05000318/LER-2025-001-01, Loss of Site Transformer U-4000-12
| ML25303A285 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 10/30/2025 |
| From: | Constellation Energy Generation |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML25303A283 | List: |
| References | |
| LER 2025-001-01 | |
| Download: ML25303A285 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| 3182025001R01 - NRC Website | |
text
Abstract
At 0842 7/2/25 with Unit 2 in Mode 1 at 100% power, an actuation of the Engineered 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. The cause of 1BKR252-1103 (U-4000-12 Feeder Breaker) tripping open due to the actuation of Differential Protection Relay 1RY287/T-12 was determined to be water intrusion into the switch enclosure 1H1103XSW.
(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/)
30Page 4 of 4 Water intrusion was also identified during an inspection of the U-25000-11 isophase on 02/18/2024 (04751071)
H. COMPONENT FAILURE DATA
Component IEEE 803 IEEE805 FUNCTION ID SYSTEM ID Breaker RG EB