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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 53106 | 6 December 2017 14:58:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | Diesel Fuel Oil Tank Supply Non-Conforming with Licensing Basis for Tornado Generated Missiles | On December 6, 2017, during evaluation of protection for Technical Specification (TS) equipment from the damaging effects of tornado generated missiles, Three Mile Island Nuclear Station identified a non-conforming condition in the plant design such that specific TS equipment is considered to not be adequately protected from tornado generated missiles. A tornado could generate a missile that could strike the emergency diesel generator (EDG) fuel oil supply tank (DFT) vent stack. This could result in crimping of the stack, which could affect the ability of the DFT to perform its design function if such a tornado would occur. This condition is reportable per 10 CFR 50.72(b)(3)(ii)(B) for any event or condition that results in the nuclear power plant being in an unanalyzed condition that significantly degrades plant safety, and per 10 CFR 50.72(b)(3)(v)(D) for any event or condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident. This condition is being addressed in accordance with NRC enforcement guidance provided in EGM 15-002 and DSS-ISG-2016-01. Compensatory measures have been implemented in accordance with these documents. The NRC Resident Inspector has been informed of this notification. | Emergency Diesel Generator | 05000289/LER-2017-004 |
| ENS 52049 | 28 June 2016 14:55:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Both a & B Trains Hpi Inoperable Due to Void in Common Suction Line Resulting in Loss of Safety Function | At 1055 (EDT) on 06/28/16 a gas void was found during the monthly surveillance inspection located in the common suction line to the High Pressure Injection / Makeup (HPI / MU) pumps. At 1150 on 06/28/16 the HPI suction line cross-connect valves were closed to isolate and separate the 'A' & 'B' Trains of HPI. The 'A' train of HPI was declared degraded and initiated a 72 hour LCO (Limiting Condition of Operation) under TS (Technical Specification) 3.3.2. Investigation and analysis by Engineering determined that the size of the void did not meet the acceptance criteria for system operability. Due to the size of the void and location at time of discovery, both trains of HPI were determined to be inoperable until the suction cross connect valves were closed. This condition is reportable under 10 CFR 50.72(b)(3)(v)(D) as a Condition That Could Have Prevented Fulfillment of a Safety Function to mitigate the consequences of an accident. The void is being vented to restore a water-solid condition. The last successful surveillance was conducted on 05/31/16. The cause of the void is being investigated. The NRC Resident Inspector has been informed.
Following the 8-hour 10 CFR 50.72 notification made on 06/28/16 (EN 52049), further engineering analysis determined that the as-found void size was insufficient to cause the high pressure injection pumps to become inoperable or unable to fulfill their safety function. The cause for the void continues to be under investigation including the development of actions to prevent recurrence. Void checks are being performed at an increased frequency until cause is determined, and actions to prevent recurrence are in place. As determined through analysis, both trains of HPl were operable and available such that the safety function was never lost. Therefore, this event notification is being retracted as it is not reportable pursuant to 10 CFR 50.72(b)(3)(v)(D). The licensee notified the NRC Resident Inspector. Notified R1DO (Dimitriadis). | ||
| ENS 50108 | 12 May 2014 14:20:00 | 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | Postulated Hot Short Fire Event That Could Adversely Impact Safe Shutdown Equipment | During a review from industry operating experience it was identified that there are three additional unprotected DC control circuits for non safety related DC motors which are routed from the turbine building to other separate fire areas (this is in addition to the one circuit that was previously identified and submitted under event #50059). Fuses used to protect the motor power conductors appear to be inadequate to protect the control conductors. The concern is that under fire safe shutdown conditions, it is postulated that a fire in one area can cause short circuits potentially resulting in secondary fires or cable fires in other areas where the cables are routed. The secondary fires or cable failures are outside the assumptions of the 10 CFR 50 Appendix R Safe Shutdown Analysis. This condition is reportable as an 8 hour ENS report in accordance with 10 CFR 50.72(b)(3)(ii)(B) as an unanalyzed condition. Compensatory measures (fire watches) have been implemented for affected areas of the plant. The NRC Resident Inspector has been notified. | 05000289/LER-2014-001 | |
| ENS 50059 | 25 April 2014 15:13:00 | 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | Postulated Hot Short Fire Event That Could Adversely Impact Safe Shutdown Equipment | A review of industry Operating Experience identified that there were unprotected DC control circuits for non safety-related DC motors which are routed from the turbine building to other separate fire areas. Fuses used to protect the motor power conductors appear to be inadequate to protect the control conductors. The concern is that under fire safe shutdown conditions, it is postulated that a fire in one area can cause short circuits potentially resulting in secondary fires or cable failures in other fire areas where the cables are routed. The secondary fires or cable failures are outside the assumptions of the 10 CFR 50 Appendix R Safe Shutdown Analysis. This condition is reportable as an 8-hour ENS report in accordance with 10 CFR 50.72(b)(3)(ii)(B) as an unanalyzed condition. Compensatory measures (fire watches) have been implemented for affected areas of the plant. The NRC Resident Inspector has been notified. | 05000289/LER-2014-001 | |
| ENS 47294 | 26 September 2011 19:00:00 | 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | New River Hydraulic Analysis Raises Maximum Flood Level | TMI new river analysis indicates level above existing UFSAR (Updated Final Safety Analysis Report) flood analysis. At about 15:00 (EDT) on September 26, 2011, a revised River Stage Discharge Analysis was completed and concluded that the Probable Maximum Flood (PMF) water level is higher than previously described in the safety analysis report. This unanalyzed condition is reportable in accordance with 10 CFR 50.72(b)(3)(ii)(B). Actions to protect the plant for the higher PMF river level have been implemented. The flood barrier gates that protect safety related equipment have been modified to accommodate the revised river levels. No onsite flood water levels have occurred that could potentially challenge the existing flood barrier system. The licensee notified the NRC Resident Inspector. The licensee will be making a courtesy media notification. | ||
| ENS 43139 | 2 February 2007 18:50:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | Low Pressure Injection (Lpi) Net Positive Suction Head Flow Requirements Not Met for Certain Accident Sequences | At 1350 hours on February 2, 2007, with the plant at 100% power, it was determined (that) the low pressure injection (LPI) system net positive suction head calculation does not account for the additional flow through the failed LPI pump recirculation line during certain accident scenarios. The additional flow is upstream of the flow element used by control room operators to throttle system flow to maintain net positive suction head flow requirements. The additional flow could result in net positive suction head below required design limits. The system design is not affected in events where both LPI trains perform as designed. Emergency operating procedures direct control room operators to open the LPI system discharge flow cross-connect line isolation valves, if accessible, following a LPI pump failure. Operators are then directed to throttle system flow through the operable LPI pump to maintain proceduralized values. These values are designed to provide sufficient design flow and maintain pump NPSH. During a simulator training scenario, operators identified when the discharge cross-connect line isolation valves were opened, the idle Building Spray train indicated flow. Follow-up investigation identified the increased flow was due to back flow through the failed LPI pump minimum flow recirculation line. This additional flow is upstream of the flow element used by operators to maintain adequate net positive suction head for the operable LPI pump. The additional flow could result in not meeting NPSH design requirements. The licensee entered the 72 hour Technical Specification limiting condition for operation (LCO) for one inoperable LPI train. The licensee is revising calculations and emergency operating procedures to account for the additional flow. This condition is reportable in accordance with 10CFR 50.72(b)(3)(ii) and (b)(3)(v) as an unanalyzed condition, and a condition that could have prevented the fulfillment of the safety function of the LPI system to mitigate the consequences of an accident, respectively. The NRC Resident Inspector was notified of this event by the licensee.
The purpose of this report is to retract the ENS report made on February 2, 2007 at 2105 hours ( ENS #43139) under 10CFR50.72(b)(3)(ii) and (b)(3)(v) as an unanalyzed condition, and a condition that could have prevented the fulfillment of the safety function of the Low Pressure Injection (LPI) system to mitigate the consequences of an accident, respectively. The initial report was made when it was determined that the LPI system net positive suction head (NPSH) calculation does not account for the additional flow through the LPI pump recirculation line during certain accident scenarios. The additional flow could result in net positive suction head below required design limits. Due to this condition, it was not certain if the LPI system could have met its design basis requirements. The licensee entered the 72 hour Technical Specification limiting condition for operation (LCO) for one inoperable LPI train. The LCO was exited on February 3, 2007 at 9:25PM following implementation of a procedure change that accounted for the additional flow and ensured that adequate NPSH was maintained. A subsequent engineering evaluation has determined that sufficient LPI pump NPSH would have been available to perform its design basis function prior to the procedure change. The engineering evaluation shows that the LPI pumps remained capable of performing their design basis functions based on the following three independent assessments: 1) the LPI pumps would have operated well beyond their mission time without significant cavitation damage at the available NPSH 2) proceduralized operator actions would have throttled flow to restore required NPSH if signs of cavitation occurred 3) an evaluation using realistic Reactor Building pressures showed that sufficient NPSH would exist. The licensee notified the NRC Resident Inspector. Notified R1DO (Hott) | ||
| ENS 42527 | 25 April 2006 17:30:00 | 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | Unanalyzed Condition - Control Logic Error | TMI Issue Report # 482679 identified an issue while performing reviews of fire abnormal operating procedures to assure compliance with the Fire Hazards Analysis Report (FHAR), in that a control logic error was identified in the circuitry elementary drawing for the isolation valves DH-V-6A and DH-V-6B between the Borated Water Storage Tank (BWST) and the Reactor Building (RB) sump. Plant circuitry was verified to be wired as per the elementary drawing. This circuitry design was to prevent a hot short, due to a fire, from opening the valve. However, the identified control logic error could allow a spurious opening to occur on DH-V-6A or DH-V-6B due to a fire. The FHAR credits these valves as being protected from spuriously opening due to a fire in AB-FZ-5 (Auxiliary Building 281' general area). If this protection is not provided, then spurious opening could result in draining the BWST inventory to the RB sump. This hot short condition would result in the depletion of the BWST inventory and loss of the High Pressure Injection (HPI) makeup capability, resulting in an unanalyzed condition that significantly degrades plant safety. This condition is reportable under 10 CFR 50.72(b)(3)(ii)(B), 'Any event or condition that results in the nuclear power plant being in an unanalyzed condition that significantly degrades plant safety.' A 60-day LER is also required under 10 CFR 50.73(a)(2)(ii)(B) for the same degraded condition. An hourly fire-watch has been established in the affected fire zone in the 281' elevation Auxiliary Building as an interim compensatory measure. Additionally, the control circuitry at the 1A and 1B ES MCCs will be modified to prevent the RB sump isolation valves DH-V-6A and DH-V-6B from spuriously opening due to a hot short. The licensee notified the NRC Resident Inspector. | ||
| ENS 42475 | 5 April 2006 12:04:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Both Trains of High Pressure Injection (Hpi) Declared Inoperable Due to Potential Air Binding of Pumps | TMI declared both High Pressure Injection Trains not operable due to air void in the suction line from the Sodium Hydroxide tank. The postulated issued is that in the event of a small break LOCA where the plant would need to go on HPI piggy back Ops (the Low Pressure Injection supplying suction to the High Pressure Injection pumps) the air could cause the HPI pumps to become air bound. The Plant entered a shutdown Tech Spec 3.0.1 at 0804 (EDT) and exited the timeclock at 0850 (EDT) when the Sodium Hydroxide tank was isolated, thus isolating the air void from the ECCS (Emergency Core Cooling System) pumps. The licensee is continuing their investigation into root cause and operability. The licensee will inform the NRC Resident Inspector. * * * RETRACTION FROM A. MILLER TO P. SNYDER AT 1301 EDT ON 6/2/06 * * * The purpose of this call is to retract the notification (Event Number 42475) made by TMI Unit 1, Docket No. 50-289 / License No. DPR-50. On April 5, 2006, at 1408 hours, the Shift Manager made a notification (Event Number 42475) to the NRC Operations Center in accordance with 10 CFR 50.72 (b)(3)(v)(D) (i.e. any event or condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident). The event was reported as 'Both trains of High Pressure Injection (HPI) Declared Inoperable due to potential air binding of Pumps.' On April 5, 2006, air voids were found in the NaOH tank piping, upstream of the HPI pumps, and the Shift Manager conservatively declared both trains of HPI inoperable due to the air voids. This placed TMI-1 in a 1-hour shutdown Limiting Condition for Operation (LCO). The isolation valves for the NaOH tank line piping were then Closed to eliminate the possibility that the voids could be transported to the HPI pumps. The HPI pumps were then declared operable and TMI-1 entered a 72-hour shutdown LCO. During the 72-hour LCO, the air bubble was vented from the system. An initial extent of condition evaluation was completed and an event response team was established. Numerical Applications, Inc. (NAI) was retained to perform GOTHIC Model run on the two phase flow conditions and determine the percent air density of the water at the suction to the Low Pressure Injection (LPI) pumps and the HPI pumps. The NAI analysis concluded that the densities of air found at the suction of the LPI and HPI pumps were below the safe operating level as stated by the pump manufacturers. Based on the results of the evaluation, TMI-1 has determined that the LPI and HPI pumps were operable. Past operability of these pumps with the maximum size air bubble found is affirmed. Therefore, this event does not meet the 10 CFR 50.72 or 10 CFR 50.73 reporting criteria and the notification for Event Number 42475 is retracted. The resident inspector has been notified. Notified R1DO (T. Jackson). | ||
| ENS 41663 | 3 May 2005 17:10:00 | 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | Appendix R Fire Scenario Involving Multiple High Impedance Faults | TMI Issue Report # 329440 identifies an issue associated with a previously unidentified/unanalyzed Appendix R fire scenario involving multiple high impedance faults. An engineering evaluation has determined that certain safety related power circuits are not protected against multiple high impedance faults, which in combination with a fire in the 305' elevation of the Control Building, could cause a loss of safe shutdown functions from the control room and the remote shutdown panel. An hourly fire-watch has been established in the affected fire zone in the 305' elevation of the Control Building as an interim compensatory measure. The NRC Resident Inspector will be notified. | Remote shutdown | |
| ENS 41444 | 16 February 2005 01:55:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | Possible Failure to Meet Design Basis Requirements of Positive Pressure in the Control Tower Envelope Following a Design Basis Accident. | The licensee provided the following information: During operator rounds it was discovered that a double door for the control tower habitability envelope was propped open (from painting earlier in the day). This condition would have resulted in not meeting the design basis requirements of maintaining a positive pressure inside the control tower envelope following a design basis accident. The doors were immediately closed. An issue report was generated and a prompt investigation was commenced in accordance with station policies. The NRC resident Inspector was notified.
The licensee provided the following information: An ENS notification (EN# 41444) was made at approximately 00:59 on 2/20/2005 regarding a potentially unanalyzed condition associated with a double door for the Control Tower Habitability Envelope, which was propped open. It was initially thought that this condition could have resulted in not meeting the design basis requirements for the Control Tower Envelope. However, an analysis of an air flow measurement across the open door has shown that the unfiltered air in-leakage into the Control Tower Habitability Envelop would not exceed the value assumed in the design basis accident analysis for Control Room Habitability. Since this event did not result in an unanalyzed condition, this event is being retracted. The licensee notified NRC Resident Inspector. |