One of four heavily damaged reactor buildings at Japan's tsunami-battered Fukushima nuclear power plant has been cleared of radioactive fuel rods, the operator said Saturday.

It was a significant step in the decommissioning efforts, but workers still have three heavily crippled reactors to clean up after they were sent into meltdown in the 2011 quake-tsunami disaster.

The overall cleanup work of the Fukushima plant is expected to take decades.

A total of 1,535 fuel rod assemblies have been now taken out of the building after Tokyo Electric Power Co.'s (TEPCO's) yearlong operation, a company spokesman said.

"Completion of the removal work is a milestone, but the decommission work will continue," plant chief Akira Ono told reporters.

The nuclear fuel was removed from a pool used to store the rods -- which were mostly spent -- in the reactor number 4 building, which was offline for regular checkups at the time of the March 2011 disaster.

The tsunami battered the plant's cooling system and sent reactors number 1 to 3 into meltdown, setting off the worst atomic accident in a generation.

TEPCO will remove fuel rod assemblies from the pools of other damaged buildings before extracting the melted fuel from the reactors.

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Tokyo Electric Power