A power plant operator will restart a reactor in southern Japan today, the first under new safety requirements following the Fukushima disaster and a milestone for the nation’s return to nuclear power.

Nuclear power returned to Japan's energy mix today as the first reactor to be restarted since last year's earthquake and tsunami came back online.

A worst-case scenario sketched out by the Japanese government foresaw the end of Tokyo in a chain of nuclear explosions as the Fukushima crisis erupted last year, an independent panel said.

Emergency crews are still battling to cool overheated nuclear fuel at a stricken nuclear plant a week after the devastating earthquake and tsunami struck Japan.