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 Entered dateSiteScramRegionReactor typeEvent description
ENS 5422416 August 2019 15:05:00Palo VerdeAutomatic ScramNRC Region 4At 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.
ENS 5347728 June 2018 05:37:00Palo VerdeAutomatic ScramNRC Region 4The 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.
ENS 5342423 May 2018 17:37:00Palo VerdeAutomatic ScramNRC Region 4CE

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.

ENS 5321516 February 2018 02:50:00Palo VerdeAutomatic ScramNRC Region 4CE

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).

ENS 522268 September 2016 04:27:00Palo VerdeManual ScramNRC Region 4CEOn 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.
ENS 496002 December 2013 23:26:00Palo VerdeAutomatic ScramNRC Region 4CEThe 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.
ENS 4783715 April 2012 17:13:00Palo VerdeManual ScramNRC Region 4CEThe 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.
ENS 4747222 November 2011 23:03:00Palo VerdeManual ScramNRC Region 4CEThe 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.
ENS 471336 August 2011 17:41:00Palo VerdeAutomatic ScramNRC Region 4CEOn 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.
ENS 4655620 January 2011 00:08:00Palo VerdeAutomatic ScramNRC Region 4CEThe 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.
ENS 4602518 June 2010 12:04:00Palo VerdeManual ScramNRC Region 4CE

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).

ENS 455373 December 2009 09:14:00Palo VerdeManual ScramNRC Region 4CEOn 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.
ENS 449704 April 2009 08:54:00Palo VerdeManual ScramNRC Region 4CE

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)

ENS 4452528 September 2008 02:35:00Palo VerdeAutomatic Scram
Manual Scram
NRC Region 4CEThe 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.
ENS 4449616 September 2008 19:23:00Palo VerdeManual ScramNRC Region 4CEThe 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.
ENS 442746 June 2008 05:40:00Palo VerdeManual ScramNRC Region 4CE

On Thursday June 5, 2008 at 2356 MST Palo Verde Nuclear Station Unit 1 initiated a normal reactor shutdown to comply with condition C of Technical Specification (TS) LCO 3.5.1 and to facilitate a weld repair on a nitrogen leak found on the Safety Injection Tank (SIT) 1A vent line. LCO 3.5.1 requires that all four SITs be operable in Modes 1 and 2. On June 5, 2008, at 0225 hours MST, Unit 1 entered Condition B which provides allowance for one SIT to be inoperable for a 24 hour period. The SIT will not be restored to operable status within the TS required 24 hour period, therefore, Condition C will be applicable at 0225 MST on June 6 2008. Condition C requires shutdown to Mode 3 in six hours and to reduce pressurizer pressure to less than 1837 psia within 12 hours.

On June 06 at 0148 hours MST, Unit 1 was manually tripped from approximately 20% power. The shutdown did not result in a 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 primary plant is being stabilized in Mode 3 in forced circulation with both steam generators used for heat removal. Unit 1 is stable at normal operating temperature and pressure in Mode 3. S/G's are being feed via main feed. All other safety related systems are operable. Decay heat is via SBC system to the condenser. There is no impact on the other units. The licensee notified the NRC Resident Inspector.

ENS 4424629 May 2008 02:40:00Palo VerdeManual ScramNRC Region 4CEThe 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.
ENS 436976 October 2007 15:32:00Palo VerdeManual ScramNRC Region 4CEThe 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.
ENS 4317319 February 2007 19:14:00Palo VerdeManual ScramNRC Region 4CEThe 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 02/19/2007 at approximately 14:57 hours Mountain Standard Time (MST), Palo Verde Nuclear Generating Station (PVNGS) Unit 2 initiated a plant shutdown as required by Condition 'C' of Technical Specification (TS) LCO 3.5.3 to be in Mode 3 with Pressurizer pressure < 1837 psia and Reactor Coolant System (RCS) Tc < 485 degrees F. Limiting Condition for Operability (LCO) 3.5.3 requires that two ECCS trains be Operable. High Pressure Safety Injection Pump (HPSI) 2A was declared inoperable on 02/16/2007 at 13:01 MST and was not restored to Operable status within the TS 72 hour Completion Time due to pump bearing oil leakage exceeding the allowable leakage limit. Efforts are in progress to correct the oil leakage issue. 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 observed pump bearing oil leakage is approximately 3 drops/hr. Unit 2 completed a normal reactor shutdown with a manual reactor trip at 20% power. All rods fully inserted. Decay heat is currently being removed via the Main Condenser. The licensee informed the NRC Resident Inspector.
ENS 4292521 October 2006 21:37:00Palo VerdeAutomatic ScramNRC Region 4CEThe 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.
ENS 4292019 October 2006 17:27:00Palo VerdeManual ScramNRC Region 4CEThe 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.
ENS 4273026 July 2006 14:20:00Palo VerdeAutomatic ScramNRC Region 4CEOn 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.
ENS 426812 July 2006 01:23:00Palo VerdeManual ScramNRC Region 4CE

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)

ENS 423875 March 2006 11:12:00Palo VerdeAutomatic ScramNRC Region 4CEThe 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.
ENS 4195127 August 2005 00:19:00Palo VerdeAutomatic ScramNRC Region 4CEThe 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.
ENS 4087014 July 2004 07:35:00Palo VerdeAutomatic ScramNRC Region 4CEThe 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.
ENS 4081514 June 2004 11:39:00Palo VerdeAutomatic ScramNRC Region 4CE

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

ENS 4081614 June 2004 11:39:00Palo VerdeAutomatic ScramNRC Region 4CE

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

ENS 4081414 June 2004 11:39:00Palo VerdeAutomatic ScramNRC Region 4CE

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

ENS 407379 May 2004 02:56:00Palo VerdeManual ScramNRC Region 4CEOn 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.