The massive earthquake and tsunami that hit Japan in 2011 damaged the cooling system at the Fukushima nuclear power plant and caused the collapse of three reactor cores. Now, a set of robots has managed to capture some of the traces of the disaster.
The remote-controlled robot captured what appeared to be a mound of nuclear fuel melting and falling to the bottom of the most damaged reactor at the devastated Fukushima nuclear plant.
Power plant operator Tokyo Electric Power Company Holdings (TEPSO) said earlier attempts to send a small robot with a camera to the Unit 1 reactor failed, but images taken this week by the ROV-A robot show damaged structures, pipes and mounds that appear to be liquid fuel and other debris submerged in cooling water.
About 900 tonnes of melted nuclear fuel remain in the plant's three damaged reactors, including about 280 tonnes in Unit 1. Its removal is a formidable task as officials say the process will take 30-40 years. That too, critics say, is an overly optimistic prediction.
Quoted from India Today, the robot, which carries several tiny cameras on its body, acquires internal images of the reactor's main containment vessel while on a mission to set a path for the next investigation.
TEPCO spokesman Kenichi Takahara said piles of debris rose from the bottom of the container, including some inside the pedestal, a structure directly below the core, suggesting the mound was liquid fuel that fell in the area. Further investigation will be required to confirm the objects in the image.
"At one location, the robot measured a radiation level of 2 sieverts, which is fatal to humans. The annual exposure limit for factory workers is set at 50 millisieverts," said Takahara.
The probe into the Robotic Unit 1 reactor began Tuesday (Feb 8) and is the first since 2017, when the robot previously failed to obtain images of the melted fuel due to extremely high radiation and interior structural damage. The fuel in Unit 1 was submerged in radioactive water to a depth of 2 meters (6.5 feet).
TEPCO said it would carry out additional investigations after analyzing the data and images collected by the first robot. The other five robots, jointly developed by Hitachi-GE Nuclear Energy and the International Research Institute for Nuclear Decommissioning, a Japanese government-funded consortium, will be used in the investigation over the next few months.
The investigation in Unit 1 aims to measure the mounds of melted fuel, map them in three dimensions, analyze their isotopes and radioactivity, and collect samples.
It was key to developing equipment and strategies for the safe and efficient disposal of molten fuel, allowing eventual reactor shutdown. Details on how the highly radioactive material can be safely removed, stored and disposed of at the end of the cleanup have not been decided.
TEPCO hopes to use a robotic arm by the end of this year to remove an initial one scoop sample of liquid fuel from Unit 2, where an internal robotic probe has made the most progress.