Six years after Fukushima, robots finally find reactors’ melted uranium fuel — The New York Times

” FUKUSHIMA DAIICHI NUCLEAR POWER PLANT, Japan — Four engineers hunched before a bank of monitors, one holding what looked like a game controller. They had spent a month training for what they were about to do: pilot a small robot into the contaminated heart of the ruined Fukushima nuclear plant.

Earlier robots had failed, getting caught on debris or suffering circuit malfunctions from excess radiation. But the newer version, called the Mini-Manbo, or “little sunfish,” was made of radiation-hardened materials with a sensor to help it avoid dangerous hot spots in the plant’s flooded reactor buildings.

The size of a shoe box, the Manbo used tiny propellers to hover and glide through water in a manner similar to an aerial drone.

After three days of carefully navigating through a shattered reactor building, the Manbo finally reached the heavily damaged Unit 3 reactor. There, the robot beamed back video of a gaping hole at the bottom of the reactor and, on the floor beneath it, clumps of what looked like solidified lava: the first images ever taken of the plant’s melted uranium fuel.

The discovery in July at Unit 3, and similar successes this year in locating the fuel of the plant’s other two ruined reactors, mark what Japanese officials hope will prove to be a turning point in the worst atomic disaster since Chernobyl.

The fate of the fuel had been one of the most enduring mysteries of the catastrophe, which occurred on March 11, 2011, when an earthquake and 50-foot tsunami knocked out vital cooling systems here at the plant.

Left to overheat, three of the six reactors melted down. Their uranium fuel rods liquefied like candle wax, dripping to the bottom of the reactor vessels in a molten mass hot enough to burn through the steel walls and even penetrate the concrete floors below.

No one knew for sure exactly how far those molten fuel cores had traveled before desperate plant workers — later celebrated as the “Fukushima Fifty” — were able to cool them again by pumping water into the reactor buildings. With radiation levels so high, the fate of the fuel remained unknown.

As officials became more confident about managing the disaster, they began a search for the missing fuel. Scientists and engineers built radiation-resistant robots like the Manbo and a device like a huge X-ray machine that uses exotic space particles called muons to see the reactors’ innards.

Now that engineers say they have found the fuel, officials of the government and the utility that runs the plant hope to sway public opinion. Six and a half years after the accident spewed radiation over northern Japan, and at one point seemed to endanger Tokyo, the officials hope to persuade a skeptical world that the plant has moved out of post-disaster crisis mode and into something much less threatening: cleanup.

“Until now, we didn’t know exactly where the fuel was, or what it looked like,” said Takahiro Kimoto, a general manager in the nuclear power division of the plant’s operator, Tokyo Electric Power Co., or Tepco. “Now that we have seen it, we can make plans to retrieve it.”

Tepco is keen to portray the plant as one big industrial cleanup site. About 7,000 people work here, building new water storage tanks, moving radioactive debris to a new disposal site, and erecting enormous scaffoldings over reactor buildings torn apart by the huge hydrogen explosions that occurred during the accident.

Access to the plant is easier than it was just a year ago, when visitors still had to change into special protective clothing. These days, workers and visitors can move about all but the most dangerous areas in street clothes.

A Tepco guide explained this was because the central plant grounds had been deforested and paved over, sealing in contaminated soil.

During a recent visit, the mood within the plant was noticeably more relaxed, though movements were still tightly controlled and everyone was required to wear radiation-measuring badges. Inside a “resting building,” workers ate in a large cafeteria and bought snacks in a convenience store.

At the plant’s entrance, a sign warned: “Games like Pokemon GO are forbidden within the facility.”

“We have finished the debris cleanup and gotten the plant under control,” said the guide, Daisuke Hirose, a spokesman for Tepco’s subsidiary in charge of decommissioning the plant. “Now, we are finally preparing for decommissioning.”

In September, the prime minister’s office set a target date of 2021 — the 10th anniversary of the disaster — for the next significant stage, when workers begin extracting the melted fuel from at least one of the three destroyed reactors, though they have yet to choose which one.

The government admits that cleaning up the plant will take at least another three to four decades and tens of billions of dollars. A $100 million research center has been built nearby to help scientists and engineers develop a new generation of robots to enter the reactor buildings and scoop up the melted fuel.

At Chernobyl, the Soviets simply entombed the charred reactor in concrete after the deadly 1986 accident. But Japan has pledged to dismantle the Fukushima plant and decontaminate the surrounding countryside, which was home to about 160,000 people who were evacuated after accident.

Many of them have been allowed to return as the rural towns around the plant have been decontaminated. But without at least starting a cleanup of the plant itself, officials admit they will find it difficult to convince the public that the accident is truly over.

They also hope that beginning the cleanup will help them win the public’s consent to restart Japan’s undamaged nuclear plants, most of which remain shut down since the disaster.

Tepco and the government are treading cautiously to avoid further mishaps that could raise doubts that the plant is under control.

“They are being very methodical — too slow, some would say — in making a careful effort to avoid any missteps or nasty surprises,” said David Lochbaum, director of the nuclear safety project at the Union of Concerned Scientists, who was a co-author of a book on the disaster.

“They want to regain trust. They have learned that trust can be lost much quicker than it can be recovered.”

To show the course followed by the Manbo, Tepco’s Mr. Hirose guided me inside the building containing the undamaged Unit 5 reactor, which is structurally the same as two of the destroyed reactors.

Mr. Hirose pointed toward the spot on a narrow access ramp where two robots, including one that looked like a scorpion, got tangled in February by debris inside the ruined Unit 2.

Before engineers could free the scorpion, its monitoring screen faded to black as its electronic components were overcome by radiation, which Tepco said reached levels of 70 sieverts per hour. (A dose of one sievert is enough to cause radiation sickness in a human.)

Mr. Hirose then led me underneath the reactor, onto what is called the pedestal.

The bottom of the reactor looked like a collection of huge bolts — the access points for control rods used to speed up and slow down the nuclear reaction inside a healthy reactor. The pedestal was just a metal grating, with the building’s concrete floor visible below.

“The overheated fuel would have dropped from here, and melted through the grating around here,” Mr. Hirose said, as we squatted to avoid banging our heads on the reactor bottom. The entire area around the reactor was dark, and cluttered with pipes and machinery.

To avoid getting entangled, the Manbo took three days to travel some 20 feet to the bottom of Unit 3.

To examine the other two reactors, engineers built a “snake” robot that could thread its way through wreckage, and the imaging device using muons, which can pass through most matter. The muon device has produced crude, ghostly images of the reactors’ interiors.

Extracting the melted fuel will present its own set of technical challenges, and risks.

Engineers are developing the new radiation-resistant robots at the Naraha Remote Technology Development Center. It includes a hangar-sized building to hold full-scale mock-ups of the plant and a virtual-reality room that simulates the interiors of the reactor buildings, including locations of known debris.

“I’ve been a robotic engineer for 30 years, and we’ve never faced anything as hard as this,” said Shinji Kawatsuma, director of research and development at the center. “This is a divine mission for Japan’s robot engineers.” “

by Martin Fackler, The New York Times

source with photos, video and internal links

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In Fukushima, a land where few return — The Japan Times

” A cherry tree is blooming in the spring sunshine outside the home of Masaaki Sakai but there is nobody to see it. The house is empty and boarded up. Weeds poke through the ground. All around are telltale signs of wild boar, which descend from the mountains to root and forage in the fields. Soon, the 60-year-old farmhouse Sakai shared with his mother and grandmother will be demolished.

“I don’t feel especially sad,” Sakai says. “We have rebuilt our lives elsewhere. I can come back and look around — just not live here.”

A few hundred meters away the road is blocked and a beeping dosimeter begins nagging at the bucolic peace. The reading here is a shade over 1 microsievert per hour — a fraction of what it was when Sakai’s family fled in 2011.

The radiation goes up and down, depending on the weather, Sakai says. In gullies and cracks in the road, and up in the trees, it soars. With almost everyone gone, the monkeys who live in the forests have grown bolder, stopping to stare at the odd car that appears instead of fleeing, as they used to.

A cluster of 20 small hamlets spread over 230 square kilometers, Iitate was undone by a quirk of the weather in the days that followed the nuclear accident in March 2011. Wind carried radioactive particles from the Fukushima No. 1 nuclear power plant, which is located about 45 kilometers away, that fell in rain and snow on the night of March 15, 2011. After more than a month of indecision, during which the villagers lived with some of the highest radiation recorded in the disaster (the reading outside the village office on the evening of March 15 was a startling 44.7 microsieverts per hour), the government ordered them to leave.

Now, the government says it is safe to go back. With great fanfare, all but the still heavily contaminated south of Iitate, Nagadoro, was reopened on March 31.

The reopening fulfills a pledge made by Mayor Norio Kanno: Iitate was the first local authority in Fukushima Prefecture to set a date for ending evacuation in 2012, when the mayor promised to reboot the village in five years. The village has a new sports ground, convenience store and udon restaurant. A clinic sees patients twice a week. All that’s missing is people.

Waiting to meet Kanno in the government offices of Iitate, the eye falls on a book displayed in the reception: “The Most Beautiful Villages in Japan.” Listed at No. 12 is the beloved rolling patchwork of forests, hills and fields the mayor has governed for more than two decades — population 6,300, famous for its neat terraces of rice and vegetables, its industrious organic farmers, its wild mushrooms and the black wagyu cow that has taken the name of the area.

The description in the book is mocked by reality outside. The fields are mostly bald, shorn of vegetation in a Promethean attempt to decontaminate it of the radiation that fell six years ago. There is not a cow or a farmer in sight. Tractors sit idle in the fields. The local schools are empty. As for the population, the only part of the village that looks busy is the home for the elderly across the road from Kanno’s office.

“The village will never return to how it used to be before the disaster,” Kanno says, “but it may develop in a different way.”

Recovery has started, Kanno says, wondering whether returnees will be able to start building a village they like.

“Who knows? Maybe one day that may help bring back evacuees or newcomers,” Kanno says. “Life doesn’t improve if you remain pessimistic.”

Even for those who have permanently left, he adds, “it doesn’t mean that their furusato can just disappear.”

The pull of the furusato (hometown) is exceptionally strong in Japan, says Tom Gill, a British anthropologist who has written extensively about Iitate.

Yearning for it “is expressed in countless sentimental ballads,” Gill says. “One particular song, simply titled ‘Furusato,’ has been sung by children attending state schools in Japan since 1914.”

The appeal has persisted despite — or perhaps because of — the fact that the rural/urban imbalance in Japan is more skewed than in any other developed nation, Gill says; just 10 percent of the nation’s population live in the country.

This may partly explain the extraordinary efforts to bring east Fukushima back to life. By one study, more than ¥2.34 trillion has been spent decontaminating an area roughly half the size of Rhode Island.

There has been no official talk of abandoning it. Indeed, any suggestion otherwise could be controversial: When industry minister Yoshio Hachiro called the abandoned communities “towns of death” in September 2011, the subsequent outrage forced him to quit a week later.

Instead, the area was divided into three zones with awkward euphemisms to suggest just the opposite: Communities with annual radiation measuring 20 millisieverts or less (the typical worldwide limit for workers in nuclear plants) are “being prepared for lifting of evacuation order,” districts of 20-50 millisieverts per year are “no-residence zones” and the most heavily contaminated areas of 50 millisieverts or more per year, such as Nagadoro, are “difficult-to-return.”

In September 2015, Naraha, which is located 15 kilometers south of the Fukushima No. 1 nuclear plant, became the first town in the prefecture to completely lift the evacuation order imposed after the triple meltdown. Naraha has a publicly built shopping street, a new factory making lithium batteries, a kindergarten and a secondary school.

A team of decontamination workers has been sent to every house — in some cases several times. Of the pre-disaster 7,400 residents, about 1,500 mainly elderly people have returned, the local government says, although that figure is likely inflated.

In Iitate, the cost of decontamination works out at about ¥200 million per household. That, and the passage of time, has dramatically reduced radiation in many areas to below 20 millisieverts a year. However, Kanno says, the cleanup extends to only 20 meters around each house, and three-quarters of the village is forested mountains. In windy weather, radioactive elements are blown back onto the fields and homes.

“All that money, and for what?” asks Nobuyoshi Itoh, a farmer and critic of the mayor. “Would you bring children here and let them roam in the fields and forests?”

Itoh opted to stay in one of the more heavily toxic parts of the village after everyone fled, with little apparent ill effect, although he says his immune system has weakened.

One of the reasons why Iitate was such a pleasant place to live before the nuclear crisis, he recalls, was its unofficial barter system. “Most people here never bought vegetables; they grew them,” he says. “I would bring someone potatoes and they would give me eggs. That’s gone now.”

At most, he says, a few hundred people are back — but they’re invariably older or retired.

“They alone will not sustain the village,” Itoh says. “Who will drive them around or look after them when they are sick?”

As the depth of the disaster facing Iitate became clear, local people began to squabble among themselves. Some were barely scraping a living and wanted to leave, although saying so out loud — abandoning the furusato — was often difficult. Many joined lawsuits against the government.

Even before disaster struck, the village had lost a third of its population since 1970 as its young folk relocated to the cities, mirroring the hollowing-out of rural areas across the country. Some wanted to shift the entire village elsewhere, but Kanno wouldn’t hear of it.

Compensation could be a considerable incentive. In addition to ¥100,000 a month to cover the “mental anguish” of being torn from their old lives, there was extra money for people with houses or farms. A five-year lump sum was worth ¥6 million per person — twice that for Nagadoro. One researcher estimates a rough figure of ¥50 million for the average household, sufficient to leave behind the uncertainties and worries of Iitate and buy a house a few dozen miles away, close enough to return for work or to the village’s cool, tranquil summers.

Many have already done so. Though nobody knows the true figure, the local talk is that perhaps half of the villagers have permanently left. Surveys suggest fewer than 30 percent want to return, and even less in the case of Nagadoro.

Yoshitomo Shigihara, head of the Nagadoro hamlet, says many families made their decision some time ago. His grandchildren, he says, should not have to live in such a place.

“It’s our job to protect them,” Shigihara says. He lives in the city of Fukushima but returns roughly every 10 days to inspect his house and weed the land.

Even with so much money spent, Shigihara doubts whether it will bring many of his friends or relatives back. At 70 years of age, he is not sure that he even wants to return, he says.

“I sometimes get upset thinking about it, but I can’t talk with anyone in Fukushima, even my family, because we often end up quarreling,” he says. “People try to feel out whether the others are receiving benefits, what they are getting or how much they received in compensation. It’s very stressful to talk to anyone in Iitate. I’m starting to hate myself because I end up treating others badly out of frustration.”

Kanno has won six elections since 1996 and has overseen every step of Iitate’s painful rehabilitation, navigating between the anger and despair of his constituents and the official response to the disaster from the government and Tokyo Electric Power Company Holdings (Tepco), operator of the crippled nuclear plant.

He wants more money to complete decontamination work (the government claims it is finished), repair roads and infrastructure. Returnees need financial support, he says. However, it is time, he believes, to end the monthly compensation, which, in his view, induces dependency.

“If people keep saying that life is hard, they will not be able to recover,” he says. “What we need is support for livelihoods.”

A new system gives seed money to people who voluntarily come back to start businesses or farms.

“We don’t want to give the impression that we are influencing people’s decisions or forcing them to return,” the mayor says, using the phrase “kokoro ni fumikomu,” which literally means “to step into hearts.”

Yet, next year, thousands of Iitate evacuees will face a choice: Go back or lose the money that has helped sustain them elsewhere for six years. Evacuation from areas exposed to less than 20 millisieverts per year will be regarded as “voluntary” under the official compensation scheme.

This dilemma was expressed with unusual starkness last month by Masahiro Imamura, the now sacked minister in charge of reconstructing Tohoku. Pressed by a freelance reporter, Imamura tetchily said it was up to the evacuees themselves — their “own responsibility, their own choice” — whether or not to return.

The comment touched a nerve. The government is forcing people to go back, some argued, employing a form of economic blackmail, or worse, kimin seisaku — abandoning them to their fate.

Itoh is angry at the resettlement. For him, politics drives the haste to put the disaster behind.

“It’s inhuman to make people go back to this,” he says. Like the physical damage of radiation, he says, the psychological damage is also invisible: “A lot of people are suffering in silence.”

Itoh believes the government wants to show that the problems of nuclear power can be overcome so it can switch the nation’s idling nuclear reactors back on. Just four are in operation while the fate of 42 others remains in political and legal limbo. Public opinion remains opposed to their restart.

Many people began with high hopes in Iitate but have gradually grown distrustful of the village government, says Kenichi Hasegawa, a farmer who wrote a book titled “Genpatsu ni Furusato o Ubawarete” (“Fukushima’s Stolen Lives”) in 2012. Right from the start, he says, the mayor desperately tried to hide the shocking radiation outside his office.

“Villagers have started losing interest,” Hasegawa says.

Meetings called by the mayor are poorly attended.

“But they hold meetings anyway,” Hasegawa says, “just to say they did.”

Kanno rejects talk of defeatism. A tourist shop is expected to open in August that will attract people to the area, he says. Some villagers are paving entrances to their houses, using money from the reconstruction budget. As for radiation, everyone “has their own idea” about its effects. The lifting of the evacuation is only the start.

Itoh says he once trusted public officials but those days are long gone. By trying to save the village, he says, the mayor may in fact be killing it. ”

by David McNeill and Chie Matsumoto, The Japan Times

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Finding and removing melted fuel rods at Fukushima No. 1 — Nikkei Asian Review, The Japan Times

Nikkei Asian Review, “Survey fails to find melted rods at Fukushima reactors”:

” TOKYO — A remote survey of the Fukushima Daiichi nuclear plant’s No. 1 reactor was unable to locate and photograph melted nuclear fuel, Tokyo Electric Power Co. Holdings said Thursday, complicating efforts to remove that material as part of an extensive cleanup.

Tepco on Saturday sent a robot equipped with a camera into the containment vessel for the No. 1 unit. The majority of fuel rods have melted through the unit’s pressure vessel since the plant was struck by the March 11, 2011, earthquake and tsunami. The prevailing view has been that those melted fuel rods are now sitting under 2.5m of water at the bottom of the containment vessel.

The plan was to explore the bottom section by dipping a camera into the pool of water for the first time. But unexpected barriers such as pipes kept the camera around 1 meter from the bottom in most of the 10 positions surveyed instead of the intended depth of about 40cm from the bottom. While the camera was able to capture sand-like sediment, there was no trace of the melted fuel rods. Adding a fifth day to the investigation turned up no further evidence.

Yuichi Okamura, acting general manager of Tepco’s onsite nuclear power division, offered few comments at the utility’s Thursday news conference, saying only that “photographs and radiation data will need to be evaluated in conjunction with one another.”

The timeline set by Tepco and the government for decommissioning the Fukushima plant aims to begin extraction of melted-down material from the No. 1, No. 2 or No. 3 reactor in 2021 or earlier. An extraction plan is to be decided this summer. But the fact that the status of the melted rods still remains unknown underscores the seriousness of the accident.

The results of the robot survey were “limited,” according to Masanori Naitoh, director of nuclear safety analysis at the Institute of Applied Energy’s Nuclear Power Engineering Center. “It would be difficult to set a plan for extraction based on the information from this survey alone.”

An investigation of the No. 2 reactor also fell short, with the survey robot unable to reach the targeted spot right under the unit’s pressure vessel. ”

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The Japan Times, “Tepco’s biggest hurdle: How to remove melted fuel from crippled Fukushima reactors”:

” Six years after the triple meltdown at the Fukushima No. 1 nuclear power plant, recent investigations underneath the damaged reactor 2 using cameras and robots came close to identifying melted fuel rods for the first time.

Experts say getting a peek inside the containment vessel of reactor 2 was an accomplishment. But it also highlighted how tough it will be to further pinpoint the exact location of the melted fuel, let alone remove it some time in the future.

The biggest hurdle is the extremely lethal levels of radiation inside the containment vessel that not only prevent humans from getting near but have also crippled robots and other mechanical devices.

Safely removing the melted fuel would be a best-case scenario but the risks and costs should be weighed against the option of leaving the melted fuel in the crippled reactors, some experts said.

“The work to probe inside the containment vessels and remove the fuel debris will be extremely tough because of the high radiation levels,” said Hiroshi Miyano, who heads a panel of the Atomic Energy Society of Japan, which is discussing ways to decommission the Fukushima plant and making recommendations to the government.

The government and Tokyo Electric Power Company Holdings Inc. are trying to find a way to remedy the situation but existing methods and technologies may not be sufficient, Miyano said.

In search of melted fuel

The world’s attention turned to the melted fuel rods in late January when Tepco inserted a 10-meter-plus tube equipped with a camera into the containment vessel of reactor 2 to capture images under the pressure vessel that housed the fuel rods.

The images showed black lumps scattered beneath the pressure vessel.

When the March 11, 2011, Great East Japan Earthquake and monstrous tsunami hit, the plant suffered a blackout and lost its key cooling system, triggering meltdowns in reactors 1, 2 and 3. The melted nuclear fuel rods penetrated the pressure vessels and fell into the containment vessels.

Tepco had put cameras inside the containment vessels several times in the past six years but January’s probe was the first to apparently find melted fuel debris.

“We understand that this is a big milestone. We could finally get to see what it was like underneath the pressure vessel,” said Yuichi Okamura, general manager of Tepco’s nuclear power and plant siting division.

“This is critical information in order to remove the fuel debris.”

Radiation barrier

But Tepco hasn’t confirmed that the black lumps are melted fuel, saying they could be paint or cable wrappings, and further investigation is needed.

Capturing the images may be progress but the robot and camera forays have not provided enough information about how to deal with the melted fuel.

Last month, Tepco sent a remote-controlled, scorpion-shaped robot in to further probe inside the reactor 2 containment vessel. But the robot failed before it reached under the pressure vessel after a tire became stuck.

The robot’s dosimeter measured radiation levels of 210 sieverts per hour — enough to kill humans instantly.

While 210 sieverts per hour indicate the melted fuel was nearby, the radiation crippled the robot’s electronics, including its semiconductors and cameras, indicating that the further use of robots to pinpoint the melted fuel will be difficult, robotics experts said.

There are computer chips “designed to withstand a certain level of radiation, but the level inside the containment vessel is totally different,” said Satoshi Tadokoro, a professor at Tohoku University who is an expert on disasters and rescue robots.

The radiation can damage a robot’s chips that serve as their brains, causing the devices to lose control, said Tadokoro, whose robots have also been used at the Fukushima plant.

“On top of the high level of radiation, the entrance (to the containment vessel) for the robot is very small,” restricting what types of robots can be used to hunt for the melted fuel, he said.

Tepco said the opening it created on the side of the reactor 2 containment vessel is about 11 cm in diameter.

Fuel removal strategy

Tepco is set to conduct internal probes of the reactor 1 containment vessel this month and is preparing similar missions for reactor 3.

The government and utility then plan to adopt a basic fuel removal strategy this summer and fine-tune the plan next year, with the actual fuel removal taking place in or after 2021.

There are essentially three options for the strategy, according to the Tokyo-based International Research Institute for Nuclear Decommissioning (IRID), which is developing technologies for the Fukushima plant decommission.

One option is to flood the containment vessels with water and use a crane above the reactors to hoist up the melted fuel. The second option is to carry out the same process but without water. The third is to install removal equipment through the side of the containment vessel.

There are merits and drawbacks to each option, said Shoji Yamamoto, who heads the team developing technologies to create the fuel removal devices at IRID.

The flooding option can block radiation using water, but if the fuel melts into the water, it could pose a risk of recriticality. The debris may need to be cut into pieces for removal, but this process would enable water to get between multiple pieces, creating the condition for recriticality. For nuclear chain reactions to happen there needs to be a certain distance between nuclear fuel and water.

If there is no water, the recriticality risk is minimal but the massive radiation levels cannot be blocked, Yamamoto said.

Tepco’s Okamura said being able to block radiation with water is a huge plus, but noted the reactor 2 containment vessel had cracks and holes that could let injected coolant water escape.

With the Three Mile Island nuclear accident in the U.S., the flooding option was used to retrieve the melted fuel in the 1980s. But the key difference was that all of the melted fuel stayed inside the pressure vessel, so it was easier to flood the reactor.

Because the melted fuel in reactors 1, 2 and 3 at the Fukushima plant all penetrated the pressure vessels and fell into the containment vessels, extracting it from the top or the side was a tough call, Yamamoto said, noting it was important to know the exact location of the melted fuel.

The distance between the top of the pressure vessel and the bottom of the containment vessel is about 45 meters and some parts inside the pressure vessels will need to be removed if Tepco tries to remove the debris inside the containment vessels from the top.

“If we know that the melted fuel is concentrated in the containment vessels, it will be more efficient to remove it from the side” because the entry point is closer, Yamamoto said.

Whatever option is decided, Yamamoto stressed that maintaining the fuel removal device will be difficult because the radiation will probably cripple it.

“The fuel removal device will be controlled remotely … it will be broken somewhere down the line and the parts will have to be replaced, considering its (ability to withstand) radiation,” he said.

“Given that, maintenance will have to be done remotely, too, and that will be a big challenge.”

To remove or not

Another option altogether is for Tepco to leave the melted fuel where it is.

During a media tour of the Fukushima No. 1 plant last month, Okamura of Tepco said the utility intended to collect the melted fuel because leaving it was “not an appropriate way” to manage nuclear fuel.

Miyano of the Atomic Energy Society of Japan said the debris must be removed because radioactive materials, including nuclear fuel, must be strictly controlled under international rules requiring strict monitoring.

Domestic nuclear power plant operators have to report the amount of nuclear fuel they have to the Nuclear Regulation Authority, which then reports to the International Atomic Energy Agency.

“There is the question of whether the government and Tepco decide not to remove the fuel debris. That would be an international issue,” said Miyano, adding that a consensus from the international community would be needed.

At the same time, Miyano said debate and analysis will be required to decide which choice would be best by looking at various factors, including how much it will cost to pick up all the melted fuel and where to store it. ”

by Kazuaki Nagata

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Fukushima cleanup chief urges better use of probe robot — The Seattle Times

” TOKYO (AP) — The head of decommissioning for the damaged Fukushima nuclear plant said Thursday that more creativity is needed in developing robots to locate and assess the condition of melted fuel rods.

A robot sent inside the Unit 2 containment vessel last month could not reach as close to the core area as was hoped for because it was blocked by deposits, believed to be a mixture of melted fuel and broken pieces of structures inside. Naohiro Masuda, president of Fukushima Dai-ichi Decommissioning, said he wants another probe sent in before deciding on methods to remove the reactor’s debris.

Unit 2 is one of the Fukushima reactors that melted down following the 2011 earthquake and tsunami.

The plant’s operator, Tokyo Electric Power Co., needs to know the melted fuel’s exact location as well as structural damage in each of the three wrecked reactors to figure out the best and safest ways to remove the fuel. Probes must rely on remote-controlled robots because radiation levels are too high for humans to survive.

Despite the incomplete probe missions, officials have said they want to stick to their schedule to determine the removal methods this summer and start work in 2021.

Earlier probes have suggested worse-than-anticipated challenges for the plant’s cleanup, which is expected to take decades. During the Unit 2 probe in early February, the “scorpion” robot crawler stalled after its total radiation exposure reached its limit in two hours, one-fifth of what was anticipated.

“We should think out of the box so we can examine the bottom of the core and how melted fuel debris spread out,” Masuda told reporters.

Probes are also being planned for the other two reactors. A tiny waterproof robot will be sent into Unit 1 in coming weeks, while experts are still trying to figure out a way to access the badly damaged Unit 3.

TEPCO is struggling with the plant’s decommissioning. The 2011 meltdown forced tens of thousands of nearby residents to evacuate their homes, and many have still not been able to return home due to high radiation levels.

Cleanup of communities outside of the plant is also a challenge. The cost has reportedly almost doubled to 4 trillion yen ($35 billion) from an earlier estimate. On Thursday, police arrested an Environment Ministry employee for allegedly taking bribes from a local construction firm president, media reports said. ”

by Mari Yamaguchi, The Associated Press

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Plans to remove nuclear fuel at Fukushima delayed again — Reuters via Channel NewsAsia

” A plan to remove spent nuclear fuel from Tokyo Electric Power Co Holdings Inc’s Fukushima Daiichi nuclear plant hit by the March 2011 tsunami has been postponed again due to delays in preparation, the Nikkei business daily reported on Thursday.

Work is now set to begin in fiscal 2018 at the earliest, the Nikkei said.

Removal of the spent fuel from the No. 3 reactor was originally scheduled in the first half of fiscal 2015, and later revised to fiscal 2017 due to high levels of radioactivity around the facilities, the Japanese business daily reported.

The timeline has been changed again as it was taking longer than expected to decontaminate buildings and clean up debris, the news agency reported.

The report comes a few months after the Japanese government said in October the cost of cleaning up the Fukushima plant may rise to several billion dollars a year, adding that it would look into a possible separation of the nuclear business from the utility. ”

Reporting by Krishna V Kurup in Bengaluru, editing by Shounak Dasgupta, REUTERS

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NRA: Ice wall effects ‘limited’ at Fukushima nuclear plant — The Asahi Shimbun

” Citing “limited, if any effects,” the Nuclear Regulation Authority said a highly touted “frozen soil wall” should be relegated to a secondary role in reducing contaminated groundwater at the Fukushima No. 1 nuclear plant.

The government spent 34.5 billion yen ($292 million) to build the underground ice wall to prevent groundwater from mixing with radioactive water in four reactor buildings at the crippled plant.

But the NRA, Japan’s nuclear watchdog, concluded on Dec. 26 that the wall has been ineffective in diverting the water away from the buildings. It said that despite the low rainfall over the past several months, the amount of groundwater pumped up through wells outside the frozen wall on the seaside is still well above the reduction target.

It urged the plant operator, Tokyo Electric Power Co., to tackle the groundwater problem primarily with pumps, not the ice wall.

In response, TEPCO at the meeting said that by next autumn, it will double its capacity to pump up groundwater from the current 800 tons a day.

About 400 tons of groundwater enters the damaged reactor buildings each day and mixes with highly radioactive water used to cool melted nuclear fuel.

The ice wall project, compiled by the industry ministry in May 2013, was seen as a fundamental solution to this problem that has hampered TEPCO’s cleanup efforts since the triple meltdown in March 2011.

Some 1,568 frozen ducts were inserted 30 meters deep into the ground to circulate a liquid at 30 degrees below zero. The freezing process was supposed to have created a solid wall of ice that could block the groundwater.

TEPCO began freezing the wall on the seaside in March. It announced in the middle of October that the temperature at all measuring points in that area was below zero.

Before the frozen wall project, TEPCO had to pump up about 300 tons of contaminated water a day. The daily volume dropped to about 130 tons in recent weeks, but it was still well beyond the target of 70 tons.

Still, TEPCO boasted about the effectiveness of the ice wall at the meeting with the NRA on Dec. 26, saying, “We are seeing certain results.”

The NRA, however, said the results are limited at best.

Toyoshi Fuketa, an NRA commissioner, already warned TEPCO in October that it cannot expect the ice wall to be highly effective in containing the groundwater.

“Pumping up groundwater through wells should be the main player because it can reliably control the groundwater level,” Fuketa said at that time. “The ice wall will play a supporting role.”

That sentiment was echoed at the Dec. 26 meeting.

However, the NRA approved the utility’s plan to begin freezing dirt for a wall on the mountain side of the nuclear plant.

The NRA was previously concerned about risks posed by the new ice wall. If it totally blocked groundwater from the mountain side, the water level within the frozen soil near the reactors could become too low, allowing highly contaminated water inside the reactor buildings to flow out more rapidly.

The NRA urged TEPCO to delay work on the mountain side until the ice wall on the seaside portion proved effective.

But it reversed its stance, saying a sharp drop in the groundwater level is unlikely based on the ineffectiveness of the existing ice wall.

“The frozen wall on the mountain side will not be able to block groundwater because the wall on the seaside was also unable to do so,” Fuketa said. “It will not be very dangerous to freeze the wall on the mountain side as long as the work is carried out carefully.”

TEPCO will start the work to freeze the ducts at five sections as early as next year.

Masashi Kamon, professor emeritus of geotechniques at Kyoto University, expressed skepticism about continuing the ice wall project without a full scrutiny of the underground conditions.

“Soil around the tunnels for underground pipes must be hard to freeze,” he said. “TEPCO should find out the conditions of the very bottom of the ice wall by drilling at least one section. It is questionable to continue with the project without a review.” ”

by Kohei Tomida

source