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	Start date	Reporting criterion	Title	Event description	System	LER
ENS 57066	4 April 2024 23:18:00	10 CFR 50.72(a)(1)(i), Emergency Class Declaration	Notification of Unusual Event Due to Fire Alarm in the Vital Area	The following information was obtained from the licensee in accordance with Headquarters Operations Officers Report Guidance: On 4/4/2024 at 1618 MST, a Notification of Unusual Event, HU4.2 was declared based on an unverified fire alarm in the containment building greater than 15 minutes. Palo Verde, Unit 3 was operating in Mode 1 at 91 percent power due to end of cycle coast down to a refueling outage. There is no known plant damage at this time. Offsite assistance cannot enter the containment building, therefore, offsite assistance was not requested. The plant is stable in Mode 1. The licensee notified State and local authorities and the NRC Senior Resident Inspector. Notified DHS SWO, FEMA Operations Center, CISA Central, FEMA NWC (email), CWMD Watch Desk (email), DHS NRCC THD Desk (email), and DHS Nuclear SSA (email). * * UPDATE ON 04/04/24 AT 2313 EDT FROM YOLANDA GOOD TO IAN HOWARD * * * The following information was obtained from the licensee in accordance with Headquarters Operations Officers Report Guidance: At 2013 MST, Palo Verde Unit 3 terminated the notification of unusual event. The basis for termination was that a containment entry was performed. All levels were inspected, and no fires were found. The NRC Resident Inspector has been notified. Notified R4DO (Deese), IR-MOC (Crouch), NRR-EO (Felts), DHS SWO, FEMA Operations Center, CISA Central, FEMA NWC (email), CWMD Watch Desk (email), DHS NRCC THD Desk (email), and DHS Nuclear SSA (email).
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. * * UPDATE ON 4/9/23 AT 0835 EDT FROM TANNER GOODMAN TO ADAM KOZIOL * * * 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) * * UPDATE ON 5/3/23 AT 1945 EDT FROM LORRAINE WEAVER TO JOHN RUSSELL * * * 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 55626	6 December 2021 19:03:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation	Unit 3 Automatic 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. At 1203 MST on December 6, 2021, the Unit 3 reactor automatically tripped on low departure from nucleate boiling ratio. A part-strength control element assembly was being moved at the time of the trip. Unit 3 is stable and in Mode 3. In response to the reactor trip, all control element assemblies inserted fully into the core. Safety-related electrical power remains energized from off-site power sources and reactor coolant pumps continue to provide forced circulation through the reactor. Decay heat is being removed by the steam bypass control system and main feedwater system. Required systems operated as expected. No emergency classification was required per the Emergency Plan. The NRC Senior Resident Inspector has been informed. Units 1 and 2 were unaffected by this transient.	Feedwater Steam Bypass Control System
ENS 55265	19 May 2021 10:15:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation	Automatic Reactor Trip Due to High Pressurizer Pressure	At 0315 MST on May 19, 2021, Unit 2 reactor automatically tripped during testing of the Plant Protection System. The Reactor Protection System actuated to trip the reactor on High Pressurizer Pressure, although no plant protection setpoints were exceeded. Main Steam Isolation Signal (MSIS), Safety Injection Actuation Signal (SIAS), and Containment Isolation Actuation Signal (CIAS) were received. No injection of water into the Reactor Coolant System occurred. Auxiliary Feedwater Actuation Signals (AFAS) 1 and 2 actuated on low Steam Generator water level post trip as designed. This event is being reported as a reactor protection system and a specified system actuation in accordance with the reporting criteria of 10 CFR 50.72(b)(2)(iv)(B) and 10 CFR 50.72(b)(3)(iv)(A). Following the reactor trip, all (Control Element Assemblies) CEAs 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. Unit 2 is stable and in Mode 3. Steam Generator heat removal is via the class 1 E powered motor driven auxiliary feedwater pump and Atmospheric Dump Valves. The NRC Senior Resident Inspector has been informed. * * UPDATE ON 5/19/21 AT 1351 EDT FROM JASON HILL TO BRIAN P. SMITH * * * The Unit 2 reactor tripped because of actual High Pressurizer Pressure that occurred as a result of a Main Steam Isolation Signal actuation. At 0337 MST, both trains of Low Pressure and High Pressure Safety Injection (LPSI and HPSI) were made inoperable when the injection valves were overridden and closed in accordance with station procedures. At 0346 MST, in accordance with station procedures, both trains of Containment Spray, LPSI, and HPSI pumps were overridden and stopped, rendering Containment Spray inoperable as well. This represents a condition that would have prevented the fulfillment of a safety function required to mitigate the consequences of an accident per 10 CFR 50.72(b)(3)(v)(D). Additionally, at the time of the Safety Injection Actuation Signal (0315 MST), both trains of Emergency Diesel Generators actuated as required and both 4160 VAC busses remained energized from off-site power. The NRC Senior Resident Inspector has been informed. Notified R4DO (Young) * * UPDATE ON 7/02/21 AT 1943 EDT FROM YOLANDA GOOD TO JEFFREY WHITED * * * The inoperability of both trains of Low Pressure and High Pressure Safety Injection (LPSI and HPSI) and both trains of Containment Spray (CS) following the Unit 2 reactor trip has been determined to be an unanalyzed condition per 10 CFR 50.72(b)(3)(ii)(B). Additionally, inoperability of both trains of HPSI resulted in a reportable condition that could prevent fulfillment of its credited safety function to maintain the reactor in a safe shutdown condition per 10 CFR 50. 72(b)(3)(v)(A). The additional reporting criteria were discovered during review of the event and corresponding safety analyses. The NRC Senior Resident Inspector has been informed. Notified R4DO (Werner)	Steam Generator Reactor Coolant System Reactor Protection System Emergency Diesel Generator Auxiliary Feedwater Main Steam Containment Spray
ENS 55114	26 February 2021 17:33:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation	Reactor Trip Due to Loss of Two Reactor Coolant Pumps	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 1033 MST on February 26, 2021 the Unit 2 reactor automatically tripped due to a loss of two Reactor Coolant Pumps stemming from a loss of a 13.8 kV non-class bus during maintenance. Following the reactor trip, all Control Element Assemblies inserted fully into the core. All systems operated as expected. No emergency plan classification was required per the Emergency Plan. Unit 2 is stable and in Mode 3. Decay heat is being removed by the Steam Bypass Control System and Main Feedwater System. The NRC Senior Resident Inspector has been informed. Unit 1 and Unit 3 were not affected by the Unit 2 reactor trip.	Feedwater Steam Bypass Control System
ENS 54560	4 March 2020 03:50:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation	Reactor Trip Due to Low Steam Generator Level	At 2050 MST on March 3, 2020, Unit 2 reactor automatically tripped on Low Steam Generator (SG) Number 1 level signal from the Reactor Protection System. The low SG level occurred as the result of a trip of both Main Feedwater Pumps, which tripped during restoration of power to the Main Feedwater Pump Lube oil control panel. Auxiliary Feedwater (AFAS-1 and AFAS-2) actuated due to low SG levels in both SG post reactor trip as designed. This event is being reported as a reactor protection system and a specified system actuation in accordance with the reporting criteria of 10 CFR 50.72(b)(2)(iv)(B) and 10 CFR 50.72(b)(3)(iv)(A). Following the reactor trip, all (control element assemblies) CEAs 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. Unit 2 is stable and in Mode 3. Steam Generators are being fed via the class 1E powered motor driven auxiliary feedwater pump. The NRC Senior Resident Inspector has been informed. Units 1 and 3 were unaffected by the trip and remain at 100 percent power. * * UPDATE FROM ALLAN BRIEFE TO DONALD NORWOOD AT 1231 EDT ON 5/4/2020 * * * The event reported on March 4, 2020 (EN 54560) also included actuations of the Emergency Diesel Generators in response to the AFAS-1 and AFAS-2 actuations. The Class 4.16kV buses remained energized from off-site power. The NRC Senior Resident Inspector has been informed. Notified R4DO (Drake).	Steam Generator Feedwater Reactor Protection System 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 53424	23 May 2018 18:28:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation	Automatic Reactor Trip on Low Departure from Nucleate Boiling Ratio	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 23, 2018, at approximately 1128 Mountain Standard Time (MST), the Palo Verde Nuclear Generating Station (PVNGS) Unit 2 control room received reactor protection system alarms for low departure from nucleate boiling ratio and an automatic reactor trip occurred. Prior to the reactor trip, Unit 2 was operating normally at 100 percent power. Plant operators entered the reactor trip procedures and diagnosed an uncomplicated reactor trip. All CEAs (control element assemblies) fully inserted into the core. No emergency classification was required per the PVNGS Emergency Plan. The Unit 2 safety-related electrical buses remained energized from normal offsite power during the event. There was no impact to the required circuits between the offsite transmission network and the onsite Class 1E Electrical Power Distribution System; 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 2 is currently stable in Mode 3 with the reactor coolant system at normal operating temperature and pressure. 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 is being removed via steam dumps to condenser. Units 1 and 3 at Palo Verde were unaffected by the transient and continue to operate at 100 percent power.	Reactor Coolant System Reactor Protection System
ENS 53215	16 February 2018 04:53:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(b)(3)(xiii), Loss of Emergency Preparedness	Automatic Reactor Trip Due to Low Departure from Nucleate Boiling 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. On February 15, 2018, at approximately 2153 Mountain Standard Time (MST), the Palo Verde Nuclear Generating Station (PVNGS) Unit 1 Control Room received Reactor Protection System alarms for Low Departure from Nucleate Boiling Ratio and an automatic reactor trip occurred. Prior to the reactor trip, Unit 1 was operating normally at 100 percent power. Plant operators entered the emergency operations procedures and diagnosed an uncomplicated reactor trip but noted that Reactor Coolant Pumps 1B and 2B were not running due to a loss of power. All CEAs (Control Element Assemblies) fully inserted into the core. Following the reactor trip, all nuclear instruments responded normally. No emergency classification was required per the PVGS Emergency Plan. The PVGS Unit 1 safety related electrical busses remained energized from normal offsite power during the event. The Unit 1 'B' Diesel Generator is currently removed from service for maintenance. Due to ongoing planned maintenance on NAN-X02, Startup Transformer 2, fast bus transfer for NAN-S02 (from NAN-S04) was blocked. This resulted in a loss of offsite power to NAN-S02 and NBN-S02. The offsite power grid is stable. Unit 1 is currently stable in Mode 3 with the reactor coolant system at normal operating temperature and pressure. 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 1 reactor trip. * * UPDATE ON 2/16/18 AT 1640 EST FROM DAVID HECKMAN TO DONG PARK * * * Unit 1 is stable in Mode 3 following an uncomplicated trip. Offsite power has been restored to non-safety related electrical busses. Troubleshooting continues to determine the cause of the event. During performance of the alarm response procedure, it was identified that the seismic monitoring (SM) system had been in alarm since the reactor trip and was incapable of performing its emergency plan function. Pursuant to 10 CFR 50.72(b)(3)(xiii), this condition constitutes a major loss of emergency assessment capability. Compensatory measures have been implemented in accordance with PVNGS procedures to provide alternative methods for HU2.1 event classification with the SM system out of service. Maintenance is currently in progress to restore SM system functionality. The licensee notified the NRC Resident Inspector. Notified R4DO (Werner). * * UPDATE AT 1537 EDT ON 03/30/18 FROM LORRAINE WEAVER TO JEFF HERRERA * * * Station staff completed an evaluation of event EN #53215 reported on February 15, 2018, and determined that the seismic monitoring system remained capable of assessing a seismic event following the reactor trip. Therefore, a major loss of emergency assessment capability pursuant to 10 CFR 50.72(b)(3)(xiii) did not occur as reported in the update on February 16, 2018. The NRC Resident Inspectors have been notified. Notified the R4DO (Gaddy).	Reactor Coolant System Reactor Protection System
ENS 52435	15 December 2016 11:10:00	10 CFR 50.72(a)(1)(i), Emergency Class Declaration	Alert Declared - Catastrophic Failure of an 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. During a scheduled surveillance test run of the PVNGS (Palo Verde Nuclear Generating Station) Unit 3 'B' Train Emergency Diesel Generator, there was a catastrophic failure of a piston to include crankcase damage and diesel trip. The Emergency Plan has been entered and an ALERT was declared at 0410 (MST) on 12/15/16 based on an explosion resulting in visible damage to a safety system required for safe shutdown. The cause of the failure is unknown at this time. PVNGS Fire Department responded and no fire was observed. Unit 3 remains on line at 100% power. No other safety functions are impacted. No personnel injuries occurred. The unit is in a ten day technical specification on an emergency diesel generator being inoperable. The licensee notified the NRC Resident Inspector. Notified DHS, DOE, EPA, FEMA, NICC, USDA, HHS, FDA, NSSA, Mexico, and OIP (Skeen). * * UPDATE AT 0947 EST ON 12/15/2016 FROM MICHAEL GOODRICH TO MARK ABRAMOVITZ * * * This serves as the notification of the termination of Alert HA2.1 declared at 0410 MST at Palo Verde Nuclear Generation Station. The event terminated at 0636 MST. The licensee will notify the NRC Resident Inspector. Notified R4DO (Keller), NRR EO (Miller), IRD (Stapleton), DHS, DOE, EPA, FEMA, NICC, USDA, HHS, FDA, NSSA, Mexico, and OIP (Skeen).	Emergency Diesel Generator
ENS 52226	8 September 2016 04:31:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation	Manual Reactor Trip Due to Stuck Open Pressurizer Main Spray Valve	On September 7th, 2016 at approximately 2131 Mountain Standard Time (MST), Palo Verde Unit 1 was manually tripped due to a stuck open main spray valve. Unit 1 was operating at 100 percent power at normal operating temperature and pressure prior to the event. A 120 VAC non-class instrument distribution panel was being transferred to its alternate power supply to establish maintenance conditions. The distribution panel failed to transfer. The panel remained energized from its normal power supply; however, multiple components powered from the distribution panel began to exhibit uncharacteristic behavior. At this time, it was noted that a reactor coolant system main spray valve was open. The alarm response procedure was followed; however, the actions taken were unsuccessful at closing the main spray valve. The plant was then manually tripped due to pressurizer pressure continuing to lower. The reactor coolant pumps were turned off to terminate main pressurizer spray flow to control pressurizer pressure due to the inability to close the main spray valve. No ESF (Engineered Safety Features) actuations occurred and none were required. No emergency classification was required per the emergency plan. Safety related buses remained energized during and following the reactor trip. The emergency diesel generators did not start and were not required. The offsite power grid is stable. Limiting condition for operation 3.4.1 was entered due to low pressurizer pressure. No major equipment was inoperable prior to the event that contributed to the event. Unit 1 is stable at normal operating temperature and pressure in Mode 3. Reactor coolant pumps are secured and natural circulation has been verified. Primary pressure is being maintained at its normal operating pressure manually with pressurizer heaters and auxiliary spray, from the charging system. 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 minimum RCS pressure was approximately 2070 psia (normal 2250). The event did not adversely affect the safe operation of the plant or the health and safety of the public. All rods inserted and the trip was uncomplicated. Units 2 and 3 were not affected and continue to run at full power. The NRC Resident Inspector has been notified.	Reactor Coolant System Emergency Diesel Generator	05000528/LER-2016-002
ENS 51522	9 November 2015 12:47:00	10 CFR 50.72(a)(1)(i), Emergency Class Declaration	Unusual Event Declared Due to Containment Fire Alarm	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. During Palo Verde Nuclear Generating Station Unit 2 containment pressurization for integrated leak rate testing in Mode 5, a containment fire alarm in Fire Zone 63B (Steam Generator 2 all elevations of containment) was received. Containment temperature and pressure at time of event were 72 degrees F and 13 PSIG. Due to the inability to access containment to validate the fire alarm, an Unusual Event (HU2.1) was declared at 0547 (MST) for a Fire in containment which was unable to be validated within 15 minutes of receipt. No safety functions have been impacted due to the fire alarm. No automatic or manual RPS or ESF actuations occurred and none were required. Actions are being taken to depressurize containment to enter and validate the fire alarm. The NRC Resident Inspector has been notified. There has been no effect on U-1 or U-3 due to this fire alarm. Notified DHS SWO, FEMA Ops Center, NICC Watch Officer and via E-mail only FEMA NWC and Nuclear SSA. * * UPDATE FROM ROB WARNER TO DONALD NORWOOD AT 1125 EST ON 11/9/2015 * * * Containment was entered following depressurization. Operations and Fire Protection personnel inspection of containment and Fire Zone 63B identified no indication of fire or smoke and the fire alarm was determined to be invalid. No other impacts to plant equipment were identified. The Unusual Event was terminated on 11/9/2015 at 0901 MST. The NRC Resident Inspector has been notified. Notified R4DO (Proulx), NRR EO (Morris), and IRD (Grant). Notified DHS SWO, FEMA Ops Center, NICC Watch Officer and via E-mail only FEMA NWC and Nuclear SSA.	Steam Generator
ENS 51403	17 September 2015 06:01:00	10 CFR 50.72(a)(1)(i), Emergency Class Declaration	Notification of Unusual Event Due to Rapid Combustion of a Load Center Breaker	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. Non Class Load Center Breaker, 2ENGN-L04 failed, resulting an a visible observation of rapid combustion and resultant charring (burned area) of the breaker enclosure and housing. No physical deformation to the breaker housing or surrounding area has been identified. The rapid combustion self-extinguished immediately following the audible and visible combustion event. As a result, an Emergency Classification of HU2.2, EXPLOSION was declared due to the Load Center breaker failure and noise and visible indication observed in the field. The plant was, and continues to operate at 100% full power operations on normal power alignment. The 2ENGN-L04 Non-Class Load Center breaker supplies power to non-essential service loads and has no immediate impact to plant operation or safety mitigating systems. The plant remains stable and the event did not adversely affect the safe operation of the plant or health and safety of the public. The NRC Resident Inspector has been notified. Notified DHS SWO, DHS NICC, FEMA, and Nuclear SSA via email. * * UPDATE FROM ROBERT PIERCE TO HOWIE CROUCH AT 0702 EDT ON 9/17/15 * * * PVNGS Unit 2 terminated the Unusual Event HU2.2 on 9/17/15 at 04:04 MST. Non-Class load center 2ENGN-L04 has been isolated and de-energized. There was no reflash or fire at the breaker and no hazard to plant personnel exists. Damage appears to be limited to the NGN-L04D3 breaker cubicle and a spare breaker cubicle below NGN-L04D3. There was no damage to any safety related equipment. The licensee will be notifying the state of Arizona, Maricopa County authorities and the NRC Resident Inspector. Notified R4DO (Farnholtz), NRR EO (Morris), IRD MOC (Gott), DHS SWO, FEMA Ops, DHS NICC and NuclearSSA (email).
ENS 50237	29 June 2014 05:06:00	10 CFR 50.72(a)(1)(i), Emergency Class Declaration	Unusual Event - Earthquake Felt on Site	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. An event classification of Unusual Event (HU1.1) was declared at 22:17 MST for the Palo Verde Nuclear Generating Station because of an earthquake that originated 50km NW of Lordsburg, New Mexico at 21:59 MST. Per the USGS website, the magnitude of the earthquake was 5.2 on the Richter scale. Initial walkdowns of plant equipment and review of plant parameters have found no unusual conditions or damage to plant equipment. No abnormalities caused by the seismic event were observed. No reactor protection system (RPS) or engineered safety feature (ESF) actuations occurred and none were required. Palo Verde Unit 1, 2, and 3 are at 100 percent power with all offsite power supplies available. Initial analysis of the Seismic Monitoring Instrumentation System indicated a seismic event, below the magnitude of the 0.10g spectra Operating Basis Earthquake (OBE) and the 0.20g spectra Safe Shutdown Earthquake (SSE). The NRC Resident Inspector has been notified of seismic activity and this ENS call. This event time is 2206 MST because this is the time the control room was notified by plant Operators that an earthquake had been felt on site. Notified DHS, FEMA, and NICC. FEMA NWC and Nuclear SSA were notified via email. * * UPDATE AT 0424 EDT ON 6/29/2014 FROM DENNIS MARTIN TO MARK ABRAMOVITZ * * * Emergency classification termination was declared at 6/29/14 01:12 MST. All required power block inspections were completed with no deficiencies noted. No other conditions require an emergency classification, there are no challenges to fission product barriers or radiological release, and plant conditions offer no possibility of adverse impact on health and safety of the public. The licensee notified the NRC Resident Inspector, state and local governments. Notified the R4DO (Allen), NRR (Hiland), IRD (Gott), DHS, FEMA, and NICC. FEMA NWC and Nuclear SSA were notified via email.	Reactor Protection System
ENS 49600	3 December 2013 00:58:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation	Automatic Reactor Trip Following the Loss of the 1A Reactor Coolant Pump	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 December 2, 2013, at approximately 1758 Mountain Standard Time (MST), the Palo Verde Nuclear Generating Station (PVNGS) Unit 2 control room received reactor protection system alarms for low departure from nucleate boiling ratio and an automatic reactor trip occurred. Prior to the reactor trip, Unit 2 was operating normally at 100% power. Plant operators entered the emergency operations procedures and diagnosed an uncomplicated reactor trip but noted the 1A reactor coolant pump (RCP) was not running. All CEAs fully inserted into the core. Following the reactor trip, indications on the train A logarithmic (log) power nuclear instrument initially responded normally but then did not trend as expected. All other nuclear instruments responded normally and the train A log power channel was declared inoperable and technical specification limiting conditions for operation 3.3.10 and 3.3.11 were entered. No emergency classification was required per the PVNGS Emergency Plan. The Unit 2 safety related electrical busses remained energized from normal offsite power during the event. Due to planned maintenance on one switchyard breaker, the Ruud offsite power line was disconnected from the PVNGS switchyard when the Unit 2 main generator output breakers opened. There was no impact to the required circuits between the offsite transmission network and the onsite Class 1E Electrical Power Distribution System; 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 2 is currently stable in Mode 3 with the reactor coolant system at normal operating temperature and pressure. Preliminary information indicates the reactor trip resulted from an electrical protection trip of the power supply circuit breaker for the 1A RCP. 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. There was no impact on either Unit 1 or Unit 3.	Reactor Coolant System Reactor Protection System	05000529/LER-2013-002
ENS 49317	3 September 2013 02:26:00	10 CFR 50.72(a)(1)(i), Emergency Class Declaration	Unusual Event Declared Due to Fire in the Turbine Building	An Event Classification of Unusual Event (HU2.1) was declared at 1926 (MST) for the Palo Verde Nuclear Generating Station. At 1912, smoke was detected by a security officer by the 'A' train Main Feed pump. An Auxiliary Nuclear Operator investigated and identified a fire on lagging, with one foot flames behind the main standard 'A' train Main Feed pump. The fire team responded to the fire and is currently on scene. Fire was declared out at 1957. No reactor protection system (RPS) or engineered safety feature (ESF) actuations occurred and none were required. The event did not result in any challenges to the fission product barrier or result in any releases of radioactive materials. There were no adverse safety consequences, and this event did not adversely affect the safe operation of the plant or health and safety of the public. The 'A' Main Feed pump high vibration alarm was received, but the continued operation of the main feed pump is currently not in jeopardy. While removing lagging, during the recovery process, the licensee had 2 reflash events. The flame was extinguished and the licensee continues to remove the oil soaked lagging for the 'A' Main Feed pump. The licensee has notified the NRC Resident Inspector, State, and Local Authorities. The Tonopah Fire Department was contacted and did respond to the site. Notified DHS SWO, FEMA, DHS NICC, and Nuclear SSA (email only). * * UPDATE FROM WAYNE TIMOTHY TO JOHN SHOEMAKER AT 0352 EDT ON 9/3/13 * * * PVNGS Unit 2 Terminated the Unusual Event HU2.1 on 9/3/13 at 0029 MST. The fire no longer constitutes a hazard to plant or personnel. 'A' Main Feed Pump is running and Unit 2 is operating at 100% power. The fire was extinguished at 1957 MST (per fire team advisor) and was declared extinguished by the incident commander at 2055 MST. A small oil vapor leak was identified coming from the high pressure bearing seal. Vapor extraction differential pressure was increased to eliminate the oil vapor leak. At 2134 MST, received a report of two reflash events while the Fire Department was removing additional lagging with no sustained flame or fire. All the affected lagging has been removed and the fire emergency was terminated at 2345 MST on 9/2/13. The licensee updated event times to reflect MST. The licensee has notified the NRC Resident Inspector, State, and Local Authorities. Notified R4DO (Hagar), NRR (Galloway), IRD (Marshall), DHS SWO, FEMA, DHS NICC, and Nuclear SSA (email only).	Reactor Protection System
ENS 49169	3 July 2013 07:00:00	10 CFR 50.72(a)(1)(i), Emergency Class Declaration	Notice of Unusual Event Due to Explosion in a Non-Safety Related Load Center	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 7/2/2013, at approximately 2027 MST, Palo Verde Unit 1 experienced a reactor power cutback from 100% rated thermal power due to explosion (in a non-safety related load center (1ENGNL02)). The unit was at normal temperature and pressure prior to the cutback. At 2035 (MST) PVNGS Unit 1 declared an Unusual Event due to the explosion EAL HU 2.2. Unit 1 is stable at 61% rated thermal power. No ESF actuations occurred and none were required. The event did not result in any challenges to the fission product barrier or result in any releases of radioactive materials. There were no adverse safety consequences or implications as a result of this event. The event did not adversely affect the safe operation of the plant or health and safety of the public. The licensee will notify the NRC Resident Inspector. Notified DHS SWO, FEMA, DHS NICC, and Nuclear SSA via email. * * * UPDATE ON 7/3/13 AT 0229 EDT FROM JEONG LIM TO PETE SNYDER * * * Palo Verde Unit 1 is stable at 58% rated thermal power and is implementing abnormal operating procedures for reactor power cutback due to loss of one Main Feedwater Pump and degraded electrical power due to loss of non-class 13.8kV load center 1ENGNL02. Load center 1ENGNL02 was damaged from an apparent electrical malfunction that originated within the load center. The 13.8kV supply breaker to load center 1ENGNL02 tripped to deenergize the load center. Palo Verde Fire Department personnel responded but determined that the load center was deenergized and no fire existed and no extinguishing agents were applied. No damage to other equipment in proximity to load center 1ENGNL02 was identified during a preliminary inspection of the area around the damaged load center. The NRC Resident Inspector has been notified. At 2315 (MST) on 07/02/2013, the Unusual Event was terminated. Notified R4DO (Gaddy), NRR EO (Nieh), IRD MOC (Gott), DHS SWO, FEMA, DHS NICC, and Nuclear SSA via email.	Feedwater
ENS 47837	15 April 2012 19:20:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation	Manual Reactor Trip Due to Control Rod Deviation During Startup	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 15, 2012 at approximately 1220 Mountain Standard Time (MST), Palo Verde Unit 3 was manually tripped during low power physics testing. While conducting low power physics testing following a refueling outage, Regulating Group 1 rods were being inserted while simultaneously diluting to maintain a constant power level below the Point of Adding Heat. While inserting rods one rod deviated from its subgroup when it stopped moving. The Reactor Operator immediately ceased rod motion and the dilution was stopped. The residual positive reactivity in the core caused a corresponding reactor power increase that approached procedural power limits set forth in the low power physics testing procedure. Based on these indications, operators initiated a manual reactor trip. Following the reactor trip, all CEAs inserted fully into the core. All systems operated as expected and this event was diagnosed as an uncomplicated reactor trip. 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 Feedwater Pump 'N'. 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. The electrical lineup remained normal. Decay heat is being removed via the steam bypass to the main condenser.	Steam Generator Auxiliary Feedwater Main Condenser Control Rod	05000530/LER-2012-001
ENS 47472	23 November 2011 02:25:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation	Manual Reactor Trip Due to Control Element Deviation	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. PVNGS (Palo Verde Nuclear Generating Station) (Unit 1 was in the process of Low Power Physics Testing following a refueling outage. The Unit was at 0.4 percent power and performing individual CEA (Control Element Assembly) group worth testing. Specifically Regulating Group (RG) 2 was being inserted while RG 4 was being withdrawn. During the CEA manipulations, it was identified that there was a CEA deviation on RG 2 subgroup 17 that exceeded 6 inches from the remainder of the RG. RG 2 subgroup 18 was at 134 inches withdrawn and RG 2 subgroup 17 had two CEAs at 124 inches, one CEA at 122 inches and one CEA at 118 inches withdrawn. The CEA Malfunctions abnormal operating procedure 40AO-9ZZ11 was entered and a manual reactor trip was directed by the Control Room Supervisor. The reactor was tripped at 1925 hours. Unit 1 was at normal temperature and pressure prior to the trip. All CEAs inserted fully into the reactor core. This was an uncomplicated reactor trip. No ESF actuations occurred and none were required. Safety related buses remained energized during and following the reactor trip. The offsite power grid is stable. No significant LCOs have been entered as a result of this event. There was no loss of normal heat removal capabilities, or loss of any safety functions associated with this event. 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 was informed of the Unit 1 reactor trip and this notification.		05000528/LER-2011-005
ENS 47333	8 October 2011 23:19:00	10 CFR 50.72(b)(2)(xi), Notification to Government Agency or News Release 10 CFR 50.72(a)(1)(i), Emergency Class Declaration	Notification of Unusual Event Due to Severe Electrical Fault in Rcp Junction Box	Reactor Coolant Pump 2A tripped at approximately 1535 MST, resulting in numerous simultaneous electrical distribution alarms. A walkdown of containment was performed and at 1609 MST it was determined that a junction box, supplying power to the 2A Reactor Coolant Pump, had failed, resulting in the pump tripping on overcurrent protection and an 86 lockout. The plant was operating in forced circulation and had one train of shutdown cooling in service. As a result, an Emergency Classification of HU2.2, Explosion was declared due to the junction box failure and noise that had been heard in containment. The plant is currently stable with one train of shutdown cooling in service, the opposite train of shutdown cooling is available to be placed in service. The Unit 1 Reactor Coolant System is currently at 160 degrees Fahrenheit and 375 psia with the 1A Reactor coolant pump in service for forced circulation. 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. The licensee has notified appropriate state and local agencies. * * UPDATE FROM DAN DAILEY TO DONALD NORWOOD AT 2306 EDT ON 10/8/2011 * * * The Notification of Unusual Event at Palo Verde Unit 1 was terminated at 1916 MST on 10/8/2011. The termination was based on conducting inspections which did not reveal any additional damage or plant impact as a result of this event. Unit 1 remains stable in Mode 5 with RCPs 1A and 1B in service along with one train of RHR in service. The licensee notified the NRC Resident Inspector and appropriate state and local agencies. Notified R1DO (Gray), NRR EO (Hiland), IRD (Grant), DHS (Flinter), and FEMA (Castro).	Reactor Coolant System Shutdown Cooling
ENS 47133	6 August 2011 18:19:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation	Automatic Reactor Trip Due to Dropped Control Element Assembly	On August 6, 2011, at approximately 1119 MST, the Palo Verde Unit 1 reactor tripped from approximately 100% rated thermal power due to a valid Reactor Protection System (RPS) actuation. The actuation was caused by a dropped Shutdown Group Control Element Assembly (CEA) during surveillance testing to exercise the CEAs. Following the reactor trip, one Regulating Group CEA indicated a failure to insert, however the CEA subsequently indicated fully inserted with no additional operator actions approximately 2 minutes after the trip. All CEAs are currently inserted fully into the reactor core. With the exception of the delayed indication of one CEA to fully insert, this was an uncomplicated reactor trip. No emergency classification was required per the Palo Verde Emergency Plan. No automatic or manual ESF actuations occurred and none were required. Safety related electrical buses remained energized during and following the reactor trip. The Emergency Diesel Generators did not start and were not required. The offsite power grid is stable. No major equipment was inoperable prior to the event that contributed to the event. Unit 1 is stable at normal operating temperature and pressure in Mode 3." Decay heat is being removed via the steam generators to the main condenser using the turbine bypass valves. The licensee notified the NRC Resident Inspector.	Steam Generator Reactor Protection System Emergency Diesel Generator Main Condenser	05000528/LER-2011-004
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 46025	18 June 2010 15:08:00	10 CFR 50.72(a)(1)(i), Emergency Class Declaration	Unusual Event Declared Due to Damaged Energized Equipment	On June 18, 2010, at approximately 0807 MST, a manual turbine trip was initiated due to loss of cooling for Main Transformer X01C. The power supplies for the transformer cooling system was lost due to an inadvertent actuation of the transformer fire protection deluge system. The damage to the energized equipment met the definition for an Emergency Action Level HU 2.2. Based on HU 2.2 the Unit 1 Shift Manager declared a Notification of an Unusual Event (NOUE) at 0808 MST applicable to Palo Verde Unit 1 only. The manual trip of the turbine initiated a Reactor Power Cutback Large Load Rejection actuation which was successful. The reactor is stable at 25% with Heat Removal via main feedwater and steam bypass to main condenser. A down power to approximately 12% power is being planned. No anomalies were noted during the manual turbine trip. (There is) no release in progress and no safety systems actuations were required. Palo Verde Unit 1 is in a normal post-trip electrical lineup. State and local authorities have been notified as well as the NRC Resident Inspector. * * UPDATE FROM BRIAN FERGUSON TO DONG PARK @ 1333 EDT ON 6/18/10 * * * The licensee terminated the Unusual Event at 1030 MST. The reactor remains stable at approximately 12% power, and heat removal is via main feedwater and steam bypass to the main condenser. Notified IRD (Gott), NRR EO (Cheok), R4DO (Jones), DHS (Inzer) and FEMA (Hollis).	Feedwater Main Transformer Main Condenser
ENS 45823	8 April 2010 17:15:00	10 CFR 50.72(a)(1)(i), Emergency Class Declaration	Earthquake	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 reporting requirements of 10 CFR 50.73. An Event Classification of Unusual Event (HU1.1) was declared at 10:15 MST for the Palo Verde Nuclear Generating Station because of an earthquake that originated in Baja California location 32.220 N, 115.276 W at 09:44 MST. Per the USGS website and via phone conversation at 10:03, the magnitude of the earthquake was preliminarily 5.5 on the Richter scale. Initial walk downs of plant equipment and review of plant parameters have found no unusual conditions or damage to plant equipment. No abnormalities caused by the seismic event were observed. No reactor protection system (RPS) or engineered safety feature (ESF) actuations occurred and none were required. Palo Verde Unit 1 is in mode 6 for a scheduled refueling outage and Units 2 & 3 are at 100 percent power with all offsite power supplies available. Seismic Monitoring Instrumentation system is currently functional and did not indicate a seismic event. Currently based on the Modified Mercalli scale the seismic event was below the magnitude of the 0.10g spectra Operating Basis Earthquake (OBE) and the 0.20g spectra Safe Shutdown Earthquake (SSE). The licensee notified the NRC Resident Inspector. * * * UPDATE FROM JIM BLAZEK TO PETE SNYDER AT 1606 ON 4/8/10 * * * Emergency classification termination was declared at 4/08/10, 12:54 MST. All required power block inspections were completed with no deficiencies noted. No other conditions required an emergency classification, there are no challenges to fission product barriers or radiological release, and plant conditions offer no possibility of adverse impact on health and safety of the public. The NRC Resident Inspector has been notified of NUE termination. Notified R4DO (Proulx), NRR EO (Thorp), DPR (McDermott), DHS (McDonald), and FEMA (Hollis).	Reactor Protection System
ENS 45811	4 April 2010 22:42:00	10 CFR 50.72(a)(1)(i), Emergency Class Declaration	Unusual Event Declared Due to an Earthquake	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. An Event Classification of Unusual Event (HU1.1) was declared at 1549 MST for the Palo Verde Nuclear Generating Station because of an earthquake that originated in Baja California, (Mexico) location 32.093?N, 115.249?W at 1542 MST. Per the USGS (U.S. Geological Survey) website, the magnitude of the earthquake was 6.9 on the Richter scale. Initial walkdowns of plant equipment and review of plant parameters have found no unusual conditions or damage to plant equipment. No abnormalities caused by the seismic event were observed. No Reactor Protection System (RPS) or Engineered Safety Feature (ESF) actuations occurred and none were required. Palo Verde Unit 1 is in mode 5 for a scheduled refueling outage, and Units 2 & 3 are at 100 percent power with all offsite power supplies available. Initial analysis of the Seismic Monitoring Instrumentation system indicated a seismic event, below the magnitude of the 0.10g spectra Operating Basis Earthquake (OBE) and the 0.20g spectra Safe Shutdown Earthquake (SSE). The licensee has notified the NRC Resident Inspector. * * UPDATE FROM GORDON TIMOTHY TO VINCE KLCO AT 0003 EDT ON 4/5/2010 * * * Emergency classification termination was declared at 4/4/10, 2045 MST. All required power block inspections were completed with no deficiencies noted. No other conditions require an emergency classification, there are no challenges to fission product barriers or radiological release, and plant conditions offer no possibility of adverse impact on health and safety of the public. NRC Resident Inspector has been notified of NUE termination. Notified the R4DO (Okeefe), NRR-EO (Bahadur), FEMA (Via), DHS (Wallace) and IRD via email (Gott).	Reactor Protection System
ENS 45784	23 March 2010 01:11:00	10 CFR 50.72(a)(1)(i), Emergency Class Declaration	Notification of Unusual Event Due to Unidentified Leakage Greater than 10 Gpm	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 requirement of 10CFR50.73. On March 22, 2010 at approximately 1756 MST, Palo Verde Nuclear Generating Station (PVNGS) Unit 1 identified a rising level and temperature trend in the Reactor Drain Tank (RDT). PVNGS Unit 1 was in Mode 1 (Power Operation) at 93% power with normal RCS temperature and pressure at the time of discovery. Containment temperature and humidity trends are normal. Technical Specification Limiting Condition for Operation 3.4.14 (RCS Operational Leakage), Condition 'A' was entered at 1811 due to unidentified leakage >10 gpm and the LCO allows 4 hours to restore leakage to <1 gpm. Also at 1811, a Notification of Unusual Event (NOUE) was declared due to unidentified leakage >10 gpm (MU5.1). PVNGS Unit 1 remains at power with all normal systems in operation; periodic pumping of the RDT is occurring. No automatic or manual reactor protection system or engineered safety features actuations occurred and none were required. There were no other component failures, testing or work in progress that contributed to the leak. The leak is located within the containment building, therefore there is no release of radioactivity to the environment and no impact to the health and safety of the public. There is no elevated RCS activity and heat removal is via normal steaming to the main turbine condenser. The electric grid is stable. Current plans are to enter containment and identify the source of leakage. State and Local authorities have been notified. The NRC Senior Resident Inspector has been notified. The licensee notified the following state and local agencies: Maricopa County Sheriff, Arizona Department of Public Safety, Buckeye Police Department, Arizona Radiation Regulatory Agency, Arizona Division of Emergency Management, and the Maricopa County Emergency Management Agency. * * UPDATE FROM BRAD ROBINSON TO DONG PARK AT 0028 EDT ON 3/23/2010 * * * At 2112 MST, the shift manager advised that the Pressurizer Main Spray Valve, 100E, packing leakage has been manually isolated. As of 2125 MST, the level trend in the RDT has stabilized. The licensee is working to verify the leakage rate, and remains in an Unusual Event. The plant remains stable in Mode 1 at 93% power. The licensee has notified the NRC Resident Inspector, and the NRC Resident Inspector remains on site. * * UPDATE FROM BRAD ROBINSON TO DONG PARK AT 0121 EDT ON 3/23/2010 * * * At 2146 MST, the licensee exited Technical Specification Limiting Condition for Operation 3.4.14, RCS Operational Leakage. At 2219 MST, the Unusual Event was terminated. The licensee will notify the NRC Resident Inspector. Notified R4DO (Deese), NRR EO (Brown), IRD (McDermott), DHS (Moore), and FEMA (Canupp).	Reactor Protection System Main Turbine
ENS 45748	7 March 2010 18:24:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(a)(1)(i), Emergency Class Declaration	Notification of Unusual Event Due to Electrical Fault Causing Damage to Equipment	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 March 7, 2010, at approximately 1124 MST Palo Verde Unit 1 declared a Notification of Unusual Event (NOUE) due to an electrical fault (explosion) experienced on the 13.8 KV Non-Class busses being supplied from the Unit Auxiliary Transformer. The fault resulted in a minor explosion and damage to the bus work leading from NAN S03 to NAN S01. The fault resulted in the loss of the NAN S01, which caused a reactor trip due to the loss of 2 of 4 reactor coolant pumps. There was no fire detected after the initial event. The reactor trip (RPS actuation at 1117 MST) was from 100% rated thermal power due to low departure from nucleate boiling (DNBR) trips on all four channels of the core protection calculators (CPCs). The unit was at normal temperature and pressure prior to the trip. All of the control rods fully inserted into the core. Four of eight steam bypass control valves quick opened, per design, directing steam flow to the condenser. No main steam or primary relief valves lifted and none were required. There was no loss of heat removal capability or loss of safety functions associated with the event. ESF Electrical buses remain energized from off-site power. The Shift Manager determined this event was an uncomplicated reactor trip. No significant LCOs have been entered as a result of this event. No major equipment was inoperable prior to the event nor contributed to the event. Unit 1 is stable at normal operating temperature and pressure in Mode 3. No ESF actuations (other than RPS) occurred and none were required. The event did not result in any challenges to the fission product barrier or result in any releases of radioactive materials. There were no adverse safety consequences or implications as a result of this event. The event did not adversely affect the safe operation of the plant or health and safety of the public. Decay heat is being removed via the steam bypass valves to the condenser. The plant is in its normal shutdown electrical lineup with the exception of powering the NAN S01 bus. Unit 2 and Unit 3 were not affected by the transient on Unit 1. The licensee has notified the NRC Resident Inspector. * * UPDATE FROM ALFRED ERDELJI TO HOWIE CROUCH @ 1723 EST ON 3/7/10 * * * Palo Verde Unit 1 has terminated the NOUE at 1516 MST. The termination criteria was that the plant is stable, the area around the fault has been inspected and no other conditions exist that would prevent termination of the event. Decay heat path has been changed from steam dumps to condenser to atmospheric dumps due to difficulty in maintaining temperature. There is no known primary to secondary leakage. The licensee has notified the NRC Resident Inspector. Notified R4DO (Cain), NRR EO (Holian), IRD (Gott), DHS (Roper) and FEMA (LaForte).	Control Rod Main Steam	05000528/LER-2010-001
ENS 45537	3 December 2009 11:30:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation	Manual Reactor Trip After Loss of Instrument Air to Containment	On December 3, 2009 at approximately 04:30 Mountain Standard Time (MST) Palo Verde Unit 3 operators manually tripped the reactor from approximately 100% rated thermal power due to loss of Instrument Air (IA) to Containment. This loss was apparently caused by a failure (closed) of the outboard IA Containment Isolation Valve (CIV) solenoid valve. Loss of IA to Containment resulted in closure of the inboard Reactor Coolant Pump (RCP) controlled seal bleedoff CIV. The RCP seal bleedoff was then being diverted via relief valve to the Reactor Drain Tank (RDT) inside Containment. Following the manual reactor trip all CEAs (Control Element Assemblies) fully inserted into the reactor core. All 4 RCPs were stopped to allow for isolation of bleedoff to the RDT. Upon completion of Standard Post Trip Actions, the crew entered the Optimal Recovery Procedure for Loss of Forced Circulation. No emergency classification was required per the Emergency Plan. No automatic ESF actuations occurred and none were required. Safety related buses remained energized during and following the reactor trip. The Emergency Diesel Generators did not start and were not required. The offsite power grid is stable. LCO 3.6.3 was entered due to failure of the IA CIV. No major equipment was inoperable prior to the event which contributed to the need for manual reactor trip. The reactor was manually tripped for equipment preservation. No safety or relief valves lifted other than noted above. After the trip, decay heat was being removed using the turbine bypass valves and steam generator level was being maintained with the auxiliary feedwater pumps. The licensee also entered LCO 3.4.5, "RCS Loop Operability" because the RCPs were stopped. The licensee notified the NRC Resident Inspector.	Steam Generator Emergency Diesel Generator Auxiliary Feedwater	05000530/LER-2009-001
ENS 44970	4 April 2009 06:54:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation	Manual Reactor Scram Due to High Vibrations in the Turbine	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 3, 2009, at approximately 2345 Mountain Standard Time (MST), Palo Verde Unit 3 operators manually tripped the reactor from approximately 29% rated thermal power in response to increasing vibration on the main turbine. The unit was being shutdown from 100% power for a refueling outage at the time of the trip. Following the manual reactor trip, all CEAs fully inserted into the reactor core. This was an uncomplicated reactor trip. No emergency classification was required per the Emergency Plan. No automatic ESF actuations occurred and none were required. Safety related buses remained energized during and following the reactor trip. The Emergency Diesel Generators did not start and were not required. The offsite power grid is stable. No LCOs have been entered as a result of this event. No major equipment was inoperable prior to the event that contributed to the event. No relief or safety valves lifted during the event. Decay heat is being removed via the steam dump to condenser valves. The licensee will continue to cool the plant down to support their planned refueling outage. There was no effect on Unit 1 or Unit 2. The licensee has notified the NRC Resident Inspector. * * UPDATE FROM DANIEL HAUTALA TO JOHN KNOKE AT 1429 EDT ON 05/22/09 * * * This notification is being made to retract Event Notification (EN 44970) made by Arizona Public Service Company (APS) on April 4, 2009, that reported a reactor protection system actuation in Unit 3 during a planned shutdown for a refueling outage. Further review of the reporting guidance in NUREG 1022 (revision 2) has concluded that since the manual trip was not initiated to mitigate an event and the decision to trip the reactor was at the discretion of the licensed operators the reporting threshold was not met. The procedure for a normal reactor shutdown directs that a manual reactor trip be initiated at approximately 20% rated thermal power. Due to prior issues with vibration of the main turbine monoblock rotor during power reductions related to plant shutdown, just-in-time training was provided to the plant operators which included action to trip the reactor if main turbine bearing vibration increased. Without the pre-determined discretion provided through the just-in-time training, the main turbine alone could have been tripped, followed by lowering reactor power to 20%, and then tripping the reactor. The plant design does not include an automatic reactor trip when the main turbine is tripped. Event Summary: On April 3, 2009, at approximately 23:45 Mountain Standard Time (MST) Palo Verde Unit 3 operators manually tripped the reactor from approximately 29% rated thermal power in response to increasing vibration on the main turbine. The unit was being shutdown from 100% power for a refueling outage at the time of the trip. Following the manual reactor trip all CEAs fully inserted into the reactor core. This was an uncomplicated reactor trip. No emergency classification was required per the Emergency Plan. No automatic ESF actuations occurred and none were required. Safety related buses remained energized during and following the reactor trip. The Emergency Diesel Generators did not start and were not required. The offsite power grid is stable. No LCOs have been entered as a result of this event. No major equipment was inoperable prior to the event that contributed to the event. NRC Resident Inspector has been notified. Notified R4DO (William Jones)	Reactor Protection System Emergency Diesel Generator Main Turbine
ENS 44525	28 September 2008 04:51:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation	Unit 3 Reactor Manually Tripped Following Automatic Turbine Trip on High Vibration	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 under the reporting requirements of 10CFR50.73. On September 27, 2008, at approximately 21:51 Mountain Standard Time (MST) Palo Verde Unit 3 operators manually tripped the reactor from approximately 34% rated thermal power in response to an automatic trip of the main turbine. The unit was being shutdown from 100% power due to a chemistry excursion in the secondary plant. Following the manual reactor trip all CEAs fully inserted into the reactor core. This was an uncomplicated reactor trip. No emergency classification was required per the Emergency Plan. No automatic ESF actuations occurred and none were required. Safety related buses remained energized during and following the reactor trip. The Emergency Diesel Generators did not start and were not required. The offsite power grid is stable. No LCOs have been entered as a result of this event. 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. Decay heat removal is via the Steam Generators and Main Feedwater to the Main Condenser using the Steam Bypass Control System. 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 main turbine tripped on high vibration. The Senior Resident Inspector was informed of the Unit 3 reactor trip.	Steam Generator Feedwater Emergency Diesel Generator Main Turbine Steam Bypass Control System Decay Heat Removal Main Condenser	05000530/LER-2008-002
ENS 44496	16 September 2008 21:00:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation	Manual Reactor Trip During Troubleshooting of Control Rod Drive Mechanism Motor Generators	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 September 16, 2008 at approximately 1400 hours Mountain Standard Time (MST) Palo Verde Nuclear Station Unit 3 experienced a manual reactor trip. At the time of the trip trouble shooting efforts were in progress to investigate abnormalities with the control element drive mechanism (CEDM) motor generators (MG). The MGs (2 - 100% each) normally operate in parallel to supply the necessary power to grip, move and hold the control element assemblies (CEA). During the trouble shooting activities the 'B' MG was removed from service. The 'A' MG initially provided power to the CEDMs but did not maintain the power. As a result of the pre-job briefing contingency actions, a manual reactor trip was ordered. All CEAs fully inserted into the core. No other emergency actuation signals were initiated and none were required. Off site power provided power to the class buses during and after the event. Decay heat removal is being provided by the steam bypass control system to the main condenser. No major equipment was inoperable prior to the event that contributed to the event. The unit is in Mode 3, Hot Standby, at normal temperature and pressure. The cause of the MG abnormality is under investigation. Normal feedwater remained in service providing water to the steam generators. The licensee notified the NRC Resident Inspector.	Steam Generator Feedwater Steam Bypass Control System Decay Heat Removal Main Condenser Control Rod	05000530/LER-2008-001
ENS 44246	29 May 2008 04:34:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation	Manual Reactor Trip Due to Improper Movement of Cea'S	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. On May 28, 2008, at approximately 2134 Mountain Standard Time (MST) Palo Verde Unit 2 operators manually tripped the reactor, as directed by procedures, when four Control Element Assembly (CEAs 7, 9, 11 &13) of shutdown bank A slipped to the fully inserted position while conducting low power physics testing following Unit 2's fourteenth refueling outage. Unit 2 was critical (Intermediate Range 5.0E-2)and at normal operating temperature and pressure prior to the trip. Following the manual reactor trip all remaining CEAs inserted fully into the reactor core. This was an uncomplicated reactor trip. No emergency classification was required per the Emergency Plan. No automatic ESF actuations occurred and none were required. Safety related buses remained energized during and following the reactor trip. The Emergency Diesel Generators did not start and were not required. The offsite power grid is stable. No LCOs have been entered as a result of this event. No major equipment was inoperable prior to the event that contributed to the event. Unit 2 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 or the health and safety of the public. The cause of the slipped CEAs is not known at this time and is under investigation. The Senior Resident Inspector was informed of the Unit 2 reactor trip.	Emergency Diesel Generator
ENS 43764	2 November 2007 14:44:00	10 CFR 50.72(b)(2)(xi), Notification to Government Agency or News Release 10 CFR 50.72(a)(1)(i), Emergency Class Declaration	Suspicious Explosive Device Discovered in Vehicle at Oca Access Checkpoint	On November 2, 2007 at 0744 (MST), Palo Verde Nuclear Generating Station Units 1, 2 and 3 declared a Notification of an Unusual Event as specified in the Emergency Plan. The basis for the Emergency Class declaration was detection of a credible threat: an explosive device was detected during a vehicle search at the site access check point. The site has entered its Deliberate Acts procedure. The device was discovered in a contract employee's vehicle at 0525 MST. It was confirmed to be an explosive device at 0730 MST by the Maricopa County Sheriff's Office (MCSO). The explosive device was removed from the site by MCSO and Federal Bureau of Investigation (FBI) at 0852. The individual driving the vehicle has been detained by MCSO. No other individuals were in the vehicle at the time. Palo Verde Unit 1 is in Mode 2 at approximately 2% power. Unit 2 is in Mode 1 at 100% power. Unit 3 is defueled undergoing steam generator replacement. No reactor protection system or engineered safety feature system actuations have occurred and none are required. No major structures, systems, or components are inoperable impacting the continued safe operation of the units. Plans are to continue Mode 2 operations in Unit 1 and Mode 1 full power operation in Unit 2. Further investigation is ongoing in cooperation with MCSO and the FBI. Security is conducting searches of the site. No additional concerns have been identified at this time. The security event has not resulted in any challenges to the fission product barrier or result in any releases of radioactive materials. There were no adverse safety consequences or implications as a result of the security event declaration. A news release was made at 11:10 a.m. The licensee notified the NRC Resident Inspector. * * UPDATE FROM DON VOGT TO J. KNOKE AT 1809 EDT ON 11/02/07 * * * At 1447 MST site security posture has changed from Code Red to Code Yellow Heightened Awareness, and at 1504 MST licensee exited the Unusual Event,. The licensee has notified the NRC Resident Inspector, state and local agencies, and will be issuing a press release this evening. Notifications were given to the following: R4 (Art Howell), R4DO(Powers), NRR EO (Bateman), IRD Manager (Blount), ILTAB (Sandler), DHS (York), FEMA (Dunker), DOE (Wyatt), FBI-SIOC (Curry), HHS (White), USDA (Phillip). * * UPDATE FROM WAREN HENDRIX TO J. KNOKE AT 1416 EDT ON 11/03/07 * * * The licensee downgraded the security posture at the site from Code Yellow Heightened Awareness to Code Yellow. The licensee notified the NRC Resident Inspector. Notified R4DO (Powers) and ILTAB (Sandler). * * UPDATE FROM DAN HAUTALA TO W. HUFFMAN AT 1600 EST ON 12/19/07 * * * Arizona Public Service Company (APS) is retracting security-related Event Notification #43764 and notification of unusual event (NUE) reported on November 2, 2007. Based upon investigations performed by the Federal Bureau of Investigation (FBI), Maricopa County Sheriff's Office (MCSO) and Palo Verde Security department, APS has determined that there was no explicit nor credible threatened action as described in 10 CFR 73.71, Appendix G, Paragraph I. These investigations revealed that the previously reported explosive device was placed in the owner's truck bed without his knowledge. Therefore, there is no reason to believe that a person has committed or caused, or attempted to commit or cause, or has made a credible threat to commit or cause: theft or unlawful diversion of special nuclear material; or significant physical damage to a power reactor; or interruption of normal operation of a licensed nuclear power reactor. The licensee notified the NRC Resident Inspector. R4DO (Farnholtz) has been notified and an e-mail sent to ILTAB and the 73.71 group.	Steam Generator Reactor Protection System
ENS 43697	6 October 2007 17:59:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation	Manual Reactor Trip Due to Condenser Tube Rupture	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 6, 2007, at approximately 10:59 Mountain Standard Time (MST) Palo Verde Unit 2 plant operators manually tripped the reactor from approximately 100% rated thermal power. The reactor was tripped when sodium levels in both steam generators reached trip criteria following a condenser tube rupture. Unit 2 was at normal temperature and pressure prior to the trip. All CEAs inserted fully into the reactor core. This was an uncomplicated reactor trip. No ESF actuations occurred and none were required. Safety related buses remained energized during and following the reactor trip. The offsite power grid is stable. No significant LCOs have been entered as a result of this event. There was no loss of normal heat removal capabilities, or loss of any safety functions associated with this event. No major equipment was inoperable prior to the event that contributed to the event. " No PORVs or MSSVs lifted. Decay heat is being removed with Auxiliary Feedwater feeding the steam generators steaming to the condenser. There are no primary to secondary tube leaks in the steam generators. Emergency buses are powered by offsite power with Emergency Diesel Generators in standby. 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 2 reactor trip and this notification.	Steam Generator Emergency Diesel Generator Auxiliary Feedwater
ENS 42925	21 October 2006 22:48:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation	Automatic Reactor Trip Due to Control Element Assembly Position Transmitter Output Deviations	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 21, 2006 at approximately 1549 MST Palo Verde Unit 1 experienced a reactor trip (RPS actuation) from 100% rated thermal power due to low departure from nucleate boiling (DNBR) trips on all four channels of the core protection calculators (CPCs). The unit was at normal temperature and pressure prior to the trip. Several minutes prior to the Reactor Trip, RSPT#1 (Reed Switch Position Transmitter) CEA deviation alarms were received for CEA#29 (Shutdown Group B CEA). Operators observed that the magnitude of the deviation was fluctuating erratically. While investigating the alarms CEAC #1 Sensor Fail alarms were received and at 1549 MST, the Reactor automatically tripped on a CPC generated Lo DNBR trips on all 4 channels of CPCs. The apparent cause is presently suspected to be a failure of RSPT#1. An investigation has commenced to determine the root cause of the reactor trip. All of the control rods fully inserted into the core. The Steam Bypass Control System operated as designed, directing steam flow to the condenser. No main steam or primary relief valves lifted and none were required. There was no loss of heat removal capability or loss of safety functions associated with the event. Electrical buses transferred to offsite power as designed. The Shift Manager determined this event was an uncomplicated reactor trip. No significant LCOs have been entered as a result of this event. No major equipment was inoperable prior to the event nor contributed to the event. Unit 1 is stable at normal operating temperature and pressure in Mode 3. No ESF actuations occurred and none were required. The event did not result in any challenges to the fission product barrier or result in any releases of radioactive materials. There were no adverse safety consequences or implications as a result of this event. The event did not adversely affect the safe operation of the plant or health and safety of the public. The NRC Resident was notified at 17:38 MST.	Steam Bypass Control System Control Rod Main Steam
ENS 42920	19 October 2006 18:47:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation	Manual Reactor Trip Following the Trip of Secondary Condensate Pumps	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 19, 2006, at approximately 1147 Mountain Standard Time (MST) Palo Verde Unit 3 plant operators manually tripped the reactor from approximately 100% rated thermal power. The reactor was tripped when lowering hotwell levels caused two condensate pumps to trip. The preliminary cause for the lowering hotwell level was the hotwell draw-off valve spuriously failing open. Unit 3 was at normal temperature and pressure prior to the trip. All CEAs inserted fully into the reactor core. This was an uncomplicated reactor trip. No ESF actuations occurred and none were required. Safety related buses remained energized during and following the reactor trip. The offsite power grid is stable. No significant LCOs have been entered as a result of this event. There was no loss of normal heat removal capabilities, or loss of any safety functions associated with this event. 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 Resident Inspector was informed of the Unit 3 reactor trip and this notification. The current decay heat removal path is auxiliary feedwater supplying water to the steam generators steaming to the condenser. Emergency Diesel Generators are available.	Steam Generator Emergency Diesel Generator Auxiliary Feedwater Decay Heat Removal
ENS 42730	26 July 2006 14:35:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation	Variable Overpower Reactor Trip Following Turbine Control Valve Maintenance	On July 26, 2006, at approximately 07:34 Mountain Standard Time (MST) Palo Verde Unit 2 experienced an automatic reactor scram on Variable Overpower. Unit 2 was operating at 90% power at normal operating temperature and pressure prior to the event. A main turbine control valve (CV02) was being returned to service following maintenance. CV02 initially started to open which caused reactor power to decrease to approximately 89%. During the evolution, six steam bypass control valve opened (three valves opened 100 percent, one opened 60 percent, and two opened 5 percent). Reactor power rapidly increased to 98% which resulted in an auxiliary Variable Power Trip (VOPT). The VOPT trip set point is 8 percent. The main turbine automatically tripped in response to the reactor trip. All rods inserted, as required. No ESF actuations occurred and none were required. No emergency classification was required per the Emergency Plan. Safety related buses remained energized during and following the reactor trip. The Emergency Diesel Generators did not start and were not required. The offsite power grid is stable. No LCOs have been entered as a result of this event. No major equipment was inoperable prior to the event that contributed to the event. The maximum power level during the transient was approximately 98%. Unit 2 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 maximum RCS pressure was approximately 2260 psia (normal 2240). The maximum steam generator pressure was approximately 1090 psia (normal 1055). 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.	Steam Generator Emergency Diesel Generator Main Turbine	05000529/LER-2006-003
ENS 42681	2 July 2006 02:28:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation	Manual Reactor Trip Following Large Leak in Condensate System	On July 1, 2006, at approximately 19:28 MST Palo Verde Unit 3 experienced a manual reactor trip from approximately 100% rated thermal power due to a large leak in the condensate system. The sight glass for the 'A' condensate demin vessel blew out of the vessel creating an approximate 6 inch diameter hole. Several thousand gallons of condensate were discharged to the Turbine Building and the environment. Radiation Protection has sampled the condensate water and have verified no activity is present. Unit 3 was at normal operating temperature and pressure prior to the trip. The 'A' Main feedwater pump tripped on low suction pressure and a Reactor Power Cutback Signal was received. Condenser hotwell levels continued to decrease. When the main control board annunciator for the 'B' Main Feedwater Pump Trip Circuit Energized was received the reactor was manually tripped. All CEAs fully inserted into the reactor core. The event was diagnosed as an uncomplicated reactor trip. No ESF actuations occurred and none were required. Safety related buses remained energized during and following the reactor trip. The offsite power grid is stable. No significant LCOs have been entered as a result of this event. There was no loss of normal heat removal capabilities, or loss of any safety functions associated with this event. No major equipment was inoperable prior to the event that contributed to the event. No primary or secondary safety valves lifted during 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. Unit 3 is stable at normal operating temperature and pressure in Mode 3. There is no estimated time and date for the Unit 3 restart at the time this call is being made. AFW is being used to feed the steam generators and is discharging steam to the main condenser. The licensee stated that the leak has been secured and that there is no significant standing water in the turbine building lower levels. All the water has drained into sumps or out doors. There does not appear to be any electrical or personnel safety hazards as a result of the water leak. The licensee notified the NRC Resident Inspector. UPDATE FROM RAY BUZZARD TO JOHN KNOKE AT 17:28 ON 07/03/06 *** 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 notification is a follow-up to the manually initiated reactor trip event reported on July 1, 2006 (ENS 42681). The notification indicated that the reactor was manually tripped from approximately 100% rated thermal power due to a large leak in the condensate system. Prior to the transient the unit was operating at approximately 100 % rated thermal power, however, the manual trip was actually initiated from approximately 55% rated thermal power following a reactor power cutback caused by the loss of the A train main feedwater pump on low suction pressure. In addition, the ENS report stated that Radiation Protection had sampled the condensate water and verified no activity is present. The condensate actually was found to contain tritium at a concentration of 1.22E-5 uCi/ml. The water from the spill flowed to the onsite storm drains, was captured behind dams, and transferred to the onsite retention basins. Samples of resin from the spill were also collected, analyzed by gamma spectroscopy, and found to not contain licensed radioactive material. The licensee notified the NRC Resident Inspector. Notified R4DO (Shannon)	Steam Generator Feedwater Main Condenser
ENS 42387	5 March 2006 14:10:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation	Automatic Reactor Trip Due to Low Departure from Nucleate Boiling Ratio.	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. On March 5, 2006 at approximately 0710 MST Palo Verde Unit 3 experienced a reactor trip (RPS actuation) from 100% rated thermal power due to low departure from nucleate boiling (ratio) (DNBR) trips on all four channels of the core protection calculators (CPCs). The unit was at normal temperature and pressure prior to the trip. Prior to the reactor trip, at approximately 0704 MST, a CEAC (Control Element Assembly Calculator) #1 sensor fail alarm was received. While investigating the alarm, at 0710 MST, a control element assembly (CEA) deviation alarm for CEAC #1, all four CPC channel sensor fail alarms, and a CEA withdrawal prohibit alarm were received. The reactor tripped six seconds later. A CEA calculator (CEAC) fail alarm was received on CEAC #1. The apparent cause is presently suspected to be a failure of CEAC #1. An investigation has commenced to determine the root cause of the reactor trip. All of the control rods fully inserted into the core. Four of eight steam bypass control valves quick opened, per design, directing steam flow to the condenser. No main steam or primary relief valves lifted and none were required. There was no loss of heat removal capability or loss of safety functions associated with the event. Electrical buses transferred to offsite power as designed. The Shift Manager determined this event was an uncomplicated reactor trip. No significant LCOs have been entered as a result of this event. No major equipment was inoperable prior to the event nor contributed to the event. Unit 3 is stable at normal operating temperature and pressure in Mode 3. No ESF actuations occurred and none were required. The event did not result in any challenges to the fission product barrier or resulted in any releases of radioactive materials. There were no adverse safety consequences or implications as a result of this event. The event did not adversely affect the safe operation of the plant or health and safety of the public. The licensee notified the NRC Resident Inspector.	Control Rod Main Steam	05000530/LER-2006-002
ENS 41951	27 August 2005 01:24:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation	Rps Actuation - Reactor Scram on High Steam Generator 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 or under the reporting requirements of 10CFR50.73. On August 26, 2005, at approximately 18:24 Mountain Standard Time (MST) Palo Verde Unit 1 experienced an automatic reactor scram on high steam generator #1 level. All rods inserted, as required. Unit 1 was at normal operating temperature and pressure prior to the trip. The main turbine was not yet synchronized to the grid; turbine chest warming was in progress. The main turbine automatically tripped in response to the reactor trip. A reactor startup had been completed and operators were transferring feedwater from a motor driven auxiliary feedwater pump to the steam driven 'A' main feedwater pump at approximately 1.2% reactor power. Steam generator #1 level decreased from a normal level of approximately 40% narrow range (approx. 77% wide range) to approximately 12% narrow range (approx. 66% wide range). An operator took manual control of feedwater to increase level. Upon returning feedwater control to automatic after level was restored, steam generator #1 level continued to increase, resulting in a reactor trip on high steam generator level at approximately the Technical Specification reactor trip and Main Steam Isolation Signal (MSIS) setpoint of 91.5%. The MSIS (ESF actuation) functioned as required. No other ESF actuations occurred or were required. No emergency classification was required per the Emergency Plan. Safety related buses remained energized during and following the reactor trip. The Emergency Diesel Generators did not start and were not required. The offsite power grid is stable. No LCOs have been entered as a result of this event. No major equipment was inoperable prior to the event that contributed to the event. The maximum power level during the feedwater transient was approximately 8.5%. Unit 1 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 maximum RCS pressure was approximately 2251 psia (normal 2250). The maximum steam generator pressure was approximately 1188 psia (normal 1165). 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.	Steam Generator Feedwater Emergency Diesel Generator Auxiliary Feedwater Main Turbine Main Steam
ENS 40870	14 July 2004 08:35:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation	Automatic Reactor Trip Following a Main Generator Trip	The following information was received from 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 July 14, 2004, at approximately 01:35 Mountain Standard Time (MST) Palo Verde Unit 2 experienced a Main Generator Trip immediately followed by an automatic Reactor Trip. The reactor was at approximately 100% power and normal operating temperature and pressure prior to the event. The cause of the Main Generator Trip was most likely the result of electrical storm conditions present at the site at the time of the trip. Unit 2 was at normal operating temperature and pressure prior to the trip. All CEAs inserted fully into the reactor core. Heat removal was maintained to the condenser via the steam bypass control system. This was an uncomplicated reactor trip, No emergency classification was required per the Emergency Plan. No automatic ESF actuations occurred and none were required. Safety related buses remained energized during and following the reactor trip. The Emergency Diesel Generators did not start and were not required. The offsite power grid is stable. No LCOs have been entered as a result of this event. No major equipment was inoperable prior to the event that contributed to the event. Unit 2 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 or the health and safety of the public. The (NRC) Senior Resident Inspector was informed of the Unit 2 reactor trip. No primary or secondary power-operated or manual relief valves lifted as a result of the plant transient. Units 1 and 3 were unaffected by the trip on Unit 2. Offsite power was maintained to Unit 2 safety busses throughout the event.	Emergency Diesel Generator Steam Bypass Control System	05000529/LER-2004-002
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. * * Update at 1815 @ 06/14/04 * * * 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 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. * * Update at 1815 @ 06/14/04 * * * 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 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. * * Update at 1815 @ 06/14/04 * * * 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 40795	7 June 2004 21:58:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation	Reactor Trip Due to Main Turbine Electro-Hydraulic Control System Failure	On June 7, 2004, at approximately 14:58 Mountain Standard Time (MST) while at 99% RTP (rated thermal power), Palo Verde Unit 3 experienced an apparent electro-hydraulic control (EHC) system fault resulting in Combined Intercept Valve (CIV) closure. This plant upset was followed by a Reactor Power Cutback System (RPCS) initiation. Several seconds later the Reactor automatically tripped on Lo DNBR from approximately 65% RTP. Unit 3 was at normal temperature and pressure prior to the trip. All CEAs (control rod assemblies) inserted fully into the reactor core. This was an uncomplicated reactor trip. No emergency classification was required per the Emergency Plan. No automatic ESF actuations occurred and none were required. Safety related buses remained energized during and following the reactor trip. The Emergency Diesel Generators did not start and were not required. The offsite power grid is stable. No significant LCOs have been entered as a result of this event. No major equipment was inoperable prior to the event that contributed to the event. Unit 3 is stabilized at normal temperature and pressure at approximately 565 degrees F and 2250 psia in Mode 3. The reactor coolant system remains in normal forced circulation with heat removal via the steam bypass control system to the condenser and feedwater from the non-essential auxiliary feedwater system. 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 Senior Resident Inspector was informed of the Unit 3 reactor trip and this notification. The Senior Resident Inspector was on-site at the time of the reactor trip.	Reactor Coolant System Feedwater Emergency Diesel Generator Auxiliary Feedwater Main Turbine Steam Bypass Control System	05000530/LER-2004-002
ENS 40737	9 May 2004 03:39:00	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation	Manual Reactor Trip During Physics Testing Due to Control Element Assembly Slipping 6 Inches.	On May 8, 2004, at approximately 20:39 Mountain Standard Time (MST) Palo Verde Unit 1 operations manually tripped the reactor when a Control Element Assembly (CEA) slipped approximately 6 inches (CEA # 89) while conducting physics testing (at 10E-02 percent power) following Unit 1's eleventh refueling outage. Unit 1 was at normal operating temperature and pressure prior to the trip. All CEAs inserted fully into the reactor core (Initial Conditions: Regulating groups 1, 2 & 5 were fully withdrawn, regulating group 3 was fully inserted, regulating group 4 was being inserted when CEA # 89 slipped approximately 6 inches. Shutdown groups were fully withdrawn). This was an uncomplicated reactor trip. No emergency classification was required per the Emergency Plan. No automatic ESF actuations occurred and none were required. Safety related buses remained energized during and following the reactor trip. No LCOs (Limiting Conditions of Operations) have been entered as a result of this event. No major equipment was inoperable prior to the event that contributed to the event. Unit 1 is stable at normal operating temperature and pressure in Mode 3 (Hot Standby). 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 Senior Resident Inspector was informed of the Unit 1 reactor trip.

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