“The Japan Atomic Energy Agency (JAEA) on Aug. 30 started work to decommission the Monju prototype fast-breeder reactor in Fukui Prefecture…
The decommissioning work is scheduled to take 30 years and cost $ 3.33 billion.”
Staff members of the Japan Atomic Energy Agency operate equipment to remove nuclear fuel assemblies from a storage tank at the plant of the Monju prototype fast-breeder reactor in Tsuruga, Fukui Prefecture, on Aug. 30.
The Japan Atomic Energy Agency (JAEA) on Aug. 30 started work to decommission the Monju prototype fast-breeder reactor in Fukui Prefecture, a once-promising project that struggled with problems, even in preparations for its dismantlement.
The work started a month later than scheduled because of a series of equipment trouble. The JAEA workers also face an enormous challenge because Japan has no experience in decommissioning a fast-breeder reactor.
The JAEA will use overseas experiences as a reference for the delicate process.
Before the start of the work, JAEA President Toshio Kodama told staff members in a speech at the plant in Tsuruga, “I want you to tackle this work by bracing yourselves.”
Monju had been a key facility in the government’s nuclear fuel recycling program.
Construction of the reactor started in 1985, but a series of accidents, including a sodium coolant leak in 1995, as well as cover-ups kept the reactor offline for most of its life.
In 2016, after 1 trillion yen ($9 billion) had been spent on the project, the government finally decided to abolish Monju.
The decommissioning work is scheduled to take 30 years and cost 375 billion yen.
One of the riskiest parts in the decommissioning process is handling the liquid sodium, which reacts strongly with water and air.
In the first of the four-stage decommissioning project, the JAEA will transfer 530 nuclear fuel assemblies, currently kept in the liquid sodium-filled nuclear reactor and storage tank, to a water-filled pool by fiscal 2022.
In the work that began on Aug. 30, the JAEA will remove 160 nuclear fuel assemblies from the storage tank, wash away the sodium, and place them in the pool.
From 2019, the agency will transfer nuclear fuel assemblies from the reactor to the storage tank and then to the pool.
In December this year, the JAEA will also start to transfer about 760 tons of sodium, which has not been exposed to radioactive substances, to its storage tank. Later, the agency will remove about 910 tons of radioactive sodium from the reactor and other equipment.
In the following stages, the agency will dismantle the nuclear reactor, the turbine and other facilities.
However, no decision has been made on how to dispose of the nuclear fuel removed from the reactor and the storage tank. Monju has used mixed oxide (MOX) fuel, which contains plutonium and currently cannot be reprocessed in Japan.
“It’s realistic to ask an overseas company to reprocess it,” said Toyoshi Fuketa, chairman of the Nuclear Regulation Authority, the government’s nuclear watchdog.
If reprocessing expenses in a foreign country are added, the overall decommissioning costs will sharply increase.
September 3, 2018
Posted by dunrenard |
Japan | *, decommissioning, Monju Reactor |
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Japanese firms used foreign trainees for Fukushima clean-up
Vietnamese in Japan for professional training were among those picking up soil as part of decontamination work at the crippled nuclear power plant
Four Japanese companies made foreign trainees who were in the country to learn professional skills take part in decontamination work after the Fukushima nuclear disaster, the government said on Friday.
The discovery is likely to revive criticism of the Technical Intern Training Programme, which has been accused of placing workers in substandard conditions and jobs that provide few opportunities for learning.
The misconduct was uncovered in a probe by the Justice Ministry conducted after three Vietnamese trainees were found in March to have taken part in clean-up work in Fukushima.
The Vietnamese were supposed to do work using construction machines according to plans submitted by the company.
“But they joined simple clean-up work such as removing soil without machines,” an official said.
A powerful earthquake in March 2011 spawned a huge tsunami that led to meltdowns at the Fukushima nuclear plant, causing the world’s worst such accident since Chernobyl in 1986.
One of the four companies has been slapped with a five-year ban on accepting new foreign trainees as it was found to have paid only 2,000 yen (US$18) per day to the trainees out of the 6,600 yen provided by the state as a special allowance for decontamination work.
The ministry is still investigating how many trainees in the other three firms were involved.
The four companies cited in the interim report no longer send foreign trainees to help with the radiation clean-up. It did not name the four firms.
The ministry has finished its investigation into 182 construction companies that hire foreign trainees, and will look into another 820 firms by the end of September.
Japan has been accepting foreign trainees under the government programme since 1993 and there were just over 250,000 in the country in late 2017.
But critics say the trainees often face poor working conditions including excessive hours and harassment.
The number of foreign trainees who ran away from their employers jumped from 2,005 in 2012 to 7,089 in 2017, according to the ministry’s survey. Many cited low pay as the main reason for running away.
The investigation comes as Japan’s government moves to bring more foreign workers into the country to tackle a labour shortage caused by the country’s ageing, shrinking population.
The government in June said it wanted to create a new visa status to bring in foreign workers, with priority given to those looking for jobs in sectors such as agriculture that have been hardest hit by the labour shortage.
The workers would be able to stay for up to five years, but would not be allowed to bring their family members.
The government put the number of foreign workers in Japan in 2017 at 1.28 million people.
But more than 450,000 of those are foreign spouses of Japanese citizens, ethnic Koreans long settled in Japan, or foreigners of Japanese descent, rather than workers coming to Japan simply for jobs. Another nearly 300,000 are students.
Japan firms used Vietnamese, foreign trainees at Fukushima cleanup
Four Japanese companies have been found to made foreign trainees take part in decontamination work after the Fukushima nuclear disaster.
The discovery is likely to revive criticism of the foreign trainee program, which has been accused of placing workers in substandard conditions and jobs that provide few opportunities for learning, the government said Friday.
The misconduct was uncovered in a probe by the Justice Ministry conducted after three Vietnamese trainees, who were in the country to learn professional skills, were found in March to have participated in cleanup work in Fukushima.
The Vietnamese were supposed to do work using construction machines according to plans submitted by the company.
“But they joined simple cleanup work such as removing soil without machines,” an official told AFP.
A powerful earthquake in March 2011 spawned a huge tsunami that led to meltdowns at the Fukushima nuclear plant, causing the world’s worst such accident since Chernobyl in 1986.
The justice ministry said after the discovery this March that decontamination work was not appropriate for foreign trainees.
One of the four companies has been slapped with a five-year ban on accepting new foreign trainees, and the ministry is still investigating how many trainees in the other three firms were involved.
The ministry has finished its investigation into 182 construction companies that hire foreign trainees, and will look into another 820 firms by the end of September.
Japan has been accepting foreign trainees under the government program since 1993 and there were just over 250,000 in the country in late 2017.
But critics say the trainees often face poor work conditions including excessive hours and harassment.
The number of foreign trainees who ran away from their employers jumped from 2,005 in 2012 to 7,089 in 2017, according to the ministry survey. Many cited low pay as the main reason for running away.
The investigation comes as Japan’s government moves to bring more foreign workers into the country to tackle a labor shortage caused by the country’s aging, shrinking population.
The government in June said it wanted to create a new visa status to bring in foreign workers, with priority given to those looking for jobs in sectors such as agriculture that have been hardest hit by the labor shortage.
The workers would be able to stay for up to five years, but would not be allowed to bring their family members.
The government put the number of foreign workers in Japan in 2017 at 1.28 million people.
But more than 450,000 of those are foreign spouses of Japanese citizens, ethnic Koreans long settled in Japan, or foreigners of Japanese descent, rather than workers coming to Japan simply for jobs. Another nearly 300,000 are students.
July 19, 2018
Posted by dunrenard |
Fukushima 2018 | decommissioning, decontamination, Foreign Trainees, Fukushima, Fukushima Daiichi |
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It may take 40 years for the site to appear like “a normal reactor at the end of its life.”
A schematic of the Fukushima nuclear power plant hints at the complexity of decontamination and decommissioning operations.
TEPCO workers survey operations at reactor buildings.
Seven years on from the Great East Japan Earthquake of March 2011, Fukushima Daiichi nuclear power plant has come a long way from the state it was reduced to. Once front and center in the global media as a catastrophe on par with Chernobyl, the plant stands today as the site of one of the world’s most complex and expensive engineering projects.
Beyond the earthquake itself, a well understood series of events and external factors contributed to the meltdown of three of Fukushima’s six reactors, an incident that has been characterized by nuclear authorities as the world’s second worst nuclear power accident only after Chernobyl. It’s a label that warrants context, given the scale,
complexity, and expense of the decontamination and decommissioning of the plant.
How does a plant and its engineers move on from such devastation? The recovery initiatives have faced major challenges, constantly being confronted by issues involving radioactive contamination of everything from dust to groundwater. And those smaller issues ultimately complicate the remediation effort’s long-term goal: to locate and remove the nuclear fuel that was in the reactors.
Jonathan Cobb, spokesperson for the World Nuclear Association, spoke with Ars about the scale of Fukushima, explaining that radioactive releases in Japan were much smaller than at Chernobyl, and the accident resulted in no loss of life from radiation: “Of course, this doesn’t take away from the enormous task currently being faced at Fukushima.”
The UN Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) reported in May 2013 that radiation exposure following the Fukushima accident didn’t cause any immediate health effects and that future health effects attributable to the accident among either the general public or the vast majority of workers are unlikely. A 2017 paper from UNSCEAR reports that these conclusions remain valid in light of continued research since the incident.
Even the most at-risk citizens, those living in Fukushima prefecture, are only expected to be exposed to around 10mSv as a result of the accident over their lifetimes. “For reference, the global average natural background radiation tends to be around 2.4mSv/year, but even 20mSv/year isn’t exceptional,” said Cobb.
Still, the accident was rated a 7 on the International Nuclear and Radiological Event Scale (INES), which is the highest rating possible, and designates it a Major Accident due to high radioactive releases. Estimates vary slightly, but Japan’s Nuclear Safety Commission report puts total releases at 570 petabecquerels (PBq) iodine-131 equivalent. (For comparison, Chernobyl released 5,200PBq iodine-131 equivalent.)
But the severity of the accident is probably most keenly felt in the scale of the cleanup. The incident has necessitated the ongoing cleanup and decommissioning of the plant—something that Tokyo Electric Power Company (TEPCO), the plant’s owner and operator, is responsible for. Even though the plant is seven years into the cleanup and has accomplished a great deal, we won’t see a conclusion for decades yet.
Damage to reactor Units 1-4 in the aftermath of the March 2011 earthquake.
In addition to damage to infrastructure and buildings, a large amount of wreckage was left strewn around the plant complex.
Remotely operated machines were involved in clean-up of the most contaminated areas.
A look inside the Primary Containment Vessel (PCV) of Unit 2.
A composite image of photographs taken inside the Primary Containment Vessel (PCV) of Unit 2.
A look at debris in the spent fuel pool of Unit 3.
Meltdowns and immediate priorities
Remarkably, seismic shocks of the magnitude 9 earthquake didn’t cause any significant damage to the earthquake-proofed reactors; rather, the tsunami knocked out power that precipitated reactor meltdowns in Units 1, 2, and 3. Subsequent explosions caused by hydrogen buildup (from zirconium cladding of fuel assemblies melting and oxidizing) in Units 1, 3, and 4 then expelled radioactive contamination, most of which fell within the confines of the plant.
Cobb explained that in the aftermath of this, the ongoing risk posed by radionuclides (notably, iodine-131 and cesium isotopes 134 and 137) depended on their half-lives. Iodine-131, with a half-life of just eight days, posed virtually no threat at all after just several months. It has been cesium-134, with a two-year half-life, and cesium-137, with a 30-year half-life, that have been the major focus of decontamination efforts. “Radioactive decay means that we’ve seen a reduction in contamination simply through time passing; at the plant, however, my expectation is that the majority of reduction has been due to efforts of TEPCO. Conditions have improved markedly and a sense of normalcy has returned.”
It’s useful to take stock of what TEPCO had to contend with from the outset. Lake Barrett, a veteran of the US nuclear energy industry who spent several years at the helm of decommissioning work at Three Mile Island reactor 2, is currently an independent special advisor to the Japanese Government and TEPCO board of directors. He told Ars, “When everything goes to hell on you, you go back to basics. You’re concerned with accident response and immediate recovery of the situation. Over the longer timeframe, the decontamination & decommissioning (D&D) focus shifts to a more deliberate approach to major technical challenges.”
Barrett explained that reactor stabilization at Fukushima—an imperative of the immediate recovery—has long since been achieved. Temperatures within the Reactor Pressure Vessels (RPVs) and Primary Containment Vessels (PCVs) of Units 1-3 are stable at between 15 to 30ºC, and there have been no significant changes in airborne radioactive materials released from reactor buildings. This qualifies as a ‘comprehensive cold shutdown’ condition.
Barrett explained how the issue of cooling is mostly non-existent at this point: “The three melted reactor cores emit less heat than a small car. Decay heat was a huge issue in the first weeks, but it’s no longer an issue. And while TEPCO still injects water onto the cores, this is more for dust suppression than anything else.”
With the reactors stable, early phases of TEPCO’s work simply involved debris clearing and restorative efforts throughout buildings and across the 3.5 square miles of the plant—both having been ravaged by the earthquake and tsunami. In the most contaminated places, remotely operated machines undertook most of the work. To reduce environmental contamination, they also removed top soils and vegetation, deforested the site, and then applied a polymer resin and concrete across much of the plant complex. This has locked contaminated material in place and limited the flow of groundwater through the site.
Other work has been more substantial. Units 1, 3 and 4 were blown apart and have had to be reinforced and encased, both for safety and to prevent spread of radioactive material. Although Unit 2 retained its roof, TEPCO decided to dismantle the upper building nonetheless, as it will facilitate removal of fuel from the reactor.
At the peak of these operations, some 7,450 persons worked at Fukushima. As operations have evolved, the workforce has declined to a not inconsiderable 5,000 daily personnel. With such levels of permanent staffing, it’s little wonder that a new rest-house, cafeteria, shops, and office building have all been built.
The efforts have, in a practical sense, meant that the majority of the site has transitioned to a stable, relatively risk-free environment. Describing the decommissioning as an “enormous challenge never before undertaken by humanity,” Seto Kohta of TEPCO told Ars: “We have overcome the state of chaos that ensued after the accident and have succeeded in reducing site dose levels to an average of less than 5μSv/h, with the exception of the vicinity of Units 1-4.” (Global background levels are <0.5µSv/h.)
TEPCO reports that the additional effective dose (i.e. additional to natural background radiation) at the plant’s boundary has declined to the target value of less than 1mSv/y.
This is not to say the plant is without signs of past problems—far from it. Felled trees sit waiting for incineration; huge mounds of soil lie under tarps; buildings retain marks of past trauma; and with environmental dosage a perennial concern, close to a hundred dose-rate monitors are positioned around the site.
Kohta also noted that while “95 percent of the site no longer requires the donning of full- or half-face masks or coveralls,” some level of protection is still required for working around the plant according to three levels of contamination. The vast majority of the plant grounds are in what’s termed Zone G, which requires just generic coveralls and disposable medical masks. Zone Y provides a perimeter around the Units 1-4 and necessitates heavier-duty coveralls and either full- or half-face masks. And lastly there is Zone R, closer to and including the reactor buildings, requiring double-layered coveralls and full-face masks.
A steel structure is built around Unit 1 as part of reconstruction works.
An outer shell is constructed around Unit 1.
Reconstruction work at Unit 4.
A labyrinth of subterranean tunnels and access points lie around reactor buildings.
The Little Sunfish submersible used for investigations at Unit 3.
A TEPCO schematic illustrates measures taken to manage groundwater.
An impermeable wall constructed of interlocking columns extends along the seafront to restrict contaminated water reaching the sea.
Above ground apparatus of the frozen wall which descends 30m and surrounds Units 1-4.
A visitor to the plant performs a low-tech check on the frozen wall.
The groundwater bypass pump works to reduce the amount of water leaking into the reactor buildings.
Temporary storage tanks for water pumped up via the groundwater bypass.
Flanged tanks of the sort used for indefinite storage of tritium-laced water arrive at the docks of Fukushima nuclear power plant.
Visitors from IAEA visit the ALPS water treatment facility where radionuclides are removed from contaminated water.
Defueling of the spent fuel pool at Unit 4 was performed in a conventional manner; it won’t be so easy at other Units where radiation and damage is more severe.
The giant fuel handling machine (background) and fuel handling crane (foreground) arrive for installation at Unit 3.
The final segment of the domed containment roof is lifted into place at Unit 3.
While they’re now stable in terms of nuclear activity, Units 1-3 remain highly contaminated. As such, while the structural integrity of these buildings has been restored, relatively little work has been undertaken within them. (One notable exception is removal of contaminated water from condensers, completed last year.)
Over recent years, a variety of remotely operated devices and imaging technologies have performed investigations of these units. The intention has been to gather information on internal physical and radiological conditions of the PCVs—the heavily reinforced bell-shaped structures that host reactors. TEPCO wants, and needs, to understand what has happened inside. Some things are known: once melted, fuel mixed with structural materials including steel and concrete to form something known as corium. But precisely where the corium ended up, how much there is, and whether it’s submerged are just some of the questions in play.
The International Research Institute for Nuclear Decommissioning (IRID), which was established in April 2013 to guide R&D of technologies required for reactor defueling and decommissioning, is supporting TEPCO in seeking answers. IRID is composed of multiple stakeholders, including Japanese utilities and the major nuclear vendors Hitachi, Mitsubishi, and Toshiba.
Naoaki Okuzumi, senior manager at IRID, described for Ars the investigative approaches and technologies. Early work utilized Muon tomography, which Okuzumi described as “a kind of standard practice applied to each unit… to locate high density material (fuel) within PCVs.” It yielded low-resolution data on the approximate location of corium. But with pixels representing 25cm-square cross-sections, the information has been useful only in so far as validating computational models and guiding subsequent robotic investigations.
The latter task hasn’t been easy. In addition to the challenge of navigating the dark, cramped labyrinths of tangled wreckage left behind, TEPCO has had to contend with radioactivity—the high levels act something like noise in electronic circuits. The wreckage has made access a challenge, too, although varying points of ingress have been established for each PCV.
The circumstances mean that TEPCO hasn’t been able to simply purchase an off-the-shelf kit for these investigations. ”An adaptive approach is required because the situation of each PCV is different… there is no standard with investigating the PCVs by using robots,” said Okuzumi, describing an approach that has translated into devices being specially developed and built in response to conditions of each PCV.
But they’re making progress. As recently as January 2018, corium was identified for the first time inside Unit 2 using an enhanced 13m-long telescopic probe and a revised approach designed to overcome problems encountered during investigations in 2017. The situation was hardly easier at Unit 3, where the PCV is flooded to a depth of around 6.5m. Here, it took a remotely operated, radiation-shielded submersible called ‘Little Sunfish’ to locate corium in July 2017.
Altogether the investigations—featuring a litany of robotic devices—have revealed that little fuel remains in any of the cores of Units 1-3. In Unit 2, a large amount of corium is present at the bottom of the RPV; in Units 1 and 3, almost all fuel appears to have melted through the RPVs entirely and into the concrete floor of PCVs beneath. The information is crucial, as we’ll come to see, for future deconstruction work at the reactors, but it continues to be extended as investigations continue.
PCV investigations at Unit 2
Pumps, ice-walls, and storage: Water management
One of TEPCO’s major concerns has been groundwater, which runs down from mountains west of the plant and can become contaminated by the low-lying reactors before flowing out to sea. Groundwater management has subsequently become one of TEPCO’s greatest efforts, as well as one of the most challenging of the tasks it has faced.
First off, it ought to be noted that marine environment monitoring for radionuclide concentrations near the plant and as far away as Tokyo indicate that levels are well within WHO standards. “The levels of radioactivity that have been found and can be attributed to Fukushima are absolutely dwarfed by natural levels of radioactivity in the water, or even levels of cesium that came from historic nuclear weapons testing,” noted Cobb.
Still, the effort to limit further contamination—seemingly driven as much by societal-political dynamics as safety considerations—remains paramount. To this end, measures have been deployed along three principles: remove sources of contamination, isolate water from contamination, and prevent leakage of contaminated water.
Some measures have been simple enough in design. Installation of an impermeable, underground wall along the sea front, completed in October 2015, is intended to keep groundwater that passes Units 1-4 from reaching the sea. Waterproofing pavement against rainwater is another widely applied step.
After this, solutions become more sophisticated. A groundwater bypass that intercepts and pumps up water before it reaches the reactors is a key development. This water is inspected for contamination before being discharged into the sea. By November 2017, more than 337,000 cubic meters of water had been released to the ocean in this way; this bypass reduced the amount flowing into the building basements by up to 100 tons per day and successfully reduced groundwater levels around the reactor buildings.
To further limit groundwater flow into reactors buildings, TEPCO actually froze the ground around them, creating a kind of frozen wall down to a depth of about 30 meters. Approximately 1,500 meters long, the wall is kept frozen by pipes filled with an aqueous solution of calcium chloride cooled to -30ºC. Freezing commenced in March 2016 and is now “99 percent complete,” according to Kohta.
On either side of the frozen wall, sub-drains and groundwater drains have been installed; they pump water up to keep it from reactor buildings and reaching the sea, respectively. Pumped water is purified at a purpose-built treatment facility. Barrett commented: “With water released from sub-drains and the bypass, there’s an agreement with the fishing industry that releases must be below 1,500 becquerels per liter. Negotiations took several years to agree that level was ‘clean’.”
All this has come at enormous expense, but according to TEPCO, it has been successful. Before any measures were implemented, inflow was around 400m3/day, Kohta told Ars. “The average amount of water flowing into [Units 1-4] for the period from December 2015 to February 2018, before the closure of the land-side impermeable wall, was 190m3/day, and it has decreased to 90m3/day after the closure for December 2017 to February 2018.”
At face value, it’s a sound outcome. As Kohta noted, the amount of contaminated water now being generated—a mix of groundwater, rainwater and water pumped into reactors for cooling—has decreased from about 520m3/day to about 140m3/day between last December and February. Even so, treating that amount of contaminated water is proving taxing.
Water treatment is happening at large-scale facilities that have been built onsite, including a multi-nuclide removal facility. Here, a so-called Advanced Liquid Processing System (ALPS) reduces concentrations of cesium isotopes, strontium, and other radionuclides to below legal limits for release. But one radionuclide remains: tritium.
Cobb explained: “The difficulty is that tritium is basically an isotope chemically identical to hydrogen, so it’s impractical to remove. Levels of tritium in that water are low, but nevertheless there’s great sensitivity to the suggestion that it be discharged.”
Without a feasible alternative for cleaning up the tritium, the (only) solution for ALPS-treated water has been storage. Well over a thousand tanks, each holding 1,200 cubic meters, now store tritium-laced water at the south end of the plant. Several years ago, these tanks hit the news because several were found to be leaking. Barrett acknowledged it as an unfortunate and avoidable incident resulting from use of flange-tanks. TEPCO has since moved to more sturdy welded-joint water storage tanks.
The ultimate plan for stored water is unknown; tritium has a half life of a dozen years, so physics won’t clean up the water for us. Some kind of controlled, monitored discharge—the likes of which is typical within the nuclear industry—is possible, according to Barrett.
Indeed, the International Atomic Energy Agency has endorsed such a plan, which was proposed by the Atomic Energy Society of Japan in 2013. The plan involved diluting tritiated water with seawater before releasing it at the legal discharge concentration of 0.06MBq/L and monitoring to ensure that normal background tritium levels of 10Bq/L aren’t exceeded.
Discussions at both national and international levels would need to come first. Part of the difficulty here harkens back to societal dynamics surrounding risk and contamination: “In nuclear there is no such thing as absolute zero—sensitivity goes down to the atom. This makes discussion about decontamination or levels of acceptable contamination difficult. There’s tritium in that water that’s traceable to the accident; it’s entirely safe, but for the time being, with the event still in recent memory, it’s not acceptable,” observed Barrett.
Toward permanent solutions
In some sense, much of the restoration of order at Fukushima has been superficial—necessary but concerned with handling consequences more than root causes (see, TEPCO interactive timeline). Ultimately, Fukushima’s reactors must be decommissioned.
Broadly, this work involves three phases: removing used fuel assemblies that are stored within ten-meter-deep spent fuel pools of each reactor building, management of melted-down reactors and removal of corium debris, and deconstruction of reactor buildings and the greater plant.
At Unit 4, spent fuel removal operations took around 13 months and concluded in December 2014. “When we began we didn’t know if fuel assemblies or racks were distorted. It turned out they weren’t, and we were able to remove all fuel conventionally without any issues at all. Actually, it went exceedingly well, concluding ahead of schedule and under cost,” recalled Barrett. In all, 1,533 fuel assemblies were removed and transferred to a common spent fuel pool onsite.
Spent fuel removal at Unit 4 was accomplished with conventional techniques.
Defueling of pools at Units 1 through 3, which suffered meltdowns, isn’t going to be as straightforward. For one, there’s some expectation of debris and circumstances requiring extraordinary removal procedures. “I wouldn’t be surprised if we find some structurally bent fuel assemblies caused by large pieces of concrete or steel,” said Barrett.
Additionally, although radiation in Unit 3 has been reduced sufficiently to allow rotating shifts of workers to install defueling equipment, the already painstaking operations will have to be conducted remotely. The same is likely true for Units 1 and 2.
At Unit 3, the next in line for defueling, preparation is already well underway. In addition to decontamination and installation of shielding plates, TEPCO has removed the original fuel handling crane, which had fallen into the pool seven years ago, and installed a new fuel handling crane and machine. An indication of extraordinary containment methods being used, workers have built a domed containment roof at Unit 3. TEPCO’s Kohta told Ars, “Removal of spent fuel [at Unit 3] is scheduled to begin from around the middle of 2018;” meanwhile, Unit 1 is also in a preparatory stage and Unit 2 will be handled last.
Further down the line still, corium will have to be removed from melted-down reactors. It’s a daunting task, the likes of which has never been undertaken before. The reactors held varying, but known, amounts of uranium oxide fuel, about 150 tonnes each. But how much extra mass the fuel collected as it melted through reactor vessels is uncertain.
“At TMI there was exactly 93 tonnes in the reactor. Once we were done digging out fuel debris, we’d removed 130 tonnes. At Fukushima, I expect maybe a factor of five to ten more mass in core debris. It’s an ugly, ugly mess underneath the PCVs,” suggested Barrett.
High-powered lasers, drills and core boring technologies for cutting, and strong robotic arms for grappling and removing corium are already under development, according to IRID, but precise methodologies remain undecided.
The original plan, Barrett explained, was to flood PCVs and work underwater—a conventional nuclear operations technique that affords protection from contamination. But this requires water-tight PCVs, something that cannot be practically achieved at Fukushima. Discussions also continue over whether a side or top-down entry would be best. “Altogether, we don’t have enough physical data about PCVs to commit to a final decision,” said Barrett, referring back to the need for continued PCV investigations. According to Kohta, fuel debris removal isn’t scheduled to commence before the end of 2021.
Without doubt, the road ahead of TEPCO is a long one, beset with challenges greater than those faced to date. The Mid- and Long-Term Roadmap—the Japanese state-curated document outlining the decommissioning of Fukushima—envisions operations stretching a full 30-40 years into the future. Some have suggested it’s an optimistic target, others say that the plan lacks details on key, long-term issues such as permanent solid-waste storage beyond the onsite repository currently being employed. Certainly it is the case that key decisions remain.
For his part, Barrett concluded: “I believe that the 40-year timeframe is reasonable for a scientifically based decommissioning; that’s to say, to reach a point similar to that of a normal reactor at the end of its life. That’s not reaching the point of a green field where you’d want to put a children’s school. Could it be a brown-field, industrial site, though? Yes it could. That’s a rational, reasonable end point.”
By all accounts, it is hard to gauge the costs for the Fukushima clean-up. Kohta told Ars that works completed to date have cost about 500.2 billion yen, or $4.7 billion—a tremendous sum, to be sure, but fractional compared to the estimate of 8 trillion yen ($74.6 billion) approved by the Japanese state last May for the complete decommissioning of Fukushima Daiichi.
May 12, 2018
Posted by dunrenard |
Fukushima 2018 | decommissioning, Fukushima Daiichi, Nuclear Disaster, Remediations |
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In this July 27, 2017 file photo, contaminated water storage tanks are seen on the Fukushima No. 1 nuclear plant grounds, in Okuma, Fukushima Prefecture
Over the past year, clumps appearing to be melted fuel debris have been found inside three reactors at Tokyo Electric Power Co. (TEPCO)’s Fukushima No. 1 Nuclear Power Plant — which will soon mark seven years since being struck by disaster, on March 11.
However, the specific properties of the fuel debris remain unclear, and the decision on how to go about extracting the material has been delayed. The mammoth task of decommissioning the nuclear power plant, which is expected to take 40 years, is moving at a sluggish pace.
Removing the debris is the most difficult part of the decommissioning process. During an internal probe of nuclear containment vessels at the site, which involved robots, debris-like clumps were discovered in the No. 2 and No. 3 reactors, and sand-like sediment was found spread across the bottom of the No. 1 reactor. However, the specific properties and distribution of the debris has not yet been ascertained.
In September 2017, the government and TEPCO re-examined its decommissioning operation schedule. Initially, it was planned that the reactor which would undergo decommissioning first, as well as the method, would be decided by the end of the first half of fiscal 2018. However, the decision was delayed until the end of fiscal 2019 due to a lack of information concerning the situation inside the reactors, as well as the debris.
Meanwhile, as part of countermeasures against contaminated water, an ice wall designed to block the flow of underground water has almost been completed. In addition, a sub-drain well that pumps away subterranean water has been reinforced. As a result, the volume of underground water flowing into the buildings housing the reactors has been reduced from roughly 400 metric tons per day, which was the figure immediately after the outbreak of the disaster, to about 80 tons per day — indicating that there has been some progress regarding the “entrance” policy designed to reduce the volume of contaminated water generated at the site.
However, the “exit” policy, designed to dispose of treated water after most of the radioactive materials have been removed from the contaminated water, is still up in the air. The major issue concerning this policy is that the radioactive material tritium (tritiated hydrogen) cannot be removed, in principle, from treated water.
Tritium is something that appears in the natural world. Based on the fact that it has been flowing out into the sea from nuclear facilities across the globe, the Nuclear Regulation Authority stresses that Fukushima’s treated water containing tritium should be diluted and flushed out into the sea. However, due to fears that this could damage the reputation of the local fishing industry, the government and TEPCO continue to keep the treated water stored in tanks.
As a result, the amount of radioactive water stored at the site, including the treated water, has risen to about 1.05 million tons, and the number of tanks has increased to roughly 850. The government has set up a committee looking into how to dispose of the treated water, but consensus has not yet been reached.
Meanwhile, with regard to the extraction of fuel from pools of spent nuclear fuel, removal is planned from the No. 1 and No. 2 reactors in fiscal 2023, three years later than initially scheduled, and from the No. 3 reactor sometime around mid-FY2018. Special cranes are being installed to prepare for the job.
March 15, 2018
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Fukushima 2018 | Contaminated Water, decommissioning, Fukushima Daiichi |
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Workers wearing protective suits and masks work on the No. 2 reactor building at the Fukushima Daiichi nuclear power plant.
TOKYO – A state-backed entity tasked with supporting the decommissioning of the Fukushima nuclear power station proposed Thursday that melted fuel be removed from the side of three of the crippled reactors as part of the process to scrap the complex.
Based on a formal proposal, the government and the plant operator Tokyo Electric Power Company Holdings Inc (TEPCO) will determine specific approaches to carry out the process on each reactor next month and update the plant decommissioning road map.
Under its strategic plan for 2017, the Nuclear Damage Compensation and Decommissioning Facilitation Corp called for the removal of the fuel by partially filling the three reactors with water to cover some of the nuclear debris while allowing access to carry out the work.
The entity also pointed out that the decommissioning work requires phased efforts while maintaining flexibility, as the project still faces many uncertainties.
The extraction work from the Nos. 1-3 reactors at the Fukushima Daiichi nuclear complex, which suffered meltdowns following the massive 2011 earthquake and tsunami disaster, is seen as the most difficult step toward the ultimate goal of decommissioning the entire complex, set to take at least 30 to 40 years to complete.
The government and TEPCO are currently aiming to start the extraction work from 2021.
Under the plan, the Nuclear Damage Compensation and Decommissioning Facilitation body proposed using a remotely controlled apparatus to shave debris from the underside of the lower section of the reactors’ containment vessel while controlling the level of water.
Debris remains not only in the reactors’ pressure vessel but also piled and scattered at the bottom of the containment vessel that houses the reactor vessel.
As for debris left in the reactors’ pressure vessel, the entity will consider removing it from the upper part of the reactors, it said.
The decommissioning body had previously considered a strategy to fill the containment vessel with water as water is effective in containing radiation, but it has shelved the idea as the reactor containers are believed to have been damaged and would leak.
Following a magnitude-9.0 earthquake in March 2011, tsunami inundated the six-reactor plant, located on ground 10 meters above sea level, and flooded power supply facilities.
Reactor cooling systems were crippled and the three reactors suffered fuel meltdowns, while hydrogen explosions damaged the buildings housing the Nos. 1, 3 and 4 reactors.
The Nuclear Damage Compensation and Decommissioning Facilitation entity was established after the Fukushima crisis, the worst nuclear disaster since Chernobyl, to help the utility pay damages. The state-backed entity holds a majority stake in the operator.
https://japantoday.com/category/national/Debris-to-be-removed-from-side-of-Fukushima-reactors
September 2, 2017
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Fukushima 2017 | decommissioning, Fukushima Daiichi |
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Hitachi-GE testing variety of simply structured, radiation-resistant equipment
The Unit 1 reactor building at the Fukushima Dai-ichi nuclear power plant of the Tokyo Electric Power Co. (TEPCO) in Okuma town, Fukushima prefecture, June 21, 2017.
TOKYO — A joint venture between Japanese and American high-technology power houses Hitachi and General Electric is developing special robots for removing nuclear debris from the Fukushima Daiichi nuclear power plant, the most difficult task in decommissioning the plant’s six reactors, three of which suffered core meltdowns in the March 2011 accident.
The machines under development by Hitachi-GE Nuclear Energy are called “muscle robots,” as their hydraulic springs operate like human muscles. The company, based in Hitachi, Ibaraki Prefecture, is stepping up efforts to complete the development project in time for the start of debris removal in 2021.
Hitachi-GE is testing the arms of the robots at a plant of Chugai Technos, a Hiroshima-based engineering service company, located a 30-minute drive from the center of the city. The testing is taking place in a structure with a life-size model of the primary containment vessel of the No. 1 reactor at the Fukushima plant. The robots awkwardly move about, picking up concrete lumps standing in for fuel debris.
“The robots are based on a concept completely different from those of conventional robots,” said Koichi Kurosawa, a senior Hitachi-GE engineer heading the development project. Hydraulics are being used because electronics cannot survive in the extreme environment inside the reactors.
“Asked if the robots are applicable to other nuclear power plants, I would say the possibility is low,” Kurosawa said, noting that the robots are designed to work amid intense radiation.
New challenges
While Hitachi-GE has built many nuclear reactors, it is encountering a variety of new challenges in developing the muscle robots simply because of the tough work required to retrieve fuel debris.
In the nuclear accident caused by the March 2011 earthquake and tsunami, cooling the fuel rods became impossible, and melted uranium fuel dropped from them. Some of the fuel broke through nuclear reactor pressure vessels and solidified as fuel debris containing uranium and plutonium.
The debris is estimated to weigh more than 800 tons in total. The insides of the PCVs at the Fukushima plant are directly exposed to the debris and are emitting radioactivity strong enough to kill a human within a few minutes.
The International Research Institute for Nuclear Decommissioning, a Tokyo-based research institute for decommissioning nuclear plants, and three reactor makers — Hitachi-GE, Toshiba and Mitsubishi Heavy Industries — have been attempting to ascertain conditions inside the reactor buildings at the Fukushima plant by means of camera- and dosimeter-equipped equipment.
https://asia.nikkei.com/Tech-Science/Science/Muscle-robots-being-developed-to-remove-debris-from-Fukushima-reactors
September 2, 2017
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Fukushima 2017 | decommissioning, Fukushima Daiichi, Robots |
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The head of the Nuclear Regulation Authority told Tepco’s top management he questions their attitude toward decommissioning the Fukushima No. 1 nuclear power plant and the company’s ability to resume operating its other reactors.
“I feel a sense of danger,” NRA Chairman Shunichi Tanaka said during a special meeting Monday with the top management of Tokyo Electric Power Company Holdings Inc.
Tanaka also said Tepco does “not seem to have the will to take the initiative” toward decommissioning the crippled nuclear power station that suffered three reactor meltdowns in March 2011.
Tepco Chairman Takashi Kawamura and President Tomoaki Kobayakawa attended the meeting. The authority felt it is necessary to hear from the top executives before it could make a decision on whether to approve Tepco’s plan to resume operation of reactors 6 and 7 at its massive Kashiwazaki-Kariwa plant in Niigata Prefecture.
Tepco filed for a safety assessment of the two reactors in September 2013 to reactivate them, hoping to restore its financial condition as it needed massive funds to pay compensation related to the Fukushima disaster and to scrap the plant.
The NRA’s safety screening found that Tepco failed to report insufficient earthquake resistance for an emergency response center at the Niigata complex even though it knew about the insufficiency for three years.
In June, Tepco submitted to the watchdog its revised safety measures for the Kashiwazaki-Kariwa complex.
“An operator lacking the will to take the initiative does not have the right to resume operation of nuclear reactors,” Tanaka said.
Tepco’s chairman responded by saying: “There are citizens who believe nuclear power is necessary. Operating reactors is our responsibility.”
But Kawamura also admitted there is room for only two more years’ worth of space in the tanks to accommodate the contaminated water building up at Fukushima No. 1.
During the meeting the NRA asked Tepco’s management about the company’s safety measures for the Niigata complex — the biggest nuclear power station in the world — as well as its safety awareness.
Tanaka said the NRA does consider Tepco’s responses at the meeting as sufficient and requested that it submit further explanations on its plan to decommission Fukushima No. 1 and resume operation of the two reactors at Kashiwazaki-Kariwa.
Tanaka plans to conduct on-site checkups at the two reactors, saying, “Tepco, which caused the (Fukushima) accident, is not an ordinary operator.”
The two boiling water reactors at the Niigata plant are the same type that suffered core meltdowns at Fukushima No. 1, and no such reactors have cleared the authority’s safety screening since the 2011 crisis.
http://www.japantimes.co.jp/news/2017/07/10/national/japans-nuclear-safety-chief-raps-tepcos-attitude-fukushima-no-1-crisis-restarting-reactors/
July 10, 2017
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Fukushima 2017 | decommissioning, Fukushima Daiichi, Nuclear Regulation Authority, Reactors Restart, Tepco |
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The Monju prototype fast-breeder reactor in Tsuruga, Fukui Prefecture
Fukui governor accepts decision to decommission Monju reactor
Fukui Governor Issei Nishikawa has ditched his opposition to the central government’s plans to decommission the Monju prototype fast-breeder reactor in his prefecture.
Nishikawa had criticized Tokyo for deciding to decommission the reactor in Tsuruga without offering adequate assurances to local residents about such a massive project.
But during a meeting held at the prime minister’s office in Tokyo early June 7, he said, “Decommissioning of the Monju fast-breeder reactor is inevitable.”
At the meeting, attended by relevant Cabinet ministers, the government presented Nishikawa with a basic policy to remove spent nuclear fuel from the reactor in five and a half years and complete decommissioning in 30 years.
Hirokazu Matsuno, the science and technology minister, explained that the basic policy includes a plan to transfer spent nuclear fuel outside the prefecture as demanded by Fukui prefectural authorities.
The government will soon formally adopt the basic policy on decommissioning. The Japan Atomic Energy Agency, which operates the Monju reactor, will then draft its own plan for the project.
The government decided to decommission Monju at the end of last year and was initially expected to present the basic plan in April. However, Nishikawa had been airing concerns about the decommissioning.
http://www.asahi.com/ajw/articles/AJ201706070036.html
Fukui governor approves scrapping of Monju reactor
The governor of Fukui in central Japan has consented to dismantling the prototype fast-breeder nuclear reactor in the prefecture.
The Japanese government decided in December to scrap the Monju reactor over a period of 30 years, following a series of safety management problems. It cited rising costs.
Governor Issei Nishikawa had opposed the plan, expressing concerns about the safety of the dismantling process.
Nishikawa met with Chief Cabinet Secretary Yoshihide Suga and science minister Hirokazu Matsuno on Wednesday in Tokyo.
Matsuno explained the basic plan for scrapping the reactor. The science minister said spent nuclear fuel and sodium coolant would be moved out of the prefecture in future.
He also said the government will come up with a development plan for the host city of Tsuruga by the next fiscal year. He said this would make the city a hub of nuclear research and personnel training.
Governor Nishikawa said he confirmed the government’s basic plan for decommissioning and revitalizing the community. He said he had no choice but to accept the decommissioning. He emphasized that the process be carried out safely.
https://www3.nhk.or.jp/nhkworld/en/news/20170607_15/
June 9, 2017
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Japan | decommissioning, Fukui Governor, Monju Reactor |
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On May 25, the Tokyo Electric Power Co. (TEPCO) released a status report on the ongoing decommissioning work at the Fukushima Daiichi Nuclear Power Plants, which suffered a tsunami-caused meltdown in March 2011.
Starting two months ago, in March, a self-propelled robot has been used to investigate the interior of the primary containment vessel (PCV) of Unit 1 at Fukushima Daiichi—a necessary step before fuel debris can be removed. As of April 6, the robot had sampled deposits twice.
Fluorescent X-ray spectroscopy has now confirmed the presence of elements that had originally existed in the PCV, such as iron and nickel within the reactor core internals, stainless steel in the heat-insulating materials, zinc in the paint, and lead in the shielding materials.
Although uranium was confirmed as the primary radioactive nuclide within Unit 1, it is not necessarily part of the fuel debris there, given that that element exists naturally. TEPCO said that it would carry out more detailed analyses to confirm the uranium’s source.
As the water level in the PCV of Unit 3 is higher than that in Units 1 and 2, its so-called “X-6 penetration”—which would give easier access to the inside of the pedestal (under the reactor pressure vessel)—is submerged. TEPCO plans to investigate the interior of that unit’s PCV at an undetermined date this summer using a submersible robot that can both crawl and swim. Earlier this month, the power utility began taking measurements using muon observation technology to determine the location of fuel debris.
Under the “Mid-and-Long-Term Roadmap” toward decommissioning, TEPCO will determine policies on fuel debris removal at each Fukushima Daiichi unit this summer. According to its May 22 report to an expert panel of the Nuclear Regulation Authority (NRA), the power company has already made investigations to determine general conditions inside the individual PCVs.
TEPCO will continue to focus on gathering information during the current fiscal year (ended March 31, 2018), including that on the forms and distribution of fuel debris—necessary to determine the means to remove it—and safety measures for the actual removal work.
http://www.jaif.or.jp/en/submersible-crawling-robot-to-examine-interior-of-fukushima-daiichi-3-pcv-before-fuel-debris-is-removed/
June 5, 2017
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Fukushima 2017 | decommissioning, Fukushima Daiichi, Reactor 3, Robot Probe |
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of the week
November 29th and 30th and December 1st, Navajo Nation Museum, Hwy 264 & Post Office Loop, Window Rock, Navajo Nation, AZ
December 2nd, Flagstaff, AZ
December 6th, Guild Cinema, 3405 Central Ave, Albuquerque, NM
December 7th, Grants, NM
December 9th, Jean Cocteau Cinema, 418 Montezuma Ave, Santa Fe, NM
PETITIONS
