Fukushima Japan Earthquake: nuclear plants Fukushima part 2

[etudiant]

Thank you LabratSR.
Good video, shows some significant progress, somehow gives a bit of reassurance.
It takes time but the Japanese seem to be working steadily towards their goals.

- One thing that doesn't seem to be going too well (and therefore isn't mentioned in this video either) is the ice wall. If my impression is right, most of the measuring points for soil temperature show an increasing trend (for example: http://www.tepco.co.jp/nu/fukushima-np/handouts/2016/images1/handouts_160114_03-j.pdf). Tepco simply shares the data but doesn't comment much on this. Why isn't it working - and why are they still trying to accomplish it, what makes them believe it will work in the end?

Sotan, thank you for keeping us posted. This will be a very long slog and it does not get the coverage it deserves.
Re the ice wall, there had been some discussion suggesting that the salinity of the plant site groundwater was rising, indicating increased seawater infiltration as the ice wall reduces land side inflows. Apparently the ALPS system is not set up to cope with saline contamination, so letting the ice wall slide may be the lesser of two evils.

 

[Sotan]

Thanks for that answer etudiant.
I understand two things from there, 1 - that even if the ice wall is successful, it might stop/reduce the land side inflow more than it stops/reduces the sea side inflow, and 2 - that the possibility of giving up the ice wall does in fact exist. This clears some of my questions.

----------------
Different topic:
In a new post on its site Tepco shows updated plans and developments for removing the spent fuel from the SFP of Unit 3.
http://www.tepco.co.jp/nu/fukushima-np/handouts/2016/images1/handouts_160118_03-j.pdf
(in Japanese)

Page 2 lists the main steps towards that goal. Step 1 - removing large debris from the operating floor (completed inb Oct 2013) and from the SFP (completed in Nov 2015). Step 2 - decontamination and shielding, still under way. Step 3 - installation of a new building cover to be used for spent fuel removal (including practice and mock-ups, first at a plant located in Iwaki at 60km distance and later directly on site). Step 4 - removal of the 566 spent fuel bundles, to begin within fiscal 2017.
Page 3 - images with the operating floor and Unit 3 reactor building "before and after" removal of large debris.
Page 4 - same with the the SFP, with accent on the removal of the FHM that had fallen in as a result of the hydrogen explosion.
Page 5 - overview of the work for decontamination and shielding of the operating floor
Page 6 - general presentation of the new building cover. To be placed over a working platform which will be built 6m above the original operation floor.
Page 7 - presentation of the process of installing the new building cover. I - shielding; II - placement of a support platform for the heavy cylinder used for fuel transfer (I can't remember its proper name right now); III - installation of beams for the new FHM; IV - new working platform; V, VI - roof and walls of the new cover; VII - new FHM structures; VIII-IX - completion.
Page 8 - images from the practice sessions for installation of the new cover.
Pages 9, 10 - overview of the use of new facilities (cover and FHM) for further removal of debris and eventually removal of spent fuel
Page 11 - schedule. Actual removal of spent fuel - planned to start early 2018.
Pages 12 to end: a presentation (by Toshiba) of the new cover building concept and its components.

 

[LabratSR]

Following up on Sotan's post -

Toshiba unveils remote-controlled device to remove reactor 3 fuel assemblies at Fukushima No. 1

http://www.japantimes.co.jp/news/20...-fuel-assemblies-fukushima-no-1/#.VpzK5GcUUdW

 

[etudiant]

Again very impressive, the effort appears to be moving forward with considerable determination. There is a lot of heavy engineering work on display here.

After this Toshiba will have the most capable heavy remote handling system in the world. I expect that will wind up being useful elsewhere, even outside the nuclear space.

 

[Sotan]

If you have a good internet connection, here is a 200 Mb video (almost 9 minutes) showing images from the Tepco labs which analyze sea and underground water samples for radioactive contamination. Very important every day activity, which must be well done. The film doesn't look bad at all, I suppose a chemist could appreciate it better than me, but still, anyone gets an idea of the size of the job, the technology used and the way they handle it. Last year 87,000 samples were analyzed.
http://www.tepco.co.jp/tepconews/library/archive-j.html?video_uuid=v1x9t3o4&catid=61699
(unfortunately all captions are in Japanese only.)

 

[etudiant]

Very interesting video. These guys are working industrial scale on a tough gig.
Have to say I'm surprised by the size of the samples that are used and by the amount of handling involved.
There has been so much work done on automated sample handling for the health care industry, much of it developed in Japan, that one would have expected something similar here.
Separately, is it still necessary to wear full gowns and masks for the working near Fukushima? Even the researchers taking samples offshore seemed fully outfitted. That has got to make work much more difficult still. Does anyone have any idea when they can maybe just go with face masks?

 

[Sotan]

Latest report (of Dec. 24) on 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 has been translated in English and posted on the METI site:
http://www.meti.go.jp/english/earthquake/nuclear/decommissioning/pdf/20151224_e.pdf

 

[turi]

Separately, is it still necessary to wear full gowns and masks for the working near Fukushima? Even the researchers taking samples offshore seemed fully outfitted. That has got to make work much more difficult still. Does anyone have any idea when they can maybe just go with face masks?

The last page on the pdf Sotan posted shows some info about where normal face masks are allowed. The progress video earlier also talked about this.

http://www.meti.go.jp/english/earthquake/nuclear/decommissioning/pdf/20151224_e.pdf

 

[Sotan]

http://ajw.asahi.com/article/0311disaster/fukushima/AJ201601270040
"Nuclear reactor mockup to be used to advance decommissioning technology"
Life-size model of Unit 1 Reactor will be ready in Mid March.

 

[Cire]

Found what looks like tepco's 2016 road map.. Does anyone know a translation to this?

http://www.tepco.co.jp/nu/fukushima-np/roadmap/images1/images1/d160128_08-j.pdf

 

[Sotan]

Cire, the file you found is part of the update of Tepco's "Mid-and-Long-Term Roadmap towards the Decommissioning of TEPCO's Fukushima Daiichi Nuclear Power Station Units 1-4". The update published on January 28 can be found at http://www.tepco.co.jp/decommision/planaction/roadmap/index-j.html and consists of 13 files.

These updates - or at least some of the files - do get translated in English, but it can take about a month. For example, the update published on December 24, 2015 has been translated and posted on January 15. As far as I know the translations get posted on the METI site: http://www.meti.go.jp/english/earthquake/nuclear/decommissioning/index.html

----
Back to the file you mentioned, it is the file in this roadmap update which refers to "Preparations in view of the extraction of the fuel debris" and contains 2 parts:

- First part (pages 3-10) is a report from IRID regarding the development of techniques for the investigation of the interior of the PCVs, in this particular case in preparation for the investigation of the pedestal area in the PCV of Unit 1.
Page 4 shows the steps of this planned investigation, which will require access through the X-100B penetration: step B1 is the investigation of the grating at 1st floor (finished in fact in April 2015); step B2 will be the actual investigation of the outside of the pedestal area, hopefully with images of the situation of the molten fuel. B2 may be followed by further investigations of this area, depending on what they find.
Pages 5-6 are a recapitulation of what was done in step B1.
Page 7 presents some conclusion obtained from B1 and their effect on B2. Before their plan was to go back to the grating at 1st floor and then lower a device through the grating onto the pedestal level. However, they fear it might be difficult to drive a robot on the pedestal level, so they changed that and now they plan to send the robot farther away on the grating, to a place where it can be lowered much closer to the area of interest and get a view of it, perhaps while hanging.
Page 8 - considerations regarding the technique for B2 investigation. First they plan to do plenty of simulations aimed at obtaining date regarding the position and spreading of the molten feel based on radiation measurements in the area. A device for precise measuring of radiation underwater will have to be designed, as well as all the reliable technology for driving and lowering sensors below the grating. Also it is hoped that visual imaging of the molten mass will be possible, providing precious date to be analyzed and used later.
Pages 9-10 further explain the concept of the planned B2 investigation. A "transformer" type robot similar to the one used before will be driven onto the grating up to the suitable spot and a camera + radiation sensor (hopefully as small as 20 mm diameter) will be lowered towards the pedestal.

- Second part (pages 11-18) is a report from Tepco regarding the progress in the decontamination of the X-6 penetration area of Unit 2.
Page 12 explains that until now they have done scraping the melted/solidified matter from the floor, vacuuming the scraped matter, steaming the surfaces and treating them with a chemical foam, and finally a deeper scraping of the surface. This last step is the subject of this report.
Page 13 shows radiation dose data measured in the area. The red rectangle shows the most recent ones, taken on Jan 19.
Pages 14-15 shows the floor in the area of X-6 penetration, before and after the deep scraping as well as after the chemical cleaning operations.
Page 16 gives the schedule (this decontamination will actually take a while, maybe through March).
Page 17 shows the planning that has been done to deal with the dust that arises during the scraping of the cement surfaces. On Dec 17, 2015 there was an instance when dust was produced in the area due to the malfunction of the vacuuming machine. Additional measures were taken then to prevent a reocurrence - but on Jan 7 they had some dust again. They are still investigating the causes. (All this dust was limited to that area only, no effect outside of the reactor building. A measurement performed on the the dust gave Cs 137: 1.0E-03Bq/cm3,Cs-134: 2.4E-04Bq/cm3.)

 

[SteveElbows]

I thought the X-6 penetration decontamination attempts looked like something of a failure in that document. And indeed I just noticed that TEPCO made an English press release in late January that admitted there would be a delay:

http://www.tepco.co.jp/en/press/corp-com/release/2016/1266495_7763.html

After several decontamination measures were conducted, the radiation level in the vicinity of the X-6 penetration pipe is beginning to decrease partially. But the radiation level being still high as a whole, TEPCO has concluded that the insertion of the robot should be rescheduled, likely for some time after FY 2015. The rescheduling is not expected to have a impact on the medium-term road map.

 

[jim hardy]

What goes through X-6? A letdown pipe ? Wires ? TIP probes ?

IOW is the radiation from inside a pipe or from ' stuff ' that's dripped onto X-6 ?

 

[Sotan]

@jim hardy:
In a Tepco report of 28 Sep 2015 where they talked about the melted "stuff" that appears to have leaked from the X-6 penetration flange/lid, they speculate it may come mainly from the melted O-ring of the flange or the plastic covers of the cables located inside the penetration pipe, identified as "power cables of the machine for changing the CRD". There doesn't seem to be anything else in that pipe. These cables appear mentioned in another older report, too and they will have to be removed or dealt with somehow, before sending in the robot, when that time comes. As for the radiation observed at this moment in the small room around the penetration end, it can't come from the melted stuff, as it has been removed already (was easily scraped away with a metal blade). In an older report they mention that the radiation coming from inside the PCV should account only for roughly 100 mSv/h and the larger values observed in the area must be due to the general contamination of surfaces (at that time the melted stuff had not been removed, either). Incidentally, their goal for the decontamination of this area is 100 mSv/h or lower.

@SteveElbows:
Indeed it is kind of a failure, at least they didn't expect it to be so difficult to decontaminate the area, and this is described in the text at the top of page 13, together with the Table on the same page, in the file posted by Cire above:

The Table shows measured radiation doses in various spots in the area (spots indicated in the first two columns, meaning Left, Center and Right, each of these having 5 additional places indicated as A ~ E; measurements were done at 6 times, given in the 6 numerical columns, from left to right: 1) after the removal of the concrete blocks in front of X-6 lid; 2) after removing the melted stuff; 3) after 2 steam treatments; 4) after 7 chemical treatments; 5) after 5 attempts to scrape away a layer of some surfaces, and 6) after 2 more chemical treatments.

The text above the table says this:
- Removing the melted stuff led to a decrease in the radiation values in Left and Center portions.
- After the steam treatments there were spots where the radiation value increased, as well as spots where a decrease was noticed.
- After the chemical treatments, all values fell below 12 Sv/h (measurement range maybe). Even spots where the steam led to an increase of the radiation value returned close to whatever they had after the removal of the melted stuff.
- After 5 scraping operations, when further scraping was attempted there was unacceptable dust release, so the work stopped. Some additional chemical decontamination was then done again.
- The scraping of the floor surface led to a decrease in radiation in certain places, but not an overall decrease for all the area. Final values in the red rectangle in the Table.

So indeed they are not happy with the results (as mentioned above they would like to lower the values below 100 mSv/h).
Considering the failure to decrease radiation values even by scraping 2.5 mm of concrete surfaces(including paint) and then mopping the area with chemicals, they suspected that the surfaces are contaminated more deeply.

 

[jim hardy]

"power cables of the machine for changing the CRD".

Thanks Sotan. I'm sorry, i missed that September report - shouldn't have had to ask.

Wires could be nigh impossible to decon if 'stuff' has got in the interstices between filaments.

 

[Sotan]

No worries Jim, nobody can keep up with these thousands of reports. Plus they are mostly in Japanese. I browsed through them for an hour to post that reply, I don't remember them either.

As for the cables/wires inside the penetration, I don't think they plan to decontaminate them. They'll probably be happy to be able to just cut and remove them or push them inside the PCV, if they obstruct the access of the robot. I have a feeling I read they did something like that for another penetration/robot/reactor investigation... but I couldn't find it now.

 

[jim hardy]

Thanks Sotan. Not of major consequence and I'm sorry it took so much of your time.

I just try to keep my alleged mind aware of little peculiarities that don't seem to fit.
This fits perfectly with the old ORNL predictions that penetration seals would melt allowing whatever awful stuff is no longer 'contained' to seep out. Were it a piping penetration i'd be curious why it didn't respond to flushing. But wires with melted jackets are tough going. Ever had to fix a burnt car wiring harness ?

keep it simple(i have to)

old jim

 

[Sotan]

http://www.tepco.co.jp/en/press/corp-com/release/2016/1267045_7763.html
The "ice wall" construction is complete.

The actual operation of the wall "must await approval of Japan's Nuclear Regulation Authority, which in turn will depend, at least in part, on TEPCO showing a method to ensure that the wall (and other groundwater pumping operations) do not invert the water level difference in any way that would cause contaminated water to flow out of the buildings' basements."

 

[etudiant]

http://www.tepco.co.jp/en/press/corp-com/release/2016/1267045_7763.html
The "ice wall" construction is complete.

The actual operation of the wall "must await approval of Japan's Nuclear Regulation Authority, which in turn will depend, at least in part, on TEPCO showing a method to ensure that the wall (and other groundwater pumping operations) do not invert the water level difference in any way that would cause contaminated water to flow out of the buildings' basements."

Presumably the NRA now believes that the water in the buildings is a relatively stagnant pool sitting on top of 3 reactors worth of corium. Logically they are reluctant for TEPCO to disturb this relatively stable state by altering the water flows.
It should be possible to better assess the actual state of affairs by sampling the water in the reactor buildings at various levels, but afaik there has not been any communication regarding this.

 

[Sotan]

While building the ice wall they have been definitely working on how to address the points raised by the NRA.
They have just published this report (in Japanese only, for now)
http://www.tepco.co.jp/nu/fukushima-np/handouts/2016/images1/handouts_160215_02-j.pdf
which is a point-by-point explanation of how they believe they can handle the various situations that can occur, during the operation of the ice wall, so that to permanently keep the water level in the basements of the reactor buildings below the level of the underground water of the surrounding areas, which is one of the essential principles for avoiding the contamination of the ocean.

It's a very complex document and it will take me some time to translate some significant parts of it, but I will post some of the conclusions given in a second report - which is like a summary of the one given above. (http://www.tepco.co.jp/nu/fukushima-np/handouts/2016/images1/handouts_160215_01-j.pdf)
It appears that TEPCO submitted to NRA that they want to first fully close the wall on the ocean side, and then gradually close the wall on the mountain side, wile continuously watching and working on the water levels.

By first closing in the sea side ice wall they believe they greatly eliminate one risk that has been pointed out until now - that is, the risk that the underground water levels in the facility might decrease too much (and thus contaminated water from basements might spread towards the sea). They even took the analysis one step further and set a "minimum admissible water level", defined as the level of the ocean during the (average) maximum tide. The envisioned working rules are designed to eliminate the risk of water level inversion even if the water level in the areas surrounding the building basements approaches this "minimum admissible water level".

- The basement of Unit 1 reactor building is scheduled to be dried up during fiscal 2016 - after all there are only about 200 m3 of water in there, easily pumped up if/when needed (pumps can manage 10 m3/h). The total amount of contaminated water in all basements (down to the "minimum admissible water level") is 36,000 m3; they already have storage tank space for it and some extra (70,000 m3 to be exact). Another parameter to be considered is the capacity of the water treatment instalations, which is 1200 m3/day. This means they have the capacity to lower the level of the water in the basements by 1 cm/day, which they believe is enough manoeuvering capacity to prevent an inversion of the water levels.

- In order to prevent an inversion of water levels (in other words, to always keep the water level in basements below the water level in the surrounding areas within the plant premises) there are in fact two things that can be done: one is to decrease the water level in basements by pumping (explained above) - but another is to actually raise the underground water level in the surroundings - for example by stopping the pumping from the "subdrain" wells, or by stopping the pumping of cold brine through the pipes of the frozen wall (and thus increasing its "permeability"), or by a smart combination of the two methods.

- What will happen when the first close the sea-side ice wall? There is a risk of water building up in the undergroundin the areas inside the ice wall. They evaluated this risk and obtained these numbers: at present, the amount of "new" contaminated water per day is about 550 m3. If they first closing the mountain side ice wall this parameter would decrease to 50 m3 a day. If they first close the sea-side ice wall, the value would be 270-330 m3/day, so an extra 200-250 m3/day. Therefore they re thinking to try starting the gradual closing of the mountain side ice wall as early as possible.

- They also have designed a 4 STEP procedure of operating the ice walls (sea-side and mountain side) which they believe would work best. Step 1 - freeze the sea-side wall, freeze just an experimental portion of the mountain side wall; Step 2 - while the frozen portion of the mountain side wall starts showing effects, keep operating the subdrains; Step 3 - continue to freeze further portions of the mountain side wall - and also gradually stop the pumping from the subdrains; Step 4 - reaching the situation of the whole ice wall fully frozen. I feel these 4 steps should be more fully presented in a another post based on the detailed report - but I don't have the time right now. They also present a set of "operating rules" which take into account, overall, the experience accumulated until now regarding the possible manipulation of water levels, as well as some of the uncertainties that cannot be eliminated.

 

[etudiant]

Wow, that is a massive document, a big amount of work just to translate, a huge amount of work to create. Thank you so much for this posting.

It does suggest the way forward is very murky. Is it even desirable to dry out the basement of Reactor 1 when there is a large lump of corium somewhere outside the reactor vessel, perhaps between the reactor vessel and the floor?
The uncertainty as to where the fuel is now probably complicates the decisions, even though one could argue that no contamination that could conceivably arise at this point is within even 1 percent of that incurred to date.
TEPCOs desire to move ahead with the ice wall is surely motivated by their wish to slow the accumulation of treated water.
It seems that there is now almost a million cubic meters of treated water held on the site, which still has mostly residual tritium. Tritium removal is a very expensive and difficult proposition and is not done afaik at any commercial reactor sites.
Could that treated water not get dumped, maybe after transporting it far offshore in a barge? .The tritium quantities are not so high as to make that impractical iIrc.
That would obviate the need for the ice wall.

 

[Sotan]

The drying-up of the basement of Unit 1 was mentioned just in passing, in the context of the discussion about water levels; it didn't sound to me like they are desperate to do it, they will take their time. It's just something that will occur at some point, probably - I will explain that again below. The cooling of the corium will continue even after that, they will just be pumping away all the water that reaches the basement, I suppose.

But I also must correct one phrase: the 200 m3 of contaminated water in Unit 1 basement, which they mention they can pump away in less than 1 day, is just the amount situated below the "minimum acceptable level" defined/introduced in relation to the underground water level in the surrounding areas. (Context: for all the other units except Unit 1, the installed pumps can pump away contaminated water until its level goes below the "minimum acceptable level", therefore even if the underground water level in the surrounding level reaches this minimum, they have pumps to keep the basements below that level, thus obeying the general principle.)

So, assuming the underground water level in surrounding areas goes down (due to some effect of their manoeuvers with the ice wall and subdrains), they can and will keep pumping water from the basements trying to keep the desired level difference. When/if outside of the buildings the water level goes down to the "minimum acceptable", they will have almost dried the basement of Unit 1; in fact, in order to keep a level difference, in such a case they would probably pump away the remaining 200 m3 and thus "dry it". I'd say it won't be actually "dry", as cooling and water infiltration from the surroundings will continue, but they will keep pumping it all away as it comes.

Wanted to correct that; I wasn't quite right the first time, it's getting clearer to me too as I post...

The seem eager to put all these instruments at work, both in order to reduce the daily amount of contaminated water - but also in preparation for the day when they start actually working on the coriums. They need to be sure that won't cause additional contamination of the ocean.

 

[etudiant]

The drying-up of the basement of Unit 1 was mentioned just in passing, in the context of the discussion about water levels; it didn't sound to me like they are desperate to do it, they will take their time. It's just something that will occur at some point, probably - I will explain that again below. The cooling of the corium will continue even after that, they will just be pumping away all the water that reaches the basement, I suppose.

But I also must correct one phrase: the 200 m3 of contaminated water in Unit 1 basement, which they mention they can pump away in less than 1 day, is just the amount situated below the "minimum acceptable level" defined/introduced in relation to the underground water level in the surrounding areas. (Context: for all the other units except Unit 1, the installed pumps can pump away contaminated water until its level goes below the "minimum acceptable level", therefore even if the underground water level in the surrounding level reaches this minimum, they have pumps to keep the basements below that level, thus obeying the general principle.)

So, assuming the underground water level in surrounding areas goes down (due to some effect of their manoeuvers with the ice wall and subdrains), they can and will keep pumping water from the basements trying to keep the desired level difference. When/if outside of the buildings the water level goes down to the "minimum acceptable", they will have almost dried the basement of Unit 1; in fact, in order to keep a level difference, in such a case they would probably pump away the remaining 200 m3 and thus "dry it". I'd say it won't be actually "dry", as cooling and water infiltration from the surroundings will continue, but they will keep pumping it all away as it comes.

Wanted to correct that; I wasn't quite right the first time, it's getting clearer to me too as I post...

The seem eager to put all these instruments at work, both in order to reduce the daily amount of contaminated water - but also in preparation for the day when they start actually working on the coriums. They need to be sure that won't cause additional contamination of the ocean.

Thank you for this extra update, it makes the situation as articulated by TEPCO much clearer.
It would be most informative if there were some comment or perspective from the NRA, to better understand their reservations. That would help get a sense of the extent of the work still needed before this goes ahead.

 

[etudiant]

It seems that TEPCO has accepted the NRA approach and will freeze the ocean side first. http://www3.nhk.or.jp/nhkworld/english/news/20160215_25.html
Given the 8 months interval for the wall to freeze up, there should be the ability to adjust as needed. The concern would be that the adjustments will also take time to take effect.

 

[Sotan]

Again from http://www.tepco.co.jp/nu/fukushima-np/handouts/2016/images1/handouts_160215_02-j.pdf
The 4 step procedure that is being planned (using the page numbers inscribed in lower-right corner of the PDF document):
(sorry for the long post, perhaps it's not that interesting but... I kind of promised, so I'll just put it here)

Page 51: a table showing the definitions and characteristics of the 4 steps (percentage of "wall closing", percentage of "water stopping", general situation at the end of each step).
Step 1 = freezing the sea-side wall, as well as the 18 portions of the mountain side wall which have been cooled experimentally already (they have no significant effect on the flow of underground water). There will be 18 portions of wall frozen, but the water stopping percentage is practicalli 0%. Due to the sea-side wall being closed/frozen causing a "dam effect", undergound water level will rise.
Step 2: In this stage the mountain side frozen portions will start showing an effect of decreasing the influx of undergound water. But this can be countered by stopping the operation of the subdrain wells (stopping them tends to lead to the rise of water level). Wall closing: 95%; water stopping: about 50%.
Step 3: continue to slowly freeze portions of the mountain side wall. Wal closing 95~100%; water stopping 50~100%. Some of the subdrain wells will stop operating.
Step 4: 100% of the wal closed, 100% of the influx of water stopped. The desirable difference in water level between buildings basements and their surroundings will be maintained.

Pages 52 to 55 list, for each step, the items and parameters which need to be measured and confirmed in order to consider that step finished and move forward.

Page 56: They analyzed the best scenario regarding the unfrozen portions in the mountain-side wall: should they be just a few such portions, but relatively long? Or is it better to have a lot of very short unfrozen segments. Good and bad points in each of these cases so... they chose a middle ground (compromise) variant.

Page 57 lists some considerations regarding the chosen locations for these unfrozen portions in the mountain side wall. They are spread over the length of the wall so that the decrease in water level should be as uniform as possible. That requires to maintain some uniform water flow around the buildings (portions 1), between the two big building blocks, meaning between Units 1+2 and Units 3+4 (portion 2) and some waterf low on the margins of the facilty too (portions 3).

The next pages again explain the 4-steps procedure:

Step 1
Page 58: Freezing 100% of the sea side (690m) and 6% of the mountain side wall (52m).

Step 2
Page 59: At the end of this step 815m of the 860m (95%) of the mountain side wall will be frozen. The 6 red circles at the bottom of the page indicate the small portions that will remain unfrozen.
Page 60: The unfrozen portions corresponding to the 6 red circles mentioned translate in segments of 4,6,9,7,8,7 and 4 meters length, respectively (a total of 45 m). The lower diagram shows portion number 3 (7 m long segment) made of 9 pipes through which no cold brine will be circulated. There is an extra non-brine pipe at each side of the interval. A well for measuring the level of the undeground water is in the vicinity.

Step 3 - the wall will be 95%~100% closed.
Page 61: As the closing percentage increases, the effect of the amount of rain becomes more and more important. In order to minimize the risc of an inversion in the water levels, they will proceed very carefully with the further freezing of the remaining portions of the wall. They will have to take measures to compensate for the increased speed of the current of underground water which can make the freezing more difficult (possible such measures: additional construction works to install more freezing pipes, pumping out some water form suitable wells in the vicinity thus slowing down the overall flow of water). Also, if no more water can be pumped out of a subdrain well, which means the underground water level went down too much, then stop the freezing operation and evaluate next steps.
Page 62: The underground water flow is expected to intensify in the segments where the wall is not frozen. Some additioanl works (additional brine pipes) can be installed in such areas if the water speed is so high that it prevents the freezing of the soil in the area.

Page 63: The debit of underground water coming through the mountain side wall will start decreasing after about 0.5 months from Step 2-beginning, and will reach the minimum level after about 1 month from the start of this step. The water debit at this point, Q-step2 is what they will have at the start of Step 3 too, which will be executed slowly and carefully. Further brine pipes may need to be installed in the fast flow areas, but eventually they expect to slowly freeze the whole mountain side wall. All the time watching the underground water level: if sudden changes are seen, they can always stop the freezing of these last portions and return to a previous known, safe state.

Pages 64-66 show calculations regarding the (ensuring of the) stability of the soil when the speed of the undergound water current increases.

Page 67: timeline of the 4 steps. About 9 months for everything.
[...]
Finally I would like to include this slide:
Page 73: what's to be done when something goes wrong:
Should the water level in the surrounding of the buildings goes down too fast, they plan to (1) actually pour in some water through designated wells. If the effects is not enough, then (2) stop the freezing or even unthaw some portions of the ice wall, then (3) pump away some more of the contaminated water from the basements and finally (4) remove some portion(s) of the ice wall. The measure (1) is also to be carried out in periods of extremely low rain amount, as needed.

 

[etudiant]

Thank you, Sotan, for this extra information. There has clearly been a lot of thought given to this effort.
It would be very helpful if TEPCO or the NRA would lay out what this considerable effort is expected to achieve, if anything, other than reducing the water storage problem. In a sense, it may be just another task whose purpose is to help clear the decks for the more difficult work yet to come, much like the removal of the Reactor 4 fuel from that reactors SFP.

 

[Sotan]

Well, I was trying to finds something about NRA's position (nothing on their site) when I found this short article in Yomiuri Shinbun:
http://www.yomiuri.co.jp/feature/TO000303/20160213-OYT1T50099.html?from=yartcl_popin
It is in Japanese, and I hope I don't make any major translation mistakes, but it includes the following:

On Feb. 13th Shunichi Tanaka, chairman of the NRA, spoke to reporters about the "frozen ground wall" which has been promoted by Tokyo Electric Power Company as one of the pillars of the contaminated water measures at the Fukushima Daiichi Nuclear Power Station plan. He said he was "not very much interested in that subject. (Even if it is completed) that will not mean the contaminated water issue is solved." He then repeated his opinion that the contaminated water should be purified and then pumped into the sea.
The comments were made after his inspection visit to Fukushima Daiichi.
[...]
Chairman Tanaka also said " if a continuous solution is not reached, such as purifying the water and returning it to the sea, then decommissioning process will not advance".

So... Tepco and NRA don't seem to agree much on this subject :/

 

[etudiant]

Wow, that is quite extraordinary. So the NRA sees the ice wall as a waste of time.
That puts the focus on what Chairman Tanaka means when he says the water needs to be 'purified'. If the NRA requirement is to remove the tritium, TEPCO faces a huge problem, because no good removal process exists afaik, only various fractionation schemes that would require distilling a million tons of water, perhaps repeatedly. Just finding space for the processing equipment would be difficult. Even worse, the 'purified' water would still have a sizeable tritium level, so getting approval for its release may still not be easily achieved.
'The best is the enemy of the good' was a dictum often quoted by the late Admiral Gorshkov. That seems to again be clearly illustrated in this situation.

 

[Sotan]

A search on internet makes it pretty clear that NRA and Mr. Tanaka have long advocated the release of tritium-containing water into the ocean.
for example this one year old article: http://blogs.wsj.com/japanrealtime/...or-calls-on-tepco-to-discharge-tritium-water/
"...The regulator discussed Wednesday a http://www.nsr.go.jp/committee/kisei/h26fy/data/0051_02.pdf by Tepco to address risks at the plant that sets out a 2017 start for discharging the water."
also
"Tepco has been storing the tritium-contaminated water in about 1,000 tanks, but is reluctant to release it into the ocean to avoid adding to tension with local communities and criticism from neighboring countries and some nations with a Pacific Ocean coastline."

Even the Feb. 13 statements mentioned in my previous post, when reported by another newspaper, include this:
http://www.minyu-net.com/news/news/FM20160214-049830.php
"Mr. Tanaka expressed his opinion that the release into the ocean of the water treated by ALPS, including the tritium-containing water stored in tanks on site, would lead to the solving of the contaminated water issue."

So they are realistic, no intention to try and remove tritium, rather a problem of when to do it (I mean the release in the sea of tritium-containing water) and how to convince the public that it's ok to do it.

 

[etudiant]

That is just stunning to me.
Who is in charge if the regulators and the regulate have a difference of opinion? Does not the government have a duty to reach a conclusion?
As is, it seems the ice wall effort is a way to keep the site work force busy doing something while the preparations for the other work, notably the clearing of the other 3 spent fuel pools, get completed..

 

[Sotan]

Until new info on this subject appears, here are two new videos available on Tepco's site at:
http://photo.tepco.co.jp/
One presents several instances of an "ordinary day" at Fukushima Daiichi nowadays. Workers reporting in, preparations, bus trip to the work site, taking a meal... Quite interesting.
The second shows the moments when the tunnel boring machine used to build an alternative to the "K drainage" arrives at destination.

--------------------
*info about the "K drainage" and other subjects, in English, in this Sep 2015 file that I found buried somewhere on the site of the Ministry of Foreign Affaris:
http://www.mofa.go.jp/files/000100392.pdf

 

[Sotan]

Latest report (of Jan 28) on 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 has been translated in English and posted on the METI site, possibly a few days ago but I haven't noticed it until now:
http://www.meti.go.jp/english/earthquake/nuclear/decommissioning/pdf/20160128_e.pdf

 

[Sotan]

This is in the news all over the internet; examples of links:
http://www.bbc.com/news/world-asia-35650625
http://edition.cnn.com/2016/02/24/asia/tepco-fukushima-meltdown/

Basically, Tepco had the data - and the operating manuals at the time apparently asked for it - to declare a meltdown as soon as March 14, 2011. But they chose to avoid that word for several more months.

"While it did not tell the public until May, TEPCO said that it had informed the government of the ongoing meltdown within days of the disaster, as required by law."We apologize for the great inconvenience and worry" the delay caused, TEPCO said.

 

[Azby]

It's been a long time since I've posted, so hello to everyone. Some of you may remember I'm very involved with Safecast. I'm working on an update to the Safecast Report which includes a section about the situation at the Daiichi site. I figured I'd check to see what was being discussed here, and found this great thread. I've been looking at many of the same documents you all have been discussing, and I have to say that Sotan's translations and summaries are fantastic, and have clarified a number of points for me. I'll probably include links to this discussion for people who really want to know the details.

To add my 2 cents, my impression is that the NRA has only given permission to start freezing the ocean side of the frozen wall. They may well give permission to do the sectional freezing of the mountainside wall in a couple of months after the ocean side wall is frozen and working, but from what I can tell they're not giving TEPCO reason to be optimistic about that, despite the detailed freezing proposals Sotan translated. What do you think, Sotan? I agree that NRA, represented by Tanaka, seems to really want to just dump the tritiated water. TEPCO has said all along that unless the water infiltration is controlled, many of the other steps in the decommissioning process will be difficult or impossible to perform. They really seem to be trying to keep the H3 levels in the denucleated water an under 1500 Bq/L, and decided not to dump water pumped up from 5 subdrains near the seawall ("impervious seaside wall") a few months ago after it was clear it had much more H3 than that.

Here are some recent news items about the NRA's position (sorry if I'm reposting something already posted):

Sankei Shimbun - Jan 22 2016 - Japan NRC calls for reconsideration of seaside frozen wall (Japanese)
http://www.sankei.com/affairs/news/150322/afr1503220003-n1.html

Asahi Shimbun -Feb 10, 2016 - NRA calls a halt to TEPCO's plan to freeze soil at Fukushima plant
http://ajw.asahi.com/article/0311disaster/fukushima/AJ201602100079 Asahi Shimbun - Feb 15, 2016 - NRA to allow part of frozen soil wall at Fukushima plant
http://ajw.asahi.com/article/0311disaster/fukushima/AJ201602150062

Asahi Shimbun - Feb 21, 2016 -TEPCO nears 'deep freeze' of soil wall at Fukushima plant
http://ajw.asahi.com/article/0311disaster/fukushima/AJ201602210030

Another NRA commissioner, Toyoshi Fuketa, seems to oppose removing all the melted fuel debris in comments he made a few days ago. He said, “There are a variety of options, including removing as much fuel debris as possible and solidifying the rest,”
I don't know what he means by "solidifying" though. Encasing it in place perhaps? Maybe if we can find the original Japanese we can figure it out. Maybe encasing is a reasonable idea, but I'm imagining lots of potential downsides.

Japan Times - Jan 20, 2016 - NRA commissioner suggests plan to remove all fuel debris at Fukushima plant may not be best option
http://www.japantimes.co.jp/news/20...shima-plant-may-not-best-option/#.Vs6dHJN96gQ
The other day we were discussing for how much longer it will be necessary to keep recirculating the cooling water. Maybe someone knowledgeable can weigh in. Perhaps after 10 years or so the melted fuel will have cooled enough that just keeping it under water will be enough? Therefore, no more large-scale nuclide removal necessary, and the end of the tritiated water problem as well? Speaking of tritium, has anyone taken a close look at Kurion's detritiation system proposals? They claim that they could have a system in place at Daiichi in 18 months if TEPCO said yes right away:

Bloomberg, Feb 5, 2016 - How Kurion Plans to Clean Up Fukushima’s Tritium Nuclear Waste
http://www.bloomberg.com/news/artic...to-clean-up-fukushima-s-tritium-nuclear-waste

Kurion Tritium removal system: 8.6 million dollar METI grant
https://nuclearstreet.com/nuclear_p...ion-system-for-japan-090801.aspx#.VflQnM5OoXh

Kurion Building a Prototype Modular Detritiation System
http://kurion.com/kurion-building-a-prototype-modular-detritiation-system/

http://kurion.org/wp-content/uploads/2014/11/MDS-Brochure-for-WEB.pdf

http://kurion.com/technologies/tritium-removal/

Actually, just speculating here, because they're running out of room for new tanks while the amount of accumulated water continues to increase, I imagine that TEPCO could start dumping tritiated water within a year. The Fisheries Cooperative would certainly demand more compensation, but until now they've always acquiesced eventually. Periodic dumping might continue for a couple of years, until a system like KURION's is in place. Like I said, I'm only speculating.

Finally, this TEPCO geological study regarding groundwater is in Japanese, but it's very detailed. It appears to be from the same meeting as the big frozen wall document Sotan translated:
http://www.nsr.go.jp/data/000139732.pdf

+++
Azby

 

[Azby]

Here's another article about the "meltdown" declaration manual, in the Nikkei Shimbun, a pretty conservative paper:

http://asia.nikkei.com/Business/Companies/Meltdown-the-crisis-that-dared-not-speak-its-name

 

[Sotan]

Hello Azby and welcome back to the thread!
- The Nikkei Shinbun article is the best and most complete I encountered, a much better read than the two links I gave.
- As for the matter of the permission given by NRA for ground freezing:
>> in this document (in Japanese) of Feb 22nd Tepco makes clear that they asked permission to start freezing the whole ocean-side of the ice wall, plus many small portions of the mountain-side of the ice wall (according to the figure on page 4 of the document). After this is done / if this goes well, they intend to file for another permission to go forward with additional portions of the mountain-side wall.
>> a similar content is on NRA's site https://www.nsr.go.jp/data/000140705.pdf (in Japanese), from an explanatory meeting of the two sides that took place on Feb 17.
This is Tepco's wish which has been submitted to NRA. My feeling is that the NRA hasn't actually given the actual go ahead, but might give an answer presumably shortly.

 

[Azby]

Sotan,

Thanks! The Nikkei Journalist is Junichi Taki. I have a pretty positive impression of him from earlier articles as well. Now, as you may be aware, people are posting links to early press comments where govt and TEPCO spokespersons did in fact say that "there is a possibility of meltdowns." Such as this one from March 14, 2011 (original in Japanese, pardon my lousy translation):

http://www.asahi.com/special/10005/TKY201103140442.html
"At a press conference after 9pm on March 14, Chief Cabinet Secretary Yukio Edano said concerning the trouble at the Fukushima Daiichi nuclear power plant that there is a high possibility that core meltdown is occurring in all of the units, 1 to 3 ."

Of course the word they used, roshin yōyū, is really "melting" not "meltdown" (but I'm not sure there's another term in Japanese besides using the English "meltdown"). And they knew this several days earlier.

About the freezing, based on the docs you shared, TEPCO did get permission to freeze small "control" sections of the mountain-side wall as well as the ocean side portion. None of the press reports I've seen seemed to have grasped that, nor how the overall plan for gradually controlling flow is intended to work.

 

[nikkkom]

http://kurion.org/wp-content/uploads/2014/11/MDS-Brochure-for-WEB.pdf

Kurion's proposed detritiator works by electrolyzing tritiated water (and then processing H2 stream).
How much is that going to cost? :(

 

[Azby]

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.

 

[Sotan]

I am satisfied with the Nikkei article linked above; at the end it summarizes things pretty well:
"Tepco essentially knew that meltdown had occurred. Crews on the ground at Fukushima Daiichi were responding to the crisis on that very assumption. Had Tepco acknowledged meltdown on March 14, the course of events probably would have changed little. But the revelation provides yet another suggestion that neither Tepco nor the government had taken real precautions for such a contingency, having believed a "myth of safety" that surrounded nuclear power in Japan."

Different subject:
http://www.tepco.co.jp/tepconews/library/archive-j.html?video_uuid=ta22eew8&catid=61699
Presentation video of the new incineration facility built by Tepco. Contaminated stuff such as protection suits worn by workers is going to be burned there from now on.

 

[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...