TOKYO (AP) – A draft investigation report on the 2011 Fukushima nuclear collapse, adopted by Japanese nuclear regulators on Wednesday, says it has detected dangerously high levels of radioactive contamination in two of the three reactors. adds to the concern about the challenges of deactivation.
The interim report indicated that the data collected by the researchers showed that the sealing plugs sitting on top of the reactor vessels no. 2 and 3 were as deadly polluted as the remnants of nuclear fuel that had melted and fallen to the bottom of the reactors after the tsunami and earthquake of March 2011..
Experts said the bottom of the closed cap, a 12-meter-diameter three-layer concrete disc-shaped lid sitting on top of the primary containment container, is coated with high levels of 137 radioactive cesium.
Reactor cover no. 1 was less contaminated, presumably because the plug was slightly dislocated and disfigured due to the impact of the hydrogen explosion.
Experts measured radiation levels at various locations within the three reactor buildings and examined the movement of radioactive materials and the operation of safety equipment during the crash. They also said that the attempt to exit Unit 2 to prevent damage to the reactor never worked and that safety measures and equipment designs still need to be examined.
Contamination of the lid does not affect the environment, as the containment containers are closed inside the reactor buildings. The report did not give further details on whether or how the contamination of the lid would affect the progress of dismantling.
Nuclear Regulatory Commission Chairman Toyoshi Fuketa called the findings “extremely serious” and said they would make it difficult to remove the fuel from the melt. He said figuring out how to remove the lids would be a major challenge.
Removing approximately 900 tons of fuel from outside three reactors is a daunting task that is expected to take decades and officials have not been able to describe exactly when or how it may end up.
The Fukushima plant would begin disposing of off-site fuel waste from Unit 2, the first of three reactors, later this year before the 10th anniversary of the crash. But in December, plant operator Tokyo Electric Power Co. and the government announced a delay until 2022. They said the development of a robotic arm for waste disposal (a joint project with Britain) has been delayed due to the pandemic.
According to the current plan, a remotely controlled robotic arm will be introduced from the side of the reactor to reach the molten fuel mixed with the molten parts and the concrete floor of the reactor. Finally, the lids should also be removed, but their contamination is a major setback.
The team of experts entered areas of 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.
Massive radiation from the reactors has led to the evacuation of some 160,000 people from the vicinity of the plant. Tens of thousands are still unable to return home.
___
Follow Mari Yamaguchi on Twitter at https://www.twitter.com/mariyamaguchi