05000318/LER-2025-001, Loss of Station Transformer U-4000-12
| ML25241A294 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 08/29/2025 |
| From: | Constellation Energy Generation |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML25241A292 | List: |
| References | |
| LER 2025-001-00 | |
| Download: ML25241A294 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3182025001R00 - NRC Website | |
text
Abstract
At 0842 7/2/25 with Unit 2 in Mode 1 at 100% power, an actuation of the Engineering Safety Feature Actuation System (ESFAS) Undervoltage (UV) occurred on Safety Related 4 kV Bus #21 during steady state conditions. The cause of the UV actuation was the loss of 13/4 kV transformer U-4000-12 due to its feeder breaker 252-1103 tripping open. The 2A Emergency Diesel Generator (EDG) automatically started as designed when the UV signal was received and re-powered 4 kV Bus #21. Non-Safety Related 4 kV Bus #22 automatically fast transferred to its alternate power supply. Additional information will be provided when the causal product evaluating this event is completed.E (See Page 2 for required number of digits/characters for each block)
(See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/) Page 3 of 3
D. CAUSE OF EVENT
The cause of the issue is under investigation. The supplement LER will provide detailed information from the causal product.
E. SAFETY ANALYSIS
The subject event satisfies the criteria in NUREG-1022, Revision 3, for any event or condition that resulted in manual or automatic actuation of any of the systems listed in 10 CFR 50.73, paragraph (a)(2)(iv)(B).
Specifically, for this event, the ESFAS actuated. Therefore, this event is reportable pursuant to 10 CFR 50.73(a)(2)(iv)(A).
No SSCs that were inoperable at the start of the event contributed to the event and the failure mode, mechanism, and the effect of each failed component is known.
F. CORRECTIVE ACTIONS
The cause of the issue is under investigation. The supplement LER will provide corrective actions from the causal product.
G. PREVIOUS OCCURRENCES
The cause of the issue is under investigation. The supplement LER will provide detailed information regarding
previous occurrences
H. COMPONENT FAILURE DATA
Component IEEE 803 IEEE805 FUNCTION ID SYSTEM ID Breaker BKR EB