TOKYO (AFP) - The operator of the crippled Fukushima nuclear plant said it has removed a 20-ton piece of rubble from a destroyed reactor in what it called a "major step forward" in decommissioning.

After months of planning, Tokyo Electric Power Co (Tepco) said it used giant cranes on Sunday to lift one fuel handling machine, which was destroyed when a quake-sparked tsunami sent some of the plant's reactors into meltdown in March 2011.

The company described the delicate operation as a critical step toward clearing highly radioactive spent fuel rods from the cooling pool inside its badly damaged Reactor number 3.

The fuel handling machine was a key part of the process that transferred nuclear fuel assemblies into the reactor core.

"It paves the way for continued progress and is a milestone in reducing the risk of removing spent fuel assemblies," said the company's chief decommissioning officer Naohiro Masuda.

Removing fuel from the pool at the site's reactors is scheduled to last until the second half of 2021.

However, decommissioning efforts to clean up the debris at the shattered plant are expected to last some four decades.

The announcement comes several days after the government said compensation costs from the worst nuclear disaster since Chernobyl in 1986 are expected to be more than US$57 billion (S$78 billion).

Tokyo has poured billions of dollars into the embattled company to keep it afloat as it stumps up cash for decommissioning the reactors, cleaning up the mess from the disaster and paying compensation.