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TEPCO prepares to remove fuel from damaged reactor

 

May 28, 2018
The operator of the damaged Fukushima Daiichi nuclear power plant has started laying the groundwork to retrieve fuel from one of the plant’s reactor buildings. It’s a crucial step toward scrapping the complex.
 
Tokyo Electric Power Company began the work on Monday to move 615 fuel rod units from a storage pool on the top floor of the No. 2 reactor to a more secure location.
 
The No. 2 reactor is one of 3 at the plant that melted down in the 2011 accident. Radiation levels inside the reactor building remain high.
 
TEPCO will open a hole measuring 5 by 7 meters in the building’s wall and send a robot through it to measure radiation levels inside.
 
A section of the wall will be divided into 29 blocks, each with a handle to facilitate its removal.
 
From a control room some distance from the reactor building, TEPCO officials will remotely operate a machine to remove the blocks.
 
The work is expected to continue until mid-June.
 
The plant operator will measure radiation levels before deciding how to retrieve the fuel rods. The company plans to start retrieving the fuel in fiscal 2023.
 
TEPCO official Hiroshi Noda says that although the decommissioning work for the No. 2 reactor has just started, it’s a major step forward.
 
He says the company will make sure that the work will have no impact on the environment.

 

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June 5, 2018 Posted by | Fukushima 2018 | , | Leave a comment

New Data for Unit 2’s Missing Fuel

u2_pedestal_web.jpg
TEPCO published a Roadmap document right before leaving for Golden Week vacation. In this document is a 30+ page section of new data for unit 2’s missing fuel.
 
TEPCO has given varying explanations for unit 2’s meltdown and fuel location. Two muon scans have been completed for unit 2. The first found no fuel remaining in the RPV. A second scan by TEPCO claimed to have found some fuel in the bottom of the RPV, our analysis of the scan found otherwise. It is likely that all of the fuel inside the reactor vessel melted and all of it except for some residues is no longer in the RPV.
 
Fuel debris volume:
The volume of fuel debris inside unit 2 is difficult to calculate due to a number of factors. The debris is spread between multiple areas including the floor grate level, the pedestal floor and whatever debris may have burned down into the pedestal floor. The total volume of the fuel core is known for unit 2 but the exact size of the pedestal diameter is not known.
 
A fuel debris volume estimate was made for unit 1 based on known data and meltdown events at that reactor. Unit 1 is smaller than unit 2 in both fuel core size and size of the reactor structures. The general reactor building sizes and the fuel core sizes should be something that could roughly scale up for unit 2. Unit 1 estimate showed a fuel volume of all of the fuel and related melted structural materials as 60-100 cm deep.
 
Inside unit 2 about 50% of the pedestal floor was found to be covered with 70 cm of fuel debris. Additional fuel debris in an unknown volume is on the floor grate level. An unknown amount is burned down into the pedestal concrete basemat. Further fuel debris may be in lower reactor piping systems or the outer drywell floor. Unit 2’s fuel debris volume would also be reduced as the control rod drive array and bottom head of the reactor vessel are still intact. That large amount of metal structural material is known to not be part of the melted fuel debris in unit 2.
 
What has been found on inspection may be all of the fuel debris for unit 2 if a portion of the material is burned down into the pedestal basemat concrete. In most meltdown scenarios that is a given assumption unless the containment structure was heavily and repeatedly flooded with water at the time the fuel first dropped into the pedestal. With unit 2 that is an unlikely scenario.
 
There is an alternative possibility that a large amount of the radioactive materials in the fuel vaporized during the meltdown and escaped containment. This concept requires more investigation to confirm vaporization but this possibility for unit 2 is not completely ruled out. Fused microparticles containing nuclear fuel and other meltdown related materials have been found over a wide swath of Fukushima and beyond. Unit 2’s refueling floor blow out panel and reactor well containment gasket are one escape path for micro materials, steam and other gasses. Unit 2’s venting attempts are another concern. TEPCO has claimed the direct drywell venting of unit 2 didn’t work and the rupture disc for this system did not break as intended. TEPCO has provided no conclusive proof of this claim such as photos, video or other tangible evidence for this claim. Due to this, there is still the possibility that unit 2’s venting released some of these fused microparticles of fuel.
 
Radiation levels:
The radiation levels found in unit 2’s pedestal including a reading close to the fuel debris pile were between 7-8 Sieverts/hour. The high reading found along the CRD rail in 2017 was between 200-300 Sieverts/hour. These pedestal readings are drastically lower than what would be expected near an unshielded large pile of fuel debris.
By comparison, radiation levels along the outer containment wall in 2012 were within a similar range of the lower readings found on the CRD rail in 2017.
 
The elephant’s foot at Chernobyl, measured within the first year of the disaster, converted to Sieverts was 100 Sievert/hour.
 
Underwater readings in unit 1’s torus room near what is suspected fuel debris, taken in 2012 were 100,000 to 1 million Sieverts/hour.
 
Radiation levels near the fuel debris indicate that the top layers of debris may be mostly metallic materials with little fuel.
 
Radiation levels indicate that fuel bearing debris is not in the visible layer in the pedestal. (other possible locations – vaporized/vented, beneath the metallic layer, sml amounts in piping).

Roadmap document, section on unit 2:
http://www.tepco.co.jp/nu/fukushima-np/roadmap/2018/images1/d180426_08-j.pdf#page=3

TEPCO photo page for unit 2 findings:
http://photo.tepco.co.jp/date/2018/201804-j/180426-01j.html

May 10, 2018 Posted by | Fukushima 2018 | , , | Leave a comment

Lethal radiation detected at Fukushima plant reactor 2

 

 
 
The operator of the crippled Fukushima Daiichi nuclear power plant has released the results of its latest probe of the site.
 
A remote-controlled inspection of the Unit 2 reactor containment vessel last month detected a maximum of 8 sieverts per hour of radiation.
 
Experts say exposure to such radiation for about an hour would be fatal.
 
Officials from Tokyo Electric Power Company, or TEPCO, released the results on Thursday.
 
They said the radiation reading was taken near what appeared to be fuel debris, the term used to describe a mixture of molten fuel and broken interior parts.
 
The finding shows that nearly 7 years after the meltdowns, radiation levels remain so high that they present a major challenge to decommissioning work.
 
During the probe, 42 sieverts per hour of radiation was also detected outside the foundations of the reactor.
 
But officials said they have doubts about the accuracy of the reading because a cover had not been removed from the measuring instrument at the time.
 
They added that they don’t know why radiation levels were lower near the suspected fuel debris than around the foundations.
 
They gave a number of possible reasons, such as that cooling water may have washed radioactive materials off the debris.
 
TEPCO’s Chief Decommissioning Officer, Naohiro Masuda, says the company will develop debris-removal technology based on the outcome of the investigation.
 
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February 1, 2018 Posted by | Fukushima 2018 | , , | Leave a comment

The corium of reactor 2 of Fukushima Daiichi is clearly visible

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Fukushima Blog by Pierre Fetet
Translation Hervé Courtois
 
It has been almost seven years since this deadly magma was created thanks to the imbecility of men. 7 years that we talk about it without ever really seeing it. And now Tepco, in January 2018, unveils, for the first time and in a very discreet manner, some very telling images of the corium of Fukushima Daiichi’s reactor 2.
 
Above illustration: screenshot made from a Tepco video
 
At first, all the media published again the photos provided by Tepco, where one sees for example a piece of a fuel assembly’s handle. It was deduced that the rest had melted but nothing more could be said.
 
In a second time, 3 days later, Tepco added a video of 3min34 that shows a selection of footage filmed inside the containment. In this video, we see very precisely corium flows that have solidified on metal structures under the reactor vessel.
 
The camera that filmed this hyper-radioactive material was designed to support 1000 Sieverts. But this device can not hide the ionizing radiation that forms many random clear points on the film.
 
The men who manipulated the probe outside the containment were certainly irradiated because the dose rate is still very high in the reactor. But Tepco has not yet released this information.
 
To summarize in images what happened in March 2011, the corium of reactor 2 passed through the reactor vessel, then made a 1 m wide large hole in the platform just below the reactor vessel:
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Source Tepco
Then it continued on its way encountering obstacles, forming stalactites in various places:
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Screenshots of the Tepco video
Finally, it spread to the bottom of the containment by cutting into the concrete. And there, we lose track because the investigations could not go further.
 
Has it gone far off the ground plate ? Did it join the toric pool by the pipes connecting the enclosure and the pool?
Let’s not forget that an explosion was heard by technicians on March 15, 2011 at 6:10 from reactor 2. Steam explosion?
Do not forget that the water that is injected continuously to cool the corium does not fill the enclosure because it is no longer intact.The water is permanently contaminated by the corium, before reaching the bottom of the plant and the groundwater. Let’s not forget that this moving groundwater flows into the Pacific, despite the ice wall, which is not perfectly watertight.
 
It will be observed that Tepco has not yet dared to provide a picture of the hole in the reactor vessel. It’s like the explosion of reactor 4, there are things that are better not to be disclosed because they tarnish the image of civil nuclear.
 
In the same manner, the people in charge of communication preferred to broadcast uncertain images on the 19th of January rather than these very interesting images which I extracted from the video.
 
Certainly, robotics in a radioactive environment has made real progress, but that hides the reality: we have not yet invented the machines that can dismantle the Fukushima Daiichi nuclear plant. And the forty years promise to complete this dismantling will certainly be insufficient.
 
Let’s not forget that there are all in all 3 coriums to recover and 3 swimming pools full of fuel to empty.
 
While Tepco “amuses” us with its technique, Tepco hopes to release 1 million tons of radioactive water in the Pacific that its has collected on the site, as if this ocean had not already suffered enough. It also makes it possible to forget the thousands of people suffering from thyroid disorders or other various pathologies due to radioactivity and the tens of thousands of displaced people who are being forced to return to contaminated territories.
 
Let’s wait for the big communication from TEPCO: the athletes of 2020 (Tokyo Olympics) must be amazed by the Japanese hyper-technicality so as to forget the basic dangers of ambient radioactivity.
 

January 28, 2018 Posted by | Fukushima 2018 | , , | Leave a comment

Fukushima Unit 2 in the News Again

From Majia’s Blog

TEPCO tells us they have identified the remains of “part of a nuclear fuel assembly” scattered at the bottom of unit 2’s containment vessel:

CHIKAKO KAWAHARA January 20, 2018 Melted nuclear fuel seen inside No. 2 reactor or at Fukushima plant. The Asahi Shimbun http://www.asahi.com/ajw/articles/AJ201801200017.html

A remote-controlled camera captured what appears to be melted fuel inside a reactor of the stricken Fukushima No. 1 nuclear power plant, operator Tokyo Electric Power Co. said. The released footage showed pebble-like nuclear fuel debris and part of a nuclear fuel assembly scattered at the bottom of a containment vessel, located just below the pressure vessel.

Where is the rest of the fuel?

Fukushima’s reactor 2 held quite a bit more than a single fuel assembly. According to a November 16 report by TEPCO titled, ‘Integrity Inspection of Dry Storage Casks and Spent Fuel at Fukushima Daiichi Nuclear Power Station,’ as of March 2010 the Daini site held 1,060 tons of spent uranium fuel. 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.

Unit 2 has been in the news. Last February, Akio Matsumura described a potential catastrophe at Unit 2:

Akio Matsumura (2017, February 11). The Potential Catastrophe of Reactor 2 at Fukushima Daiichi: What Effect for the Pacific and the US? Finding the Missing Link, http://akiomatsumura.com/2017/02/the-potential-catastrophe-of-reactor-2-at-fukushima-daiichi.html, accessed November 20, 2017

It can hardly be said that the Fukushima accident is heading toward a solution. The problem of Unit 2, where a large volume of nuclear fuels remain, is particularly crucial. Reactor Unit 2 started its commercial operation in July 1974. It held out severe circumstances of high temperature and high pressure emanating from the March 11, 2011, accident without being destroyed. However, years long use of the pressure vessel must have brought about its weakening due to irradiation. If it should encounter a big earth tremor, it will be destroyed and scatter the remaining nuclear fuel and its debris, making the Tokyo metropolitan area uninhabitable.

Unit 2 has been in the news because of persistent high radiation levels. In Feb 2017, TEPCO reported measuring radiation levels of 530 SIEVERTS AN HOUR (10 will kill you) and described a 2-meter hole in the grating beneath unit 2’s reactor pressure vessel (1 meter-square hole found in grating):

Radiation level at Fukushima reactor highest since 2011 disaster; grating hole found. The Mainichi, February 2, 2017, http://mainichi.jp/english/articles/20170202/p2g/00m/0dm/087000c

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.

…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. 

This extraordinarily high radiation in unit 2 was reported by the Japanese media in January 2017 as presenting a barrier to the decommissioning timeline:

MASANOBU HIGASHIYAMA (January 31, 2017) Images indicate bigger challenge for TEPCO at Fukushima plant. The Asahi Shimbun, http://www.asahi.com/ajw/articles/AJ201701310073.html

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.

…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.

UNIT 2 HISTORY

Looking back at testimony by Masao Yoshida, Fukushima’s plant manager, and media coverage of that testimony, I see that unit 2 was identified as posing the greatest immediate risk, although the explosion at unit 3 was clearly larger (this discrepancy is perplexing).  Here is an excerpt of the testimony published by the Asahi Shimbun:

Yoshida feared nuclear ‘annihilation’ of eastern Japan, testimony shows. (September 12, 2014) THE ASAHI SHIMBUN http://ajw.asahi.com/article/0311disaster/fukushima/AJ201409120034

Plant manager Masao Yoshida envisioned catastrophe for eastern Japan in the days following the outbreak of the Fukushima nuclear disaster, according to his testimony, one of 19 released by the government on Sept. 11. . . .

. . . In his testimony, Yoshida described the condition of the No. 2 reactor at the Fukushima plant between the evening of March 14, 2011, and the next morning: “Despite the nuclear fuel being completely exposed, we’re unable to reduce pressure. Water can’t get in either.”

Yoshida recalled the severity of the situation. “If we continue to be unable to get water in, all of the nuclear fuel will melt and escape from the containment vessel, and radioactive substances from the fuel will spread to the outside,” he said. Fearing a worst-case scenario at the time, Yoshida said, “What we envisioned was that the entire eastern part of Japan would be annihilated.”

You can read more excerpts from the 400-pages of testimony published by the Asahi Shimbun, which both applauds and critiques the panel investigation of the disaster that produced the testimonies:

The Yoshida Testimony: The Fukushima Nuclear Accident as Told by Plant Manager Masao Yoshida The Asahi Shimbun http://www.asahi.com/special/yoshida_report/en/

Although the panel interviewed as many as 772 individuals involved, it failed to dig deep into essential aspects of the disaster because it made it a stated policy that it would not pursue the responsibility of individuals.

What is true about unit 2? Yoshida provides this account from the article cited immediately above:

At around 6:15 a.m. on March 15, 2011, four days after the Great East Japan Earthquake and tsunami, a round table presided by Yoshida in an emergency response room on the second floor of the Fukushima No. 1 nuclear plant’s quake-proof control center building heard two important reports, almost simultaneously, from front-line workers.

One said that pressure in the suppression chamber, or the lower part of the containment vessel for the No. 2 reactor, had vanished. The other said an explosive sound had been heard.

Question: Well, this is not necessarily in the No. 2 reactor, but sometime around 6 a.m. or 6:10 a.m. on March 15, pressure in the No. 2 reactor’s suppression chamber, for one thing, fell suddenly to zero. And around the same time, something …

Yoshida: An explosive sound.

http://majiasblog.blogspot.fr/2018/01/fukushima-unit-2-in-news-again.html

January 27, 2018 Posted by | Fukushima 2018 | , , | Leave a comment

Fukushima Daiichi Reactor 2: new investigation

Tepco has just released the results of an investigation made in the containment of reactor 2. Nothing really new, apart from a found assembly element, we are waiting for radioactivity measurements now.
20 janvier 2018
A new 10-hour investigation was conducted in the Fukuishima Daiichi reactor 2 containment enclosure, according to a report released by Tepco on January 19, 2018. However, Tepco does not indicate the date of the operation. The images and measurements were taken using a 13 meter probe with a camera. TEPCO will only broadcast the radioactivity measurements later.
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Photo: an assembly element was found
According to this document, TEPCO gives two main informations:
– The entire bottom of the base of the reactor base is covered with deposits of sandy and clay.
– Some fuel assembly components have fallen to the base of the reactor base and are considered fuel debris.
As usual, Tepco does not use the word “corium”. It does not speak more about the radioactive environment of the place which is lethal (a last year made measure at this place was 530 Sieverts) but promises to return soon. I will update this page when the information falls.
The deposit of sandy and clay types is what is at the bottom of the enclosure and which had already been spotted last year around the pedestal. This vase prevents a clear view of the bottom of the enclosure because the slightest movement of the camera, the water is troubled.
For the first time, Tepco discloses a diagram showing the inside of the reactor pedestal. We see :
– an upper platform, which was already known, which allows access to control rods located just below the reactor vessel. This, according to the February 2017 report, is pierced with a hole 1 meter in diameter. It is the mass of the corium coming from the tank during the meltdown that made this hole.
– an intermediate platform that Tepco claims has not been piereced (but the diagram does not show it in full)
– An annular lower platform bordering the wall of the pedestal, which Tepco also claims that it has no hole. But, same remark, the diagram shows only half.
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The piece of assembly that emerges very clearly from a pile of various materials is an upper tie plate. It is surmounted by a bar (“bail handle”), a kind of handle for moving the assembly using an articulated arm. This photo makes it possible to deduce that at least one whole assembly has passed through the tank, which implies that the tank has a hole of at least the width of an assembly (approximately 50 cm). The probe has certainly taken pictures of this hole but Tepco do not release them.

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Type of assembly element found on the lower platform of the No. 2 reactor pedestal.
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This element is the upper part that we see for example in these assemblies of the reactor pool
Toshiba’s probe, during its presentation in Yokohama, December 22, 2017. The telescopic arm carries a panoramic camera.
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Here are the photos of the interior of the BR2 containment building released by Tepco on January 19, 2018:
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Here are some pages from the report on the same date:
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Tepco’s full report of 19 January 2018

[pdf] HANDOUTS_180119_01-E

Source : http://www.fukushima-blog.com/2018/01/reacteur-2-de-fukushima-daiichi-nouvelle-investigation.html

Special thanks to Pierre Fetet of the Fukushima Blog

Translation Hervé Courtois (Dun Renard)

January 21, 2018 Posted by | Fukushima 2018 | , , , | Leave a comment

TEPCO claims to have found ‘fuel debris’ in No. 2 reactor

reactor 2 melted fuel spotted 2018-01-19.png
TEPCO finds ‘fuel debris’ in No. 2 reactor
 
The operator of the damaged Fukushima Daiichi nuclear power plant says it has found what looks like fuel debris in the plant’s No. 2 reactor.
The nuclear accident occurred in March, 2011.
 
Tokyo Electric Power Company, or TEPCO, on Friday looked inside the containment vessel of the No. 2 reactor.
 
TEPCO confirmed, for the first time, the existence of chunks that are believed to be a mixture of melted nuclear fuel and parts of bindings.
 
The company plans to determine how to remove the debris based on the results of the investigation.
 

January 19, 2018 Posted by | Fukushima 2018 | , , | Leave a comment

Tepco to resume attempt to probe damaged reactor at Fukushima No. 1 plant

Reactor 2.jpg
The operator of the Fukushima No. 1 nuclear power plant has said it will resume late this week a survey of the crippled No. 2 reactor using a telescopic arm, hoping to obtain images of melted nuclear fuel.
In Friday’s survey, Tokyo Electric Power Company Holdings Inc. aims to investigate the area beneath the reactor’s pressure vessel, through which nuclear fuel is believed to have melted. The step is needed to help develop a plan for removing the fuel for the ultimate decommissioning of the plant.
Tepco, in announcing the move on Monday, said it will insert a 13-meter long pipe at the bottom of the pressure vessel and then deploy a camera at the tip of the pipe to film the bottom of the outer primary containment vessel, where fuel is believed to have accumulated.
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The device will also measure the temperature and radioactivity levels in the area. The survey is expected to take one day.
In January last year, an inserted camera with a limited view captured possible melted fuel in the interior of the No. 2 reactor.
The following month, Tepco attempted a survey using a scorpion-shaped robot inside the unit, but the effort ended in failure due to a technical flaw.
Nearly seven years after the March 2011 earthquake and tsunami that wrecked the plant, details of the damage to the reactors remain largely unknown due to high levels of radiation.
Reactors 1, 2 and 3 at the four-reactor plant suffered core meltdowns due to a loss of cooling water in the world’s worst nuclear crisis since the 1986 Chernobyl disaster.

January 18, 2018 Posted by | Fukushima 2018 | , , | Leave a comment

Fukushima Unit 2 Radiation Readings Revised

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TEPCO revised unit 2’s containment inspection radiation readings done earlier in 2017, claiming a set of instrument and calibration errors caused the inaccurate readings.

TEPCO claims that their camera based radiation estimates were too high due to an oversight where they forgot to reset the sensitivity threshold on the equipment that was reading camera interference.

The final claim made in the report for downgrading the radiation readings was that one of the 4 sensors was reading considerably higher than the other 3. When they took that sensor out of the readings the other 3 sensors read considerably lower.

Source : Tepco’s handout

http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170727_03-e.pdf

 

 

July 31, 2017 Posted by | Fukushima 2017 | , , , | Leave a comment

Search for melted nuclear fuel at Fukushima plant’s No. 2 reactor faces obstacles

a never ending story 2017.jpg

 

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.”

http://mainichi.jp/english/articles/20170227/p2a/00m/0na/011000c

February 28, 2017 Posted by | Fukushima 2017 | , , , | Leave a comment

Pics from Fukushima robots not enough to devise fuel-removal plan for reactor 2: Tepco

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Members of the media take in the No. 1 reactor at the Fukushima No. 1 power plant in Fukushima Prefecture on Thursday.

OKUMA, FUKUSHIMA PREF. – While a recent investigation found what may be melted nuclear fuel rods in reactor No. 2 containment vessel at the Fukushima No. 1 plant, that information isn’t nearly enough to devise an effective method for removing it, the chief of the plant told reporters during a media tour Thursday.

We put in cameras and robots and obtained valuable images, though they were partial . . . but it’s still unclear what is really going on there,” said Shunji Uchida, who became chief of the crippled plant last July. “We first need to know the situation of the debris.”

Last month, the utility inserted a 10.5-meter rod with a camera on its tip into a hole in the No. 2 reactor’s primary containment vessel and discovered black lumps sticking to the grating directly underneath the suspended pressure vessel, which holds the core.

Tepco claims it is still unsure whether the lumps are really melted fuel that burned through the bottom of the pressure vessel. Although it is still years away from actually trying to remove the fuel, Tepco, the government and related parties are planning to decide on a basic strategy this summer and go into more detail next year.

Uchida described last month’s surveillance operation as “just peeking.”

Engineers are playing with the idea of refilling the primary containment vessel with water during debris cleanup operations to reduce the intensity of the radiation, but since the PCV was probably damaged during the meltdown crisis in March 2011, the water that’s being pumped in 24/7 to keep the fuel cool is just leaking back out.

According to past analyses, some of the melted fuel rods penetrated the pressure vessel and fell into the containment vessel surrounding it after the March 11 quake and tsunami caused a station blackout at the plant, crippling all cooling functions.

http://www.japantimes.co.jp/news/2017/02/23/national/pics-fukushima-robots-not-enough-devise-fuel-removal-plan-reactor-2-tepco/#.WK8m0PL9KM9

February 24, 2017 Posted by | Fukushima 2017 | , , | Leave a comment

Radiation levels at Fukushima reactor puzzle nuclear experts

It is unclear why there is less radioactivity under the reactor vessel, when it is where there should be the most.

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A robot was expected to solidify ways to clean up the No. 2 reactor at the Fukushima No. 1 nuclear plant, but its short-lived mission raised puzzling questions that could derail existing decommissioning plans.

The robot, Sasori, was abandoned in the melted-down reactor after it became stuck in deposits and other debris that are believed to have interfered with its drive system.

But it did take radiation measurements that indicate Tokyo Electric Power Co., operator of the plant, was too optimistic about the state and location of the melted fuel within the reactor. The melted fuel, in fact, may be spread out all over the reactor’s containment vessel.

Scientists had believed the melted nuclear fuel fell through the reactor’s pressure vessel and landed on metal grating and the floor of the containment vessel.

The results of Sasori’s investigation, coupled with previous data taken from possible images of the melted fuel, show the situation within the reactor is much worse than expected. And a fresh investigation into the reactor is now nowhere in sight.

A remote-controlled video camera inserted into the reactor on Jan. 30 took what are believed to be the first images of melted fuel at the plant, which suffered a triple meltdown after the March 2011 Great East Japan Earthquake and tsunami.

Based on the images, TEPCO estimated 530 sieverts per hour at a point almost halfway between the metal grating directly beneath the pressure vessel and the wall of the containment vessel. Black lumps on the grating are believed to be melted fuel.

A different robot sent in on Feb. 9 to take pictures and prepare for Sasori’s mission estimated 650 sieverts per hour near the same spot.

Both 530 and 650 sieverts per hour can kill a person within a minute.

Sasori, equipped with a dosimeter and two cameras, on Feb. 16 recorded a reading of 210 sieverts per hour near the same location, the highest figure measured with instruments in the aftermath of the disaster.

Sasori was supposed to travel along a rail connecting the outer wall of the containment vessel with the metal grating to measure radiation doses and shoot pictures inside, essential parts of work toward decommissioning the reactor.

After traveling only 2 meters, the robot became stuck before it could reach the metal grating.

TEPCO at a news conference repeatedly said that Sasori’s investigation was not a “failure” but had produced “meaningful” results.

However, an official close to TEPCO said, “I had great expectations for Sasori, so I was shocked by how it turned out.”

Hiroaki Abe, professor of nuclear materials at the University of Tokyo who has studied TEPCO’s footage, tried to explain why high doses were estimated between the pressure vessel and the containment vessel.

Instead of directly landing on the rail, the melted nuclear fuel may have flown off after it reacted violently with the concrete, which had a high moisture content, at the bottom of the containment vessel, just like what happens when lava pours into the sea,” Abe said.

But he said this scenario raises a puzzling question, considering the estimated radiation readings near the area below the pressure vessel were down to 20 sieverts per hour, according to an analysis of the video footage.

If nuclear fuel debris had splattered around, the radiation levels at the central area below the pressure vessel must be extremely high,” he said. “In addition, deposits on the rail would have taken the shape of small pieces if they were, in fact, flying nuclear fuel debris. The findings are puzzling.”

Images by the remote-controlled camera also showed that equipment in the lower part of the pressure vessel was relatively well preserved, indicating that the hole at the bottom of the vessel is not very large.

How to remove nuclear fuel debris will all depend on how much remains inside the pressure vessel and how much fell out,” Abe said.

Toru Obara, professor of nuclear engineering at the Tokyo Institute of Technology, stressed the need to retrieve substances from the bottom of the robots or elsewhere.

We could get clues as to the state of the melted nuclear fuel and the development of a meltdown if we could figure out which materials mixed with the nuclear fuel,” he said.

The surveys by the camera and robots were conducted from a makeshift center at the No. 2 reactor. The center’s walls are made from radiation-blocking metal.

TEPCO and the government plan to determine a method to remove nuclear fuel debris in fiscal 2018 before they proceed with the actual retrieval process at one of the three destroyed reactors.

One possible method involves filling the containment vessels with water to prevent radioactive substances from escaping.

http://www.asahi.com/ajw/articles/AJ201702190042.html

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February 21, 2017 Posted by | Fukushima 2017 | , , | Leave a comment

Robot stuck in Fukushima No. 2 reactor on 1st try, abandoned. Damage inside No. 2 reactor building at Fukushima plant greater than expected

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The Sasori robot is stuck inside the containment vessel of Fukushima No. 1 nuclear power plant’s No. 2 reactor on Feb. 16. (Provided by International Research Institute for Nuclear Decommissioning)

Robot stuck in Fukushima No. 2 reactor on 1st try, abandoned

In the latest hitch in efforts to decommission reactors at the Fukushima No. 1 nuclear power plant, a robotic surveyor became mired in deposits and was lost on its maiden journey on Feb. 16.

Tokyo Electric Power Co., which operates the plant in Fukushima Prefecture, had to abandon the Sasori (scorpion) robot after it became stuck inside the containment vessel of the power station’s No. 2 reactor that morning.

The highly touted probe was specially developed for the important task of surveying the interior of the crippled reactor and collecting data to assist in removing the melted fuel.

But with the environment inside too treacherous for a key component in the process, TEPCO’s decommissioning project seems to have come to a standstill.

According to the utility, the robot entered the containment vessel around 8 a.m. It traveled along a 7.2-meter-long rail connecting the outer wall of the containment vessel with its central portion immediately beneath the pressure vessel.

But about 5 meters into its mission, the robot’s controls started to become less responsive. TEPCO believes it was due to deposits and other debris that are blocking the rail entering its drive system.

The operator tugged on the electrical cable connected to the robot and had it pull back to an area along its path with less obstacles, but it ultimately became stuck there.

The robot measured the radiation levels in the area at 210 sieverts per hour, which is lethal enough to kill a human in two minutes. Earlier, the company had estimated the level in the area at 650 sieverts per hour from video footage captured on Feb. 9 by another robot that paved the way for the Sasori.

With the robot completely immobilized, TEPCO gave up on retrieving it around 3 p.m. The operator cut the electric cable and closed the tunnel bored into the wall of the containment vessel, entombing the robot inside.

The probe was cast aside to the edge of the 0.6-meter-wide rail so that it would not impede future surveyor robots.

Had everything gone according to plan, TEPCO would have sent the Sasori onto the grating in the heart of the containment vessel, which is covered in black chunks believed to be melted fuel rods that fell from the pressure vessel above.

The utility had hoped to measure the dosage of these radioactive lumps, as well as capture images of the underside of the pressure vessel, which contains holes from when the nuclear fuel burned through it in the meltdown that was triggered by the Great East Japan Earthquake and tsunami in 2011.

http://www.asahi.com/ajw/articles/AJ201702170048.html

 

Damage inside No. 2 reactor building at Fukushima plant greater than expected

Damage within the No. 2 reactor building at the Fukushima No. 1 Nuclear Power Plant was found to be greater than expected, based on images sent back by a robot sent into the structure by plant owner Tokyo Electric Power Co. (TEPCO) in a mission that concluded Feb. 16.

The operation used a self-propelled scorpion-shaped robot, with the goal of investigating the inside of the reactor’s containment vessel and the area directly beneath the reactor, but the area under the reactor was not reached. The No. 2 reactor building was thought to be comparatively undamaged compared to the No. 1 and No. 3 reactor buildings, where hydrogen explosions occurred. Worse damage than expected was discovered, however, such as holes in the grating foothold inside the containment vessel.

At a press conference, TEPCO official Yuichi Okamura stressed, “This investigation was the first of its type in the world and uncovered information about the debris inside. The mission wasn’t a failure.”

The robot’s camera also took footage of the condition of pipes in the structure, and image processing could make these pictures clearer. However, the robot’s treads stopped moving after it proceeded over 2 meters along a rail, and TEPCO was not able to use it to check the melted nuclear fuel.

TEPCO plans to decide as early as this summer on how to remove the melted fuel from the No. 1 through No. 3 reactors and start the decommissioning process in earnest. The results of the investigation were to be used as base data for the decommissioning, but with it having not produced an overall understanding of the No. 2 reactor building’s interior, a new investigation will probably be sought.

However, no plan for the next investigation has been decided, and it may begin with the development of a new robot. TEPCO plans to send in a different robot to the No. 1 reactor building next month. For the No. 3 reactor building, a robot capable of moving in water is being developed because there is a large amount of contaminated water at the bottom of its containment vessel.

http://mainichi.jp/english/articles/20170217/p2a/00m/0na/011000c

February 18, 2017 Posted by | Fukushima 2017 | , , | Leave a comment

Fukushima Unit 2 Scorpion Probe Dies But Sends Back Some Data

 

While the press reported Scorpion’s mission as a failure, it provided useful data before being abandoned. It collected some radiation readings and a number of useful images.

The robot seems to have become stranded on a pile of debris on the rail. Radiation data from along this inspection route provided only one radiation reading, no telemetry as other videos had. Tepco’s video is heavily edited but still provides some useful information.

A reminder, these readings are the result of venturing into the more deadly areas of the reactor where they have been unable to previously, no resulting from an increase of radiation. While this is much lower than the earlier camera estimates of radiation it is still extremely high and quite deadly.

Arond the same area where the high radiation source was found, TEPCO stated they found a 210 Sv/h reading with the on board radiation sensor.

New images from inside the pedestal were obtained as were some images looking up into the containment structure.

Image below from TEPCO. White ghosting on the image is likely due to radiation levels rather than steam. The existing melt hole in the pedestal floor grate can be partially seen in the upper mid section of the image. A very thick amount of fuel debris can be see in the lower right section of the image. The mark “clean” on this image with an arrow indicates an area where the floor grate may have failed after the molten fuel had splattered on the area. Further below, more fuel debris and structures can be seen.

u2_pedestal_markup

 

The red circle shows an area where it appears fuel debris was moved or blocked by a fallen piece of sheet steel.

In both images, sections of light colored piping can be seen below the area where the grate is missing. On the far left of the image a partially melted section of flexible conduit can be seen.

This appears to indicate that high temperatures within the pedestal were very localized.

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Sources:

TEPCO handout for this work

http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170216_01-e.pdf

February 18, 2017 Posted by | Fukushima 2017 | , , | Leave a comment

Reactor 2’s Platform has 3 Holes

reactor-2-platform-3-trous-feb-15-2017

 

 

Tepco released a new image of the reactor 2: at least three holes in the platform and still no corium.

The platform is made of metal (grating), just below the tank, intended to access the control rods. The bottom of the containment is a little over 3 m below.

reactor-2-15-feb-2017

 

Tepco’s document in Japanese:

http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170215_08-j.pdf

 

February 17, 2017 Posted by | Fukushima 2017 | , , , | Leave a comment