Images captured by an underwater robot show massive deposits of what's believed to be melted nuclear fuel on the floor of a damaged reactor at Japan's Fukushima nuclear plant.
The robot's images also showed large amounts of solidified lava-like rocks and lumps under Fukushima's Unit 3 reactor, according to the plant's operator, Tokyo Electric Power Co.
A 2011 earthquake and tsunami caused multiple meltdowns, ultimately destroying the plant.
Locating and analyzing the fuel debris could provide significant information needed for decommissioning the plant. So far, the search for melted fuel in two other reactors has been unsuccessful because of damage and high radiation levels.
During the three-day probe of Unit 3, cameras showed extensive damage including fuel debris mixed with broken reactor parts, indicating the decommissioning process will be a long one.
TEPCO spokesman Takahiro Kimoto said it will take time to thoroughly analyze the images in order to determine the best plan of action to remove the debris.
The Associated Press contributed to this report.