Tokyo Electric Power Company Holdings (Tepco) says it will have to delay to late 2023 the removal of melted nuclear fuel debris from the unit 2 reactor at the Fukushima Daiichi NPP while adjustments are made to the robotic arms which will undertake the work. Tepco had initially planned to start the debris removal on a trial basis in 2021 but postponed it to 2022 in face of the coronavirus pandemic.
Tepco said the further delay will not affect the overall schedule for the decommissioning of the plant, which suffered a triple-meltdown accident following the tsunami and earthquake in March 2011. Decommissioning at the plant is expected to take 30-40 years.
During the accident, an estimated 880 tons of highly radioactive nuclear fuel in the three damaged reactors melted and fell to the bottom of their primary containment vessels. There it hardened and mixed with broken parts of the reactor and the concrete foundation. Its removal is the most difficult challenge of the decommissioning process.
Tepco has used a series of remote-controlled robots to assess the condition of the fuel in the reactors. However, data and images provided by the robots are still incomplete. Additional work is needed to improve the performance of the huge robotic arm robotic developed by the UK’s Veolia Nuclear and Japan’s Mitsubishi Heavy Industries to help with the debris removal. Adjustments are needed to the extendable robot arm and the so-called “dual-arm manipulator” used to attach a debris removal device to the robot arm.
The device has been transported to Japan where it is now undergoing performance tests in Naraha, a Fukushima Prefecture town close to the NPP.
The fuel debris removal process will begin unit 2 reactor where Tepco has a better understanding of the internal conditions. The robot arm, which extends to a maximum length of approximately 22 metres, will be inserted into the unit’s containment vessel, from which it will extract portions of the debris before gradually increasing the amount removed.
Image: Tepco will delay the removal of melted nuclear fuel debris from unit 2 at the Fukushima Daiichi NPP until late 2023 while adjustments are made to the robotic arms which will undertake the work
