Six years after Fukushima, robots finally find reactors’ melted uranium fuel — The New York Times

” FUKUSHIMA DAIICHI NUCLEAR POWER PLANT, Japan — Four engineers hunched before a bank of monitors, one holding what looked like a game controller. They had spent a month training for what they were about to do: pilot a small robot into the contaminated heart of the ruined Fukushima nuclear plant.

Earlier robots had failed, getting caught on debris or suffering circuit malfunctions from excess radiation. But the newer version, called the Mini-Manbo, or “little sunfish,” was made of radiation-hardened materials with a sensor to help it avoid dangerous hot spots in the plant’s flooded reactor buildings.

The size of a shoe box, the Manbo used tiny propellers to hover and glide through water in a manner similar to an aerial drone.

After three days of carefully navigating through a shattered reactor building, the Manbo finally reached the heavily damaged Unit 3 reactor. There, the robot beamed back video of a gaping hole at the bottom of the reactor and, on the floor beneath it, clumps of what looked like solidified lava: the first images ever taken of the plant’s melted uranium fuel.

The discovery in July at Unit 3, and similar successes this year in locating the fuel of the plant’s other two ruined reactors, mark what Japanese officials hope will prove to be a turning point in the worst atomic disaster since Chernobyl.

The fate of the fuel had been one of the most enduring mysteries of the catastrophe, which occurred on March 11, 2011, when an earthquake and 50-foot tsunami knocked out vital cooling systems here at the plant.

Left to overheat, three of the six reactors melted down. Their uranium fuel rods liquefied like candle wax, dripping to the bottom of the reactor vessels in a molten mass hot enough to burn through the steel walls and even penetrate the concrete floors below.

No one knew for sure exactly how far those molten fuel cores had traveled before desperate plant workers — later celebrated as the “Fukushima Fifty” — were able to cool them again by pumping water into the reactor buildings. With radiation levels so high, the fate of the fuel remained unknown.

As officials became more confident about managing the disaster, they began a search for the missing fuel. Scientists and engineers built radiation-resistant robots like the Manbo and a device like a huge X-ray machine that uses exotic space particles called muons to see the reactors’ innards.

Now that engineers say they have found the fuel, officials of the government and the utility that runs the plant hope to sway public opinion. Six and a half years after the accident spewed radiation over northern Japan, and at one point seemed to endanger Tokyo, the officials hope to persuade a skeptical world that the plant has moved out of post-disaster crisis mode and into something much less threatening: cleanup.

“Until now, we didn’t know exactly where the fuel was, or what it looked like,” said Takahiro Kimoto, a general manager in the nuclear power division of the plant’s operator, Tokyo Electric Power Co., or Tepco. “Now that we have seen it, we can make plans to retrieve it.”

Tepco is keen to portray the plant as one big industrial cleanup site. About 7,000 people work here, building new water storage tanks, moving radioactive debris to a new disposal site, and erecting enormous scaffoldings over reactor buildings torn apart by the huge hydrogen explosions that occurred during the accident.

Access to the plant is easier than it was just a year ago, when visitors still had to change into special protective clothing. These days, workers and visitors can move about all but the most dangerous areas in street clothes.

A Tepco guide explained this was because the central plant grounds had been deforested and paved over, sealing in contaminated soil.

During a recent visit, the mood within the plant was noticeably more relaxed, though movements were still tightly controlled and everyone was required to wear radiation-measuring badges. Inside a “resting building,” workers ate in a large cafeteria and bought snacks in a convenience store.

At the plant’s entrance, a sign warned: “Games like Pokemon GO are forbidden within the facility.”

“We have finished the debris cleanup and gotten the plant under control,” said the guide, Daisuke Hirose, a spokesman for Tepco’s subsidiary in charge of decommissioning the plant. “Now, we are finally preparing for decommissioning.”

In September, the prime minister’s office set a target date of 2021 — the 10th anniversary of the disaster — for the next significant stage, when workers begin extracting the melted fuel from at least one of the three destroyed reactors, though they have yet to choose which one.

The government admits that cleaning up the plant will take at least another three to four decades and tens of billions of dollars. A $100 million research center has been built nearby to help scientists and engineers develop a new generation of robots to enter the reactor buildings and scoop up the melted fuel.

At Chernobyl, the Soviets simply entombed the charred reactor in concrete after the deadly 1986 accident. But Japan has pledged to dismantle the Fukushima plant and decontaminate the surrounding countryside, which was home to about 160,000 people who were evacuated after accident.

Many of them have been allowed to return as the rural towns around the plant have been decontaminated. But without at least starting a cleanup of the plant itself, officials admit they will find it difficult to convince the public that the accident is truly over.

They also hope that beginning the cleanup will help them win the public’s consent to restart Japan’s undamaged nuclear plants, most of which remain shut down since the disaster.

Tepco and the government are treading cautiously to avoid further mishaps that could raise doubts that the plant is under control.

“They are being very methodical — too slow, some would say — in making a careful effort to avoid any missteps or nasty surprises,” said David Lochbaum, director of the nuclear safety project at the Union of Concerned Scientists, who was a co-author of a book on the disaster.

“They want to regain trust. They have learned that trust can be lost much quicker than it can be recovered.”

To show the course followed by the Manbo, Tepco’s Mr. Hirose guided me inside the building containing the undamaged Unit 5 reactor, which is structurally the same as two of the destroyed reactors.

Mr. Hirose pointed toward the spot on a narrow access ramp where two robots, including one that looked like a scorpion, got tangled in February by debris inside the ruined Unit 2.

Before engineers could free the scorpion, its monitoring screen faded to black as its electronic components were overcome by radiation, which Tepco said reached levels of 70 sieverts per hour. (A dose of one sievert is enough to cause radiation sickness in a human.)

Mr. Hirose then led me underneath the reactor, onto what is called the pedestal.

The bottom of the reactor looked like a collection of huge bolts — the access points for control rods used to speed up and slow down the nuclear reaction inside a healthy reactor. The pedestal was just a metal grating, with the building’s concrete floor visible below.

“The overheated fuel would have dropped from here, and melted through the grating around here,” Mr. Hirose said, as we squatted to avoid banging our heads on the reactor bottom. The entire area around the reactor was dark, and cluttered with pipes and machinery.

To avoid getting entangled, the Manbo took three days to travel some 20 feet to the bottom of Unit 3.

To examine the other two reactors, engineers built a “snake” robot that could thread its way through wreckage, and the imaging device using muons, which can pass through most matter. The muon device has produced crude, ghostly images of the reactors’ interiors.

Extracting the melted fuel will present its own set of technical challenges, and risks.

Engineers are developing the new radiation-resistant robots at the Naraha Remote Technology Development Center. It includes a hangar-sized building to hold full-scale mock-ups of the plant and a virtual-reality room that simulates the interiors of the reactor buildings, including locations of known debris.

“I’ve been a robotic engineer for 30 years, and we’ve never faced anything as hard as this,” said Shinji Kawatsuma, director of research and development at the center. “This is a divine mission for Japan’s robot engineers.” “

by Martin Fackler, The New York Times

source with photos, video and internal links

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Frozen soil wall nearly complete; NRA still doubts effect — The Yomiuri Shimbun

” A construction project to create frozen soil walls that encircle the ground beneath Tokyo Electric Power Company Holdings Inc.’s disaster-hit Fukushima No. 1 nuclear power plant is nearly finished.

Although TEPCO insists that the inflow of groundwater beneath the reactor buildings has been reduced, some members of the Nuclear Regulation Authority are skeptical about the project’s effectiveness. With ¥34.5 billion of public funds being spent on this project, the centerpeice of countermeasures for contaminated water, its cost-effectiveness is being carefully watched.

The project entails building a 1.5-kilometer-long frozen soil wall encircling the Nos. 1 to 4 reactors, with 1,568 pipes buried to a depth of about 30 meters below ground and coolant running through the pipes at minus 30 C to chill the soil.

The process is expected to prevent groundwater from flowing into the contaminated, highly radioactive underground water at such sites as the reactor buildings, and to avoid an increase of contaminated water.

The project began in March last year, and operations to freeze the final section, about seven meters wide, on the mountain side began in August this year.

The temperature of the underground soil has remained below zero, except for a part close the surface that is affected by outdoor air, meaning the project to create the 30-meter-deep walls is almost complete.

According to TEPCO’s assessment, before the project started, about 400 tons of groundwater was flowing into the ground underneath the reactor buildings and other sites daily.

TEPCO had initially calculated that the daily inflow of groundwater could decrease to dozens of tons once the walls were installed. However, between April and September the inflow per day was between 120 tons and 140 tons, and in October it was around 100 tons. That the amount of inflow has decreased in stages as the soil freezing progressed seems to prove that the project has been effective to a certain extent. However, it is unclear if the inflow will decrease further in the future.

In parallel with the frozen soil wall project, TEPCO dug about 40 subdrain wells to pump up groundwater before it flows into the reactor buildings. It also reinforced measures to prevent rainwater from soaking into the ground by paving 1.33 million square meters of surface.

In the NRA view, those measures must also contribute greatly to reducing the inflow, casting doubt on the frozen soil walls project by saying the effect of them alone may be limited. The agency has become distrustful of TEPCO and urged the company to verify the effects.

Hiroshi Miyano, visiting professor at Hosei University specializing in system safety, said: “There is sure to be a part that doesn’t freeze completely, and it’s impossible to reduce the inflow to zero. TEPCO must continue applying this measure in tandem with draining the nearby wells for a while.” ”

by The Yomiuri Shimbun

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Radioactivity and Operation Tomodachi documentary — Dailymotion

Here is an excellent documentary of the young military service men and women who aided the Japanese following the tsunami on March 11, 2011. They were exposed to high levels of radiation during their mission, Operation Tomodachi (which means friend in Japanese). They are in an ongoing class action lawsuit against the Fukushima No. 1 Nuclear Power Plant operator, Tokyo Electric Power Company (TEPCO), for allegedly not warning the military personnel of the high levels of radiation released from the power plant during the triple meltdowns. As a result, hundreds of these young men and women are suffering from debilitating health conditions, including cancer, and are seeking financial support and accountability. This documentary is in Japanese, but it is still worth watching.

published on Dailymotion

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Fukushima debris heading to intermediate storage facility — The Asahi Shimbun

” The Environment Ministry on Oct. 28 will start bringing radiation-contaminated soil to an intermediate storage site in Fukushima Prefecture, despite having acquired less than half of the land needed for the overall project.

The ministry’s announcement on Oct. 24 marks a long-delayed step toward clearing temporary sites that were set up around the prefecture to store countless bags of radioactive debris gathered after the triple meltdown at the Fukushima No. 1 nuclear power plant in March 2011.

The entire intermediate storage project will cover a 16-square-kilometer area spanning the towns of Futaba and Okuma around the nuclear plant. It is designed to hold up to 22 million cubic meters of contaminated debris for a maximum period of 30 years.

However, the ministry is still negotiating with landowners on buying parcels of land within the area. As of the end of September, the ministry had reached acquisition agreements for only about 40 percent of the land for the project.

The soil storage facility that will open on Oct. 28 is located on the Okuma side. It has a capacity of about 50,000 cubic meters.

Bags of contaminated soil stored in Okuma will be transferred to the facility, where the debris will be separated based on radiation dosages.

A similar storage facility is being constructed on the Futaba side.

The ministry initially planned to start full-scale operations of the entire storage facility in January 2015. However, it took longer than expected to gain a consensus from local residents and acquire land at the proposed site.

In March 2015, a portion of the contaminated soil was brought to the Okuma facility for temporary storage. ”

by The Asahi Shimbun

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Radioactive material accumulating on beaches near Fukushima — Red, Green and Blue

” Radioactive material from the Fukushima Dai-ichi nuclear power plant disaster is accumulating in the sands and brackish groundwater beneath beaches up to 60 miles away from the nuclear power plant itself, according to a new study published in the Proceedings of the National Academy of Sciences on October 2. The study is the first to identify accumulations of radioactive cesium in this previously unsuspected place.

“No one is either exposed to, or drinks, these waters, and thus public health is not of primary concern here,” the researchers noted in the new study, but “this new and unanticipated pathway for the storage and release of radionuclides to the ocean should be taken into account in the management of coastal areas where nuclear power plants are situated.”

The theory proposed in the new study is that high levels of radioactive cesium-137 were transported along the coast following the 2011 nuclear disaster, and subsequently got “stuck” to surfaces of grains of sand, rather than being nearly immediately dispersed and diluted as was “expected.”

“No one expected that the highest levels of cesium in ocean water today would be found not in the harbor of the Fukushima Dai-ichi nuclear power plant, but in the groundwater many miles away below the beach sands,” stated researcher Virginie Sanial of Woods Hole Oceanographic Institution.

That may well be true, but it’s also true that there people who acknowledge that accurately modeling systems as complex as those found in the natural world is essentially impossible — and who would argue that the precautionary principle should be kept in mind when dealing with something as dangerous as nuclear power. After all, predictions relating to outcomes are only ever going to be of related accuracy.

The press release provides more: “Cesium-enriched sand resided on the beaches and in the brackish, slightly salty mixture of fresh water and salt water beneath the beaches. But in salt water, cesium no longer ‘sticks’ to the sand. So when more recent waves and tides brought in salty seawater from the ocean, the brackish water underneath the beaches became salty enough to release the cesium from the sand, and it was carried back into the ocean.

“The scientists estimated that the amount of contaminated water flowing into the ocean from this brackish groundwater source below the sandy beaches is as large as the input from two other known sources: ongoing releases and runoff from the nuclear power plant site itself, and outflow from rivers that continue to carry cesium from the fallout on land in 2011 to the ocean on river-borne particles. All three of these ongoing sources are thousands of times smaller today compared with the days immediately after the disaster in 2011.

“The team sampled eight beaches within 60 miles of the crippled Fukushima Dai-ichi Nuclear Power Plant between 2013 and 2016. They plunged 3- to 7-foot-long tubes into the sand, pumped up underlying groundwater, and analyzed its cesium-137 content. The cesium levels in the groundwater were up to 10 times higher than the levels found in seawater within the harbor of the nuclear power plant itself. In addition, the total amount of cesium retained more than 3 feet deep in the sands is higher than what is found in sediments on the seafloor offshore of the beaches.”

So, what the new research does in essence is provide yet another example of the way that nuclear disasters and nuclear contamination can impact the natural environment in ways that aren’t immediately expected or intuitive to most. ”

by James Ayre

source with internal links

Fukushima’s decommissioning delays, challenges and unknowns remain roadblocks to cleanup — Beyond Nuclear

” Six and a half years after the Fukushima Daiichi triple meltdown, Japan’s government, the nuclear regulator and Tokyo Electric Power Company’s (TEPCO) most rudimentary plan of attack for recovery from radioactive catastrophe is delayed again. The first steps of decommissioning cannot legitimately begin until undamaged but highly radioactive “spent” fuel assemblies are removed from vulnerable reactor storage ponds, sufficiently cooled and re-contained in qualified dry storage casks.  Then, there are the three melted fuel cores that still must be located, retrieved and somehow re-contained. Where all of the massive radioactive contamination will go is a mystery.  In fact, there are an alarming number of challenges, continuing delays and unknowns that remain before securing the destroyed nuclear power station site and halting the ongoing release of radioactivity to the land, water and air.

Among the most immediate concerns is the management of 1007 highly radioactive and thermally hot irradiated nuclear fuel assemblies still in the two cooling pools perched atop the destroyed Units 1 and 2 outside of any containment structure. Each of the site’s six-units has an elevated nuclear waste storage pond. The site has a large common pool located near Unit 4. The government recently admitted that previously unknown, possibly undisclosed, damage in these irradiated fuel storage ponds and radioactive contamination has again delayed the plan to move the dangerous fuel assemblies by at least another three years, now 2023. Unit 3 remains on schedule in 2018 to begin the two-year transfer of 514 irradiated fuel assemblies from its rooftop storage pool to a jam-packed common onsite pool located at ground level. This common pool and its massive radioactive inventory requires reliable cooling power.  Unit 4 completed a three-year project to transfer its irradiated fuel into the common pool in 2014. The common pool now has 6,726 irrradiated fuel assemblies with a maximum design capacity of 6,840. As this common pool is already densely packed, it is ever more critical that Japan expedite the transfer of the sufficiently cooled irradiated nuclear fuel into qualified, individualized dry storage casks that can passively cool the hot nuclear waste without the need for water and electrical power. Currently, only 1,412 irradiated assemblies have been secured in onsite dry cask storage. These dry casks further need to be hardened against another natural disaster and possible terrorism.

The recurring delays at securing the irradiated fuel currently in wet pool storage (individual units to the common pool) and then into scientifically-qualified and hardened dry cask storage systems raises concern for public health, safety and the environment given the prospect of another large nearby earthquake causing a loss of cooling with the risk of a nuclear waste fire and radioactive releases. A 6.9 magnitude offshore earthquake on November 21, 2016 caused a temporary loss of cooling to wet storage systems at Fukushima Daiichi. Significant earthquakes of 6.0 to 6.9 magnitude occur in Japan on average 17 times per year, roughly one-tenth of all large earthquakes in the world. More severe earthquakes must be anticipated. The loss of cooling power and water to some or all of the more than 11,577 hot nuclear waste assemblies onsite outside of containment remains a significant public health, safety and environmental concern.

Japan is still technologically conceptualizing the “most challenging part” of Fukushima Daiichi’s decommissioning and the recovery of three missing melted reactor cores if and when they can be located. The unprecedented operation has now been delayed until 2019.  A viable technology for scooping up melted nuclear fuel does not yet exist. Re-containment and removal of the melted fuel cores is key to addressing the ongoing massive buildup of radioactive water now estimated at 800,000 tons that is being stored in growing onsite tank farms.  Groundwater flowing down into the reactor wreckage must be constantly pumped out, partially filtered of radioactivity and stored onsite in the large tanks. The tank farms themselves represent an additional environmental threat in the event of another severe earthquake that could rupture the structures with a radioactive flood into the ocean. ”

by Beyond Nuclear

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