A new submersible robot set to probe into the No. 1 reactor containment vessel at the crippled Fukushima No. 1 nuclear power plant to determine the locations of the melted nuclear fuel is unveiled on March 28. (Video by Chikako Kawahara)

The lead member of a special team of six robots tasked with probing the inside of a reactor containment vessel at the crippled Fukushima No. 1 nuclear power plant was unveiled March 28.

The remote-controlled submersible robot, which is about 1 meter long, is expected to start surveying the interior of the damaged No. 1 reactor with five other such devices as early as summer, according to Hitachi-GE Nuclear Energy Ltd. and other entities.

Maneuvered by workers, the lead robot will place ring-shaped objects at eight locations on the wall inside the reactor vessel to indicate the route for the others.

The large size of five of the robots allows them to carry more powerful devices, such as cameras, ultrasonic scanners and dosimeters, for collecting more accurate data in an effort to locate melted fuel during the approximate six-month mission.

The team of robots will study in detail the conditions inside the containment vessel and collect sediment.

A similar probe conducted in 2017 uncovered numerous sand-like deposits at the base of the No. 1 reactor's containment vessel. However, no melted nuclear fuel debris has yet to be spotted.

The Fukushima plant suffered a triple meltdown as a result of tsunami triggered by the Great East Japan Earthquake in March 2011.

To proceed with decommissioning work, locating fuel debris is vital, leading to the development of the necessary robotic devices with a variety of instruments.

"We'll do our utmost to collect a vast range of data in preparation for removing debris," said an official of Hitachi-GE Nuclear Energy, which developed the robot in tandem with the International Research Institute for Nuclear Decommissioning, comprising nuclear reactor makers and other companies.