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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 47624 | 30 January 2012 16:01:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation 10 CFR 50.72(a)(1)(i), Emergency Class Declaration 10 CFR 50.72(b)(3)(iv)(A), System Actuation 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown | Unusual Event Due to Loss of Offsite Power Greater than 15 Minutes | At 1101 EST, Byron Unit-2 experienced a reactor trip due to RCP undervoltage. All rods fully inserted, MSIV's were manually closed and decay heat is being removed by Auxiliary Feedwater pumps running and steam leaving via atmospheric relief valves. The unit is currently in a natural circulation cooldown with the diesels supplying station emergency loads. Licensee will be cooling the plant down to Mode 5. At 1118 EST, Byron declared an Unusual Event due to a loss of offsite power on Unit 2 from a faulted Station Auxiliary Transformer (SAT). The faulted SAT caused both 6.9 kV and 4.1 kV bus voltage to drop. Smoke was observed coming from the SAT with no visible flames being apparent. This caused bus loads to trip without a complete loss of ESF busses 241 and 242. These buses were manually disconnected from the SAT, which transferred the load to the emergency diesel generators 2A and 2B. Both diesel generators started and loaded without incident. Offsite assistance was requested from the local fire department as a precaution. The licensee is also declaring notification for 10 CFR 50.72(b)(3)(v)(D) Unit 1 is not being affected by this event and remains at 100% power. The licensee has notified the NRC Resident Inspector.
At 2000 CST on 1/31/12, Byron terminated their Unusual Event due to the Loss of Offsite Power to Unit 2. Switchyard repairs were completed and offsite power has been restored to essential busses 241 and 242 thru System Auxiliary Transformers 242-1 and 242-2. Unit 2 Emergency Diesel Generators have been shutdown. The licensee is citing classification 10 CFR 50.72(c)(1)(iii) The licensee has notified the NRC Resident Inspector. Notified R3DO (James Cameron), NRR EO (Louise Lund), IRD MOC (Scott Morris), DHS (Konopka) and FEMA (Hollis). Licensee may issue a press release. | Emergency Diesel Generator Auxiliary Feedwater | |
| ENS 43735 | 19 October 2007 23:30:00 | 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown | Tech Spec Required Shutdown Due to Ultimate Heat Sink Inoperability | lnitiated Unit 1 and Unit 2 plant shutdown due to inoperability of ultimate heat sink system. The inoperability is due to structural integrity failure of ASME Class 3 piping through wall leakage of the 0C Essential Service Water riser piping of the mechanical draft cooling tower. Licensee is in Technical Specification 3.7.9 which requires the units be in Mode 3 in 6 hours and Mode 5 in 36 hours. The licensee has notified the NRC Resident Inspector. | Service water |