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Fukushima Daiichi Nuclear Power Plant, method to remove debris by submerging the buildings in water: Symbolic of project difficulties after repeated changes, with no prospects for feasibility

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

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October 26, 2022 Posted by | Fuk 2022 | , , , | Leave a comment

Fukushima: Japan attempts to safely remove nuclear fuel from crippled reactors

More than a decade after the second-worst nuclear disaster in history, engineers want to construct a huge water-filled tank around one of the damaged reactors and carry out underwater dismantling work.

The proposal would permit experts to deploy robots to more closely examine the condition of the crippled reactor

September 22, 2022

Nuclear experts pondering the safest way to decommission the three crippled reactors at the Fukushima Daiichi atomic energy plant have devised a new plan to recover highly radioactive debris at the site, with even anti-nuclear campaigners giving the proposal their qualified support.  

They warn, however, that the situation at the plant — on the northeast coast of Japan— remains precarious more than a decade since three of the six reactors suffered meltdowns after an offshore earthquake of magnitude 9 triggered a series of powerful tsunamis.  

In their latest annual strategy report on progress at the plant, experts at the Nuclear Damage Compensation and Decommissioning Facilitation Office (NDF) have proposed the construction and filling with water of a massive concrete tank to completely enclose one of the reactor buildings. 

The water would act as a shield to prevent radiation from escaping into the surrounding environment and give engineers more space, in which to operate heavy equipment to dismantle and remove the outer shell of the reactor building.

That, in turn, would permit experts to deploy robots to more closely examine the condition of the reactor, as well as the fuel that has escaped and pooled in the building’s basement levels.  

The plan was presented to the government at a meeting in Iwaki, just south of the plant, in early September, during which NDF President Hajimu Yamana explained the benefits. 

Safe from radioactivity 

“No radioactive materials would be swirling up underwater, so there would be almost zero impact on the outside,” Yamana told the Asahi newspaper.

NDF experts plan to construct a massive concrete tank arond one of the reactor buildings

He emphasized, however, that the proposal was in the initial stages and no final decision had been taken. If it worked, however, then the same strategy could be deployed to help in the decommissioning of the remaining two damaged reactors at the facility. 

“I cannot say anything for sure yet,” Yamana said. “We are still in the very, very early stages of the concept study. There are still a lot of things to study as the attempt would be the first of its kind in the world.”

Hajime Matsukubo, secretary-general of the Tokyo-based Citizens’ Nuclear Information Center, remains a vocal critic of the Japanese government’s insistence on the need for atomic energy, but agreed that the NDF plan appeared to offer a number of benefits for the decommissioning process. 

“The work cannot go ahead without the water shield because it would expose workers to dangerously high levels of radiation so this idea for the construction of a tank around one of the reactors is positive,” he told DW.  

“But that does not mean that I am not concerned,” he said. “It will be very difficult to construct this tank, to make sure it does not leak, and it will be very expensive and take more time, of course.”

Another earthquake 

Another concern that has been a constant since the March 2011 disaster is the possibility of another major earthquake or tsunami damaging the tank and potentially exposing radioactive debris to the air.

“We have already seen what long-term exposure to salt water at the site does to metal and other materials, and if there was another major tremor then that could very easily affect the tank and even see it collapse,” Matsukubo said. “To me, that is the biggest worry.”  

He also questioned why it had taken the Tokyo Electric Power Company (TEPCO), decommissioning experts, the government and Japan’s nuclear regulators more than a decade to think up the plan. It is likely that the delay will further extend the schedule and total cost of rendering the site safe.

Government estimates put the cost of decommissioning at 8 trillion yen (€56 billion, $55.3 billion), although that figure may increase if new complications crop up, while the work will probably continue for another 30 years.  

Kazuto Suzuki, a professor of science and technology policy at Tokyo University, agreed that the new approach to the decommissioning of the reactors “seems to be a good one, but the problem will be in the execution.” 

“I’m not an expert, but I can see problems with leaks — as they have already experienced from the tanks holding contaminated water at the site — and then that water escaping into the sea,” he said. “This is a really big issue for the people still living in the region and they have to be able to guarantee a safe level of water within the tank surrounding the reactor.” 

Seismic concerns 

There are also concerns about the stability of the ground that the tank will stand on due to the immense weight it will have to bear, Suzuki pointed out.  

He was less worried, however, about the possibility of another earthquake wreaking further havoc at the site.  

“Concern about another earthquake is legitimate, but we have to remember that the original damage to the Fukushima plant was almost entirely the result of the tsunami, not the earthquake,” he said.  

“I actually believe that Japan can be quite proud of the sophisticated anti-seismic technology that is incorporated into all buildings here, but especially our nuclear plants,” Suzuki said.

“I am confident that thanks to the lessons we have learned at Fukushima already, the impact of another earthquake on the walls of a tank around a reactor would be factored into the construction process.” 

September 26, 2022 Posted by | Fuk 2022 | , | Leave a comment

New submersion method in consideration for Fukushima debris cleanup

The Fukushima Daiichi nuclear complex is seen on Feb. 9, 2022. From left, the No. 4, No. 3, No. 2 and No. 1 reactors.

September 2, 2022

TOKYO (Kyodo) — The operator of the Fukushima Daiichi nuclear power plant, which suffered core meltdowns in 2011, is considering a new submersion method for removing radioactive fuel debris that would wholly encase a reactor building in a water-filled, tank-like structure, a source close to the company said Thursday.

Conceptual breakthroughs with the method, whose advantages include using water’s ability to interrupt radiation and thereby provide a safer working environment, have made it a promising candidate for the cleanup of the defunct nuclear plant, according to the source close to Tokyo Electric Power Company Holdings Inc.

But with no proven track record in the nuclear field, investigations are ongoing into future technological issues and costs, among other contingencies. The source said it could “require advanced technology to stop water leaking out and become a huge construction project.”

Were it to go ahead, the process from building to actual debris removal would be lengthy and would likely affect total decommissioning costs, currently pegged at about 8 trillion yen ($57.45 billion).

In the aftermath of the March 2011 Great East Japan Earthquake and tsunami, nuclear fuel cooling processes failed at the Fukushima plant’s reactors 1 through 3, causing the fuel to melt and resolidify into radioactive debris mixed with concrete, metal and other materials present in the reactors.

Debris removal is the operator’s most challenging issue in the Fukushima plant cleanup. Some 880 tons of the radioactive waste material is estimated to have been created by the nuclear meltdown across the three reactors.

The new submersion method, which is currently expected to be applied to the No. 3 reactor, would involve building a strong, pressure-resistant structure, such as a ship’s hull or a plane’s body, completely encapsulating the reactor, including underground.

The structure could then be filled with water, and removal work would take place from the top.

The operator initially considered a similar method to fill the reactor’s containment vessel with water. But the idea was abandoned due to potential difficulties fixing holes in the structure and the possibility it would increase workers’ exposure to radiation.

Preparations are being made to include the new submersion method in the 2022 edition of a strategic plan for decommissioning to be compiled by the state-backed Nuclear Damage Compensation and Decommissioning Facilitation Corp., which is helping the operator scrap the reactors.

In the case of the No. 2 reactor, preparations remain under way for its debris removal via a dry method, involving extracting the material without filling the reactor with water. The NDF intends to keep it as a potential option in its strategic plan.

While the No. 2 reactor’s cleanup was slated to begin this year, on Aug. 25, the government said removal work would be delayed a further 12 to 18 months to ensure safety and reliability.

The government and the power company are operating under a plan to complete debris removal and finish decommissioning work sometime between 2041 and 2051.

Amid the extensive cleanup in Fukushima, the Japanese government said on Aug. 24 that it is considering the construction of the next generation of nuclear plants amid an increasingly fraught energy supply environment and the country’s dependency on imported natural resources.

https://mainichi.jp/english/articles/20220902/p2g/00m/0na/002000c

September 4, 2022 Posted by | Fuk 2022 | , , | Leave a comment