Swimming robot to probe damage at Japanese nuclear plant
A Japanese industrial group has unveiled a swimming robot designed to go underwater to probe damage from meltdowns at the Fukushima Dai-Ichi nuclear plant.
Remote-controlled robots are key to the decades-long decommissioning process, but super-high radiation and structural damage hampered earlier attempts to probe damage to the reactors after a massive earthquake and tsunami in March 2011.
The developers said they plan to send the probe into the primary containment vessel of Unit 3 at Fukushima this summer to study the extent of damage and locate melted fuel thought to have fallen to the bottom of the chamber and to have been submerged by highly radioactive water.
The robot, about the size of a loaf of bread and mounted with lights, manoeuvres with tail propellers and collects data using two cameras and a dosimeter radiation detector.
Japan hopes to locate and start removing the fuel after Tokyo's 2020 Olympics.
The biggest challenge is removing hundreds of tons of melted nuclear fuel and debris from the plant's three wrecked reactors.
Snake and scorpion-shaped robots have been tried but became stuck inside two reactors.
The scorpion robot's crawling function failed and it was left inside the plant's Unit 2 containment vessel. The other, designed for cleaning debris for the scorpion, was called back after two hours when two of its cameras stopped working after its total radiation exposure reached 1,000 Sievert - a level that would kill a human in seconds.
The plan had been to use the robot for 10 hours at an exposure level of 100 Sievert per hour.
The swimming robot, shown to reporters at a Toshiba test facility near Tokyo, was co-developed by the debt-strapped Japanese nuclear and electronics company and the government's International Research Institute for Nuclear Decommissioning.
Scientists need to know the melted fuel's exact location and understand structural damage in each of the three wrecked reactors to work out the best way to remove the fuel.
"The fuel debris will be a challenge," said Dale Klein, a former US Nuclear Regulatory Commission chief, who now serves as an outside adviser to the Tokyo Electric Power Co (Tepco), the plant's operator. He said it could take six months to a year to obtain necessary data and decide how to remove the fuel.
"They will have to identify where it is, then they will have to develop capability to remove it. No one in the world has ever had to remove material like this before. So this is something new and it would have to be done carefully and accurately," he said.
Japanese officials want to determine preliminary removal methods this summer and start work in 2021.
The decommissioning technology developer IRID and its partners have designed some basic robots, including a "muscle" arm robot made by Hitachi-GE Nuclear Energy, and a different arm robot made by Mitsubishi Heavy Industries, that are designed to approach the debris from the side of the reactors.
Tepco is struggling with the plant's decommissioning, now estimated at a cost of 8 trillion yen (£57 billion), four times an earlier estimate. Part of that cost will be included in Japanese utility bills.
The 2011 meltdown forced tens of thousands of nearby residents to evacuate their homes. Many are still unable to return due to high radiation levels.