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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

In search of melted fuel

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

The images showed black lumps scattered beneath the pressure vessel.

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

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

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

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

Radiation barrier

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

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

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

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

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

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

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

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

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

Fuel removal strategy

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

To remove or not

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

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

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

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

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

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

by Kazuaki Nagata

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6 Years after Fukushima disaster, robots continue search for radioactive fuel — Bloomberg, Insurance Journal; The Japan Times

” The latest robot seeking to find the 600 tons of nuclear fuel and debris that melted down six years ago in Japan’s wrecked Fukushima Dai-Ichi power plant met its end in less than a day.

The scorpion-shaped machine, built by Toshiba Corp., entered the No. 2 reactor core [on Thursday, Feb. 16] and stopped 3 meters (9.8 feet) short of a grate that would have provided a view of where fuel residue is suspected to have gathered. Two previous robots aborted similar missions after one got stuck in a gap and another was abandoned after finding no fuel in six days.

After spending most of the time since the 2011 disaster containing radiation and limiting ground water contamination, scientists still don’t have all the information they need for a cleanup that the Japanese government estimates will take four decades and cost 8 trillion yen ($70.6 billion). It’s not yet known if the fuel melted into or through the containment vessel’s concrete floor, and determining the fuel’s radioactivity and location is crucial to inventing the technology needed to remove it.

“The roadmap for removing the fuel is going to be long, 2020 and beyond,” Jacopo Buongiorno, a professor of nuclear science and engineering at the Massachusetts Institute of Technology, said in an e-mail. “The re-solidified fuel is likely stuck to the vessel wall and vessel internal structures. So the debris have to be cut, scooped, put into a sealed and shielded container and then extracted from the containment vessel. All done by robots.” … ”

Continue reading about the fuel-removal status of Fukushima No. 1’s Units 1 through 3.

by Emi Urabe and Stephen Stapczynski, Bloomerg via Insurance Journal

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Read a similar article by The Japan Times

Cleaner robot pulled from Fukushima reactor due to radiation — Beloit Daily News

” TOKYO (AP) — A remote-controlled cleaning robot sent into a damaged reactor at Japan’s Fukushima nuclear plant had to be removed Thursday before it completed its work because of camera problems most likely caused by high radiation levels.

It was the first time a robot has entered the chamber inside the Unit 2 reactor since a March 2011 earthquake and tsunami critically damaged the Fukushima Da-ichi nuclear plant.

Tokyo Electric Power Co. said it was trying to inspect and clean a passage before another robot does a fuller examination to assess damage to the structure and its fuel. The second robot, known as the “scorpion,” will also measure radiation and temperatures.

Thursday’s problem underscores the challenges in decommissioning the wrecked nuclear plant. Inadequate cleaning, high radiation and structural damage could limit subsequent probes, and may require more radiation-resistant cameras and other equipment, TEPCO spokesman Takahiro Kimoto said.

“We will further study (Thursday’s) outcome before deciding on the deployment of the scorpion,” he said.

TEPCO needs to know the melted fuel’s exact location and condition and other structural damage in each of the three wrecked reactors to figure out the best and safest ways to remove the fuel. It is part of the decommissioning work, which is expected to take decades.

During Thursday’s cleaning mission, the robot went only part way into a space under the core that TEPCO wants to inspect closely. It crawled down the passage while peeling debris with a scraper and using water spray to blow some debris away. The dark brown deposits grew thicker and harder to remove as the robot went further.

After about two hours, the two cameras on the robot suddenly developed a lot of noise and their images quickly darkened — a sign of a problem caused by high radiation. Operators of the robot pulled it out of the chamber before completely losing control of it.

The outcome means the second robot will encounter more obstacles and have less time than expected for examination on its mission, currently planned for later this month, though Thursday’s results may cause a delay.

Both of the robots are designed to withstand up to 1,000 Sieverts of radiation. The cleaner’s two-hour endurance roughly matches an estimated radiation of 650 Sieverts per hour based on noise analysis of the images transmitted by the robot-mounted cameras. That’s less than one-tenth of the radiation levels inside a running reactor, but still would kill a person almost instantly.

Kimoto said the noise-based radiation analysis of the Unit 2’s condition showed a spike in radioactivity along a connecting bridge used to slide control rods in and out, a sign of a nearby source of high radioactivity, while levels were much lower in areas underneath the core, the opposite of what would normally be the case. He said the results are puzzling and require further analysis.

TEPCO officials said that despite the dangerously high figures, radiation is not leaking outside of the reactor.

Images recently captured from inside the chamber showed damage and structures coated with molten material, possibly mixed with melted nuclear fuel, and part of a disc platform hanging below the core that had been melted through. ”

by Mari Yamaguchi

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Fukushima frozen wall status 2017; Unit 3 cover building installation — SimplyInfo.org

SimlyInfo.org shows a map of the current status of the frozen ice wall at Fukushima No. 1.

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Read SimplyInfo.org’s article on the current construction of a cover building for Fukushima Daiichi’s Unit 3, which will hopefully allow for robotic removal of spent fuel.

 

Fukushima’s ¥8 trillion cleanup leaves foreign firms in the cold — The Japan Times

” Cleaning up the Fukushima nuclear plant — a task predicted to cost 86 times the amount earmarked for decommissioning Japan’s first commercial reactor — is the mother of all salvage jobs. Still, foreign firms with decades of experience are seeing little of the spoils.

Safely dismantling the Japanese power plant, wrecked by the 2011 earthquake and tsunami, will cost about ¥8 trillion ($70 billion), the Ministry of Economy, Trade and Industry said on Dec. 9, quadrupling the previous estimate. While a contract to help clean up the facility would be a windfall for any firm with specialized technology, the lion’s share of the work has gone to local companies that designed and built most of Japan’s atomic infrastructure.

The bidding process for Fukushima contracts should be more open to foreigners, as Japan has never finished decommissioning a commercial nuclear plant, let alone one that experienced a triple meltdown, according to Lake Barrett, an independent adviser at Japan’s International Research Institute for Nuclear Decommissioning. While the Fukushima cleanup is unlike any nuclear disaster in history, foreign firms that have experience decommissioning regular facilities could provide much-needed support, according to Barrett, and even the plant’s operator, Tokyo Electric Power Co. Holdings Inc.

‘Cultural Resistance’

“Internationally, there is a lot more decontamination and decommissioning knowledge than you have in Japan,” Barrett, a former official at the U.S. Nuclear Regulatory Commission, said in an interview in Tokyo. “I hope the Japanese contracting system improves to get this job done safely. There is this cultural resistance — it is almost like there is an isolated nuclear village still.”

An opaque bidding process plays to the heart of criticisms put forward by independent investigators, who said in a 2012 report that collusion between the government, regulators and the plant’s operator contributed to the scale of the disaster.

Of 44 subsidized projects publicly awarded by the trade and economy ministry since 2014, about 80 percent went to the International Research Institute for Nuclear Decommissioning. The group, known as IRID, was established in the wake of the Fukushima disaster and is comprised entirely of Japanese corporations, according to the ministry’s website.

Japan’s trade and industry ministry awarded funds directly to only two foreign firms during the same period. Many of the contracts had only one or two bidders.

Of about 70 contracts awarded since the March 2011 disaster, nine have gone to foreign companies, according to an official in the ministry’s Agency of Natural Resources and Energy who asked not be named, citing internal policy.

To provide opportunities for foreign companies, the ministry has created an English website for bids and also provides English information sessions to explain the contracts, the official said.

Toshiba, Hitachi

IRID’s contracts are given to its members, including Toshiba Corp., Hitachi Ltd. and Mitsubishi Heavy Industries Ltd., which have partnerships and joint ventures with foreign firms, spokesman Yoshio Haruyama said by phone. While it doesn’t directly contract work to companies overseas, IRID taps foreign experts as advisers and participates in international collaborative projects, he said.

Mitsubishi Heavy has about five or six contracts through IRID, but can’t share how many partnerships it has with foreign firms, spokesman Shimon Ikeya said by phone. Hitachi has sub-contracts with foreign suppliers related to the Fukushima cleanup, but can’t provide details about these agreements because they aren’t public, a spokesperson said by email.

As of March, IRID had about ¥30 billion worth of ongoing contracts primarily related to research and development of fuel removal and waste treatment. IRID, which aims to “gather knowledge and ideas from around the world” for the purpose of nuclear decommissioning, doesn’t disclose how much of their money ultimately goes to foreign businesses, according to its spokesman. Barrett, its adviser, said he thinks it’s “very low,” but should ideally be 5 percent to 10 percent.

‘Nuclear Village’

Japan’s biggest nuclear disaster isn’t void of foreign technology. Toshiba, which owns Pennsylvania-based Westinghouse Electric Co., and Hitachi, which has a joint venture with General Electric Co., are tapping American expertise. A giant crane and pulley system supplied by Toshiba to remove spent fuel from the wrecked reactors employs technology developed by Westinghouse.

“We bring in knowledge from foreign companies, organizations and specialists in order to safely decommission the reactors,” Tatsuhiro Yamagishi, spokesman for Tepco, said by email. While the company can’t say the exact number of foreign firms involved in the Fukushima cleanup, companies including Paris-based Areva SA, California-based Kurion Inc. and Massachusetts-based Endeavor Robotics are engaged in work at the site, according to Yamagishi.

For foreign firms, however, independently securing contracts is still a tall order.

“When it comes to Japan’s nuclear industry, the bidding system is completely unclear,” Hiroaki Koide, a former assistant professor at Kyoto University Research Reactor Institute, said in an email. “The system is designed to strengthen the profits of Japan’s nuclear village,” he added, referring to the alliance of pro-nuclear politicians, bureaucrats and power companies that promote reactors.

Tepco’s annual cost to decommission its Fukushima plant may blow out to several hundred billion yen a year, up from the current estimate of ¥80 billion, the trade and industry ministry said in October. As of June, almost ¥1 trillion has been allocated for decommissioning and treating water at Fukushima, according to Tepco’s Yamagishi.

‘Ripe for Corruption’

With that much money at stake, Japan has become ground zero for a plethora of companies looking to benefit from the cleanup work. The structure of Japan’s nuclear industry and the closed procurement preferred by the utilities that operate atomic plants means that the most lucrative opportunities for foreign companies are in the area of subcontracting, according to a report by the EU-Japan Centre for Industrial Cooperation released in March.

“Foreign firms have long argued that the Japanese bidding process is one that is ripe for corruption due to a lack of openness and transparency,” Daniel Aldrich, professor and director of the security and resilience studies program at Northeastern University in Boston, said in an email. For nuclear decommissioning “there is even less clarity and transparency due to security and proliferation concerns,” he said.

Rigging Bids

The Japan Fair Trade Commission raided the offices of five companies last year in relation to rigged bids for maintenance contracts from Tepco, according to Jiji Press. Eleven road-paving companies were fined in September on projects to repair roads following the March 2011 earthquake and tsunami, Jiji reported.

Andrew DeWit, a political economy professor at Rikkyo University in Tokyo, agrees that the contract-awarding process isn’t transparent. A lot of foreign companies seek Japanese partners to better their chances, he said.

Purolite Corp., a closely held water purifying company, spent millions of dollars developing and testing a system that could be used to treat radioactive water at Fukushima. Pennsylvania-based Purolite partnered with Hitachi to help win a contract to use its technology at the wrecked facility.

Those plans didn’t pan out. Purolite is suing Hitachi in New York and Tokyo, alleging that Hitachi is using its technology at Fukushima in breach of agreements made in 2011, shutting it out of more than $1 billion in contracts, according to court documents filed in September.

Hitachi doesn’t comment on ongoing legal matters, a spokesperson said by email.

“With a smaller pool of competitors, firms can expand their profit margins,” said Northeastern University’s Aldrich. “There are French and Russian firms that have the technical expertise to participate in nuclear decommissioning processes, but it is unclear if they will be able to compete on a level playing field with Japanese firms, which have far more experience with Japanese regulations and expectations.” ”

by Stephen Stapczynski, Bloomberg

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Underwater robots to assist with Fukushima cleanup — Engineering and Technology Magazine

” Radiation-sensing amphibious robots will help speed up decommissioning of the damaged Fukushima nuclear power plant.

Currently under development by an international research team, the technology will finally provide means for assessing radiation in the submerged parts of the reactor.

“Our research will focus on developing a remote-operated submersible vehicle with detection instruments that will be able to identify the radioactive sources,” said Malcolm Joyce, Professor of Nuclear Engineering at Lancaster University, who leads the team.

“This capability does not currently exist and it would enable clean-up of the stricken Fukushima reactors to continue.”

Focusing particularly on dangerous neutron and gamma radiation, the robots will be able to assess how stable the situation is in the submerged parts of the nuclear power plant. For safe decommissioning, debris as well as fuel needs to be removed from the reactor, but the high risk is that some accidental reaction could be triggered by the manipulation.

“A key challenge with the remote-operated vehicle will be to design it so that it can fit through the small access ports typically available in nuclear facilities,” explained Barry Lennox, Professor of Applied Control at the University of Manchester. “These ports can be less than 100 mm in diameter, which will create significant challenges.”

Scientists from universities in Lancaster and Manchester are working on the project, which is funded by the Engineering and Physical Sciences Research Council, together with partners from Japan and private company Hybrid Instruments.

The remotely controlled vehicle that will come out of the project could also be used in decommissioning of undamaged nuclear sites, such as the Sellafield Reprocessing facility in Cumbria, or it could serve the oil and gas industry in assessing natural deposits of radioactive materials.

The reactors of the Fukushima Daiichi nuclear power plant, damaged during the 9.0-magnitude earthquake in 2011, had to be flooded with sea water to cool them down.

“A key task is the removal of the nuclear fuel from the reactors,” Joyce said. “Once this is removed and stored safely elsewhere, radiation levels fall significantly making the plant much more safer, and cheaper, to decommission.” ”

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