Story highlights Submersible robot sends back images thought to be of melted nuclear fuel

Data acquired by robot will be key to cleaning up the ruined nuclear plant

Tokyo (CNN) A robot operating deep inside a failed reactor at the stricken Fukushima nuclear plant north of Tokyo has revealed what appears to be stalactites of melted nuclear fuel, the plant's operator has said.

The discovery is considered a key development in the decommissioning process of the plant, which suffered a catastrophic meltdown in 2011 after a huge tsunami swamped the facility.

Operating remotely within submerged parts of the Fukushima Daiichi plant's Unit 3 reactor, the robot sent back 16 hours worth of images of massive, lava-like fuel deposits on the floor of the pedestal, a part of the reactor that sits underneath and supports the core.

"You can see something melted and solidified fallen from the inside of the reactor," Takahiro Kimoto, acting director for nuclear power and placement, told journalists.

"So we believe there is high possibility that it was molten metal and fuel debris."

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