An attempt to use an extendable robot to remove a fragment of melted fuel from a wrecked reactor at Japan’s tsunami-hit Fukushima Dai-ichi nuclear power plant was suspended yesterday due to a technical issue.
The collection of a tiny sample of the debris inside 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, at which three reactors were destroyed after a tsunami hit the site following an earthquake measuring 9.0 on the Richter scale on March 11, 2011.
The work was stopped when workers noticed that five 1.5m 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, said Tokyo Electric Power Co Holdings (TEPCO), the plant’s operator.
Photo curtesy of TEPCO via AP
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 22m 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.
A new start date had not been decided, TEPCO said.
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 Niigata Prefecture, where he visited to discuss another TEPCO-operated nuclear power plant with the local community.
The sample-return mission is the first crucial step of a decades-long decommissioning at the Fukushima Dai-ichi site.
However, its goal to bring back less than 3g of an estimated 880 tonnes of radioactive molten fuel underscores the daunting challenges.
Despite the small amount of the debris sample, it would provide key data to develop 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 Japanese government and TEPCO are sticking to a 30-to-40-year cleanup target set soon after the meltdown, despite criticism that it is unrealistic. No specific plans for the full removal of the melted fuel debris or its storage have been decided.
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