On November 04, 2012, at 1115 hours, Primary Coolant System (PCS) loop 2 was declared inoperable due to the discovery of an un-isolable steam/water leak near a drain valve of an atmospheric dump valve from the “B” Steam Generator. The leak originated from a pin-hole size through-wall flaw in the socket weld on the inlet side of the drain valve. The drain valve is part of the ASME Section Xl Class 2 piping system that provides steam to the turbine.

Due to the inoperable PCS loop, Technical Specification 3.4.4, Condition A, required the plant be placed in Mode 3 within six hours. The plant entered Mode 3 at 1621 hours on November 4, 2012. At 1224 hours on November 5, 2012, the plant entered Mode 5 to execute repairs.

During fabrication of the socket weld in 1986, the welder did not utilize proper welding techniques to create a quality weld for the shield metal arc welding process used at that time. Lack of a quality weld resulted in a through-wall flaw. The drain valve was replaced using a gas tungsten arc welding process.

CAUSE OF THE EVENT

During fabrication of the socket weld in 1986, the welder did not utilize proper welding techniques to create a quality weld for the shield metal arc welding process used at that time. Lack of a quality weld resulted in a through-wall flaw and subsequent leak.

CORRECTIVE ACTIONS TAKEN

The drain valve was replaced utilizing a gas tungsten arc welding process. An extent of condition review identified one additional weld that was fabricated by the same welder, in approximately the same time period. That weld was replaced in 2010 during a plant modification process.