Japan has developed a swimming robot that began an underwater probe inside one of Fukushima's tsunami-destroyed nuclear reactors to look for traces of melted fuel.
Japan hopes to clean up the damaged reactors which are contaminated with high levels of radiation in Fukushima with the help of a swimming robot.
The underwater robot named The Little Sunfish, has captured images and other data inside Japan's crippled Fukushima nuclear plant on its first day of work.
The robot is on a mission to study damage and find fuel that experts say has melted and mostly fallen to the bottom of a chamber and has been submerged by highly radioactive water.
Plant operator Tokyo Electric Power Co said on Wednesday that the robot entered the primary containment vessel of the Unit 3 reactor at Fukushima, which was destroyed by the March 2011 earthquake and tsunami.
Remote-controlled robots are key to the decades-long decommissioning of the plant, but super-high radiation and structural damage have hampered earlier probes at two other Fukushima reactors.
Tohoku earthquake and the tsunami afterwards devastated Japan's coastline in 2011, killing more than 18,000 people.
It also hit the Japanese nuclear power plant in Fukushima, which resulted in the largest nuclear accident since Chernobyl.