Robots make progress in probing leaky reactors

JIJI

Research robots of various types are playing significant roles in understanding the situation with crippled reactors 1 to 3 at the Fukushima No. 1 nuclear plant.

The reactors at the quake- and tsunami-damaged plant run by Tokyo Electric Power Co. are inaccessible because of the high radiation produced by the multiple core meltdowns they suffered in March 2011.

In June 2011, the Quince, a robot developed by a group led by Chiba Institute of Technology, became the first Japanese robot to enter the reactor 2 building.

Tomoaki Yoshida, 39, a senior researcher at the institute, said the group contacted Tepco in late March that year to prepare the way for using the robot for research at the crippled plant.

The group conducted repeated tests to make sure the robot can safely climb stairs and be used to shoot images and measure radiation inside the reactors.

Images shot by the Quince were published in July 2011.

“The robot could collect information inside the building to a certain extent, although it was unable to get into narrow spaces or open doors,” Yoshida said.

In April 2012, Topy Industries Ltd. put its Survey Runner research robot into the basement of the reactor 2 building. The robot, just 51 cm wide, can easily approach the lower part of the reactor’s containment vessel.

Shingo Tsukui, 43, who was involved in developing the robot, said it had been built to climb even narrow stairs built at a 45-degree angle.

In the containment vessel of reactor 1, meanwhile, water leaks and pipe damage were found last November by a small boat equipped with a camera developed in a government project.

Yosuke Takatori, 35, an engineer from Hitachi-GE Nuclear Energy Ltd., a joint venture between Hitachi Ltd. and General Electric Co. of the United States, said he devised ways to prevent the boat’s cable from getting tangled up when it is rewound. He added that it was very hard to shrink the equipment to a small enough size.

If the broken sections of the reactors’ containment vessels can be pinpointed and repaired, it should be possible to cool the melted nuclear fuel inside and curb the buildup of radioactive water. The fuel must be submerged at all times.

Even if research robots are used, however, collecting information will still be difficult because their paths may be blocked by contaminated water and there may be multiple sections damaged in each reactor.