NEW : Anti-nuclear activists warn of a potential environmental catastrophe . The San Onofre nuclear plant has been shut down since radioactive gas escaped . Score: 6 The head of the NRC says the plant wo n't restart until a cause and plan is put forward .
NEW : Anti-nuclear activists warn of a potential environmental catastrophe . The San Onofre nuclear plant has been shut down since radioactive gas escaped . Officials have said there 's no harm to the public health , but ca n't identify problem 's cause . The head of the NRC says the plant wo n't restart until a cause and plan is put forward .