A new small robot will be used to inspect the condition of melted nuclear fuel at the second reactor of the Fukushima No. 1 nuclear power plant as early as this summer, marking the first full-scale probe since the disaster caused by the massive earthquake and ensuing tsunami in 2011.
The use of the robot, which is now being developed, will mark the initial step toward removal of the melted fuel from Tokyo Electric Power Co.'s nuclear facility, which may begin in 2021, according to sources close to TEPCO and other related entities.
The results of the inspection will be used to help work out the details of a design for the robot tasked with removing the fuel.
Two robots were sent into the No. 1 reactor in April to examine the condition of the area around the pressure vessel, photographing debris and other damage.
In the probe of the No. 2 reactor, on the other hand, a robot will be sent in via a work route that passes through the bottom of the pressure vessel, into the centre of the containment vessel.
The fuel in the Nos. 1-3 reactors has melted, but the No. 2 reactor was chosen for the first inspection since its route to the lower pressure vessel was not damaged as much as the other reactors.
Based on computer simulations, some of the melted fuel in the No. 2 reactor is thought to have fallen to the bottom of the containment vessel.
If the area directly under the pressure vessel can be photographed, TEPCO could confirm how the fuel melted and dropped down, and whether it has accumulated in the bottom of the containment vessel.
The position and shape of the melted fuel would be used to decide the functions, capacities and other aspects of the robots that will be needed to remove the fuel.
The robot to be used in this probe is being developed by the International Research Institute for Nuclear Decommissioning (IRID), whose members are domestic power companies and related manufacturers.
The robot is 54 centimeters long, but has a width and height of only nine centimeters, so it can fit through the pipe leading to the reactor.
It is controlled remotely via a cable. After passing through the pipe and entering the containment vessel, its rear portion flips upward, making it look something like a scorpion.
A camera and LED light on its front end will be used to photograph the vessel, and it is also equipped to measure temperature and radiation levels.
Toshiba Corp., which is leading the development project, has been conducting experiments with the robot using a mock-up of the No. 2 reactor at its offices in Yokohama.
Radiation levels in the containment vessel are thought to be about 100 sieverts per hour.
"The robot is built to withstand 1,000 sieverts, so it should be able to operate for about 10 hours," a Toshiba employee in charge of the project said.