Japan Earthquake: nuclear plants Fukushima part 2

[etudiant]

Here's a news report from the evening of March 12, 2011, which says (my translation again):

"TEPCO admitted the possibility of core melt (roshin yōyū) as pointed out by NISA."

Asahi Shimbun March 12, 2011 20:26
http://www.asahi.com/special/10005/TKY201103120510.html

How and why this got downplayed for so long afterward is the bigger story, I think, as is the role of the Japanese govt in "shaping" the message.

The government spokesman at the time who mentioned the word 'meltdown' was immediately replaced. Perhaps this was also seen as a message to the press to back off.

 

[Sotan]

Lots of new reports (unfortunately only in Japanese for now) have been posted on Tepco's "Mid- and Long-Term Roadmap" section (http://www.tepco.co.jp/decommision/planaction/roadmap/index-j.html) on Feb 22 and 25.

I glanced through some of them:

http://www.tepco.co.jp/nu/fukushima-np/roadmap/images1/images1/d160225_08-j.pdf
This one presents the recently finished 3D laser-scan of the torus room of Unit 3. Acquired data to be used for the evaluation of obstacles and identification of possible water leaks.
On the page numbered 7 they give some radiation dose values, but warn that they are only estimations because the measuring device used was not a calibrated one.
Measured values were between 48.2 and 161.0 mSv/h, in general showing a decrease compared to the values measured in July 2012 (given on Page 8).

http://www.tepco.co.jp/nu/fukushima-np/roadmap/images1/images1/d160225_07-j.pdf
About the stage of the cover removal process at Reactor 1 building.
After removing the roof, they started cutting some of the twisted steel beams which hinder access.
Page numbered 4: some photos of the operating floor, before and after removing some rubble.

http://www.tepco.co.jp/nu/fukushima-np/roadmap/images1/images1/d160225_16-j.pdf
Very interesting report regarding the wide range of studies and research activities being carried out regarding technologies and procedures to be used in the decommissioning works, from investigations techniques to be used for acquiring information regarding the interior of the reactors, to methods for removing the molten debris of nuclear fuel, to procedures for treating and storing contaminated stuff.
It's very long and complex, unfortunately, so I can only mention a few points now (comments made in a hurry, might need some additions/corrections later):
- the studies are being carried out keeping in mind the summer of 2017 as the tentative deadline for proposing variants from which to select (sometime around the summer of 2018) the actual method for removing the molten nuclear fuel;
- most of the items are discussed first in general terms, then on the lower-right of the page they give specific tasks/objectives planned for fiscal 2016-2017.
- for example Page 5 of 49 (page numbers refer to what the browser or PDF reader indicates) talks about the need to know more, in general, about the properties of molten nuclear fuel / corium. The task for 2016-2017 is to compile a more complete database with such information.
- Page 7 of 49 talks about getting a better image of the interior of the PCVs. In fiscal 2016 they plan to examine the lower pedestal area of PCV of Reactor 1 from the grating placed one floor above, hoping to see the molten debris; in 2017 they plan similar investigations for the PCVs of Reactor 2 and 3;
- Page 9 of 49 is on the same subject - the state of the molted fuel inside the PCVs. Tasks for 2016-2017: develop the concept for the machine and method used to open a hole at the top of the PCV for the purpose of investigating the inside and then test and verify the machine and method on mockup.
- Page 12 of 49: in 2016: prepare a database with information on thinkable methods for retrieving the debris; evaluate their compatibility with each of the reactors based on their specifics; develop concepts of machines and methods for retrieving samples of the molten fuel;
- Page 15 of 49: in 2016: evaluation of the basic elements and feasibility of the various methods for removing the molten fuel (water submerged method / in-air method, access from the top / access from the lateral).
- Page 17 of 49: objective for 2016: evaluation of methods for preventing the corrosion of the RPV and PCV, selection of anti-corrosion agents and their evaluation.
- Page 19 of 49: resistance of the RPVs/PCVs in case of earthquakes. Identification of possible weaknesses and methods to mitigate them.
- Page 21 of 49: need to study and prepare for/prevent criticalities while handling the molten fuel. Objectives for 2016: progress regarding the methods to reduce exposure of workers to radiation, and regarding methods to monitor, detect and prevent criticalities; in 2017 a well-defined method for all these should be put together.
- Page 23 of 49: studies regarding methods for repairing the PCVs and stopping the water leaks in view of filling up the PCVs with water. Some conclusions regarding their feasibility should be obtained in 2016-2017. The discussion continues on page 25 of 49, with experimental and demonstration works in these areas.
- Page 27 of 49: studies regarding the handling and storage of removed molten fuel debris. Concepts, mockups and experimental/demonstration works scheduled to advance significantly in 2016-2017.
- Discussion of studies aimed at the storage (including long term) of the contaminated debris continues on the following pages.

Then there are a few pages containing the IRID logo (these pages deserve a more detailed look into, I will try to do it later):
- Page 35 of 49 presents the stage reached in Feb 2016 regarding the model analysis of the nuclear accident.
- Page 36 of 49: present stage information regarding the properties of molten fuel/corium
- Page 37 and 38 of 49: present stage info regarding investigation techniques/robots. Interesting, on page 38, the proposed investigation through a hole made in the RPV lid.
- Page 39 and 40 of 49: present stage / concepts regarding the removal of molten fuel debris;
- Page 41 of 49: present stage, methods for evaluating the health of the RPV / PCV (corrosion, resistance to earthquakes...)
- Page 42 of 49: management of criticalities
- Page 43 and 44 of 49: techniques and experiments for repairs to the PCV
- Page 45 of 49: transport, storage and manipulation of removed molten fuel debris
- Page 46 of 49: again present stage of studies regarding the storage of contaminated debris
- Page 47 of 49: studies on the long-term resistance of fuel bundles recovered from spent fuel pools
- Page 48 of 49: robots and remote-controlled devices for the decontamination of plant installations and surfaces
- Page 49: finally, latest info regarding techniques for pinpointing the location of the molten cores.

 

[etudiant]

Seems like a huge amount of work with very little reward.
I can understand the desire of some to simply cordon off the entire site rather than to embark on the costly and uncertain effort to locate and remove the residual corium.

 

[nikkkom]

Seems like a huge amount of work with very little reward.
I can understand the desire of some to simply cordon off the entire site

More like "cordon off" reactor buildings only. Or even only parts of them. In Hanford, all military Pu-producing reactors (except the very first one) were "cocooned" - thoroughly isolated from the outside by concrete.

"""The C Reactor was the first of Hanford’s nine plutonium production reactors to be cocooned (encased in a concrete shell). The cocooning of C Reactor took place in 1998, which showed the promise of a number of new technologies aimed at reducing worker contamination to radiation, lowering costs associated with these older reactors, and accelerating the cleanup mission.
As the C Reactor was the first reactor to be cocooned at Hanford, it was also the first to undergo a five-year annual “check-up”. All reactors that are cocooned are entered by radiation technicians once every five years to confirm that no contamination is leaving the sealed reactor core, and that nothing is entering the building from the outside. The C Reactor passed both its five-year check-up in 2003, as well as its ten-year check-up in 2008.
If the cocoon continues to prevent contamination from leaking out of C Reactor while also keeping anything outside the reactor from entering it, the cocoon could be in place for up to 75 years."""

 

[Sotan]

Another subject discussed from time to time is the tritium contaminated water.
This time the update on Mid and Long-term Roadmap includes a document addressing this subject, dated Feb. 11:
http://www.tepco.co.jp/nu/fukushima-np/roadmap/images/c151211_09-j.pdf
(in Japanese)

It's a detailed report from the 13th meeting of the "tritium taskforce" explaining where they stand at this moment in the evaluation of the various options which are available for dealing with the tritium water.
They are looking at these 11 methods and variants (page 5/29)
- disposing of it in the soil (without any treatment / after dilution / after separation)
- pouring it into the sea (after dilution / after separation)
- disposing of it into the atmosphere, as steam (without any treatment / after dilution / after separation)
- disposing of it as hydrogen gas (? page 21/29, after electrolysis) (without any treatment / after separation)
- "burying" the tritium undergound (without any further treatment)
The report goes into details about the various conditions and limitations which must be taken into account for each method, as well as some concept presentations, some of them with certain detail. Criteria to be used for comparison are proposed in the end (page 29): the time needed to finish the stocks of contaminated water using that method; economic arguments; previous accomplishments with that method; agreement with regulations.
However, this report doesn't go beyond that - it just proposes a basis for further discussions and evaluations.

 

[nikkkom]

Tritiated water can also be locked up in concrete.
With polymer sealing of the resulting concrete blocks, internal water can be prevented from gradually leaking out of them. Tritium is beta-active (IOW: not gamma), so such concrete does not need any further shielding.

This may be a viable way to dispose of it if there are large construction projects reasonably close to Fukushima.
IIRC there is a lot of coastal dam construction along the coast now?

 

[Sotan]

Right as you say nikkkom - this is actually one of the methods they are considering (my translating it only as "burying" the tritium underground was incomplete and thus misleading).
Page 22/29 in the above mentioned document refers to it in some detail.
"Variants A5-1, A5-2: Burying (the tritiated water) underground (without further treatment)"
The method requires digging a hole in the ground and preparing a concrete pit, surrounded on all sides by a 1-2m layer of bentonite-soil mixture with the role of preventing underground water from seeping in and tritiated water from seeping out. Tritiated water would be mixed with a cement-type "solidification agent", in time making it into a block unified with the concrete pit. After closing the concrete pit, a layer bentonite-soil mixture would be added above, and additional soil gathered up above it under the form of a mound.
Page 23/29 gives additional details and a sketch. With a depth of 8m, a total of 285,000 m2 area of concrete pit would be needed.
Page 27/29 shows how they would compute the thickness of the bentonite layer (I couldn't understand that but it seems to depend on the tritium content of the water; for water containing 4.2 million Bq/l they conclude 2m would be enough, while for 0.5 million Bq/l a layer of 1m would be enough). At the top of the page they mention something which suggests they consider such a method for controlling water seepage because it is the least "man-made" one - I suppose, in contrast with waterproofing methods such as the polymer sealing you mentioned. (Why does it need to be non-artificial, non-man-made, I don't know - perhaps to avoid some criticism.)

Page 29/29, regarding this particular method, says:
Time require for construction = not clear, as there are no matching precedents (general experience regarding the underground storage of low-level contaminated matters could be used as reference);
Time needed to complete the operation = would depend to some extent on applicable regulations;
Initial cost: not clear, as there are no matching precedents (general experience regarding the underground storage of low-level contaminated matters could be used as reference);
Running costs: probably low, as the buried block would not require maintenance
Previous experience and accomplishments: not regarding tritiated water, but has been used before in the country for the underground storage of low-level contaminated matters.
Regulation issues: permits for the construction works.
Notes: requires land; requires land access/management even after finishing burying the tritiated water.

 

[Sotan]

http://www3.nhk.or.jp/nhkworld/en/news/20160303_29/
"TEPCO to create frozen wall soon"

"On Thursday, the Nuclear Regulation Authority basically approved the plan to begin the freezing."
"The regulator is to give final approval this month if it receives a concrete emergency response plan from the firm and finds no problems."

 

[nikkkom]

Page 27/29 shows how they would compute the thickness of the bentonite layer (I couldn't understand that but it seems to depend on the tritium content of the water; for water containing 4.2 million Bq/l they conclude 2m would be enough, while for 0.5 million Bq/l a layer of 1m would be enough). At the top of the page they mention something which suggests they consider such a method for controlling water seepage because it is the least "man-made" one - I suppose, in contrast with waterproofing methods such as the polymer sealing you mentioned. (Why does it need to be non-artificial, non-man-made, I don't know - perhaps to avoid some criticism.)

This devolves into some ridiculous exercise, doesn't it? There are gazillions of standard products to render concrete completely waterproof. For example, youtube search for some:

https://www.youtube.com/results?search_query=concrete+sealing

One of the videos:


Since isolation of tritium-bearing material is necessary only for 100 years or so to decrease its radioactivity thousandfold, no need to use super-durable, super-thick layers of protection. If concrete is partitioned into blocks which are sealed individually, a few mechanically damaged blocks would leak only their contents.

 

[Sotan]

I totally agree nikkkom.
An internet search on bentonite water insulation will find many resources too (a Japanese site stresses exactly the environmental advantages of using bentonite, "it is friendly to nature and friendly to people", and another site stresses that bentonite barriers have a long life - after all bentonite itself is 90 million years old...) but apart from that, why one couldn't use polymers like you mentioned... I don't know.
It's also hard to understand because in other areas they are innovative and eager to introduce new techniques and materials (e.g. the muon visualisation, or the fluid stuff used to fill the trenches).

During my searches, however, I found numerous earlier version of the this document, for example this one of 2014:
http://www.meti.go.jp/earthquake/nuclear/pdf/141024/141024_01_003.pdf
(in Japanese)
That is almost the same content, so it seems to me like they are taking this matter rather slowly...

 

[etudiant]

I totally agree nikkkom.

During my searches, however, I found numerous earlier version of the this document, for example this one of 2014:
http://www.meti.go.jp/earthquake/nuclear/pdf/141024/141024_01_003.pdf
(in Japanese)
That is almost the same content, so it seems to me like they are taking this matter rather slowly...

Is this perhaps the regulators method, 'study' the problem long enough and eventually everyone will accept the regulators preferred solution, which in this case is just dumping the tritium contaminated water?

 

[Sotan]

That was what I thought too etudiant.
I even wrote, as a joke, "they look like they're waiting for tritium to decay" but right before posting it didn't look too funny.
But yes, tritium keeps decaying, and yes, it is a rare case, when the regulator says "why don't you take this easy way" and Tepco is stubborn.

 

[mathman]

Harnessing[/PLAIN] Cosmic Rays to Peer Into Fukushima’s Deadly Reactors
Physicists use particles called muons to map the melted nuclear cores25 Feb
Above is title of article from Mar 2016 IEEE Spectrum.

 

[Jim S]

FYINuclear Street News

Tue, Mar 1 2016Kurion Completes Commissioning Of Modular Detritiation System

Kurion, Inc. said Monday that it had completed construction and acceptance testing of its prototype Modular Detritiation System and has initiated the system’s mission, which is to push the technology for additional performance through various experiments.

http://file:///C:/Users/Ozknox/AppData/Local/Temp/msohtmlclip1/02/clip_image002.jpg The MDS has completed an extensive cold and hot commissioning phase and is achieving its design goals based on scaling-up its proven bench scale system. This milestone comes less than six months after Kurion announced the development of the prototype system, delivering on patent-pending technology that removes tritium from contaminated water.

Kurion said its MDS is the world’s first solution to process large volumes of light water across a range of concentrations to remove tritium contamination. The system allows for the recycling or clean release of reactor cooling water for light water reactors.

The technology builds upon proven heavy water solutions and applies advances in throughput and efficiency for light water detritiation. Kurion’s MDS is a cost-effective solution to manage tritium and eliminate the release of tritiated water to the environment, the company said. The new system will use a full-scale catalytic exchange column, which is a central facet of Kurion’s technology.

Kurion is currently in discussions with a number of customers domestically and abroad to introduce its mature MDS technology to provide nuclear operators a new tool to manage tritium removal. Interest ranges across both operating and decommissioning plants.

David Carlson, Kurion's senior vide president of the Separation Business Unit, said tritium removal presents a unique cleanup challenge around the globe. “We are working with leading tritium experts and customers globally to achieve this success. We combine more than three decades of innovation and improved economics to provide cost-effective and environmentally friendly technology to remove tritium and improve the environment now and in the future,” he said.

 

[etudiant]

The Kurion website claims each MDS module can process 7 tons of water/day, so TEPCO would need several dozen modules.
No insights as to industrially significant aspects including operating costs, reliability or maintenance requirements.
http://kurion.org/wp-content/uploads/2014/11/MDS-Brochure-for-WEB.pdf

 

[mheslep]

The WSJ has a substantive, 5yrs out article (pay-walled) on the Fukushima clean-up operation. The authors, Negishi and Pfanner, are both Japanese based correspondents. The article has a graphic illustrating the overall ground water flow intercept plan, cites flow rate at 400 tons/day, total clean up cost at $100B.

 

[etudiant]

Fukushima Diary ( http://fukushima-diary.com/2016/03/tepco-considering-discharging-tritium-to-the-pacific/ ) reports that Mr Matsuda, identified as the 'plant decommissioning chief' , has indicated that the tritium bearing water may need to be dumped.
In light of the earlier information from Sotan San, it seems the regulator view has prevailed. Not sure about the potential for the courts to block such a move.

 

[mheslep]

Fukushima Diary ( http://fukushima-diary.com/2016/03/tepco-considering-discharging-tritium-to-the-pacific/ ) reports that Mr Matsuda, identified as the 'plant decommissioning chief' , has indicated that the tritium bearing water may need to be dumped.
In light of the earlier information from Sotan San, it seems the regulator view has prevailed. Not sure about the potential for the courts to block such a move.

When dumping tritiated water to the Pacific, I'm curious if it makes sense to pump it into the deep ocean where it would decay before reaching surface waters, rather than a surface dump to begin with.

 

[etudiant]

Following on to this idea, there is a big overhang of surplus tankers worth only scrap value.
Buy a few, gut them of any environmental hazards, fill their tanks with the tritium bearing water and tow them to their sinking site.
All the water in question should fit easily into a half dozen large tankers.

 

[Sotan]

http://www.tepco.co.jp/nu/fukushima-np/handouts/2016/images1/handouts_160317_06-j.pdf
(in Japanese)

Tepco is starting, sometime this month, the muon measurement on Reactor 2.
Considering the placement of the measuring device, there will be a "dead angle" of about 8 degrees, meaning the lower part of the PCV will not be imaged; but the whole RPV region is probably going to show up.
Again because of the placement, the fuel in the reactor and the fuel in the SFP will not be superimposed in the resulting image (the SFP will not affect the main target of the measurement).
The measurement will take about 3 months, same as it took for R1.

 

[etudiant]

http://www.tepco.co.jp/nu/fukushima-np/handouts/2016/images1/handouts_160317_06-j.pdf
(in Japanese)

Tepco is starting, sometime this month, the muon measurement on Reactor 2.
Considering the placement of the measuring device, there will be a "dead angle" of about 8 degrees, meaning the lower part of the PCV will not be imaged; but the whole RPV region is probably going to show up.
Again because of the placement, the fuel in the reactor and the fuel in the SFP will not be superimposed in the resulting image (the SFP will not affect the main target of the measurement).
The measurement will take about 3 months, same as it took for R1.

As with the ice wall, this rather gives the impression of 'going through the motions'.
I don't believe that anyone doubts that the three reactors all experienced complete core meltdowns. Moreover, all simulations agree that the molten material would breach the RPV in short order (minutes, not days). So there is a high likelihood that the new study will again find a 'significantly small' amount of nuclear material in the reactor 2 RPV, just as we all expect.
A more ambitious effort which would have required deeper placement of the muon probes might have located the core material. Yet TEPCO chose not to attempt that. Has there been any discussion as to why TEPCO is so incurious?

 

[Sotan]

There is another, a little more detailed document on this subject available on NRA site:
https://www.nsr.go.jp/data/000143713.pdf
(in Japanese)
First of all, in this matter (muon scanning) TEPCO works together with IRID and I suppose the decision making process is even more complicated than in other areas.
Also, the mentioned documents indicate that there are many issues to be considered when doing these measurements, especially related to the coordination with other works that are going on.
For example, the measurement that is about to start on Reactor 2 will be done with a new device, weighing only about 300 kg, which had to be rapidly developed because the much larger one used on Reactor 1 (20 tons) could not be placed near Reactor 2 due to the lack of a suitable crane.
Also, there are two types of muon scanning techniques; all mentioned until now are of the "transmission" type, but IRID has also been researching a "muon scattering" method, which makes use of two detector panels placed as to "sandwich" the targeted object (be it PCV or RPV). The transmission method has a resolution of about 1m; the scattering method has better resolution (~30 cm) but requires huge (10m/10m) panels which weigh 60 tons and more. They have been developing this method specifically for Reactor 2, where previous models indicated that there might be a significant amount of fuel left, but those models evolved and now the "significant" part is under question. So they are actually considering very carefully whether this more difficult scattering technique is really worth developing and applying. For now they decided to use the cheaper faster easier - and previously tested - transmission method.

I can't say anything / haven't read anything about why it was not possible to perhaps dig in the ground and place the muon detector in a lower position so it could better "catch" the location of the molten fuel. My feeling is that... if it was possible they would have done it. They need that information.

 

[etudiant]

There is another, a little more detailed document on this subject available on NRA site:
https://www.nsr.go.jp/data/000143713.pdf
(in Japanese)
First of all, in this matter (muon scanning) TEPCO works together with IRID and I suppose the decision making process is even more complicated than in other areas.
Also, the mentioned documents indicate that there are many issues to be considered when doing these measurements, especially related to the coordination with other works that are going on.
For example, the measurement that is about to start on Reactor 2 will be done with a new device, weighing only about 300 kg, which had to be rapidly developed because the much larger one used on Reactor 1 (20 tons) could not be placed near Reactor 2 due to the lack of a suitable crane.
Also, there are two types of muon scanning techniques; all mentioned until now are of the "transmission" type, but IRID has also been researching a "muon scattering" method, which makes use of two detector panels placed as to "sandwich" the targeted object (be it PCV or RPV). The transmission method has a resolution of about 1m; the scattering method has better resolution (~30 cm) but requires huge (10m/10m) panels which weigh 60 tons and more. They have been developing this method specifically for Reactor 2, where previous models indicated that there might be a significant amount of fuel left, but those models evolved and now the "significant" part is under question. So they are actually considering very carefully whether this more difficult scattering technique is really worth developing and applying. For now they decided to use the cheaper faster easier - and previously tested - transmission method.

I can't say anything / haven't read anything about why it was not possible to perhaps dig in the ground and place the muon detector in a lower position so it could better "catch" the location of the molten fuel. My feeling is that... if it was possible they would have done it. They need that information.

Thank you for digging out this added information. It very much helps put things into context. Even if they just get it confirmed that the fuel has left the reactor 2 RPV, that will be useful. Knowing where the fuel is not should help with the water management, as why pour water into an empty RPV?

One guess is that digging in the sensors may have been an issue for the ground water management.

 

[Rive]

Even if they just get it confirmed that the fuel has left the reactor 2 RPV, that will be useful. Knowing where the fuel is not should help with the water management, as why pour water into an empty RPV?

It's not that easy. There are levels for the fuel relocation: it can be damaged but in place: it can be molten and sunk to the bottom of RPV: the RPV bottom can be broken and the fuel is (partially or entirely) down on the bottom of drywell - but some of the fuel (even if not detectible by this equipment) can be in its original place in any of these versions, so the cooling cannot not be stopped till more accurate measurements takes place (actually, till they got close visuals form RPV internals).

 

[Sotan]

Japanese TV stations report that Tepco has started today the soil freezing for creating the ice wall around Fukushima Daiichi plant, after finally receiving the approval from NRA yesterday March 30.
http://www3.nhk.or.jp/nhkworld/en/news/20160331_21/

 

[Sotan]

Progress Status and Future Challenges of the Mid-and-Long-Term Roadmap toward the Decommissioning of TEPCO’s Fukushima Daiichi Nuclear Power Station Units 1-4 (Outline) (PDF:5,165KB) - Updated on March 28, 2015
http://www.meti.go.jp/english/earthquake/nuclear/decommissioning/pdf/20160225_e.pdf

 

[etudiant]

Thank you, Sotan, for posting this.
It is the best status report that I've seen, better graphics and good discussions. It does give a sense of how much work Japan has been doing, without minimizing how much remains to be done.

 

[nikkkom]

The plan to dissolve RPVs into rust with constant water injection for years on end is not progressing fast enough. I think they need to try to switch to acid solution. [Sarcasm]

 

[Rive]

The plan to dissolve RPVs into rust with constant water injection for years on end is not progressing fast enough. I think they need to try to switch to acid solution. [Sarcasm]

Well, that's my idea.
As I know there is a way for uranium mining with pumping down acids... So why would it be sarcasm? [Sarcasm]

 

[etudiant]

Freezing the surroundings and leach mining the corium may eventually wind up getting used.
Certainly seems less implausible than some of the mechanical approaches that have been floated.
Plus TEPCO now has a lot of practical experience dealing with highly radioactive fluids.

 

[Sotan]

http://www.tepco.co.jp/nu/fukushima-np/handouts/2016/images1/handouts_160412_02-j.pdf
(in Japanese)
An April 12th report about the installation of supporting beams and then of shielding plates on the operating floor of Reactor 3 Building (this time in the area designated by "A".
Just one page, might not even be worth mentioning... except for that striking photo, with the rubble in front and the blue ocean as background.

 

[turi]

except for that striking photo, with the rubble in front and the blue ocean as background.

If it is just for the photo:

 

[Sotan]

I confess I didn't manage to get to that photo at that size/resolution :) Only much smaller ones.
Thank you Turi!

 

[Sotan]

Tepco is now publishing periodically reports on the progress of the ice wall operation.
Latest example is of 21 April (in Japanese):
http://www.tepco.co.jp/nu/fukushima-np/handouts/2016/images1/handouts_160421_04-j.pdf
Page numbered 1 shows the evolution of soil temperatures (in general, in operating areas they are approaching freezing point by now).
Pages 2-6 show the levels of underground water measured in various wells (these are indicated on Page 7).

I find suggestive and interesting the graphs given on pages 7-13. Each graph corresponds to a section of the contour of the ice wall; the color gives the temperature of the soil in that area - at various depths reaching OP -24m. More and more blue areas expected to appear on these graphs as the freezing progresses.

 

[Sotan]

English version of the ice wall report mentioned above:
http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2016/images/handouts_160421_01-e.pdf