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.