The chief of Japan's shuttered Fukushima nuclear power plant warned Wednesday that the biggest risk the crippled facility faces is another major earthquake and tsunami -- though insisted the chaos of nearly five years ago won't be repeated. Radiation spread over a wide area and forced tens of thousands of people from their homes -- many of whom will likely never return -- in the worst nuclear accident since Chernobyl in 1986. Videographic about radioactive contamination.VIDEOGRAPHIC