Japan Earthquake: nuclear plants Fukushima part 2

[Sotan]

http://www.tepco.co.jp/nu/fukushima-np/handouts/2015/images/handouts_151022_04-j.pdf
(in Japanese)

Continuation of the investigation in the PCV of Unit 3

Page 1: This is a quick report on the activities carried out on Oct 22.
They were aiming to take water samples and to evaluate the corrosion inside of the PCV (based on pH, conductivity, salt content). Also to check the access routes (vicinity of X-6 penetration; 1st floor grating; CRD rails) for the investigation of the pedestal area.

Page 2: Using the pan-tilt camera of the water sampling device they checked some immersed structures from the inside of the PCV (electric cables, supporting structures, X-6 penetration, CRD rails) and, as far as they could see, no damage was observed. Some "sediments" ("Deposits") were confirmed on the CRD rails and on the 1st floor grating (see photo 3).

Page 3: Conclusions
- Two samples of water (800 ml each) were taken, one from right near the surface (about 10 cm below surface) and one from a little deeper (about 70 cm under the surface).
- No damage on structures
- Deposits on the CRD-rails and grating
- No obstacles that might cause trouble on the installation of measurement instruments in the PCV.

Page 4: Schedule
Mock-up work will be done throughout November
In late December some measuring instruments are scheduled to be installed in the PVC.

Film (92.4 Mb) available here:
http://www.tepco.co.jp/tepconews/library/archive-j.html?video_uuid=e1x74582&catid=69619

 

[Hiddencamper]

Another thing to consider:

The drywell was inserted with nitrogen during operation specifically to prevent an explosion wholly inside the containment.

Temperature and pressure went up in containment with no drywell cooling. This would prevent air Inleakage, as drywell pressure would be greater than outside air.

When the hot debris ejection occurred, any remaining steam inventory would have further raised pressure.

My guess is a penetration finally failed or the drywell head burped as a result of the debris ejection. Alternatively, water injection attempts may have introduced oxygen as air was purged through feed lines. Either way, not enough info yet.

 

[Most Curious]

Another thing to consider:

The drywell was inserted with nitrogen during operation specifically to prevent an explosion wholly inside the containment.

Temperature and pressure went up in containment with no drywell cooling. This would prevent air Inleakage, as drywell pressure would be greater than outside air.

When the hot debris ejection occurred, any remaining steam inventory would have further raised pressure.

My guess is a penetration finally failed or the drywell head burped as a result of the debris ejection. Alternatively, water injection attempts may have introduced oxygen as air was purged through feed lines. Either way, not enough info yet.

I missed something along the way. WHAT "hot debris ejection"?? Are you referring to the melt through of the fuel through the bottom of the reactor vessel or something else??

 

[Sotan]

http://www.tepco.co.jp/nu/fukushima-np/handouts/2015/images/handouts_151026_04-j.pdf
Tepco report (in Japanese) regarding the inspection of the big "exhaust tower" of Units 1-2.

(They found cracks and shape deformations here and there, but they conclude that it still has sufficient resistance in case of earthquake.)
But what I want to point out here are the new results of radiation measurements.
Page numbered 16 shows values of radiation measured in September 2015 - compared to results obtained in August 2011, in the areas where the "SGTS pipes" connect to the exhaust tower. (Standby Gas Treatment System "through which steam was vented to relieve reactor pressure during the accident in March 2011" - quoting from a source found through Google, http://www.world-nuclear-news.org/RS_Second_high_radiation_reading_308112.html)

From over the scale values (>10,000 mSv/h) in 2011 - down to 2,000 mSv/h today. But, still, so high...

 

[Hiddencamper]

I missed something along the way. WHAT "hot debris ejection"?? Are you referring to the melt through of the fuel through the bottom of the reactor vessel or something else??

In the BWR owners group severe accident guidelines, A debris ejection is the specific moment when the vessel melts through. It is industry lingo. A Hot debris ejection is when the melt through happens while the vessel is pressurized and results In a pressure boundary rupture.

BWR EOPs direct blowing down the reactor to depressurize it after you lose adequate core cooling for many reasons, one of which is to prevent a hot debris ejection which can damage the containment. Typically by the point you get to a debris ejection occurring, the containment is already at or over its heat capacity limit, meaning a hot debris ejection will result in exceeding containment's analyzed conditions.

Units 1 and 2 were not depressurized prior to the debris ejection. Unit 3 did have its ADS (automatic depressurization system) have an invalid actuation (logic circuits worked right, plant conditions weren't right, suppression pool pressure was so high that it pressure up the ECCS injection headers and tricked the ADS logic into thinking the ECCS pumps were running) and was at a reduced but not depressurized state when the core rupture occurred. I don't know the details but I suspect not enough relief valves opened to allow the core to fully depressurize. Typically for dual function SRV BWRs, you need at least 5 ADS SRVs to get pressure down with 10 minute post scram decay heat.

For reference: the ADS logic
Low level 3 plus low low low level 1 water level signals, a high drywell pressure signal, a 105 second time delay, and a check that at least one ECCS pump has sufficient discharge pressure. The logic is 2 out of 2 twice (two channels, two divisions, either division can actuate the ADS). Some plants removed the high drywell signal or put a bypass timer on it to ensure adequate core cooling for small break LOCAs or loss of feedwater events with no operator action. The level 3 signal and 105 second timer are only installed on one channel per division. The operator can inhibit the 105 second timer from starting, can reset the 105 second timer (annoying as hell having to hit the reset every 105 seconds), or can manually actuate the logic even if none of the permissive are made up.

 

[Most Curious]

Thank you Hiddencamper for the explanation! I suspected it had to do with the melt through but having not been exposed to the BWR owners group did not know the correct definition of the term. The additional info was very welcome as well.

 

[jim hardy]

I remember reading, long time ago, on other sites how some people believed that the explosion that took place at Unit 3 was not a hydrogen explosion, but rather some sort of "nuclear blast", "atomic explosion" and I think I saw some other terms used as well. Many other people tried to debunk that theory, with more or less success, as it happens in such cases.

i'm guilty of thinking that , and of suggesting it.
From the sheer size of the explosion, coupled with reports of high radiation readings accompanying it, i thought it must have been a small excursion with steam explosion. This, one of the few early views of 3, had me convinced there was a hole in the operating deck over the reactor.

Later pictures that are more clear show the plug in place with a crane laying on it.
The preponderance of evidence says the energy for explosion was hydrogen (chemical not nuclear).

Still, i'd like to see the top of the reactor vessel particularly around the head closure bolts. Its being in place should remove even unreasonable doubt.

..........................

Unrelated question to you BWR guys - do you use much hydrazine for O2 scavenging?

 

[Hiddencamper]

i'm guilty of thinking that , and of suggesting it.
From the sheer size of the explosion, coupled with reports of high radiation readings accompanying it, i thought it must have been a small excursion with steam explosion. This, one of the few early views of 3, had me convinced there was a hole in the operating deck over the reactor.

View attachment 90975

Later pictures that are more clear show the plug in place with a crane laying on it.
The preponderance of evidence says the energy for explosion was hydrogen (chemical not nuclear).

Still, i'd like to see the top of the reactor vessel particularly around the head closure bolts. Its being in place should remove even unreasonable doubt.

..........................

Unrelated question to you BWR guys - do you use much hydrazine for O2 scavenging?

Jim I recommend taking a look at Ian Goddard's video and webpage about this for unit 3. http://iangoddard.com/fukushima01.html

Couldn't find the video link directly but he has one on this. (Here is the video )

The BWR mark I containment has a known issue where high pressure excursions can cause the drywell head seals to give way and the head to momentarily lift to create a release path. This was known in the 70s and I believe is part of what lead the US to require a vent system for the drywell.

Ian's evidence points to a drywell steam release triggered by the hot debris ejection.

Furthermore, millstone and Brunswick have both had some type of drywell head lift/leakage during containment type A pressure testing (can google this).

And as much as I hate the site, Goddard pointed me to this: http://www.fukuleaks.org/web/?p=10740
As far as I know BWRs use nitrogen and do a purge of containment. No hydrazine. Push nitrogen in one side, allow oxygen to escape the other, and once oxygen concentration is low enough use nitrogen to maintain drywell pressure to prevent further Inleakage. Let me check though, it's been a while since I've been in a Mark I.

 

[Rive]

The preponderance of evidence says the energy for explosion was hydrogen (chemical not nuclear).

Still, i'd like to see the top of the reactor vessel particularly around the head closure bolts. Its being in place should remove even unreasonable doubt.

I'd say some kind of release paths will be found there, but hose were reasons of the H2 buildup in the building, not the explosion itself.
There were some simulations as I recall, which could account for both the power and direction of the blast only by suggesting H2 buildup in the whole building (even below the top floor).
For me this would suggest a steam/H2 release over a (relative) long period, not only around a specific event.

 

[Sotan]

Anticipating Hiddencamper's surely more detailed answer about the hydrazine:
The handouts released every couple of days by Tepco do mention briefly: "Adding hydrazine to the SFP and reactor well of each unit, appropriately/as needed."
Other documents periodically add the expression "to help prevent corrosion".

-------------
Also I would like to mention that the site of METI presents the English translation of the main document of the release of October 1, namely "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:5,775KB)".

Link is here:
http://www.meti.go.jp/english/earthquake/nuclear/decommissioning/pdf/20151001_e.pdf

 

[etudiant]

Was the reactor 3 a mark 1 BWR?
I'd thought that only unit 1 was that, with the others later vintage designs. Or is that cap lifting leak path a more general BWR containment design issue?

 

[Hiddencamper]

Was the reactor 3 a mark 1 BWR?
I'd thought that only unit 1 was that, with the others later vintage designs. Or is that cap lifting leak path a more general BWR containment design issue?

Units 1 through 5 utilized mark I containment systems (torus). Units 6 and all daini units utilized the Mark II containment system (over/under).

Unit 1's NSSS was different, it was among the first BWR/3, and the first few BWR/3s have some differences to the later 3s. I believe units 2-5 were BWR/4s? And unit 6 was a BWR/5.

As for hydrazine I know pretty much nothing about this. We don't use it at my plant and I don't know who does. Hmm.

 

[Sotan]

- I've been looking for more info on hydrazine and I found this document from Tepco (in Japanese), dated 16 April 2012, about some trouble (leak) with the hydrazine pump/pipes at SFP of Unit 4:
http://www.tepco.co.jp/nu/fukushima-np/images/handouts_120416_02-j.pdf
Page 5 explains why and how they use hydrazine:
"Purpose:
Immediately after the earthquake and tsunami, sea water was used for cooling the Spent Fuel. As a result, there is increased danger of corrosion affecting the SFP parts made of stainless steel. The anti-rust agent hydrazine is added periodically to the SFP to control corrosion.
Facilities used:
Hydrazine solution (22% hydrazine aqueous solution) is added to the SFP 3 times a week through the cooling circuit.
The photo shows a mobile hydrazine tank (installed on a vehicle)."

- There are also many other sources which indicate that Tepco didn't use hydrazine during normal operation of those reactors, it is one of the special measures taken after the accident.

- Difficult to find indications of "how much" hydrazine they use.
This site (in Japanese) http://fukumitsu.xii.jp/syu_f/FukushimaGenpatsu_1.html mentions one operation when about 2 m3 of hydrazine solution were added to the SFP of unit 3, and another instance when 2 m3 of hydrazine solution were added to SFP of Unit 4.

 

[nikkkom]

That's only about 17 gallons per minute. Pretty low, well below what I would expect for water cleanup operations.

That's "only" a gallon of water every 3.5 seconds.

 

[nikkkom]

But what I want to point out here are the new results of radiation measurements.
Page numbered 16 shows values of radiation measured in September 2015 - compared to results obtained in August 2011, in the areas where the "SGTS pipes" connect to the exhaust tower. (Standby Gas Treatment System "through which steam was vented to relieve reactor pressure during the accident in March 2011" - quoting from a source found through Google, http://www.world-nuclear-news.org/RS_Second_high_radiation_reading_308112.html)

From over the scale values (>10,000 mSv/h) in 2011 - down to 2,000 mSv/h today. But, still, so high...

I expected to see some shielding installed around that location. A few concrete blocks or something. I am surprised. There is no shielding there on the picture.

 

[Hiddencamper]

That's "only" a gallon of water every 3.5 seconds.

You need to remember an operating reactor water cleanup system is 300 gpm (about 1% of feedwater capacity). A steaming reactor in hot standby from startup is anywhere from 50 to 200 gpm and 600 gpm in hot shutdown. A full power 1000 MWe reactor is 32000 gpm. Each reactor recirculation loop also pushed about 32000 gpm through the jet pumps.

17 is a trickle at best.

 

[Astronuc]

Page 5 explains why and how they use hydrazine:
"Purpose:
Immediately after the earthquake and tsunami, sea water was used for cooling the Spent Fuel. As a result, there is increased danger of corrosion affecting the SFP parts made of stainless steel. The anti-rust agent hydrazine is added periodically to the SFP to control corrosion.
Facilities used:
Hydrazine solution (22% hydrazine aqueous solution) is added to the SFP 3 times a week through the cooling circuit.
The photo shows a mobile hydrazine tank (installed on a vehicle)."

Hydrazine would be used as an oxygen scavenger, i.e., it is used to reduce dissolved oxygen (DO), which in conjunction with chloride ions is implicated in stress corrosion cracking of stainless steel.

BWRs have typically used hydrogen injection in the coolant system to reduce DO, with many now using noble metal (rhodium) injection in order to reduced the electrochemical potential in the coolant in order to protect the stainless steel structures in and around the core.

GE NMCA - http://www.power-eng.com/articles/print/volume-102/issue-11/features/noble-metal-technique-cuts-corrosion-and-radiation.html

 

[nikkkom]

You need to remember an operating reactor water cleanup system is 300 gpm (about 1% of feedwater capacity). A steaming reactor in hot standby from startup is anywhere from 50 to 200 gpm and 600 gpm in hot shutdown. A full power 1000 MWe reactor is 32000 gpm. Each reactor recirculation loop also pushed about 32000 gpm through the jet pumps.

17 is a trickle at best.

I know that a working or recently shutdown reactor uses much more water. The point it, these reactors are not recently shutdown.

 

[Sotan]

TEPCO's page for Mid- and Long-Term Roadmap reports (http://www.tepco.co.jp/decommision/planaction/roadmap/index-j.html) has a new batch of documents, released on October 29. All in Japanese language only, unfortunately.
They are reviews and updates based on what happened since the last release (about a month ago) and therefore the "new" content is limited.
However, based on a quick peek, one document appeared very rich in information - the one about "Preparations for the extraction of the nuclear fuel debris".
http://www.tepco.co.jp/nu/fukushima-np/roadmap/images/d151029_08-j.pdf
Below are a few points from it:

Page 3 and after: Investigation of the TIP room (Unit 1) and several adjacent areas
TIP = Transverse In-Core Probe
Page 8: Radiation measurement results. Highest reading in the TIP room appears to be 290 mSv/h right near the PCV wall, but values towards the turbine room are low (under 2 mSv/h).
Page 9: Gamma camera image and 3D scan image of the room. Radiation hotspot in the area of X-31,32,33 penetrations - corresponding to the place where the 290 mSv mentioned above was recorded.
Page 10: Photos of the various penetrations and valve units in the area. Photo 1: Under X-35A there are some brown traces left by something that flew. However the gamma camera doesn't indicate that the traces are a sources of radiation. Photo 2: no flow traces in the valve units of X-35A~D. The valves are known to have been in a closed state at the time of the accident.
Page 11: About X-31,32,33 penetrations: Photo 4, 5: no obvious traces of leaks or flows
Page 12: Electric penetrations X-101A, X-101C/D - photos, no obvious traces of leaks or flows
Page 13: Conclusions: with some decontamination and reduction of the radiation dose there are prospects of being able to use these rooms for further work.
Page 16: Further explanations about what these penetrations are and where they are positioned. X-31A~D are measurement devices for the main steam circuits. X-31E,F are measurement devices for SHC (reactor shutdown cooling system?). X-32A~D are for measurement devices for PLR (primary loop recirculation). X-32E,F are for CUW (reactor water clean-up system). X-33A~D are again for main steam circuits; X-33E is for PCV water level sensors; X-33F is for “safety nitrogen gas release valve”; X-35A~D are for the TIP devices; X-101A is the penetrations for power cables for the recirculation pumps, X-105C/D are for other electric cables.

Page 17 and after: Investigation of the contamination in the X-6 penetration area (Unit 2)
You might remember that after they removed those concrete blocks that shielded the X-6 penetration lid they found traces of something that had leaked from the lid onto the floor.
Page 18: the robot used for investigation
Page 19: the radiation values increase downward, from the ceiling of the small room to the floor where the molten and re-solidified deposit is located. It is believe that the radiation dose coming from inside the X-6 penetration is about 1 mSv/h. The robot, equipped with a spatula, was able to scratch away easily some of the deposit.
Page 22: more radiation dose results, this time gamma and beta rays;

Page 23 and after: Investigation inside the PCV of Unit 3
I have posted before most of the results of this investigation too.
Page 26-28 show annotated versions of the photos previously released as well as 3D scans (pre-accident) for a better understanding of the structural elements that appear in the photographs.
Page 35: results of the analysis of the water samples taken from the PCV. They show that the PCV corrosion did not advance much (the corrosion danger is low).

Page 38 and after: a new robot developed for the decontamination of pillars, floors and walls, using dry ice blasting. It can access places up to 8 meters high, it blasts dry ice particles onto the surface to be decontaminated and then sucks up the dry ice with dust and particles up to 10 mm in size. In tests it managed to remove 98% of the contaminants and recover 92% of the CO2 blasted as dry ice.

 

[turi]

Seawater monitoring results after closing the seawall: http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2015/images/handouts_151105_01-e.pdf

 

[Sotan]

http://www.tepco.co.jp/nu/fukushima-np/handouts/2015/images/handouts_151127_08-j.pdf
(PDF file in Japanese published on 27 Nov 2015)

Report on an investigation of the Unit 3 PCV machinery hatch area

Page 2. General aspects of this investigation
The Unit 3 PCV machinery hatch is located on the 1st floor of Reactor Building, North side.
Because traces of water (radioactive, 1300 mSv/h) were observed in 2011 in the rails used to move the shield plug, it was suggested at that time that there might be a water leak from this hatch.
On September 9 this year, a camera was inserted through the openings on the side of the sheild plug and the machinery hatch was studied. No changes in shape and no leaks were observed.
The present investigation, using a small robot, aims to get even closer and to investigate the state of the hatch seals.

Page 3. Access route
Left-side photo: The shield plug offers a space of about 13 cm on its side which allows the access of a small robot.
Right side photo shows the whiteboard with documents filled in on the occasion of maintenance rounds, but also a portion where the hatch seal might be examined.

Page 4.
When the robot advanced into an area which is located under the level of the water known for the inside of the PCV, rust and dirt could be observed. In contrast, the "ceiling" of the space is clean. (The computer generated image in center-low explains this better: the "blue" portion means there is water up to that point on the other side of the hatch, and they found dirt and rust in the area of the hatch seal all the way round the circle in the "blue" area, while the seal is clean in the upper portion of the hatch.)

Page 5.
Some water stains observed in the area come from rain. The stains change shape, and appear/disappear with rain. Some rain water droplets appear to make their way down on the hatch room wall too. This is how water is supposed to have filled those shield plug rails too, in the past - even though they seem dry now.

Page 6. Radiation dose results
Measurements were made in several spots along the path that leads through the space left by the shield plug. The radiation gets stronger and stronger as we go "deeper", the highest value measured being 1220 mSv/h, on the floor at about 2 meters from the beginning of the shield plug space. The value at 1m above floor was 270 mSv/h (to be compared with 1300 mSv/h measured in air in same area in 2011).

Page 7. Conclusions
- rust and dirt in the hatch seal area, everywhere below the level of the water in the PCV;
- rain water somehow comes in;
- the shield plug displacement rails are now dry.

Pages 8-9. Information on the robot they used this time.

*A video (212 Mb) is also available at http://photo.tepco.co.jp/date/2015/201511-j/151127-01j.html

 

[Sotan]

Another batch of documents was released by Tepco on November 25 in the section regarding the Mid- and Long-term Roadmap towards decommissioning (section URL: http://www.tepco.co.jp/decommision/planaction/roadmap/index-j.html)

For now I would like to point out this document (in Japanese)
http://www.tepco.co.jp/nu/fukushima-np/roadmap/images/d151126_08-j.pdf

Pages 11~ to end show the decontamination operations in the vicinity of the X-6 penetration of Unit 2. (The one which gave them a hard time when they had to remove the concrete blocks wall in front of the penetration, and where they found some melted substance leaked from the penetration lid.)

Page 12 shows the robot with a scoop - and later with a steam cleaner - used to remove some of the dirt/deposit on the floor, as well as a vacuum cleaner and a nice blue plastic bucket. (Weird feeling - such a domestic job, if it wasn't for the high radiation level which requires for everything to be done remotely.) Also notice the "Packbot" used for observation.

Page 13: values of radiation in different spots in the area (left, center and right side), after successive cleaning operations (after removing the concrete blocks, after removing the melted and re-solidified substance, after the first steam cleaning and after the second steam cleaning). Values for "Center, B" for example were, in that order, in Sv/h gamma: 1.0, 0.43, 0.68, 2.8 (not clear why they are rising after the steam cleaning...). Also very large values (>10) in the D-E area, near the ditch left behind after the concrete blocks, which was in the end filled with water from the condensed steam.

Page 14: photos during the operation. 3rd photo shows the deposit/melted substance, collected in the bucket. 4th photo shows a piece of mud-like wet dirt that got stuck to the vacuum cleaner handle. Some water appears to be dripping from the bottom of the lid/flange that closes the penetration.

Page 15 - again photos during cleaning, this time with steam. The orange dotted line rectangle frame shows the area with remarkably high radiation level.

Page 16 - decontamination schedule from now on

Page 17: They checked for water dripping from the bottom of the flange, by placing a piece of cloth under it.
The assume that steam from inside the PCV condensates inside the penetration pipe (temperature inside: 30.5Celsius, temperature in the building in front of the X-6 penetration: about 10 Celsius) and comes out dripping.

 

[Sotan]

Long time with no posting. I just didn't find anything to share.

This time there's this very interesting report from Tepco - in fact, only about 4 photos, dated December 21 - with an intruder walking freely in the Reactor 2 building:
http://photo.tepco.co.jp/date/2015/201512-j/151228-01j.html

I will take this opportunity to wish you all a Happy New Year and hopefully we will all enjoy a 2016 with a lot of progress at Fukushima Daiichi plant.

 

[zapperzero]

Long time with no posting. I just didn't find anything to share.

This time there's this very interesting report from Tepco - in fact, only about 4 photos, dated December 21 - with an intruder walking freely in the Reactor 2 building:
http://photo.tepco.co.jp/date/2015/201512-j/151228-01j.html

I will take this opportunity to wish you all a Happy New Year and hopefully we will all enjoy a 2016 with a lot of progress at Fukushima Daiichi plant.

Thank you very much for the update and the kind words. Still lurking after all this time...

 

[HowlerMonkey]

That's a very large fox.

 

[eXorikos]

http://link.springer.com/book/10.1007/978-3-319-12090-4

A book was released on the accident. It is free available at Springer.

 

[mheslep]

That's a very large fox.

Clearly a mutant.

 

[etudiant]

During the early days after the accident, various creatures could be seen roaming the site, mostly raccoon dogs. I'd thought that with the increased human presence now that they would have gone, but clearly that is wrong.
Meanwhile, their behavior demonstrates that animals have no radiation sensing capability either. The area where it was strolling is pretty hot, I believe.

 

[LabratSR]

The current situation at Fukushima Daiichi NPS” –From 3.11 toward the future-(ver,Jan,2016)

 

[Sotan]

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?

 

[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.)