Tokyo Electric sends submersible robot into containment vessel of Fukushima reactor unit 3

Tokyo Electric yesterday sent a submersible robot into the primary containment vessel of the No 3 reactor at the Fukushima No 1 nuclear plant to locate the melted fuel debris.

The exercise, which lasted three hours on the first day failed to find the fuel. But engineers and technicians learned the inside of the structure had sustained substantial damage, Tokyo Electric Power Company Holdings Inc said in an evening news conference.

''This was the first time that a robot has entered the containment vessel of reactor 3,'' said Takahiro Kimoto, a Tepco spokesman. ''We think this is a big step.''

He added, the first day's mission was to see what conditions were like and assess the feasibility of the robot to moving deeper into the vessel's waters, where the company believed the fuel debris has fallen.

Video recorded by the robot revealed some equipment parts inside the structure. The utility added that steel gratings in the vessel designed to work as a scaffolding under regular circumstances were not where they should have been, which engineers could not explain.

However, the company remained hopeful of the robot being able to travel to deeper levels in the next phase of the probe scheduled for tomorrow, said Kimoto. The water level inside the No 3 containment vessel was about 6 metres deep.

The robot, nicknamed ''the Little Sunfish,'' was left inside the reactor near a structure called the pedestal, and was expected to go deeper inside for a fuller investigation tomorrow in hopes of finding the melted fuel.

''The damage to the structures was caused by the melted fuel or its heat,'' Kimoto told a late-night news conference held nine hours after the probe ended its exploration earlier in the day.

The robot was co-developed by Toshiba Corp, the electronics and energy company charged with helping clean up the plant, and the International Research Institute for Nuclear Decommissioning, a government-funded consortium.

The robot is about the size of a loaf of bread and has lights, five propellers to manoeuvre and collects data with two cameras and a dosimeter.