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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 57047 | 24 March 2024 23:34:00 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Valid Specified System Actuations of Unit 2 Train B Emergency Diesel Generator and Train B Auxiliary Feedwater | The following information was provided by the licensee via email: At 1634 MST on March 24, 2024, an engineered safety features (ESF) service transformer deenergized resulting in a loss of power to the Unit 2 Train B 4.16 kV Class 1E Bus. The Unit 2 Train B emergency diesel generator (EDG) automatically started and energized the Unit 2 Train B 4.16 kV Class 1E Bus. As a result of the loss of power on the Unit 2 Train B 4.16 kV Class 1E Bus and subsequent load sequencing after the Unit 2 Train B EDG started, the Unit 2 Train B auxiliary feedwater (AFW) pump automatically started as designed. The Train B AFW pump was not needed for steam generator level control and no auxiliary feedwater valves repositioned. The Train B AFW Pump did not supply feedwater to the steam generators. All systems operated as designed. Per the emergency plan, no classification was required due to the event. Units 1, 2, and 3 remain in Mode 1 at 100 percent power. The 4.16 kV Class 1E Buses in Units 1 and 3 were not affected by the deenergization of the ESF service transformer. The cause of the ESF service transformer being deenergized is under investigation. 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 emergency AC electrical power systems and auxiliary feedwater system. The NRC Resident Inspectors have been informed. | Steam Generator Feedwater Emergency Diesel Generator Auxiliary Feedwater | |
| ENS 56551 | 2 June 2023 11:05:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Automatic Reactor Trip | 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 (Emergency Notification System) or under the reporting requirements of 10 CFR 50.73. At 0405 MDT on June 2, 2023, the Unit 2 reactor automatically tripped on low steam generator water levels due to degraded flow from the A main feedwater pump. Steam generator water levels reached the automatic Auxiliary Feedwater Actuation System (AFAS) setpoint resulting in automatic AFAS-1 and AFAS-2 actuations and subsequent start of both class auxiliary feedwater pumps. Steam Generator water levels are being restored to normal band with the class 1E powered motor driven auxiliary feedwater pump. Following the reactor trip, all control element assemblies inserted fully into the core. No emergency plan classification was required per the Emergency Plan. Safety related buses remained powered from offsite power during the event and the offsite power grid is stable. Both emergency diesel generators automatically started on the AFAS-1 and AFAS-2 actuations as designed and are currently running unloaded. This event is being reported as a reactor protection system actuation in accordance with the reporting criteria of 10 CFR 50.72(b)(2)(iv)(B) and a specified system actuation in accordance with 10 CFR 50.72(b)(3)(iv)(A). The NRC Senior Resident Inspector has been informed. Unit 1 and 3 are in Mode 1 at 100 percent power. The following additional information was obtained from the licensee in accordance with Headquarters Operations Officers Report Guidance: Decay heat is being removed to main condenser via automatic steam bypass and B auxiliary feedwater pump. | Steam Generator Feedwater Reactor Protection System Emergency Diesel Generator Auxiliary Feedwater Main Condenser | |
| ENS 56459 | 9 April 2023 04:44:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Automatic Reactor Trip Due to Loss of Reactor Coolant Pumps | 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. At 2144 MST on April 8, 2023, the Unit 1 reactor automatically tripped due to the loss of reactor coolant pumps stemming from the loss of 13.8 kV power to the pumps. Prior to the reactor trip, the main turbine tripped due to a loss of hydraulic pressure. The main generator output breakers did not automatically open on the turbine trip as expected so the control room operators opened the breakers per procedural guidance. Once the breakers were opened, the two 13.8 kV electrical distribution buses failed to complete a fast bus transfer, which resulted in the loss of power to the reactor coolant pumps, initiating the reactor trip. The control room operators manually actuated a main steam isolation signal per procedure, requiring use of the atmospheric dump valves. Following the reactor trip, all control element assemblies inserted fully into the core. No automatic specified system actuation was required or occurred. No emergency plan classification was required per the Emergency Plan. Safety related buses remained powered from offsite power during the event and the offsite power grid is stable. Unit 1 is stable and in Mode 3. Decay heat is being removed by the atmospheric dump valves and the class 1E powered motor driven auxiliary feedwater pump. The loss of hydraulic pressure, the main generator output breakers failing to automatically open and the fast bus transfer not actuating are being investigated. This event is being reported as a reactor protection system actuation in accordance with the reporting criteria of 10 CFR 50.72(b)(2)(iv)(B). The NRC Senior Resident Inspector has been informed. Unit 2 is in a refueling outage in Mode 5 and Unit 3 is in Mode 1 at 100 percent power.
This update is being made to report the manual actuation of the B-train auxiliary feedwater pump and manual main steam isolation signal (MSIS) actuation affecting multiple main steam isolation valves (MSIVs) following the reactor trip. This event is being reported as a reactor protection system actuation in accordance with the reporting criteria of 10 CFR 50.72(b)(2)(iv)(B) and a specified system actuation in accordance with 10 CFR 50.72(b)(3)(iv)(A). The NRC Senior Resident Inspector has been informed of the update. Notified R4DO (Warnick)
This update is intended to clarify the initial description of the event that occurred on 4/8/2023. Prior to the reactor trip, the main turbine tripped due to a loss of hydraulic pressure. The main generator output breakers did not automatically open on the turbine trip. The control room operators manually opened the breakers per procedural guidance. Once the breakers were opened, the two 13.8 kV electrical distribution buses de-energized. A fast bus transfer did not occur per design, which resulted in the loss of power to the reactor coolant pumps, initiating the reactor trip. The control room operators manually actuated a main steam isolation signal per procedure, requiring use of the atmospheric dump valves. The NRC Senior Resident Inspector has been informed of the update. Notified R4DO (Gaddy) | Reactor Protection System Main Steam Isolation Valve Auxiliary Feedwater Main Turbine Main Steam | |
| ENS 56044 | 15 August 2022 00:02:00 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Valid Actuations of Unit 1 and Unit 3 Emergency Diesel Generators and Unit 1 Auxiliary Feedwater Pump | The following information was provided by the licensee via phone and email: At 1702 MST on August 14, 2022, a start-up transformer de-energized, resulting in a loss of power to the Unit 1 Train B 4.16 kV Class 1E Bus and the Unit 3 Train A 4.16 kV Class 1E Bus. The Unit 1 Train B Emergency Diesel Generator (EDG) and Unit 3 Train A EDG automatically started and energized their respective 4.16 kV Class 1E Buses. As a result of the loss of power on the Unit 1 Train B 4.16 kV Class 1E Bus, the B Auxiliary Feedwater Pump automatically started, as expected. The B Auxiliary Feedwater Pump was not needed for steam generator level control and no auxiliary feedwater valves repositioned. The B Auxiliary Feedwater Pump did not supply feedwater to the steam generators. 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 emergency AC electrical power systems and an auxiliary feedwater system. All systems operated as expected. Per the Emergency Plan, no classification was required due to the event. The 4.16 kV Class 1E Buses in Unit 2 were not affected by the de-energization of the start-up transformer since it was not aligned as normal power for Unit 2. Units 1, 2 and 3 remain in Mode 1 at 100% power. The cause of the start-up transformer being de-energized is under investigation. No plant transient occurred as a result of this failure. The NRC Resident Inspectors have been informed. | Steam Generator Feedwater Emergency Diesel Generator Auxiliary Feedwater | |
| ENS 55878 | 5 May 2022 02:55:00 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Valid Actuation of Unit 2 and Unit 3 Emergency Diesel Generators and Unit 3 Auxiliary Feedwater Pump | The following information was provided by the licensee via email: At 1955 on May 4, 2022, a start-up transformer de-energized, resulting in a loss of power to the Unit 2 Train A 4.16 kV Class 1E Bus and the Unit 3 Train B 4.16 kV Class 1E Bus. The Unit 2 Train A Emergency Diesel Generator (EDG) and Unit 3 Train B EDG automatically started and energized their respective 4.16 kV Class 1E Buses. As a result of the Loss of Power on the Unit 3 Train B 4.16 kV Class 1E Bus, the B Auxiliary Feedwater Pump automatically started, as expected. The B Auxiliary Feedwater Pump was not needed for steam generator level control and no auxiliary feedwater valves repositioned. The B Auxiliary Feedwater Pump did not supply feedwater to the steam generators. 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 emergency AC electrical power systems and an auxiliary feedwater system. | Steam Generator Feedwater Emergency Diesel Generator Auxiliary Feedwater | |
| ENS 55534 | 20 October 2021 21:46:00 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Valid Specified System Actuations of Unit 1 and Unit 3 Emergency Diesel Generators | At 1446 MST on October 20, 2021, a start-up transformer de-energized, resulting in a loss of power to the Unit 1 Train B 4.16 kV Class 1E Bus and the Unit 3 Train A 4.16 kV Class 1E Bus. The Unit 1 Train B Emergency Diesel Generator (EDG) and Unit 3 Train A EDG automatically started and energized their respective 4.16 kV Class 1E Buses. 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 emergency AC electrical power systems. All systems operated as expected. Per the Emergency Plan, no classification was required due to the event. Units 1 and 3 both remain in Mode 1 at 100 percent power. Unit 2 is currently in a refueling outage and defueled. The 4.16 kV Class 1E Buses in Unit 2 were not affected by the de-energization of the start-up transformer since it was not aligned as normal power for Unit 2. The cause of the start-up transformer being de-energized is under investigation. The NRC Resident Inspectors have been informed.
As a result of the Loss of Power on the Unit 1 Train B 4.16 kV Class 1E Bus, the B Auxiliary Feedwater Pump automatically started, as expected. The B Auxiliary Feedwater Pump was not needed for steam generator water level control and no auxiliary feedwater valves repositioned. The B Auxiliary Feedwater Pump did not supply feedwater to the steam generators. The NRC Resident Inspector will be notified. Notified R4DO (Taylor). | Steam Generator Feedwater Emergency Diesel Generator Auxiliary Feedwater | |
| ENS 54224 | 16 August 2019 15:21:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Automatic Reactor Trip Due to Turbine Trip | At 0821 MST, on August 16, 2019, a main turbine trip occurred followed by a loss of power to all reactor coolant pumps. The Palo Verde Nuclear Generating Station (PVNGS) Unit 2 control room then received reactor protection system alarms for low departure from nucleate boiling ratio and an automatic reactor trip occurred. Following the reactor trip, auxiliary feedwater was manually started to maintain steam generator levels. A Main Steam Isolation Signal was manually initiated as directed by the Emergency Operating Procedures. Unit 2 is currently stable in Mode 3. Prior to the reactor trip, Unit 2 was operating normally at 100 percent power. No major equipment was inoperable prior to the event that contributed to the event or challenged operator response. All control element assemblies fully inserted into the core and no emergency classification was required per the PVNGS Emergency Plan. The cause of the reactor trip is under investigation. The event did not result in any challenges to fission product barriers and there were no adverse safety consequences as a result of this event. The event did not adversely affect the safe operation of the plant or the health and safety of the public. The NRC Resident Inspector has been informed of the Unit 2 reactor trip. Decay heat is being removed via the atmospheric steam dump valves. Units 1 and 3 were unaffected by this event. | Steam Generator Reactor Protection System Auxiliary Feedwater Main Steam | |
| ENS 53477 | 27 June 2018 07:00:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Automatic Reactor Trip on Low Steam Generator Water Level | 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 (Emergency Notification System) or under the reporting requirements of 10 CFR 50.73. On June 27th, 2018 at approximately 2310 Mountain Standard Time (MST), in Palo Verde Unit 3, the #1 Steam Generator Economizer valve started closing. This caused Steam Generator #1 water level to decrease. Both Feed water pumps speed increased to raise Steam Generator level. At approximately 2311 (MST), the B Main Feed water pump tripped resulting in a Reactor Power Cutback. Steam Generator #1 level continued to decrease resulting in an Automatic Reactor Trip on Low Steam Generator #1 water level. All control rods inserted to shut down the Reactor to Mode 3 using Main Feed water and Steam Bypass. Post trip Steam Generator #1 level then increased and at approximately 2316 (MST) a Main Steam Isolation Signal (MSIS) was received on high Steam Generator level. The 'B' Auxiliary Feed water pump was manually started to maintain Steam Generator water levels and Steam Generator pressure was controlled using the Atmospheric Dump Valves (ADVs). Following the reactor trip, all CEAs (Control Element Assemblies) inserted fully into the core. All systems operated as expected. No emergency plan classification was required per the Emergency Plan. Safety related busses remained powered during the event from offsite power and the offsite power grid is stable. No major equipment was inoperable prior to the event that contributed to the event or complicated operator response. Unit 3 is stable and in Mode 3 feeding Steam Generators with Auxiliary Feed water Pump 'B'. The event did not result in any challenges to fission product barriers and there were no adverse safety consequences as a result of this event. The event did not adversely affect the safe operation of the plant or the health and safety of the public. The NRC Resident Inspector was informed of the Unit 3 reactor trip. Unit 1and Unit 2 were unaffected by the Unit 3 trip. | Steam Generator Auxiliary Feedwater Control Rod Main Steam | |
| ENS 46633 | 22 February 2011 03:01:00 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Auto Start and Load of Edgs on Units 1&3 Following Loss of Start-Up Transformer | On February 21, 2011, at approximately 2001 Mountain Standard Time (MST) a valid actuation of the Palo Verde Nuclear Generating Station Unit 1 Train 'B' Emergency Diesel Generator (EDG) and Unit 3 Train 'A' Emergency Diesel Generator occurred as a result of undervoltage on their respective safety buses. Both EDGs started and loaded as designed to energize the respective safety buses. No Emergency Plan declaration was made and none was required. The loss of power to the Unit 1 and Unit 3 safety buses was the result of protective relay actuations on the A-E-NANX02 Startup Transformer which deenergized the transformer and the Unit 1 13.8KV Intermediate Bus 1-E-NAN-S06 and the Unit 3 13.8KV Intermediate Bus 3-E-NAN-SOS. The affected intermediate buses provide power to the Unit 1 safety bus 1-E-PBB-S04 and the Unit 3 safety bus 3-E-PBA-S03 respectively. The Auxiliary Operators responded to inspect the Startup Transformer and affected buses and determined that there was no fire or smoke and no obvious equipment damage to transformers or associated 13.8 KV Buses. At the time of the actuations, the Unit 1 Control Room received alarms for Startup Transformer A-E-NAN-X02 'Phase, Winding Ground Differential Trip'. Subsequent inspection by the Electricians identified damage to the cabling from the 'Y' winding of A-E-NAN-X02 Start-Up Transformer to the alternate supply breaker on Unit 2 Intermediate Bus 2-E-NAN-SOS. Unit 1 and Unit 3 entered Technical Specification LCO 3.8.1, Condition 'A', for one (of two) required offsite circuits inoperable. Unit 2 currently has the 'B' EDG out of service for a planned maintenance outage and the Unit 2 safety buses and required offsite circuits were unaffected by the Startup Transformer trip. Unit 2 safety buses are being supplied by Startup Transformers A-E-NAN-X01 and A-E-NAN-X03. Both Unit 1 and Unit 3 were at approximately 100% power, at normal operating temperature and pressure prior to and following the EDG actuations. No other ESF actuations occurred and none were required. No major equipment was inoperable prior to the event that contributed to the event. The event did not result in any challenges to fission product barriers and there were no adverse safety consequences as a result of this event. The event did not adversely affect the safe operation of the plant or the health and safety of the public. The NRC Resident Inspector has been notified of the ESF actuations and this ENS notification. The licensee is working to restore normal electrical power to the affected safety buses from alternate available sources on Startup Transformers X01 and X03. The licensee stated that no significant non-safety related equipment has been deenergized. The licensee noted that while the cause of the damaged cabling noted in the above report is still under investigation, water intrusion repairs were recently conducted near the location where the current damages were found.
The licensee has restored offsite power to the affected safety buses. The Unit 3 safety bus was restored from Startup Transformer X03 at 0106 MST. The Unit 1 safety bus was restored from Startup Transformer X01 at 0153 MST. The EDGs are in the process of being shutdown and reset. The LCO for required offsite power source to the buses has been exited. R4DO (Gaddy) and NRR (Brown) notified. | Emergency Diesel Generator | 05000528/LER-2011-001 |
| ENS 46556 | 20 January 2011 01:41:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Reactor Trip Due to Main Feedwater Pump Trip | 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. On January 19, 2011, at approximately 1840 Mountain Standard Time (MST), Palo Verde Unit 3 received a Reactor Power Cutback (RPCB) due to the 'B' Main Feedwater Pump (MFP) tripping on low suction pressure in response to the 'A' MFP mini-flow valve failing open. Reactor power lowered to approximately 60% in response to the RPCB. Steam Generator levels continued to decrease and a Reactor Trip occurred on Low Steam Generator #1 level at 18:41. Unit 3 was at normal operating temperature and pressure prior to the trip. Following the automatic reactor trip all CEAs (Control Element Assemblies) inserted fully into the reactor core. No emergency classification was required per the Emergency Plan. An AFAS-2 (Auxiliary Feedwater Actuation Signal) occurred at 1844 on low Steam Generator #2 level. Safety related busses remained energized during and following the reactor trip. The Emergency Diesel Generators started in response to the AFAS-2 actuation but did not energize the class 4.16kV buses as they remained energized from off-site power. The offsite power grid is stable. No major equipment was inoperable prior to the event that contributed to the event. Unit 3 is stable at normal operating temperature and pressure in Mode 3 feeding the steam generators with Auxiliary Feedwater pump 'B'. The event did not result in any challenges to fission product barriers and there were no adverse safety consequences as a result of this event. The event did not adversely affect the safe operation of the plant or the health and safety of the public. The (NRC) Senior Resident Inspector was informed of the Unit 3 reactor trip. Unit 3 is in a normal post-trip electrical lineup. Decay heat is being removed via the turbine bypass valves to the main condenser. No safety valves on the secondary or primary side opened. | Steam Generator Feedwater Emergency Diesel Generator Auxiliary Feedwater Main Condenser | 05000530/LER-2011-001 |
| ENS 42938 | 27 October 2006 06:53:00 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Loss of Power to the Unit 1 and Unit 3 Train B Safety Buses with Emergency Diesel Generator 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 10CFR50.73. On October 26, 2006, at approximately 23:53 Mountain Standard Time (MST) a valid actuation of the Palo Verde Nuclear Generating Station Unit 1 Train B Emergency Diesel Generator (EDG) and Unit 3 Train B EDG occurred as a result of undervoltage on their respective safety buses. Both EDGs started and loaded as designed. No Emergency Plan declaration was made and none was required. The loss of power to the two safety buses was the result of an apparent spurious protective relay actuation of Startup Transformer X01 output breakers to Unit 1 NAN-S06 and Unit 3 NAN-S06 busses. Unit 1 NAN-S06 bus was being supplied by its Alternate breaker (1ENANS06F) and Unit 3 NAN-S06 was being supplied by its Normal breaker (3ENANS06C). Prior to the event, maintenance personnel were restoring potential Transformer (PT) fuses at Unit 1 breaker 1ENANS06, Cubicle G. Preliminary information is that the two simultaneous LOP conditions occurred when the outer doors were closed on 1ENANS06, Cubicle G. This condition apparently caused the output breakers of Startup Transformer X01 to open. There was no electrical fault or damage to any electrical components. Both Units 1 and 3 entered Technical Specification LCO 3.8.1 Condition A for one (of two) required offsite circuits inoperable. (The licensee is) proceeding with restoration of Normal offsite power to each safety bus in Units 1 and 3. Once offsite power is restored, the LCOs will be exited and the Unit 1 and 3 train B EDGs will be returned to standby. Both Unit 1 and Unit 3 were at approximately 100% power, at normal operating temperature and pressure prior to and following the EDG actuations. Unit 2 was defueled and was not impacted by the electrical disturbance. No other ESF actuations occurred and none were required. No major equipment was inoperable prior to the event that contributed to the event. The event did not result in any challenges to fission product barriers and there were no adverse safety consequences as a result of this event. The event did not adversely affect the safe operation of the plant or the health and safety of the public. The licensee notified the NRC Resident Inspector. | Emergency Diesel Generator | |
| ENS 42609 | 30 May 2006 15:13:00 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Loss of Power to Train "a" 4 Kv Safety Bus | 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 CFR50.73. On May 30, 2006, at approximately 08:13 Mountain Standard Time, Palo Verde Nuclear Generating Station, Unit 1 experienced a Loss Of Power (LOP) to Train 'A' (PBAS03) 4 KV safety bus. At the time of the LOP the 'A' Emergency Diesel Generator (EDG) had just been manually removed from the PBAS03 bus following a maintenance surveillance run and was still operating in a post run cool down mode. The PBAS03 bus was still powered from the off site power source and was at rated voltage. An invalid Load Shed signal was received from the Train 'A' Load Sequencer, which opened the normal off site supply breaker to PBAS03 bus, and stripped all of the Ioads off the bus. Next, a valid LOP signal developed, since the PBAS03 bus was de-energized. The EDG 'A' received a valid emergency run mode signal and returned to rated frequency and voltage; however its output breaker did not reclose on bus PBAS03. This reclosure was blocked by the Train 'A' Load Sequencer which had 'stalled' and was not able to provide the permissive for the DG output breaker to close. The failure of the load sequencer is currently under investigation by the PVNGS engineering department. Offsite power was available to both safety buses throughout the event; however the invalid Load Shed signal blocked immediate restoration of off site power to the Train 'A' bus. The other (Train 'B') safety bus is being supplied by offsite power; however Train 'B' EDG is not available due to planned outage related maintenance. The offsite electrical grid is stable. Efforts are currently in progress to restore the Train 'B' DG for a redundant power source. In addition, efforts are in progress to clear the Load Shed signal off the Train 'A' bus to allow restoration of power from the off site power source. Palo Verde Unit 1 is shutdown and Defueled in a mid-cycle repair outage. The entire core is off loaded to the Spent Fuel Pool and is currently being maintained with inventory and cooling by the Train 'B' components powered from off site power. No other ESF actuations occurred and none were required. The event did not result in the release of radioactivity to the environment and did not adversely affect the safe operation of the plant or health and safety of the public. At 13:04 MST the 'B' EDG was restored and operable. The licensee also indicated that Train 'A' offsite power is expected to be restored within about 1 hour, or 16:20 EDT. The licensee notified the NRC Resident Inspector. | Emergency Diesel Generator | 05000528/LER-2006-003 |
| ENS 42559 | 6 May 2006 23:35:00 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Valid Actuation of Emergency Diesel Generator Due to Low Voltage Condition | 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. On May 6, 2006, at approximately 16:35 US Mountain Standard Time (MST) a valid actuation of the Palo Verde Nuclear Generating Station Unit 3 Train 'A' Emergency Diesel Generator (EDG) occurred as a result of an undervoltage condition on its respective safety bus (PBA-S03). EDG 'A' started and loaded as designed to energize PBA-S03. The loss of power to the safety bus occurred during Gas Turbine Generator testing. GTG number 1 was supplying safety bus PBA-S03 at a low voltage when supply breaker PBA-S03L opened unexpectedly. This resulted in the deenergization of the safety bus PBA-S03. The emergency diesel generator started and all required related safety equipment started as expected. No Emergency Plan declaration was made and none was required. Unit 3 was in mode 5 at 50 psia and140 degrees F. Shutdown Cooling Train B was OPERABLE and in service. No other ESF actuations occurred and none were required. The event did not result in any challenges to fission product barriers and there were no adverse safety consequences as a result of this event. The event did not adversely affect the safe operation of the plant or the health and safety of the public. The NRC Resident Inspector has been notified of the ESF actuation and this ENS notification. | Emergency Diesel Generator Shutdown Cooling | 05000530/LER-2006-004 |
| ENS 42468 | 3 April 2006 03:54:00 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Emergency Diesel Trip During Testing | 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. On April 2, 2006 at approximately 20:54 Mountain Standard Time, Palo Verde Nuclear Generating Station Unit 3 experienced a valid Loss of Power (LOP) actuation on the Train 'B' 4.16 kV safety bus. The event occurred due to personnel error during performance of surveillance test 73ST-9DG02 (Class 1 E Diesel Generator and Integrated Safeguards Test Train B). EDG 'B' had been started In Emergency Mode per the surveillance test by opening the normal supply breaker to the associated 4.16 kV bus and initiating simulated Safety Injection Actuation System (SIAS) and Containment Isolation Actuation System (CIAS) signals. A subsequent portion of the surveillance test was in progress which demonstrates that the EDG 'test mode' trips are bypassed with the EDG operating in Emergency Mode. The step being performed was intended to simulate an Overcurrent (test mode) trip by installing a jumper at the Overcurrent relay. However the jumper was inadvertently installed at the Differential Current relay, which generated an 'Emergency Mode' trip of EDG 'B'. This resulted in the deenergization of the 4.16 kV bus. The operations staff entered Abnormal Operating Procedure (AOP) 40AO-9ZZ12 (Degraded Electrical) and reset EDG 'B'. Upon reset at approximately 21:26 MST, EDG 'B' automatically started in response to a valid Loss of Power (LOP) signal from the deenergized 4.16 kV bus. The EDG 'B' output breaker automatically closed to restore power to the Train 'B' 4.16 kV and equipment sequenced onto the 4.16 kV bus. Due to the loss of power on the Train 'B' 4.16 kV bus, the Train 'B' Control Room Essential Filtration System (CREFS) and Control Room Emergency Air Temperature Control System (CREATCS) were rendered inoperable and LCOs 3.7.11 Condition 'A' and 3.7.12 Condition 'A' were entered. Operability of Train 'B' CREFS and CREATCS was restored when the Train 'B' 4.16 kV bus was reenergized and these LCO Conditions were exited. Offsite power remained available to the Train 'A' 4.16 kV bus and EDG 'A' remained operable throughout the event. Shutdown Cooling was unaffected since it was being provided by the Train 'A' safety train, which was supplied by offsite power. The offsite electrical grid is stable. Palo Verde Unit 3 Is shutdown and in Mode 5 for its 12th refueling outage. No other ESF actuations occurred and none were required. There were no structures, systems, or components that were inoperable at the time of discovery that contributed to this condition. The event did not result in the release of radioactivity to the environment and did not adversely affect the safe operation of the plant or health and safety of the public. The NRC Resident Inspector has been notified of the ESF actuation and this ENS notification. The site performed a work stand down to discuss this event and prevent recurrence. | Shutdown Cooling | |
| ENS 41379 | 7 February 2005 05:19:00 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Emergency Diesel Start Due to Bus Deenergization | The following information was provided by the licensee via facsimile: 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. On February 6, 2005, at approximately 22:19 Mountain Standard Time (MST) a valid actuation of the Palo Verde Nuclear Generating Station Unit 1 Train `B' Emergency Diesel Generator (EDG) occurred as a result of undervoltage on its respective safety bus (PBB-S04). EDG 'B' started and loaded as designed to energize PBB-S04. The loss of power to the safety bus was the result of a fault associated with 13.8KV breaker NAN-SO6J which caused breakers NAN-SO6H (normal power supply), NAN-S06K (alternate power supply), and NAN-SO6J (EOF & TSC Bldg power supply) to all trip open on Overcurrent. This action resulted in the deenergization of NAN-S06, NAN-S04, and PBB-S04. The PVNGS Fire Department and Auxiliary Operators responded to a report of smoke and upon arrival found no fire. The Fire Department verified the fire was completely extinguished and there were no extensions (secondary fires). Unit 1 entered Technical Specification LCO 3.8.1, Condition 'A', for one (of two) required offsite circuits inoperable. Various other Technical Specifications LCO's were momentarily entered and exited for PBB-S04 being deenergized for approximately 7 seconds. No Emergency Plan declaration was made and none was required. Unit 1 was at approximately 100% power, at normal operating temperature and pressure prior to and following the EDG actuation. No other ESF actuations occurred and none were required. No major equipment was inoperable prior to the event that contributed to the event. The event did not result in any challenges to fission product barriers and there were no adverse safety consequences as a result of this event. The event did not adversely affect the safe operation of the plant or the health and safety of the public. The NRC Resident Inspector has been notified of the ESF actuation and this ENS notification. The B EDG is providing power to PBB-S04. Due to loss of power to the TSC, the TSC Diesel started and is providing power to the TSC. The Backup EOF located in Buckeye, AZ will be used in the case of an emergency event. There were no reported injuries. There was damage to the NAN-S06J breaker and it has been isolated. The event has been entered into the site's corrective action program for determining the cause of the breaker trip and damage. This event has no effect on the operation of the other site units. | Emergency Diesel Generator | 05000528/LER-2005-001 |
| ENS 41304 | 31 December 2004 17:42:00 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Plant Had Auto Start and Loading of Two Emergency Diesel Gererators | On December 31, 2004, at approximately 10:42 Mountain Standard Time (MST) a valid actuation of the Palo Verde Nuclear Generating Station Unit 2 Train A Emergency Diesel Generator (EDG) and Unit 3 Train B EDG occurred as a result of undervoltage on their respective safety buses. Both EDGs started and loaded as designed. The loss of power to the two safety buses was the result of the deenergization of Startup Transformer X01 when Westwing transmission line #2, one of seven 525 kV transmission lines at the Palo Verde switchyard, relayed off. Prior to the event, maintenance and testing were in progress on Westwing Line #1. The apparent cause of the event was inadvertent operation of an adjacent Line #2 protective relay while testing Line #1. Both Units 2 and 3 entered Technical Specification LCO 3.8.1 Condition A for one (of two) required offsite circuits inoperable. Normal offsite power was restored to each safety bus in Units 2 and 3 (at 11:45 MST), the LCO exited and the Unit 3 EDG returned to standby. During shutdown of the Unit 2 A EDG following successful loading of the Safety bus, the EDG was declared inoperable due to a Jacket Water leak and LCO 3.8.1 Condition B was entered. No Emergency Plan declaration was made and none was required. Both units were at approximately 100% power, at normal operating temperature and pressure prior to and following the EDG actuations. No other ESF actuations occurred and none were required. No major equipment was inoperable prior to the event that contributed to the event. The event did not result in any challenges to fission product barriers and there were no adverse safety consequences as a result of this event. The event did not adversely affect the safe operation of the plant or the health and safety of the public. The NRC Resident Inspector has been notified of the ESF actuation and this ENS notification. | Emergency Diesel Generator | 05000529/LER-2004-003 |
| ENS 40816 | 14 June 2004 14:44:00 | 10 CFR 50.72(b)(2)(xi), Notification to Government Agency or News Release 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(a)(1)(i), Emergency Class Declaration 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Unusual Event Due to Reactor Trip Due to Loss of Off Site Power | On June 14, 2004, at approximately 07:44 Mountain Standard Time (MST) all three units at the Palo Verde Nuclear Generating Station experienced automatic reactor trips coincident with a grid disturbance and loss of offsite power in the Palo Verde Switchyard. Unit 3 declared a NOTIFICATION OF UNUSUAL EVENT at 07:53 MST due to a loss of offsite power to essential buses for greater than 15 minutes. The NOTIFICATION OF UNUSUAL EVENT was terminated at 12:07 MST. Unit 3 received an automatic Main Steam Isolation System ESF actuation. Due to the loss of offsite power, the Emergency Plan Technical Support Center (TSC) was unavailable. The Unit 2 Satellite TSC was to be staffed by the Emergency Response Organization in response to the loss of assessment capability. Power to the TSC has since been restored. The unit was at normal operating temperature and pressure prior to the trip. All CEAs inserted fully into the reactor cores. All Emergency Diesel Generators (EDGs) (2 per unit) associated with the unit started as expected in response to the loss of offsite power to their safety buses. The offsite power grid had several perturbations for approximately one hour following the event but has been stable since. LCO 3.8.1, AC Sources - Operating, was entered as a result of this event. Heat removal is to atmosphere via atmospheric dump valves in natural circulation. Main steam safety valves may have lifted for a brief time. Restoration of forced reactor coolant circulation is pending assurance that the offsite power grid can reliably support the load. No major equipment was inoperable prior to the event that contributed to the event. The Unit is stable at normal operating temperature and pressure in Mode 3. The event did not result in any challenges to fission product barriers and there were no adverse safety consequences as a result of this event. The event did not adversely affect the safe operation of the plant NRC Resident Inspector was notified. FBI Jeff Muller and Mr. Rosales (Mexican National Commission of Nuclear Safety and Safeguards (CNSNS)) were notified.
Notified Reg 4 RDO (Graves), NRR (Bateman), DHS (Lee), FEMA (Canupp), DOE (Sal Moroni), EPA (Stalcup), EPA (Crews), HSS (Davidson), and Mexico (Rosales) Note: see related events 40815 , 40814 and 40818 | Emergency Diesel Generator Main Steam Safety Valve Main Steam | |
| ENS 40815 | 14 June 2004 14:44:00 | 10 CFR 50.72(b)(2)(xi), Notification to Government Agency or News Release 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(a)(1)(i), Emergency Class Declaration 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Unusual Event Declared Due to Reactor Trip Due to Loss of Off Site Power | On June 14, 2004, at approximately 07:44 Mountain Standard Time (MST) all three units at the Palo Verde Nuclear Generating Station experienced automatic reactor trips coincident with a grid disturbance and loss of offsite power in the Palo Verde Switchyard. Unit 1 declared a NOTIFICATION OF UNUSUAL EVENT at 07:53 MST due to a loss of offsite power to essential buses for greater than 15 minutes. The NOTIFICATION OF UNUSUAL EVENT was terminated at 12:07 MST. Unit 1 manually initiated a Main Steam Isolation System ESF actuation by procedure. Due to the loss of offsite power, the Emergency Plan Technical Support Center (TSC) was unavailable. The Unit 2 Satellite TSC was to be staffed by the Emergency Response Organization in response to the loss of assessment capability. Power to the TSC has since been restored. The unit was at normal operating temperature and pressure prior to the trip. All CEAs inserted fully into the reactor cores. All Emergency Diesel Generators (EDGs) (2 per unit) associated with the unit started as expected in response to the loss of offsite power to their safety buses. The offsite power grid had several perturbations for approximately one hour following the event but has been stable since. LCO 3.8.1, AC Sources - Operating, was entered as a result of this event. Heat removal is to atmosphere via atmospheric dump valves in natural circulation. Main steam safety valves may have lifted for a brief time. Restoration of forced reactor coolant circulation is pending assurance that the offsite power grid can reliably support the load. No major equipment was inoperable prior to the event that contributed to the event. The Unit is stable at normal operating temperature and pressure in Mode 3. The event did not result in any challenges to fission product barriers and there were no adverse safety consequences as a result of this event. The event did not adversely affect the safe operation of the plant NRC Resident Inspector was notified. FBI Jeff Muller and Mr. Rosales (Mexican National Commission of Nuclear Safety and Safeguards (CNSNS)) were notified.
Notified Reg 4 RDO (Graves), NRR (Bateman), DHS (Lee), FEMA (Canupp), DOE (Sal Moroni), EPA (Stalcup), EPA (Crews), HSS (Davidson), and Mexico (Rosales) Note: see related events # 40814, 40816 and 40818 | Emergency Diesel Generator Main Steam Safety Valve Main Steam | |
| ENS 40814 | 14 June 2004 14:44:00 | 10 CFR 50.72(b)(2)(xi), Notification to Government Agency or News Release 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(a)(1)(i), Emergency Class Declaration 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Alert Declared - Reactor Trip Due to Loss of Off Site Power | On June 14, 2004, at approximately 07:44 Mountain Standard Time (MST) all three units at the Palo Verde Nuclear Generating Station experienced automatic reactor trips coincident with a grid disturbance and loss of offsite power in the Palo Verde Switchyard. Unit 2 declared an ALERT Emergency Plan classification at approximately 07:54 due to a loss of AC power to essential buses reduced to a single power source for greater than 15 minutes such that any additional single failure would result in a station blackout. Subsequently, at 09:51 Unit 2 downgraded the Emergency Plan classification to a NOTIFICATION OF UNUSUAL EVENT when AC power was restored from a single essential bus to both essential buses. Units 1 and 3 declared a NOTIFICATION OF UNUSUAL EVENT at 07:53 MST due to a loss of offsite power to essential buses for greater than 15 minutes. The NOTIFICATION OF UNUSUAL EVENT was terminated for all 3 units at 12:07 MST. Unit 1 and 2 manually initiated a Main Steam Isolation System ESF actuation by procedure. Unit 3 received an automatic Main Steam Isolation System ESF actuation. Due to the loss of offsite power, the Emergency Plan Technical Support Center (TSC) was unavailable. The Unit 2 Satellite TSC was to be staffed by the Emergency Response Organization in response to the loss of assessment capability. Power to the TSC has since been restored. The Emergency Plan ALERT declaration includes staffing of the Joint Emergency New Center to address expected media interest. All three units were at normal operating temperature and pressure prior to the trip. All CEAs inserted fully into the reactor cores. All Emergency Diesel Generators (EDGs) (2 per unit) associated with each of the 3 units started as expected in response to the loss of offsite power to their safety buses. Unit 2's train "A" EDG started, but did not indicate volts or amps and was manually shutdown. The offsite power grid had several perturbations for approximately one hour following the event but has been stable since. LCO 3.8.1, AC Sources - Operating, was entered in each unit as a result of this event. Heat removal is to atmosphere via atmospheric dump valves in natural circulation. Main steam safety valves may have lifted for a brief time. Restoration of forced reactor coolant circulation is pending assurance that the offsite power grid can reliably support the load. No major equipment was inoperable prior to the event that contributed to the event. All 3 units are stable at normal operating temperature and pressure in Mode 3. The event did not result in any challenges to fission product barriers and there were no adverse safety consequences as a result of this event. The event did not adversely affect the safe operation of the plant NRC Resident Inspector was notified. FBI Jeff Muller and Mr. Rosales (Mexican National Commission of Nuclear Safety and Safeguards (CNSNS)) were notified.
Notified Reg 4 RDO (Graves), NRR (Bateman), DHS (Lee), FEMA (Canupp), DOE (Sal Moroni), EPA (Stalcup), EPA (Crews), HSS (Davidson), and Mexico (Rosales) NOTE: See events 40815, 40816 and 40818 | Emergency Diesel Generator Main Steam Safety Valve Main Steam | |
| ENS 40349 | 22 November 2003 05:53:00 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation | Valid Actuation of the "a" Emergency Diesel Generator During Testing | 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. On November 21, 2003, at approximately 22:53 Mountain Standard Time, Palo Verde Nuclear Generating Station Unit 2 experienced a valid actuation (start) of the 'A' Emergency Diesel Generator (EDG). Unit 2 had been performing testing of the capability to parallel the EDG 'A' with the Gas Turbine Generator #1 (alternate AC Power source for station blackout.) The Train 'A' 4.16 Kv bus had been successfully transferred to the EDG and loads carried by the EDG for approximately 5 minutes. When the EDG speed control was taken from 'droop' mode (load sharing) to 'isochronous' mode (fixed frequency,) the EDG output breaker tripped opened, resulting in a valid Loss of Power (LOP) signal based on undervoltage on the Train 'A' bus. The EDG resupplied the bus in the LOP mode. Offsite power remained available to both safety buses throughout the event. The other (Train 'B') safety bus is being supplied by offsite power and its EDG is operable. The offsite electrical grid is stable. Palo Verde Unit 2 is shutdown and defueled in its 11th refueling outage. No other ESF actuations occurred and none were required. There were no structures, systems, or components that were inoperable at the time of discovery that contributed to this condition. There were no failures that rendered a train of a safety system inoperable and no failures of components with multiple functions were involved. The event did not result in the release of radioactivity to the environment and did not adversely affect the safe operation of the plant or health and safety of the public. Troubleshooting will be conducted to determine the cause of the EDG output breaker opening. The licensee has notified the NRC Resident Inspector. | Emergency Diesel Generator | 05000529/LER-2003-002 |