Japan Earthquake: nuclear plants Fukushima part 2

[zapperzero]

Very disappointing. They continue to misunderestimate radiolysis as a source of hydrogen for the unit 4 explosion, there is absolutely no discussion of steam radiolysys at all, no discussion of the temperature of water in SFP4, absolutely no discussion of reflected shockwaves as a mechanism for deflagration/detonation transition which would lower the required amount of hydrogen, nothing but a reiteration of the SGTS argument.

Plus, of course, weasel wording like this:

Among the issues above, the NRA have selected and analyzed Issues (2) to (4) and (6), and
then compiled the results in this report. As for Issue (1), "very few of the seismic back checks
against the design basis earthquake ground motions and anti-seismic reinforcement works had been done." is true. By the reason of this fact, however, the NRA cannot say "It is thought that the
earthquake ground motion from the earthquake was strong enough to cause damage to some key
safety facilities." It is valid to say "there is possibility that the earthquake ground motion from the
earthquake might cause damage to some key safety facilities." Accordingly, in this report, the NRA
decided to analyze only Issues (2) to (4) and (6), which addressed
equipment damages.

 

[etudiant]

Surely any radiolysis in the SFP4 would have also left evidence in the fuel, which is now available for analysis.

 

[gmax137]

Surely any radiolysis in the SFP4 would have also left evidence in the fuel, which is now available for analysis.

What do you have in mind there, Etudiant?

 

[etudiant]

The comment suggests steam radiolysis took place in the reactor 4 SFP.
That pretty much requires the spent fuel to be uncovered at least partially, which should apart from boiling the remaining water also show heating effects on the unsubmerged fuel and fuel racks. There have been no indications of anything unusual with the SFP4 fuel or fuel racks apart from a small number of damaged elements known to have been there for several years.

 

[turi]

Update: All the spent fuel has now been removed from SFP 4. 180 new fuel assemblies remain to be moved.

 

[Sotan]

From the Tepco site:

Efficacy of dust-fixing resin
In Japanese, but mainly photos. Simple but convincing (I think) report on an experiment that shows how dust scattering is prevented by the agent they are spraying now on the operating floor of Reactor 1 building.

turi has already reported this one:
One page report about the end of spent fuel removal operation at SPF of Reactor 4. In Japanese. There are some photos revisiting the road to this result. The 180 new fuel assemblies are scheduled to be moved too, until the end of December.
Bigger and better photos here. Some of the photos are said to depict the handling of one of those deformed spent fuel assemblies. (Just in case somebody notices, parts of the photos are blurred by Tepco, this is clearly stated.)

 

[zapperzero]

The comment suggests steam radiolysis took place in the reactor 4 SFP.
That pretty much requires the spent fuel to be uncovered at least partially

No it doesn't. You can have steam bubbles around the fuel elements without the pool even being close to boiling yet.

 

[etudiant]

No it doesn't. You can have steam bubbles around the fuel elements without the pool even being close to boiling yet.

Not sure there is any increased likelihood of radiolysis just because there are steam bubbles. To do radioactivity powered splitting of water molecules is pretty aggressive and really needs a lot more than just local heating, at least afaik.
Please help me and lay out the scenario that you envision happened.

 

[nikkkom]

No it doesn't. You can have steam bubbles around the fuel elements without the pool even being close to boiling yet.

How? The most active fuel in Unit 4's pool was at least a month old, IIRC. It should have heat output of several 100s W/kg. That does not seem enough to cause localized boiling.

 

[Joffan]

How? The most active fuel in Unit 4's pool was at least a month old, IIRC. It should have heat output of several 100s W/kg. That does not seem enough to cause localized boiling.

Unit 4 was taken offline in late November 2010, so the newest spent fuel rods were over 3 months aged.

 

[Rive]

How? The most active fuel in Unit 4's pool was at least a month old, IIRC. It should have heat output of several 100s W/kg. That does not seem enough to cause localized boiling.

That depends on the water temperature/timing.

As I recall there was a calculation aimed for determining the stable temperature of the pool (without additional cooling): by this calculation the whole pool could be on the edge of boiling which definitely suggests, that at least some localized boiling happened. This clearly applies for the time when the first close-up photos were made about that pool.

The question is, that how fast could the temperature of the pool rise after the loss of cooling.

Ps.: let's say if it could reach 80 C degree for half day before the explosion, then I would accept the possibility of the discussed scenario - however for me the presence of contamination there suggests that the source of H in U4 was a melted core, not some 'clean' source.

 

[etudiant]

Afaik, it does not matter at all whether there was boiling in the pool, water molecules are just about as hard to break apart when in steam as when in water. The fuel racks are in reasonable shape, so there was no zirconium fire. So I don't understand how there could have been a large burst of radiolysis in the SFP4. Even if the whole pool was boiling, that fuel would still produce way less radiolytic activity than an ongoing reactor.
It might be illuminating if 'zapperzero' would share his scenario, because the destruction of the reactor 4 building is massive enough to make the 'official' scenario, that hydrogen leaked into #4 from #3 through the shared stack pipe, very hard to credit.

 

[zapperzero]

water molecules are just about as hard to break apart when in steam as when in water

Yes, but the mean free path of alphas is way longer. I think the original thread has links to some open-source Russian papers that I dug up specifically to table the issue, but I don't really have the time to dig for them right now. I might later.

http://books.google.ro/books?id=-UF...6AEwATgU#v=onepage&q=steam radiolysis&f=false
contains a reference to a paper stating 6 molecules of water split for every 100 eV, which I also cannot dig up because I'm not an academic and can't afford to pay for science articles.

 

[Joffan]

Yes, but the mean free path of alphas is way longer.

There wouldn't be any alphas impacting water (/steam) in the spent fuel pool. The cladding stops them.

 

[Sotan]

Asahi Shinbun article in English:
http://ajw.asahi.com/article/0311disaster/fukushima/AJ201411100047 .
Aerial photo allows a peek in through the large roof opening.

 

[Sotan]

A TEPCO report of Nov 19 regarding the investigations planned on the operating floor of Unit 1 (in Japanese) as a step towards the removal of the debris from the area.

The photos included in the report can be seen separately here, but they are more or less of the same small size as those from the report. Would have been nice to have some better photos.

Investigations on the state of debris, radiation level and dust concentration will be carried out from Nov 20 to Dec 2. An investigation of the temperatures in the area above the reactor well will take place on Nov 26.

 

[Sotan]

Asahi Shinbun article in English:
http://ajw.asahi.com/article/0311disaster/fukushima/AJ201411210037

 

[Sotan]

According to this article (http://www.yomiuri.co.jp/science/20141121-OYT1T50134.html in Yomiuri Shinbun, TEPCO has given up on freezing the connection sport between the underground and the Reactor 2 building, as the freezing was not complete and water continued to leak. The new plan involves pump out water from the trench and at the same time pumping in a special concrete mixture, in order to fill up the place and thus stop the flow of contaminated water. The plan was presented in a NRA meeting today and granted approval. If possible they would like to start this operation next week.

The document presented by TEPCO in the NRA meeting can be seen http://www.nsr.go.jp/committee/yuushikisya/tokutei_kanshi/data/0029_01.pdf There is a lot of data shown in there too; I will only mention here a few aspects.

The graph on page 5 (numbered 5 in lower right) shows the effect of pumping out water from the trench for about 6 hours, after freezing the ends of the tunnel. The water level (red line) decreased temporarily, but once pumping stopped, it came back up. (The 6 cm level difference compared to the blue line - measured at a different point, near the turbine building end of the tunnel - is considered simply a measuring error as level measurements were made manually). This shows that freezing the ends of the tunnel, and the additional measures taken, have been unsuccessful and that there are plenty of unfrozen gaps through which contaminated water continues to flow.

Page 8 and 10 shows some of the properties of the concrete mixture that they intend to use. It does not "dissolve" in water, stays fluid for at least 12 hours, can flow to at least 80 meters distance and keeps its properties over that distance. Two layers (each 50cm thick) of concrete were poured, one 100m long, the upper 86m long.The first layer of concrete was poured at a rate of 100-150 litres/min. It was confirmed that the concrete poured at one end of the tunnel went through all those 82m then began to rise upward at the other end, keeping a horizontal surface. There were only a few obstacles placed in the way of this first layer, namely a few cables and some gravel. A first version of the results of this experiment (after pouring the first layer) has been apparently shown to NRA on Oct 3 but I think I missed that report.

Page 11: As for the pouring of the second layer, similar good results were obtained, with a few observations though: a few mm thick layer of "bubbles" forming on the surface concrete over the first few meters (photo 1), presumably due to the incorporation of air during pouring. There were plenty of obstacles over the whole length of the experimental tunnel this time, but the concrete went nicely and filled in all the spaces, even among cables and pipes (photo 3). Second layer was poured in Oct 10.

Page 14: The planned steps towards the filling of the Unit 2 trenches with concrete.

(I'll add more if anybody is interested. Kind of got to run now.)

 

[nikkkom]

Page 8 and 10 shows some of the properties of the concrete mixture that they intend to use. It does not "dissolve" in water, stays fluid for at least 12 hours, can flow to at least 80 meters distance and keeps its properties over that distance. Two layers (each 50cm thick) of concrete were poured, one 100m long, the upper 86m long.The first layer of concrete was poured at a rate of 100-150 litres/min. It was confirmed that the concrete poured at one end of the tunnel went through all those 82m then began to rise upward at the other end, keeping a horizontal surface. There were only a few obstacles placed in the way of this first layer, namely a few cables and some gravel. A first version of the results of this experiment (after pouring the first layer) has been apparently shown to NRA on Oct 3 but I think I missed that report.

Page 11: As for the pouring of the second layer, similar good results were obtained, with a few observations though: a few mm thick layer of "bubbles" forming on the surface concrete over the first few meters (photo 1), presumably due to the incorporation of air during pouring. There were plenty of obstacles over the whole length of the experimental tunnel this time, but the concrete went nicely and filled in all the spaces, even among cables and pipes (photo 3). Second layer was poured in Oct 10.

Sounds like an ideal floor-leveling mix to me!
(My attempts to level the floor with some German mixes were less than ideal).

 

[zapperzero]

There wouldn't be any alphas impacting water (/steam) in the spent fuel pool. The cladding stops them.

What do we know about the Cs contents of the unit 4 SFP?

 

[Joffan]

There wouldn't be any alphas impacting water (/steam) in the spent fuel pool. The cladding stops them.

What do we know about the Cs contents of the unit 4 SFP?

And what do we know about the price of tea in China? Which is just as relevant to the subject at hand.

I'll tell you what we do know. We know that the fuel rods have been closely reviewed during their move for any signs of damage - and there has been essentially none - and you would need very extensive damage to allow any significant alpha flux into the SFP water.

 

[etudiant]

I don't know whether the SFP for the #4 reactor ever had water dumped on it by pumper as did the #3 pool.
As they even used sea water to cool things, at least in the early days, there may be widespread sodium contamination still, but cesium seems unlikely.
It would be interesting to see the analysis of the water in the SFPs, as that might indicate how much the overheating reactors burped, but I've not seen anything on this.
More generally, SFP #4 was surely the easiest problem to tackle, just fuel racks in a pool located in a very damaged building. The others three are all adjacent to melted down reactors, much harder to approach and to work on. I give great credit to the Japanese, they have been reducing the problem steadily, despite the enormous difficulties and costs. That said, the job is no more than 2-3% done at present, something that the 20-30 year long decommissioning plans recognize.

 

[Sotan]

http://www3.nhk.or.jp/news/html/20141128/t10013551261000.html
According to this NHK report (in Japanese) the level of radiation in Unit 3 of Fukushima Daichi has not been decreasing as first expected and additional measures will be needed to achieve this objective and be able to move on with the plain aimed at removing the spent nuclear fuel from the storage pool.
The plan had been to scrub the floor and remove the dust from the operating areas of the reactor so that the level of radioactivity decreases under 1 mSv/h, thus allowing the access of workers. However, measurements taken after decontamination procedures have shown spots with up to 60 mSv/h, while many other areas display values well above 10 mSv/h.
Additional measures planned include installation of metal shielding and further scraping of floors, but there is uncertainty about whether the initially proposed timeline can be maintained under these conditions.

http://www.tepco.co.jp/nu/fukushima-np/roadmap/conference-j.html
This is the Tepco homepage dedicated to the ~monthly updates regarding progress on the Mid- and Long-Term Roadmap towards decommissioning.
There are new posts and documents dated November 13, 25 and 27. Unfortunately, only in Japanese.
(English translations of the main documents usually become available after a month or so.)

http://www.tepco.co.jp/nu/fukushima-np/roadmap/images/d141127_11-j.pdf
Starting on page 3 of this TEPCO report (in Japanese) there are some results of the recently finished 3D laser scan of the torus room of Reactor 1. The 3D images thus acquired are thought to prove useful in planning the future operations.

 

[turi]

http://www.tepco.co.jp/en/press/corp-com/release/2014/1244484_5892.html
Strontium 90 in water solution density measurement has been sped up orders of magnitude by using inductively coupled plasma-mass spectrometry. It has been developed in cooperation with Fukushima university.

 

[nikkkom]

http://www3.nhk.or.jp/news/html/20141128/t10013551261000.html
According to this NHK report (in Japanese) the level of radiation in Unit 3 of Fukushima Daichi has not been decreasing as first expected and additional measures will be needed to achieve this objective and be able to move on with the plain aimed at removing the spent nuclear fuel from the storage pool.
The plan had been to scrub the floor and remove the dust from the operating areas of the reactor so that the level of radioactivity decreases under 1 mSv/h, thus allowing the access of workers. However, measurements taken after decontamination procedures have shown spots with up to 60 mSv/h, while many other areas display values well above 10 mSv/h.
Additional measures planned include installation of metal shielding and further scraping of floors, but there is uncertainty about whether the initially proposed timeline can be maintained under these conditions.

This should have been expected.

TMI cleanup effort have seen this before: concrete soaked up contaminants, even aggressive surface cleaning is not very effective.
Apparently TEPCO did not read TMI post-accident reports. Google for "NP-6931.pdf".

Maybe there is still time to read it, so that TEPCO doesn't reinvent the wheel?

 

[Sotan]

- re: Latest post on http://ex-skf.blogspot.ro/
To my surprise he seems very pessimistic about the result of filling the trenches with that "special cement"...
Somehow I imagine that the sheer length of the trenches in which cement will be poured will make up for any imperfections of the filling on the way and thus manage to seal them well enough. This time.

- In the comments posted on the same blog mentioned above I found this link - a paper regarding the "2013 UNSCEAR Report on Fukushima" - I confess I didn't yet have time to go through it but might be interesting:
http://www.iwanami.co.jp/kagaku/Kagaku_201410_Baverstock.pdf

Later edit:
I'm sorry, I read this paper now and it is not what I thought it is (I thought it might contain more technical, engineering aspects and in fact it is focused mainly on radiation doses and possible health effects). It still may be of interest so I will leave the link there. I hope it doesn't cause much controversy in this forum.

 

[Rive]

This should have been expected.

TMI cleanup effort have seen this before: concrete soaked up contaminants, even aggressive surface cleaning is not very effective.
Apparently TEPCO did not read TMI post-accident reports. Google for "NP-6931.pdf".

Maybe there is still time to read it, so that TEPCO doesn't reinvent the wheel?

One or two years ago Tepco already made some 'live' experiments about the effectiveness of available cleanup methods for concrete surface. The 'heavy scrub' and the 'peel off paint' was the winner, as I recall.

- re: Latest post on http://ex-skf.blogspot.ro/
To my surprise he seems very pessimistic about the result of filling the trenches with that "special cement"...
Somehow I imagine that the sheer length of the trenches in which cement will be poured will make up for any imperfections of the filling on the way and thus manage to seal them well enough. This time.

The filling is a last resort. It'll work, but when the time comes and they have to clean up that trench the fill would mean many more contaminated rubbish to deal with.
What I failed to understand is, that why they don't just cut those pipes which prevented the freezing to work.

 

[etudiant]

One or two years ago Tepco already made some 'live' experiments about the effectiveness of available cleanup methods for concrete surface. The 'heavy scrub' and the 'peel off paint' was the winner, as I recall.The filling is a last resort. It'll work, but when the time comes and they have to clean up that trench the fill would mean many more contaminated rubbish to deal with.
What I failed to understand is, that why they don't just cut those pipes which prevented the freezing to work.

There have to be some serious access problems that impede the efforts to freeze the trench.
Sharply rising contamination levels as one moves closer to the reactors is a plausible issue.
It does seem that this would be an ideal test site for a submersible robot, run it along the trench, locate the fissures and discontinuities,
maybe eventually even help plug these. Of course submerging a batch of electronics into a radioactive bath may cause operating problems,
but the work here is pretty much out of other options.
Meanwhile, the idea that one can pour in concrete at one end of an 80' trench and have it flow evenly to fill all the way to the other end is just implausible. Much more likely it will pile up along the way, leaving the leaks less accessible than ever. The waterfront barrier may wind up being the only impediment to the ongoing outflow of contamination.

 

[Rive]

There have to be some serious access problems
...
Meanwhile, the idea that one can pour in concrete at one end of an 80' trench and have it flow evenly to fill all the way to the other end is just implausible. Much more likely it will pile up along the way, leaving the leaks less accessible than ever. The waterfront barrier may wind up being the only impediment to the ongoing outflow of contamination.

I think it won't be any more difficult than cleaning up the rubble on the U3 top.

You have a point with the piling of the concrete. However, if they fill up only the vertical part closer to the turbine building, then the inflow will stop and the other side can be used as a cleaning well (just reverse the water flow and what has leaked will slowly come back - so the contamination problem is reduced to water purification problem).
Unfortunately I don't know much about their intentions.

 

[etudiant]

I think it won't be any more difficult than cleaning up the rubble on the U3 top.

You have a point with the piling of the concrete. However, if they fill up only the vertical part closer to the turbine building, then the inflow will stop and the other side can be used as a cleaning well (just reverse the water flow and what has leaked will slowly come back - so the contamination problem is reduced to water purification problem).
Unfortunately I don't know much about their intentions.

Filling in starting nearer the turbine building is definitely the more logical approach, but apparently they cannot get into the trench there.
Afaik, the U3 cleanup plan is to use remote control tools dangling from a crane to do the job, but that approach will not give access to the trench, which is some meters underground nearer the turbine building. I believe the opening near the shoreline is the only one easily accessible.
A dumb robot dragging a cement injection hose to the right point might be a useful tool.

 

[Sotan]

Meanwhile, the idea that one can pour in concrete at one end of an 80' trench and have it flow evenly to fill all the way to the other end is just implausible. Much more likely it will pile up along the way, leaving the leaks less accessible than ever. The waterfront barrier may wind up being the only impediment to the ongoing outflow of contamination.

But they actually made what looks like a pretty good experiment regarding this method.
They actually poured that stuff, in water, in a 100 meter long trough, and it reached the end (the bright green layer in the figure below).
Then they poured a second layer (light blue one in the figure), and 86 meters down the road it came up nicely, still fluid.
The actual trenches are in fact a little shorter (I quote from memory but I think there are 60-70 meters at most between the designated pouring points).
When planning the filling order they took into consideration the slopes of the trenches.
In my opinion there might be pockets of water or air left here and there on the way, but overall it should work well...

 

[etudiant]

But they actually made what looks like a pretty good experiment regarding this method.
They actually poured that stuff, in water, in a 100 meter long trough, and it reached the end (the bright green layer in the figure below).
Then they poured a second layer (light blue one in the figure), and 86 meters down the road it came up nicely, still fluid.
The actual trenches are in fact a little shorter (I quote from memory but I think there are 60-70 meters at most between the designated pouring points).
When planning the filling order they took into consideration the slopes of the trenches.
In my opinion there might be pockets of water or air left here and there on the way, but overall it should work well...

Thank for a very informative post.
That is a real technical achievement. Wonder what the formulation is, as it needs to resist water inflows even though it is unpressurized.

 

[Sotan]

A detailed recipe of the mixture is not given; I can though translate this page from the same document:

- The mixture is made of cement, fly ash and an “additive that prevents dissolution in water” (can’t figure out the English term. It has high stability in water and high fluidity. The fluidity is maintained for at least 12 hours and allows it to travel, when poured, to more than 80 meters distance, keeping its properties when arriving to the destination (verified by experiment).
- Unlike usual concrete, it does not make use of aggregates (no sand, no gravel). Therefore it can flow through very narrow cracks and fill in even small places.
- To avoid dissolution in water it must be poured through a pipe that is submersed in water– like “blowing” more and more material into the bubble of mixture underwater to “inflate” it. The slope of the flowing mixture is about 1:200 (0.5%); when reaching an end/wall, it takes about 2 hours for the mixture to form a horizontal surface (self levelling).
- Photo 1 shows the front of mixture advancing through water (shows fluiditiy).
- Photo 2 shows how the mixture does not “dissolve” in water when poured.
- Photo 3 shows how the mixture is able to fill small and complicated spaces around obstacles (there are a pipe and a few cables shown there).

 

[etudiant]

Impressive stuff!
This should be very popular in construction circles if the strength is decent and the cost even near reasonable.

 

[Sotan]

New Tepco report (in Japanese) on the investigations and operations related to Unit 1:
http://photo.tepco.co.jp/date/2014/201412-j/141219-01j.html

The focus of the report is on the monitoring of radiation during the partial removal of the building roof. Apparently the dust-fixing resin sprayed in the building helped prevent further scattering of radioactive dust.

Page 7 shows the locations of the operating floor where the camera was lowered to take photos, as well as the direction of the camera views.

They have a general idea of what is some of the debris that should be removed first.

SFP - no visible sign of damage to the fuel assemblies.
The ceiling crane has fallen and is supported in part by the FHM, pretty close to the surface of the SFP water.

Page 10: walls, pillars and roof debris
Page 11, 12: state of some wall metallic structures. Some bolts have failed, girders sustained damage.
Page 13: remains of the collapsed roof. Photo 3 shows the concrete slab over the reactor well. Photo 2 shows the FHM, hanging pretty close to the SFP water surface.
Page 14: part of the fallen ceiling crane (girder); photo 5 = displaced concrete cover of the "new fuel storage room" (it held no fuel at the time of the accident).
Page 16: radioactivity level values (77 mSv/h seems to be highest value)
Page 19: infrared photo of the operating floor (no signs of heat).The photos are also listed individually here:
http://photo.tepco.co.jp/date/2014/201412-j/141219-01j.html