TOKYO • New images captured in the past few days show what is likely to be melted nuclear fuel from one of Japan's wrecked Fukushima reactors, a potential milestone in the cleanup of one of the worst atomic disasters in history.

Tokyo Electric Power Co (Tepco), Japan's biggest utility, has released images of mounds of black rock and sand-like substances at the bottom of the No. 3 reactor containment vessel at Fukushima, which is likely to contain melted fuel, said Tepco official Takahiro Kimoto.

A survey had found black icicles hanging from above the pressure vessel, which was "highly likely" to contain melted fuel. Mr Kimoto noted it would take time to confirm if this debris contains melted fuel.

"The pictures that we have gained will assist us in devising a plan for removing the melted fuel," he said.

If confirmed, the pictures would be the first discovery of the fuel that melted during the triple-reactor accident at Fukushima six years ago.

Removing the fuel is one of the most important steps in a cleanup that may take as long as 40 years.

The pictures were taken by a Toshiba-designed, 30cm-long robot the firm sent to explore the inside of the reactor for the first time. The robot, which can swim in the flooded unit, was tasked with surveying the damage and finding the location of corium - a mixture of the atomic fuel rods and other structural materials that forms after a meltdown.

Due to the high radioactivity levels inside the reactor, only specially designed robots can probe the unit. Tepco is pinning its efforts on technology not yet invented to get the melted fuel out of the reactors.

"If some of these fragments can be brought out of the reactor and studied, it would allow nuclear engineers and scientists to better model what happened during the accident," said Professor M. V. Ramana of the Liu Institute for Global Issues at the University of British Columbia.

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