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The final pieces of a jelly roll-shaped cover are being put in place atop Fukushima's most damaged nuclear reactor.

Huge cranes have been installed to begin removing 566 sets of still-radioactive fuel rods from a storage pool later this year. It's taken seven years just to get this far, the first concrete step toward dismantling the Tokyo Electric Power Co. nuclear plant, damaged in an earthquake and tsunami.

Cleaning up the Fukushima Dai-ichi plant is a monumental task expected to take three to four decades.

Taking out the stored fuel rods is only a preliminary step. Ahead lies the uncharted challenge of removing an estimated 800 tons of melted fuel and debris, six times the amount from the 1979 Three Mile Island accident.