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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 55926 | 12 April 2022 03:45:00 | 10 CFR 50.73(a)(1), Submit an LER | Invalid System Actuation | The following information was provided by the licensee via email: The following event description is based on information currently available. If, through subsequent reviews of this event, additional information is identified that is pertinent to this event or alters the information being provided at this time, a follow-up notification will be made via the ENS or under the reporting requirements of 10 CFR 50.73. This telephone notification is being made pursuant to the reporting requirements of 10 CFR 50.73(a)(1) and 10 CFR 50.73(a)(2)(iv)(A) to describe invalid actuations of the Palo Verde Nuclear Generating Station (PVNGS) Unit 1 B Train Auxiliary Feedwater (AF) system and Essential Spray Pond (ESP) system that occurred while in a refueling outage. On April 11, 2022, at approximately 2045 Mountain Standard Time, an automatic start of the Unit 1 B Train AF and ESP systems occurred during restoration from a surveillance test. The station was conducting a surveillance test during a Unit 1 refueling outage to verify the proper responses of the Engineered Safety Features Actuation Systems to simulated design basis events. The test portion was completed satisfactorily; however, during the restoration portion, the load sequencer inadvertently cycled between Mode 0 and Mode 1 three times in immediate succession. At the time of the system actuations, one of the actuation signals associated with this portion of the test had been reset per procedure. Another actuation signal was still in while restoration steps were ongoing, but the sequencer was not expected to cycle between Modes. The system actuations did not occur as a result of actual plant conditions or parameters and are therefore invalid. The Unit 1 B Train AF and ESP system actuations were complete and the systems started and functioned successfully. For the systems that did not actuate, the reasons are clearly understood as those systems were in an overridden condition due to test configuration. The spurious actuation was not able to be replicated and a direct cause was not identified. There were no adverse impacts to public health and safety nor to plant employees. The NRC Resident Inspectors have been informed. | Auxiliary Feedwater Spray Pond | |
| ENS 55032 | 11 December 2020 07:00:00 | 10 CFR 50.73(a)(1), Submit an LER | 60-Day Option Telephonic Notification of an Invalid Specified System Actuation | On October 13, 2020, at approximately 02:25 (MST), an automatic start of the Unit 1 'A' Train EDG and SP systems occurred following the restoration of power to the 'A' Train 4160 Volt Class Bus. The station was conducting a surveillance test during a Unit 1 refueling outage to verify the proper responses of the EDG and the Engineered Safety Features Actuation Systems to simulated design basis events. During the test, technicians installed a jumper across incorrect relay points that caused the running Unit 1 'A' Train EDG to trip, resulting in a loss of power to the 'A' Train 4160 Volt Class Bus. Following restoration of normal offsite power to the 'A' Train 4160 Volt Class Bus, the Loss of Power Actuation signal was reset, however, EDG start relay logic was not reset at the EDG Local Panel. This resulted in the Unit 1 'A' Train EDG and SP system actuations with the EDG running unloaded. The system actuations did not occur as a result of valid plant conditions or parameters and are therefore invalid. The Unit 1 'A' Train EDG and SP system actuations were complete and the systems started and functioned successfully. The event was attributed to a human performance error and entered into the corrective action program. There was no adverse impact to public health and safety nor to plant employees. The NRC Resident Inspectors have been informed. | ||
| ENS 54701 | 14 March 2020 19:44:00 | 10 CFR 50.73(a)(1), Submit an LER | Invalid Actuation of Spray Pond Pump System - 60 Day Reports | The following event descriptions are based on information currently available. If through subsequent reviews of these events additional information is identified that is pertinent to the events or alters the information being provided at this time a follow-up notification will be made via the ENS or under the reporting requirements of 10 CFR 50.73. This telephone notification is being made pursuant to the reporting requirements of 10 CFR 50.73(a)(2)(iv)(A) and 50.73(a)(1) to describe invalid actuations of both trains of the Palo Verde Nuclear Generating Station (PVNGS) Unit 3 essential spray pond (SP) system, which serves as an emergency service water system that does not normally run and serves as an ultimate heat sink as described in 10 CFR 50.73(a)(2)(iv)(B)(9). This notification covers two similar, but separate invalid actuations occurring in Unit 3 on March 14, 2020 at 12:44 (MST) and again on April 25, 2020 at 12:10 (MST). On each day, an invalid actuation of the Unit 3 train "B" Fuel Building Essential Ventilation Actuation Signal (FBEVAS) occurred during performance of the Balance of Plant Engineered Safety Features Actuation System weekly auto test. The auto/manual pushbutton was depressed to initiate the test and the sequencer immediately tripped FBEVAS train "B" with subsequent cross trip of FBEVAS train "A". These actuations resulted in complete and successful actuations of both trains of essential spray pond pumps. The events were entered into the PVNGS corrective action program and a station evaluation is in progress. There was no adverse impact to public health and safety nor to plant employees. The NRC resident inspectors have been informed. | Service water Spray Pond | |
| ENS 52413 | 17 October 2016 22:19:00 | 10 CFR 50.73(a)(1), Submit an LER | Invalid Engineered Safety Features Actuation System (Esfas) Signal | The following event description is based on information currently available. If through subsequent reviews of this event additional information is identified that is pertinent to this event or alters the information being provided at this time a follow-up notification will be made via the ENS or under the reporting requirements of 10CFR50.73. This telephone notification is being made pursuant to the reporting requirements of 10 CFR 50.73(a)(2)(iv)(A) and 50.73(a)(1) to describe an invalid actuation of the Palo Verde Nuclear Generating Station (PVNGS) Unit 1 train A emergency diesel generator (EDG), train A high pressure safety injection (HPSI) pump, and train A essential spray pond (SP) pump. These components are portions of the emergency ac electrical power system, the emergency core cooling system, and the emergency service water system, respectively, as described in 10 CFR 50.73(a)(2)(iv)(B). On October 17, 2016 at approximately 1519, Mountain Standard Time, a portion of the Unit 1 train A engineered safety features equipment was automatically started by the balance-of-plant (BOP) engineered safety features actuation system (ESFAS) while the plant was at steady state conditions. Initiation of the train A ESFAS actuation signal was momentary, and the ESFAS actuation signal cleared 0.2 seconds after being initiated. The invalid ESFAS signal initiated a test-mode start signal for the train A EDG and started the train A HPSI pump. The train A essential SP pump started in support of the train A EDG. All actuated components started and functioned successfully. No systems started in response to actual plant conditions, and no actuation was required to mitigate the consequences of an event. The invalid HPSI actuation neither resulted in an emergency core cooling system discharge, nor should it have. The invalid actuation was the consequence of a spurious momentary signal into the BOP-ESFAS control panel due to an intermittent high resistance electrical connection. The event was entered into the PVNGS corrective action program. There were no adverse impacts to public health and safety nor to plant employees. The NRC Resident Inspectors have been informed. | Service water Emergency Diesel Generator Spray Pond Emergency Core Cooling System | |
| ENS 52228 | 12 July 2016 12:50:00 | 10 CFR 50.73(a)(1), Submit an LER | Invalid Actuation of Both Trains Essential Spray Pond System | The following event description is based on information currently available. If through subsequent reviews of this event additional information is identified that is pertinent to this event or alters the information being provided at this time a follow-up notification will be made via the ENS or under the reporting requirements of 10CFR50.73. This telephone notification is being made pursuant to the reporting requirements of 10CFR50.73(a)(2)(iv)(A) and 50.73(a)(1) to describe an invalid actuation of both trains of the Palo Verde Nuclear Generating Station (PVNGS) Unit 2 essential spray pond (SP) system. The SP system serves as an emergency service water system that does not normally run and serves as an ultimate heat sink as described in 10CFR50.73(a)(2)(iv)(B)(9). On July 12, 2016, at approximately 0550, Mountain Standard Time, Unit 2 experienced a manual actuation of both trains of the SP system. Approximately 20 minutes earlier, the failure of a +15VDC power supply on the containment purge isolation actuation signal (CPIAS) module resulted in a trip of the B train CPIAS and a momentary cross trip of the A train CPIAS, and both trains of the control room essential filtration actuation system (CREFAS). These brief actuation signals resulted in starting of some but not all essential equipment because the actuation signals cleared before most of the equipment received a start signal. Both trains of the SP system were started manually in accordance with the alarm response procedure. The A train CPIAS and both trains of CREFAS were reset. The B train CPIAS remained in a partially tripped state because of the failed power supply. The manual actuation of both A and B trains of the SP system was complete. Both trains of the SP system started and functioned successfully. The invalid actuation was the consequence of a failed +15VDC power supply on the B train CPIAS module which resulted in momentary trips of both trains of CPIAS and CREFAS. The containment building radiation monitors that actuate CPIAS exhibited normal radiation levels which would not have required CPIAS actuation. The event was entered into the PVNGS corrective action program. There was no adverse impact to public health and safety nor to plant employees. The NRC Resident Inspectors have been informed. | Service water Spray Pond | |
| ENS 49807 | 12 December 2013 03:11:00 | 10 CFR 50.73(a)(1), Submit an LER | 60 Day Report for an Invalid Main Steam Line Actuation | The following event description is based on information currently available. If through subsequent reviews of this event additional information is identified that is pertinent to this event or alters the information being provided at this time, a follow-up notification will be made via the ENS or under the reporting requirements of 10 CFR 50.73. This telephone notification is being made pursuant to the reporting requirements of 10 CFR 50.73(a)(2)(iv)(A) to describe an invalid actuation of the Palo Verde Nuclear Generating Station Unit 2 'A' train Main Steam and Feedwater Isolation System (MSFIS) logic. On December 11, 2013, at approximately 2011, Mountain Standard Time, Unit 2 was shut down in Mode 4 with Reactor Coolant System (RCS) temperature at approximately 425 degrees Fahrenheit and 1900 pounds per square inch absolute. While starting up the plant following completion of repairs to the 1A reactor coolant pump, an invalid actuation of the 'A' train MSFIS fast close logic occurred due to a random electrical failure in the 'A' train MSFIS logic cabinet. This resulted in the closure of all four Main Steam Isolation Valves and the two 'A' train Economizer Feed Water Isolation Valves. No other engineered safety feature actuations occurred and none were required. The invalid actuation was initiated by a ground fault in a 30-volt direct current power supply in the 'A' train MSFIS Logic cabinet. Repairs were completed on December 12, 2013. This was a complete actuation of 'A' train MSFIS equipment and all the affected equipment responded as designed. RCS temperature and pressure were maintained stable using atmospheric dump valves. Feed water to the steam generators was being provided by Auxiliary Feed Water and was not affected by the event. The NRC Resident Inspector has been notified. | Steam Generator Reactor Coolant System Feedwater Main Steam Isolation Valve Auxiliary Feedwater Main Steam Line Main Steam | |
| ENS 48615 | 26 October 2012 04:08:00 | 10 CFR 50.73(a)(1), Submit an LER | 60-Day Optional Telephonic Notification for an Invalid Actuation of the Essential Spray Pond System | The following event description is based on information currently available. If through subsequent reviews of this event additional information is identified that is pertinent to this event or alters the information being provided at this time, a follow-up notification will be made via the ENS or under the reporting requirements of 10CFR50.73. This telephone notification is being made pursuant to the reporting requirements of 10 CFR 50.73(a)(2)(iv)(A) and 50.73(a)(1) to describe an invalid actuation of the Palo Verde Nuclear Generating Station (PVNGS) Unit 2 essential spray pond system (SP) which serves as the ultimate heat sink as described in 10 CFR 50.73(a)(2)(iv)(B)(9). On October 25, 2012, at approximately 2108, Mountain Standard Time, during refueling outage 2R17, Unit 2 experienced an invalid actuation of the train B essential spray pond system. Testing of the train B engineered safeguards features actuation system (ESFAS) was in progress. During the test, following activities to reset the train B containment spray actuation signal (CSAS), the procedure required a check of contact status on a relay contact which provides input to the train B Load Sequencer. The guidance required the use of a digital multi-meter to perform the contact status check. When the digital multi-meter test leads were landed and removed from the circuit, the train B Load Sequencer changed output modes which resulted in automatic starting of the train B essential chilled water system, essential cooling water system, essential fuel building air filtration unit and essential spray pond system. This was a partial actuation of the train B ESF equipment and all the affected equipment responded as designed. No equipment failures resulted from the event. The event was entered into the PVNGS corrective action program. The invalid actuation was caused by an incorrect testing methodology in the procedure instructions which resulted in the unintended interaction of the digital multi-meter and the digital train B Load Sequencer. The inadequate procedures will be revised to modify the testing methodology for verification of relay contact status. The licensee has notified the NRC Resident Inspector. | Spray Pond Containment Spray | |
| ENS 46898 | 3 April 2011 21:44:00 | 10 CFR 50.73(a)(1), Submit an LER | 60-Day Optional Notification of Invalid Start of the 'A' Emergency Diesel Generator | The following event description is based on information currently available. If through subsequent reviews of this event, additional information is identified that is pertinent to this event or alters the information being provided at this time, a follow-up notification will be made via the ENS or under the reporting requirements of 10CFR50.73. This report is being made under 10 CFR 50.73 (a) (2) (iv) (A) for a reportable invalid actuation. On April 3, 2011, at approximately 1444 Mountain Standard Time, Palo Verde Nuclear Generating Station Unit 2 experienced an invalid actuation (start) of the 'A' Emergency Diesel Generator (EDG). EDG 'A' inadvertently started during integrated safeguards surveillance testing to demonstrate that the EDG overspeed trip is not bypassed. Prior to the test, the EDG overspeed governor was actuated, but the butterfly valve was not verified to be fully closed as required. The valve closure actuates a limit switch which activates the interlock that prevents the EDG start following an overspeed trip. The test requires the operator to ensure the butterfly valve is fully closed because it may not fully close as the EDG is not running when it is actuated for the overspeed test. When the demand signal was inserted, the EDG started unexpectedly since the butterfly valve was not fully closed and the limit switch was not engaged. EDG 'A' Train completely actuated in the Emergency Mode and the EDG came up to rated speed and voltage as designed. The supporting 'A' train Essential Spray Pond System, used for engine cooling, was already running prior to the test. The Essential 'A' Train EDG Exhaust Room air handling unit started as required. No damage occurred to the EDG or related equipment as a result of the unplanned actuation. The EDG was secured and the test was successfully re-performed. This report is not considered an LER. The licensee has notified the NRC Resident Inspector. | Emergency Diesel Generator Spray Pond | |
| ENS 42734 | 6 June 2006 01:44:00 | 10 CFR 50.73(a)(1), Submit an LER | Invalid Emergency Diesel Generator Start | 'The following event description is based on information currently available. If through subsequent reviews of this event, additional information is identified that is pertinent to this event or alters the information being provided at this time, a follow-up notification will be made via the ENS or under the reporting requirements of 10CFR50.73. This report is being made under 50.73 (a)(2)(iv)(A). On June 5, 2006, at approximately 1844 Mountain Standard Time (MST), Palo Verde Nuclear Generating Station Unit 1 experienced an invalid 'A' train emergency diesel generator (EDG) start in the emergency mode. The EDG had been stopped at 1835 MST following completion of troubleshooting steps related to the balance of plant engineered safety features actuation system (BOP-ESFAS) sequencer. The start occurred as additional troubleshooting steps progressed. The related 4160 vac class 1E bus, PBA-S03, remained energized by off-site power during the event. The EDG started successfully and remained unloaded until it was stopped at 2014 MST. No other engineered safety feature (ESF) equipment in the 'A' train actuated. (a) The specific train(s) and svstem(s) that were actuated: Unit 1 'A' train EDG started in the emergency mode. (b) Whether each train actuation was complete or partial: Only EDG 'A' started as a single component and remained unloaded until it was stopped. No other ESF equipment actuated or was required. Essential spray pond pump 'A' was already running to provide EDG 'A' cooling water, from the previous EDG run. Bus PBA-S03 remained energized by off-site power throughout the duration of the event. (c) Whether or not the system started and functioned successfully: EDG 'A' started successfully and reached required speed, frequency, and voltage. Loading onto bus PBA-S03 was not required. Operations noted the EDG started with no anomalies. The exact cause of the invalid start was not known at the time of this report. The licensee notified the NRC Resident Inspector. | Emergency Diesel Generator Spray Pond | |
| ENS 41804 | 29 April 2005 07:43:00 | 10 CFR 50.73(a)(1), Submit an LER | Invalid System Actuation | This report is being made under 50.73 (a)(2)(iv)(A). On April 29, 2005, at approximately 0043 Mountain Standard Time, Palo Verde Nuclear Generating Station Unit 2 experienced an invalid 1/2 leg Engineered Safety Feature Actuation Signal (ESFAS) actuation (B train) when operations personnel prematurely implemented a tag out causing loss of vital power to the 'B' train ESFAS cabinet. The following alarms were received; Recirculation Actuation Signal B, Auxiliary Feedwater Actuation Signal-1B, Containment Spray Actuation Signal B, Main Steam Isolation Signal B, Containment Isolation Actuation Signal B, Safety Injection Actuation Signal B, Auxiliary Feedwater Actuation Signal-2B (all Leg 1-3), and Emergency Diesel Generator (EDG) Start Signal B. At the time of the event Unit 2 was in the 'B' train work window for refueling outage 2R12 and not all 'B' train equipment actuated - EDG B, Low Pressure Safety Injection B, Containment Spray B, and the B train Recirculation Actuation Signal sump valves were tagged out of service for maintenance. During the performance of the 'Inadvertent Plant Protection System - ESFAS Actuations' procedure, Operations personnel determined that all 'B' ESFAS equipment operated as expected considering the 'B' train equipment that was tagged out for maintenance. The licensee notified the NRC Resident Inspector. | Emergency Diesel Generator Auxiliary Feedwater Main Steam Containment Spray |