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Six Years After Fukushima, Robots Finally Find Reactors’ Melted Uranium Fuel


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 Mini-Manbo, at a demonstration in Yokosuka, Japan, is an underwater robot fitted with radiation-hardened materials and sensors. It succeeded where previous robots had failed, maneuvering around debris and avoiding excess radiation to locate the Fukushima plant’s spent, and highly dangerous, uranium fuel. Credit Ko Sasaki for The New York Times

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.

Robot finds potential fuel debris in reactor 3 at the Fukushima No. 1 power plant Video by International Research Institute for Nuclear Decommissioning, via The Japan Times

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.


The Unit 1 reactor at the Fukushima plant, whose top was blown away when it melted down on March 11, 2011. Credit Ko Sasaki for The New York Times

From left, Unit 2, damage to Unit 1, and a tank at the Naraha technology center, situated in the evacuation zone around the Fukushima plant, where the Mini-Manbo was tested. Credit Ko Sasaki for The New York Times

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.”

Continue reading the main story


A robot in a tank at the Naraha technology center, where engineers are testing new devices to explore the ruined Fukushima nuclear plant. Credit Ko Sasaki for The New York Times

Other projects at the Naraha technology center. “This is a divine mission for Japan’s robot engineers,” said its director of research and development, Shinji Kawatsuma. Credit Ko Sasaki for The New York Times

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.

Continue reading the main story


Mr. Hirose entering the reactor of the undamaged Unit 5. The Japanese government has set a target date of 2021 to begin extracting the melted fuel from at least one of the three destroyed reactors. Credit Ko Sasaki for The New York Times

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.”

NY Times

16 Comments on "Six Years After Fukushima, Robots Finally Find Reactors’ Melted Uranium Fuel"

  1. j.kruszewski on Sun, 19th Nov 2017 10:28 am 

    Interesting on how there’s no mention of the millions of radioactive contaminated water is and has been pouring into our oceans off the coast that is contaminating all oceans and killing fish, mammals and other aquatic beings and how the consumers of this radioactive fish (us) will be affected in years to come.

  2. Keith Bare on Sun, 19th Nov 2017 10:41 am 

    This is Absolute bullshit times a million propaganda

    Let’s say 2030 at the earliest to even think of retrieving molten spent fuel

    And a few trillion in costs ????

  3. Sissyfuss on Sun, 19th Nov 2017 11:10 am 

    This could all have been avoided if they had placed the backup generators higher on the hill next to them. Godlike technology in the hands of chimps.

  4. Nick Bennett on Sun, 19th Nov 2017 12:26 pm 

    Backup generators in the basement instead of on a hill? GENIUS.

    But in all seriousness we really do need a moderately decentralized renewable power grid. If Fukashima had it’s own wind generators they would could have cooled the reactor down before the water separated.

    Or if they had a Hydrogen bleeder system (a 120 year old invention) they could have bled off the hydrogen before it reached it’s LEL.

  5. Billyboy on Sun, 19th Nov 2017 1:09 pm 

    And where is all the contaminated nuclear waste going??? Back into the earth in a “protected” landfill??? And what about those Zillions of gallons of radioactive water pouring into the ocean? How much can nature fix itself?
    We all like our electricity but at what cost…how about that wind energy?

  6. Bull on Sun, 19th Nov 2017 1:27 pm 

    Yup they never talk about this but funny thing is in all the nuclear textbooks journals etc a single meltdown was considered one of the worst disasters that could happen!!!!! We have three but little to no mention other than japanese propaganda. They’ll save the planet through carbon taxes though don’t you worry. The 1% have nothing to worry about. For now! They’ve raped and pillaged the planet and want us the worker bees to carry their guilt.

  7. Bull ony on Sun, 19th Nov 2017 1:29 pm 

    Yup they never talk about this but funny thing is in all the nuclear textbooks journals etc a single meltdown was considered one of the worst disasters that could happen!!!!! We have three but little to no mention other than japanese propaganda. They’ll save the planet through carbon taxes though don’t you worry. The 1% have nothing to worry about. For now! They’ve raped and pillaged the planet and want us the worker bees to carry their guilt.

  8. don gordon on Sun, 19th Nov 2017 1:45 pm 

    Japan should be held accountable for the entire disaster.

  9. Bull on on Sun, 19th Nov 2017 1:53 pm 

    This is a real disaster that got away from them. They control it only through the media. I think this one is even keeping them awake at night so we’ll just focus on carbon to preoccupy the masses.

  10. Kris von Graff on Sun, 19th Nov 2017 2:11 pm 

    If they had built a Westinghouse-style pressurized water reactor rather than a GE boiling water reactor, then all the radioactivity and problems would have been in an enclosed concrete containment building (see TMI), rather than using the GE open reactor building design. All to spend a few less Yen, they polluted the world with radioactivity. And protected diesel generators would have been nice. Note that a sister site only a few dozen miles south was saved from just such a disaster by the quick thinking of those site personnel, rigging a new electric source for the cooling pumps! Cool heads in a time of crisis prevailed.

  11. JJC on Sun, 19th Nov 2017 5:49 pm 

    Dumping the radioactive water in the ocean did not affect anything, even though I was fishing there last week and caught a 47 LB anchovy !!

  12. Go Speed Racer on Sun, 19th Nov 2017 7:57 pm 

    Hey JJC did it glow green?

    Anybody who said put the generators further up the hillside, was fired for insubordination,
    their retirement plan cancelled, their kids
    sold into slavery, their wife sent to Syria
    to join ISIS and their house burnt to the
    ground. That way nobody would dare
    speak up and The Management (capital T, capital M) made sure the engines were put where they would be flooded. Because
    The Management knows best.

    The Management is now very proud that they
    receive countless billions of dollars in
    government clean-up subsidy. They are more
    more profitable now, than in the old days
    when they produced electricity.

  13. David P Baganha on Mon, 20th Nov 2017 10:57 am 

    “The Management is now very proud that they
    receive countless billions of dollars in
    government clean-up subsidy. They are more
    more profitable now, than in the old days
    when they produced electricity”

    Is that a Joke ? Profitable ? Is that all that’s on their minds ?

    So they’ve found the Corium ! Now what ? How & what is the time frame for removing & containing it ?

    & what about the flowing Ground water that continues to Contaminate the Pacific Ocean with Radioactivity ? & the Thousands of Gallons of Radioactive Waste water stored on site ? This whole Debacle is a modern day episode of the keystone cops !

  14. Go Speed Racer on Mon, 20th Nov 2017 5:28 pm 

    Well David yeah it’s Keystone cops.

    I have been explaining for a long time
    the only way to clean up that facility is
    pile up a bunch of old tires and sofa’s
    Next to each reactor building.

    But instead of light the sofa’s on fire,
    Get yourself a little ole hydrogen fusion
    Nuclear bomb from the fireworks stand.

    Put the fusion bomb in between reactors
    3 and 4. Light fuse and get away.

    KABLAM-O , thenwhole complex turns
    into tiny little dust particles and blows away
    to the ocean winds. The wind will blow
    it to North Korea.

    Bikini Atoll style, a few years later ya gots
    a nice blue lagoon that glows at night, run
    your speedboat around with your girlfriend
    on the front deck.

    Gas drinks postcards and hamburgers
    at the dock back by shore.

    Oh ya know why they don’t do that?
    Not cause the sofa’s we’re hard to come by.
    It’s cause if the whole problem got solved
    in 20 minutes, no more government payout
    on the welfare cleanup program. They want
    those checks keep flowing.

    And it’s not the cost of the fusion bomb,
    they got a special going right this minute.
    Between now and New Year’s, buy two
    fusion warheads and they will throw in
    4 bazooka’s and a shoulder launched tank
    buster at no extra charge. And a handful
    of lighter punks, snakes and a dozen
    smoke grenades.

  15. Kenz300 on Mon, 20th Nov 2017 6:42 pm 

    nuclear energy – sold as “too cheap to meter”
    We were lied to.
    Now “too costly to clean up”
    The clean up cost will go on FOREVER.

    No more nuclear plants should ever be built and existing one should be phased out of the next 15 years.

    Wind or solar are safer, cleaner and cheaper.

  16. Go Speed Racer on Tue, 21st Nov 2017 3:17 am 

    We should build more nuclear power plants.

    We can pile all the spent fuel rods up in a
    great big heap so it glows green at night.

    We can throw old sofa’s on the pile of
    spent rods, and it will all self-ignite into
    a great big beautiful nuclear waste,
    sofa, and tire fire. It will look
    pretty as Chernobyl. They said a lot of
    beautiful blue flames went way far up
    into the sky, while the reactor burnt up.

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