Japan Earthquake: nuclear plants Fukushima part 2

[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.

 

[Rive]

Yes.

And in the same time you are talking like as if Uranium would be the main concern there.

 

[nikkkom]

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

TMI-2 accident happened on the very first fuel load, after only three months of operation. Therefore, the plutonium generated in its fuel was quite low on Pu-240.

Why do you think TMI-2 corium was sent for storage to _DOD_ facilities instead of being stored in civilian dry storage?

 

[HowlerMonkey]

It will likely heat up if there weren't a ton of water being circulated.

 

[nikkkom]

It will likely heat up if there weren't a ton of water being circulated.

By very little. (I would guesstimate that if all air and water circulation would be closed, the hottest location would go to about 60-70 celsius). The accident happened almost seven years ago.

Let's compare it to TMI:
NP-6931.pdf
The Three Mile Island accident occurred on March 28, 1979. Two years later, decay heat became so low that reactor was cooling itself just by conducting heat to outside:

 

[Hiddencamper]

It will likely heat up if there weren't a ton of water being circulated.

At this point it's not so much about temperature, it's more about keeping stuff wet to reduce airborne contamination and holding fission products in the liquid. Letting stuff dry out is a great way for stuff to potentially go airborne. Water also provides shielding.

 

[Rive]

At this point it's not so much about temperature

Before we knew how the stuff actually deposited it was said here that water is needed because there are configurations which limits cooling, so we can't guarantee the temperature without active cooling.

As it is now, we already has some idea about the configuration (stuff embedded in sand-like substance in the bottom of a big bucket) and this configuration is precisely one of the worst. All previous worries are now justified.

It would not be a miracle to find some underwater mud/heat springs there.

Let's compare it to TMI:

TMI had far less stuff melt together, without being embedded into a flow-blocking substance.

 

[nikkkom]

TMI had far less stuff melt together, without being embedded into a flow-blocking substance.

Wrong. TMI-2 had all "stuff" tightly packed in one place (RPV), sealed in it, then sealed in containment building, practically none of major heat generating nuclides (Cs, Sr) were removed - unlike Fukushima, where Cs must be largely removed by 7-year leaching now.

And yet, ~2 years from accident, TMI-2 heating was low enough that no forced cooling was necessary to keep it below 100 celsius, when they closed valves to OTSGs (steam generators).

TMI-2 reactor temperature fell below 100 celsius much earlier than that - on 1979-04-27. Ironically, this happened exactly on the day when they switched *off* pumped recirculation through OTSGs, since the pump was generating 2/3 of the heat load.
Recirculation through OTSGs continued after 1979-04-27 for ~1 year by natural flow due to hotter water's lower density.

 

[nikkkom]

TMI-2 cooling:

 

[Rive]

Wrong. TMI-2 had all "stuff" tightly packed in one place (RPV)

Man, take a look at any picture about the final configuration of the TMI reactor internals and give some deep thoughts about convection and surface.

 

[nikkkom]

Man, take a look at any picture about the final configuration of the TMI reactor internals and give some deep thoughts about convection and surface.

I read this as "I have an argument why TMI-2 situation wrt heat generation by corium was better than Fukushima, but I won't tell you what this argument is. Guess it".

Sorry, but this is not how discussions work. You need to lay out your arguments yourself.