05000281/LER-2006-002
| Docket Numbersequential Rev Month Day Year Year Number No. Month Day Year Surry Power Station, Unit 1 05000 - 280 | |
| Event date: | 10-07-2006 |
|---|---|
| Report date: | 12-05-2006 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2812006002R00 - NRC Website | |
1.0 DESCRIPTION OF THE EVENT operators received indications of a secondary side transient. As a result, the operating team responded promptly by manually tripping Unit 2. The incident resulted in reportable events for both units as described in the following discussions.
At 17:11:18 on October 7, 2006, a spurious signal from the Unit 2 Turbine Overspeed Protection Circuit (OPC) [EIIS-JJ] momentarily closed the turbine governor and intercept valves [EIIS-TA-FCV]. When the OPC signal cleared, the governor valves re-opened immediately followed by the intercept valves opening a few seconds later. High Steam Flow, Steam Flow/Feed Flow Mismatch, Tave/Tref Deviation, and Steam Generator (SG) Level Error alarms were received in the main control room (MCR) for all three Unit 2 SGs. The Unit 2 cross-under safety valves [EIIS-TA-FCV] located on both sides of the turbine building lifted causing portions of the Unit 2 Turbine Building siding [EIIS-NM] to detach and contact the bus bars on two of the three Reserve Station Service Transformers (RSST) [EIIS-EA]. As a result, power was lost to two of three transfer busses [El IS-EA-BU] that supply offsite power to the emergency busses, Unit 1 Emergency Busses 1J and 1H, and the Unit 2 Emergency Bus 2J. Emergency Diesel Generator (EDG) 1 [EIIS-EK] started and restored power to the Unit 1 Emergency Bus 1H and EDG 3 started and restored power to the Unit 2 Emergency Bus 2J, as designed. Unit 1 Emergency Bus 1J remained de-energized. Unit 2 Emergency Bus 2H continued to be energized from offsite power.
At 17:11:37, within approximately 20 seconds of the initial alarms and after receiving a report of a steam leak in the turbine building, a conservative decision was made by the operating team to manually trip the Unit 2 reactor. The steam leak report was later determined to be associated with the lifting of the cross-under safety valves.
Emergency systems functioned as designed, including the Reactor Protection System, Emergency Diesel Generators, and Auxiliary Feedwater System. The #4 Turbine Stop Valve [EllS-SB-V] did not indicate fully closed, which was later determined to be an indication problem, and the operating team responded by closing all three Unit 2 Main Steam Trip Valves (MSTVs) [EIIS-SB-V] as directed by operating procedures. As a result, AFW and the SG pressure operated relief valves (PORVs) [EIIS-SB-RV] were used to remove decay heat.
As a result of the power loss to the transfer busses, two of the three Unit 2 Reactor Coolant Pumps (RCPs) [El IS-AB-P] and the Unit 2 containment air radiation monitor