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Unit 2 automatically tripped from 100% reactor power as a result of the over-current trip of the 2C Reactor Coolant Pump. Both station auxiliary transformers on Unit 2 subsequently tripped offline. All control rods fully inserted on the trip. Auxiliary feedwater auto-started and maintained Steam Generator water level. The unit is stable in Mode 3. The Emergency Diesel Generators auto started and loaded supplying both emergency busses with power. All systems functioned as required. There was no affect on Unit 1. The licensee notified the NRC Resident Inspector.

• * * UPDATE AT 0218 ON 8/2/2009 FROM DEAN YARBROUGH TO MARK ABRAMOVITZ * * *

At 2059 on July 30, 2009, a reactor trip of Unit 2 at Braidwood occurred. A loss of offsite power occurred and an Unusual Event was declared at 2108. NRC Headquarter Operations was notified at 2155 (ENS call # 45238). Power from System Auxiliary Transformer (SAT) (credited offsite power supply) 242-2 was restored to buses 241 and 242 (safety related buses) at 0036 on August 2, 2009. The Unusual Event was terminated at 0036 on August 2, 2009. This call is being made due to the termination of the Unusual Event declared on July 30, 2009. An Event Summary Report is required by Exelon procedures within 24 hours of termination of the Unusual Event and will be communicated to the Headquarter Operations later today. The initial event was the result of the actuation of the SAT sudden pressure relay. When the transformer tripped, a slow automatic bus transfer resulted. When the RCPs (Reactor Coolant Pump) and condensate pumps were reenergized, they tripped on overcurrent causing the reactor trip. The sudden pressure relay has subsequently tripped during testing and may have caused the initial event. The licensee reported no damage to the plant. The licensee notified the NRC Resident Inspector. Notified the R3DO (Daley), IRD (McDermott), NRR (Howe), DHS (An), and FEMA (Biscoe).

• * * UPDATE AT 1617 ON 8/2/2009 FROM SCOTT BUTLER TO VINCE KLCO * * *

The Event Summary Report was received and documented the following technical conclusions: The Unusual Event declaration was caused by a sudden pressure relay on SAT 242-1 causing a lockout of both SATs followed by a trip of Unit 2 due to the 2C RCP tripping during the automatic bus transfer for bus 258. This led to a loss of offsite power to Unit 2. It is currently unknown why the sudden pressure relay on SAT 242-1 actuated. Troubleshooting on the sudden pressure relay is in progress. The licensee will notify the NRC Resident Inspector. Notified the R3DO (Daley). Notified the IRD (McDermott) and NRR (Howe) via e-mail.