Clearing the radioactive rubble heap that was Fukushima Daiichi, 7 years on — Scientific American

” Seven years after one of the largest earthquakes on record unleashed a massive tsunami and triggered a meltdown at Japan’s Fukushima Daiichi nuclear power plant, officials say they are at last getting a handle on the mammoth task of cleaning the site before it is ultimately dismantled. But the process is still expected to be a long, expensive slog, requiring as-yet untried feats of engineering—and not all the details have yet been worked out.

When the disaster knocked out off- and on-site power supplies on March 11, 2011, three of the cooling systems for the plant’s four reactor units were disabled. This caused the nuclear fuel inside to overheat, leading to a meltdown and hydrogen explosions that spewed out radiation. The plant’s operator, Tokyo Electric Power Co. (TEPCO), responded by cooling the reactors with water, which continues today. Meanwhile thousands of people living in the surrounding area were evacuated and Japan’s other nuclear plants were temporarily shut down.

In the years since the disaster and the immediate effort to stanch the release of radioactive material, officials have been working out how to decontaminate the site without unleashing more radiation into the environment. It will take a complex engineering effort to deal with thousands of fuel rods, along with the mangled debris of the reactors and the water used to cool them. Despite setbacks, that effort is now moving forward in earnest, officials say. “We are still conducting studies on the location of the molten fuel, but despite this we have made the judgment that the units are stable,” says Naohiro Masuda, TEPCO’s chief decommissioning officer for Daiichi.

Completely cleaning up and taking apart the plant could take a generation or more, and comes with a hefty price tag. In 2016 the government increased its cost estimate to about $75.7 billion, part of the overall Fukushima disaster price tag of $202.5 billion. The Japan Center for Economic Research, a private think tank, said the cleanup costs could mount to some $470 billion to $660 billion, however.

Under a government roadmap, TEPCO hopes to finish the job in 30 to 40 years. But some experts say even that could be an underestimate. “In general, estimates of work involving decontamination and disposal of nuclear materials are underestimated by decades,” says Rod Ewing, a professor of nuclear security and geological sciences at Stanford University. “I think that we have to expect that the job will extend beyond the estimated time.”

The considerable time and expense are due to the cleanup being a veritable hydra that involves unprecedented engineering. TEPCO and its many contractors will be focusing on several battlefronts.

Water is being deliberately circulated through each reactor every day to cool the fuel within—but the plant lies on a slope, and water from precipitation keeps flowing into the buildings as well. Workers built an elaborate scrubbing system that removes cesium, strontium and dozens of other radioactive particles from the water; some of it is recirculated into the reactors, and some goes into row upon row of giant tanks at the site. There’s about one million tons of water kept in 1,000 tanks and the volume grows by 100 tons a day, down from 400 tons four years ago.

To keep more water from seeping into the ground and being tainted, more than 90 percent of the site has been paved. A series of drains and underground barriers—including a $325-million* supposedly impermeable “wall” of frozen soil—was also constructed to keep water from flowing into the reactors and the ocean. These have not worked as well as expected, though, especially during typhoons when precipitation spikes, so groundwater continues to be contaminated.

Despite the fact contaminated water was dumped into the sea after the disaster, studies by Japanese and foreign labs have shown radioactive cesium in fish caught in the region has fallen and is now within Japan’s food safety limits. TEPCO will not say when it will decide what to do with all the stored water, because dumping it in the ocean again would invite censure at home and abroad—but there are worries that another powerful quake could cause it to slosh out of the tanks.

Fuel Mop-up

A second major issue at Fukushima is how to handle the fuel¾the melted uranium cores as well as spent and unused fuel rods stored at the reactors. Using robotic probes and 3-D imaging with muons (a type of subatomic particle), workers have found pebbly deposits and debris at various areas inside the primary containment vessels in the three of the plant’s reactor units. These highly radioactive remains are thought to be melted fuel as well as supporting structures. TEPCO has not yet worked out how it can remove the remains, but it wants to start the job in 2021. There are few precedents for the task. Lake Barrett—director of the Three Mile Island nuclear plant during its decommissioning after a partial meltdown at the Middletown, Pa., facility in 1979—says TEPCO will use robots to remotely dig out the melted fuel and store it in canisters on-site before shipping to its final disposal spot. “This is similar to what we did at Three Mile Island, just much larger and with much more sophisticated engineering because their damage is greater than ours was,” Barrett says. “So although the work is technically much more challenging than ours was, Japan has excellent technological capabilities, and worldwide robotic technology has advanced tremendously in the last 30-plus years.”

Shaun Burnie, senior nuclear specialist with Greenpeace Germany, doubts the ambitious cleanup effort can be completed in the time cited, and questions whether the radioactivity can be completely contained. Until TEPCO can verify the conditions of the molten fuel, he says, “there can be no confirmation of what impact and damage the material has had” on the various components of the reactors—and therefore how radiation might leak into the environment in the future.

Although the utility managed to safely remove all 1,533 fuel bundles from the plant’s unit No. 4 reactor by December 2014, it still has to do the same for the hundreds of rods stored at the other three units. This involves clearing rubble, installing shields, dismantling the building roofs, and setting up platforms and special rooftop equipment to remove the rods. Last month a 55-ton dome roof was installed on unit No. 3 to facilitate the safe removal of the 533 fuel bundles that remain in a storage pool there. Whereas removal should begin at No. 3 sometime before April 2019, the fuel at units No. 1 and 2 will not be ready for transfer before 2023, according to TEPCO. And just where all the fuel and other radioactive solid debris on the site will be stored or disposed of long-term has yet to be decided; last month the site’s ninth solid waste storage building, with a capacity of about 61,000 cubic meters, went into operation.

As for what the site itself might look like decades from now, cleanup officials refuse to say. But they are quick to differentiate it from the sarcophagus-style containment of the 1986 Chernobyl catastrophe in the Soviet Union, in what is now Ukraine. Whereas the Chernobyl plant is sealed off and the surrounding area remains off-limits except for brief visits—leaving behind several ghost towns—Japanese officials want as many areas as possible around the Daiichi site to eventually be habitable again.

“To accelerate reconstruction and rebuilding of Fukushima as a region, and the lives of locals, the key is to reduce the mid- and long-term risk,” says Satoru Toyomoto, director for international issues at the Ministry of Economy, Trade and Industry’s Nuclear Accident Response Office. “In that regard, keeping debris on the premises without approval is not an option.” ”

by Tim Hornyak, Scientific American

source

Advertisements

Fukushima debris heading to intermediate storage facility — The Asahi Shimbun

” The Environment Ministry on Oct. 28 will start bringing radiation-contaminated soil to an intermediate storage site in Fukushima Prefecture, despite having acquired less than half of the land needed for the overall project.

The ministry’s announcement on Oct. 24 marks a long-delayed step toward clearing temporary sites that were set up around the prefecture to store countless bags of radioactive debris gathered after the triple meltdown at the Fukushima No. 1 nuclear power plant in March 2011.

The entire intermediate storage project will cover a 16-square-kilometer area spanning the towns of Futaba and Okuma around the nuclear plant. It is designed to hold up to 22 million cubic meters of contaminated debris for a maximum period of 30 years.

However, the ministry is still negotiating with landowners on buying parcels of land within the area. As of the end of September, the ministry had reached acquisition agreements for only about 40 percent of the land for the project.

The soil storage facility that will open on Oct. 28 is located on the Okuma side. It has a capacity of about 50,000 cubic meters.

Bags of contaminated soil stored in Okuma will be transferred to the facility, where the debris will be separated based on radiation dosages.

A similar storage facility is being constructed on the Futaba side.

The ministry initially planned to start full-scale operations of the entire storage facility in January 2015. However, it took longer than expected to gain a consensus from local residents and acquire land at the proposed site.

In March 2015, a portion of the contaminated soil was brought to the Okuma facility for temporary storage. ”

by The Asahi Shimbun

source

Japan pictures likely show melted Fukushima fuel for first time — Bloomberg

” New images show what is likely to be melted nuclear fuel hanging from inside one of Japan’s wrecked Fukushima reactors, a potential milestone in the cleanup of one of the worst atomic disasters in history.

Tokyo Electric Power Co. Holdings Inc., Japan’s biggest utility, released images on Friday showing a hardened black, grey and orange substance that dripped from the bottom of the No. 3 reactor pressure vessel at Fukushima, which is likely to contain melted fuel, according to Takahiro Kimoto, an official at the company. The company sent a Toshiba-designed robot, which can swim and resembles a submarine, to explore the inside of the reactor for the first time on July 19.

“Never before have we taken such clear pictures of what could be melted fuel,” Kimoto said at a press briefing that began at 9 p.m. Friday in Tokyo, noting that it would take time to analyze and confirm whether it is actually fuel. “We believe that the fuel melted and mixed with the metal directly underneath it. And it is highly likely that we have filmed that on Friday.”

If confirmed, the substance — which has the appearance of icicles — would be the first discovery of the fuel that melted during the triple reactor accident at Fukushima six years ago. For Tokyo Electric, which bears most of the clean-up costs, the discovery would help the utility design a way to remove the highly-radioactive material.

The robot, which is about 30 centimeters (12 inches) long, will search for melted fuel at the bottom of the reactor on Saturday. It is possible that the company will take more pictures of what could be melted fuel spread across the floor and lower levels, according to Tokyo Electric’s Kimoto. Fuel from a nuclear meltdown is known as corium, which is a mixture of the atomic fuel rods and other structural materials.

Early Signs

“It is important to know the exact locations and the physical, chemical, radiological forms of the corium to develop the necessary engineering defueling plans for the safe removal of the radioactive materials,” said Lake Barrett, a former official at the U.S. Nuclear Regulatory Commission who was involved with the cleanup at the Three Mile Island nuclear power plant in the U.S. “The recent investigation results are significant early signs of progress on the long road ahead.”

Because of the high radioactivity levels inside the reactor, only specially designed robots can probe the unit. And the unprecedented nature of the Fukushima disaster means that Tepco, as the utility is known, is pinning its efforts on technology not yet invented to get the melted fuel out of the reactors.

Removal Plans

The company aims to decide on the procedure to remove the melted fuel from each unit as soon as this summer. And it will confirm the procedure for the first reactor during the fiscal year ending March 2019, with fuel removal slated to begin in 2021.

Decommissioning the reactors will cost 8 trillion yen ($72 billion), according to an estimate in December from the Ministry of Economy, Trade and Industry. Removing the fuel is one of the most important steps in a cleanup that may take as long as 40 years.

Similar to the latest findings on Friday, Tepco took photographs in January of what appeared to be black residue covering a grate under the Fukushima Dai-Ichi No. 2 reactor, which was speculated to have been melted fuel. However, a follow-up survey by another Toshiba-designed robot in February failed to confirm the location of any melted fuel in the reactor after it got stuck in debris.

A robot designed by Hitachi-GE Nuclear Energy Ltd. also failed to find any melted fuel during its probe of the No. 1 reactor in March.

The significance of Friday’s finding “might be evidence that the robots used by Tepco can now deal with the higher radiation levels, at least for periods of time that allow them to search parts of the reactor that are more likely to contain fuel debris,” M.V. Ramana, professor at the Liu Institute for Global Issues at the University of British Columbia, said by email.

“If some of these fragments can be brought out of the reactor and studied, it would allow nuclear engineers and scientists to better model what happened during the accident.” ”

by Stephen Stapczynski, Bloomberg

source

AP Interview: Fukushima plant’s new ice wall not watertight — AP via ABC News

” Coping with the vast amounts of ground water flowing into the broken Fukushima nuclear plant — which then becomes radiated and seeps back out — has become such a problem that Japan is building a 35 billion yen ($312 million) “ice wall” into the earth around it.

But even if the frozen barrier built with taxpayers’ money works as envisioned, it won’t completely block all water from reaching the damaged reactors because of gaps in the wall and rainfall, creating as much as 50 tons of contaminated water each day, said Yuichi Okamura, a chief architect of the massive project.

“It’s not zero,” Okamura said of the amount of water reaching the reactors in an interview with The Associated Press earlier this week. He is a general manager at Tokyo Electric Power Co., or TEPCO, which operates the facility that melted down after it was hit by a tsunami in 2011, prompting 150,000 people to evacuate.

Workers have rigged pipes that constantly spray water into the reactors to keep the nuclear debris inside from overheating, but coping with what to do with the resulting radiated water has been a major headache. So far, the company has stored the water in nearly 1,000 huge tanks around the plant, with more being built each week.

TEPCO resorted to devising the 1.5-kilometer (1-mile)-long ice wall around the facility after it became clear it had to do something drastic to stem the flow of groundwater into the facility’s basement and keep contaminated water from flowing back out.

“It’s a vicious cycle, like a cat-and-mouse game,” Okamura said of the water-related issues. “We have come up against many unexpected problems.”

The water woes are just part of the many obstacles involved in controlling and dismantling the Fukushima Dai-chi plant, a huge task that will take 40 years. No one has even seen the nuclear debris. Robots are being created to capture images of the debris. The radiation is so high no human being can do that job.

The ice wall, built by construction company Kajima Corp., is being turned on in sections for tests, and the entire freezing process will take eight months since it was first switched on in late March. The entire wall requires as much electricity as would power 13,000 Japanese households.

Edward Yarmak, president of Arctic Foundations, based in Anchorage, Alaska, which designs and installs ground freezing systems and made an ice wall for the Oak Ridge reactor site, says the solution should work at Fukushima.

“The refrigeration system has just been turned on, and it takes time to form the wall. First, the soil freezes concentrically around the pipes and when the frozen cylinders are large enough, they coalesce and form a continuous wall. After time, the wall increases in thickness,” he said in an email.

But critics say the problem of the groundwater reaching the reactors was a no-brainer that should have been projected.

Building a concrete wall into the hill near the plant right after the disaster would have minimized the contaminated water problem considerably, says Shigeaki Tsunoyama, honorary professor and former president of University of Aizu in Fukushima.

Even at the reduced amount of 50 tons a day, the contaminated water produced at Fukushima will equal what came out of Three Mile Island’s total in just eight months because of the prevalence of groundwater in Fukushima, he said.

Although TEPCO has set 2020 as the goal for ending the water problems, Tsunoyama believes that’s too optimistic.

“The groundwater coming up from below can never become zero,” he said in a telephone interview. “There is no perfect answer.”

Okamura acknowledged the option to build a barrier in the higher elevation near the plant was considered in the early days after the disaster. But he defended his company’s actions.

The priority was on preventing contaminated water from escaping into the Pacific Ocean, he said. Various walls were built along the coastline, and radiation monitors show leaks have tapered off over the last five years.

Opponents of nuclear power say the ice wall is a waste of taxpayers’ money and that it may not work.

“From the perspective of regular people, we have serious questions about this piece of research that’s awarded a construction giant,” says Kanna Mitsuta, director of ecology group Friends of the Earth Japan. “Our reaction is: Why an ice wall?” ”

by Yuri Kageyama and Mari Yamaguchi

source

Fukushima cleanup described by Tepco chief as ‘like working in a field hospital in a warzone’ — ABC News

” Fukushima power plant operators’ recent update on the nuclear accident clean-up makes it clear there is still a long way to go to remediate the area.

It has been almost five years since the nuclear accident at Fukushima, where three reactors experienced core meltdowns and the plant spewed radioactivity across a huge area, forcing hundreds of thousands of people to leave their homes and livelihoods.

The operators said they have picked up the debris from the accident and built some new protective structures on the site but the trickiest job of finding and removing the nuclear fuel in the reactors have not yet started.

Naohiro Masuda, the man tasked with the job of decommissioning the plant, said “in the first couple of years it was like working in a field hospital in a warzone”.

“It was like running through flames,” he said.

Tokyo will host the Olympics in four years and many in the Government would prefer the message from Fukushima to be a lot more positive.

Mr Masuda said there was still melted fuel in reactors one, two and three.

“But honestly we don’t know about the situation, we don’t know where it’s fallen,” he said.

In the five years since the nuclear accident, work at the plant has focused on a physical clean-up of the site, debris from earthquake and tsunami damage to the buildings has been removed.

But the most difficult and complex work has yet to begin and was not known where the melted nuclear debris is inside the reactors.

In the wake of the nuclear disaster, Japan’s 54 nuclear reactors were switched off and a safety review carried out.

The three reactors are operating again — with plans to switch on many more as soon as they meet the requirements of a new, stricter safety code.

Buddhist monk says Government has not ‘learnt its lesson’

The Buddhist monk Tokuo Hayakawa, who resides in the 600-year-old Hokyoji temple in the hills behind the Fukushima power plant, said that Japan has not learnt its lesson from the nuclear accident.

“It’s clear that it’ll happen again,” he said.

He and his community were forced to flee in the aftermath of the nuclear accident.

Dressed in his black prayer robes, adorned with anti-nuclear badges, monk Hayakawa said the Government had let the people down and he believed the situation at the plant was far from under control.

The evacuation order has been lifted in a nearby town, but young people were not returning.

Mr Hayakawa said he believed as the decommission progresses in the area will disappear.

He said the Government should abandon its nuclear energy policy.

“They must stop using nuclear power because safety can’t be guaranteed,” Mr Hayakawa said.

“I feel sad and angry, even more than I did at the time of the accident.”

source