Fukushima nuclear fuel debris retrieval to start as early as August
The operator of the crippled Fukushima nuclear power plant plans to begin retrieving debris that contains melted nuclear fuel at one of the three meltdown-hit reactors as early as this month, with the unit to be the first to undergo the procedure.
The removal of the radioactive debris is considered one of the most challenging tasks in decommissioning the Fukushima Daiichi plant, whose reactors were severely damaged by the loss of cooling functions triggered by the 2011 earthquake and tsunami in northeastern Japan.
Tokyo Electric Power Company Holdings Inc. intends to retrieve only a few grams of debris from the No. 2 unit in its first effort, with the roadmap for removing an estimated 880 tons of debris from Nos. 1 to 3 that suffered meltdowns remaining unclear.
According to the decommissioning schedule by the government and TEPCO, the debris removal will be the third and final phase of the process that is projected to take 30 to 40 years.
The upcoming operation, which is expected to take around two weeks to complete, will involve inserting a remote-controlled extendable pipe into the reactor containment vessel to trial retrieving debris.
The tubular device comprises connected pipes with an outside diameter of 20 and 16 centimeters, which can be extended like a fishing rod to a length of around 22 meters.
It will be inserted through a penetration point located on the side of the containment vessel, which has an internal diameter of about 55 cm and a length of approximately 2 meters.
According to TEPCO, debris removal officially begins once the device passes through an “isolation valve” installed just before the penetration point. This valve blocks radioactive material from escaping the containment vessel.
Further in sits an approximately 7.2-meter rail connected to the base of the reactor pressure vessel where the debris is located. Upon reaching this rail, an arm at the tip of the pipe will rotate downward to move toward the base.
The tip of the pipe is equipped with a two-pronged metal claw to grip the pebble-sized debris. After entering the base, the claw will be lowered toward the debris at the bottom to retrieve the less than 3 grams.
The pipe will be withdrawn from the containment vessel along the same route, with the debris placed in a transportation box, which will then be transferred by dolly into a nuclear glove box designed for handling radioactive material within the reactor building.
After measuring radiation levels and other parameters inside the box, the debris will moved into a transportation container to be taken to an analysis facility in neighboring Ibaraki Prefecture.
TEPCO had initially planned to start retrieving debris from the No. 2 unit in 2021 but postponed it to 2022 due to the coronavirus pandemic and the need to improve the robotic arm. It said then that it aimed to carry out the process in the latter half of fiscal 2023 but gave up on the plan due to technical difficulties.
