More than six years after the core meltdowns triggered by March 2011 mega-quake and tsunami, Tokyo Electric said Saturday that the robot probing reactor 3 at the defunct Fukushima No. 1 power plant had likely spotted fuel debris for the first time at the bottom of its primary containment vessel.

Some of the debris looks like rocks and sand, and was accompanied by scaffolding and other objects from the reactor that had formed a pile about a meter high.

On Friday, Tokyo Electric Power Company Holdings Inc. announced that the same robot had found what appeared to be melted fuel at the bottom of the pressure vessel, which holds the core.