Tokyo Electric Power Company announced on February 23 that it had completed a robot probe survey lasting five days in the reactor containment vessel of Fukushima Daiichi nuclear power plant Unit 1.
Its goal was to confirm the whereabout of the melted nuclear fuel, but it was blocked by piping and could not put the camera in athe place where nuclear fuel could be seen.
Information necessary for taking out the nuclear fuel to decommission the reactor remains inadequate, and some voices began to question the robot conducted investigation method.
During the 5-day survey, there was also a point where the measuring instrument with an camera and a radiation dosimeter integrated together was hung up in a range from 0 to 3 meters from the bottom of the containment vessel, pipes and debris blocking its path in many points. The radiation dose in the water is from 3.0 to 11 Sv. Per hour. It was not possible to directly check the melted nuclear fuel.
TEPCO and the country are facing the decommissioning of a furnace …
A photo taken by a robot on Wednesday shows an underwater image of water pool on the bottom of the containment vessel of the reactor 1 at the Fukushima No. 1 plant
Tokyo Electric said Thursday that it failed to get any photos of potential fuel debris during a five-day probe of the primary containment vessel at reactor 1 of the Fukushima No. 1 power plant.
Tokyo Electric Power Company Holdings Inc., however, stressed that the investigation was worthwhile because its robot was able to take underwater images in the pool of water at its bottom and gauge its radiation level, which will help it estimate where the melted fuel lies.
The monstrous tsunami of March 11, 2011, tipped reactors 1, 2 and 3 into core meltdowns. The molten fuel rods then penetrated their pressure vessels before apparently dropping to the bottom of the giant containment vessels.
There is about a 2.5-meter deep water pool at the bottom of the primary containment vessel of reactor 1, and Tepco believes most of its melted fuel rods fell into it. Thus the main mission of the robot investigation this time was to capture underwater images.
The robot traversed gratings set up several meters above the vessel’s bottom and lowered a wire with a camera and dosimeter on its tip at 10 locations in the water.
Yet none of the images disclosed by Tepco showed anything resembling fuel debris, while parts of machinery, such as a valve, were captured.
When the robot dangled the camera on spots where Tepco thought there was a higher probability of locating the fuel, it instead found a 90-cm pile of sediment.
Tepco spokesman Yuichi Okamura said the sediment is probably not fuel debris, given the relatively low radiation readings, which ranged from 5.9 to 9.4 sieverts per hour.
Although the readings indicate extreme danger to people, Okamura said the readings would have been much higher had they been melted fuel rods. He said Tepco had no idea what the sediment is but added that there was a possibility it was covering the fuel.
According to Okamura, radiation readings get weaker by a hundredth if blocked by a meter of water. Since the robot detected readings from 5.9 to 9.4 sieverts per hour about 90 cm above the pool’s bottom, there might be something down there emitting strong radiation.
Tepco plans another investigation this month to pick up samples of the sediment.
While no fuel debris was recognized, Okamura said Tepco would review the data and analyze it further. By comparing radiation readings from various locations, the utility might be able to roughly pinpoint where the melted rods lay, he said.
He added that it was an achievement that the robot lasted for five days in the deadly radiation and that Tepco was able to retrieve it.
The Unit 2 reactor building at Tokyo Electric Power Co.’s Fukushima Daiichi nuclear power plant.
The level of radiation was measured by a special robot on Sunday at a point about 30cm (one foot) from the bottom of the containment vessel of Reactor 1, the Japan Times reported on Tuesday.
The current radiation level is 11 sieverts per hour, the highest detected in water inside the containment vessel. A person exposed to this amount of radiation would likely die in about 40 minutes, the Japan Times reports.
Sunday’s probe also revealed sandy substances building up at the bottom of the vessel. Tokyo Electric Power Company Holdings (TEPCO) officials, however, dismissed the idea that it might be melted nuclear fuel.
Experts have been looking for the melted fuel, which they believe has been accumulating in tainted water.
In March 2011, a 9.1 earthquake and the 15-meter tsunami that followed disabled the cooling system of Fukushima’s three reactors, causing the worst nuclear incident since the 1986 Chernobyl incident in Ukraine.
TEPCO, which operates the crippled power plant, has been obliged to deal with the consequences of the incident.
In February, a robot sent to explore Reactor 2 broke down because of the “unimaginable” levels of radiation, close to 650 sieverts per hour. This was the first time a robot entered this reactor since the plant’s meltdown in 2011.
Previously, the highest radiation level was recorded one year after the disaster and went up to 73 sieverts per hour.
TEPCO has promised extract the hazardous material stuck in the plant’s second reactor, its president Naohiro Masuda said, according to the Japan Times.
In December, TEPCO nearly doubled the estimated cost for the Fukushima clean-up to $188 billion.
A zone of more than 300 square miles around the plant is currently uninhabitable due to the continuing radiation.
A robot on March 18 took this image of a valve and a pipe in cooling water at the bottom of the containment vessel of the No. 1 reactor at the Fukushima No. 1 nuclear power plant.
Cooling water in the No. 1 reactor of the Fukushima No. 1 nuclear plant has improved in transparency, which should make it easier to pinpoint the location of melted nuclear fuel, the plant’s operator said.
The improved transparency, compared with the level two years ago, was confirmed on March 18, when a research robot took an image that clearly showed a valve and a pipe in the water at the bottom of the reactor’s containment vessel, Tokyo Electric Power Co. said March 19.
Devices on the robot measured radiation levels of 7.8 sieverts per hour on a metal stage for workers and 1.5 sieverts per hour in the water.
The research robot on March 20 and 21 will study areas where the melted nuclear fuel could exist.
Juan Carlos Lentijo of the International Atomic Energy Agency looks at tanks holding contaminated water and the Unit 4 and Unit 3 reactor buildings during a February 2015 tour of the tsunami-stricken Fukushima Daiichi nuclear power plant.
Almost six years after a tsunami caused a meltdown at the Fukushima Daiichi Nuclear Power Plant, the facility’s operator, Tokyo Electric Power (Tepco) faces overwhelming problems to clean up the site. Tepco now reports radiation in reactor 2 that would kill a worker in thirty seconds, and even destroys robots. Arjun Makhijani, the President of the Institute for Energy and Environmental Research and host Steve Curwood discuss the implications of this new report and the challenges of cleanup.
Arjun Makhijani is the President of the Institute for Energy and Environmental Research.
CURWOOD: It’s Living on Earth, I’m Steve Curwood.
Six years after an earthquake and resulting tsunami devastated Fukushima, Japan and led to the meltdown of three nuclear power reactors there on the coast, radiation levels have reached a staggering 530 sieverts an hour, many times higher than any previous reading. Tepco, the plant’s operator, claims that radiation is not leaking outside reactor number two, site of these readings, but concedes there’s a hole in the grating beneath the vessel that contains melted radioactive fuel.
Joining us now to explain what it all means is Arjun Makhijani, President of the Institute for Energy and Environmental Research. Welcome back to Living on Earth Arjun.
MAKHIJANI: Thank you, Steve. Glad to be back.
CURWOOD: So, this report from TEPCO seems serious, maybe even ominous. What what exactly is going on?
MAKHIJANI: Well, they are exploring the molten core of the reactor in reactor number two with robots, and the robot called Scorpion went farther into the bottom of the reactor in an area called “the pedestal” on which the reactor kind of sits and measured much higher levels of radiation than before. The highest level was 73 Sieverts per hour before and this time they measured a radiation level more than seven times higher. It doesn’t mean it’s going up. It just was in a new area of the molten core that had not been measured before.
CURWOOD: Still, it sounds to me like it’s problematic, that six years after this meltdown there’s such a high reading.
MAKHIJANI: It is a very high reading; they may encounter even higher readings. The difficulty with this high reading is that the prospect that workers can actually go there, even all suited up, becomes more and more remote. Robots are going to have to do all this work – That was mostly foreseen – but the radiation levels are so high that even robots cannot survive for very long. So now they’re going to have to go back to the drawing board and redesign robots that can survive longer or figure out how to do the work faster, and it’s going to be more costly and more complicated to decommission the site.
The lid of Unit 4’s Primary Containment Vessel lies close to the reactor building. The reactor was shut down for maintenance at the time of the accident.
CURWOOD: Remind us, Arjun, please, of the human impact of this kind of radiation. What’s toxic to humans?
MAKHIJANI: Right. So, if you get high levels of radiation in a short period of time, four Sieverts is a lethal dose for about half the people within two months. So, in 530 Sieverts per hour would give you a lethal dose in less than 30 seconds.
MAKHIJANI: So, it’s a very, very, very high level of radiation. That’s why people cannot go into the reactor and work there. That’s not the end of the bad news, but that’s quite a bit of it.
CURWOOD: OK. All right, there is more bad news. I’m sitting down. Tell me.
MAKHIJANI: Yes, so the bottom of the reactor under the reactor there is a grating and then under the grating there’s the concrete floor, and what this robot discovered — It was supposed to go around the grating and survey the whole area, but it couldn’t because a piece of the grating was deformed and broken. So, now it appears that some of the molten fuel may have gone through the grating and maybe onto the concrete floor. We don’t know because even robotic surveys are now difficult, and a high radiation turns into heat, so the whole environment around the molten fuel is thermally very hot, and so whether it is going through the concrete, whether it is under the concrete, I don’t know that we have a good grip on that issue.
CURWOOD: So, Arjun, what’s going on with the reactors one and three? There have been published reports that TEPCO, Tokyo Electric Power Company that has these reactors, hasn’t really taken a good look at those reactors. What do you know?
MAKHIJANI: Well, they have to develop the robots, and I think that developing them, by looking at reactor two, and they’re finding these surprises, radiation levels much higher than previously measured. It shouldn’t actually be unanticipated. The big surprise here was that a part of the grating was gone, and so that the molten fuel would possibly have gone through the grating. So, I think similar surprises will await reactors one and three because each meltdown will have a different geometry.
Storing contaminated water in tanks at the Fukushima Daiichi site presents an ongoing risk, says Makhijani.
URWOOD: So, now what about the decay products here? We’re starting with the Uranium family, but we wind up with Cesium and Strontium – Strontium 90. What risk is there of Strontium 90 getting into groundwater there?
MAKHIJANI: Yeah, so the peculiar thing about a nuclear reaction is the initial fuel, Uranium, is not very radioactive. It’s radioactive but you can hold the uranium fuel pellets in your hand without getting a high dose of radiation. After it’s gone through the nuclear reaction – Fission, that’s what generates the energy – the fission products which result from splitting the Uranium atom are much more radioactive than Uranium, and Strontium 90 and Cesium 137 are two of the products that last for quite a long time, half-life 30 years, and are quite toxic. So, Strontium 90 is specially a problem when it comes in to contact with water. It’s mobilized by water. It behaves like calcium, so if it gets into like sea water and get into the fish, the bones of the fish, or human beings, of course, it gets into the bone marrow and bone surface, increases the risk of cancer, leukemia. So it’s a pretty nasty substance, and Strontium 90 has been contacted with water. You know, rainwater goes and contacts the molten fuel. Groundwater may be contacting the molten fuel. So, we have had Strontium 90 contamination and discharges into the ocean. They also collect the water. They’ve got about more than 1,000 tanks of contaminated water stored at the Fukushima site. By my rough estimate may be about 100 million gallons of contaminated water is being stored there.
CURWOOD: What happens if there’s an earthquake?
MAKHIJANI: That’s exactly right. So about a week into the accident, I sent a suggestion to the Japan Atomic Energy Commission that they should buy a supertanker, put the contaminated water into the supertanker, and send it off elsewhere for processing. They do have a site in the north of Japan which was supposed to be for plutonium separation, but it could be used to support the cleanup of Fukushima. But they rejected that proposal more than once and decided to build these tanks instead. They have a decontamination process on-site, and there are a very vast number of plastic bags on the site filled with contaminated soil. Nobody wants the stuff and nobody knows what’s going to happen with it.
CURWOOD: It’s six years after the original meltdown. How much of a disaster is Fukushima today?
MAKHIJANI: Well, Fukushima is possibly the longest running, continuous industrial disaster in history. It has not stopped because the risks are still there. This is going to take decades to decommission the site, and then what is going to happen with all this highly radioactive waste, ‘specially the molten fuel? Nobody knows.
CURWOOD: Arjun Makhijani is President of the Institute for Energy and Environmental Research. Thanks for taking time with us today, Arjun.
MAKHIJANI: So good to be back with you, Steve.
Tepco’s scorpion-shaped robot. | IRID
Six years after the triple meltdown at the Fukushima No. 1 nuclear power plant, recent investigations underneath the damaged reactor 2 using cameras and robots came close to identifying melted fuel rods for the first time.
Experts say getting a peek inside the containment vessel of reactor 2 was an accomplishment. But it also highlighted how tough it will be to further pinpoint the exact location of the melted fuel, let alone remove it some time in the future.
The biggest hurdle is the extremely lethal levels of radiation inside the containment vessel that not only prevent humans from getting near but have also crippled robots and other mechanical devices.
Safely removing the melted fuel would be a best-case scenario but the risks and costs should be weighed against the option of leaving the melted fuel in the crippled reactors, some experts said.
“The work to probe inside the containment vessels and remove the fuel debris will be extremely tough because of the high radiation levels,” said Hiroshi Miyano, who heads a panel of the Atomic Energy Society of Japan, which is discussing ways to decommission the Fukushima plant and making recommendations to the government.
The government and Tokyo Electric Power Company Holdings Inc. are trying to find a way to remedy the situation but existing methods and technologies may not be sufficient, Miyano said.
In search of melted fuel
The world’s attention turned to the melted fuel rods in late January when Tepco inserted a 10-meter-plus tube equipped with a camera into the containment vessel of reactor 2 to capture images under the pressure vessel that housed the fuel rods.
The images showed black lumps scattered beneath the pressure vessel.
When the March 11, 2011, Great East Japan Earthquake and monstrous tsunami hit, the plant suffered a blackout and lost its key cooling system, triggering meltdowns in reactors 1, 2 and 3. The melted nuclear fuel rods penetrated the pressure vessels and fell into the containment vessels.
Tepco had put cameras inside the containment vessels several times in the past six years but January’s probe was the first to apparently find melted fuel debris.
“We understand that this is a big milestone. We could finally get to see what it was like underneath the pressure vessel,” said Yuichi Okamura, general manager of Tepco’s nuclear power and plant siting division.
“This is critical information in order to remove the fuel debris.”
But Tepco hasn’t confirmed that the black lumps are melted fuel, saying they could be paint or cable wrappings, and further investigation is needed.
Capturing the images may be progress but the robot and camera forays have not provided enough information about how to deal with the melted fuel.
Last month, Tepco sent a remote-controlled, scorpion-shaped robot in to further probe inside the reactor 2 containment vessel. But the robot failed before it reached under the pressure vessel after a tire became stuck.
The robot’s dosimeter measured radiation levels of 210 sieverts per hour — enough to kill humans instantly.
While 210 sieverts per hour indicate the melted fuel was nearby, the radiation crippled the robot’s electronics, including its semiconductors and cameras, indicating that the further use of robots to pinpoint the melted fuel will be difficult, robotics experts said.
There are computer chips “designed to withstand a certain level of radiation, but the level inside the containment vessel is totally different,” said Satoshi Tadokoro, a professor at Tohoku University who is an expert on disasters and rescue robots.
The radiation can damage a robot’s chips that serve as their brains, causing the devices to lose control, said Tadokoro, whose robots have also been used at the Fukushima plant.
“On top of the high level of radiation, the entrance (to the containment vessel) for the robot is very small,” restricting what types of robots can be used to hunt for the melted fuel, he said.
Tepco said the opening it created on the side of the reactor 2 containment vessel is about 11 cm in diameter.
Fuel removal strategy
Tepco is set to conduct internal probes of the reactor 1 containment vessel this month and is preparing similar missions for reactor 3.
The government and utility then plan to adopt a basic fuel removal strategy this summer and fine-tune the plan next year, with the actual fuel removal taking place in or after 2021.
There are essentially three options for the strategy, according to the Tokyo-based International Research Institute for Nuclear Decommissioning (IRID), which is developing technologies for the Fukushima plant decommission.
One option is to flood the containment vessels with water and use a crane above the reactors to hoist up the melted fuel. The second option is to carry out the same process but without water. The third is to install removal equipment through the side of the containment vessel.
There are merits and drawbacks to each option, said Shoji Yamamoto, who heads the team developing technologies to create the fuel removal devices at IRID.
The flooding option can block radiation using water, but if the fuel melts into the water, it could pose a risk of recriticality. The debris may need to be cut into pieces for removal, but this process would enable water to get between multiple pieces, creating the condition for recriticality. For nuclear chain reactions to happen there needs to be a certain distance between nuclear fuel and water.
If there is no water, the recriticality risk is minimal but the massive radiation levels cannot be blocked, Yamamoto said.
Tepco’s Okamura said being able to block radiation with water is a huge plus, but noted the reactor 2 containment vessel had cracks and holes that could let injected coolant water escape.
With the Three Mile Island nuclear accident in the U.S., the flooding option was used to retrieve the melted fuel in the 1980s. But the key difference was that all of the melted fuel stayed inside the pressure vessel, so it was easier to flood the reactor.
Because the melted fuel in reactors 1, 2 and 3 at the Fukushima plant all penetrated the pressure vessels and fell into the containment vessels, extracting it from the top or the side was a tough call, Yamamoto said, noting it was important to know the exact location of the melted fuel.
The distance between the top of the pressure vessel and the bottom of the containment vessel is about 45 meters and some parts inside the pressure vessels will need to be removed if Tepco tries to remove the debris inside the containment vessels from the top.
“If we know that the melted fuel is concentrated in the containment vessels, it will be more efficient to remove it from the side” because the entry point is closer, Yamamoto said.
Whatever option is decided, Yamamoto stressed that maintaining the fuel removal device will be difficult because the radiation will probably cripple it.
“The fuel removal device will be controlled remotely … it will be broken somewhere down the line and the parts will have to be replaced, considering its (ability to withstand) radiation,” he said.
“Given that, maintenance will have to be done remotely, too, and that will be a big challenge.”
To remove or not
Another option altogether is for Tepco to leave the melted fuel where it is.
During a media tour of the Fukushima No. 1 plant last month, Okamura of Tepco said the utility intended to collect the melted fuel because leaving it was “not an appropriate way” to manage nuclear fuel.
Miyano of the Atomic Energy Society of Japan said the debris must be removed because radioactive materials, including nuclear fuel, must be strictly controlled under international rules requiring strict monitoring.
Domestic nuclear power plant operators have to report the amount of nuclear fuel they have to the Nuclear Regulation Authority, which then reports to the International Atomic Energy Agency.
“There is the question of whether the government and Tepco decide not to remove the fuel debris. That would be an international issue,” said Miyano, adding that a consensus from the international community would be needed.
At the same time, Miyano said debate and analysis will be required to decide which choice would be best by looking at various factors, including how much it will cost to pick up all the melted fuel and where to store it.
Naohiro Masuda, head of decommissioning for the damaged Fukushima
On March 2, 2016, five years after the meltdown caused by the 2011 earthquake and tsunami, Naohiro Masuda the Chief Decommissioning Officer of the Fukushima nuclear plant said that operators have yet to locate where the melted nuclear fuel has gone: “There are melted fuels in units 1, 2 and 3,” Masuda said. “Frankly, we do not really know what the situation is for these (melted fuel), nor where it has gone.”
One year later the melted fuel has not yet been located with certainty. The two major problems are first to find where it is, and if found how to remove it from where it is. Both jobs rendered extremely difficult by high levels radiation frying the robots’ electronic semiconductors….
How will melted fuel at Fukushima plant be removed?
The Mainichi answers common questions readers may have about how disaster-response workers plan to remove melted fuel from the disaster-stricken Fukushima No. 1 Nuclear Power Plant.
Question: What methods are being considered for removing the fuel?
Answer: Innovation will be needed in order to avoid exposing people to radiation, due to the high levels of radiation released from the fuel. One method under consideration is to fill the containment vessels holding the fuel with water, since water has radiation-blocking properties.
Q: Aren’t the containment vessels ruptured?
A: Just like you can’t fill a cup with water if it has a hole in it, the water-filling method won’t work if the containment vessels are ruptured. If they are, then another possible method is removing the fuel from the air.
Q: Which way is better?
A: Both have advantages and disadvantages. The water method could require finding and patching holes in the containment vessels. The air method wouldn’t need this, but could cause dust and other particles containing radiation to be released. The national government and plant owner Tokyo Electric Power Co. (TEPCO) will discuss as early as this summer about these two plans.
Q: What is the fuel like now?
A: At the time of the meltdown, the reactors at the plant were heated to over 2,000 degrees Celsius. The melted fuel is thought to have mixed with equipment in the plant, concrete and other materials, and to have cooled to a rock-like state. It will have to be cut out and removed.
Q: How will the fuel be cut loose?
A: The plan is to use a remotely-controlled robot. However, high-tech electronics using semiconductors are easily broken by radiation. There are ideas to make the robot use hydraulics or springs for its movement, to make it resistant to the radiation. Robot technology will be the key to a successful decommissioning of the reactors.
(Answers by Mirai Nagira, Science & Environment News Department)
Although nearly six years have passed since the nuclear disaster at the Fukushima No. 1 Nuclear Power Plant in 2011, the search for the melted nuclear fuel inside the plant continues.
The operators of the plant, Tokyo Electric Power Co. (TEPCO), deployed over 800 workers inside the No. 2 reactor at the No. 1 plant between December 2016 and February 2017 — but so far, they have been unable to identify the location of the melted nuclear fuel.
TEPCO also plans to conduct studies inside the No. 1 and No. 3 reactors, but they are surely headed for a rough road as the search for the melted nuclear fuel continues to be extremely difficult. It is likely that struggles in that search will have a negative effect on the government and TEPCO’s target of completing the Fukushima decommissioning work between 2041 and 2051.
Apart from humans, robots have also been involved in the search. In the case of the No. 2 reactor for example, robots have been used in the following way.
The mission to get a good look inside the No. 2 reactor containment vessel had four steps; first, workers would drill a hole measuring 11.5 centimeters in diameter into the containment vessel wall, allowing robots to enter the vessel; then workers would insert a pipe with a camera into the hole so that the situation inside the vessel could be observed; a cleaning robot would then be sent inside the vessel to clear away any sediment in the way for the next robot; and finally a self-propelled, scorpion-shaped robot would travel to the area directly below the nuclear reactor, in search of the melted fuel. However, a number of unexpected problems emerged along the way.
Heavy machinery giant IHI Corp.’s Keizo Imahori, 38, who oversaw the mechanical boring of the containment vessel in December 2016, explains that, “A number of unexpected dents were found on the floor of the nuclear reactor building.” This was a surprising discovery for Imahori and his team. The presence of the dents meant that it would be difficult for machines to get sufficiently close to the necessary areas to drill a hole, which in turn has a detrimental effect on the entire search for melted nuclear fuel.
As an emergency measure, 1-meter by 1-meter iron sheets were used to cover the dents, but workers involved in laying the sheets were exposed to extra radiation because of this additional work.
In addition to the dents, the No. 1 to No. 3 reactors at the Fukushima plant, which first started operating in the 1970s, had many parts that have undergone repair work not reflected in their original construction plans. It was impossible to check such changes in the structure beforehand due to high levels of radiation.
There was another problem — the machines could not be attached to the side of the containment vessel, which meant workers were unable to carry out drilling work. This was caused by the containment vessel’s paint peeling away. The problem was solved after workers peeled off the paint by hand, but this also caused them to be exposed to more radiation.
The hole-boring process at the No. 2 reactor took approximately 20 days to complete — during which, workers involved in the project were exposed to approximately 4.5 millisieverts of radiation on average. Based on national guidelines, many companies involved in decommissioning work set the annual upper radiation dose at 20 millisieverts for their workers. Therefore, workers can only be involved in this project up to five times before their level of radiation exposure exceeds the limit. However, as Imahori points out, “We have no way of knowing the situation unless we actually go in there.”
Nevertheless, in order to ensure that highly-skilled professionals with expert knowledge in nuclear power plants continue to be involved in the search for the melted nuclear fuel, it is necessary to use robots as much as possible to reduce the amount of radiation to which humans are exposed.
At the same time, with the Fukushima No. 1 Nuclear Power Plant being somewhat like a “burning house,” manpower is also required to make effective progress with the search. Yasuo Hirose, of IHI Corp., states, “If we completely rely on robots for the decommissioning work, they will not be able to deal with any unexpected problems. The decommissioning process is likely to be a very long task.”
TEPCO and its partners launched a communication operation about the “scorpion” robot, which will be sent to the containment reactor of reactor n ° 2 in an attempt to locate the corium, ie the highly radioactive molten fuel, mixed with debris. It is not certain that the mission will be a success, the cleaning robot having lasted only two hours in this enclosure because of the extreme radiations, without being able to finish its task.
A press release announces what we already know and insists on the challenges: “every step is a new challenge for TEPCO, but TEPCo welcomes the challenges”. The company would be almost happy with the accident? It is accompanied by a promotional video with a comparison to the kendô fights posted on its Facebook page.
The Japanese nuclear industry wants to place itself on the decommissioning market and highlights the technologies being developed. This robot was designed by IRID, Toshiba and TEPCO. IRID benefits from public funds. As for Toshiba, it is almost bankrupt because of its nuclear branch and TEPCO is financially in a bad shape.
The press release and the video do not provide any relevant information and are in complete discrepancy with reality.
1. Current conditions of Unit 2 Primary Containment Vessel (PCV)
Nuclear fuel in the Primary Containment vessel (PCV) was exposed to the air and melted from the impact of March 2011 Great Earthquake.
As a result of the accident analysis, it was found that a portion of melted nuclear fuel might have been fallen inside the pedestal.
To remove fuel debris, it is necessary to investigate the PCV and clarify the conditions of debris and surrounding structures.
2. Outline of Unit 2 PCV investigation
[Purpose]: To obtain feedback information (deformation of platform, etc.) for the design and
development of next investigation devices inside the pedestal
To inspect conditions on the platform inside pedestal, fuel debris fallen to the CRD housing, and conditions of structures inside pedestal.
[Investigation point]: Platform and Control Rod Drive (CRD) will be investigated from the platform inside pedestal
3. Work steps for Unit 2 PCV investigation
4. Preparatory investigation results from X-6 penetration to CRD rail
4. Preparatory investigation results at the entrance of pedestal area
4. Preparatory investigation results of pedestal area
5. Additional results expected from the self-propelled investigation device
6. Investigation by the self-propelled investigation device to the end of CRD rail
6. Investigation by the self-propelled investigation device to the end of CRD rail
Reference: Investigation results on the platform inside the pedestal
Technical information for the media is available here:
In Japanese about the upcoming mission http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170215_08-j.pdf
And in English http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170215_01-e.pdf
And about radiation protection measures http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170215_09-j.pdf
And in English http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170215_02-e.pdf
Translated from L’ACROnique de Fukushima http://fukushima.eu.org/operation-de-communication-sur-le-robot-scorpion-qui-va-etre-envoye-dans-lenceinte-de-confinement-du-reacteur-n2/
The news headlines concerning Fukushima Daiichi over the last week have been rather confusing because some seem to imply that radiation levels have risen, as illustrated in this article by The Guardian:
Justin McCurry. February 3, 2017. Fukushima nuclear reactor radiation at highest level since 2011 meltdown. The Guardian, https://www.theguardian.com/environment/2017/feb/03/fukushima-daiichi-radiation-levels-highest-since-2011-meltdown
Radiation levels inside a damaged reactor at the Fukushima Daiichi nuclear power station are at their highest since the plant suffered a triple meltdown almost six years ago.
I have not interpreted the latest news from TEPCO as indicating that radiation levels have risen.
Rather, I interpret the latest news as indicating that TEPCO was successful in getting a robot into an existing high-radiation area in the plant, under the reactor-pressure vessel of unit 2, as explained in this excerpt from an article published in The Japan Times:
Highest radiation reading since 3/11 detected at Fukushima No. 1 reactor. The Japan Times, Feb 3, 2017,http://www.japantimes.co.jp/news/2017/02/03/national/fukushima-radiation-level-highest-since-march-11/#.WJiKT_L5-YQ
The radiation level in the containment vessel of reactor 2 at the crippled Fukushima No. 1 power plant has reached a maximum of 530 sieverts per hour, the highest since the triple core meltdown in March 2011, Tokyo Electric Power Co. Holdings Inc. said.
Tepco said on Thursday that the blazing radiation reading was taken near the entrance to the space just below the pressure vessel, which contains the reactor core…
Tepco also announced that, based on its analysis of images taken by a remote-controlled camera, that there is a 2-meter hole in the metal grating under the pressure vessel in the reactor’s primary containment vessel. It also thinks part of the grating is warped.
As the article observes, the hole was probably made when the fuel “escaped the pressure vessel after the mega-quake and massive tsunami triggered a station blackout.”
Simply Info, an excellent source of information and technical analysis about Fukushima, offers this summary analysis of the origins of the hole:
Fukushima Unit 2 Failure Point Found! Simply Info, Feb 2, 2017, http://www.fukuleaks.org/web/?p=16083
This large but concentrated hole appears to be the failure point for the unit 2 reactor pressure vessel (RPV). Melted fuel (corium) likely flowed through this hole and collected into the sump in the containment structure floor. The slow failure and small opening melted through the RPV likely allowed the molten fuel to burn down as it collected in the sump. This new visual evidence shows conditions that could have led to the molten fuel burning down into the reactor building concrete basemat. Without sufficient cooling, it could have potentially burned down through the basemat.
Simply Info has a follow up article where Nancy Foust offers her analysis. Here is her hypothesis concerning what happened to the fuel in reactor 2 after the earthquake 3/11:
Foust, Nancy. Feb 2, 2017. What The New Fukushima Unit 2 Inspection May Indicate. Simply Information, http://www.fukuleaks.org/web/?p=16050
What has been found seems to track with the theory of a slow failure and melt out that may have burned down into the concrete basemat rather than flowed out across the containment floor.
These reports beg the question as to where the reactor fuel from unit 2 is now located. Is it under the site? Is it in the basement? How structurally intact is the basement? TEPCO stated several years ago that water in the basement of unit 2 was encountering melted fuel and that this contaminated water was not entirely contained by the building (I have this documented in my published work on Fukushima).
And what are the conditions of reactors 1 and 3? These reactors remain too hot for robots.
There is a near continuous stream of atmospheric emissions that can be seen nightly on the webcam around unit 3. I always presumed that the MOX remains of unit 3 reactor’s fuel were responsible for that stream of visible heat/steam.
Could slumped fuel from unit 2 have ended up moving toward unit 3?
Here is a screenshot from today of the emission stream:
Well, no way to know for sure but I do feel safe concluding that Daiichi’s mysterious missing fuel is probably dispersing in ground water, ocean, earth, and atmosphere….
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TOKYO (Kyodo) — The radiation level inside the containment vessel of the No. 2 reactor at the crippled Fukushima Daiichi nuclear complex stood at 530 sieverts per hour at a maximum, the highest since the 2011 disaster, the plant operator said Thursday.
Tokyo Electric Power Company Holdings Inc. also announced that based on image analysis, a hole measuring 2 meters in diameter has been found on a metal grating beneath the pressure vessel inside the containment vessel and a portion of the grating was distorted.
According to TEPCO, the extremely high radiation level was found near the entrance area in the space just below the pressure vessel. The previously highest radiation level monitored in the interior of the reactor was 73 sieverts per hour.
The hole could have been caused by nuclear fuel that penetrated the reactor vessel as it overheated and melted due to the loss of reactor cooling functions in the days after a powerful earthquake and tsunami on March 11, 2011 hit northeastern Japan.
According to the image analysis, about 1 square meter of the grating was missing.
The plant operator plans to deploy a robot at the bottom of the reactor containment vessel, which houses the reactor pressure vessel, to check the conditions there.
The analysis follows TEPCO’s discovery Monday of a black mass deposited on the grating directly beneath the pressure vessel, possibly melted fuel after the unit suffered a meltdown along with two other Fukushima Daiichi reactors.
Images captured using a camera attached to a telescopic arm on Monday also showed part of the grating has gone. A further analysis of the images found a 2-meter hole in an area beyond the missing section on the structure.
If the deposits are confirmed as fuel debris, it would be the first time the utility has found any at the three units that suffered meltdowns.
Following one of the world’s worst nuclear disasters since the 1986 Chernobyl catastrophe, the No. 1 to 3 reactors suffered fuel meltdowns.
Portions of the fuel in the reactors are believed to have melted through the pressure vessels and accumulated at the bottom of the containment vessels.
The actual condition of the melted fuel has remained unknown due to high radiation levels.
A video taken on Jan. 30 shows the bottom of the No. 2 reactor’s pressure vessel at the Fukushima No. 1 nuclear power plant. Water used to cool the nuclear fuel is dripping, and possible melted fuel is seen strewn on grating for maintenance work. (Provided by Tokyo Electric Power Co.)
If confirmed, the first images of melted nuclear fuel at the Fukushima No. 1 nuclear plant show that Tokyo Electric Power Co. will have a much more difficult time decommissioning the battered facility.
The condition of what is believed to be melted fuel inside the No. 2 reactor at the plant appears far worse than previously thought.
Before the pictures were taken by a remote-controlled video camera on Jan. 30, TEPCO presumed that most of the nuclear fuel at the No. 2 reactor had remained within the reactor’s pressure vessel. That presumption was based on findings of a study conducted last year involving cosmic rays.
As a result, TEPCO did not expect the camera to detect possible nuclear fuel debris below the pressure vessel.
But the images showed black lumps scattered on a wire-mesh grating in the lower part of the containment vessel, which encloses the pressure vessel. This indicates that the fuel melted through bottom of the pressure vessel, spilled through the grating and fell on the floor of the containment vessel.
This image of the area below the No. 2 reactor’s pressure vessel at the Fukushima No. 1 nuclear power plant was taken on Jan. 30. Experts believe nuclear fuel melted the paint and components of equipment nearby and has hardened. (Provided by Tokyo Electric Power Co.)
The grating, which was used by maintenance workers before the disaster, was partially bent.
The images could show only part of the melted fuel in the No. 2 reactor. And there is still no indication on how widespread the black lumps were strewn, their volume and state.
TEPCO and government authorities in fiscal 2018 plan to decide on a method to retrieve the melted fuel from each of the three crippled reactors and start the removal work in 2021.
But a number questions remain unanswered, such as how to reduce workers’ radiation exposure, where the removed fuel will be kept, and when it will be disposed of.
The pictures raise another question: How will workers cut out the wire-mesh grating embedded with lumps of melted fuel?
The images were the first of possible nuclear fuel debris at the nuclear plant since the Great East Japan Earthquake and tsunami caused the triple meltdown there in March 2011.
Sasori (Scorpion), an investigative robot, is expected to be sent in the containment vessel of the No. 2 reactor of the Fukushima No. 1 nuclear power plant in February.
High radiation levels have prevented workers from entering the No. 2 reactor, as well as the No. 1 and No. 3 reactors at the plant.
A number of problems have hampered investigations by robots into the location of melted fuel at the No. 1 and No. 3 reactors.
The footage released on Jan. 30 by Tokyo Electric Power Co. (TEPCO) showing what could be melted fuel inside the No. 2 reactor at the disaster-stricken Fukushima No. 1 Nuclear Power Plant has highlighted the difficulty of salvaging the object, which is apparently stuck to footholds and other equipment at the facility.
TEPCO took the footage as part of its in-house probe into the No. 2 reactor and found that black and brown sediments — possible melted fuel — are stuck inside the reactor’s containment vessel over an extensive area.
“If what was captured in the footage was melted fuel, that would provide a major step forward toward trying our hand at unprecedented decommissioning work,” said Yoshiyuki Ishizaki, head of TEPCO’s Fukushima Revitalization Headquarters, during a press conference in the city of Fukushima on Jan. 30. “The finding may provide a major clue to future work to retrieve the object,” he added.
At the time of the March 2011 meltdowns at the plant, there were 548 nuclear fuel rods totaling some 164 metric tons inside the No. 2 reactor, but they apparently melted down after the loss of power sources for the core cooling system, with part of the melted fuel penetrating through the pressure vessel before cooling down at the bottom of the containment vessel. The temperature of the reactor core topped 2,000 degrees Celsius at the time of the accident, melting metals including nuclear fuel inside the reactor.
The melted fuel has since come in contact with underground water flowing from the mountain side, generating radioactively contaminated water every day. In order to dismantle the reactor, it is necessary to take out the melted fuel, but high radiation levels inside the reactor had hampered work to locate the melted debris.
On Jan. 30, apart from the footage, TEPCO also released 11 pictures taken inside the No. 2 reactor. The images show the sediments in question stuck to metal grate footholds and water is dripping from the ceiling. Further analysis of those images may provide information on the current status of the disaster and positional clues to decommissioning work.
The in-house probe, however, has only focused on the No. 2 reactor, and there is no prospect of similar probes into the No. 1 and No. 3 reactors starting anytime soon as they were severely damaged by hydrogen explosions following the 2011 meltdowns.
In April 2015, TEPCO introduced a remote-controlled robot into the No. 1 reactor by way of a through hole in its containment vessel, but the device failed to locate melted fuel inside due to high radiation levels. While the utility is planning to send a different type of robot into the No. 1 reactor this coming spring, it would be difficult to carry out a survey similar to that conducted at the No. 2 reactor, as radiation levels are high around the through hole in the No. 1 reactor’s containment vessel, from which a device could access to right below the No. 1 reactor.
The No. 3 reactor, meanwhile, holds roughly 6.5-meter-deep contaminated water inside its containment vessel, a far larger volume than that accumulated at the No. 1 and No. 2 reactors. TEPCO has thus been developing a robot that can wade through water.
Material found below the damaged No 2 reactor at Fukushima nuclear plant, believed to be melted fuel, from footage taken on 30 January.
Operator says it has seen what may be fuel debris beneath badly damaged No 2 reactor, destroyed six years ago in triple meltdown
Hopes have been raised for a breakthrough in the decommissioning of the wrecked Fukushima Daiichi nuclear plant after its operator said it may have discovered melted fuel beneath a reactor, almost six years after the plant suffered a triple meltdown.
Tokyo Electric Power (Tepco) said on Monday that a remote camera appeared to have found the debris beneath the badly damaged No 2 reactor, where radiation levels remain dangerously high. Locating the fuel is the first step towards removing it.
The operator said more analysis would be needed before it could confirm that the images were of melted uranium fuel rods, but confirmed that the lumps were not there before Fukushima Daiichi was hit by a powerful earthquake and tsunami on 11 March 2011.
The tsunami, triggered by a 9.0-magnitude quake, killed more than 18,500 people along the coast of north-east Japan and destroyed the backup power supply at Fukushima Daiichi, triggering the world’s worst nuclear accident since Chernobyl 25 years earlier.
Meltdowns in three of the plant’s six reactors forced about 160,000 people to evacuate and sent plumes of radiation across the Fukushima region. Many of the evacuees are unlikely to return home.
If Tepco can confirm that the black mass comprises melted fuel, it would represent a significant breakthrough in a recovery effort that has been hit by mishaps, the buildup of huge quantities of contaminated water, and soaring costs.
“This is a big step forward as we have got some precious data for the decommissioning process, including removing the fuel debris,” a Tepco official said.
Using a remotely controlled camera attached to the end of a 10.5-metre-long telescopic arm, Tepco technicians located black lumps on wire-mesh grating just below the reactor’s pressure vessel, local media reported.
The company plans to send a scorpion-like robot equipped with cameras, radiation measuring equipment and a temperature gauge into the No 2 reactor containment vessel next month, according to the Asahi Shimbun.
Three previous attempts to use robots to locate melted fuel inside the same reactor ended in failure when the devices were rendered useless by radiation.
Developing the means to remove the fuel – a task Tepco has said will become easier once it can gauge its condition – would be the biggest step forward in the mission to clean up Fukushima Daiichi since the removal of hundreds of spent fuel rods from a damaged reactor building in late 2013.
The delicate, potentially dangerous task of decommissioning the plant has barely begun, however.
Japanese media said last week that plans to remove spent fuel from the No 3 reactor building had been delayed, while decommissioning the entire plant was expected to take at least 40 years.
In December, the government said the estimated cost of decommissioning the plant and decontaminating the surrounding area, as well as paying compensation and storing radioactive waste, had risen to 21.5 trillion yen ($187bn), nearly double an estimate released in 2013.
A government committee estimated that 2.4 trillion yen of the total cost would be passed on to consumers through higher electricity bills.
Tokyo Electric Power Co. said Jan. 30 it may have finally pinpointed the location of melted fuel at the Fukushima No. 1 nuclear plant, nearly six years after the triple meltdown unfolded there.
If confirmation is made, it would represent a breakthrough in the daunting task of decommissioning the stricken nuclear plant.
A remote-controlled camera fitted on a long pipe detected black lumps on grating in the lower part of the containment vessel of the No. 2 reactor at the plant early on Jan. 30, TEPCO said.
The wire-mesh grating is located below the pressure vessel of the reactor. The lumps were not there before the Great East Japan Earthquake and tsunami on March 11, 2011, caused the nuclear disaster, according to TEPCO.
The utility plans to determine whether the lump is melted fuel based on images and radiation levels taken by an investigative robot and other data. The robot, called “Sasori” (scorpion) and fitted with two cameras, a dosimeter and a temperature gauge, will be sent into the No. 2 reactor containment vessel next month.
High radiation levels have hampered efforts at the nuclear plant to determine the condition and location of melted nuclear fuel.
TEPCO tried–and failed–three times to locate melted fuel using an industrial endoscope at the No. 2 reactor.
The latest investigation inside the No. 2 reactor began on Jan. 26 to locate the melted fuel.
The company is preparing to devise a method to retrieve the melted fuel in fiscal 2018 as part of the decommissioning work.
The image shows what is believed to be the remains of melted nuclear fuel that seeped through the grating below the pressure vessel of the No. 2 reactor at the Fukushima No. 1 nuclear power plant. (Provided by Tokyo Electric Power Co.)