Japan Earthquake: nuclear plants Fukushima part 2

[Astronuc]

Page 27 speculates that another object could be the upper "tie plate" (definitive conclusion was not possible). It could be from a A-type 9x9 fuel unit, or from a MOC unit, or from a so-called "dummy fuel unit".

It could be a component similar to the bale/handle of an upper tie plate, but one does not see the tool plate(see two images on the right side of page) that would interface with the fuel rods. It could be the handle of some tool.

 

[Sotan]

Thank you for those clarifications Astronuc.
The tie plate... I understand you are skeptical but so should they be - and yet, they tend to say tie plate as a possibility. Just for the sake of the argument; for such an object to be found like that on the bottom of the PCV, there should be a pretty large hole somewhere in the RPV, right? Or am I making a terrible mistake here (wouldn't be the first time...)

 

[Astronuc]

for such an object to be found like that on the bottom of the PCV, there should be a pretty large hole somewhere in the RPV, right?

Correct. For an upper tie plate from a fuel assembly to be found underneath the pressure vessel is rather strange. The upper tie plate in a fuel assembly is fastened to eight tie-rods, which are special fuel rods that fasten the upper tie plate to the lower tie plate. The channel surrounding the fuel assembly is fastened to the upper tie plate as well.

I have seen fuel handling tools with similar handle/bale designs, but it is strange to find such an object below the RPV.

On the last page (25) of d171130_08-j.pdf, the diagram shows the structures (e.g., core support plate) and hardware (e.g., control rod drives and housing) that would block release of fuel assemblies or their parts from leaving a core if it melted. The XM-19 does not appear to have melted, whereas it appears the SS304 is severely corroded to the point of chemical dissolution. It would help to see the array of CRD housings and/or the RPV from below to determine what breach exists in the RPV. In addition to possibly melting, oxidation of metals and chemical dissolution of the fuel and core components is possible.

 

[MadderDoc]

Page 14: Water surface disturbance has been observed in locations 1 to 4.

The fact that the water surface is disturbed is revealed when light from the robot happens to hit the disturbed surface from below, to be reflected in it, in angles such as to be registered back at the camera of the robot. Of course the water surface is not disturbed only in those locations where -- through this phenomenon -- the disturbance is actually observed.

 

[Sotan]

The word in Japanese is "yuragi" which most of the times means "tremor, swing, sway, tremble". I translated as disturbance. In my mind I imagined it like being underwater with the robot and looking up, and I would see from there how a small water shower was falling from above in these 4 spots. As such, the rest of the water surface is probably undulating a little, too, but in these spots the difference is remarkable.

- I do not know how to quote so I will just paste this fragment of post #1316 from this thread, back in July:
"Edit: Then I found the video images of 21st too. Totally as impressive! Take a look (I only know this way to access them : http://www.tepco.co.jp/tepconews/library/archive-j.html?video_uuid=f1ak69jq&catid=69619) Especially intriguing moments: 00:12 and 00:53, that can't be steel corrosion, too conspicuous and non-uniform? they rather look like blobs of material splattered over structures. What's that at 00:19, a little current of water - under water? Or bubbles? And at 00:44, a large irregular mass near the still nicely rounded pedestal wall."

At that time I was confused, I didn't realize they were looking up - but indeed one of these "disturbances" can be seen around 00:19. The amount of water falling seems pretty small.

Edit: on the film of 22 July at 02:06 when the robot is pulled up into the air at the end of the investigation we can see the water surface being very still:
http://www.tepco.co.jp/tepconews/library/archive-j.html?video_uuid=ji55t6eq&catid=61699

 

[MadderDoc]

on the film of 22 July at 02:06 when the robot is pulled up into the air at the end of the investigation we can see the water surface being very still:

That is the video "170724_02j.mp4". http://www.tepco.co.jp/tepconews/library/archive-j.html?video_uuid=ji55t6eq&catid=61699

Yes, that is true, however the water surface we see in that video segment, from about 02:06, is outside the piedestal area, meaning it is not being disturbed by water falling out of the broken bottom of the reactor pressure vessel. In the same video segment, after the camera is pulled up into the air, we see a couple of drops falling unto the surface producing the characteristic train of circular ripples propagating out from the point where the drop hits the surface. Note, that specular reflections from those ripples on the surface are seen by the camera only when the ripples pass though the area lighted upon by the lights of the camera in an angle close to perpendicular. That illustrates the effect I was pointing to.

 

[Sotan]

Thanks @MadderDoc.
I am not contradicting you, I am just not sure we are of the same opinion with Tepco or not :) They appear to give importance to these water surface disturbances, because if little showers of water are pouring down in several places this could indicate multiple holes in the RPV, some of which might not be on the lower surface of the RPV but somewhere in higher places, on its cylindrical portion. I am not sure if you mean to say 1) there is probably much more disturbance on the water surface, these 4 spots were just suitably located for the light/camera combination to catch them, or 2) if you mean to imply they shouldn't draw such a conclusion (lateral damages to the RPV), or that their argument is weak? Again, just making sure I understand correctly. Always appreciate your valuable input.

 

[MadderDoc]

I am not sure if you mean to say 1) there is probably much more disturbance on the water surface, these 4 spots were just suitably located for the light/camera combination to catch them, or 2) if you mean to imply they shouldn't draw such a conclusion (lateral damages to the RPV), or that their argument is weak?

I would think it unlikely, that the robot managed to come by detecting and locating every center of disturbance there may in fact be of the water surface. However, it would be expected that the water coming out from the broken RPV bottom would come out rather through a number of prefererential paths small or large. The robot may have located some of those.

I would understand Tepco's mention of possible lateral damages to the RPV to be linked to the location of the observation in the photo/frame numbered 4 in the report. This frame is not in the released parts of the video, however the observation is made very close to the far piedestal wall. Water coming down there would at least indicate a source outlet above close to the circumference of the rpv bottom, and far removed from the rpv bottom center. In the released parts of the video, glimpses of reflections from disturbance of the water surface is seen nearby in that same area, while the camera is peeking up through the broken and tilted support layer under the CRDMs, which are hanging on there. A frame of the observation at that particular spot is not shown as a photo in the report, but it can be seen at about 01:04 in the video at:
http://www.tepco.co.jp/tepconews/library/archive-j.html?video_uuid=f1ak69jq&catid=61699

 

[Charles Smalls]

Domed roof and gantry crane in situ over Unit 3 for fuel and debris removal.

 

[HowlerMonkey]

So the water droplets didn't come from the robot itself?

 

[MadderDoc]

So the water droplets didn't come from the robot itself?

The droplets are falling from the wet surface of the robot once it is retracted from the water.

 

[HowlerMonkey]

That's my point.

 

[Sotan]

There are of course a few drops of water falling from the robot when it is pulled out in the air at the end of the underwater swimming investigation.
But what Tepco is talking about with interest are 4 areas of the PCV water surface filmed from below, while the robot is underwater and looking up.
Very small "showers" of water are falling in those areas from somewhere.
See an example around 00:18 in http://www.tepco.co.jp/tepconews/library/archive-j.html?video_uuid=f1ak69jq&catid=69619

 

[MadderDoc]

Very small "showers" of water are falling in those areas from somewhere.

They were at the time injecting water into the RPV through the CS or FDW lines at a rate of 70 m³/day. That is just about 0.8 liter/s [~0.2 gallons/s]. That could be it :-)

 

[Sotan]

Very possible.
Problem is, the most widely accepted theory - supported by investigation results too - is that the molten core damaged the RPV somewhere at its bottom - and in this case that is where the water from the RPV should be dripping, somewhere in the "middle". However, from the areal distribution of these water drips TEPCO seems to believe that the RPV might be damaged elsewhere too, not only at the bottom. Maybe it's not the RPV itself, maybe some weldings/pipes...

 

[MadderDoc]

Well, observations just does not seem consistent with a theory, that implies dripping only somewhere in the "middle". The widely accepted theory likely also did not predict that it would be possible to find identifiable CR guide tubes ejected from the RPV, in the space underneath it. So the theory must be revised.

 

[Sotan]

http://www.tepco.co.jp/nu/fukushima-np/handouts/2018/images1/handouts_180119_08-j.pdf
Quick report (in Japanese) and photos from the new inspection in Unit 2 PCV.
Slightly bigger photos at http://photo.tepco.co.jp/date/2018/201801-j/180119-01j.html

Page 6/10 lists some conclusions, among which there are these:
- all over the pedestal floor there is sediment which small gravel and clay appearance;
- there are fuel assemblies fallen on the floor of the pedestal and the sediment around those assemblies is presumed to be fuel debris.

http://www.tepco.co.jp/tepconews/library/archive-j.html?video_uuid=tr79wagc&catid=69619
Press conference of Tepco regarding this inspection
min 25: the camera was operated for about 8-8.5 hours inside the PVC.
min 33: there must be some sort of hole of a size suitable for a fuel bundle to fall like that on the floor of the pedestal.
min 36: all that sediment is not under water is it? yes it's more like it's being rained upon. As you know the water level in Unit 2 is rather low. We're still evaluating temperature values. 1h14: they are not worried about cooling though
min 45: we used the word "clay" just for its appearance and to show it's different from the "gravel" elsewhere, we didn't mean it's something soft, we don't know it's properties

 

[SteveElbows]

http://www.tepco.co.jp/nu/fukushima-np/handouts/2018/images1/handouts_180119_08-j.pdf
Quick report (in Japanese) and photos from the new inspection in Unit 2 PCV.
Slightly bigger photos at http://photo.tepco.co.jp/date/2018/201801-j/180119-01j.html

Page 6/10 lists some conclusions, among which there are these:
- all over the pedestal floor there is sediment which small gravel and clay appearance;
- there are fuel assemblies fallen on the floor of the pedestal and the sediment around those assemblies is presumed to be fuel debris.

Thanks so much for drawing attention to this document and explaining it.

Are they saying that a fuel bundle handle is shown in one of those photos? Certainly an object that shape is rather the star of one of the photos in that document. If so its certainly the most interesting 'corium' type photo I've seen to date from Fukushima, the sort of thing we've been waiting over 6 years to see! I knew it would take a long time, probably hoped it would be a few years sooner than this but they got there in the end.

edited - ah yes I see its been in the news, eg: https://www.japantimes.co.jp/news/2...-fuel-rod-assembly-fell-reactor/#.WmTQI9ucba4

 

[nikkkom]

I have no idea how they imagine realistically cleaning that corium up.

TMI-2 containment building basement was left not decontaminated, and it was only contamination by water, not by molten nuclear fuel dripping down.

 

[Cire]

The best way to clean that up is to dissolve it and slurp it out. I am amazed that the handle is in such good shape. How do you get a handle in that good condition under the pedestal? It had to have fallen through a large hole sometime after the reactor sludge cooled. I can't image it moving out of the RPV with everything molten and still look that good.

 

[jim hardy]

Good pictures.

sure looks like part of a GE 7X7 assembly .
From https://www.osti.gov/scitech/servlets/purl/5898210 page 143

 

[Rive]

I have no idea how they imagine realistically cleaning that corium up.

I can't see any real problem with drilling/milling that stuff and then move it with some underwater 'vacuum cleaner'.
They can mill up the concrete or steel too as needed. Just has to store the nasty stuff in small packages to prevent recriticality.

It had to have fallen through a large hole sometime after the reactor sludge cooled.

Yeah, that handle alone sure cleans up a lot of guessing. Way back seemed to be a reasonable idea to limit the vessel breakage to smaller holes around the drive mechanisms: now it's off the table.

 

[jim hardy]

Yep. The unthinkable happened...

 

[Azby]

The English-language version of Tepco's recent Unit 2 investigation report that Sotan linked to is now available:
http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2018/images/handouts_180119_01-e.pdf

Photos and videos here:
http://photo.tepco.co.jp/en/date/2018-e/201801-e/180119-01e.html

The 3-minute video is interesting:
http://www.tepco.co.jp/en/news/library/archive-e.html?video_uuid=uikti9fd&catid=61785

 

[nikkkom]

I can't see any real problem with drilling/milling that stuff and then move it with some underwater 'vacuum cleaner'.
They can mill up the concrete or steel too as needed.

TMI-2 cleanup team tried it, and decided that it is far too difficult and costly.

 

[Rive]

TMI-2 cleanup team tried it, and decided that it is far too difficult and costly.

I'm sure you did not expect me giving an answer valid for financial viewpoint too...

Mechanically, there is no real issue with drilling/milling and sucking that stuff out. (What does not mean that other means might not be more easy, cheaper, safer, more heroic or even: funny.)

 

[Azby]

Tepco, NDF (Nuclear Damage Compensation and Decommissioning Facilitation Corporation), and the IRID consortium which is developing a lot of the new technologies for this decommissioning, seem to believe that it will be possible to remove the melted fuel material. Last summer it was announced that a side-entry method would be given priority. The equipment will be remotely operated, and they seem to be prepared for it to take decades. The attached image shows a recent schematic of the proposed equipment, much of which has already been built and is undergoing tests (annotations mine). Now we know, of course, that the melted fuel is not in nice coherent clumps...

This detailed 2016 report from NDF describes the removal scenarios that have been considered and the results of planning and testing in great detail. The “partial submersion-side access” scenario is described starting on p. 4-96:

NDF: Technical Strategic Plan 2016 for Decommissioning of the Fukushima Daiichi Nuclear Power Station of Tokyo Electric Power Company Holdings, Inc., July 13, 2016
http://www.dd.ndf.go.jp/en/strategic-plan/book/20170322_SP2016eFT.pdf

The 2017 NDF Technical Strategic Plan (Japanese only available so far) was released on August 31, 2017. A fairly detailed schematic and photos of the currently planned robotic removal equipment are on p. A-61
http://www.dd.ndf.go.jp/jp/strategic-plan/book/20170831_SP2017FT.pdf

 

[nikkkom]

I'm sure you did not expect me giving an answer valid for financial viewpoint too...

My point is precisely about economic feasibility of doing this.
I have no doubt that technically it can be done, but cost/benefit ratio looks very bad. Benefit is near-zero. There are no economical reasons to have corium removed from PCVs, the reasons are almost purely emotional ("we cleaned up this mess") with a tinge of perceived improvement in nuclear material security.
How is it worth spending several billion dollars and ~10 years to achieve?

 

[Rive]

My point is precisely about economic feasibility of doing this.

Your original post were mixing the complete decontamination with the corium cleanup, on basis of the 'how', which is exactly the technological aspect.

There are no economical reasons to have corium removed from PCVs, the reasons are almost purely emotional ("we cleaned up this mess") with a tinge of perceived improvement in nuclear material security.

The term 'cleaning up' can mean many things in this aspect. If you ask 'should they retrieve and safely deposit the corium and the most seriously affected materials' then my answer is 'yes': that stuff cannot be safely stored in that damaged PCV for long term, so it must be retrieved, and in this cost has only limited meaning.

If you ask decontamination as 'should they restore the buildings as they was before', then my answer is 'no'.

 

[nikkkom]

that stuff cannot be safely stored in that damaged PCV for long term

...why? You are just assuming it. Give me the reasons why it cannot be safely stored there.

 

[Rive]

...why? You are just assuming it. Give me the reasons why it cannot be safely stored there.

Safe storage in this context means control over the stuff. Do you feel like anybody there has any real control over that stuff there?
Other than pouring water endlessly they are totally helpless even with such basic matters as cooling.

Dry storage, with scheduled supervision. That's 'storage'. The actual situation is just 'rubble pile'.

 

[nikkkom]

Safe storage in this context means control over the stuff. Do you feel like anybody there has any real control over that stuff there?

Yes. I'm pretty sure no one can steal it. It is a thick steel-lined concrete structure without possibility of human entry.
Also, unlike TMI-2 corium, this corium's Pu is not weapon-grade, so the material is not useful as bomb material, there are no incentives to steal it.

Other than pouring water endlessly they are totally helpless even with such basic matters as cooling.

It does not require cooling now.

Dry storage, with scheduled supervision. That's 'storage'. The actual situation is just 'rubble pile'.

Why it can not be dry there?
Why being in the shape of rubble is particularly bad?
Why it can not be supervised there?
(Aside from the question "what exactly you are expecting to prevent by supervising it?". Magically disappearing? However, if it makes you feel better, by all means, supervise it as often as you want. Install a CCTV camera in a glass box inside.)

 

[Rive]

I'm pretty sure no one can steal it.

Are you able to guarantee that it won't go away by itself? Would you bet your neck on it?
Just 'cause it was quite a hassle to keep that water in check, you know: with all the typhoons and raining and such. Somehow, that building does not seems to be watertight.

It does not require cooling now.

You don't even know how it is deposited there, are you sure you have the qualification to say such thing?

(Aside from the question "what exactly you are expecting to prevent by supervising it?". Magically disappearing?)

There are quite number of 'magical' disappearings, leaks and such in this context already. Even dry storage not infallible - not without regular checks, and re-storage as necessary.

 

[nikkkom]

Are you able to guarantee that it won't go away by itself? Would you bet your neck on it?

Yes. I'm positive, 100.00% certain uranium ceramic resolidified melt does not evaporate. :D

You don't even know how it is deposited there, are you sure you have the qualification to say such thing?

Yes.

 

[Hiddencamper]

Yes. I'm pretty sure no one can steal it. It is a thick steel-lined concrete structure without possibility of human entry.
Also, unlike TMI-2 corium, this corium's Pu is not weapon-grade, so the material is not useful as bomb material, there are no incentives to steal it.
It does not require cooling now.
Why it can not be dry there?
Why being in the shape of rubble is particularly bad?
Why it can not be supervised there?
(Aside from the question "what exactly you are expecting to prevent by supervising it?". Magically disappearing? However, if it makes you feel better, by all means, supervise it as often as you want. Install a CCTV camera in a glass box inside.)

What are you talking about. TMI2 corium having weapons grade plutonium. That's pretty bogus.