The draft report on the investigation of the nuclear meltdown in Fukushima in 2011, adopted by Japanese nuclear regulators on Wednesday, said it had revealed dangerously high levels of radioactive contamination in two of the three reactors, raising concerns about the challenges of decommissioning.
The interim report said that data collected by investigators showed that the seals above the containment vessels of Reactors No. 2 and 3 were deadly contaminated as debris from nuclear fuel that melted and fell to the reactor bed following the tsunami and earthquake in March 2011..
Experts said the bottom of the sealed seal, a 12-meter (39-foot) disk-shaped three-layer concrete covering located above the primary containment vessel, was covered with high levels of radioactive cesium-137.
The report stated that the cap for Reactor No. 1 was less contaminated, possibly because the stopper was slightly out of place and deformed by the effect of the hydrogen explosion.
The experts measured radiation levels at multiple sites within the three reactor buildings, and examined how the radioactive materials moved and safety equipment functioned during the accident. They also said that attempting to vent into Unit 2 to prevent damage to the reactor was never successful, and that safety measures and equipment designs still needed to be examined.
Cover contamination does not affect the environment as containment vessels are enclosed within the reactor buildings. The report did not provide further details on whether or how cover contamination would affect the decommissioning progress.
Nuclear Regulatory Commission Chairman Toyoshi Fukita described the results as “extremely dangerous” and said they would make removing the dissolved fuel “more difficult”. He said figuring out how to remove the covers will be a huge challenge.
Removing an estimated 900 tons of molten fuel debris from three reactors is a daunting task expected to take decades, and officials have been unable to describe exactly when or how it might end.
The Fukushima plant was due to begin removing molten fuel debris from the second unit, the first of three reactors, later this year ahead of the 10th anniversary of the accident. But in December, Tokyo Electric Power Company, the operator of the station, and the government announced it would be postponed until 2022. They said the development of a robotic arm to remove debris – a joint venture with Britain – had been delayed due to the pandemic.
Under the current plan, a robotic arm would be inserted remotely controlled from the reactor side to access the molten fuel mixed with the molten parts and the concrete floor of the reactor. Ultimately the covers will also have to be removed, but contaminating them is a major setback.
The team of experts has entered areas within the three reactors that were previously heavily polluted and inaccessible after radiation levels have dropped dramatically. They look for data and evidence before they get lost in the cleaning process.
The tremendous radiation from the reactors evacuated about 160,000 people from around the plant. Tens of thousands are still unable to return home.
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