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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 57091 | 25 March 2024 01:56:00 | 10 CFR 50.73(a)(1), Submit an LER | Invalid Actuation of Automatic Turbine Driven Auxiliary Feedwater Pump | The following information was provided by the licensee via phone and email: This report is being made in accordance with 10 CFR 50.73(a)(2)(iv)(A), under the provision of 10 CFR 50.73(a)(1), detailing the event in which an unplanned actuation of the turbine driven auxiliary feedwater pump (TDAFP) at the Callaway plant occurred in response to an invalid actuation signal. The actuation occurred at 2056 (CDT) on 3/21/2024 during restoration from maintenance on the NN12 inverter. The actuation signal was received while closing breaker NK0211 (for connecting the inverter to its associated 125-VDC bus). In response to the TDAFP actuation, operators closed the flow control valves and reduced turbine load by approximately 10 MW electrical. Initial investigation showed that a spurious manual actuation signal had been received and cleared 5 seconds later. The direct cause of the event was due to a voltage transient generated on the NK02 125-VDC bus during closure of the NK0211 breaker. The actuation occurred due to degradation of a 48-VDC power supply (PS1) within engineered safety features actuation system (ESFAS) logic cabinet SA036C. The power supply exhibited elevated ripple during testing as part of troubleshooting efforts, which was indicative of degradation of the regulation circuitry within the supply. This degradation prevented the power supply from sufficiently filtering the transient that occurred on the 125-VDC bus associated with the NN12 inverter. The power supply was replaced. The following additional information was obtained from the licensee in accordance with Headquarters Operations Officers Report Guidance: The licensee originally submitted this event under 10 CFR 50.72(b)(3)(iv)(A) in EN 57043. The licensee has retracted EN 57043. | Auxiliary Feedwater | |
| ENS 55972 | 2 May 2022 04:05:00 | Other Unspec Reqmnt 10 CFR 50.73(a)(1), Submit an LER | Invalid Specified System Actuation | The following information was provided by the licensee via phone and email: This non-emergency notification is being made pursuant to the provisions of 10 CFR 50.73(a)(1) to report the occurrence of an invalid automatic actuation satisfying the reporting criterion of 10 CFR 50.73(a)(2)(iv)(A), specifically for the actuation of one train of the Essential Service Water (ESW) system that occurred on May 1, 2022. On May 1, 2022, with the plant shut down and the core offloaded, control room personnel were performing a fast power transfer from Engineered Safety Feature (ESF) transformer XNB02 to ESF transformer XNB01. In anticipation of this activity, the `B' load shedder and emergency load sequencer (LSELS) had been removed from service. Also, at the time, a portion of the `A' ESW train was isolated to support performance of a local leak rate test (LLRT) of a containment isolation valve in the affected portion of `A' ESW train piping. Service Water was supplying cooling water flow to `A' train loads (in lieu of ESW cooling water). When the power transfer was performed, an unexpected automatic start of the `A' ESW pump, along with some associated, automatic valve repositioning, occurred. The actuation occurred due to inadvertent satisfaction of automatic start logic for the ESW pump. The logic is intended to detect loss of ESW flow when the opposite train LSELS isolates Service Water during an undervoltage condition on a safety bus. The flow transmitter involved in the actuation is situated in a portion of the ESW piping that was isolated for the LLRT. The low-flow signal from the transmitter was consequently not reflective of low cooling water flow to plant loads in light of the fact that cooling water flow was being supplied to plant loads and the transmitter was locally isolated. In regard to the ESW train actuation, therefore, although the undervoltage signal was considered a valid signal due to the voltage drop caused by the fast transfer activity, the low-flow signal from the noted transmitter was considered to be invalid. For this invalid actuation, it was concluded that the actuation was not part of a pre-planned sequence, that the affected system was not properly removed from service during the occurrence, and that the safety function had not already been performed relative to the occurrence. (The) NRC Resident Inspector has been notified and an email of this report has been sent to hoo.hoc@nrc.gov. | Service water | |
| ENS 49141 | 24 April 2013 09:04:00 | 10 CFR 50.73(a)(1), Submit an LER | 60-Day Optional Telephone Notification for an Invalid Specified System Actuation | This 60-day telephone notification is being made per the reporting requirements specified in 10CFR50.73(a)(2)(iv)(A) and 10CFR50.73(a)(1) to report an event involving an invalid actuation signal affecting the Auxiliary Feedwater (AFW) and Essential Service Water (ESW) systems. Initial conditions on 04/24/2013: refueling outage was in progress, there was no fuel in the reactor vessel (No MODE), a B safety-related train outage was in progress, and the A ESW train was in operation to support cooling of the A train safety-related equipment. Some separation group 2 bistables were in a tripped condition because instrument power bus NN02 was de-energized. At approximately 0400 (CDT) on 04/24/2013, Separation Group 4 DC bus NK04 experienced a ground condition. Plant personnel were using a plant procedure to search for the ground. When breaker NK5409 was opened, some unexpected Engineered Safety Features Actuation System (ESFAS) signals occurred. Opening the breaker removed power to the B ESFAS cabinet. With power removed to the B ESFAS cabinet, the circuit cards that generate cross-train trips failed to a tripped condition (thus generating cross-train trip signals) which resulted in some A train ESFAS actuations, in particular, auxiliary feedwater actuations for the A motor-driven and the turbine-driven AFW pumps. Additionally, an AFW Low Suction Pressure (LSP) circuit card tripped, and when combined with the bi-stable that was in a tripped state because bus NN02 was de-energized, the 2-out-of-3 logic was made up, resulting in an auxiliary feedwater LSP actuation. The LSP actuation resulted in the A Train ESW pump receiving a start signal, and the A motor-driven and the turbine-driven AFW pump suction supply valves receiving an actuation signal to transfer the suction supply from the normal source to the ESW system. Neither the motor-driven nor the turbine-driven auxiliary feedwater pumps started because they had been properly removed from service earlier in the outage. The A ESW pump was already running. No water was transferred from the ESW system to the AFW system since system tagging had been previously placed to isolate the two systems. The actuations were considered invalid because they were caused by opening breaker NK5409 which resulted in loss of power to the B ESFAS cabinet. The Senior Resident Inspector was notified. | Service water Auxiliary Feedwater | |
| ENS 49103 | 11 April 2013 06:28:00 | 10 CFR 50.73(a)(1), Submit an LER | 60-Day Optional Telephone Notification for an Invalid Specified System Actuation | This 60-day telephone notification is being made per the reporting requirements specified in 10CFR50.73(a)(2)(iv)(A) and 10CFR50.73(a)(1) to describe an invalid actuation signal affecting the emergency feedwater system. While the plant was in Mode 5 on 4/11/2013, during performance of a maintenance procedure for AMSAC system logic verification, an invalid MDAFAS occurred. (Note: AMSAC is ATWAS Mitigation System Actuation Circuitry and MDAFAS is Motor Driven Auxiliary Feedwater Actuation Signal). Both trains of the Motor Driven Auxiliary Feedwater Pumps (MDAFPs) started. While generation of the actuation signal is an expected result of the procedure, the actuation occurred several steps earlier in the procedure than expected. Additionally, the Control Room Operators were not expecting the MDAFPs to start. The pumps were manually stopped. The actuation was caused by procedural guidance not containing a sufficiently prescribed sequence of activities that should occur when simulating plant conditions leading to the intended actuation of the AMSAC system. The plant was not in a condition where feedwater was required. The Senior NRC Resident Inspector was notified. | Feedwater Auxiliary Feedwater | |
| ENS 44560 | 11 October 2008 05:49:00 | Other Unspec Reqmnt | Discovery of an After-The-Fact Notification of Unusual Event | At 0049 on 10/11/08 Letdown Relief valve BG8117 lifted prior to set point, resulting in Pressurizer water inventory being diverted the Pressurizer Relief Tank. Letdown was isolated within 13 minutes, isolating the leakage. Upon review of the level trends of the Pressurizer Relief Tank level changes, approximately 574 gallons were diverted from the Reactor Coolant system. This would result in an RCS leakage rate of 44 gpm of RCS Identified Leakage. At the time that the calculation of leakage rate was discovered, it was immediately recognized that this met the requirements for EAL 4R, 'RCS Identified Leakage greater than 25 gpm'. As a result of identification that the criteria of an EAL was exceeded, and no longer existed, a notification was made to the NRC Operation Center in accordance with 10 CFR50.72(a)(1)(i). Licensee has notified NRC Resident Inspector and will notify state and local agencies on the next business day. | Reactor Coolant System | |
| ENS 42852 | 8 September 2006 15:15:00 | Other Unspec Reqmnt | Discovery of After-The-Fact Emergency Condition: Inapproriate Change Made to Emergency Action Level 3J Back in 1997 Caused an Emergency, Alert, Not to Be Declared. | On 9/08/2006 at 1015 during painting activities in a safety-related area the Methanol Short Term Exposure Limit was exceeded. In accordance with Callaway Plant procedures the location was determined to contain a Hazardous ATMOSPHERE. Subsequently, Callaway Plant Emergency Action Levels (EAL) were reviewed and it was determined that the event did not meet the EAL criteria for Callaway Plant EAL 3J related to release of flammable or toxic gases in a safety - related area. On 9/21/2006 following a debrief that was conducted by Region IV NRC personnel, it was determined at 1025 that an inappropriate change to the intent of EAL 3J was made in 1997. As a result of this discussion, it was determined that an Alert should have been declared in accordance with plant EAL 3J. Per guidance given in NUREG 1022, Revision 2, Section 3.1.1. "Immediate Notifications", an ENS notification is being made within one hour of discovery of the event. No actual declaration of the emergency class will be made since the event has been concluded and the basis for the emergency no longer exists. The NRC Resident Inspector has been notified." Licensee also notified State, Local Officials and other government agencies. | ||
| ENS 41326 | 12 January 2005 19:30:00 | Other Unspec Reqmnt 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | 24 Hour Condition of License Report Regarding Halon System Actuator Port Connection Error | At 1330 on January 12, 2005, station personnel identified an error in connection of pilot lines to the manual-pneumatic actuator on halon bottles required for fire suppression. The vendor was contacted to confirm the configuration. The vendor indicated that the halon bottles would not properly discharge if the pilot lines were not properly connected. The system engineer inspected the halon systems. It was determined that five of six fire areas protected by halon systems were affected. Fire watches were implemented for the affected fire areas. Affected areas: A-27, Load Center/MG set Room, main - correct, reserve - 1 valve correct/1 valve incorrect A-17, South Electrical Penetration Room, main - correct, reserve - incorrect A-18, North Electrical Penetration Room, Main - correct, reserve - correct C-9, ESF Switchgear room 1*, main - incorrect, reserve - incorrect C-10, ESF Switchgear room 2*, main - incorrect, reserve - incorrect C-27, Control room cable trenches/chases**, bottle 1 - correct, bottle 2 - incorrect The main bank is sufficient to suppress a fire in a fire area.
The design and licensing basis for the fire protection system does not require consideration of a fire in more than one fire area at a time. No degraded fire barriers between the above fire areas were identified which would have allowed a fire to affect more than one of the fire areas at a time. Repairs were immediately initiated to correct the condition. As of 2010 CST, the repairs have been completed for the affected fire areas and restored to operable status. The licensee notified the NRC Resident Inspector.
Investigation - Informational tests conducted by the Vendor (Chemetron) and witnessed by Wolf Creek, Callaway, and NRC personnel on January 26, 2005 determined that the Halon systems would have properly actuated in the as-found incorrect configuration (port 'A' and 'B' connections reversed). The only identified difference in the actuation sequence between the tests conducted in the incorrect configuration versus the correct configuration is a delay of less than 2 seconds from the time the solenoid received the discharge signal until the first cylinder actuated. There is no regulatory or National Fire Protection Association standard or guideline that places a time requirement on this interval. This very slight time delay would have had no effect on the designed function of the Halon suppression system to extinguish a fire. Additional details are provided in the Chemetron report, 'Report on Actuation Arrangements for Halon Extinguishing System Units,' (Correspondence ULNRC 05-121) that includes the test procedure and results. Halon system function is to establish sufficient halon concentration for sufficient time to suppress a fire. This capability was not lost with the delay in actuation. Regulatory Evaluation - Guidance for reporting to the criterion of 10 CFR 50.73(a)(2)(ii) is provided in section 3.2.4 of NUREG 1022 rev 2, 'Event Reporting Guidelines 10 CFR50.72 and 50.73.' This guidance states that an LER is required for a seriously degraded principal safety barrier or an unanalyzed condition that significantly degrades plant safety. Operating License Condition 2.C(5)(c) states the following: The Operating Corporation shall maintain in effect all provisions of the approved fire protection program as described in the SNUPPS Final Safety Analysis Report for the facility through Revision 15, the Callaway site addendum through Revision 8, and as approved in the SER through Supplement 4, subject to provisions d below. Conclusion: - Based upon the information provided, the Halon suppression system would have operated to extinguish a fire. This condition is not considered reportable to the requirements of 10 CFR 50.72(b)(3)(ii)(B), 10 CFR 50.73(a)(2)(ii), nor is it a violation of the Operating License Condition 2.C(5)(c). Consistent with this conclusion, ENS notification number 41326 for this event is to be retracted. The licensee notified the NRC Resident Inspector. | ||
| ENS 41205 | 18 September 2004 22:35:00 | Other Unspec Reqmnt | Discovery of After-The-Fact Emergency Condition (Unusual Event) | At 1735, 9/18/04, Callaway Control Room received an alarm on K0008 (Fire Protection Alarm and Control Workstation) for the Communication Corridor Lobby 2047 elevation. Initial investigation found significant smoke in the area of the Communication Corridor Elevator Room. During the investigation, a report was received in the Control Room that a small fire had occurred on the roof and had been extinguished. At 1743, the Callaway Fire Brigade was activated to investigate the source of the smoke. Upon arriving at the scene, no flames were observed and the Brigade began removing visquene (plastic) to facilitate observing additional areas within the room. At this time, small flames were observed and plant Emergency Alarm Level (EAL) 3E, 'Fire within the Protected Area boundary not extinguished within 15 minutes of verification' 15-minute time limit was entered. The fire was extinguished using a single powder type extinguisher and declared out at 1754. At 1910, an Operator reported that the Communication Corridor fire had reflashed. The Fire Brigade was reactivated and the fire was extinguished at 1919 using a single powder type extinguisher. After determining the temperature of the elevator room ceiling was 250 degrees F, water was applied to the ceiling from inside the room and from the roof above. After verification that the fire was extinguished, a continuous fire watch was established for both the affected room and roof area. Initial evaluation of the fire event concluded that the fire was extinguished within 15 minutes of discovery, and due to the size and location of the fire, the fire did not pose any safety significance. No safety systems had been impacted, Control Room habitability was not impacted, no safety system functions were required, and no safety functions were lost. Based upon this evaluation, it was decided that in accordance with guidance provided by EAL 3E, declaration of an Unusual Event was not required. Upon further review of the event associated with NRC Integrated Inspection Report 05000483/2004004, at 0925, 11/18/04, it was determined that a fire existed from the initial alarm at 1735 and lasted longer than 15 minutes. Because the initial fire lasted longer than 15 minutes, an Unusual Event should have been declared in accordance with plant Emergency Alarm Level 3E, 'Fire within the Protected Area boundary not extinguished within 15 minutes of verification.' Per guidance given in NUREG 1022, Revision 2, Section 3.1.1, 'Immediate Notifications', an ENS notification is being made within one hour of discovery of the event. No actual declaration of the emergency class will be made since the event has been concluded and the basis for the emergency no longer exists. The licensee will inform both state and local agencies and has informed the NRC Resident Inspector. | ||
| ENS 40705 | 26 April 2004 22:11:00 | Other Unspec Reqmnt | Technical Specifications Required Report of Steam Generator Defective Tubes | During Refueling Outage RF13, interim results of 'A' Steam Generator (S/G) tube inspections indicate 59 tubes out of 5341 tubes (i.e., > 1 %) have been determined to be defective. This S/G tube inspection result for the 'A' S/G is classified as category C-3 in accordance with Technical Specification 5.5.9, Table 5.5.9-2. Per NUREG 1022, Section 3.2.4 Discussion (A)(3), the present C-3 classification of the 'A' S/G tubes does not meet the listed criteria for serious S/G tube degradation and thus is not a degraded or unanalyzed condition. Since this report is required by Administrative Technical Specification 5.5.9, this notification is being listed as an 'Other Unspecified Requirement'. All defective tubes will be removed from service before the S/G is returned to service. There were no adverse safety consequences or implications as a result of this event. This event did not adversely affect the safe operation of Callaway Plant or the health and safety of the public. The licensee notified the NRC Resident Inspector. | Steam Generator | 05000483/LER-2004-006 |