Testing No Cause For Concern at San Onofre

There has been some concern about testing being conducted at San Onore Nuclear Generating Station’s Unit 2 reactor, which is currently shut down. On Monday, as part of a plan by Southern California Edison (SCE) to test the plant’s auxiliary feedwater pumps, as well as other equipment, the plant was heated to normal operating temperature of about 535 degrees and normal operating pressure of 2,200 psi. Heat is being supplied to the system by running reactor coolant pumps, not the reactor. The heat forms steam in the steam generators, which is needed to test this equipment. During this testing, the reactor remains shutdown.

The licensee is required to perform this testing at the conclusion of a refueling outage. They expect to remain in this testing condition (Mode 3) for about one week, and then return the plant to cold shutdown conditions (Mode 5). During the extended shutdown of Unit 2, Southern California Edison plugged degraded tubes. As a preventive measure, several hundred additional tubes were plugged and removed from service because of their physical location at the top of the steam generators. This was to prevent further tube to tube wear during potential future operations.

On Sunday, October 21, 2012, craftsmen at the plant identified a small hydrogen leak coming from the hydrogen supply piping system on Unit 2. The craftsmen were checking for leaks by spraying soapy water on piping joints. This is a routine leakage check. A minute amount of bubbles were observed, indicating that a very low amount of hydrogen was leaking at a mechanical piping joint. The piping joint was tightened and the leak was stopped.

Hydrogen is used at electric power plants (not just nuclear power plants) for main electrical generator cooling. At San Onofre, the affected hydrogen piping that transports hydrogen to the generator on the non-nuclear side of the plant is outdoors near the turbine building. The small amount of hydrogen leaking from the mechanical joint did not pose a threat to the public or workers on site. Since it was outdoors, a significant amount of hydrogen at combustible concentrations could not accumulate in one area.

Victor Dricks
Senior Public Affairs Officer
Region IV