(CNN) -- A small amount of radioactive gas escaped from a steam generator at Southern California's San Onofre nuclear power plant during a water leak, but there was no threat to public health, federal regulators said Wednesday.
Operators shut down the plant's No. 3 reactor on Tuesday after the water leak was discovered, Nuclear Regulatory Commission spokesman Victor Dricks said. The gas was vented from the steam generator into an auxiliary building, where it triggered a radiation monitor, he said.
The amount of gas that leaked was not immediately known, but it was a small amount that won't endanger the public or plant workers, Dricks said. He said the water leak was about six-hundredths of a gallon per minute, far below the levels required to declare an "unusual event" -- the lowest of four NRC alert levels.
NRC inspectors will conduct a follow-up review of the incident, Dricks said. The plant's owner, Southern California Edison, reported the problem Tuesday, but had no new comment on Wednesday.
The water leak occurred in the thousands of tubes that carry heated water from the reactor core through the steam generator, a 65-foot-tall, 640-ton piece of equipment that boils water used to drive the unit's turbines. Though leaking tubes periodically occur in older units, Dricks said, Southern California Edison replaced the steam generators at San Onofre between 2009 and 2011.
CNN's Karan Olson and Matt Smith contributed to this report.