Six years after the Fukushima nuclear accident in Japan, operators of the affected Daiichi Power Plant are using robot technology to check for new damage.
Tokyo Electric Power Company started the full-scale robotic probe on Wednesday.
It follows fears the metal scaffolding right below No.3 reactor has melted and fallen to the bottom of the containment vessel that covers it.
The nuclear fuel is thought to lie within water which is 6-metres deep and was injected for cooling.
The new underwater robot moves slowly at 4 centimetres per second and is just 30 centimetres long and 13 centimetres wide,
TEPCO and the Japanese government plan to remove the nuclear fuel debris as part of decommissioning of the reactor. But they need to locate all the debris first.