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| Entered date | Event description | |
|---|---|---|
| ENS 55265 | 19 May 2021 08:35:00 | 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.
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)
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) |
| ENS 54701 | 11 May 2020 13:07:00 | The following event descriptions are based on information currently available. If through subsequent reviews of these events additional information is identified that is pertinent to the events or alters the information being provided at this time a follow-up notification will be made via the ENS or under the reporting requirements of 10 CFR 50.73. This telephone notification is being made pursuant to the reporting requirements of 10 CFR 50.73(a)(2)(iv)(A) and 50.73(a)(1) to describe invalid actuations of both trains of the Palo Verde Nuclear Generating Station (PVNGS) Unit 3 essential spray pond (SP) system, which serves as an emergency service water system that does not normally run and serves as an ultimate heat sink as described in 10 CFR 50.73(a)(2)(iv)(B)(9). This notification covers two similar, but separate invalid actuations occurring in Unit 3 on March 14, 2020 at 12:44 (MST) and again on April 25, 2020 at 12:10 (MST). On each day, an invalid actuation of the Unit 3 train "B" Fuel Building Essential Ventilation Actuation Signal (FBEVAS) occurred during performance of the Balance of Plant Engineered Safety Features Actuation System weekly auto test. The auto/manual pushbutton was depressed to initiate the test and the sequencer immediately tripped FBEVAS train "B" with subsequent cross trip of FBEVAS train "A". These actuations resulted in complete and successful actuations of both trains of essential spray pond pumps. The events were entered into the PVNGS corrective action program and a station evaluation is in progress. There was no adverse impact to public health and safety nor to plant employees. The NRC resident inspectors have been informed. |
| ENS 54272 | 12 September 2019 03:25:00 | 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. Radiation monitor RU-140 (#2 Steam Generator Main Steam Line radiation monitor) experienced a communication failure on both ports A and B. The RU-140 monitor is off line and non-functional at this time. At least one channel of RU-140 is required to perform a Steam Generator Tube Rupture (SGTR) dose assessment. This represents an unplanned loss of radiological assessment capability for the inability to perform dose assessments that require the radiation monitor. The ability to make emergency classifications from other radiological data collection methods such as field sampling remains available. Actions have been initiated to restore the radiation monitor. The NRC Resident Inspector has been informed. |
| ENS 49616 | 8 December 2013 10:53:00 | 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 approximately 0800 Mountain Standard Time on December 8, 2013, Palo Verde Nuclear Generating Station (PVNGS) removed the Technical Support Center (TSC) uninterruptable power supply (UPS) from service for a planned replacement. The outage disables the Emergency Response Facility Data Acquisition and Display System (ERFDADS) inside the TSC, remote meteorological data display in the emergency response facilities and control rooms, and transmission of plant data to the Emergency Operations Facility (EOF) and to the NRC's Emergency Response Data System (ERDS). The outage is expected to be completed within five days. The TSC and EOF remain functional during the outage. The outage does not affect the availability of normal power to the TSC or back-up power from the TSC diesel generator. Existing telecommunication systems provided for the emergency response organization (ERO) remain functional to provide the ERO within the TSC and EOF the necessary emergency assessment capabilities, as described in the PVNGS Emergency Plan. The ERFDADS system in each of the three unit control rooms and unit satellite TSCs remain functional and are not affected by the TSC UPS outage. Compensatory measures exist within emergency plan implementing procedures to obtain meteorological tower data locally and from the National Weather Service. The ERO has been briefed on the effects of the planned TSC UPS outage. The NRC Resident Inspector has been informed. PVNGS will inform the NRC after the outage has been completed and the functionality of affected equipment has been restored.
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 an update to EN 49616 which provided notification of pre-planned maintenance activities on the Palo Verde Nuclear Generating Station (PVNGS) Technical Support Center (TSC) uninterruptable power supply (UPS) that disabled various Emergency Plan (E-Plan) data systems. At approximately 0915 Mountain Standard Time on December 12, 2013, PVNGS restored the affected data systems to service such that the functions of the E-Plan can now be performed without the use of alternate methods. The NRC Resident Inspector has been informed. Notified R4DO (Werner). |