New Data for Unit 2’s Missing Fuel

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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).

 

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Melted fuel Deposits in Fukushima N°2 Reactor

TEPCO footage shows deposits inside damaged Fukushima reactor
TOKYO — Tokyo Electric Power Co. (TEPCO) on April 26 released footage taken inside the containment vessel of the No. 2 reactor at the disaster-hit Fukushima No. 1 Nuclear Power Plant, showing spots where molten fuel appears to have fallen through the reactor pressure vessel.
Photos and video footage show deposits — believed to be fuel debris — at the bottom of the containment vessel. In two spots, the debris is piled higher than in other places. TEPCO officials said they suspect that the bottom of the pressure vessel, situated at the upper part of the containment vessel, was damaged in more than one place, which allowed melted fuel to fall into the containment vessel.
TEPCO captured the images in January using a camera attached to a pipe inserted into the containment vessel, and found deposits spread across the bottom of the vessel. The nuclear plant operator will use a robot arm to analyze the containment vessel in more detail.
(Japanese original by Ei Okada and Riki Iwama, Science & Environment News Department)
reactor 2 April 27 2018.jpg
Full extent of melted fuel in Fukushima No. 2 reactor revealed
Inside the bottom of the containment vessel in the No. 2 reactor of the Fukushima No. 1 nuclear power plant in January, revealed fully by new image processing.
The bottom of the inside of Fukushima No. 1 nuclear plant’s crippled No. 2 reactor has been revealed in a much clearer and wider range in footage released by plant operator Tokyo Electric Power Co. on April 26.
The film shows the clearest pictures yet inside the containment vessel just below the pressure vessel of the nuclear reactor, which went into meltdown due to the 2011 earthquake and tsunami disaster.
Melted nuclear fuel debris is seen attached to pillars, walls and the ceiling, and accumulations between approximately 40 and 70 centimeters thick are piled up and cover the whole floor.
TEPCO captured the footage on Jan. 19 by attaching a remote-controlled camera to an extendable rod with a span of 16 meters into the containment vessel from an opening in its side.
Excerpts were released at the time, but new processing of the footage has revealed a much clearer picture.
In the bottom of the containment vessel, fuel debris has fused to some areas particularly thickly. It is possible that the bottom of the reactor has several holes that caused the debris to fall and solidify as it cooled.
The improved knowledge of the nuclear reactor’s state will help to calculate an estimate of the amount of the debris inside, and suggest at how it could be removed in the future. TEPCO hopes to start its next investigation inside the reactor within this fiscal year.

Fresh analysis of Fukushima Daiichi ‘fuel debris’

april 26 2018.jpg
April 26, 2018
A fresh video analysis by the operator of the Fukushima Daiichi nuclear power plant shows that molten fuel at the No.2 reactor may have fallen along several paths. The unit is one of the 3 reactors that experienced a meltdown in 2011.
 
Tokyo Electric Power Company processed images that were taken inside the reactor’s containment vessel in January. The firm pieced them together so that the resulting footage can better show conditions within the entire vessel.
 
The footage shows all of the vessel’s bottom covered with what looks like pebbles and clay. A roughly 70-centimeter-high pile of such materials is located near where part of the fuel casing was spotted in the January probe.
 
Another heap is close to a pillar-like structure at the bottom.
 
The utility says the materials may be fuel debris, which is a mixture of molten nuclear fuel and structural parts.
 
The firm also released a 3-dimensional video that reconstructs the interior of the containment vessel of the No.3 reactor. The unit also suffered from a meltdown.
 
The footage shows a mound of materials near the center of the vessel’s bottom. The company says it may have emerged after fuel debris fell onto structural parts that had already dropped there during the 2011 accident.
 
The utility says the new images provide clues to determine the paths along which molten fuel fell. It plans to decide in the next fiscal year how to remove the fuel debris.
 
The company is seeking to remove the molten fuel as part of its effort to decommission the plant.

 

First samples of Fukushima plant nuclear fuel debris to be collected in FY 2019

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March 16, 2018
The government and Tokyo Electric Power Co. (TEPCO) are set to extract a small sample of melted nuclear fuel from the bottom of the No. 2 reactor’s containment vessel at the disaster-stricken Fukushima No. 1 nuclear plant as early as fiscal 2019.
 
The operation will be a test before starting full-scale collection of the fuel, targeted for 2021 or earlier. If development of technologies for debris retrieval shows promise, the operation may be moved up to the end of fiscal 2018. The government and TEPCO hope to ascertain the properties of the melted fuel and use the information for developing collection devices and debris containers.
 
This will be the first attempt to sample nuclear fuel debris from a reactor. Other materials, including those floating in contaminated water and substances stuck to robot probes, have been extracted from the plant’s reactors before. The No. 1, 2 and 3 reactors at the Fukushima No. 1 plant melted down in the March 2011 nuclear disaster.
 
The road map for collecting the melted fuel, last revised in September 2017, states that TEPCO would choose a first reactor to tackle by the end of fiscal 2019 and decide on a collection method. The utility would then start the retrieval process in 2021. As deciding on this process requires finalizing ways to contain, transfer and store the debris, the government and utility concluded that they would need to grasp the fuel’s current condition by extracting samples beforehand.
 
In January this year, a camera and dosimeter were sent into the containment vessel of the No. 2 reactor through an existing passage to find pebble- and clay-like masses at its bottom believed to be melted fuel. A source close to the government says the plan is to remotely guide a robot arm equipped with a camera and dosimeter into the containment vessel through the same passage, and extract a small amount of the suspected fuel debris.
 
The January probe of the containment vessel revealed radiation around the pebble-like masses measured 8 sieverts per hour — a level potentially lethal to humans after just one hour of exposure. Due to the ultrahigh radiation, the sampled material will be placed in a special radiation-shielded container before being removed from the reactor. After that, the sample will be brought to a Japan Atomic Energy Agency facility in Ibaraki Prefecture for analysis.
 
A government source told the Mainichi Shimbun that sampling the suspected fuel debris is different from the debris collection specified in the road map, and stressed that extracting samples should be beneficial to determine a method for retrieving the fuel.
 

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.

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 3 minutes 34 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 it 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.
 

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