Southern California Edison declared the alert at 3 p.m. PDT after about 30 gallons of ammonia leaked from the steam system in the Unit 3 reactor at the San Onofre Nuclear Power Plant on the border between San Diego and Orange Counties.
"The alert was required because fumes could prevent access to certain areas of the plant," Edison said in a written statement. "The control room is staffed and fully operational, and both units are at full power."
The alert was called off by early evening after repairs were made, the Orange County (Calif.) Register said.
Edison, the majority owner of the plant, which has a capacity of 2,200 megawatts, said the steam system is separate from the radioactive system and there was no danger to the public.