The plant is testing the siren system that alerts communities of an emergency.
The plant has been offline since Jan. 31 to repair corroded steam generator tubes. So far, there's no word on when it might start producing electricity again.
Meanwhile, the San Onofre Nuclear Generating Station has been selected as one of seven nuclear facilities that will take part in a government study on cancer risks.
The $2 million study will look at multiple types of cancer in populations around plants in California, Connecticut, Illinois, Michigan, New Jersey and Tennessee and near a uranium fuel producer in Tennessee. It also will specifically examine cancers in children living near the facilities.
The study, by the National Regulatory Commission, will begin in the next few months and could pave the way for a future study of all 65 U.S. nuclear plants.
The Associated Press contributed to this report.