Tokyo Electric Wednesday sent a submersible robot into the primary containment vessel of the No. 3 reactor at the Fukushima No. 1 nuclear plant to probe for the exact location of melted fuel debris.

The the first day of the operation, which lasted for about three hours, failed to find the fuel. Still, engineers and technicians learned the inside of the structure was quite damaged, 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 said the first day’s mission was to see what conditions were like and whether it was possible for the robot to move deeper into the vessel’s waters, where the company believes the fuel debris has fallen.

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

Still, the company is hopeful the robot will be able to travel to deeper levels in the next phase of the probe scheduled for Friday, said Kimoto. The water level inside the No. 3 containment vessel is about 6 meters deep.

The cylindrical 30-cm robot, which was developed by Toshiba Corp., is equipped with a 180 degree-capable camera whose angle can be controlled and another fixed camera on its rear. Toshiba has been heavily involved with the Fukushima decommissioning process.

The No. 1, No. 2 and No. 3 reactors underwent core meltdowns as a result of a power stoppage caused by the mega-earthquake and massive tsunami on March 11, 2011. The heated fuel rods melted and then penetrated their pressure vessels to apparently fall to the bottom of the surrounding containment vessels.

Tepco deployed different robot types to investigate inside the containment vessels at the No. 1 and No. 2 reactors in January and March, respectively. But they failed to find any fuel debris.

Locating the exact location of the fuel is crucial in order to come up with possible ways to remove the debris and eventually to scrap the crippled Fukushima plant.

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