Daisuke Hirose, a Tepco spokesman, inside the Unit 5 reactor at the Fukushima nuclear power plant. Tepco used underwater robots that finally found the melted uranium fuel inside Unit 3, another reactor that was destroyed.  Four engineers hunched before a bank of monitors, one holding what looked like a game controller. They had spent a month training for what they were about to do: pilot a small robot into the contaminated heart of the ruined Fukushima nuclear plant. Earlier robots had failed , getting caught on debris or suffering circuit malfunctions from excess radiation. But the newer version, called the Mini-Manbo, or “little sunfish,” was made of radiation-hardened materials with a sensor to help it avoid dangerous hot spots in the plant’s flooded reactor buildings. The size of a shoe box , the Manbo used tiny propellers to hover and glide through […]