TEPCO unveils plan to use robotic arm for fuel debris extraction from crippled reactors

Tokyo Electric Power Co. (TEPCO) disclosed on May 31 a proposed method of extracting melted nuclear fuel debris from three crippled reactors as part of work to decommission its Fukushima Daiichi nuclear power plant wrecked by tsunami and explosions that followed the 2011 earthquake. The method, which has yet to be examined in detail, features the use of a robotic arm inserted through an opening in the wall of the containment vessel of each reactor. It is the first time that the utility presented a specific full-scale method designed to remove fuel debris. TEPCO plans to begin debris extraction after probing the inside of the Nos. 1 to 3 reactors, initially focusing on small debris accumulated on the bottom of the containment vessel and gradually expanding to other portions. At present it is assumed small debris will be extracted through the opening on the side of each containment vessel, a channel also used for assessment of inside situations. The utility is considering improving the robotic arm including redesigning and reinforcing a device on top of the arm's tip. TEPCO does not intend to open new apertures on reactor buildings or containment vessels to prevent the work from affecting the stability of the reactors, including the functions to cool debris inside the containment vessels, prevent the reactors from reaching criticality and shield radioactive substances. The draft TEPCO method envisages robotic arm insertion through the opening at the same location on the side of each reactor to extract debris. But the level of water inside the containment vessel of the No. 3 reactor is high, making it necessary to drain it. As for the No. 1 unit, the airborne radiation dosage near the opening is so high at 630 millisieverts per hour that TEPCO plans to also consider using another opening used to bring in large equipment and for other purposes. Probes so far suggest that large lumps of debris exist on the bottom and other parts of the containment vessels. Using equipment to be developed in the future, TEPCO plans to drill and smash such debris inside the vessels in preparation for extraction. The utility will also continue examining robotic arm insertion from above the pressure vessel of each reactor as well as from the container vessel side. There is a possibility of making new openings elsewhere. (Translated by Kyodo News)