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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 53776 | 13 October 2018 05:00:00 | 10 CFR 50.73(a)(1), Submit an LER | 60-Day Optional Telephonic Notification of Invalid Specified System Actuation | This 60-day telephone notification is being made per the reporting requirements specified by 10 CFR 50.73(a)(2)(iv)(A) and 10 CFR 50.73(a)(1) to describe an invalid actuation of a Primary Containment Isolation System (PCIS) Group 1 for Main Steam Isolation Valves (MSIVs), Group 3 for Reactor Water Cleanup (RWCU), Group 6 for Secondary Containment isolation, Group 7 for Reactor Water Sampling, Diesel Generator, Reactor Core Isolation Cooling (RCIC) System logic, and Residual Heat Removal (RHR) logic. Group 1, Group 6, Diesel Generator actuation, RCIC actuation and RHR actuation are within scope of 10 CFR 50.73(a)(2)(iv). Group 3 and Group 7 are not within scope as they affect only one system. Cooper Nuclear Station (CNS) was shut down in Mode 5 at the time of the event with the reactor cavity flooded. On October 13, 2018, at 0028 Central Daylight Time, CNS received full PCIS Groups 1, 3, and 6, and a half Group 7 on the Division 1 side. The MSIVs and RWCU isolation valves were already closed for maintenance. The Secondary Containment isolated. Control Room Emergency Filter and the Standby Gas Treatment Systems initiated. The inboard Reactor Water Sample valve isolated. Diesel Generator #1 started but was not required to connect to the critical bus. Reactor Core Isolation Cooling System logic actuated with no expected response due to being isolated for shutdown conditions. Division 1 RHR pump logic actuated. Division 1 RHR system was operating in shutdown cooling mode. The actuation caused the Division 1 RHR outboard injection and heat exchanger bypass valves to open. Shutdown cooling was unaffected and remained in service throughout the event. The plant systems responded as expected with no Emergency Core Cooling System injection. At the time of the event, an in-service inspection of welds inside the reactor vessel was taking place using a robot scanner that uses two vortex thrusters to hold the robot to the vessel wall. The robot inadvertently passed over an instrument penetration, drawing suction on the process leg, resulting in low reactor water level indications and the subsequent invalid Level 1 and 2 system actuations. Actual reactor vessel water level remained steady at cavity flooded conditions. The NRC Resident Inspector has been notified of this event. | Secondary containment Main Steam Isolation Valve Primary Containment Isolation System Reactor Core Isolation Cooling Shutdown Cooling Residual Heat Removal Reactor Water Cleanup Standby Gas Treatment System Emergency Core Cooling System | |
| ENS 52436 | 28 October 2016 07:39:00 | 10 CFR 50.73(a)(1), Submit an LER | Invalid Actuation of Containment Isolation Valves | This telephone notification is being made in lieu of a Licensee Event Report in accordance with 10CFR50.73(a)(1) to notify the NRC of on invalid actuation of a group isolation, reportable under 10CFR50.73(a)(2)(iv)(A). On October 28, at 0139 Central Daylight Time, electricians were removing a test jack from a terminal on a primary containment isolation system relay due to the test jack being installed on the wrong relay. During removal of the test jack, a neutral wire came out of the terminal causing multiple relay actuations resulting in a half Group 2 isolation signal on the Division 2 side. Because of the plant being in Mode 5, refueling, the only isolation valves that closed because of the invalid isolation signal were the Division 2 isolation valves associated with the drywell ventilation monitor and the drywell floor and equipment sumps. The specific train and system actuated was the Primary Containment Isolation System (PCIS) Division 2 portion of the Group 2 isolation circuit (i.e. half group isolation). This was a partial actuation affecting only half of the logic and causing isolation of two systems. Based on the inadvertent actuation of the affected PCIS relays, the system isolated and functioned as expected. The isolation signal was reset at 0230 and the affected systems restored to service. The licensee notified the NRC Resident Inspector. | Primary Containment Isolation System | |
| ENS 46367 | 31 August 2010 22:37:00 | 10 CFR 50.73(a)(1), Submit an LER | Invalid Primary Containment Isolation System Actuation Due to a Voltage Transient | This telephone report is being made in accordance with 10 CFR 50.73(a)(2)(iv)(A) as an event or condition caused by an invalid signal that resulted in an automatic Group 6 isolation. On August 31, 2010 at 1737 CDT, Group 6 of Primary Containment Isolation System (PCIS) actuated. This resulted in completion of Secondary Containment isolation, initiation of the Standby Gas Treatment System and Control Room Emergency Filtration System. An invalid signal occurred apparently as a result of a voltage transient on the Nebraska City 345kV line. This was from a 3-phase fault to ground due to a structural failure during a severe thunder storm with high winds. The equipment associated with the Group 6 isolation functioned successfully and the isolation was complete. The Group 6 PCIS was reset. Cooper Nuclear Station operators reviewed the parameters that would cause a Group 6 trip signal (i.e. reactor water level, drywell pressure, reactor building radiation) and determined there were no valid conditions that would have caused the isolation. This event was most likely due an act of nature, thus no corrective actions were required. The NRC Resident Inspector will be notified. | Secondary containment Primary Containment Isolation System Standby Gas Treatment System Control Room Emergency Filtration System | |
| ENS 43097 | 20 November 2006 02:28:00 | 10 CFR 50.73(a)(1), Submit an LER | Invalid Actuation of Primary Containment Isolation System | This telephone report is being made in accordance with 10 CFR 50.73(a)(2)(iv)(A) as an event or condition caused by an invalid signal that resulted in an automatic actuation on November 19, 2006 at 2028 CST of the following Primary Containment Isolation System (PCIS) groups:
The systems above functioned as designed. Reactor Protection System (RPS) bus 'B' had lost power from its Motor Generator (MG) and was found de-energized which caused the actuations. Power was restored to the RPS bus 'B' from auxiliary power, and plant systems were recovered. In addition to the actuations reported above, the following actuations also occurred and functioned as designed.
* Group 1, Main Steam Isolation Valves (valves were already shut),
* Group 3, Reactor Water Clean-up (one valve shut),
* Group 7, Recirculation Loop Sample Lines (valves were already shut),
The cause of the invalid signal was 'B' RPS MG set high voltage condition produced by a faulty voltage adjust potentiometer in the voltage regulator. This caused a protective relay to trip the RPS MG exciter field which caused the subsequent low voltage and loss of the 'B' RPS bus. The licensee notified the NRC Resident Inspector. | Secondary containment Reactor Protection System Main Steam Isolation Valve Primary Containment Isolation System Primary containment Shutdown Cooling Standby Gas Treatment System Control Room Emergency Filtration System | |
| ENS 40697 | 9 March 2004 18:42:00 | 10 CFR 50.73(a)(1), Submit an LER | Invalid System Actuation Due to Momentary Power Interruption | This report is being made under 10 CFR 50.73(a)(2)(iv)(A). Actuations occurred on the following systems (System-Actuation Status) -Primary Containment (Drywell and Suppression Chamber) Atmospheric Control Isolation Valves - Complete -Drywell Vent Monitor - Partial -Off-gas Treatment - Partial -Secondary Containment - Complete -Control Room Ventilation - Complete -Standby Gas Treatment - Complete System response indicated that the cause was a momentary power interruption to a portion of the Primary Containment Isolation System Division 2 logic. Print verification determined that the system functioned as designed on loss of power. The Licensee will notify the NRC Resident Inspector. | Primary Containment Isolation System |