Challenges ahead for debris removal at Fukushima — NHK World

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

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

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

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

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

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

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

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

by NHK World

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

by Chikako Kawahara, The Asahi Shimbun

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Japan pictures likely show melted Fukushima fuel for first time — Bloomberg

” New images show what is likely to be melted nuclear fuel hanging from inside one of Japan’s wrecked Fukushima reactors, a potential milestone in the cleanup of one of the worst atomic disasters in history.

Tokyo Electric Power Co. Holdings Inc., Japan’s biggest utility, released images on Friday showing a hardened black, grey and orange substance that dripped from the bottom of the No. 3 reactor pressure vessel at Fukushima, which is likely to contain melted fuel, according to Takahiro Kimoto, an official at the company. The company sent a Toshiba-designed robot, which can swim and resembles a submarine, to explore the inside of the reactor for the first time on July 19.

“Never before have we taken such clear pictures of what could be melted fuel,” Kimoto said at a press briefing that began at 9 p.m. Friday in Tokyo, noting that it would take time to analyze and confirm whether it is actually fuel. “We believe that the fuel melted and mixed with the metal directly underneath it. And it is highly likely that we have filmed that on Friday.”

If confirmed, the substance — which has the appearance of icicles — would be the first discovery of the fuel that melted during the triple reactor accident at Fukushima six years ago. For Tokyo Electric, which bears most of the clean-up costs, the discovery would help the utility design a way to remove the highly-radioactive material.

The robot, which is about 30 centimeters (12 inches) long, will search for melted fuel at the bottom of the reactor on Saturday. It is possible that the company will take more pictures of what could be melted fuel spread across the floor and lower levels, according to Tokyo Electric’s Kimoto. Fuel from a nuclear meltdown is known as corium, which is a mixture of the atomic fuel rods and other structural materials.

Early Signs

“It is important to know the exact locations and the physical, chemical, radiological forms of the corium to develop the necessary engineering defueling plans for the safe removal of the radioactive materials,” said Lake Barrett, a former official at the U.S. Nuclear Regulatory Commission who was involved with the cleanup at the Three Mile Island nuclear power plant in the U.S. “The recent investigation results are significant early signs of progress on the long road ahead.”

Because of the high radioactivity levels inside the reactor, only specially designed robots can probe the unit. And the unprecedented nature of the Fukushima disaster means that Tepco, as the utility is known, is pinning its efforts on technology not yet invented to get the melted fuel out of the reactors.

Removal Plans

The company aims to decide on the procedure to remove the melted fuel from each unit as soon as this summer. And it will confirm the procedure for the first reactor during the fiscal year ending March 2019, with fuel removal slated to begin in 2021.

Decommissioning the reactors will cost 8 trillion yen ($72 billion), according to an estimate in December from the Ministry of Economy, Trade and Industry. Removing the fuel is one of the most important steps in a cleanup that may take as long as 40 years.

Similar to the latest findings on Friday, Tepco took photographs in January of what appeared to be black residue covering a grate under the Fukushima Dai-Ichi No. 2 reactor, which was speculated to have been melted fuel. However, a follow-up survey by another Toshiba-designed robot in February failed to confirm the location of any melted fuel in the reactor after it got stuck in debris.

A robot designed by Hitachi-GE Nuclear Energy Ltd. also failed to find any melted fuel during its probe of the No. 1 reactor in March.

The significance of Friday’s finding “might be evidence that the robots used by Tepco can now deal with the higher radiation levels, at least for periods of time that allow them to search parts of the reactor that are more likely to contain fuel debris,” M.V. Ramana, professor at the Liu Institute for Global Issues at the University of British Columbia, said by email.

“If some of these fragments can be brought out of the reactor and studied, it would allow nuclear engineers and scientists to better model what happened during the accident.” ”

by Stephen Stapczynski, Bloomberg

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

” 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. ”

by The Mainichi

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Nuclear fuel debris that penetrated reactor pressure vessel possibly found at Fukushima No. 1 — The Japan Times

” Tepco on Monday found what may be melted nuclear fuel debris that penetrated the reactor 2 pressure vessel at the Fukushima No. 1 plant.

Tokyo Electric Power Company Holdings Inc. said more analysis and investigation is needed to confirm that the black lumps detected in the reactor’s containment vessel are indeed fuel debris.

The steel pressure vessel houses the nuclear fuel rods and is set up inside the surrounding containment vessel.

“At this point, it’s difficult to clearly identify what they are,” said Yuichi Okamura, general manager of Tepco’s nuclear power and plant siting division, during an evening news conference at the utility’s Tokyo headquarters.

Video footage from Monday’s probe showed black lumps that looked like something that had melted and then congealed, sticking to parts of a steel grating area at the base of the containment vessel.

The material could be melted paint, cable covers or pipe wrappings, Okamura said.

Still, this is the first time Tepco has detected anything in any of the facility’s three wrecked reactors that might be melted fuel rods since the outbreak of the crisis in March 2011. Okamura described the finding as “valuable information.”

The location of the debris and what form it is in are critical to eventually recovering the fuel.

Tepco plans next month to send in a remote-controlled robot equipped with a thermometer and dosimeter. Analyzing the temperature and radiation level will help identify whether the lumps are fuel debris, Okamura said.

The fuel melted after the March 11, 2011, earthquake and tsunami knocked out Fukushima No. 1’s power supply, including the vital cooling functions.

It is believed that reactor No. 2’s fuel rods melted and penetrated the bottom of the 20-cm-thick pressure vessel and fell in to the containment vessel.

Tepco has been conducting an investigation to check the interior of the containment vessel since last week.

In a previous try, workers inserted a rod equipped with a small camera as a precursor to sending in the remote-controlled robot.

The first attempt turned up nothing of note, but the utility then tried a longer rod — 10.5 meters long — on Monday that could capture images of the area beneath the pressure vessel.

The video footage also showed that water droplets were falling, which Tepco said must be cooling water being injected into the damaged pressure vessel.

Reactor 2 is one of three reactors, including 1 and 3, that experienced fuel meltdowns. ”

by Kazuaki Nagata

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Editorial: Cost estimate needed first to decommission Fukushima plant — The Asahi Shimbun

” An industry ministry panel of experts is tackling two key questions concerning the decommissioning of the crippled Fukushima No. 1 nuclear power plant.

One is how much money will be needed to decommission the plant’s reactors, three of which melted down. The other is who should foot the bill and how.

However, there are some serious flaws in the way the expert panel is working on these knotty questions, which could lead to a huge financial burden on the public.

First of all, the panel’s meetings are not open to the public. The main points of the discussions are published later, but many details, including who made specific remarks, are omitted.

The fate of Tokyo Electric Power Co., which operates the Fukushima plant and is responsible for its decommissioning, will be largely determined by whether it can restart its Kashiwazaki-Kariwa nuclear power plant in Niigata Prefecture.

Panel members include many business leaders who have been promoting nuclear power generation.

The outcome of the recent Niigata gubernatorial election underscored the strong opposition of local residents against TEPCO’s plan to bring the plant back online.

The panel’s lineup raises concerns that its discussions may be based on the assumption that the Kashiwazaki-Kariwa nuclear plant will eventually be restarted, despite the situation in the prefecture.

Another troubling fact is that the government has yet to announce any estimate of the total decommissioning cost.

In the panel’s first meeting, some members urged the government to swiftly present an estimate of the cost. In the second meeting, however, the Ministry of Economy, Trade and Industry only said that annual spending could grow to several hundreds of billions of yen from about 80 billion yen ($703 million) spent now.

The ministry says a specific estimate of the total cost will be announced as early as the end of the year, along with a plan for management reforms at TEPCO and a package of related measures the government will take.

But this timetable doesn’t make sense. Pinning down the overall decommissioning cost should be the starting point for the panel’s discussions.

With the conditions of the melted nuclear fuel remaining unclear, it is certainly difficult to accurately estimate the cost.

Still, an estimate should first be shown to ensure substantive debate on whether the method used for the work is appropriate and whether there are ways to curb the cost.

As for financing, the panel has supported the proposal that TEPCO should secure the necessary funds on its own through management reform over other options, such as the utility’s liquidation involving debt forgiveness by its creditors, tax financing by the government and a continuation of the current state control of TEPCO.

In an apparent attempt to stress the importance of TEPCO’s own efforts to save itself, the panel has also recommended that the Kashiwazaki-Kariwa nuclear plant should be spun off from TEPCO and integrated with the nuclear power business of another utility.

There is no disputing that TEPCO should push through thorough management reforms to prevent the public from shouldering part of the cost through tax financing or hikes in electricity rates.

The question, however, is whether the embattled utility’s own efforts will be enough to cover the entire decommissioning cost, expected to reach several trillions of yen.

If a plan based on the company’s own efforts fails and disrupts the decommissioning process, the reconstruction of disaster-hit areas in Fukushima Prefecture could be seriously delayed.

It is vital for the panel to win broad public support for its proposals on the national challenge of decommissioning the Fukushima No. 1 nuclear power plant.

This requires careful, exhaustive and reasonable debate, open to the public, on the cost and the financing method. ”

by The Asahi Shimbun, Oct. 27

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