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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 55240 | 10 March 2021 13:15:00 | 10 CFR 50.73(a)(1), Submit an LER | 60-Day Optional Telephonic Notification of an Invalid Specified System Actuation | This telephone notification is provided in accordance with 10 CFR 50.73(a)(1) to report an invalid actuation of containment isolation valves in more than one system required by 10 CFR 50.73(a)(2)(iv)(A). On March 10, 2021, at 0815 (CST), during the Unit 2 Refueling Outage (L2R18), while performing a test to verify functionality of an isolation relay following replacement of the relay, a Group 4 isolation signal was actuated. The Group 4 isolation logic affects both the Reactor Building Ventilation (VR) and Containment Vent and Purge (VQ) system (for both units). All equipment responded as designed to the Group 4 isolation, including startup of Standby Gas Treatment (SBGT) to maintain secondary containment pressure (for both units). Investigation determined that the cause of the isolation was an inadvertent contact of the self-retracting grip jumper between two adjacent terminals that caused a short to ground and a blown fuse during the test performance. The fuse was replaced and systems restored as needed for the plant condition. The containment isolation was not due to actual plant conditions or parameters meeting design criteria for containment isolation. Therefore, this is considered an invalid actuation. The NRC Resident Inspector has been informed of this notification. | Secondary containment Reactor Building Ventilation | |
| ENS 53083 | 6 October 2017 14:10:00 | 10 CFR 50.73(a)(1), Submit an LER | Invalid Specified System Actuation | On October 6, 2017 at 0910 CDT hours, with Unit 1 in Mode 1 (Power Operation), the 1A Diesel Generator Cooling Water Pump (DGCWP) automatically started. The cause was the misoperation of the 1B/C RHR (Residual Heat Removal) Room Cooler Fan (1VY03C) control switch, which was placed in the start position instead of the intended pull-to-lock position. The start of the 1VY03C fan resulted in the automatic actuation of the 1A DGCWP. This system actuation is reportable in accordance with 10CFR50.73(a)(2)(iv)(A). The invalid actuation was not part of a pre-planned sequence during testing or reactor operation. The 1A DGCWP, an emergency service water system that does not normally run and that serves as an ultimate heat sink, responded satisfactorily. This call is being made in accordance with 10CFR50.73(a)(1), which states that in the case of an invalid actuation reported under 10CFR50.73(a)(2)(iv), other than an actuation of the reactor protection system when the reactor is critical, the licensee may provide a telephone notification to the NRC Operations Center within 60 days after discovery of the event instead of submitting a written Licensee Event Report. The licensee notified the NRC Resident Inspector. | Service water Reactor Protection System | |
| ENS 52227 | 11 July 2016 09:30:00 | 10 CFR 50.73(a)(1), Submit an LER | Invalid Actuation of Division 1 Primary Containment Isolation Logic Due to a Blown Fuse | On July 11, 2016, at approximately 0430 CDT, while Unit 1 was operating at 100% power, the 1A Reactor Protection System (RPS) Motor Generator (M/G) set tripped causing a loss of the A RPS bus. This caused the complete actuation of the Division 1 (outboard) primary containment isolation logic. The isolation logic actuation resulted in successful closure of the Division 1 primary containment isolation valves. This was an event that resulted in the actuation of a general containment isolation signal affecting more than one system. However, as this event meets the definition of an invalid actuation (i.e., not a response to an actual plant parameter exceeding a trip set-point), this notification is being made in accordance with 10CFR50.73(a)(2)(iv)(A) in lieu of a Licensee Event Report. In response to the trip of the 1A RPS M/G Set, operators swapped the A RPS bus to the alternate power supply using the applicable response procedure. The containment isolation signal was reset and the systems were restored to their normal lineup. Reactor power was not affected by this event. All safety related equipment controlled by the affected primary containment isolation circuits operated as designed. The 1A RPS M/G Set trip was due to a blown power fuse for the 1A RPS M/G Set. This was the result of worn insulation on one of the generator output leads. The generator output leads were repaired and rerouted to prevent future problems on 07/15/16. Restoration of the normal power supply to the 1A RPS function was completed on 7/19/16. The licensee informed the NRC Resident Inspector. | Reactor Protection System Primary containment | |
| ENS 49174 | 22 May 2013 16:34:00 | 10 CFR 50.73(a)(1), Submit an LER | 60 Day Optional Telephonic Notification of Invalid Division 1 Containment Isolation Due to Motor Generator Trip | On May 22, 2013, at approximately 1134 CDT, while Unit 1 was operating at 100% power, the 1A Reactor Protection System (RPS) Motor Generator (M/G) set tripped causing a loss of the A RPS bus. This caused the actuation of the Division 1 (outboard) primary containment isolation logic. This was an event that resulted in the actuation of a general containment isolation signal affecting more than one system. However, as this event meets the definition of an invalid actuation (i.e. not a response to an actual plant parameter exceeding a trip setpoint), this notification is being made in accordance with 10 CFR 50.73(a)(1) in lieu of a Licensee Event Report. In response to the trip of the 1A RPS M/G, operators swapped the A RPS bus to the alternate power supply using the applicable response procedure. The containment isolation signal was reset and the systems were restored to their normal lineup. Reactor power was not affected by this event. All safety related equipment controlled by the affected primary containment isolation circuits operated as designed. The 1A RPS M/G trip was due to a motor fault requiring motor replacement. Replacement of the motor was completed on 5/26/13 and the A RPS bus was restored to its normal power supply on 5/27/13. The licensee has notified the NRC Resident Inspector. | Reactor Protection System Primary containment | |
| ENS 46220 | 26 July 2010 23:19:00 | 10 CFR 50.73(a)(1), Submit an LER | 60-Day Telephonic Notification in Lieu of a Written Licensee Event Report of Invalid Actuation | On July 26, 2010, at 1819 hours (CDT), with Unit 1 in Mode 1 (Run), the Division 1 Diesel Generator Cooling Water Pump (DGCWP) restarted after being secured. The DGCWP provides the Emergency Service Water to the 1A Residual Heat Removal (RHR) pump room area cooler and the Reactor Core Isolation Cooling (RCIC) water pump/Low Pressure Core Spray (LPCS) pump room area cooler. The apparent cause of the restart was the momentary interruption of the DGCWP run logic. The Division 1 DGCWP was in operation to support cooling of the Unit 1 RCIC/LPCS pump room area (run logic satisfied). When the Operator placed the Division 1 DGCWP control switch to the normal-after-stop position, the DGCWP feed breaker opened. The Operator reset the DGCWP feed breaker trip by returning the control switch to the normal-after-stop position and, because the run logic for the DGCWP was still satisfied (due to elevated room temperatures), the DGCWP restarted. This invalid start signal from the Division 1 DGCWP breaker being reset resulted in the automatic actuation of the Division 1 DGCWP. The Division 1 DGCWP responded satisfactorily. This report is being made in accordance with 10CFR50.73(a)(1), which states that in the case of an invalid actuation reported under 10CFR73(a)(2)(iv)(A), other than an actuation of the Reactor Protection System (RPS) when the reactor is critical, the licensee may provide a telephone notification to the NRC Operations Center with 60 days after discovery of the event instead of submitting a written LER. The licensee has notified the NRC Resident Inspector. | Service water Reactor Protection System Reactor Core Isolation Cooling Core Spray Residual Heat Removal | |
| ENS 45878 | 5 March 2010 10:39:00 | 10 CFR 50.73(a)(1), Submit an LER | Invalid Isolation Signal Caused Msiv'S to Close | This telephone notification is provided in accordance with 10 CFR 50.73(a)(1) to report an invalid actuation reportable under 10 CFR 50.73(a)(2)(iv)(A). On March 5, 2010, at 0539 hours, during the Unit 1 refueling outage (L1R13), the inboard and outboard Main Steam Isolation Valves (MSIVs) closed as a result of an invalid partial Group 1 PCIS (Primary Containment Isolation System) isolation signal generated during the performance of station surveillance LOS-TG-SR2 'Operability of Main Turbine Valves and Controls Following an Extended Outage.' Investigation revealed that during the resetting of the main turbine, the Group 1 PCIS logic received a signal that one of the Turbine Stop Valves (TSVs) was open. This caused the logic for Group 1 PCIS logic to be made up and the MSIVs to shut. Review of the data indicates that at no time did any of the TSVs open during the testing. This issue occurred as a result of the vibration seen by the relays in the trip logic during the resetting of the main turbine. The apparent cause of this event was attributed to a lack of questioning attitude during testing. The surveillance has multiple actions for cycling all the turbine valves, as well as performing various trips and resets of the main turbine. The surveillance has a prerequisite to ensure during performance of the various sections, that the MSIVs are shut or jumpers are installed to prevent an inadvertent closure of the MSIVs should the TSVs be cycled. The operating crew had concluded that the section of the procedure they were performing did not require the MSIVs to be shut or the jumpers to be installed. When the turbine was reset, the Reactor Protection System (RPS) Channels A1 and B2 actuated. Based upon these actuations, plant response to the partial Group 1 PCIS isolation signal was as expected. This actuation was invalid since the conditions required to bypass the low condenser vacuum Group 1 PCIS isolation were all met. With the mode switch not in run, the condenser low vacuum bypass keys in bypass and the main stop valves not full open, the Group 1 PCIS isolation is bypassed. These conditions were all met when the partial Group 1 PCIS isolation was received. The TSVs remained closed as indicated on the Digital Electro-Hydraulic Control (DEHC) system. Corrective actions include enhancements to the surveillance procedure and preparation of a case study on the circumstances, which led to this event. (Corrective actions also include presentation) to all operating crews in LORT (Licensee Operations Requalification Training) Cycle 10-4 and various site training advisory and curriculum review committees. The licensee has notified the NRC Resident Inspector. | Reactor Protection System Main Steam Isolation Valve Primary Containment Isolation System Main Turbine | |
| ENS 43358 | 15 March 2007 06:02:00 | 10 CFR 50.73(a)(1), Submit an LER | Invalid Eccs and System Actuations | This telephone notification is provided in accordance with 10 CFR 50.73(a)(1), to report an invalid actuation reportable under 10 CFR 50.73(a)(2)(iv)(A). On March 15, 2007, with Unit 2 in a refueling outage, the reactor vessel was filled to a solid condition and being depressurized following the completion of the vessel hydrostatic test. At 0102 CDST, with pressure indicating approximately 43 psig, the 2B Residual Heat Removal (RHR) pump was started in the shutdown cooling mode. With the vessel solid, the resultant pressure transient caused invalid reactor vessel low-level trip signals and Division 2 and 3 ECCS actuations. The 2C RHR pump auto-started and injected into the vessel. The 2A Diesel Generator (DG) started, and 2B RHR Injection valve (2E12-F042B) auto-opened. The Division 3 ECCS actuation did not result in any equipment starts because the High Pressure Core Spray pump and the 2B DG were properly removed from service at the time of the event. The operators verified that the reactor vessel low-level trips and ECCS actuations were invalid, and shut down the 2C RHR pump and the 2A DG. The 2B RHR Injection Valve was also closed. The cause was determined to be a knowledge deficiency compounded by less than adequate procedural guidance regarding starting shutdown cooling while the reactor vessel is in a solid condition. Corrective actions included reviewing the event with licensed operators, revising the appropriate operating procedures, and developing just-in-time training for future use. The event is reportable under 10 CFR 50.73(a)(2)(iv)(A) as an invalid ECCS actuation and invalid system actuation. The licensee notified the NRC resident inspector. | Shutdown Cooling High Pressure Core Spray Residual Heat Removal | |
| ENS 43333 | 3 March 2007 13:14:00 | 10 CFR 50.73(a)(1), Submit an LER | Invalid Eccs Actuation During Refueling Outage | This telephone notification is provided in accordance with 10 CFR 50.73(a)(1), to report an invalid actuation reportable under 10 CER 50.73(a)(2)(iv)(A). On March 3, 2007, Unit 2 was in a refueling outage. Reactor penetration nozzles were being flushed to remove crud deposits. At 0814 CST, Low Reactor Vessel Level 1, Level 2, and Level 3 alarms were received in the Main Control Room, and the Division 1 Emergency Core Cooling System (ECCS) initiated. The Low Pressure Core Spray (LPCS) pump started on the ECCS initiation signal and injected into the Unit 2 reactor vessel. In addition, the '0' Diesel Generator auto-started, and the Low Pressure Coolant Injection valve (2E12-F042A) auto-opened. Operators verified that reactor vessel and reactor cavity water levels were normal, and then stopped the ECCS injection into the vessel by placing the LPCS pump control switch in pull-to-lock. ECCS is not required to be operable in Mode 5 with the spent fuel pool storage gates removed and water level greater than or equal to 22 feet above the Reactor Pressure Vessel (RPV) flange. Investigation determined that the low reactor vessel water level signal occurred when the flushing wand was inserted into instrument nozzle N14A, which is the reference leg tap for the reactor vessel level instruments. The transient in differential pressure sensed by the level instruments resulted in the invalid actuation. Corrective actions included a revision to the model work order for this task to clearly identify the nozzles that shall and shall not be flushed during this evolution. This event is reportable under 10 CFR 50.73(a)(2)(iv)(A) as an invalid ECCS actuation and invalid system actuation. The licensee notified the NRC Resident Inspector. | Reactor Pressure Vessel Core Spray Emergency Core Cooling System Low Pressure Coolant Injection | |
| ENS 42737 | 4 June 2006 09:19:00 | 10 CFR 50.73(a)(1), Submit an LER | Invalid Rps Bus 'B' and Division 2 Pcis Actuations | This telephone notification is provided in accordance with 10 CFR 50.73(a)(1) to report an invalid actuation reportable under 10 CFR 50.73(a)(2)(iv)(A). On June 4, 2006, at 0419 (CST), with Unit 1 in Mode 1 'Run' at approximately 100% power, the 1B Reactor Protection System (RPS) bus unexpectedly de-energized. As a result, an RPS Bus B half-scram and Division 2 Primary Containment Isolation System (PCIS) isolations were received. All affected containment isolation valves closed as designed. RPS Bus B was transferred to its alternate feed, and restoration activities were begun. A walkdown found that the 1B RPS MG set output breaker had opened. Troubleshooting identified that the cause was a failure of the 1B RPS MG set voltage regulator. The voltage regulator was replaced and successfully tested, and the 1B RPS MG set was returned to service. Laboratory testing of the failed voltage regulator found that the stability potentiometer had failed, with excessive vibration identified as the apparent cause. Although the vibration levels at the MG set are considered to be normal, the voltage regulator is mounted in a control cabinet that sits directly on the generator end of the MG set. The normal vertical vibration on the 1B MG set was measured at greater than 2g, which could be sufficient over time to degrade the voltage regulator potentiometers. A design change has been initiated for both Units to isolate the voltage regulators from the RPS MG set vibrations. This event is reportable under 10 CFR 50.73(a)(2)(iv)(A) as an invalid actuation of containment isolation valves in more than one system. The licensee notified the NRC Resident Inspector. | Reactor Protection System Primary Containment Isolation System | |
| ENS 42526 | 4 March 2006 10:12:00 | 10 CFR 50.73(a)(1), Submit an LER | Invalid Emergency Diesel Generator Start | This telephone notification is provided in accordance with 10 CFR 50.73(a)(1), to report an invalid actuation reportable under 10 CFR 50.73 (a)(2)(iv)(A). On March 4, 2006, with Unit 1 in Mode 5 'Refuel,' Instrument Maintenance (IM) technicians were installing a Barton level indicator for reactor vessel level indicator 1B21-R452A as part of a system modification. At 0512 hours, momentary 'Reactor Vessel Water Low Level 2' alarms were received in the Main Control Room, and the Unit 1 High Pressure Core Spray (HPCS) Emergency Diesel Generator (1B EDG) auto-started. A Reactor Vessel Water Level Low 2 condition sends a start signal to HPCS and the 1B EDG; however, because the HPCS pump control switch was in pull-to-lock, the pump did not start and did not inject water into the reactor vessel. The initiating signal was reset, and at 0524 hours the 1B EDG was shutdown with the Maintenance Switch placed in 'Maintenance.' Investigation determined that the 1B EDG had auto-started approximately 15 minutes after the IM technicians had completed work and placed the 1B21-R452A indicator back in service. The computer point alarm typer data was reviewed, and it was observed that only a single set of alarm points were received. Typically, when an alarm is caused by improperly valving in an instrument, multiple alarm points are received due to 'ringing.' Based on the 15 minute time delay and the lack of ringing, the apparent cause was determined to be an air bubble that was introduced during the modification and then migrated to the level transmitter, resulting in an invalid low level signal and an auto-start of the 1B EDG. Corrective actions included reviewing the remaining Barton installation modification work packages for unusual piping configurations that could contribute to air entrapment, and-for adequate system isolation requirements; i.e., bypassing trip units or removing components from service in order to prevent inadvertent actuations. This event is reportable under 10 CFR 50.73(a)(2)(iv)(A) as an invalid actuation of an EDG. The licensee notified the NRC Resident Inspector. | Emergency Diesel Generator High Pressure Core Spray | |
| ENS 41560 | 7 February 2005 13:56:00 | 10 CFR 50.73(a)(1), Submit an LER | Invalid Specified System Actuation | The following information was obtained from the licensee via facsimile (licensee text in quotes): This telephone notification is provided in accordance with 10 CFR 50.73(a)(1), to report an invalid actuation reportable under 10 CFR 50.73(a)(2)(iv)(A). On February 7, 2005, at 0756 (CST), with Unit 2 in Mode 3 'Hot Shutdown' in preparation for the 2005 refueling outage, the 2A Reactor Protection System (RPS) bus unexpectedly de-energized during performance of LOS-RP-W1, 'Manual Scram Instrumentation.' As a result, an RPS Bus A half scram and Division 1 Primary Containment Isolation System (PCIS) isolations were received, including the isolation of shutdown cooling. All affected containment isolation valves closed as designed. An inspection found that the 2A RPS MG set output breaker had opened. RPS Bus A was transferred to its alternate feed, and the associated containment isolations were reset. Shutdown cooling was restored at 0845 hours on February 7, 2005. Troubleshooting found that the 2A RPS MG set voltage regulator had failed. The voltage regulator was replaced and successfully tested, and the 2A RPS MG set was returned to service. Laboratory testing of the failed voltage regulator circuit board found that a solder joint had failed on load-dropping resistor R8, which caused the excitation output voltage to decrease sharply. This resulted in a trip of the 2A RPS MG set output breaker on low voltage. The apparent cause of the failed solder joint was a manufacturing defect. Corrective actions include visual inspections of RPS MG set voltage regulatory circuit boards in the field and in the storeroom, and the development of enhanced receipt inspection requirements. This event is reportable under 10 CFR 50.73(a)(2)(iv)(A) as an invalid actuation of containment isolation valves in more than one system. The licensee has notified the NRC Resident Inspector. | Reactor Protection System Primary Containment Isolation System Shutdown Cooling |