Fukushima Japan Earthquake: nuclear plants Fukushima part 2

[MadderDoc]

Followed by white smoke or steam ?

Not to throw the conversation back six years, just refreshing my memory.

No, that would be pretty awful :-). I'd say, dust. I consider the white ground-near clouds to be secondary clouds of dust, originating from the debris of the shattered upper floor walls, which was initially spread by the explosion in a perpendicular direction to the walls, horizontally away from the building.

Due to the viewing angle, the main part of the white stuff you are looking at, in that frame, would be dust, formed from the cast out shattered panels of the upper west wall. The hydrogen explosion spread that material initially westwards 'across the road' towards the hillside. So now the lighter stuff, dust, is coming back in the opposite direction, towards the building, and further towards the ocean. The analogy would be like if you had been throwing a handful of dirt away from you, forcefully, against the wind...;-)

 

[MadderDoc]

Thus, looking at this famous photo, the cloud visible is in the main what lingers of these secondary clouds of dust. Also clearly visible, are the two distinct white clouds of steam rising from the area of the edge of the equipment pool, and from the area of the transfer gate to the SFP, respectively. Tne PCV was at that stage obviously leaking out steam in that direction, too.

 

[jim hardy]

Tne PCV was at that stage obviously leaking out steam in that direction, too.

Thanks - i had forgotten the steam was so distinct in that photo.

The land based camera was farther West looking East
so debris thrown toward the water was hidden by the cloud.

 

[MadderDoc]

Thanks - i had forgotten the steam was so distinct in that photo.

The land based camera was farther West looking East
so debris thrown toward the water was hidden by the cloud.

Yes. Farther south and west that is. The direction to the videocamera would be indicated by a line drawn from the center of the unit 3 building to the stack. In the video we are therefore incidentally looking in at the clouds movement with the wind, in an angle that is not too distant from 90 degrees, which is not too bad. Still, unfortunately, there is no other imagery of the event from any other direction.

 

[turi]

Something completely different: Until November they will test whether 3 wheel bicycles are useful for the workers on the premises. The trial will be restricted to roads with a speed limit of 20 km/h. A few roads have a 40 km/h speed limit where the bicycles won't be allowed.
http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images2/handouts_170803_03-j.pdf

 

[turi]

The first of 8 dome parts has been installed on unit 3 as part of the preparations for the fuel removal from the spent fuel pool.

 

[MadderDoc]

And now to something much lower down. This is a composite of two frames from the recent submersed investigation inside the piedestal in the PCV of unit 3. The camera is looking straight up, as revealed by reflections of its light from the water surface above (the reflections can be seen at about center in the upper frame).

I take it, that the several similar round 'foobars' (those with eight spots around the edge) which are in unobstructed view, pointing down towards the camera, are the bottom ends of control rod drive mechanisms (CRDMs) or what's left of them, hanging down from the RPV bottom head which is somewhere above the water surface, and that they are in unobstructed view, because their support frame has come off, and fallen away to somewhere down below.

There appear at first sight to be two sizes of these foobars -- however, if there is actually only one size meant to be present, they are just at different distances from the camera, meaning the large-looking foobars dive deeper into the water, in their current position, than the smaller-looking foobars. I imagine that could be because their lower supporting frame is gone missing, so they have somehow been free to move to a deeper position than the support frame would normally have allowed them to. The support frame, I imagine, is normally affixed to the RPV bottom head with vertical iron sticks, sort of like hanging under it. I don't know how much of this makes sense, I know very little of the CRDM and how it works, and have not been able to find much about it. Comments or directions are most welcome.

 

[MadderDoc]

The first of 8 dome parts has been installed on unit 3 as part of the preparations for the fuel removal from the spent fuel pool.

Well, there's an impressive reason, why Jim Hardy will need a lot of patience waiting to see the upper head area of the drywell. More humbly, I would like to see just the second shield plug layer, seeing the middle concrete slab in the top layer has broken and sunk ~30 cm _into_ the space the second concrete layer occupies. Assumedly, by Tepco without harming it. I'd like to see that. But that will take nearly as much patience. :-)

 

[jim hardy]

however, if there is actually only one size meant to be present, they are just at different distances from the camera, meaning the large-looking foobars dive deeper into the water, in their current position, than the smaller-looking foobars.

I would expect all CRDM's to be identical with bottoms at same elevation.

I couldn't tell from the pictures whether apparent distance was real or an artifact of "fisheye lens" .

But a melt through would depend on whether they had flooded the drywell to wet the vessel bottom. The old Hodge 'Severe Accident ... ' paper
describes that and is the reason he recommended cutting vents in the vessel skirt to provide for wetting.

Just stumbled across this Interesting 1988 paper that describes how they thought back then a melt through and pour would progress.

https://www.osti.gov/scitech/servlets/purl/6700980

Right there would be a sudden source of steam and pressure spike.

 

[MadderDoc]

a melt through would depend on whether they had flooded the drywell to wet the vessel bottom.

I can't imagine they ever managed to flood the drywell to that level. As I recall from reports, a pressure spike was recorded in the drywell and the wetwell, in timely connection with the sudden decompression of the RPV that occurred at ~9:00 on March 13. Some sources, including Tepco now says an increase in the drywell/wetwell pressure unintendedly produced conditions to activate the automatic decompression system, such as to _produce_ the sudden decompression of the RPV. The problem with explaining the decompression lies in its very steepness, from about 7 MPa to about 1 MPa in about 2-3 minutes. This has been difficult to model under the assumption that the RPV had _not_ suffered a large hole in connection with the pressure event.

 

[MadderDoc]

I would expect all CRDM's to be identical with bottoms at same elevation.
I couldn't tell from the pictures whether apparent distance was real or an artifact of "fisheye lens" .

They look level and identical in the photo from unit 5 which Tepco offers as reference. They look actually also a lot more densely and orderly packed. But seeing the support for the CRDMs in that section obviously has gone walkabout , some of the CRDMs could well have done so too.

 

[HowlerMonkey]

With the grate/mount missing, you would think they would all fall out but I guess it's possible that the ones we see remaining were bent over inside where the core belongs or otherwise distorted such that they can't fall out.

I believe they are getting a lot better at inspecting so we may see something soon enough.

 

[jim hardy]

This has been difficult to model under the assumption that the RPV had _not_ suffered a large hole in connection with the pressure event.

Instrument tubes should melt higher up in the core region where the heat is produced providing a lot of small leaks

CRDM tubes are larger of course. But i don't know whether they're open on outside of vessel like the TIP tubes are. .
Those aren't the only penetrations down there, though.

I'm no BWR guy so won't speculate further. It will unfold and surely will have some surprises for all of us.

 

[MadderDoc]

Instrument tubes should melt higher up in the core region where the heat is produced providing a lot of small leaks

CRDM tubes are larger of course. But i don't know whether they're open on outside of vessel like the TIP tubes are. .
Those aren't the only penetrations down there, though.
<..>.

Seeing the CRDM tubes are meant to guide a push or pull action on control rods, I imagine they would be kind of cylinders, with a piston inside. That would mean they are not in that sense open on the outside of the vessel. There would of course be other tubes for instrumentation or other stuff I do not know about. If I get what you mean, these are basically hollow tubes closed in the hot end. I'm not even an 'R guy :-)

Here is a photo of the premises (unit 5) for reference. I believe I can see a set of thinner shiny tubes coming down about there in the middle of it. (The somewhat thicker and more matte tubes, I see as the withdrawn bottom portion of the piston action in the CDRM guide tubes.)

 

[jim hardy]

Seeing the CRDM tubes are meant to guide a push or pull action on control rods, I imagine they would be kind of cylinders, with a piston inside. That would mean they are not in that sense open on the outside of the vessel.

That's my conception too. I've never been under a BWR, though.

BWR's have something called "TIP" for "Traversing Incore Probe" system .
https://www.nrc.gov/docs/ML1125/ML11258A339.pdf

I believe it is similar to our PWR "Flux Mapping System" which consists of tubes entering the vessel at bottom and extending up to top of fuel. They're of course closed at top . Other end is open so the moveable detectors can enter to measure neutron flux inside the core.. Much like the BWR TIP system.
We had fifty of those tubes in my PWR. Each is about 5/16 inside inch diameter i forget exactly.
If they all melted it would make fifty small leaks roughly equivalent to.. √ [(5/16)² X 50] = √4.88= 2.21 inch effective diameter .

That NRC training handout taken from BWR Technology manual describes 31 TIP tubes,
√ [(5/16)² X 31] = √3.02= 1.74 inch effective diameter .A BWR guy familiar with the system will be more knowledgeable .

old jim

 

[MadderDoc]

It all sums up to a lot of penetrations, however as you noted, the penetrations for the CRD mechanisms would make up for most of their total area. Unit 3, in its present sorry state, has in all likelihood even more penetrations. Here is another composite looking up in the direction of the RPV along the hanging remains of the CDRMs.

 

[MadderDoc]

This is another composite from the dive into the well under the RPV of unit 3. This one is looking more or less horizontally at some degraded metalbox-like structure, on top of which several masses of molten material appear to have fallen and consolidated in succession.

 

[jim hardy]

hanging remains of the CDRMs.

I can't say from that picture anything about them except they sure look rusty.
400 stainless will surface rust.
In seawater there's galvanic reaction between stainless and plain steel.

Don't know what to make of your layer cake photo in next post.
It's natural enough to think "China Syndrome" . I have to consciously hold myself back to contemplating "what if's'' . Cognitive Bias ?

That is the unit though whose explosion was so different from the others. Curiosity has been killing me for six years.
Awaiting samples of that stuff. Sigh.

old jim

 

[MadderDoc]

I can't say from that picture anything about them except they sure look rusty.
400 stainless will surface rust. In seawater there's galvanic reaction between stainless and plain steel.

They are rusty, no doubt. :-)

Don't know what to make of your layer cake photo in next post.
It's natural enough to think "China Syndrome" . I have to consciously hold myself back to contemplating "what if's'' . Cognitive Bias ?

I don't know about that, China syndrome is an impossibility. However the swimming robot did amply demonstrate the presence hi and lo, under the failed RPV of masses of once molten, and now consolidated material.

 

[HowlerMonkey]

I would be interested in the temperatures of the water being injected versus the water returned out of the inside.

 

[MadderDoc]

I would be interested in the temperatures of the water being injected versus the water returned out of the inside.

The figures that came out in connection with the leak found in the MSIV room of Unit 3 in January 2014, was, as I recall it ~7 C for the injected water, ~20 C for the leaking water, and ~22 C for the accumulated water in the basement.

 

[jim hardy]

the swimming robot did amply demonstrate the presence hi and lo, under the failed RPV of masses of once molten, and now consolidated material.

Yep. There's something there allright.

Nothing would surprise me now. I've finally accepted likelihood that the unthinkable happened. Took some years - i still believe in the technology

You've heard me say management science needs to catch up with technical science...
I used to quip that anti neutrinos interact detrimentally with the neurons in the decision making part of the human brain .

But i'd better stop at that - I'm not at all anti management, just i enjoy sometimes playing the role of court jester.
If we don't learn to laugh at our follies then what will we have to laugh at when we get old ?

 

[Hiddencamper]

You also have a 3" to 4" bottom head drain line for reactor water cleanup suction that's typically in the dead center of the bottom head. That's another penetration and one that is susceptible to creep failure. Wall thinning and erosion are not uncommon on the bottom head drain (we have specific throttling limits due to erosion concerns).

The CRDMs are bolted connections. There are pistons inside with graphitar seals. The seals fail at elevated temperatures, our procedures are to keep them below 250 degF because of longevity concerns. Even if the seals fail that is just the seal between the RPV side of the shaft and the mech/drive side, it doesn't produce a leak. The leak point would be through the insert and withdraw lines.

 

[jim hardy]

The leak point would be through the insert and withdraw lines.

Where do they exit the CRD assembly ? Someplace that's apt to melt, or further down and away from any debris bed?

 

[MadderDoc]

Where do they exit the CRD assembly ?

If I have understood the setup correctly, the drive mechanism is pushed up into a cylindrical housing (which is firmly attached, welded, I reckon, to the reactor vessel), and fixed there with 8 bolts to the bottom terminal flange of the housing. The inlet/outlet hydraulic lines would then come down from above, to be connected to the top side (side facing the RPV) of the housing flanges, such as to connect down through pathways in the flange and further into fitting pathways of the drive mechanism. There would seem to have been quite a jungle of hydraulic lines up there between the RPV bottom and those 8-eyed rusty monsters the robot encountered.

 

[turi]

Irid reports on full scale tests of leakage stopping technology. Due to the additional weight when filling whole parts of the suppression chamber the support columns would have to be reinforced as well. http://irid.or.jp/en/topics/原子炉格納容器漏えい箇所の補修技術の実規模試-3/

 

[MadderDoc]

This photo shows quite well the setup of the CRDMs, with the layer of hydraulic lines coming in from above them to connect to the top side of the CRD housing flanges. The rubber-hose like connection, which loops down to connect to the lowest end of the mechanism, as I understand it, is the signal line for readout of the vertical position of the control rod drive piston.

The CRDMs would exclusively be held up in position by their own housing that is welded into the RPV. They are not supported by the layer underneath, a jigsaw puzzle of rough steel elements, held together with bolts screwed unto steelbars coming down from the RPV bottom. This construction would likely be there as an accident precaution, such as to restrict the housing complete with CRD assemblies from dropping down and out of their penetrations, in case the weldings of the CRD housings should fail in the RPV bottom head during a melt-down.

 

[jim hardy]

This construction would likely be there as an accident precaution, such as to restrict the housing complete with CRD assemblies from dropping down and out of their penetrations, in case the weldings of the CRD housings should fail in the RPV bottom head during a melt-down.

The way typical accident analyses read , i'd think
it's more likely there in case of weld failure at pressure during operation
it limits travel so the rod only drops a little bit , not fully ejecting from the core . That keeps the reactivity insertion smaller..

Perhaps a BWR guy can clear up our speculations ?

 

[turi]

I would be interested in the temperatures of the water being injected versus the water returned out of the inside.

I couldn't find temperature data on the injected vs. the returned water. But http://www.tepco.co.jp/nu/fukushima-np/f1/pla/index-j.html has a lot of current temperature measurements for RPVs and PCVs.

 

[MadderDoc]

it limits travel so the rod only drops a little bit , not fully ejecting from the core . That keeps the reactivity insertion smaller..

Well, that is a perfectly fine rationale for having the metal construct there in the first place, I accept that. In the case of unit 3, the construct may then only incidentally have had some effect on the progression of the RPV failure, by limiting the travel of CRDMs housing that had their welds fail due to contact with the debris bed in the RPV bottom head. The control rods would have already melted down at that stage, presumably. It seems clear from the video, that once debris started falling out of the RPV, the construct was to some extent able to hold on to high viscosity debris-masses for a while, collecting it so to speak, at the level of CDRMs terminal ends, only later -- when degradation further progressed including such as to fail the construct itself -- to give into let accumulated debris fall to a lower level.

 

[jim hardy]

Sounds logical .

Metal melts before the ceramic fuel so it's an unknown mix down there.

.

 

[MadderDoc]

Metal melts before the ceramic fuel so it's an unknown mix down there.

And probably not even a homogenic mix. At its present stay, there will hardly be much left in unoxidized metal form except for traces and the odd piece of scrap iron. Oxides of uranium, zirconium and iron should be abundant in the lava, of course. None of the debris formations seen by the diving robot inside the piedestal of unit 3 appear to me to have solidified out of water.

 

[HowlerMonkey]

Someone listed the temperatures above so knowing the flow rate could tell us the amount of activity going on in there.

I'm guessing they have stabilized the amount injected so that they are only injecting at enough rate to maintain the level up to where it is being maintained since it doesn't seem the heating is in danger of running away.

You would think that there was enough melting to "dilute" the fuel quite a bit.

All speculation on my part.

 

[turi]

Someone listed the temperatures above so knowing the flow rate could tell us the amount of activity going on in there.

I'm guessing they have stabilized the amount injected so that they are only injecting at enough rate to maintain the level up to where it is being maintained since it doesn't seem the heating is in danger of running away.

Flow rates are published at least daily: http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images2/handouts_170809_07-j.pdf Water is injected via core spray and the regular cooling pathway (forgot its name). But I'm not sure if it's really possible to calculate much with the data available.

 

[Hiddencamper]

The way typical accident analyses read , i'd think
it's more likely there in case of weld failure at pressure during operation
it limits travel so the rod only drops a little bit , not fully ejecting from the core . That keeps the reactivity insertion smaller..

Perhaps a BWR guy can clear up our speculations ?

This is exactly right. Almost sounds like the wording right out of the USAR.

The metal structure underneath is the CRD support housing. It's designed to minimize the maximum reactivity insertion in a rod ejection event where the CRD mech weld suddenly catastrophically fails and ejects the rod.

 

[jim hardy]

Thanks, @Hiddencamper

 

[jim hardy]

None of the debris formations seen by the diving robot inside the piedestal of unit 3 appear to me to have solidified out of water.

One can "What If" it to death. I did in 2011. That discussion would be more apropos in the science fiction forum, though.

old jim

 

[turi]

Groundwater influx into the reactor and turbine buildings has been significantly reduced: http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170807_01-e.pdf

 

[MadderDoc]

One can "What If" it to death. I did in 2011. That discussion would be more apropos in the science fiction forum, though.

You are being dreadfully indistinct. Many what-if questions have been laid to rest since 2011. I fail to see how comments on results of a recent investigation of the situation in the space under the RPV of unit 3 would fit in a science fiction forum.

 

[MadderDoc]

I'm guessing they have stabilized the amount injected so that they are only injecting at enough rate to maintain the level up to where it is being maintained since it doesn't seem the heating is in danger of running away.

They have actually cut down on the rate of injection, under the impression that it wouldn't lead to any significant temperature increase, such as to take some load off the waste water treatment facilities. Along with the muon measurements, Tepco made some interferences as to the possible whereabouts of the fuel from the RPV/PCV temperatures observed in connection with the reduction of the injection rates. In unit 3, they found that temperatures remained stable, and higher in the PCV than in the RPV. They took that as an indication where the fuel most likely would be.

As would be expected, in the case of unit 3, the reduced injection appears to have lowered the water surface inside the PCV. During the previous inspection the platform inside the PCV at the X-6 penetration was found fully submersed, while it was clear out of water during the recent expedition.

 

[jim hardy]

You are being dreadfully indistinct. Many what-if questions have been laid to rest since 2011. I fail to see how comments on results of a recent investigation of the situation in the space under the RPV of unit 3 would fit in a science fiction forum.

The remark was not meant as a criticism of your observation, though i see how it might have come across that way.
It was a 'whoa' to my own overactive imagination which thinks up (especially late at night).scenarios that do belong in a Sci Fi thread..

Just that to me the 'layer cake' resembles coral growths. I've no idea how they formed. I could as easily accept they're sedimentary.

If a melt through dripped molten metal into water i'd expect the steam to scatter it
If it dripped into a dry region i'd expect stalactites

I don't know what to make of the pictures.

I do apologize for the wording of my post , certainly no belittlement or criticism was intended. I was reining in my own fantasies albeit awkwardly.

old jim

 

[MadderDoc]

No worries, Jim. We're coming at this with different backgrounds, as I said I am not an R guy, but rather a C guy (for chemistry), and more distant a G guy (for geology, which was my first academic love). So of course I am looking at things from that perspective. Molten metal in water can produce very exciting phenomena, however the bulk of what you'd expect to come out from a RPV such as the Daiichi ones. would not be molten metal in its reduced form. Rather one should think of it as a lava-like substance, containing predominantly different oxides of uranium, zirconium, and iron. Lava formations look differently, depending on whether they solidified in air, solidified on dropping into water, or solidified from a submersed formation site.

 

[Charles Smalls]

@jim hardy and others, I am glad to see a more realistic interpretation of the situation has started to solidify. I recall as recently as March 2017 seeing posts suggesting a large amount of the unaccounted for reactor fuel was likely still unmelted and 'intact' inside one or all of the RVs. And posts like this gained much credit and support here.

(https://www.physicsforums.com/threa...ear-plants-part-2.711577/page-61#post-5729504)

The fact remained that all relevant data and 1st hand statements directly from Tepco contradicted this scenario and pointed to clear signs of gross fuel damage, melt down and fuel escape yet this was largely looked over or ignored. Tepco have since continued to publish data and share information and I think now a more credible assessment of the condition inside the plant and extent of the accident can be formed. The more information we see released, the more we can account for what we see.

I theorized back in March that the images and data suggested that the deposits found inside Unit 1 were a result of concrete damage from gross fuel exit. A process known as spalling where a high heat source such as contact between ejected molten fuel and the PVC basemat would undergo a vigorous reaction, shattering and depositing sediment across the PVC floor (https://www.physicsforums.com/threa...ear-plants-part-2.711577/page-60#post-5726587).Supporting these images, were samples taken at the time which last month were found to be too inactive to be fuel based material. The latest videos from Tepco have now captured concrete underneath the reactors in this exact spalled state:

http://photo.tepco.co.jp/date/2017/201707-j/170721-01j.html

Notice the flaking and layering on the right hand surface. Typical of the high heat exposure you would expect from fuel contact. Now this is inside of Unit 3 but that goes towards my main point, a largely similar condition across the three units with signs of meltdown and RV penetration/ meltout/ ejection across all three units. In terms of Unit 1, the amount of damage to the basemat is very likely substantial if the amount of what looks like spalled concrete is an accurate indicator.

One of the clearest indicators of differences between how the accident proceed once the fuels left the RVs is the massive difference in their water levels. Unit 1 is completely flooded where as 1 and 2 are only holding small amounts. Whether that means 1 and 2 are 'good' and 3 is 'bad' or vice versa is difficult to say from this. Personally I hope something can be done to lower the viewing aspect of the Muon apparatus to try and locate more of the missing fuel to track it's progression after melting out of the RVs. That seems to be the next large unknown and could suggest which units are having the largest impact on the sites high groundwater contamination.

 

[jim hardy]

I don't buy gross vessel bottom failure.
From Sotan's link in post 1207

Don't know what or where or how big this is

but were it fuel i don't believe they'd have got the robot in there.

 

[jim hardy]

I theorized back in March that the images and data suggested that the deposits found inside Unit 1 were a result of concrete damage from gross fuel exit.

Can any of you BWR guys tell whether these rod drives are up where they belong or down on the catch rack ?

pictures are from Sotan's link , http://photo.tepco.co.jp/date/2017/201703-j/170330-01j.html

"Sediment" to me suggests a clay - asbestos mix washed out from the insulation. Of course i don't know what that plant was insulated with. We got rid of our asbestos insulation somewhere around the fifteen year mark as best i recall..

I repeat - don't stretch the evidence.

 

[Rive]

I don't buy gross vessel bottom failure.

By my understanding bottom failures are different between BWR and PWR. As far as I know for PWRs it is possible that the whole bottom breaks down, but for BWRs it is actually unlikely, since the molten material will (most likely) find its way through (or: around) the control rod mechanisms sooner than it would eat up the bottom head wall.

So in case of complete meltdown what we should look for is not a missing bottom, but big holes around some control drives.
Also, it won't look like the whole grading there would be hollowed out, but like big molten/deformed/missing sections across the floor there.

"Sediment" to me suggests a clay - asbestos mix

The sediment in U1 definitely looks like milled concrete. No clay or any fiber-like material there.

I repeat - don't stretch the evidence.

But also don't ignore it. U2 and U3 is still has some missing points, but for U1, the 'gross bottom failure' already has quite high probability.

 

[Charles Smalls]

By my understanding bottom failures are different between BWR and PWR. As far as I know for PWRs it is possible that the whole bottom breaks down, but for BWRs it is actually unlikely, since the molten material will (most likely) find its way through (or: around) the control rod mechanisms sooner than it would eat up the bottom head wall.

Exactly this. Not a gross collapse or pressurised rupture of the bottom head, but a situation where insufficient cooling gives the superheated fuel an opportunity to eat through weak points in the RV bottom head and bore it's way out of the reactor. Unit 2 has clear signs of undergoing this exact process. It has a mostly recognizable and intact CRD structures in the ceiling and a completely melted grated floor in the CRD room beneath:

[We] don't know what or where or how big this is.

We know exactly where and how large this melt damage is. These images were taken in the CRD room directly underneath the Unit 2 reactor vessel. TEPCO published these schematics of the damage sizes back in February:

(http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170215_01-e.pdf)The red arrow indicates the position of the robot taking the images. The large pizza slice shaped missing grating in the middle of the photograph is the blue/red triangle section of grating in the schematic. The well known melted grating hole at the top of the photograph is the red square of the schematic. That section was originally said to be 1x1 meter. The other large amounts of missing grating that can be seen in this photograph and the above Jim Hardy post, are the grey area of the schematic which we now know is also missing. All in all there is large scale damage to the large amount of the CRD room floor. Whether this is entirely from contact with melted fuel or also caused partly by explosions/falling debris is unknown. Either way it is clear that a large amount of fuel in a melted state passed through this area directly below the reactor. This is the reason why the robot that entered through the X6 tunnel was never able to travel further into the pedestal and complete the rest of its planned inspection. The surfaces it was supposed to travel on had been melted or blown away. In Unit 3, the big difference was that Tepco used a swimming robot in and a flooded containment building, so the probe could essentially swim it's way up to the CRD rods regardless of whether the flooring had been melted away in the process of the accident.

All in all, the lion share of the fuel in the three units seems to be down and out. Down through the rv bottom heads and outwardly spreading across and into the PVC floors. The robot images, muon scans, tepco statements and contamination readings all point towards this being the case.

 

[turi]

Tepco will run a "temperature stabilization test" in the SFP of unit 2. The expectation is that for all three SFPs natural cooling is now sufficient even with high summer temperatures. This has already been shown for the SFP of unit 1.
http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images2/handouts_170818_02-j.pdf

 

[HowlerMonkey]

Smalls hasn't learned from his previous incorrect assumptions.

You need information that does not yet exist to make the assumptions you are making.

 

[Charles Smalls]

Smalls hasn't learned from his previous incorrect assumptions.

What are you referring to? I stand by everything I have voiced so far. The one caveat is the location of the X-6 entrance AKA "top or middle of the PVC"-gate. The point I was trying to convey was that relative to the original starting location of the fuel (inside the rv) to the likely end location of the fuel (the PVC floor), the elevated 500Gy/hr reading near the X6 entrance was given the elevated location and the revised number fit much better with my expected progression of the accident. As I said in my #1333 post, many circumstances or chain of events could have caused a 530 Sv/hr reading around that area but it fits much better to have that number revised down which it was. Remember 'down and out' is what I have been putting forward. That is the likely path the fuel in the 3 reactors took and where I expect the largest of the contamination readings in the PVC floor/basemat area. Relative to the starting location, not from the top of the PVC itself. If nitpicking basic grammar is the sole argument against my hypothesis I have no problem with that.

You need information that does not yet exist to make the assumptions you are making.

I disagree. I see no problem with making assumptions or speculating so long as it's done in a measured and responsible way. That means citing relevant, credible sources, giving a logical scientific or historical basis and an agenda free presentation i.e. not endulging in fear mongering or rumours. As far possible I've done that. You hope when the data does arrive, it confirms or supports those assumptions you put forward. I made (at times) some unpopular assumptions on Unit 2 fuel meltout, a negative Unit 3 muon scan, and spall deposits in Unit 1 and so far data has come back to support each of those. That means I can be confident that my understanding of the situation at Fukushima and the progress of situation from 2011 to today is on the right track. That my understanding is relatively sound and I am well enough informed to asses the events. Remember this is the true meaning of scientific method. To begin with the hypothesis you want to prove and interpret the data from there.

Again if there is any actual scientific or mechanics based fault in any posts I have made, feel free to raise them. Typos not included.