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The following information was provided by the licensee via email: At 2056 on 3/21/24, Callaway Plant was in Mode 1 at approximately 100 percent power when an automatic start of the turbine driven auxiliary feedwater pump occurred. The event occurred while restoring inverter NN12 from maintenance. NN12 is the normal in-service inverter for the group 2 120-VAC instrument bus (NN02). The actuation occurred while swapping from the swing inverter (NN18) to the normal in-service inverter (NN12). All safety systems responded as expected. At 2334, the turbine driven auxiliary feedwater pump was secured. The plant is being maintained in a stable condition, in mode 1. The NRC Resident Inspector was notified The licensee is investigating the cause of the automatic start.

• * * RETRACTION ON 4/25/2024 AT 1432 EDT FROM GREG CIZIN TO ERNEST WEST * * *

Event Notification (EN) 57043, made on 03/21/2024 pursuant to 10 CFR 50.72(b)(3)(iv)(A), is being retracted based upon further investigation into the cause of the turbine driven auxiliary feedwater pump (TDAFP) actuation. The TDAFP received an invalid manual initiation signal caused by a voltage transient that was generated on the NK02 125-VDC bus upon closure of downstream breaker NK0211 (while restoring inverter NN12 from maintenance). This actuation signal was due to degradation of a 48-VDC power supply (PS1) within engineered safety features actuation system (ESFAS) logic cabinet SA036C. This degradation likely prevented the power supply from sufficiently filtering the transient that occurred on the 125-VDC bus associated with the NN12 inverter. Notified R4DO (Warnick)

EN Revision Text: REACTOR TRIP DUE TO SOURCE RANGE HI FLUX SIGNAL This is an 8-hour, non-emergency notification for a valid reactor trip signal with the reactor not critical, and a valid auxiliary feedwater system actuation in accordance with 10 CFR 50.72(b)(3)(iv)(A) - Valid System Actuation.

At 2303 (CDT) on May 16, 2019, the plant was administratively in mode 2 due to withdrawing control rods for startup following refuel. The reactor had not been declared critical. The P-6 permissive at 10E-10 Amps was met for one of two Intermediate Range detectors allowing for block of the Source Range high flux trip (1E5CPS). Prior to performing the block, the Source Range high flux trip setpoint was exceeded and a reactor trip received. All systems responded as expected. A feedwater isolation signal was received due to the reactor trip with feedwater temperature less than 564 degrees Fahrenheit. Auxiliary feedwater was started to maintain steam generator levels. The plant is being maintained stable in mode 3 with no complications. The NRC Resident Inspector was present during the startup and was notified of the reactor trip.

• * * UPDATE FROM JONATHAN LAUF TO HOWIE CROUCH AT 1454 EDT ON 6/5/19 * * *

A correction is being made for the sixth sentence in the second paragraph above, which states, 'A Feedwater Isolation signal was received due to the reactor trip with feedwater temperature less than 564 degrees Fahrenheit.' Within this sentence, 'feedwater temperature' is to be replaced with 'reactor coolant system temperature.' The licensee has notified the NRC Senior Resident Inspector.

At 2302 (CDT) on April 2, 2016, with the plant shutdown, (with) all control rods inserted in the reactor and while attempting to reset the reactor trip breakers to support outage activities (reset of the main turbine), the reactor trip breakers reopened. This was identified to be due to having both trains of Solid State Protection System (SSPS) out of service while in Mode 5. With both trains of SSPS out of service, a condition was met that would cause a reactor trip signal due to having a general warning condition on both trains. Per procedure, the control rods were incapable of withdrawal and fully inserted. Reactor Coolant System boron was 2280 ppm. There were no actuations as a result of the reactor trip breakers opening due to SSPS being removed from service. The licensee will be notifying the NRC Resident Inspector.

• * * RETRACTION AT 1635 EDT ON 4/4/16 FROM TIM HOLLAND TO JEFF HERRERA * * *

At 0713 EDT on April 3, 2016, EN #51846 provided notification of a Reactor Protection System actuation as revealed by the reactor trip breakers opening. Upon further investigation, it has been determined that the system actuated during maintenance activities due to a reactor trip signal caused by both trains of the Solid State Protection System (SSPS) being in test. This signal was not in response to actual plant conditions or parameters satisfying the requirements for initiation of the system and was therefore invalid. As such, the notification made by EN #51846 for a valid actuation of a specified system is hereby retracted. In addition, an editorial change to the first sentence of the original notification description is hereby made. The first sentence is revised to read as follows: At 2303 EDT on April 2, 2016, with the plant shut down and all control rods inserted into the reactor, while attempting to reset the reactor trip breakers to support outage activities (reset of the main turbine), the reactor trip breakers reopened. The NRC Resident Inspector will be notified. Notified the R4DO (Kellar).

On July 26, 2013, at 2349 CDT, the Callaway nuclear power plant declared an Unusual Event due to a fire not extinguished within 15 minutes of control room notification, EAL HU 2.1. The fire was located in the turbine building near the main generator. Concurrent with the fire, the reactor tripped due to a turbine trip. All control rods fully inserted and all reactor coolant pumps (RCPs) tripped. The fire has been extinguished and the licensee is in progress of restoring RCPs. The licensee notified the NRC Resident Inspector, State Emergency Management Agency and Local Authorities. Notified DHS SWO, FEMA, and DHS NICC.

• * * UPDATE ON 7/27/13 AT 0201 EDT FROM MARK COVEY TO BILL HUFFMAN * * *

The licensee terminated the Unusual Event at 0101 CDT. Decay heat is being removed via aux feed water from the steam generators to the condenser. Visual inspection determined the location of the fire to be in the phase B generator bus duct. Notified R4DO (Allen), NRR EO (Monninger), IRD (Marshall), DHS SWO, FEMA, and DHS NICC.

• * * UPDATE ON 7/27/13 AT 0430 EDT FROM MARK COVEY TO DONG PARK * * *

The licensee made notifications under 10CFR50.72(b)(2)(iv)(B) (RPS Actuation), 10CFR50.72(b)(2)(xi) (Offsite Notification) and 10CFR50.72(b)(3)(iv)(A) (ESF Actuation - AFW). The licensee will be making a press release and notifying the NRC Resident Inspector. Notified R4DO (Allen).

• * * UPDATE ON 7/27/13 AT 0826 EDT FROM MARK COVEY TO BILL HUFFMAN * * *

Upon further review, the licensee believes that the initially reported EAL for the UE notification, HU 2.1, was not applicable. Although indications of a fire were present for greater than 15 minutes, the criteria at Callaway apply to a fire within 50 feet of safety related equipment. There was no safety related equipment within 50 feet of where the fire occurred. The proper EAL classification should have been HU 3.1 due to release of potentially toxic gas or asphyxiant or flammable gas that could impact plant operation. This EAL is applicable due to the heavy smoke release from burning electrical insulation and melted bus and ductwork which prevented access to the turbine building area where the fire took place. The licensee will notify the NRC Resident Inspector of this update. Notified R4DO (Allen).

During plant shutdown to begin a scheduled refueling outage, with the plant at 0% power in Mode 3, an actuation of the reactor trip system (RTS) occurred when a steam generator (S/G) Low-Low water level trip inadvertently occurred during recovery from a feedwater isolation actuation that had previously occurred in response to a steam generator high water level trip condition. At approximately 0500 hours, plant operators were closing the main steam isolation valves (MSIVs) for plant shutdown. Once the MSIVs were closed, the reactor coolant system (RCS) cooldown rate decreased significantly. The 'A' atmosphere steam dump valve (ASD) was then opened. Shortly after the ASD was opened, the MSIV was also opened. With both the MSIV and ASD open, however, the 'A' S/G water level swelled until the P-14 S/G Hi Level protective interlock setpoint was reached, resulting in a feedwater isolation (FWIS) actuation at 0505 hours. Subsequent to the FWIS actuation, plant operators took action to recover from the FWIS in accordance with off-normal operating procedure OTO-SA-00001, 'Engineered Safety Feature Actuation Verification and Restoration.' The motor-driven auxiliary feedwater pumps were started to restore S/G water level. However, S/G water level lowered rapidly in response to the cold auxiliary feedwater flow to the S/G. A S/G Low-Low water level trip signal was then reached on the 'A' S/G, thus resulting in a reactor trip system actuation at 0508 hours. All systems functioned normally in response to plant conditions. The NRC Senior Resident Inspector has been informed.

• * * UPDATE AT 0239 EDT ON 10/12/08 FROM FRED BIANCO TO VINCE KLCO * * *

This report is an update to information reported under ENS notification 44561. The original notification reported a valid reactor trip system actuation as a 4-hour notification under 10CFR50.72(b)(2)(iv)(B). The correct reporting requirement is 10CFR50.72(b)(3)(iv)(A), an 8-hour notification, as the plant was in Mode 4 with the reactor subcritical at the time of the event. The (NRC) Resident Inspector will be notified. Notified R4DO (Powers).

The following information was received from the licensee via facsimile: At 1519 (CDT) on 2-15-04, the plant was at 20 power, increasing load. During the transfer from the bypass feedwater regulating valves to the main feedwater regulating valves, the main turbine tripped due to a P-14 S/G Hi-Hi level signal. The P-14 signal also caused a Feedwater Isolation Signal (FWIS), which resulted in a Motor Driven Aux Feedwater Actuation (MDAFAS), and Steam Generator Blowdown Isolation Signal. Steam Generator levels subsequently shrunk to low levels causing a Steam Generator low level reactor trip at 1524 (hrs). Sometime after the turbine trip, the turbine driven aux feed pump ((TDAFP)) was manually started to help restore S/G levels. The pump was later manually secured, but then received a subsequent auto-start signal and tripped on overspeed. The TDAFP was declared inoperable at 1535 (hrs). With the exception of the TDAFP, all safety systems operated properly. The plant is currently stable in Mode 3, with the primary plant at 557 deg F and 2235 psig, and pressurizer level at 25%. The licensee has notified the NRC Resident Inspector.

• * * UPDATE AT 0031 EST ON 2/16/04 HOPE BRADLEY TO GOTT * * *

The following information was received from the licensee via facsimile as a "rewrite of above paragraph 2. Sometime after the turbine trip, the Turbine Driven Aux Feedwater Pump (TDAFP) was manually started to help restore S/G levels. Due to decreasing reactor coolant system (RCS) temperature, it was decided to stop the TDAFP since it is a steam load. The steam supply valves were remote manually closed from the control room. At the same time the steam supply valves were closing, the steam generator levels shrunk to low levels causing a Steam Generator low level reactor trip and Turbine Driven Aux Feedwater Actuation (TDAFAS) at 1524. The steam supply valves immediately reopened due to the TDAFAS. It is postulated that this transient in the steam supply caused the pump to overspeed trip. The TDAFP was declared inoperable at 1535. With the exception of the TDAFP, all safety systems operated properly. The licensee notified the NRC Resident Inspector. Notified R4DO (Cain).

AT 0439, 02/03/04, Callaway Plant experienced a reactor trip while operating transmission breakers located in the plant switchyard. Auxiliary feedwater actuated as expected to stabilize steam generator water levels. All other plant systems responded as expected. At present, the cause of the reactor trip is undetermined. Initial indications are that there were no voltage or frequency perturbations on the electrical grid. Plant staff is investigating potential areas in an effort to identify the cause of the trip. The main generator output breakers opened when one of the transmission breakers in the switchyard was opened per the scheduled maintenance test. When the incoming Transmission line breaker was opened it should not have caused the main generator output breakers to open. All rods fully inserted into the core. Both Motor Driven Auxiliary Feedwater pumps automatically started on a loss of both main feedwater pumps and the Turbine Driven Auxiliary Feedwater pump started on low low steam generator water level. The "C" Steam Generator atmospheric steam dump valve opened for about 17 seconds before it closed (no leaking steam generator tubes in the "C" Steam Generator). All Emergency Core Cooling systems are fully operable except for the "A" Safety Injection System. It was declared inoperable when it failed a valve test last night at 0205 CST. All Emergency Diesel Generators are fully operable.

  Turbine Driven Auxiliary Feedwater Pump discharge valves were closed after it had operator for about two hours.  Approximately one hour after the valves were closed the Turbine Driven Auxiliary Feedwater pump tripped. This incident is being investigated.  

The NRC Resident Inspector was notified of this event by the licensee.