The findings were announced at the end of a three-day inspection by the remote-controlled marine vessel, nicknamed the Little Sunfish, which is about the size of a loaf of bread.
“There is a high possibility that the solidified objects are mixtures of melted metal and fuel that fell from the vessel,” a Tokyo Electric Power Company spokesman said, adding that the company was planning further analysis of the images.
The Fukushima plant was crippled by a massive undersea earthquake which sent a huge tsunami sweeping across Japan’s northeast coast on 11 March 2011.
More than 18,000 people were killed in the disaster, and the damage to the Fukushima plant was the worst of its kind since Chernobyl in 1986.
Three of Fukushima’s reactors went into meltdown, and locating the fuel debris caused by that has been a key part of the Japanese government’s decommissioning process for the plant.
The Little Sunfish was co-developed by Toshiba, which has been charged with helping clean up the power plant, and the International Research Institute for Nuclear Decommissioning (IRIND), a government-funded consortium.
It has been studying the damage caused by the earthquake and searching for the missing fuel.
Experts suspected the fuel had melted, breached the core and mostly fallen to the bottom of the primary containment chamber, where it has been submerged by highly radioactive water up to six metres (20 feet) deep.