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| Entered date | Event description | |
|---|---|---|
| ENS 57091 | 25 April 2024 13:38:00 | 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. |
| ENS 57043 | 22 March 2024 01:46:00 | 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.
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) |
| ENS 55972 | 30 June 2022 14:21:00 | 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. |
| ENS 55538 | 21 October 2021 18:46:00 | A non-licensed employee supervisor had a confirmed positive for alcohol during a random fitness-for-duty test. The employee's access to the plant has been terminated. The NRC Resident Inspector has been notified. |