Could the man-made disaster surpass the natural one? Experts are calling the Japanese nuclear crisis the worst since Chernobyl after a third explosion and a fire at the Fukushima Daiichi nuclear plant Monday. Radiation levels near one reactor were 400 times the normal amount a human should experience in a year. Japan’s government has told people living within 20 miles of the plant to stay indoors, and the Tokyo metropolitan government has said it has detected radiation levels 20 times above normal over the city. So far, winds have blown most of the radiation out to sea.