TOKYO (AP) – A draft investigative report into the 2011 Fukushima meltdown, passed by Japanese nuclear regulators on Wednesday, says it has detected dangerously high levels of radioactive contamination in two of its three reactors, raising concerns about decommissioning issues.
The interim report said data gathered by researchers showed that the sealing plugs on top of the No. 2 and 3 reactor containment vessels were as lethally contaminated as nuclear fuel waste that had melted and fell to the bottom of the reactors after the March 2011 tsunami and earthquake.
The experts said the bottom of the sealed plug, a three-layer concrete disc-shaped lid 12 meters (39 feet) in diameter on top of the primary containment vessel, is covered with a high level of radioactive cesium 137.
The lid of the No. 1 reactor was less contaminated, presumably because the plug had been slightly knocked into place and deformed by the impact of the hydrogen explosion, the report said.
The experts measured radiation levels at multiple locations in the three reactor buildings and examined how radioactive material moved and safety equipment functioned during the accident. They also said that a vent attempt at Unit 2 to prevent reactor damage has never worked, and that safety measures and equipment designs have yet to be explored.
The contamination of the lid has no environmental impact as the containment vessels are located in the reactor buildings. The report did not provide further details on whether or how the lid contamination would affect the progress of the decommissioning.
Toyoshi Fuketa, chairman of the Nuclear Regulation Commission, called the findings “extremely serious” and said they would make removal of molten fuel “more difficult.” He said it would be a big challenge to figure out how to remove the lids.
Removing an estimated 900 tons of molten fuel waste from three reactors is a daunting task expected to take decades, and officials have not been able to describe exactly when and how it could end.
The Fukushima plant was set to begin removing molten fuel waste from Unit 2, the first of three reactors, later this year, ahead of the accident’s 10th anniversary. But in December, factory operator Tokyo Electric Power Co. and the government is postponing it until 2022. They said development of a robotic debris removal arm – a joint project with Britain – has been delayed due to the pandemic.
Under the current plan, a remotely controlled robotic arm will be inserted from the side of the reactor to allow the molten fuel mixed with molten parts to reach the concrete floor of the reactor. Ultimately, the lids would also have to be removed, but their contamination is a major setback.
The expert team entered areas within the three reactors that were previously highly polluted and inaccessible after radiation levels dropped significantly. They look for data and evidence before getting lost in the cleanup.
Due to the enormous radiation from the reactors, approximately 160,000 people have been evacuated around the factory. Tens of thousands still cannot return home.
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