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/

 
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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

“Possible” – “apparently” – “what is believed to be” – “suggesting” …
A lot of qualifiers here, and obligatory glee for our cute ‘little sunfish’, but they got one thing absolutely right in this report: they didn’t call it a ‘crippled plant’, it’s now officially the “destroyed plant”; and the most important fact or folly is buried towards the end: “to remove the melted fuel, a process expected to begin sometime after the 2020 Tokyo Olympics…
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TOKYO — An underwater robot captured images of solidified lava-like rocks Friday inside a damaged reactor at Japan’s crippled Fukushima nuclear plant, spotting for the first time what is believed to be nuclear fuel that melted six years ago.
Plant operator Tokyo Electric Power Co. said the robot found large amounts of lava-like debris apparently containing fuel that had flowed out of the core into the primary containment vessel of the Unit 3 reactor at Fukushima. The plant was destroyed by a massive earthquake and tsunami in March 2011.
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.
Experts have said the fuel melted and much of it fell to the chamber’s bottom and is now covered by radioactive water as deep as 6 meters (20 feet). The fuel, during meltdown, also likely melted its casing and other metal structures inside the reactor, forming rocks as it cooled.
TEPCO spokesman Takahiro Kimoto said it was the first time a robot camera has captured what is believed to be the melted fuel.
“That debris has apparently fallen from somewhere higher above. We believe it is highly likely to be melted fuel or something mixed with it,” Kimoto said. He said it would take time to analyze which portions of the rocks were fuel.
In an earlier survey Wednesday, the robot found severe damage in the vessel, including key structures that were broken and knocked out of place.
The robot, nicknamed “the Little Sunfish,” on Friday went inside a structure called the pedestal for a closer look. TEPCO plans to send the robot farther down on Saturday in hopes of finding more melted fuel and debris.
Experts have said the melted fuel is most likely to have landed inside the pedestal after breaching the core.
Kimoto said the robot probe in its two missions has captured a great deal of useful information and images showing the damage inside the reactor, which will help experts eventually determine a way to remove the melted fuel, a process expected to begin sometime after the 2020 Tokyo Olympics.
“It’s still just the beginning of the (decades-long) decommissioning. There is still a long way to go, including developing the necessary technology,” he said. “But it’s a big step forward.”
Locating and analyzing the fuel debris and damage in each of the 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.
The submersible robot, about the size of a loaf of bread, is equipped with lights, maneuvers with five propellers and collects data with two cameras and a dosimeter. It is controlled remotely by a group of four operators. It was co-developed by Toshiba Corp., the electronics, nuclear and energy company charged with helping clean up the plant, and the International Research Institute for Nuclear Decommissioning, a government-funded consortium.
The material has smooth thick edges making it unlikely to be rust, though there are considerable areas of rust inside containment. This material also does not match any known material from previous reactor meltdowns or melted fuel (corium) research. TEPCO makes no specific mention of this substance.
Evident inside the pedestal area is a pale colored thick substance that has adhered to solid surfaces. This same material is seen throughout the area of the containment structure inspected with a scope earlier. Now this same material is found inside the pedestal area.
Special credits to Fukushima Response Campaign & Fukuleaks

The Robot Probe Cannot Confirm Where is the Melted Fuel of Unit 1

24 03 2017

 

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 …

http://www.asahi.com/articles/photo/AS20170323005483.html

Tepco robot failed to capture images of melted fuel in reactor 1

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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.

http://www.japantimes.co.jp/news/2017/03/24/national/tepco-robot-failed-capture-images-melted-fuel-reactor-1/#.WNQ_hBh7Sis

Lethal radiation levels but no melted fuel found in Fukushima reactor water

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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.

https://www.rt.com/news/381879-fukushima-reactor-radiation-lethal/

 

Clearer water inside reactor 1 should help find melted fuel at Fukushima plant

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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.

http://www.asahi.com/ajw/articles/AJ201703200028.html

Radiation Spikes At Fukushima

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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.

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Arjun Makhijani is the President of the Institute for Energy and Environmental Research.

Transcript

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.

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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.

CURWOOD: Wow.

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.

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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.

http://www.loe.org/shows/segments.html?programID=17-P13-00007&segmentID=6