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TEPCO to start removing fuel at Fukushima’s No. 3 reactor

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Workers lower the last part of a semi-cylindrical covering on top of the No. 3 reactor building.
April 12, 2019
The operator of the crippled Fukushima No. 1 nuclear power plant will start removing nuclear fuel from the No. 3 reactor as early as next week through equipment controlled remotely due to high radiation levels inside the building.
This will mark Tokyo Electric Power Co.’s first attempt to remove spent fuel from one of the three reactors that experienced a meltdown during the 2011 nuclear accident.
All spent fuel has already been removed from the No. 4 reactor.
TEPCO workers will use remote control to remove nuclear fuel assemblies kept in the pool on the upper floors of the No. 3 reactor building.
Utility officials acknowledge that the process will not be easy, as they have no experience conducting such a dangerous task remotely.
The 566 nuclear fuel assemblies in the storage pool will be removed under a plan expected to take two years to complete.
TEPCO wants to remove the assemblies as quickly as possible owing to concerns that another major earthquake or tsunami could further damage the reactor building and equipment. The No. 3 reactor will also serve as a test case for eventually removing spent nuclear fuel from the No. 1 and No. 2 reactor buildings.
Under the plan, workers will be stationed in a control room about 500 meters from the reactor building and use remote control equipment while observing the process through monitors.
Each nuclear fuel assembly will be lifted and transferred to a special transport container that can hold up to seven such assemblies in water. The container will then be carried out of the reactor building by crane, which will then lower the container outside of the building to a trailer about 30 meters below at ground level.
As a hydrogen explosion blew off the roof of the No. 3 reactor building in the wake of the 2011 nuclear accident, a semi-cylindrical copper covering has been placed over the building to prevent radioactive materials from spreading when the spent nuclear fuel is being removed.
All 1,535 nuclear fuel assemblies at the No. 4 reactor building were removed by the end of 2014. Radiation levels were comparatively low so workers could enter the building to work on the removal.
A TEPCO official in charge of the process called the removal at the No. 4 reactor “normal operating procedures,” but admitted that remote control operations added a new dimension of difficulty.
The utility has experienced problems with the crane and other equipment to be used at the No. 3 reactor.
Under TEPCO’s plan compiled shortly after the nuclear accident, all spent nuclear fuel was to have been removed from all four reactors by the end of fiscal 2021.
“We do not believe the process will proceed with zero problems,” said Akira Ono, president of the Fukushima Daiichi Decontamination and Decommissioning Engineering Co.
The work at the No. 3 reactor will serve as a model for a similar process planned for the No. 1 and No. 2 reactor buildings to start in fiscal 2023.
Government and TEPCO officials have said they will consider a detailed plan for removing spent nuclear fuel from those two buildings after reviewing the work done at the No. 3 reactor building.
The two other reactor buildings present different hurdles for workers.
The top floor of the No. 1 reactor building is covered with debris from a collapsed ceiling and damaged crane, the removal of which has proved difficult. Workers have also confirmed that the lid on top of the containment vessel has shifted, meaning radiation levels inside the building are likely even higher than in the No. 3 reactor building.
It thus remains to be seen if the same equipment to be used for the No. 3 reactor can be used for the No. 1 building. To prevent leaking of radioactive materials, the lid for the containment vessel will first have to be moved back into place.
While the No. 2 reactor building did not suffer major structural damage, large amounts of radioactive materials are believed to be trapped inside the building, meaning radiation levels are also very high there.
The level at the top floor is so high that any worker remaining there for one hour would quickly exceed the annual radiation exposure level. After decontamination, the upper part of the No. 2 reactor building will have to be taken apart to remove the spent fuel. However, this poses the major problem of preventing the spewing of radioactive materials during that process.
“To be honest, it will be difficult to say that no problems will emerge that will force a change in plans,” said Toyoshi Fuketa, chairman of the Nuclear Regulation Authority.
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April 14, 2019 Posted by | fukushima 2019 | , , | 1 Comment

Fuel removal from Fukushima reactor may be delayed

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June 29, 2018
The operator of the damaged Fukushima Daiichi nuclear power plant says work to remove spent nuclear fuel from a cooling pool at one of its reactors may be delayed.
 
A total of 566 fuel units remain in the cooling pool at the No.3 reactor, which suffered a meltdown in 2011. Tokyo Electric Power Company, or TEPCO, planned to start removing the fuel as early as this autumn, as part of the decommissioning of the nuclear complex.
 
But on Thursday, TEPCO revealed the control board of a crane used in the removal malfunctioned during a test run last month. It blamed a voltage error and said the board will be replaced.
 
The company said the test run may be delayed by one or 2 months, pushing back the start date for fuel removal.
 
TEPCO’s chief decommissioning officer, Akira Ono, says he takes the glitch seriously as it shows key equipment was not handled properly.
 
He says that although safety must come first, his team still aims to stick to the original timetable and start the removal of nuclear fuel by around the middle of the current fiscal year, which ends in March next year.
 

July 1, 2018 Posted by | Fukushima 2018 | , , | Leave a comment

TEPCO prepares to remove fuel from damaged reactor

 

May 28, 2018
The operator of the damaged Fukushima Daiichi nuclear power plant has started laying the groundwork to retrieve fuel from one of the plant’s reactor buildings. It’s a crucial step toward scrapping the complex.
 
Tokyo Electric Power Company began the work on Monday to move 615 fuel rod units from a storage pool on the top floor of the No. 2 reactor to a more secure location.
 
The No. 2 reactor is one of 3 at the plant that melted down in the 2011 accident. Radiation levels inside the reactor building remain high.
 
TEPCO will open a hole measuring 5 by 7 meters in the building’s wall and send a robot through it to measure radiation levels inside.
 
A section of the wall will be divided into 29 blocks, each with a handle to facilitate its removal.
 
From a control room some distance from the reactor building, TEPCO officials will remotely operate a machine to remove the blocks.
 
The work is expected to continue until mid-June.
 
The plant operator will measure radiation levels before deciding how to retrieve the fuel rods. The company plans to start retrieving the fuel in fiscal 2023.
 
TEPCO official Hiroshi Noda says that although the decommissioning work for the No. 2 reactor has just started, it’s a major step forward.
 
He says the company will make sure that the work will have no impact on the environment.

 

June 5, 2018 Posted by | Fukushima 2018 | , | Leave a comment

Fukushima dome roof takes shape, but radiation remains high

4 dec 2017 dome roof n3
Construction continues on a domed roof on top of the No. 3 reactor building at the Fukushima No. 1 nuclear power plant.
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.
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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.
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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.
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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.

December 4, 2017 Posted by | Fukushima 2017 | , , , | Leave a comment

Preparations to unload reactor 3’s pool

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On November 8th two machines arrived at Fukushima Daiichi : a bridge crane and a fuel handling machine. These two machines will be installed on the reactor 3’s platform in order to unload the pool of its fuel.

Source: Pierre Fetet http://www.fukushima-blog.com/

November 13, 2017 Posted by | Fukushima 2017 | , , | Leave a comment

Multiple challenges remain to Fukushima nuclear cleanup

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This Sept. 4, 2017 aerial photo shows Fukushima Dai-ichi nuclear power plant reactors, from bottom at right, Unit 1, Unit 2 and Unit 3, in Okuma, Fukushima Prefecture, northeastern Japan. The three reactors that had meltdowns together have 1,573 units of mostly used nuclear fuel rods that are still inside and must be kept cool in pools of water. They are considered among the highest risks in the event of another major earthquake, because the pools are uncovered. The plant operator, Tokyo Electric Power Co. or TEPCO, plans to begin removing the rods from reactor unit 3 in the fiscal year beginning next April 1. However, the latest roadmap delays removal of the rods from units 1 and 2 for three years until fiscal 2023, because further decontamination work and additional safety measures are needed.

Japan’s government approved on Tuesday, Sept. 26, 2017 a revision to the decommissioning plan for the Fukushima nuclear plant, delaying by two more years the removal of radioactive fuel rods in two of the three reactors damaged in the 2011 disaster. It still plans for melted fuel to be removed starting in 2021, but the lack of details about the duration raises doubts if the cleanup can be completed within 40 years. Kyodo News via AP, File)


TOKYO – Japan’s government approved a revised road map Tuesday to clean up the radioactive mess left at the Fukushima nuclear power plant after it was damaged beyond repair by an earthquake and tsunami in 2011. Decommissioning the damaged reactors is an uncertain process that is expected to take 30 to 40 years.

A look at some of the challenges:

THE FUEL RODS

The three reactors that had meltdowns together have 1,573 units of mostly used nuclear fuel rods that are still inside and must be kept cool in pools of water. They are considered among the highest risks in the event of another major earthquake that could trigger fuel rods to melt and release massive radiation due to loss of water from sloshing or structural damage because the pools are uncovered. The plant operator, Tokyo Electric Power Co., or TEPCO, plans to begin moving the rods from reactor Unit 3 in the fiscal year beginning April 1.


However, the latest road map delays removal of the rods from units 1 and 2 for three years until fiscal 2023, because further decontamination work and additional safety measures are needed. Ironically, because the building housing reactor 3 was more heavily damaged, it is easier to remove that unit’s fuel rods. The fuel rods will be moved to a storage pool outside the reactors, and eventually sent for long-term storage in what are known as dry casks.

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THE MELTED FUEL

By far the hardest part of decommissioning Fukushima will be removing the fuel that melted and presumably spilled out of the reactor cores. In July, an underwater robot for the first time captured images inside the primary containment chamber of Unit 3. They showed a large number of solidified lava-like rocks and lumps on the chamber’s floor, believed to be melted fuel mixed with melted and mangled equipment and parts of the structure.

The search for melted fuel in units 1 and 2 has so far been unsuccessful. The water level is lower, so crawling robots have been tried, but they have been obstructed by debris as well as extremely high radiation levels. Despite the unknowns about the melted fuel and debris and their whereabouts, the road map calls for finalizing the removal method in 2019, and starting actual removal at one of the reactors in 2021. The government-funded International Research Institute for Nuclear Decommissioning is developing robots and other technology to carry out the work.

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CONTAMINATED WATER

TEPCO has treated and stored a massive amount of radioactive water — about 800,000 tons — and the volume is growing every day. Cooling water leaks out of the damaged reactors and mixes with groundwater that seeps into the basements of the reactor building, increasing the amount of contaminated water. The utility has managed to halve the volume to 200 tons per day by pumping up groundwater via dozens of wells dug upstream from the reactors, as well as installing a costly “ice wall” by freezing the ground to block some of the water from coming in and going out.

The water is stored in hundreds of tanks that cover much of the plant property. They get in the way of decommissioning work and pose another risk if they were to spill out their contents in another major earthquake or tsunami. After treatment, the water still contains radioactive tritium, which cannot be removed but is not considered harmful in small amounts. Experts say controlled release of the water into the ocean is the only realistic option, but TEPCO has not moved forward with that plan because of opposition from fishermen and residents who fear a negative image and possible health impact.

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RADIOACTIVE WASTE

Japan has yet to develop a plan to dispose of the highly radioactive waste that will come out of the Fukushima reactors. Under the road map, the government and TEPCO will compile a basic plan during fiscal 2018. Managing the waste will require new technologies to compact it and reduce its toxicity. Finding a storage site for the waste seems virtually impossible, as the government has not been able to find a site even for the normal radioactive waste from its nuclear power plants. The prospect raises doubts about whether the cleanup can really be completed within 40 years.

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http://www.miamiherald.com/news/business/article175387901.html

September 26, 2017 Posted by | Fukushima 2017 | , , , | Leave a comment

Spent Nuclear Fuel Removal at Fukushima Plant Delayed Again

Japan muddles on with Fukushima’s melted and “spent” fuel. The three year delay for emptying the reactors “spent” irradiated nuclear fuel into a dry cask storage runs the risk of another major earthquake causing a loss of cooling in the pools without containments and another major release of radiation. Plans for removing the melted reactor cores from Units 1, 2 and 3 still defied by inability to locate it.

 

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Fukushima Nuclear Plant Scrapping Plan Faces Another Delay

A key decision in decommissioning the crippled Fukushima Daiichi nuclear plant is being delayed. The Japanese government and operator made the announcement on Tuesday while giving an update on the roadmap for scrapping the plant.

In their first such update in 2 years, officials said they will postpone their decision on the method for removing molten fuel debris by one year, until fiscal 2019.

Experts believe that when the plant went into triple meltdown in 2011, most of the fuel inside the reactors collected at the bottom of containment vessels. They still don’t know the exact location, but possible molten fuel debris was caught on camera in July. The removal of this debris is considered the most challenging part of the plant’s decommissioning.

Originally, officials considered filling the containment vessels with water to block radiation while removing the debris. But now, they say they’re leaning towards a method called dry removal.

Experts say that method comes with safety challenges. “Because the containment vessel will not be filled with water, there is a possibility that radioactive substances may leak and get dispersed,” says Hosei University Visiting Professor Hiroshi Miyano.

Officials also gave an update on plans for the removal of spent nuclear fuel rods in 2 of the plants reactors. The rods are in storage pools and won’t be removed until fiscal 2023. That’s 3 years later than planned. The official timeline for scrapping the plant remains the same — about 30 to 40 years in total.

https://www3.nhk.or.jp/nhkworld/nhknewsline/nuclearwatch/fukushimanuclearplantscrapping/

Spent nuclear fuel removal at Fukushima plant pushed back again

n-roadmap-a-20170927-870x438Cabinet ministers attend a meeting at the Prime Minister’s Office on Tuesday to discuss a delay in the road map for decommissioning the Fukushima No. 1 nuclear power plant.

 

The government and Tokyo Electric Power Company Holdings Inc. decided Tuesday to further delay the removal of spent nuclear fuel left near two of the three reactors that suffered meltdowns at the Fukushima No. 1 nuclear plant.

In the road map for decommissioning the plant, revised for the fourth time since it was first crafted in 2011, highly radioactive spent fuel will be extracted from the cooling pools of reactors 1 and 2 starting in fiscal 2023 instead of fiscal 2020.

The decision marks the third delay for the removal plan, with the last adjustment coming in June 2015. The government said new technical issues and the need to take safety precautions led to the latest change.

The cleanup process is set to be completed in around 30 to 40 years.

Spent fuel removal at the plant’s reactor 3 will go ahead in fiscal 2018 as planned, having already been pushed back earlier this year.

In the decommissioning process, the removal of fuel rod assemblies from the spent fuel pools in reactor buildings is one of the key steps before extracting melted fuel debris. Reactors 1, 2 and 3 suffered core meltdowns following the March 2011 earthquake and tsunami disaster.

The removal of melted fuel debris has also been delayed, with an extraction plan set to be decided in fiscal 2019, pushed back from the first half of fiscal 2018.

Despite the delay in finalizing specific methods, the road map maintains a 2021 start for debris extraction, the most challenging part of the decommissioning process.

A method currently considered feasible by the government involves removing debris from the sides of the reactors after partially filling them with water.

The road map newly sets the goal of cutting the amount of underground water at the plant to address contaminated water buildup. Underground water — which gets mixed with accumulated radioactive water generated in the process of cooling the damaged reactors — is to be cut to around 150 tons per day in 2020 from the current 200 tons.

The road map does not mention a specific schedule for the disposal of processed water that still contains radioactive tritium.

The plan was first crafted in December 2011 in the wake of the meltdowns, the world’s worst nuclear crisis since the 1986 Chernobyl disaster.

Attempts have been made to confirm the situation inside the damaged reactors using specialized robots. A survey in July this year captured for the first time images of what is likely to be melted nuclear fuel at the bottom of reactor 3.

Isamu Kaneda, deputy mayor of the Fukushima Prefecture town of Futaba, expressed regret over the delay.

The town’s rebuilding depends on the development of decommissioning. It’s unfortunate,” Kaneda said. “But at the same time, the decommissioning process is an unprecedented project. It needs to be conducted carefully, so we can’t just ask them to speed it up.”

https://www.japantimes.co.jp/news/2017/09/26/national/spent-nuclear-fuel-removal-fukushima-plant-pushed-back/#.WcqxGxdx3rc

Spent nuclear fuel removal at Fukushima plant to be delayed again

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TOKYO (Kyodo) — The government and Tokyo Electric Power Company Holdings Inc. decided Tuesday to delay again the start of removing spent nuclear fuel left near two of the three reactors which suffered a meltdown at the Fukushima complex.

In the road map for decommissioning the Fukushima Daiichi plant, revised for the fourth time since it was first crafted in December 2011, highly radioactive spent nuclear fuel will be extracted from the Nos. 1 and 2 units’ cooling pools starting in fiscal 2023 instead of fiscal 2020.

It is the third time that the schedule for spent fuel removal has been pushed back at the Nos. 1 and 2 reactors, with the previous postponement taking place in June 2015. The government said new technical issues and the need to take safety precautions led to the latest schedule change.

The cleanup process is to be completed in around 30 to 40 years.

For the No. 3 reactor at the Fukushima plant, the schedule to remove spent nuclear fuel during fiscal 2018 is unchanged after having already been pushed back earlier this year.

In the decommissioning process, taking out fuel rod assemblies from the spent fuel pools inside reactor buildings is one of the key steps before extracting melted fuel debris from the Nos. 1 to 3 reactors, all of which suffered core meltdowns following the March 2011 earthquake and tsunami disaster.

The schedule for extraction of the melted fuel debris at the reactors was also revised, with the determination of a specific approach to remove the debris to be made in fiscal 2019, rather than in the originally planned first half of fiscal 2018.

Despite the delay in finalizing specific methods, the road map kept the start of the debris extraction, the most challenging part of the decommissioning process, at 2021.

A method currently considered feasible by the government is debris removal from the side of the three crippled reactors by partially filling them with water.

The road map newly sets the goal of cutting the amount of underground water at the plant to address contaminated water buildup at the site. Underground water, which gets mixed with accumulated radioactive water generated in the process of cooling the damaged reactors — is to be cut to around 150 tons per day in 2020 from the current 200 tons.

It did not mention a specific schedule for disposal of processed water that still contains radioactive tritium.

The road map was first crafted in December 2011 in the wake of the 2011 disaster which triggered at the Fukushima plant the world’s worst nuclear crisis since the 1986 Chernobyl disaster.

Attempts have been made to confirm internal conditions of the damaged reactors using robots. A survey robot captured images of what is likely to be melted nuclear fuel at the bottom of the No. 3 reactor for the first time in July this year.

http://mainichi.jp/english/articles/20170926/p2g/00m/0dm/064000c

 

September 26, 2017 Posted by | Fukushima 2017 | , , | Leave a comment

TEPCO to delay emptying fuel storage pools at Fukushima plant

reactor 1 left reactor 2 right 21 sept 2017.pngThe No. 1 reactor building, left, and the No. 2 reactor building at the crippled Fukushima No. 1 nuclear plant

 

Plans to remove fuel rods from two spent fuel pools at the Fukushima No. 1 nuclear plant will be delayed by up to three years because of difficulties in clearing debris and reducing radiation levels.

The government and plant operator Tokyo Electric Power Co. originally expected to start emptying the storage pools at the No. 1 and No. 2 reactor buildings in fiscal 2020.

But they plan to move the starting time to fiscal 2023 in their first review in two years of the roadmap for decommissioning the stricken nuclear plant, sources said Sept. 20.

They are expected to announce the revised roadmap later this month.

A survey of the upper levels of the two reactor buildings, where the storage pools are located, found debris piled up in a much more complicated way than initially envisaged.

That will lengthen the time needed to clear the debris, thus delaying the removal of the fuel rods, the sources said.

In addition, radiation levels remain extremely high inside the buildings.

The No. 1 reactor’s storage pool holds 392 nuclear fuel assemblies, while the No. 2 reactor’s pool has 615 assemblies.

Work to remove the 566 assemblies from the No. 3 reactor’s pool is scheduled to begin in the middle of fiscal 2018 as originally planned.

The three reactors melted down in the 2011 disaster, triggered by the magnitude-9.0 Great East Japan Earthquake and tsunami.

The review of the decommissioning roadmap is also expected to revise the target of “starting the removal” of melted nuclear fuel and debris in the three reactors in 2021 to “aiming to start the removal” in 2021.

But the government and TEPCO will maintain the goal of completing the decommissioning in “30 to 40 years,” the sources said.

http://www.asahi.com/ajw/articles/AJ201709210034.html

September 22, 2017 Posted by | Fukushima 2017 | , , | Leave a comment

Tepco’s biggest hurdle: How to remove melted fuel from crippled Fukushima reactors

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Tepco’s scorpion-shaped robot. | IRID

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

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

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

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

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

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

In search of melted fuel

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

The images showed black lumps scattered beneath the pressure vessel.

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

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

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

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

Radiation barrier

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

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

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

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

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

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

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

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

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

Fuel removal strategy

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

To remove or not

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

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

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

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

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

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

http://www.japantimes.co.jp/news/2017/03/09/national/tepcos-biggest-hurdle-remove-melted-fuel-crippled-fukushima-reactors/#.WMFAFKKmnIV

March 10, 2017 Posted by | Fukushima 2017 | , , , | Leave a comment

Footage points to difficulty in removing possible melted fuel at Fukushima plant

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The footage released on Jan. 30 by Tokyo Electric Power Co. (TEPCO) showing what could be melted fuel inside the No. 2 reactor at the disaster-stricken Fukushima No. 1 Nuclear Power Plant has highlighted the difficulty of salvaging the object, which is apparently stuck to footholds and other equipment at the facility.
TEPCO took the footage as part of its in-house probe into the No. 2 reactor and found that black and brown sediments — possible melted fuel — are stuck inside the reactor’s containment vessel over an extensive area.

“If what was captured in the footage was melted fuel, that would provide a major step forward toward trying our hand at unprecedented decommissioning work,” said Yoshiyuki Ishizaki, head of TEPCO’s Fukushima Revitalization Headquarters, during a press conference in the city of Fukushima on Jan. 30. “The finding may provide a major clue to future work to retrieve the object,” he added.

At the time of the March 2011 meltdowns at the plant, there were 548 nuclear fuel rods totaling some 164 metric tons inside the No. 2 reactor, but they apparently melted down after the loss of power sources for the core cooling system, with part of the melted fuel penetrating through the pressure vessel before cooling down at the bottom of the containment vessel. The temperature of the reactor core topped 2,000 degrees Celsius at the time of the accident, melting metals including nuclear fuel inside the reactor.

The melted fuel has since come in contact with underground water flowing from the mountain side, generating radioactively contaminated water every day. In order to dismantle the reactor, it is necessary to take out the melted fuel, but high radiation levels inside the reactor had hampered work to locate the melted debris.

On Jan. 30, apart from the footage, TEPCO also released 11 pictures taken inside the No. 2 reactor. The images show the sediments in question stuck to metal grate footholds and water is dripping from the ceiling. Further analysis of those images may provide information on the current status of the disaster and positional clues to decommissioning work.

The in-house probe, however, has only focused on the No. 2 reactor, and there is no prospect of similar probes into the No. 1 and No. 3 reactors starting anytime soon as they were severely damaged by hydrogen explosions following the 2011 meltdowns.

In April 2015, TEPCO introduced a remote-controlled robot into the No. 1 reactor by way of a through hole in its containment vessel, but the device failed to locate melted fuel inside due to high radiation levels. While the utility is planning to send a different type of robot into the No. 1 reactor this coming spring, it would be difficult to carry out a survey similar to that conducted at the No. 2 reactor, as radiation levels are high around the through hole in the No. 1 reactor’s containment vessel, from which a device could access to right below the No. 1 reactor.

The No. 3 reactor, meanwhile, holds roughly 6.5-meter-deep contaminated water inside its containment vessel, a far larger volume than that accumulated at the No. 1 and No. 2 reactors. TEPCO has thus been developing a robot that can wade through water.

http://mainichi.jp/english/articles/20170131/p2a/00m/0na/007000c

 

January 31, 2017 Posted by | Fukushima 2017 | , , , | Leave a comment

Plans to remove nuclear fuel at Fukushima N° 3 reactor delayed again

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A member of the media, wearing a protective suit and a mask, looks at the No. 3 reactor building at Tokyo Electric Power Co’s (TEPCO) tsunami-crippled Fukushima Daiichi nuclear power plant in Okuma town, Fukushima prefecture, Japan February 10, 2016.

 

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

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

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

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

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

http://uk.reuters.com/article/uk-japan-fukushima-idUKKBN1592WI

January 26, 2017 Posted by | Fukushima 2017 | , , | Leave a comment

Fuel Removal from Fukushima Reactor 3 Likely to Be Put Off Again

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Tokyo, Nov. 18 (Jiji Press)–Tokyo Electric Power Co. Holdings Inc. <9501> is expected to face a further delay in the start of work to remove fuel from the storage pool at the No. 3 reactor of its disaster-stricken Fukushima No. 1 nuclear power station, it was learned Friday.
It now appears difficult to begin the work in January 2018, as currently targeted by the company, the sources said. The expected postponement is due to a delay in preparations necessary for the removal work.
All six reactors at the power station in Fukushima Prefecture, northeastern Japan, are set to be decommissioned, after the plant was knocked out by the March 2011 earthquake and tsunami. Three of the six reactors suffered core meltdowns in the accident.
The fuel removal from the No. 3 reactor pool was initially planned to begin during April-September 2015.
The No. 3 reactor building was heavily damaged by a hydrogen explosion soon after the March 11 disaster. As part of the preparations, TEPCO plans to install a cover and relevant equipment at the reactor.

http://jen.jiji.com/jc/eng?g=eco&k=2016111800715

 

 

 

 

 

November 19, 2016 Posted by | Fukushima 2016 | , , , | Leave a comment

NRA suggests Tepco to give up removing molten fuel from Fukushima plant

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On 2/19/2016, Fuketa, a committee member of NRA (Nuclear Regulation Authority) visited Fukushima plant and commented it needs to be considered if it is the best option to remove the molten fuel or not. He also suggested to remove a part of molten fuel to solidify the rest.

He added it depends on the research result.

The government of Japan and Tepco had been planning to remove the molten fuel at least from Reactor 1, 2 and 3 however it has not even been known where the molten fuel is accumulated.

http://www.logsoku.com/r/open2ch.net/newsplus/1455960843/

http://fukushima-diary.com/2016/02/nra-suggests-tepco-to-give-up-removing-molten-fuel-from-fukushima-plant/

 

February 25, 2016 Posted by | Fukushima 2016 | , | 1 Comment