Japan Earthquake: nuclear plants Fukushima part 2

[MadderDoc]

While the explosion in unit 3 managed to set objects in a motion upwards with a velocity of about 70 m/s, along with a huge cloud of steam, it is a pertinent question, what could possibly have produced this strong vertical component, and whence came that steam. After the explosion, steam was seen rising with some gusto for many days, from the outlets encircled below. They have since the explosion apparently been the exits of least restraint for any excess steam that would like to escape from the inside of the DW. Seeing these exits must have been produced in the course of the event, they may also during the event have served as main exits for steam under pressure coming out from the cavity below, thus producing the vertical thrust. There are IMO no other possible explanations. The displaced lid (position marked), also serves as an indication that the event in unit 3 came with a pressure pulse of something wanting to come out fast from below the concrete shield.

 

[Rive]

Seeing these exits must have been produced in the course of the event, they may also during the event have served as main exits for steam under pressure coming out from the cavity below, thus producing the vertical thrust.

As recall, there was some kind of simulation about the process of combustion in U3, and the conclusion was that the main event happened inside the building, but outside the PCV. The 'exit path' of the explosion was the vertical shaft (used to move the fuel) and/or the ruined corner of the building, thus the vertical thrust.

The apparent 'vertical thrust' caught on the video of the explosion would have been more than enough to move the reactor well plug would it came from under the plug. IMHO it is interesting to compare the status of the plugs of U1 and U3. In U1 the plug were lifted, but there was no vertical thrust in the explosion. In U3 the plug is in place, but there was a vertical component.
Way back I had that wild speculation that the plug in U1 were actually moved by the post-explosion vacuum, not by any pressure under the plug. The status of the plug in U3 would mean that there was no post-explosion vacuum there. This would cleanly fit with the mentioned simulation.

 

[MadderDoc]

As recall, there was some kind of simulation about the process of combustion in U3

Perhaps you can find a link to that. I do not remember anything fitting that description, but I would like to read it, if it exists.

 

[MadderDoc]

In U1 the plug were lifted, but there was no vertical thrust

In unit 1, we know that now, the plugs were very disorderly and grossly displaced, such that no distinct narrow escape route was produced. With the limited amount of steam possibly exiting, there needs to be a narrow escape route to produce an orderly vertical thrust to set things in a 70 m/s upward motion.

 

[Rive]

Browsing back the thread I found this: http://photo.tepco.co.jp/date/2017/201702-j/170217-01j.html
The images are ~ in match what I recall, and I know that there was one similar stuff about U3. Maybe you can find the English version and/or the correct one around that date..

there needs to be a narrow escape route to produce an orderly vertical thrust to set things in a 70 m/s upward motion.

The problem is, that any thrust what can cause such mushroom would widen that 'narrow' route quite fast. Especially near that plug, which is just heavy but not nailed down.

 

[MadderDoc]

any thrust what can cause such mushroom would widen that 'narrow' route quite fast. Especially near that plug, which is just heavy but not nailed down.

I believe we are talking about an upwards thrust which accelerated objects from the building top to an initial vertical speed of about 70 m/s. We know there was such a thrust, and that it was only shortlived. The plug in the case of unit 3 had the heavy overhead crane beams crashing flat on top of it.

 

[jim hardy]

There are other paths than through the concrete plug for upward exit of whatever was the gas.

Floor plan of a similar vintage plant

red are hatches that go down for lifting things from ground level to refueling floor. Seems a natural path for hydrogen.

Yellow arrows are through what has to be some sort of removable door for refueling - i don't know how stout they are
maybe a BWR guy does. But someplace in the videos exists a picture of U3 SFP with rebar blown inward, into the pool.
That'd seem a likely path for steam were the plugs already held down by the crane..

Do we know if the crane fell during earthquake , before the explosion ?
or did the explosion push these columns out from under the crane rail letting it fall across the plug ?

I don't know.

old jim

 

[MadderDoc]

Do we know if the crane fell during earthquake , before the explosion ?
or did the explosion push these columns out from under the crane rail letting it fall across the plug ? I don't know.

I think we do. It is not plausible, that it fell during the earthquake, leaving really only the option that it fell in connection with the explosion.

 

[MadderDoc]

There are other paths than through the concrete plug for upward exit of whatever was the gas.

There are no paths through the concrete plug, but obviously, since the explosion, there were preferred paths along the sides of it, in particular in the areas of the removable 'doors' to the spent fuel pool and the equipment pool - the areas which you've marked up with yellow in the sketch seen from the side, and which I marked up with red circles in the photo seen from above.

 

[jim hardy]

and which I marked up with red circles in the photo seen from above.

Ahhh so THAT's where those gates are !

This famous "minute after" satellite picture shows two plumes.

 

[MadderDoc]

This famous "minute after" satellite picture shows two plumes.

Yes. It was believed to be, hydrogen explosion. Hydrogen explosion was still quite visible in the "7 minutes after" picture. But it appears to have subsided over the next hour or so. In the "100 minutes after" picture hydrogen explosion is no longer visible. I believe it didn't reappear until late in the afternoon, after the injection of seawater had been restarted. Then it went on for days. It was believed to be, spent fuel pool.

 

[Rive]

Seeing these exits must have been produced in the course of the event, they may also during the event have served as main exits for steam under pressure coming out from the cavity below, thus producing the vertical thrust.

Those exits are really the supposed main exits of steam-hydrogen mixture. However, they are not the source of the upward thrust.

The sequence of events, as I see it:
- serious leak on the RPV/PCV top: possibly with relation to some event inside
- the leak is strong enough to dislocate the gates around the RPV-PCV cap and quickly fills up the interior of U3 with steam and hydrogen
- the hydrogen reaches the lower levels of the unit through the vertical shafts
- the hydrogen is ignited somewhere on the top floor, the blast clears the top section of the building
- the blast progressing toward the lower levels and in the closed space a high pressure area is building up
- the high pressure wrecks the building and through the vertical shafts creates an upward thrust, bringing along the dust and rubble still moving due the initial blast
- the interior of RPV slowly dries up as the pressure falling, and further steam comes only after further water injection.

Still: anything what could wreck that building to this degree would bring along that plug without much effort (regardless of that crane involved or not) if originated from below that plug.
The amount of material cleared away from the top floor is already more than the mass of that crane and the plug together. And all the stuff were further away from the plug already (so: gets significantly less push), but that plug is still there.

Sounds as realistic as a surviving sparrow from the epicentre of a daisy cutter.

 

[MadderDoc]

anything what could wreck that building to this degree would bring along that plug without much effort (regardless of that crane involved or not) if originated from below that plug.

Yes. But no one has suggested, that the wreckage of the building to that degree was caused by the kinetic energy of material exiting from below that plug.

 

[jim hardy]

Where does this displaced lid belong ?

 

[MadderDoc]

Where does this displaced lid belong ?

There are two wells in the floor section between the shield plug and the SFP, one on each side of the transfer chute to the pool. You can see one of them, the lower in the image, with its lid in place, the other one, with its pushed up lid, is hidden in the rubble under that cover Tepco has placed there. The wells are connected to the cavity under the shield through subfloor channels, such that water can pass between them, when the cavity is flooded during refueling. I am not sure I remember the exact function of these wells or what they are called.

 

[jim hardy]

EDIT i see several new posts appeared whilst i was typing. Will digest now.

Still: anything what could wreck that building to this degree would bring along that plug without much effort (regardless of that crane involved or not) if originated from below that plug.

http://allthingsnuclear.org/dlochbaum/possible-cause-of-reactor-building-explosions

suggests a large path for hydrogen to fill the building

That would be consistent with a gentle lift of shield plug after which it'd drop back down nearly in place.

My alleged mind races to too many possibilities - got to think scenarios along some further and throw out the ridiculous ones.
Trying to figure out what pressure would fail the doors to refueling cavity and equipment pool - to you BWRguys- are they even in place during operation?.

Figuring pressure at which RPV or PCV head bolts stretch is straightforward
take wetted area of the head, divide by total cross section of the bolts holding it down
that ratio is the factor by which internal pressure translates to tension in the bolts, psi to psi.
Mild steel bolts would yield(stretch) at around 40,000 psi in the bolts
so that'd mean if the ratio of areas were 400 and the bolts were 40kpsi mild steel the lid would lift at 100 psi inside .
Probably the drywell flange bolts are stronger than that , it's a huge wetted area. If they're 70,000kips steel bolts and lift is 70 PSi then ratio of areas is 1000.

Our reactor head bolts were something exotic i don't recall the exact number for yield but i think it was around 170,000 . We hydro tested our vessel to 3106psi which is coincidentally the highest[pressure you can make with steam. (I wonder how they picked that number ! :)(smilies not working?) )

I don't know at what pressure BWR vessels are designed to lift the head.
But that's why i am so curious to see the condition of bolts at 3's RPV and drywell head.

If I'm replowing old ground advise and i'll desist.

old jim
.

 

[MadderDoc]

Ah, here is a photo of that displaced lid. The original image from Tepco site is all broken up. I've mended the picture below such as to give a proper view of the scene. Tepco has weirdly titled the image: "Hatch returned to its original position". Whatever it is to be called, hatch, lid, or shield, it is meant to cover something called the skimmer surge tank.
http://photo.tepco.co.jp/en/date/2013/201304-e/130419-01e.html

 

[MadderDoc]

Trying to figure out what pressure would fail the doors to refueling cavity and equipment pool - to you BWRguys- are they even in place during operation?.

They are in place, functioning as part of the radiation shield. They are not meant to be tight, so perhaps it does not make sense to ask at which pressure they fail.

 

[jim hardy]

Thanks - so steam could well waft out around them.

 

[MadderDoc]

Thanks - so steam could well waft out around them.

Yeah, just the same as the three-layered top shield. It is meant to stop radiation, not to be airtight in any way.

 

[MadderDoc]

But that's why i am so curious to see the condition of bolts at 3's RPV and drywell head.

Don't know about the bolts, but it is a fair assumption that there is persistent passage out of primary containment, since the events on March 14 2011. There is also a hatch in the drywell head that could've failed.

 

[Rive]

That would be consistent with a gentle lift of shield plug after which it'd drop back down nearly in place.

Although U3 is a different, but still built around the same ideas as U1 which is a genuine MK1 containment: and I think it was you who brought some documents about expected DW head and EQ hatch failure in MK1 containments. From that time I tends to take this kind of failure as the most plausible explanation.

I don't think that the shield plug in U3 was lifted at all. The observed exit paths around the shield plug are more than enough to fill the building within reasonable time.

It is because of this that I suspect that it was not the steam from below which lifted the plug in U1 but something else (vacuum after the explosion).

 

[MadderDoc]

The observed exit paths around the shield plug are more than enough to fill the building within reasonable time.

The observed exit paths around the shield plugs would seem irrelevant to that purpose. Even in original state and lay out, the shield plugs will allow passage of hydrogen further into the secondary containment, once hydrogen is provided an exit path from the top of the primary containment and into the reactor cavity below the plugs. Also hydrogen could have escaped into secondary containment by other routes not involving the top of the primary containment at all. Already by the time Tepco think the vast majority of the hydrogen was produced, >24 hours before the explosion occurred, it was observed that steam was filling the lower reaches of the building. After that there were repeated containment vents which may have backflowed hydrogen into the building through the SGTS system.

 

[jim hardy]

I think it was you who brought some documents about expected DW head and EQ hatch failure in MK1 containments.

Hmmm memory fails me at this moment but i'll have a look. Was it recent ? Sometimes i can't even remember where are my feet. Don't get old ...

 

[Rive]

I think it was in the old thread, but I can't actually find it... It was something about severe accident management, SBO and such, maybe. The expected failure points were just mentioned.
But I can be wrong. It's really an old story.

 

[Rive]

Sorry for the confusion, I was wrong about who posted the thing.
https://www.osti.gov/scitech/servlets/purl/5630475
from here: https://www.physicsforums.com/threads/japan-earthquake-nuclear-plants.480200/page-62#post-3209801

Also: http://www.sciencedirect.com/science/article/pii/002954939090019T
from here: https://www.physicsforums.com/threads/japan-earthquake-nuclear-plants.480200/page-33#post-3199567

One more: https://www.physicsforums.com/threads/japan-earthquake-nuclear-plants.480200/page-349#post-3299360There might be other sources too. Generally, 'drywell head seal' is a good combination for searching in both part of the topic.

 

[jim hardy]

Sorry for the confusion, I was wrong about who posted the thing.

No apology - , Thanks for the link ! That was a week before i joined PF. Glad to see it .
I do remember making the calculation for drywell bolt stretch back in 2011 but likely for another forum that was following the accident.
And i have no recollection of what was the answer

old jim

 

[MadderDoc]

Those exits [those encircled in red] are really the supposed main exits of steam-hydrogen mixture. However, they are not the source of the upward thrust.

The sequence of events, as I see it:
- serious leak on the RPV/PCV top: possibly with relation to some event inside
- the leak is strong enough to dislocate the gates around the RPV-PCV cap and quickly fills up the interior of U3 with steam and hydrogen
- the hydrogen reaches the lower levels of the unit through the vertical shafts
- the hydrogen is ignited somewhere on the top floor, the blast clears the top section of the building
- the blast progressing toward the lower levels and in the closed space a high pressure area is building up
- the high pressure wrecks the building and through the vertical shafts creates an upward thrust, bringing along the dust and rubble still moving due the initial blast

Interesting thoughts. By vertical shart (singular), I would understand what is encircled in blue in image of the cleared unit 3 top below. What other exits do you have in mind (vertical shafts plural) involved in the creating of an upward thrust? Also, you say those exits encircled in red are the supposed main exits of steam and hydrogen -- But that is not meant to include the steam contained in the high rising, mushrooming hot 'steamball', is it?

As I see it, the 'steamball' does immediately appear to have been tightly linked to whatever caused the powerful upward thrust, which visibly set relatively massive objects in a fast upwards motion -- iow one is led to believe that the material exiting the building, delivering the initial kinetic energy to those objects, would be the same material which went on to produce the high-rising steamball.

 

[jim hardy]

Blue circle is equipment hatch, elevator shaft to its right ?

This is a video of what looks like rebar bent into 3's sfp., snip below
i tried to post justthe link but the video shows up . Click 'copy video url' for link.

Something was affecting reactor water level indication shortly before the explosion

from http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/plots/cur/out/plot-un3-t-I-full.png

but pressure was well behaved..

been scratching my head for 6½ years.

 

[MadderDoc]

but pressure was well behaved..

Well, during that period, while the water level indicators went wildly up and downscale. the PCV pressure about doubled, until at the time of the explosion, it abruptly fell back.

From basic physics, the pressure p inside the system during that period would have been directly proportional with the product of N and T, where N is the number of molecules present in the PCV atmosphere, and T is the absolute temperature. p=kNT. The simplest explanation of the observed behaviour of p would then seem to be, that during this periode, the temperature T inside the system gradually increased up to a point, after which the number of molecules inside the system was suddenly reduced.

 

[MadderDoc]

This is a video of what looks like rebar bent into 3's sfp

Yes, you mentioned that earlier. What is the significance of this observation, as you see it, I mean what does it tell?

 

[jim hardy]

Well, during that period, while the water level indicators went wildly up and downscale. the PCV pressure about doubled, until at the time of the explosion, it abruptly fell back.

Hmmm RPV and containment were coupled by then.

Just estimating from the log scale graph, 500 KPA is about 5 atmospheres , around 70-ish psi ? Likely that's enough to lift drywell head and vent a lot of steam & H2

Yes, you mentioned that earlier. What is the significance of this observation, as you see it, I mean what does it tell?

I have wondered for years where in the pool that was.
If it is a breached wall it must be up high else the pool would have drained.
Seems the weak spot would be about here, and on other side at equipment pool passageway.

which is where the steam wafted out after explosion.

But it's speculation - i have not seen any pictures of either passageway
.........

digression --

looked back at unicamp tabulations
Yes, drywell pressure, rightmost two went up around 500 KPA in last hour before the explosion

 

[jim hardy]

Any BWR I&C types here ?

Are your reactor pressure sensors gage or absolute? Are they mounted inside or outside the containment ?

old jim

 

[MadderDoc]

Just estimating from the log scale graph, 500 KPA is about 5 atmospheres , around 70-ish psi ? Likely that's enough to lift drywell head and vent a lot of steam & H2

It is ~the max design pressure for the drywell. It is absolutely not built to operate at that pressure.

I have wondered for years where in the pool that was.
If it is a breached wall it must be up high else the pool would have drained.
Seems the weak spot would be about here, and on other side at equipment pool passageway.

I think it is rebar from a concrete layer in the original upper roof construction. Quite a lot of a section of that appears to have crashed and remained as debris on the top of unit 3, there, in the area of the pool and around it. The section appears to have been pulled down towards the floor in connection with the collapse of the upper part of the southern wall. In the main, the lined pool wall appears rather intact. There are some damages in parts of the floor bordering to it, but hardly enough to explain the presence of that rebar seen in the pool video.

which is where the steam wafted out after explosion.

But it's speculation - i have not seen any pictures of either passageway

There are some. It is not like the gates are all broken, however passageways have opened nearby them, bypassing the layer of the top shield plugs. due some displacements. At the position you indicate with red, the tight barrier to the pool water consists of two hung up on hooks doors, with rubber seals, with the sealing held tight by the pressure of the water column in the pool. The inner door (facing the refueling cavity), has become unhinged and pushed out towards the outer door (facing the pool water). The outer door appears to be in original position. By the unhinging of the inner door, a channel was produced such as to become a preferred release route for steam blowout close to the side of the pool.

On the opposite side of the top shield plugs, towards the equipment pool there are no tight doors, just slabs of high density concrete plugs stacked on top of each other. The preferred steam blowout route there became naturally along the ends of the slabs, due some displacement with a channel along the westward ends being the main one.

 

[MadderDoc]

Besides those two dominant blow out routes, there are several other lesser release points from the area of the top shield plugs, along their outer perifery, up between the broken slabs and along cracks in them. Pressure will out.