An attempt to use an extendable robot to remove a fragment of melted fuel from a wrecked reactor at Japan’s tsunami-hit Fukushima Daiichi nuclear power plant was suspended Thursday due to a technical issue.
The collection of a tiny sample of the debris inside the Unit 2 reactor’s primary containment vessel would start the fuel debris removal phase, the most challenging part of the decades-long decommissioning of the plant where three reactors were destroyed in the March 11, 2011, magnitude 9.0 earthquake and tsunami disaster.
The work was stopped when workers noticed that five 1.5-meter pipes used to maneuver 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 mound using a device equipped with tongs that hang from the tip of the robot.
The mission to obtain the fragment and return with it is to last two weeks. TEPCO said a new start date is undecided.
TEPCO President Tomoaki Kobayakawa said the priority was safety rather than rushing the process and that he planned to investigate the cause of the pipe setup problem.
“I understand that the decision was to stop and not push when there was a concern,” Kobayakawa told reporters in the north-cenral prefecture of Niigata, where he visited to discuss another TEPCO-operated nuclear power plant with the local community.
The sample-return mission is a first crucial step of a decades-long decommissioning at the Fukushima Daiichi. But its goal to bring back less than 3 grams of an estimated 880 tons of fatally radioactive molten fuel underscores the daunting challenges.
Despite the small amount of the debris sample, it 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 wrecked reactors and the entire plant.
The government and TEPCO are sticking to a 30-40-year cleanup target set soon after the meltdown, despite criticism it is unrealistic. No specific plans for the full removal of the melted fuel debris or its storage have been decided.
