Tokyo Electric Power Company Holdings (Tepco) says nuclear fuel debris will be removed from the unit 2 reactor at the Fukushima Daiichi NPP in a second trial operation in mid-April.
Sample debris will be collected from a location other than that of the first trial operation in November 2024 when Tepco extracted the first sample of nuclear fuel debris from the containment vessel at unit 2 using a specially developed device.
This followed several earlier failed attempts since the plant in Fukushima Prefecture suffered a meltdown following the massive March 2011 earthquake and tsunami in which three reactors suffered a reactor meltdown. In September 2024, Tepco had suspended attempts for a second time to collect melted nuclear fuel from unit 2 after two cameras on the robotic device ceased to function.
The operation was initially scheduled to begin on 22 August but was suspended when workers noticed that five 1.5-metre pipes to be used to push the robot into the reactor had been arranged in the wrong order. The equipment was subsequently reassembled in the right order. Tepco initially planned to conduct the experimental removal work in 2021, but it was postponed by about three years due to delays in the development of necessary devices overseas and other preparations.
About 880 tonnes of fuel debris remain in the three reactors that suffered a meltdown, according to estimates by the International Research Institute for Nuclear Decommissioning. The first retrieval sought to retrieve less than 3 grams of the material for analysis.
Tepco plans to collect up to 3 grams of debris in the next retrieval. Once again, a retrieval device resembling a fishing rod that can extend up to 22 metres will be inserted from the side of the reactor, and a claw-like gripper hanging down from a cable will pick up debris at the bottom of the reactor containment vessel.
This time debris is planned to be collected near the centre of the containment vessel at a location around 1-2 metres away from the first collection point. The company will compare its composition, hardness and other factors to better understand the conditions inside the reactor, such as debris distribution. However, the debris may be collected from the same location as last time depending on the situation inside the reactor.
Tepco said that, in preparation for the second fuel debris trial retrieval, the end jig of the telescopic device has been improved and verification tests completed at the factory. For about one week starting around 25 March, training on connecting push pipes for workers will be implemented on site. After the proficiency of the workers has been confirmed, cameras attached to the body of the telescopic device will be replaced.
“As such, we will proceed with preparations with the aim of commencing the next fuel debris trial retrieval using the telescopic device around the middle of April, but the exact date will be determined based upon worker proficiency and operating condition of the device,” Tepco said. “During the first fuel debris sampling, time was required to manoeuvre the end jig because the lowering part was not stable. So we are deliberating how to improve the manoeuvrability of the end jig before sampling additional fuel debris.”
