Latest look inside Fukushima’s ruins shows mounds of melted nuclear fuel
February 16, 2022
A remote-controlled robot has captured images of melted nuclear fuel inside Japan’s wrecked Fukushima nuclear plant.
A massive earthquake and tsunami in 2011 damaged cooling systems at the power plant, causing the meltdown of three reactor cores.
Most of their highly radioactive fuel fell to the bottom of their containment vessels, making its removal extremely difficult.
A previous attempt to send a small robot with cameras into the Unit 1 reactor failed, but images captured this week by a ROV-A robot show broken structures, pipes and mounds of what appears to be melted fuel.
Other debris was also submerged in cooling water, according to Tokyo Electric Power Company Holdings (TEPCO), the plant operator.
About 900 tonnes of melted nuclear fuel remain inside the plant’s three damaged reactors, including about 280 tons in Unit 1.
Its removal is a daunting task that officials say will take 30-40 years. Critics say that’s overly optimistic.
The robot, carrying several tiny cameras, obtained the internal images of the reactor’s primary containment vessel while on a mission to establish a path for subsequent probes, TEPCO said.
TEPCO spokesperson Kenichi Takahara said the piles of debris rose from the bottom of the container, including some inside the pedestal — a structure directly beneath the core — suggesting the mounds were melted fuel that fell in the area.
Takahara said further probes will be needed to confirm the objects in the images.
At one location, the robot measured a radiation level of 2 sievert, which is fatal for humans, Takahara said. The annual exposure limit for plant workers is set at 50 millisievert.
The robot probe of the Unit 1 reactor began on Tuesday and was the first since 2017 when an earlier robot failed to obtain any images of melted fuel because of the extremely high radiation and interior structural damage.
The fuel at Unit 1 is submerged in highly radioactive water as deep as 2 meters (6.5 feet).
TEPCO said it will conduct additional probes after analyzing the data and images collected by the first robot.
The investigation at Unit 1 aims to measure the melted fuel mounds, map them in three dimensions, analyze isotopes and their radioactivity, and collect samples, TEPCO officials said.
Those are key to developing equipment and a strategy for the safe and efficient removal of the melted fuel, allowing the reactor’s eventual decommissioning.
Details of how the highly radioactive material can be safely removed, stored and disposed of at the end of the cleanup have not been decided.
TEPCO hopes to use a robotic arm later this year to remove an initial scoop of melted fuel from Unit 2, where internal robotic probes have made the most progress.
Robot photos appear to show melted fuel at Fukushima reactor
MARI YAMAGUCHI – February 10, 2022
TOKYO (AP) — A remote-controlled robot has captured images of what appears to be mounds of nuclear fuel that melted and fell to the bottom of the most damaged reactor at Japan’s wrecked Fukushima nuclear plant, officials said Thursday.
A massive earthquake and tsunami in 2011 damaged cooling systems at the power plant, causing the meltdown of three reactor cores. Most of their highly radioactive fuel fell to the bottom of their containment vessels, making its removal extremely difficult.
A previous attempt to send a small robot with cameras into the Unit 1 reactor failed, but images captured this week by a ROV-A robot show broken structures, pipes and mounds of what appears to be melted fuel and other debris submerged in cooling water, plant operator Tokyo Electric Power Company Holdings said Thursday.
About 900 tons of melted nuclear fuel remain inside the plant’s three damaged reactors, including about 280 tons in Unit 1. Its removal is a daunting task that officials say will take 30-40 years. Critics say that’s overly optimistic.
The robot, carrying several tiny cameras, obtained the internal images of the reactor’s primary containment vessel while on a mission to establish a path for subsequent probes, TEPCO said.
TEPCO spokesperson Kenichi Takahara said the piles of debris rose from the bottom of the container, including some inside the pedestal — a structure directly beneath the core — suggesting the mounds were melted fuel that fell in the area.
Takahara said further probes will be needed to confirm the objects in the images.
At one location, the robot measured a radiation level of 2 sievert, which is fatal for humans, Takahara said. The annual exposure limit for plant workers is set at 50 millisievert.
The robot probe of the Unit 1 reactor began Tuesday and was the first since 2017, when an earlier robot failed to obtain any images of melted fuel because of the extremely high radiation and interior structural damage.
The fuel at Unit 1 is submerged in highly radioactive water as deep as 2 meters (6.5 feet).
TEPCO said it will conduct additional probes after analyzing the data and images collected by the first robot.
Five other robots, co-developed by Hitachi-GE Nuclear Energy and the International Research Institute for Nuclear Decommissioning, a government-funded consortium, will be used in the investigation over the next several months.
The investigation at Unit 1 aims to measure the melted fuel mounds, map them in three dimensions, analyze isotopes and their radioactivity, and collect samples, TEPCO officials said.
Those are key to developing equipment and a strategy for the safe and efficient removal of the melted fuel, allowing the reactor’s eventual decommissioning.
Details of how the highly radioactive material can be safely removed, stored and disposed of at the end of the cleanup have not been decided.
TEPCO hopes to use a robotic arm later this year to remove an initial scoop of melted fuel from Unit 2, where internal robotic probes have made the most progress.
https://www.yahoo.com/now/robot-photos-appear-show-melted-134212334.html
Delayed robot probe of Fukushima reactor begins
Feb. 8, 2022
The operator of the damaged Fukushima Daiichi nuclear power plant has begun its delayed robot probe of the inside of the facility’s No.1 reactor.
Tokyo Electric Power Company, or TEPCO, had planned to start the survey of the reactor’s containment vessel on January 12, but postponed it due to mechanical trouble.
Engineers noticed during preparations that data from radiation-measuring equipment installed in a robot was not shown correctly.
The engineers later found out that electromagnetic waves emitted from the robot’s device for extending and winding up cables had affected its radiometers. They solved the problem, and confirmed that the data was then shown accurately.
TEPCO started the survey on Tuesday morning. Officials of the utility say they initially planned to end the probe by August, but that the schedule will be moved back due to the delay.
The probe is part of efforts to remove molten fuel debris from inside the reactor.
Fukushima Operators Send Robot Into Worst-Hit Melted Reactor
Feb. 8, 2022
By MARI YAMAGUCHI, Associated Press
TOKYO (AP) — A remote-controlled robot on Tuesday was used to probe the hardest-hit nuclear reactor at Japan’s wrecked Fukushima plant, as officials push forward with clean-up operations that have been mired in delays and controversy.
An earthquake and tsunami in 2011 unleashed a disastrous meltdown at Fukushima Daiichi’s three reactors that partly sunk their radioactive cores into the plant’s concrete foundations, making removal extremely difficult.
The plant’s operator, Tokyo Electric Power Company Holdings, said the submersible robot was sent into Unit 1’s primary containment vessel to install a guiding path for five subsequent robots, which will attempt to asses and take samples of the melted fuel that emits fatally high radiation.
Tuesday’s probe followed five years after the operators sent another robot into the same and badly-damaged reactor, but failed to get any images of the melted fuel.
The robot-led work, which was postponed from mid-January due to mechanical glitches, is expected to last for a few days before full-fledged probes begin.
Earlier probes showed that the fuel at Unit 1 is submerged by highly radioactive water as deep as 2 meters (6.5 feet).
Five other robots, co-developed by Hitachi-GE Nuclear Energy and the International Research Institute for Nuclear Decommissioning, a government-funded consortium, will be separately sent in for the investigation over the next several months.
The probe at Unit 1 aims to measure the melted fuel mounds, map them in three dimensions, analyze isotopes and their radioactivity, and collect samples, Tokyo Electric officials said.
Those are key to developing equipment and a strategy for a safe and efficient melted fuel removal.
About 900 tons of melted nuclear fuel remain inside the plant’s three reactors, including about 280 tons in Unit 1, and its removal is a daunting task that officials say will take 30-40 years. Critics say that’s overly optimistic.
Remote-controlled robots with cameras have provided only a limited view of the melted fuel in areas too dangerous for humans to reach. In 2017, super-high levels of radiation and structural damage hampered investigating Unit 1.
Details of how the highly radioactive material can be safely removed, stored and disposed at the end of the cleanup have not been decided.
Tokyo Electric hopes to use a robotic arm to remove a first scoop of melted fuel later this year from Unit 2, where internal robotic probes have made the most progress.
Fisherman and residents of Fukushima’s outlying areas have protested the operator’s plans to discharge into the nearby sea radioactive waters from the reactors, after treating and diluting them to safely releasable levels.
“We don’t know if it’s debris.” Bumpy deposits at the bottom of the reactor.
February 9, 2022
On February 9, Tokyo Electric Power Company (TEPCO) released a video of the bottom of the containment vessel of the Unit 1 reactor at the Fukushima Daiichi Nuclear Power Plant (Okuma and Futaba towns, Fukushima Prefecture) taken by an underwater robot during an internal investigation. From the images, it was confirmed that orangeish bumpy deposits were spreading and adhering to the structure inside the vessel. It is possible that it is nuclear fuel (debris) that melted down during the accident. We don’t know if it is debris at this stage,” said Kenichi Takahara, a spokesman, at a press conference.
A video of the bottom of the containment vessel of the Unit 1 reactor shows a bumpy deposit spreading from the bottom center to the right side of the vessel at TEPCO’s Fukushima Daiichi Nuclear Power Plant (Courtesy of TEPCO)
According to TEPCO, it is unclear how high the confirmed deposit is; a survey in March 2017 confirmed a deposit of 90 centimeters high near this location. According to TEPCO, the height of the debris is unknown.
A part of the piping that was cut off for the introduction of the robots has sunk to the bottom of the containment vessel of the Unit 1 reactor (Courtesy of TEPCO)
By around 1:50 p.m. on the 9th, the underwater robot that was deployed on the afternoon of the 8th had moved through the water inside the containment vessel and attached four guide rings with a diameter of 30 centimeters at intervals to the structure inside the vessel. The purpose of these rings was to prevent cables from getting tangled in the structure when the robot, which will be used in the future, moves around, and we were finally ready for a full-scale investigation.
In the containment vessel of the Unit 1 reactor, an underwater robot moves through the vessel while attaching rings to the structure (TEPCO)
Oil-like suspended matter was observed on the water surface inside the containment vessel of the Unit 1 reactor. The yellow glow in the center is a pipe illuminated by a light (TEPCO)
The radiation level in the water was 1 to 2 sievert per hour. The radiation level in the water was 1 to 2 sievert per hour. The exposure limit for workers at the nuclear power plant is 50 millisieverts per year, and even if one were to enter the water, it would take only 1 to 3 minutes to reach the exposure limit, so people are not allowed to go near the water.
A worker opens a valve leading to the containment vessel of the Unit 1 reactor to insert a robot (Courtesy of TEPCO)
Workers insert an underwater robot outside the containment vessel of the Unit 1 reactor (Courtesy of TEPCO)
Of the three reactors that suffered core meltdowns in the March 2011 accident, video footage shows deposits of what appears to be debris in Units 2 and 3, but no debris was found in Unit 1 during the 2005 survey.
Removing the debris is the most difficult task, and it is estimated that a total of 880 tons has melted down in Units 1-3. TEPCO is aiming to collect a few grams of debris from the Unit 2 reactor by the end of this year. (Shinichi Ogawa, Kenta Onozawa)
https://www.tokyo-np.co.jp/article/159265?fbclid=IwAR08nc1U0duYKVLHyBgjGnoRnhVI944BMtWrN-6F8HNVGUlKXTpkkFAItm4
Fukushima Unit 1: First internal investigation in 5 years
2022/02/08
The Tokyo Electric Power Company (TEPCO) began an internal investigation of the containment vessel at the Unit 1 reactor of the Fukushima Daiichi Nuclear Power Plant on February 8. An underwater robot was used to collect information on the sediment accumulating at the bottom of the vessel and the molten nuclear fuel (debris) underneath. This is the first time in about five years since March 2017.
According to the images taken by the camera mounted on the robot, the bottom of the containment vessel was bumpy, as if something had accumulated there. A TEPCO official said, “We don’t know yet whether it is a deposit or not, and we will proceed with the investigation.
The investigation was scheduled to start on January 12, but was postponed due to problems during the preparation work. TEPCO is now reconsidering the process, which was set to last until August.
https://www.minpo.jp/globalnews/moredetail/2022020801001260?fbclid=IwAR0YiLHqKhJNuprOuxehkLnPzsAYBMFHgQ_0hcLHnWwpllUn9CFD2zSjR10
Robots to probe Fukushima No.1 reactor from Jan.
Thursday, Nov. 25, 2021
NHK has learned that the operator of the Fukushima Daiichi nuclear plant plans to start a delayed robot survey of a damaged reactor from mid-January.
Officials of Tokyo Electric Power Company say preparations are well under way to send submersible robots inside the containment vessel of the No.1 reactor.
The probe is part of efforts to remove molten fuel debris from the reactor that suffered a meltdown accident due to the 2011 earthquake and tsunami.
The utility originally planned to start the robot survey of the reactor in 2019.
It has been postponed because preparations, such as making a hole in the door of the vessel for the robots to go through, have taken time.
The officials say they are now installing equipment to remotely control the robots, and expect to carry out a survey for more than six months from mid-January.
They plan to use a total of six robots with different functions to find and examine nuclear debris, or deposits of a mixture of molten fuel and reactor parts, inside the containment vessel.
The robots will use ultrasonic devices to locate and measure how much debris there is, and how thick the deposit is. They are also expected to collect a small amount of samples.
Previous surveys at the plant confirmed the presence of deposits believed to be fuel debris in the No.2 and No.3 reactors, which also suffered meltdowns, but not in the No.1 reactor.
Probe shows challenges posed by melted fuel at Fukushima plant
TEPCO to survey suspected fuel debris in reactor
One more expensive robot to go probe in and to get fried
Toshiba unveils device for Fukushima nuclear reactor probe
Inside Fukushima Daiichi Unit 3 Robot Probe Inspections
TEPCO released three videos of its robot probe inspections inside unit 3. The videos provided some interesting information, showing some unexplained “blobs”, thick adhered substances, concrete spalling seen in fires, possible melted fuel formations, and thought to be solidified melted fuel around the lower end of a control rod.
TEPCO think the graphite gaskets sealing the control rod holes in bottom of the reactor vessel melted allowing molten fuel to flow through these holes to drip down into the reactor pedestal. Structures in the pedestal show some of the patterns created by the thick substances that appear to have splattered around the containment structures.
TEPCO cites 364 tons of fuel debris (melted fuel, internal reactor parts and control rods) to be expected at unit 3. The videos only show very small views of the damage found making it difficult to determine how much fuel debris was actually found inside unit 3’s pedestal.
Source : Tepco
http://www.tepco.co.jp/en/news/library/archive-e.html?video_uuid=qf64ne97&catid=61785
http://www.tepco.co.jp/en/news/library/archive-e.html?video_uuid=o6lm23vu&catid=61785
http://www.tepco.co.jp/en/news/library/archive-e.html?video_uuid=u10b97j8&catid=61785
Fukushima Unit 2 Radiation Readings Revised
TEPCO revised unit 2’s containment inspection radiation readings done earlier in 2017, claiming a set of instrument and calibration errors caused the inaccurate readings.
TEPCO claims that their camera based radiation estimates were too high due to an oversight where they forgot to reset the sensitivity threshold on the equipment that was reading camera interference.
The final claim made in the report for downgrading the radiation readings was that one of the 4 sensors was reading considerably higher than the other 3. When they took that sensor out of the readings the other 3 sensors read considerably lower.
Source : Tepco’s handout
http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170727_03-e.pdf
Likely Melted Fuel Heap Found Inside Fukushima Daiichi’s Reactor 3 Shows Future Removing Difficulties
Underwater robot finds likely melted fuel heap inside Fukushima reactor
This image captured by an underwater robot provided by International Research Institute for Nuclear Decommissioning on Saturday, July 22, 2017 shows heaps of solidified lava-like rocks believed to be nuclear fuel.
TOKYO (AP) — Images captured by an underwater robot showed massive deposits believed to be melted nuclear fuel covering the floor of a damaged reactor at Japan’s crippled Fukushima nuclear plant.
The robot found large amounts of solidified lava-like rocks and lumps in layers as thick as 1 meter on the bottom inside of a main structure called the pedestal that sits underneath the core inside the primary containment vessel of Fukushima’s Unit 3 reactor, said the plant’s operator, Tokyo Electric Power Co.
On Friday, the robot spotted suspected debris of melted fuel for the first time since the 2011 earthquake and tsunami caused multiple meltdowns and destroyed the plant. The three-day probe of Unit 3 ended Saturday.
Locating and analyzing the fuel debris and damage in each of the plant’s three wrecked reactors is crucial for decommissioning the plant. The search for melted fuel in the two other reactors has so far been unsuccessful because of damage and extremely high radiation levels.
During this week’s probe, cameras mounted on the robot showed extensive damage caused by the core meltdown, with fuel debris mixed with broken reactor parts, suggesting the difficult challenges ahead in the decades-long decommissioning of the destroyed plant.
TEPCO spokesman Takahiro Kimoto said it would take time to analyze the debris in the images to figure out debris removal methods.
http://mainichi.jp/english/articles/20170723/p2g/00m/0dm/033000c
Melted nuke fuel images show struggle facing Fukushima plant
What is believed to be nuclear fuel debris has accumulated at the submerged bottom of the containment vessel in the No. 3 reactor at the Fukushima No. 1 nuclear power plant in an image taken on July 22. Part of the collapsed metal scaffolding is seen at back right.
Images captured on July 22 of solidified nuclear fuel debris at the bottom of a containment vessel of the crippled Fukushima No. 1 nuclear power plant show the enormity of decommissioning of the facility.
Plant operator Tokyo Electric Power Co. said it will closely study the images from the No. 3 reactor’s containment vessel to determine the spread and amount of nuclear fuel debris.
After analysis, TEPCO will decide on a policy to retrieve the fuel debris.
The government and TEPCO plan to start the retrieval process in one of the three crippled reactors at the plant from 2021.
It will be a formidable task, given that a method of recovering debris that is stuck to the floor has yet to be considered.
The recent images were taken by a submersible robot, which was sent into the containment vessel on July 19, 21 and 22.
The No. 3 reactor’s containment vessel is filled with water to a depth of 6.4 meters.
On the final day, the remote-controlled robot was dispatched to the deepest part of the containment vessel.
The images showed that pieces that fell from the structure and deposited material accumulated to a height of about 1 meters at the bottom of the containment vessel.
In particular, what is believed to be nuclear fuel debris is scattered in the form of rocks in the area directly beneath the pressure vessel.
The latest investigation has confirmed TEPCO’s assumption made through analyses that most of the reactor’s nuclear fuel melted through the pressure vessel and accumulated at the bottom of the containment vessel.
It also discovered that the nuclear fuel debris has spread throughout the containment vessel.
The images marked the first confirmation through a robot probe of a large amount of nuclear debris in any of the embattled No. 1 through No. 3 reactors.
Japan Pictures Likely Show Melted Fukushima Fuel for First Time
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.”
Pictures taken on July 21 inside of Fukushima reactor. Source: Tokyo Electric Power Co. Holdings Inc.
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.”
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