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| Entered date | Event description | |
|---|---|---|
| ENS 53793 | 18 December 2018 15:40:00 | On December 18, 2018 at 1126 CST, Arkansas Nuclear One, Unit 1 (ANO-1) reactor automatically tripped due to a loss of the A-1, non-vital 4160V bus. All control rods fully inserted. Loss of the A-1 bus resulted in de-energizing A-3 vital 4160V bus. Emergency Diesel Generator #1, K-4A, started automatically and is currently powering A-3 vital bus. Non-vital buses A-2, H-1, and H-2 and vital bus A-4 transferred power automatically to the Startup Transformer #1. Off-site power remains energized and available for ANO-1. The reason for loss of A-1 bus is unknown at this time. Currently, ANO-1 has stabilized in Mode 3, Hot Standby. Decay heat is being removed by the main condenser using the turbine bypass valves. The loss of the A-1, non-vital bus, is under investigation. The licensee has notified the NRC Resident Inspector and the state. |