Decommissioning and clean-up are ongoing at the Fukushima Daiichi Nuclear Power Plant (FDNPP); however, many difficult problems remain unaddressed. Chief amongst these problems is the retrieval and management of fuel debris.
Decommissioning and clean-up are ongoing at the Fukushima Daiichi Nuclear Power Plant (FDNPP); however, many difficult problems remain unaddressed. Chief amongst these problems is the retrieval and management of fuel debris. Fuel debris is the name given to the solidified mixture of melted nuclear fuel and other materials that now lie at the base of each of the damaged reactors (reactor Units 1 — 3). This material is highly radioactive and it has potential to generate enough neutrons to trigger successive nuclear fission reactions (uranium-235 breaks into two elements after capturing neutrons, emitting enormous amounts of energy, radiation, and more neutrons). Successive fission reactions would present a serious safety and material management risk.
One of the materials in nuclear reactors that can lower the number of neutrons interacting with uranium-235 is boron carbide (B4C). This was used as the control rod material in the FDNPP reactors, and it may now remain within the fuel debris. If so, it may limit fission events within the fuel debris.
Can the fuel debris be safely removed?
On March 11th 2011, the control rods were inserted into the FDNPP reactors to stop the fission reactions immediately after the earthquake, but the later tsunami destroyed the reactor cooling systems. Fuel temperatures soon became high enough (>2000 °C) to cause reactor meltdowns. Currently, the fuel debris material from each reactor is cooled and stable; however, careful assessment of these materials, including not only their inventories of radioactive elements but as well their boron content, a neutron absorber, is needed to ascertain if successive fission reactions and associated neutron flux could occur in the fuel debris during its removal. Many important questions remain: was boron from the control rods lost at high temperature during the meltdown? If so, does enough boron remain in the fuel debris to limit successive fission reactions within this material? These questions must be answered to support safe decommissioning.
Study shows direct evidence of volatilization of control rods during the accident.
Despite the importance of this topic, the state and stability of the FDNPP control rod material has remained unknown until now. However, work just published in the Journal of Hazardous Materials now provides vital evidence that indicates that most of the control rod boron remains in at least two of the damaged FDNPP reactors (Units 2 and/or 3).
The study was an international effort involving scientists from Japan, Finland, France, and the USA. Dr. Satoshi Utsunomiya and graduate student Kazuki Fueda of Kyushu University led the study. Using electron microscopy and secondary ion mass spectrometry (SIMS), the team has been able to report the first-ever measurements of boron and lithium chemistry from radioactive Cs-rich microparticles (CsMPs). CsMPs formed inside FDNPP reactor units 2 and/or 3 during the meltdowns. These microscopic particles were then emitted into the environment, and the particles hold vital clues about the extent and types of meltdown processes. The team’s new results on boron-11/boron-10 isotopic ratios (~4.2) clearly indicate that most of the boron inside the CsMPs is derived from the FDNPP control rods and not from other sources (e.g., boron from the seawater that was used to cool the reactors). Dr Utsunomiya states that the presence of boron in the CsMPs “provides direct evidence of volatilization of the control rods, indicating that they were severely damaged during the meltdowns.”
Ample boron likely remains in the reactors, but more research is needed
In the study the team also combined their new data with past knowledge on CsMP emissions. From this, they have been able to estimate the total amount of boron released from the FDNPP reactors was likely very small: 0.024-62 g.
Prof. Gareth Law, a co-author from the University of Helsinki emphasized that this “is a tiny fraction of the reactor’s overall boron inventory, and this may mean that essentially all of the control rod boron remains inside the reactors.” The team hopes that this should prevent excessive fission reactions in the fuel debris. Utsunomiya stresses that “FDNPP decommissioning, and specifically fuel debris removal must be planned so that the extensive fission reactions do not occur. Our international team has successfully provided the first direct evidence of volatilization of B4C during the FDNPP meltdowns, but critically, our new data indicated that large quantities of boron, which adsorbs neutrons, likely remains within the fuel debris.”
Prof. Rod Ewing, a co-author from Stanford University acknowledged the importance of these new findings but highlighted that the team’s measurements now need to be “extended in follow-up studies, where the occurrence and distribution of boron species should be characterized across a wide range of debris fragments.”
Prof. emeritus Bernd Grambow, a study co-author from SUBATECH, Nantes, France,highlights that the work “paves the way for improving the safety assessment of debris retrieval during decommissioning at FDNPP,” with the team’s methods “providing a template for further studies.” Utsunomiya concludes that “it is nearly 11 years since the FDNPP disaster. In addition to tireless efforts from engineers at the FDNPP, scientific contributions are becoming more and more important as tools to address the major difficulties that will be faced during decommissioning.”
Journal Reference:
Kazuki Fueda, Ryu Takami, Kenta Minomo, Kazuya Morooka, Kenji Horie, Mami Takehara, Shinya Yamasaki, Takumi Saito, Hiroyuki Shiotsu, Toshihiko Ohnuki, Gareth T.W. Law, Bernd Grambow, Rodney C. Ewing, Satoshi Utsunomiya. Volatilization of B4C control rods in Fukushima Daiichi nuclear reactors during meltdown: B–Li isotopic signatures in cesium-rich microparticles. Journal of Hazardous Materials, 2022; 428: 128214 DOI: 10.1016/j.jhazmat.2022.128214
Greenpeace has recommended that Japan suspend the current return policies, which it says “ignore science-based analysis, including potential lifetime exposure risks to the population” and abandon plans to lift evacuation orders in six municipalities
(FILES) This handout file picture taken and received by Tokyo Electric Power Co (TEPCO) on April 10, 2011 shows an aerial view of the first reactor building of TEPCO’s No.1 Fukushima nuclear power plant in the town of Okuma in Fukushima prefecture, two months after the earthquake and tsunami hit the region on March 11, 2011. – Ten years after the Fukushima disaster, Japan’s nuclear industry remains crippled, with the majority of the country’s reactors halted or on the path towards decommissioning.
Mar 4, 2021
Ten years after the worst nuclear accident since Chernobyl, land Japan identified for cleanup from the triple reactor meltdown of the Fukushima No. 1 power plant remains contaminated, according to a report from Greenpeace.
On average, just 15% of land in the “Special Decontamination Area,” which is home to several municipalities, has been cleaned up, according to the environmental advocacy group’s analysis of government data. That’s despite the government’s claims that the area has largely been decontaminated, the group said.
In addition, Greenpeace said its own radiation surveys conducted over the last decade have consistently found readings above government target levels, including in areas that have been reopened to the public. The lifting of evacuation orders in places where radiation remains above safe levels potentially exposes people to an increased risk of cancer, the report said.
“The contamination remains and is widespread, and is still a very real threat to long term human health and the environment,” the report said.
Japan’s Ministry of Environment wasn’t immediately available for comment. Decontamination efforts have reduced radiation levels in residential areas by an average of 76%, according to the ministry’s website, which has compiled monitoring data through 2018. Fukushima Prefecture wasn’t immediately available for comment.
More than 160,000 people were evacuated from the area surrounding the Fukushima nuclear plant after a magnitude 9 earthquake, the biggest ever recorded to hit Japan, caused a massive tsunami that overwhelmed the plant. While the government has been steadily lifting evacuation orders on towns since 2014, roughly 36,000 people are still displaced.
Greenpeace recommended that Japan suspend the current return policy, which “ignore science-based analysis, including potential lifetime exposure risks to the population” and abandon plans to lift evacuation orders in six municipalities.
The government concluded Friday that four companies had used foreign trainees to perform work cleaning up radioactive contamination after the March 2011 tsunami triggered meltdowns at the Fukushima No. 1 nuclear plant.
The headline figure from the final report on a survey conducted by the Justice Ministry, the labor ministry and the Organization for Technical Intern Training was the same as that in the interim report, released in mid-July, which reflected results of surveying fewer than 200 companies with foreign trainee programs.
Officials visited a total of 1,018 such companies with facilities in eight prefectures in eastern and northeastern Japan, interviewing technical interns there to confirm the situation, after the issue came to light in March.
Of the four companies, one in Iwate Prefecture has been banned from accepting foreign trainees for five years. It was found to have neglected to pay allowances for decontamination work, amounting to a combined ¥1.5 million, to three trainees.
The government has issued a similar ban for three years to a firm in Fukushima Prefecture for not paying a total of ¥180,000 to three interns for overtime work.
A company in Fukushima and another in Chiba Prefecture received warnings because foreign trainees there engaged in decontamination work, albeit for short periods of time. The names of the four companies were not revealed.
Justice Minister Takashi Yamashita told a news conference that the government gave guidance for improvement to three related regulatory organizations over insufficient inspections of companies with foreign technical interns.
“We will continue to work with the Ministry of Health, Labor and Welfare and the Organization for Technical Intern Training to guide regulatory organizations and companies that accept technical interns, so they will not let them engage in decontamination work. We will take proper measures when we find inappropriate cases,” Yamashita said.
In March, a Vietnamese trainee at an Iwate Prefecture-based construction firm revealed he had been assigned to take part in radioactive decontamination work without being given sufficient explanation of the tasks involved.
The government announced later that month that it would not allow companies to use such foreign trainees for the removal of radioactive contamination, as such work is not consistent with the purpose of the program.
The technical trainee program was introduced in 1993 with the aim of transferring skills to developing countries. But it has drawn criticism both at home and abroad as being a cover for importing cheap labor for industrial sectors, including manufacturing and construction, where blue-collar workers are in short supply.
The water is tainted, the wreckage is dangerous, and disposing of it will be a prolonged, complex and costly process.
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.
Waterworks
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.”
In this Thursday, Jan. 25, 2018, photo, an installation of a dome-shaped rooftop cover housing key equipment is near completion at Unit 3 reactor of the Fukushima Dai-ich nuclear power plant ahead of a fuel removal from… (AP Photo/Mari Yamaguchi)
OKUMA, Japan (AP) — High atop Fukushima’s most damaged nuclear reactor, the final pieces of a jelly-roll shaped cover are being put in place to seal in highly radioactive dust.
Blown apart by a hydrogen explosion in 2011 after an earthquake and tsunami hit Japan’s Fukushima Dai-ichi plant, reactor Unit 3 is undergoing painstaking construction ahead of a milestone that is the first step toward dismantling the plant.
The operating floor — from where new fuel rods used to be lowered into the core — has been rebuilt and if all goes as planned, huge cranes will begin removing 566 sets of still-radioactive fuel rods from a storage pool just below it later this year.
It has taken seven years just to get this far, but now the real work of cleaning up the Tokyo Electric Power Co. plant can begin.
“If you compare it with mountain climbing, we’ve only been preparing to climb. Now, we finally get to actually start climbing,” said Daisuke Hirose, an official at the plant’s decommissioning and decontamination unit.
Cleaning up the plant’s three reactors that had at least partial meltdowns after the earthquake and tsunami is a monumental task expected to take three to four decades. Taking out the stored fuel rods is only a preliminary step and just removing the ones in Unit 3 is expected to take a year.
Still ahead is the uncharted challenge of removing an estimated 800 tons of melted fuel and debris inside the cracked containment chambers — six times that of the 1979 Three Mile Island accident.
The area in and outside of Unit 3 is part construction site and part disaster zone still requiring protection from radiation. A makeshift elevator, then a wind-swept outdoor staircase, takes visitors to the operating floor, more than 30 meters (100 feet) above ground.
Daylight streams in through the unfinished section of the new cover, a tunnel-like structure sealed at both ends to contain radiation. An overhead crane that moves on rails stands at the side of the storage pool, the maker’s name, “Toshiba,” emblazoned in large red letters.
The explosion left major chunks of debris that have been removed from the storage pool, a painstaking operation done using remote-controlled machinery and with utmost care to avoid damaging the fuel rods. Smaller rubble lines the pool’s edge. The water’s surface is obscured by a blue netting to prevent more debris from accidentally tumbling in.
The severe damage to Unit 3 has, in the end, made it easier to clean up than the other two reactors.
Under the latest government roadmap approved last September, removal of the fuel rods from units 1 and 2 was delayed by three years until 2023, a second postponement from the original 2015, because further decontamination and additional safety measures are needed.
Unit 1 fell behind because of a delay in removing debris and repairing key components on the operating floor. The Unit 2 building remained intact, keeping high radiation and humidity inside, which makes it more difficult for workers to approach and decontaminate.
Radioactivity on the Unit 3 operating floor has fallen to a level that allows workers in hazmat suits and filter-masks to stay up to two hours at a time, though most work still needs to be done remotely.
The segments of the new cover were pre-assembled and are being installed one by one by remote-controlled cranes. With two pieces left, the plant operator says the cover will be completed in February.
Removing the fuel rods in Unit 3 will be done with a fuel-handling crane. It will move the rods out of their storage racks and pack them in a protective canister underwater. A second Toshiba crane, a 10-meter (33-foot) -high yellow structure across the operating floor, will lift the canister out of the pool and load it onto a vehicle for transport to another storage pool at the plant.
Crane operators and others assigned to the project, which requires caution and skill, have been rehearsing the procedures.
The 1,573 sets of fuel rods stored in spent fuel pools at the three reactors are considered among the highest risks in the event of another major earthquake. Loss of water from sloshing, structural damage or a power outage could cause meltdowns and massive radiation leaks because the pools are uncovered.
Hirose said that starting fuel removal at Unit 3 would be “a major turning point.”
Still, after the intact fuel rods are gone comes by far the most difficult part of decommissioning the plant: removing the melted fuel and debris from inside the reactors. Obtaining exact locations and other details of the melted fuel are crucial to determining the retrieval methods and developing the right kind of technology and robots. With most melted fuel believed to have fallen to the bottom, experts are proposing that it be accessed from the side of the containment vessel, not from the top as originally had been planned, based on the cleanup after an accident at the Three Mile Island nuclear plant in the United States.
Computer simulations and limited internal probes have shown that the melted fuel presumably poured out of the core, falling to the bottom of the primary containment vessels. Robotic probes at the Unit 3 and 2 reactors have captured images of large amounts of melted fuel, but attempts so far at Unit 1 have been unsuccessful.
Despite scarce data from inside the reactors, the roadmap says the methods for melted fuel removal are to be finalized in 2019, with actual retrieval at one of the three reactors in 2021. Hirose says it is premature to say whether Unit 3 will be the first.
From December 20, 2013, but this video made by Arnie Gundersen and his Fairwinds team gives us useful info for decades to come.
I completely agree with my friend Kitty, I could not have said it better that in her own words:
“I remember when Arnie started publishing and appearing on TV about Fukushima. Arnie Gundersen quickly won me over with his objective and detailed description of the situation. We would be very in the dark if it were not for Arnie Gundersen, Maggie Gundersen and others.
Many nuclear power plants are shutting down because of their and others, primary reporting of the ongoing Fukushima Catastrophe. Many nuclear projects discontinued. More time on earth for us and our children. Maybe some help and solace to nuclear victims and refugees everywhere.
What Arnie said in the video about why Fukushima is so hard to cleanup, is because of the groundwater. there must be enough of the groundwater and debris out of reactor two, to get a good picture now. Tepco should be doing everything it can to keep groundwater put. this includes building a dike and wall as Arnie says.”
Thank you Arnie Gundersen, thank you Maggie Gundersen, thank you Fairwinds for all the good work you did over the past years and still are doing, very much appreciated by many people in many countries.
In this, the fourth installment in their short film series, from December 2013, Fairewinds Energy Education’s Arnie Gundersen responds to questions they have received about cleanup at Fukushima Daiichi. Please consider supporting their work, so they can continue to bring us the truth about nuclear power.
Electric Power Company Holdings Inc.’s stricken Fukushima No. 1 plant topped ¥4.2 trillion by the end of fiscal 2015, it was learned Sunday.
The cumulative total at the end of last March, including costs for radioactive decontamination, reactor decommissioning and compensation payments to affected people and organizations, translate into about ¥33,000 per capita.
The public financial burden is expected to increase, with Tepco seeking further government assistance.
Jiji Press scrutinized the government’s special-account budgets through fiscal 2015 for the reconstruction of areas affected by the March 2011 earthquake and tsunami. It summed up the amounts of executed budgets related to the nuclear disaster and additional electricity rates consumers and businesses were charged by Tepco and seven other regional power utilities to help finance compensation payments, among other costs.
According to the study, a total of ¥2.34 trillion was disbursed for decontamination of affected areas, disposal of contaminated waste and an interim storage facility for tainted soil. The expense was shouldered by the government, mainly through affiliated Nuclear Damage Compensation and Decommissioning Facilitation Corp.
The costs for decontamination and tainted waste disposal will eventually be financed by the proceeds from the sale of Tepco shares held by the government-backed organization. The government guaranteed the loans provided by banks for the acquisition of Tepco shares, and if the lending becomes irrecoverable due to weakness of the Tepco stock price, tax revenue will be used to repay the loans.
The government estimates the proceeds from Tepco share sale at ¥2.5 trillion, but to generate the estimated gain, the Tepco stock price needs to trade at around ¥1,050, up sharply from current market levels of some ¥360.
In addition, the Environment Ministry expects that the cumulative total of decontamination and related costs could surpass the estimated share proceeds by the March 2017 end of the current fiscal year.
A total of ¥1.1 trillion will be used from the energy special account to finance the costs related to the interim storage facility for contaminated soil. The account mostly consists of revenue of the tax for the promotion of power resources development, which is included in electricity bills.
Elsewhere, the government spent ¥1.38 trillion on projects including the decommissioning of reactors at the disaster-crippled Fukushima No. 1 plant, checks on food for radioactive contamination and building a research and development facility.
Tepco and six other power utilities charged their customers at least ¥327 billion in electricity rate hikes after Japan’s worst-ever nuclear accident. Moreover, consumers paid ¥219.3 billion or more for Tepco, chiefly to finance the maintenance of equipment to clean up radioactive water at the plant and the operation of call centers to deal with inquiries about compensation payments.
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