Transforming robot probes Fukushima reactor vessel

The robot, developed by Hitachi-GE Nuclear Energy and the International Research Institute for Nuclear Decommissioning (IRID), was inserted into the primary containment vessel (PCV) of reactor No. 1 at the plant, which was heavily damaged by the 2011 earthquake and subsequent tsunami that devastated northern Japan.

Tokyo Electric is taking the unprecedented step to better determine the state of melted-down fuel in the reactor as part of plans to dismantle the plant, a spokesman said. The No. 2 and No. 3 reactors also suffered meltdowns.

The PCV is a 48-meter-tall steel container that houses another steel vessel that normally holds the uranium fuel that powers the station, as well as water. The exact state of the fuel is unclear, but determining it is key to removing the fuel for dismantling of the plant, a process expected to take decades.

The cylindrical robot is about 60 centimeters long and can change its shape from a form resembling the letter I to one resembling the numeral 3. The former is for movement through a pipe that runs into the PCV, while the latter is for moving around inside the vessel.

It is remote-controlled via a cable tether and runs on two crawler assemblies. The machine is equipped with a thermometer, a tilting camera to capture video, a dosimeter to gauge radiation and a laser scanner to measure distance.

The robot will stop and probe various spots in the vessel and record obstacles barring its way. It will explore the vessel in two stages -- first the ground-level grating and then the basement, where the melted fuel is thought to be.

"The radiation level is very high inside the PCV and we assume that the maximum time for investigation is five to six hours each time, though the robot can investigate for 10 hours," Tomohisa Ito, a spokesman for IRID, said via email.

Tokyo Electric has deployed a number of robots around the PCV so far, but never inside it. For instance, Rosemary, developed by Chiba Institute of Technology and Hitachi-GE Nuclear Energy, is a robot that rolls around on treads and images the surrounding area with cameras mounted on a mast and was used to explore the surrounding area.

Last month, the utility said it confirmed that the fuel in the No. 1 reactor had melted, complicating the extraction process. The confirmation was done via a tomography imaging scan that used elementary particles called muons.

Tens of thousands of people are still displaced due to radiation in the area around the Fukushima plant, which is expected to cost at least ¥2.1 trillion (US$17.4 billion) to decommission.

Tim Hornyak covers Japan and emerging technologies for The IDG News Service. Follow Tim on Twitter at @robotopia.