Injection | |
| ENS 42810 | 28 August 2006 17:00:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | High Pressure Coolant Injection Overspeed Trip Mechanism Failed to Reset | The High Pressure Coolant Injection system (HPCI) over-speed trip tappet did not reset as expected during the trip tappet test after securing from a successful HPCI operability run, thereby preventing a re-start of the HPCI system. The Automatic Depressurization System (ADS), Core Spray sub-systems, Low Pressure Coolant Injection (LPCI) and the Reactor Core Isolation Cooling (RCIC) systems are operable." The unit is in a 14 day LCO for this event. The licensee will notify the NRC Resident Inspector.
NRC Notification 42810 was conservatively made to ensure that the Eight-Hour Non-Emergency reporting requirements of 10CFR50.72 were met pending the evaluation of condition observed with the High Pressure Coolant Injection (HPCI) Overspeed Trip reset feature that was discovered while performing scheduled testing for the HPCI System. During surveillance testing on 08/28/06, the HPCI System was started and satisfied the Technical Specification requirements designed to demonstrate HPCI System Operability. Subsequently, while testing the specific components of the system, the HPCI Overspeed Trip functioned as expected, but would not reset when manually depressed (locally). The Shift Manager declared the system inoperable and remained in the Limited Condition of Operation (LCO) that was entered prior to commencing the testing activities. Subsequent investigation determined that the reset function of the HPCI turbine overspeed trip device is not required to support HPCI from performing the system safety functions as described in the station design and licensing basis. ENS Event Number 42810, made on 08/28/06, is being retracted. The licensee notified the NRC Resident Inspector. The R1DO(Hott) has been notified. | High Pressure Coolant Injection Reactor Core Isolation Cooling Core Spray Automatic Depressurization System Low Pressure Coolant Injection | |
| ENS 42219 | 22 December 2005 14:03:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Hpci Declared Inoperable | The HPCI flow control current loop was found degraded in such a manner that HPCI would not perform its intended function. HPCI was declared inoperable per TS 3.5.E.2 (14 day LCO). Repair efforts have been initiated. The licensee notified the NRC Resident Inspector.
On 12/22/05, the HPCI System flow indicator 'spiked' a number of times with the system in its normal standby line-up. Control Room Operators declared the HPCI system inoperable and entered a 14 day LCO per TS 3.5.E.2, to troubleshoot and repair the system as appropriate. The safety function of HPCI system is to provide and maintain an adequate coolant inventory inside the reactor vessel to prevent fuel clad conditions from exceeding 10CFR50.46 criteria as a result of postulated small breaks in the Nuclear System process barrier. To ensure that this safety function is met, the HPCI System must be able to deliver a minimum actual flow rate of 3570 gallons per minute (gpm) to the reactor vessel. The actual flow rate was reduced below the Technical Specification value of 4250 gpm to account for potential flow instrument string inaccuracies. The delivery of 3570 gpm of actual flow demonstrates that sufficient margin to safety function is maintained during accident conditions. In automatic operation, the HPCI flow controller uses the flow signal to maintain a flow rate of 4250 gpm and is designed to automatically adjust developed flow rate in response to changes in flow signals. System operation is tested quarterly by monitoring flow to ensure that the HPCI system can perform its safety functions. The Technical Specification surveillance requirement states that the HPCI system shall deliver at least 4250 gpm at normal reactor operating pressure when recirculating to the Condensate Storage Tank. The event investigation revealed that the cause of the flow spikes was a malfunctioning electrical component in the power supply module within the flow controller. Power to the flow transmitter is supplied by this module. The power supply would malfunction for a few seconds and then would return to normal operation, thereby resulting in step changes in the HPCI flow signal. It is conservative to assume the actual HPCI flow rate would have been reduced by the full amount of the flow rate, for the entire duration of the flow signal. Additional conservatism also exists because the HPCI system flow is unlikely to have been able to respond to the full value of a short duration flow spike. When calculating the average HPCI flow rate, the impact of the flow spikes decreases as a longer period is evaluated because the duration of all of the flow spikes added together is very short and comparably longer periods of stable performance exist between the individual spikes. Therefore, it is conservative to evaluate the shortest period of time that HPCI is required to perform its safety functions that is stated in the Design Bases Document as 1000 seconds. With HPCI operable, the worst case period occurred just prior to it being declared 'Inoperable'. HPCI was calculated to have developed an actual flow rate of greater than 4191 gpm during the worst case 1,000 second period. The calculation for 'HPCI Flow Control & Indication Loop Accuracy' provides total loop accuracy of plus or minus 216.2 gpm at 4250 gpm for Design Bases Accident conditions. A calculated flow rate of 4191 gpm, minus the flow instrument loop uncertainty of 216 gpm yields a worst case actual flow rate of 3975 gpm. A flow rate of 3975 gpm is greater than the 3570 gpm assumed in event calculations. The subject flow controller power supply module was removed and bench tested to demonstrate that sufficient operating margin existed to provide reasonable assurance that the power supply would not have failed if called upon to mitigate a design bases accident with sufficient margin. The testing simulated HPCI operation at 4250 gpm for more than 24 hours. No flow spikes were recorded during this period. Based upon these test results and the analysis provided above, if the subject power supply component had remained in service and HPCI operation was required, the system would have performed its required safety function for a duration exceeding any analyzed event. ENS Event Number 42219, completed on 12/22/05, is being retracted. The licensee notified the NRC Resident Inspector. Notified R1 DO (J. Trapp) | ||
| ENS 40343 | 20 November 2003 14:25:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | High Pressure Coolant Injection (Hpci) System Declared Inoperable | At 0925, while performing the HPCI time to rated flow surveillance, operators discovered the HPCI flow controller to be operating sluggishly in the automatic mode. The surveillance was stopped and HPCI was declared inoperable. The licensee entered a 24-hour LCO per Technical Specification 3.5.5.2 due to Torus Cooling being in service on RHR loop "A". The licensee is now in a 14-day LCO as a result of securing Torus Cooling and restoring RHR LPCI loop "A". Troubleshooting was performed with I&C prior to securing HPCI. I&C is pursuing controller restoration to operability. The licensee has notified the NRC Resident Inspector.
BASIS FOR RETRACTION: NRC Notification 40343 was conservatively made to ensure that the Eight-Hour Non-Emergency reporting requirements of 10CFR50.73 were met pending the evaluation of an atypical condition observed with the High Pressure Coolant Injection (HPCI) Flow Controller while performing scheduled preventative maintenance testing for the HPCI System. After the off-site vendor lab completed testing the circuit board, the HPCI Flow Controller performed sluggishly, and it was determined that the initial NRC Notification was not required. During surveillance testing on 11/20/03, the HPCI System was started and met or exceeded the Technical Specification minimum requirements designed to demonstrate HPCI System Operability. While testing the specific components of the system, the HPCI Flow Controller was observed to be behaving erratically. Although the HPCI System was still capable of performing its required design safety function, the Shift Manager declared the system inoperable with a concern that further degradation of the flow controller "could have" prevented the HPCI System from performing its design safety function. Troubleshooting determined that the amplifier circuit board for the controller was not performing as expected. This board was subsequently replaced with one from stock and tested satisfactorily before declaring HPCI fully operational. The faulty amplifier circuit board was sent to an off-site vendor lab for testing and analysis. The vendor determined that the problem was due a capacitor failure on the board. The capacitor was removed, and the board was re-tested to determine the extent of the effect that this condition would have on the HPCI System performance. This testing revealed the same indications and system response that was initially observed by Vermont Yankee personnel during testing and troubleshooting. Therefore, it has been concluded that with the preventative maintenance system's surveillance as-found condition, the HPCI System was capable of performing its design safety function, and the flow controller's performance would not have degraded any further as a result of this condition. Therefore ENS Event Number 40343, made on 11/20/03, is being retracted. The NRC Resident Inspector was notified. Reg 1 RDO( Holody) was informed. | High Pressure Coolant Injection |