Robot Removal of Melted Fuel Halted at Fukushima Reactor
An attempt to use a robot to remove a fragment of melted fuel from a reactor at Japan's Fukushima Daiichi nuclear power plant was suspended on August 22 due to a technical issue.
The collection of a tiny sample of the melted fuel inside the Unit 2 reactor's primary containment vessel would allow the fuel debris removal phase to start. This is the most challenging part of the decommissioning of the plant where three reactors were destroyed in the March 11, 2011, earthquake and tsunami disaster.
The work was stopped when workers noticed that five 1.5-meter pipes used to move the robot were placed in the wrong order and could not be corrected within the time limit for their radiation exposure, the plant operator Tokyo Electric Power Company Holdings said.
The pipes were to be used to push the robot inside and pull it back out when it finished. Once inside the vessel, the robot is operated remotely from a safer location.
The robot can extend up to about 22 meters to reach its target area to collect a fragment from the surface of the melted fuel.
The mission to obtain the fragment and return with it was to last two weeks.
TEPCO spokesperson Kenichi Takahara said officials are investigating the pipe problem and the retrieval mission will resume only after they find the cause and have preventive measures "so a problem like this should never be repeated."
TEPCO President Tomoaki Kobayakawa said the priority was safety rather than rushing the process.
The goal of the operation was to bring back less than 3 grams of an estimated 880 metric tons of fatally radioactive fuel. The small sample will provide key data to develop future decommissioning methods and necessary technology and robots, experts say.
Better understanding of the melted fuel debris is key to decommissioning the three reactors and the entire plant.
The government and TEPCO are sticking to a 30 to 40-year decommissioning target set soon after the 2011 disaster, despite criticism that it is unrealistic. No specific plans for the full removal of the melted fuel debris or its storage have been decided.
"Telesco-style" extendable pipe robot.
