Nuclear Watch: Robot to survey reactor

April 10, 2015

http://www3.nhk.or.jp/nhkworld/english/news/nuclearwatch/20150410.html

Robot to Survey Reactor

The managers of Japan's crippled Fukushima nuclear plant are trying to gain a better understanding of the challenges they're facing. They've spent four years sketching out a detailed picture of the damage to the reactors there. In order to get around the dangers the facility presents to humans, they've been using robots instead. And for the first time on Friday they sent one inside the containment vessel of reactor number one.

Three of the plant's reactors suffered meltdowns after the March, 2011 earthquake and tsunami. But due to the high levels of radiation, workers have not been able to gauge the true extent of the damage or locate the melted fuel.

Tokyo Electric Power Company engineers are directing their latest robot by remote control. The snake-like device can maneuver around obstacles inside the containment vessel.

But TEPCO officials say that after the robot had traveled more than 10 meters into the plant, or about two-thirds of the planned distance, they were no longer able to move it. They say they were able to receive the images and radiation data the machine had gathered before it stopped.

Until now, TEPCO has used computer simulations to try to understand what's going on inside the reactors. The results indicate that the nuclear fuel has melted and fallen to the bottom of the vessel.

Engineers hope the data collected by the robot will help them gain clues on how best to remove the fuel.

This robot went deeper inside the plant this morning than any used since the accident. Previous robots have managed to record vital information. They've given the operator a better idea of what's going on inside. But the work is difficult, even for a machine. NHK WORLD's Chiaki Ishikawa explains.

In March of last year, TEPCO engineers deployed a robot inside the building that houses the No.2 reactor. It used a drill to take samples from the contaminated concrete floor. The goal was to study the contamination levels inside the building.

A number of robots have already been used inside the plant, carrying out inspections and decontamination work. One of them sprayed dry ice onto the floors and walls, and this was then scraped off, along with the decontamination.

Robots have also been used to study the condition of the containment vessels that enclose the reactors. In November of 2013, officials confirmed for the first time that a robot had found contaminated water leaking from the containment vessel of the number 1 reactor.

But there are limits to what robots can do. The interiors of the reactor buildings are littered with debris. This makes it difficult for robots to move around freely. They often become stuck and irretrievable.

Another major obstacle is the intense levels of radiation. Images from the inside of the containment vessel of the No.2 reactor shot using an endoscopic camera show white dots generated by radiation. When approaching nuclear fuel, even robots can malfunction or fail to capture clear images.

In another examination, engineers tried to avoid such glitches by minimizing the use of computer circuits. Still, the probe could only operate for two days.

Government and TEPCO officials will eventually examine the inside of the containment vessel of the No.2 reactor as well.