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

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Challenges ahead for debris removal at Fukushima — NHK World

” This year will mark the 7th anniversary of the nuclear accident at the Fukushima Daiichi plant that occurred in March, 2011. The plant’s operator is hoping to eventually remove fuel debris from the damaged reactors.

Fuel debris is a mixture of melted nuclear fuel and broken reactor parts. Removing the debris is considered to be the biggest hurdle to the decommissioning of the reactors.

Last year, Tokyo Electric Power Company, or TEPCO, investigated the inside of the containment vessels of 3 reactors and confirmed, for the first time, the existence of lumps that are believed to be fuel debris in the No.3 reactor.

TEPCO plans to conduct a fresh probe of the No.2 reactor this month to confirm whether a mass on the floor under the reactor, observed last year, is actually fuel debris.

The government and TEPCO aim to begin removing debris in 2021. They are planning to determine which reactor to start with, and how to conduct the procedure, during fiscal 2019.

Workers will try this year to figure out which details need to be considered in order to make the decision.

Removing the debris requires thorough safety measures. For example, radioactive materials must be prevented from spreading and workers must be protected from exposure to radiation.

This autumn, the operator also plans to start removing spent nuclear fuel rods from the storage pool of the No.3 reactor building. ”

by NHK World

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*The Fukushima nuclear meltdown continues unabated – Helen Caldicott, Global Research News

Dr. Helen Caldicott really tells it how it is. No sugarcoating in this article, just the cold, hard facts.

” Recent reporting of a huge radiation measurement at Unit 2 in the Fukushima Daichi reactor complex does not signify that there is a peak in radiation in the reactor building.

All that it indicates is that, for the first time, the Japanese have been able to measure the intense radiation given off by the molten fuel, as each previous attempt has led to failure because the radiation is so intense the robotic parts were functionally destroyed.

The radiation measurement was 530 sieverts, or 53,000 rems (Roentgen Equivalent for Man). The dose at which half an exposed population would die is 250 to 500 rems, so this is a massive measurement. It is quite likely had the robot been able to penetrate deeper into the inner cavern containing the molten corium, the measurement would have been much greater.

These facts illustrate why it will be almost impossible to “decommission” units 1, 2 and 3 as no human could ever be exposed to such extreme radiation. This fact means that Fukushima Daichi will remain a diabolical blot upon Japan and the world for the rest of time, sitting as it does on active earthquake zones.

What the photos taken by the robot did reveal was that some of the structural supports of Unit 2 have been damaged. It is also true that all four buildings were structurally damaged by the original earthquake some five years ago and by the subsequent hydrogen explosions so, should there be an earthquake greater than seven on the Richter scale, it is very possible that one or more of these structures could collapse, leading to a massive release of radiation as the building fell on the molten core beneath. But units 1, 2 and 3 also contain cooling pools with very radioactive fuel rods — numbering 392 in Unit 1, 615 in Unit 2, and 566 in Unit 3; if an earthquake were to breach a pool, the gamma rays would be so intense that the site would have to be permanently evacuated. The fuel from Unit 4 and its cooling pool has been removed.

But there is more to fear.

The reactor complex was built adjacent to a mountain range and millions of gallons of water emanate from the mountains daily beneath the reactor complex, causing some of the earth below the reactor buildings to partially liquefy. As the water flows beneath the damaged reactors, it immerses the three molten cores and becomes extremely radioactive as it continues its journey into the adjacent Pacific Ocean.

Every day since the accident began, 300 to 400 tons of water has poured into the Pacific where numerous isotopes – including cesium 137, 134, strontium 90, tritium, plutonium, americium and up to 100 more – enter the ocean and bio-concentrate by orders of magnitude at each step of the food chain — algae, crustaceans, little fish, big fish then us.

Fish swim thousands of miles and tuna, salmon and other species found on the American west coast now contain some of these radioactive elements, which are tasteless, odourless and invisible. Entering the human body by ingestion they concentrate in various organs, irradiating adjacent cells for many years. The cancer cycle is initiated by a single mutation in a single regulatory gene in a single cell and the incubation time for cancer is any time from 2 to 90 years. And no cancer defines its origin.

We could be catching radioactive fish in Australia or the fish that are imported could contain radioactive isotopes, but unless they are consistently tested we will never know.

As well as the mountain water reaching the Pacific Ocean, since the accident, TEPCO has daily pumped over 300 tons of sea water into the damaged reactors to keep them cool. It becomes intensely radioactive and is pumped out again and stored in over 1,200 huge storage tanks scattered over the Daichi site. These tanks could not withstand a large earthquake and could rupture releasing their contents into the ocean.

But even if that does not happen, TEPCO is rapidly running out of storage space and is trying to convince the local fishermen that it would be okay to empty the tanks into the sea. The Bremsstrahlung radiation like x-rays given off by these tanks is quite high – measuring 10 milirems – presenting a danger to the workers. There are over 4,000 workers on site each day, many recruited by the Yakuza (the Japanese Mafia) and include men who are homeless, drug addicts and those who are mentally unstable.

There’s another problem. Because the molten cores are continuously generating hydrogen, which is explosive, TEPCO has been pumping nitrogen into the reactors to dilute the hydrogen dangers.

Vast areas of Japan are now contaminated, including some areas of Tokyo, which are so radioactive that roadside soil measuring 7,000 becquerels (bc) per kilo would qualify to be buried in a radioactive waste facility in the U.S..

As previously explained, these radioactive elements concentrate in the food chain. The Fukushima Prefecture has always been a food bowl for Japan and, although much of the rice, vegetables and fruit now grown here is radioactive, there is a big push to sell this food both in the Japanese market and overseas. Taiwan has banned the sale of Japanese food, but Australia and the U.S. have not.

Prime Minister Abe recently passed a law that any reporter who told the truth about the situation could be goaled for ten years. In addition, doctors who tell their patients their disease could be radiation related will not be paid, so there is an immense cover-up in Japan as well as the global media.

The Prefectural Oversite Committee for Fukushima Health is only looking at thyroid cancer among the population and by June 2016, 172 people who were under the age of 18 at the time of the accident have developed, or have suspected, thyroid cancer; the normal incidence in this population is 1 to 2 per million.

However, other cancers and leukemia that are caused by radiation are not being routinely documented, nor are congenital malformations, which were, and are, still rife among the exposed Chernobyl population.

Bottom line, these reactors will never be cleaned up nor decommissioned because such a task is not humanly possible. Hence, they will continue to pour water into the Pacific for the rest of time and threaten Japan and the northern hemisphere with massive releases of radiation should there be another large earthquake. ”

by Helen Caldicott, Global Research News, originally published in Independent Australia

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Fukushima dome roof takes shape, but radiation remains high — The Asahi Shimbun

” High radiation levels are still limiting recovery work at the Fukushima No. 1 nuclear plant, a stark reality that reporters saw firsthand when they observed efforts to remove risk factors there.

Media representatives were invited into the plant in early December to see construction work, with the building of a domed roof over the No. 3 reactor building as the main focus.

However, they were only allowed to stay on top of the roof for 20 minutes due to high radiation levels.

The roof is being put together directly above the storage pool for spent fuel. The dome is designed to prevent the spewing of radioactive materials when the fuel is actually removed from the pool.

The original roof of the No. 3 reactor building was severely damaged by a hydrogen explosion in the days following the March 11, 2011, Great East Japan Earthquake and tsunami, which led to the crippling of the Fukushima No. 1 plant.

Spent fuel still remains in the storage pools located on the top floors of the No. 1 to No. 3 reactor buildings.

Plans call for removing the spent fuel first from the No. 3 reactor building.

Although the dome will help prevent the spread of radioactive materials, building parts and other debris as well as some equipment have still not been completely removed from the storage pool, which holds 566 fuel rods.

The collapsed roof and walls were removed to allow for the construction of the domed roof, which began in the summer. The domed roof is about 17 meters high, and a crane was also installed under it in November.

Plans call for the removal of the spent fuel from the No. 3 building to begin in the middle of the next fiscal year.

Internal radiation exposure levels were measured before media representatives headed to the No. 3 reactor building. They were also required to don protective clothing as well as a partial face mask covering the mouth and nose from about 100 meters from the building.

Radiation levels close to the building were 0.1 millisieverts per hour.

An elevator installed into the scaffolding next to the reactor building took the media representatives to the roof, which had been covered with metal plates.

The so-called operating floor looked like any other newly constructed building roof, a sharp contrast to the twisted metal parts that covered the building shortly after the nuclear accident.

Tokyo Electric Power Co., the plant’s operator, captured video footage from within the reactors for the first time in July. Debris that appears to be melted nuclear fuel was found in various parts of the containment vessel.

To the south of the No. 3 reactor building stands the No. 4 reactor building, from where all the spent nuclear fuel has been removed.

To the north is the No. 2 reactor building, which avoided a hydrogen explosion. Beyond the building, cranes and other large equipment are working in preparation for the removal of debris from the No. 1 reactor building.

TEPCO officials cautioned media representatives about standing too long right next to the storage pool, which could be seen located about six meters below the roof. Debris was found within the pool while insulating material floated on the pool surface.

The radiation level near the pool was 0.68 millisieverts per hour. While that was a major improvement from the 800 millisieverts per hour recorded in the immediate aftermath of the nuclear accident close to seven years ago, it was still too high to allow for a stay of longer than 20 minutes. ”

by Chikako Kawahara, The Asahi Shimbun

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Image shows extent of damage to reactor at Fukushima plant — The Asahi Shimbun

” An image taken by an underwater robot shows corroded tubes stuck in a hole created by melted fuel in the pressure vessel of the No. 3 reactor at the Fukushima No. 1 nuclear plant.

The image offers clues on the extent of the damage caused when fuel rods in the reactor melted through the bottom of the pressure vessel after the disaster at the nuclear plant unfolded in March 2011.

Tokyo Electric Power Co., operator of the plant, sent the specially designed robot into the reactor in July. The company earlier released images taken by the robot that showed what is believed to be melted nuclear fuel debris.

In the image released on Nov. 30, TEPCO identified the severely corroded and damaged tubes as parts of a device used to move control rods. Normally, that device is located inside the pressure vessel.

TEPCO on Nov. 30 also said it would conduct another study inside of the containment vessel of the No. 2 reactor at the plant in January. The containment vessel surrounds the pressure vessel.

A telescopic stick more than 10 meters long and equipped with a camera will be used for the survey. ”

by The Asahi Shimbun

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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

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