NEW : Anti - nuclear activists warn of a potential environmental disaster . The San Diego nuclear plant has been shut down since radioactive gas escaped . Leaks occur periodically in older units , but plant owner Southern California Edison replaced the four steam generators at San Onofre in 2010 and 2011 as part of a $ 680 million project . Officials have said there 's no harm to the public there , but ca n't the problem 's cause . The head of the NRC says the plant wo n't safe until a cause and effect is put forward .
NEW : Anti - nuclear activists warn of a potential environmental disaster . The San Diego nuclear plant has been shut down since radioactive gas escaped . Officials have said there 's no harm to the public there , but ca n't the problem 's cause . The head of the NRC says the plant wo n't safe until a cause and effect is put forward .