Nearly a decade after the Three Mile Island accident, half those polled believe another serious nuclear power accident is likely, and eight in 10 people favor stricter safety standards. An Associated Press-Media General survey found support for continued use of nuclear plants now operating. But most opposed building new plants or starting up completed plants that are not yet in operation. Overall, 55 percent said they supported use of nuclear power to generate electricity. But 56 percent of the 1,162 adults polled said it is impossible to store radioactive waste safely.