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
Fukushima Daiichi: probe touched suspected fuel debris in reactor#2
The corium of reactor 2 of Fukushima Daiichi is clearly visible
TEPCO claims to have found ‘fuel debris’ in No. 2 reactor
Muons suggest location of fuel in unit 3
Some of the fuel in the damaged unit 3 of the Fukushima Daiichi plant has melted and dropped into the primary containment vessel, initial results from using a muon detection system indicate. Part of the fuel, however, is believed to remain in the reactor pressure vessel.
Structures within the reactor building of unit 3 can be seen in images obtained using muon data (Image: Tepco)
Muons are high-energy subatomic particles that are created when cosmic rays enter Earth’s upper atmosphere. These particles naturally and harmlessly strike the Earth’s surface at a rate of some 10,000 muons per square meter per minute. Muon tracking devices detect and track these particles as they pass through objects. Subtle changes in the trajectory of the muons as they penetrate materials and change in direction correlate with material density. Nuclear materials such as uranium and plutonium are very dense and are therefore relatively easy to identify. The muon detection system uses the so-called permeation method to measure the muon data.
Tokyo Electric Power Company (Tepco) installed a muon detection system on the first floor of unit 3’s turbine building. Measurements were taken between May and September this year.
Tepco said analysis of muon examinations of the fuel debris shows that most of the fuel has melted and dropped from its original position within the core.
Prior to the 2011 accident, some 160 tonnes of fuel rods and about 15 tonnes of control rods were located within the reactor core of unit 3. The upper and lower parts of the reactor vessel contains about 35 tonnes and 80 tonnes of structures, respectively.
The muon examination indicates that most of the debris – some 160 tonnes – had fallen to the bottom of the reactor pressure vessel and resolidified, with only about 30 tonnes remaining in the reactor core. Tepco said another 90 tonnes of debris remains in the upper part of the vessel.
The bulk of the fuel and structures in the core area dropped to the bottom of the reactor pressure vessel (RPV), Tepco believes. While part of the molten fuel is understood to have then fallen into the primary containment vessel (PCV), “there is a possibility that some fuel debris remains in the bottom of the RPV, though this is uncertain”, the company noted.
Similar muon measurements have already been conducted at units 1 and 2 at Fukushima Daiichi. Measurements taken at unit 1 between February and September 2015 indicated most of the fuel was no longer in the reactor’s core area. Measurements taken between March and July 2016 at unit 2 showed high-density materials, considered to be fuel debris, in the lower area of the RPV. Tepco said that more fuel debris may have fallen into the PCV in unit 3 than in unit 2.
The current understanding of fuel location in units 1-3 (Image: Tepco)
Tepco said the results obtained from the muon measurements together with knowledge obtained from internal investigations of the primary containment vessels using remote-controlled robots will help it plan the future removal of fuel debris from the damaged units.
http://www.world-nuclear-news.org/RS-Muons-suggest-location-of-fuel-in-unit-3-0210174.html
How to Clean Up Hundreds of Tons of Melted Nuclear Fuel
In more than 6 years they have not been able to really find yet the melted fuel, despite their beautiful PR stunt last week, and now they talk about which techniques to use to remove it. Maybe they should better find it first before talking how to remove it, that is if most of it has not been already vented and projected into our skies.
How to Clean Up Hundreds of Tons of Melted Nuclear Fuel
More than six years after three nuclear reactors melted down in Japan, the country is homing in on the lost fuel inside one of them. Japan’s biggest utility and owner of the wrecked Fukushima Dai-Ichi plant, Tokyo Electric Power Co. Holdings Inc., last week released images that for the first time showed what’s likely melted fuel inside the No. 3 reactor.
If confirmed, the nation will have to devise a way to remove the highly radioactive material, a mixture of melted nuclear fuel and reactor debris known as corium. The cleanup process that may last 40 years and cost 8 trillion yen ($72 billion) will require technology not yet invented.
Here are a few ways the removal could be done, including the government’s preferred approach by taking it out the side:
“Special tools and techniques will have to be developed to undertake such a task that has never been attempted before anywhere in the world,” said Dale Klein, an adviser to Tepco, as the utility is known, and a former chairman of the U.S. Nuclear Regulatory Commission. “Once Tepco has identified the characteristics of this material, then they can develop a plan to remove this material in a safe manner.”
The search for the fuel has left a trail of dead experimental robots specifically designed to find and photograph the estimated combined 600 metric tons of fuel and debris in the three melted reactors. While the No. 3 reactor was the last unit to be probed, its the first to produce a strong indication of where the fuel came to rest. The removal process is slated to begin in 2021.
Long-handled devices guided by a television monitor system were developed to remove fuel core debris at Three Mile Island in the U.S. after its 1979 meltdown. The so-called defueling process took from 1985 to 1990 and involved removing the partially melted fuel core from inside the pressure vessel of the No. 2 reactor, which remained intact. Fukushima offers a more complex challenge since three reactors suffered total meltdowns, with melted fuel rupturing pressure vessels and falling to the bottom of the units.
No such effort is being made at Chernobyl, where a concrete sarcophagus was used to entomb the wrecked plant that melted down in 1986.
Technology research and development should focus on removing fuel through the side, the Nuclear Damage Compensation & Decommissioning Facilitation Corp., Tepco’s top government shareholder, said Monday. That method is safer for workers than flooding the reactor, which would also require the management of radioactive water.
Japan will decide how it will remove the fuel by September, Industry Minister Hiroshige Seko said after the discovery last week, according to national broadcaster NHK.
New proposal suggests removing Fukushima plant’s melted nuclear fuel from side
A method to remove melted nuclear fuel debris on the bottom of the containment vessels of Fukushima No. 1 Nuclear Power Plant’s first, second and third reactors from the side was proposed by the Nuclear Damage Compensation and Decommissioning Facilitation Corporation (NDF) on July 31.
Hajimu Yamana, head of the NDF, which is tasked with considering how to remove fuel debris from the reactors, for the first time explained the organization’s specific method proposal to the heads of local governments at a countermeasures for the decommissioning and handling of the contaminated water council meeting held in Iwaki, Fukushima Prefecture.
The method would focus on prioritizing the removal of debris from the bottom of the vessels from the side, using robotic arms and other remote devices while flushing water over the debris.
However, ways to block radiation and countermeasures against the scattering of airborne radioactive dust still remain unsolved. The central government and Tokyo Electric Power Co. (TEPCO) plan to finalize their policy to remove the debris and amend the decommission schedule in September.
In all three of the reactors, contaminated water has collected at the bottom of the containment vessels. The NDF had previously considered a “flooding method” that would fill the containment vessels completely with water to block radiation from leaking. However, measures to repair the containment vessels and prevent leakage of the radioactive water would be difficult, so the plan was put aside for having “too many issues.”
https://mainichi.jp/english/articles/20170801/p2a/00m/0na/014000c
Footage from reactor 3 may force rewrite of Fukushima road map, officials say
This underwater robot was used in the recent probe of reactor 3 at the Fukushima No. 1 power plant.
The first images of melted fuel from the crippled Fukushima No. 1 power plant indicate that it did not burn through the pressure vessel of reactor 3, but exited through the holes used to insert the control rods, officials say.
While the landmark robot footage from the primary containment vessel of unit 3 is helping Tokyo Electric grasp the reality of the damaged fuel assemblies, it may also force it to rewrite the road map for decommissioning the meltdown-hit plant.
Tokyo Electric Power Company Holdings Inc., better known as Tepco, sent an underwater robot into reactor 3 earlier this month to confirm its hypothesis that the core — the fuel assemblies in the pressure vessel — broke apart and fell to the bottom, letting molten fuel burn through and drip into the primary containment vessel.
According to Tepco spokesman Takahiro Kimoto, however, the images taken beneath the PCV indicate the pressure vessel probably withstood the heat of the molten fuel. He said the fuel apparently seeped through the holes for the control rods.
“We do not presume that the vessel, which is 14 cm thick, melted and collapsed together with the fuel, but that part of the fuel instead made its way down through holes,” Kimoto said. The control rods are used to moderate the chain reaction and are inserted vertically into the core.
Tepco said it estimates reactor 3 has about 364 tons of fuel debris, and that similar amounts will be found in reactors 1 and 2. Removing the fuel from the reactors is the largest challenge in defueling the aged plant — a process that could take up to 40 years to complete.
The camera on the underwater robot also captured images of rubble around the fuel debris, which could slow the removal process. The rubble includes devices for supporting the control rods at the bottom of the PCV and scaffolding for maintenance workers beneath the pressure vessel.
Minister of Economy, Trade and Industry Hiroshige Seko said the government and Tepco will try to draft a plan for removing the melted fuel in September, with an eye to hammering out the specifics in the first half of fiscal 2018 and starting the work in 2021.
But the findings from reactor 3 may force them to alter the state’s road map for decommissioning Fukushima No. 1, officials said.
An entity providing technical support for the project has urged that efforts be made to remove the melted fuel from the submerged lower part of the PCV by keeping air in the upper part, according to a source familiar with the plan.
Although filling the PCV completely with water would largely reduce the radiation risk to the robot probes, the Nuclear Damage Compensation and Decommissioning Facilitation Corp. is reluctant to do so because it is damaged and the toxic water will just leak out, the source said.
At the other two reactors, Tepco thinks most of the fuel in reactor 1 fell to the bottom of the primary containment vessel, and that some of the fuel in reactor 2 remained in the pressure vessel. The company made the estimates based on cosmic ray imaging analysis and by sending robots and endoscopes into the PCVs of the two reactors.
http://www.japantimes.co.jp/news/2017/07/30/national/footage-reactor-3-may-force-rewrite-fukushima-road-map-officials-say/#.WX7Mha0ZOV5
Robotic Probe Has “Confirmed” Lumps that “Could Be” Fuel Debris in the No.3 Reactor…
Japan’s industry minister says the government hopes to have a policy in place by around September on how to remove melted fuel from the No.3 reactor of the disabled Fukushima Daiichi nuclear power plant.
Hiroshige Seko told reporters on Tuesday that a robotic probe has confirmed lumps that could be fuel debris in the No.3 reactor, giving researchers valuable information.
Seko said he hopes a policy on how to remove the debris can be formulated, based on an analysis and assessment of the probe’s findings.
During the survey last week, a submersible robot found lumps below the reactor pressure vessel and at the bottom of the containment vessel.
It’s the first time a probe has identified what could be a mixture of melted nuclear fuel and broken metal parts lodged inside a reactor container.
Removing the fuel debris would require the use of remote-controlled robots. It is considered the most challenging step in the process to decommission the reactor.
The industry minister suggested that the government plans to honor the existing timetable for decommissioning.
The plan calls for setting specific methods for removing fuel debris by the first half of 2018, so the actual work can begin by 2021.
Deposits in reactor likely to be fuel debris?
The operator of the damaged Fukushima Daiichi nuclear power plant released video footage on Monday of what is likely to be melted fuel debris.
Tokyo Electric Power Company, or TEPCO, found the solidified lumps during a robot inspection of the containment vessel of Fukushima’s wrecked No. 3 reactor. The 3-day survey ended on Saturday.
TEPCO had earlier only made public still images from the probe. The 4-minute video shows black or grey lumps hanging down close to a structure just below the reactor.
The lava-like lumps are piled in layers, a phenomenon unknown before the accident.
TEPCO officials say the debris is probably melted nuclear fuel mixed with broken reactor parts.
In addition to metal scaffolding and other structural components, rocks and sand-like sediment can be seen getting stirred up by the movement of the robot.
The government and TEPCO plan further analysis of the footage in order to determine methods for removing the debris.
https://www3.nhk.or.jp/nhkworld/en/news/20170724_27/
How Much Fuel Was in Fukushima Daiichi Unit 3 Reactor?
“Basically, at Daiichi Unit 3 TEPCO has misplaced 50 plus tons of reactor fuel that was “enriched” with plutonium and now were are being encouraged to think that shards of melted-fuel debris represent the entirety of the missing reactor core….a core that weighed more than a school bus….”
Via Majia’s Blog:
I’ve followed the Fukushima Daiichi disaster so closely for so long that I was surprised to discover this morning that I really don’t know exactly how much fuel was in reactor 3.
I have the data on fuel contained in the spent fuel pools, but NOT the data on fuel in the REACTOR CORES.
Below find the spent fuel pool data:
TEPCO. Integrity Inspection of Dry Storage Casks and Spent Fuels at Fukushima Daiichi Nuclear Power Station (16 November 2010), http://www.nirs.org/reactorwatch/accidents/6-1_powerpoint.pdf
[PARAPHRASING] The total spent uranium fuel inventory at Daiichi in March 2010 was reported as 1,760 tons. The 2010 report asserts that approximately 700 spent fuel assemblies are generated every year. The report specifies that Daiichi’s 3,450 assemblies are stored in each of the six reactor’s spent fuel pools. The common spent fuel pool contains 6291 assemblies. The amount of MOX fuel stored at the plant has not been reported.
SO, 700 spent fuel assemblies were generated at Daiichi each year. There were 6 reactors at Daiichi, although not all were operational at time of earthquake. Assuming they were operational, can we infer that each reactor core contained approximately 100 assemblies?
That estimate is supported by the US Nuclear Regulatory Commission’s information on fuel assemblies found here, which suggests a reactor may contain up to 200 assemblies, with each assembly containing 200 or more rods:
US NRC (2017, April 10). Fuel assembly (fuel bundle, fuel element). https://www.nrc.gov/reading-rm/basic-ref/glossary/fuel-assembly-fuel-bundle-fuel-element.html
A structured group of fuel rods (long, slender, metal tubes containing pellets of fissionable material, which provide fuel for nuclear reactors). Depending on the design, each reactor vessel may have dozens of fuel assemblies (also known as fuel bundles), each of which may contain 200 or more fuel rods.
The website titled Nuclear Power Net, described as non-profit and founded by nuclear engineers, suggests a typical reactor contains 157 fuel assemblies but those are composed of over 45,000 fuel rods (which is more than 200 in each assembly):
Nuclear Power Net (no date). http://www.nuclear-power.net/nuclear-power-plant/nuclear-fuel/
An 1100 MWe (3300 MWth) nuclear core may contain 157 fuel assemblies composed of over 45,000 fuel rods and some 15 million fuel pellets. Generally, a common fuel assembly contain energy for approximately 4 years of operation at full power. Once loaded, fuel stays in the core for 4 years depending on the design of the operating cycle. During these 4 years the reactor core have to be refueled.
During refueling, every 12 to 18 months, some of the fuel – usually one third or one quarter of the core – is removed to spent fuel pool, while the remainder is rearranged to a location in the core better suited to its remaining level of enrichment. The removed fuel (one third or one quarter of the core, i.e. 40 assemblies) has to be replaced by a fresh fuel assemblies.
The variation in data is puzzling but I think we can move forward assuming that there were approximately 100 fuel assemblies in each reactor.
A typical fuel assembly for a Pressured Water Reactor (PWR) “stands between four and five metres high, is about 20 cm across and weighs about half a tonne” according to the World Nuclear Association (http://www.world-nuclear.org/information-library/nuclear-fuel-cycle/conversion-enrichment-and-fabrication/fuel-fabrication.aspx).
USING THESE DATA POINTS, I can infer that Unit 3’s reactor core contained approximately 50-75 tons of fuel. Does that sound roughly correct? A ton is 2,000 pounds so 50 tons of fuel is 100,000 pounds. For metric users, that converts into 45359.237 kilograms.
Why is it so important that I determine how much fuel was in reactor 3?
The reason lies in the media representations of TEPCO’s robotic probe, Little Sunfish, which allegedly has (likely) located unit 3’s missing reactor fuel, illustrated in the media as “rocks on the floor”:
Kohei Tomida (July 23, 2017). Melted nuke fuel images show struggle facing Fukushima plant. The Asahi Shimbun, http://www.asahi.com/ajw/articles/AJ201707230012.html
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.
My point is not to deny that these found rocks might be nuclear fuel debris. Rather, my point is that these shards of melted fuel and debris can hardly be construed as representing the entirety of the fuel.
Put otherwise, there is no compelling evidence that TEPCO has located the majority of fuel that was contained in Unit 3.
I decided to search my notes, books, and the web validated statistics on how much fuel each reactor contained. I was struck by how little information is available about the missing fuel and the sanitized accounts of what happened at unit 3, the one running MOX fuel.
Basically, at Daiichi Unit 3 TEPCO has misplaced 50 plus tons of reactor fuel that was “enriched” with plutonium and now were are being encouraged to think that shards of melted-fuel debris represent the entirety of the missing reactor core….a core that weighed more than a school bus….
http://majiasblog.blogspot.fr/2017/07/how-much-fuel-was-in-fukushima-daiichi.html
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.”
Highly likely fuel debris found for 1st time at Fukushima plant
The operator of the crippled Fukushima Daiichi nuclear complex said Friday it found material likely to be nuclear fuel debris in its latest probe at one of the plant’s three damaged reactors.
It is the first time material “highly likely” to be melted fuel has been spotted inside a reactor at the complex since the 2011 massive earthquake and tsunami crippled the Fukushima nuclear power plant, the operator Tokyo Electric Power Company Holdings Inc. said.
Material found near the bottom of the damaged pressure vessel of the No. 3 reactor is likely to have been formed by fuel that melted, Takahiro Kimoto, a Tepco spokesman, said at a press conference.
“We think that the fuel inside the vessel melted and caused structures to fall from above,” Kimoto said.
Tepco is trying to confirm the condition of fuel debris inside the No. 3 reactor with a robot to start work on removing the debris in 2021, one of the most difficult stages of the decommissioning project that is expected to take at least 30 to 40 years to complete.
Decommissioning work has progressed slowly as radiation levels inside the reactors remain extremely high.
Water around 6.4 meters deep, which was injected into the reactor to cool fuel debris inside, has accumulated at the bottom of the containment vessel.
Tepco used a cylinder-shaped underwater robot with a diameter of 13 centimeters, dubbed “little sunfish.”
In Friday’s probe, following one on Wednesday, the robot looked inside the reactor’s containment vessel housing the pressure vessel, which is partially filled with contaminated water.
Another round of probe is scheduled on Saturday, where the remote-controlled robot is expected to swim deeper to the bottom of the containment vessel to locate a chunk of melted fuel that is believed to lie.
On March 11, 2011, a huge tsunami hit the six-reactor plant, located on ground 10 meters above sea level, and flooded power supply facilities.
Reactor cooling systems were crippled and the Nos. 1-3 units suffered fuel meltdowns in the world’s worst nuclear disaster since the 1986 Chernobyl crisis.
From January to March, Tepco conducted robot surveys including sending a self-propelled robot into the Nos. 1 and 2 reactors, where water levels are lower than the No. 3 reactor, but they failed to ascertain the condition of fuel debris.
Fuel debris possibly found in Fukushima Daiichi’s Reactor 3
Images show possible fuel debris
Engineers at the Fukushima Daiichi nuclear power plant are working to scrap the facility’s damaged reactors. For the first time, they’ve found what’s likely to be fuel debris in one of them.
The engineers have been trying to locate molten fuel in the No.3 reactor. The fuel is thought to have melted and fallen to the bottom of the containment vessel.
They lowered a submersible robot into the 6-meter-deep cooling water in the vessel. The image sent back by the robot shows an orange substance on a device that operates the fuel control rods. Objects shaped like icicles are also visible.
The engineers plan to use the robot to look for fuel debris at the bottom of the containment vessel.
Removing the molten fuel from the reactors is the biggest hurdle to decommissioning them.
https://www3.nhk.or.jp/nhkworld/en/news/20170722_04/
TEPCO surveys bottom of reactor containment vessel
The operator of the Fukushima Daiichi nuclear power plant has carried out another robotic survey in one of the damaged reactors. The probe is meant to confirm the existence and status of fuel debris consisting of molten fuel and reactor parts.
Officials of Tokyo Electric Power Company, or TEPCO, say the probe took place at the bottom of the containment vessel in the No.3 reactor on Saturday. The vessel’s bottom is thought to hold much fuel debris.
TEPCO used a robot designed to move through cooling water in the vessel.
The survey follows Friday’s release of photographs taken during the previous underwater robotic probe of the same vessel. The robot did not reach the vessel’s bottom during the first probe.
The images show rock-like lumps located near walls of a reactor-supporting structure and various other parts of the vessel.
TEPCO officials say it is very likely the lumps are fuel debris created after nuclear fuel in the reactor melted, mixed with reactor parts, and fell. If confirmed, this would be the first time fuel debris has been found in the No.3 reactor.
Robotic probes have so far failed to provide clear evidence showing the existence and status of fuel debris in other 2 damaged reactors.
Removing the fuel debris is one of the major hurdles to decommissioning the reactors which continues to emit extremely high levels of radiation.
https://www3.nhk.or.jp/nhkworld/en/news/20170722_22/
“Possible” melted fuel seen for first time at Fukushima plant
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