Manual Scram Due to Unisolable Circulating Water System Leak

Event Number: 46103

"At approximately 1641 EDT on July 16, 2010, Susquehanna Steam Electric Station Unit 1 reactor was manually scrammed due to a large unisolable circulating water system leak in the main condenser area. Attempts to isolate the source of the leakage were unsuccessful. During these attempts, reactor operators lowered reactor power from approximately 90% to about 39%. Based on rising water level in the condenser area and unsuccessful isolation of the source of the leakage, Operations decided to shut down the plant. The reactor operator placed the mode switch in shutdown. All control rods [fully] inserted. Reactor water level lowered to -28 inches causing Level 3 (+13 inches) isolations. The Operations crew subsequently maintained reactor water level at the normal operating band using RCIC. No steam relief valves opened. The main steam isolation valves were manually closed and the circulating water system was shut down. Pressure control was initiated using HPCI in the pressure control mode. All safety systems operated as expected. The reactor is currently stable in Mode 3. Actions to isolate and investigate the cause of the circulating water system leakage are underway. Unit 2 continued power operation."

The licensee has notified the NRC Resident Inspector, and will be issuing a press release.