October 24, 2022
In order to remove melted nuclear fuel (debris), which is considered the most difficult part of the restoration work at TEPCO’s Fukushima Daiichi Nuclear Power Plant, a method has emerged to submerge the entire reactor building, including its basement, under water. This would require unprecedented large-scale construction work, and there are doubts about its feasibility. The fact that the debris removal plan has been repeatedly changed and a proposal that seems to be grasping at a cloud has emerged is symbolic of the difficulties involved. （The fact that a proposal that seems to be grasping at a cloud has emerged is symbolic of the difficulties that lie ahead.)
Even the experts are not confident.
　The first of its kind in the world,” “Technically quite difficult,”

◆”Not confident” even experts are bearish


At a press conference held on November 11 to explain the proposal that includes a new construction method for the Unit 3 reactor, Mr. Mitsuroku Ikegami, executive director of the Nuclear Damage Liability and Decommissioning Support Organization, who is in charge of providing technical support to help bring about a restoration from the accident, repeated his bearish comments.
　The new construction method is based on the “hull construction method” used for tanker hull construction. The new method is characterized by enclosing the building with a structure that is resistant to water pressure, and ETIC is considering digging a tunnel under the building and enclosing the entire building with a structure consisting of a series of square rooms made of steel.
　If this is realized, water filled with the building will be used to shield it from radiation, thereby increasing the safety of the work. On the other hand, submerging the building in water is expected to generate about 150,000 tons of highly contaminated water that has come into contact with debris. This is equivalent to about 150 tanks storing treated water on the site, and the risk of a leakage accident is immeasurable.

◆”Flooding” first, stop once, flood again.
　At the beginning of the accident in 2011, the government and TEPCO planned to use the “flooding method” to fill the containment vessel with water and remove debris underwater. However, the containment vessels of Units 1 through 3, where debris was located, were all damaged, and even if water was filled, it would leak out of the vessels. The high radiation dose makes it inaccessible to humans, and it is still difficult to determine which parts of the containment vessels are damaged.

In 2005, they switched to the “in-air” method of removing debris without water, and are aiming to begin trial removal of debris from Unit 2 in the latter half of FY2011. However, since the method prioritizes easy access to the debris and uses a robot arm in a confined space, only about 1 gram of debris can be removed in a single operation. It is estimated that there is a total of 880 tons of debris in the three reactors, making it almost impossible to complete the removal using this method.
　Therefore, JAEA has switched to a method to remove a large amount of debris from the Unit 3 reactor. The work is expected to involve the scattering of enormous amounts of radioactive materials, such as by cutting the debris into chunks, and if the debris is not shielded by water, it will be very dangerous. Since the containment vessel cannot be filled with water, the idea of submerging the entire building outside of it has emerged. In other words, it is a flooding method that has been reshaped on a large scale.

◆Even after 11 years, it remains unrealistic.
　Debris from the Unit 1 reactor is believed to be scattered over a wide area of the containment vessel, and there is no way to remove the debris. Eleven and a half years after the accident, debris removal remains unrealistic.
　A spokesperson for TEPCO has refused to go into the feasibility of the proposed new method, saying, “It is still in the idea stage. Even the OIST’s proposal suggests a bleak outlook, concluding with the following words: “If the criteria are not met, we will be forced to take out the debris. If the criteria are not met, we will have to start over from the identification of issues.
https://www.tokyo-np.co.jp/article/209821