Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[unlurk]

Great thread!
I've read the last 800 posts and I've also gone back and read from the begining, I'm up to 2500 posts there.
What a talented cast of characters here.

I learn from you guys, I usually have no need to add my untrained inexperienced viewpoints to this dialogue. But now maybe I do have something worth chiming in with.


Japan is overwhelmed at the moment.
They would have to take resources away from others in order to properly take care of the plant workers.

The plant workers also need a pre-emptive preventative medicine program.
These guys should be following a regimen which cleans them thoroughly and keeps them clean; they need hot baths to clense in,
it's part of their culture anyway, this is a downhill push.

It's a matter of resources, and the US has the resources to take this burden off the Japanese with a flick of the wrist.

We have multiple copies of fully trained fully equipped reserve units who have the resources necessary for providing water and shelter
to thousand man units.

If they made older veterans elgible to voulinteer for the mission they would not likely have any manpower problems.

The small amounts of radiation they would expose themselves to would be meaningless to a 58 or a 68 year old veteran.

An engineering battalion could build the workers a first class, designed from the ground up, facility for decontaminating themselves.

The site has to be cleaned up, this is a long term effort.


I'm a believer in the theory of the fuel in the number three fuel pond going critical.

T Cups has made the case for a vectored hydrogen blast coming out of the "cattle chute."
He nailed that IMO.

Next comes what happens when that blast hits the back wall of the fuel pond at a point just above the tops of the fuel rods.

The hydrogen blast "assembled the package" IMO.

Someday we will learn how deep this in the pond the fision event occurred. The sides of the pond will have the scars.

But no doubt a shockwave or a collision of two shcokwaves jammed the rods, (including some brand new ones) into proximity to each other
in a temporary mass dense enough to fision and boost heat output from 2.4 megawatts to maybe 2 gigawatts in less than a microsecond.

This was certainly the largest cannon ever fired.
Powered by a steam explosion.

The fuel pond held together.

The spray of fuel rod parts and pieces are scattered in a radius of undetermined size with its epicenter at unit 3.

They need to be cleaned up and contained.
The sooner the better, the sooner the easier.

It's a job that can be done without damaging anyone's health.


Meanwhile in the plant, the battle of the fizzles.
That's what were seeing at units 3 and 4.

How can the site managers reduce the number of fizzles?

 

[Susudake]

Welcome aboard, Susudake. (Though I'm a relative newbie here myself.)
Glad to see more local residents signing up.

Just as a note, so you don't accidentally get your posts pulled, this thread is for technical discussions. There are a couple of other threads devoted to political and management aspects:
https://www.physicsforums.com/showthread.php?t=486089
https://www.physicsforums.com/showthread.php?t=493101

Looking forward to your input!

Thanks for that rowmag, my whole post is no doubt redundant (just how redundant I look forward to discovering when I read the whole of those two threads, looking forward to it) and I feel rather stupid--fortunately I have lots of experience at that :-).

I'll keep glued to this thread too--thanks again to all and keep the info coming!

 

[MadderDoc]

<..>Some pictures attached. The THawk.jpg is from the first THawk-releases, the other two is from the drone flyovers at 03.24. Any ideas?

I remember first time I looked into the green eye of Mount Unit3 and felt at the same time attracted to and abhorred by it. It was an alien, unearthly experience.

It is not easy to get a good view of what is down there. It would seem to me indicated that this part of the service floor after having being initially razed by an outward/upwards blast, suffered a final hit by a substantial amount of roof material coming down from above. Following that, I'd expect if one could dig into the eye aka the sfp3, the first solid material one would encounter would be roof material that has fallen into it and on top of what else was in there. It would follow, that I should think there is water in the pool.

Unfortunately the fallen roof debris makes it very hard to see what equipment might have sticked around the pool at its edges, at the level of the service floor.
There does appear to me some wreckage squeezed up at the southeast corner of the pool at about that level. To the southwest, we see the remains of the 'little building' from which one could once look down on the pool. To the west we may see a short section of uncovered edge of pool. To the north it's a bungled mess of tormented roof structure, there is no visual of where the edge of the pool is. One could probably assess where it is by working from an estimate of the position and size of the interfacing reactor opening.

One more thought. looking for fhm3, one would tend to look for something green, but looking in this portion of the roof, for such parts that have remained here there's the possibility that such parts might have become more rusty than green due to influence of heat and moisture.

And a caveat. There are videos as well as frames in circulation that appear to be showing a pattern of finely drawn greenish fuel racks in the sfp3, but I have had occasion to check those up against less reprocessed video material of same origin, which do not show any such pattern, so I think they must be artefacts of compression and recompression.

 

[zapperzero]

So, at least I am seeing something.

Ok. It is a pincushion efect OR the camera is tilted. To me, pincushion seems a better explanation, as the intact-looking building seems to be straight. I can't see the left-most tower well enough to decide if it looks tilted as well (which would confirm pincushion).

I'll try to come up with a way to verify. Later, all.

 

[elektrownik]

#3 temp increasing, now it is 222c, bigger water injection doesn't help, also water level for one of sensor drop, so it look that crack in rpv is bigger, and #2 torus is now 76Sv

 

[~kujala~]

If what they are saying in this is really based on TEPCO's speculations...

http://www.yomiuri.co.jp/dy/national/T110428006723.htm

... Wouldn't it be much easier to cool SFP 4 using Feedwater Line (like in unit 1) or Fire Extinguisher Line (like in unit 2 and 3)?

They could at least give it a try and see what happens. Even if the gate is still working I guess extra water in the RPV wouldn't hurt so much. Or would it?

And even if the article is not based on TEPCO's speculations it is still a good theory. So what would be the worst case adverse effects if they tried to pump some fresh water into the RPV?

 

[Samy24]

#3 temp increasing, now it is 222c, bigger water injection doesn't help, also water level for one of sensor drop, so it look that crack in rpv is bigger, and #2 torus is now 76Sv

Where did you get this data? Newest on meti is report 125.

 

[MadderDoc]

A lot of yellow "things" are seen on pictures. I have marked them. Please zoom and scroll.

Yellow is an unusual color in this imagery, and yellow might spell containment cap, however I'd expect that to a piece that is not likely to have shattered to pieces. Looking for a large yellow object , the eye easily conflates two separate lesser yellowish objects to give the appearance of the presence of one larger object camouflaged by debris. There is a suggestive visual in this photo of something big and yellow in the building in front of unit 3, but the sight from other angles of this spot is disappointing and quite confusing. My intuition is that some longish object has slid into the opening, and the yellow sighting is due to conflation (see attachment with closeup from another angle)

Up on the building, one column in from the collapsed corner,behind a pillar half sunk into the servicefloor, there is in many visuals a strong appearance of a large object, but its yellowishness in some visuals is due to conflation of other lesser yellow objects on top of the pile. There may still be some large object there, but I am pretty sure it is not the containment cap. I find it curious that I cannot seem to get a handle on what it might then be (if it is anything but an illusion). We have actually pretty good images of that corner (see attachment)

 

[jpquantin]

I made some rough sketching of core burnup distributions assuming 12 month equilibrium cycles, 80 % availability, 6 irradiation cycles for each assembly prior to final discharge, and 170 kg uranium weight per assembly. For different batches I assumed the relative power fractions of 1.1, 1.2, 1.1, 1, 0.9 and 0.8. Roughly, for a 400-assembly unit with 1380 MWth around 140 EFPD I got the batch average burnups 3, 10, 17, 23, 28 and 33 and for a 548-assembly 2381 MWth unit about 4, 12, 21, 28, 35, and 42 MWd/kgU at the time of shutdown.

Then I took the decay heat data from burnup/shut down cooling calculations made (by someone else - credits due) for a "generic" BWR fuel assembly with different void histories, and calculated core-average power-weighted decay heats at different cooldown times. The results are in the attached file. This approach should give somewhat overestimated values, since it does not take into account the cooldown periods at refueling outages, but rather burns the fuel with constant power density starting from fresh fuel, and ending at 5, 10, 15 MWd/kgU etc., and then continuing with the cooldown calculation for 1800 days.

This is just an exercise I made in order to get some kind of an idea of the decay heats one could assume at this time. Therefore I have not had the time to do any double-checking of the results. Qualitatively, however, they seem to appear sensible. A decent decay heat calculation would follow the decay heat from each nuclide separately and take into accound the different saturation and cooldown periods during plant operation, but that's beyond my resources at the moment. It would, however, be nice to hear what kind of estimates others have for the decay heat of the earthquake-stricken reactors.

Thank you so much !

Well on Nov. 29th 2010 548 fuel assemblies went out of the core, assuming they had one year burn; so the pink line is a simulation for this part of the fuels; today (157 days after Nov. 29th 2010), it would indicate about 1MW residual heat today, 1.4 MW at time of the earthquake.

Then the other ones are 783 fuel assemblies: may have been burnt one year also, but taken out of the core earlier (1 year more than the 548 ones). This would be 522 days now from it, I would use the result of the blue line times 2 => 0.2 MW x 2 => 0.4 MW today, a little more at time of the earthquake (0,5 MW).

This gives roughly 1.4 MW today, 1.9 MW at time of the earthquake. We are back to AESJ estimate ...

Can you explain what simulation tool did you use, and which tool or formula did you use for cooldown calculation ? Just to know about the background of the figures.

To be continued for comparison with other estimates (AntonL, IRSN and MIT).

 

[~kujala~]

"The water is mainly concentrated from the tsunami that has leaked into the plant and then got contaminated"
http://www.houseoffoust.com/fukushima/5_3_vid.html

SO this is a new confirmation (I mentionned it already from sources cited in an other article) that part of the water in the basement is from tsunami, then got contaminated by leaks from reactors.

Good work, jlduh! I said before TEPCO wants most of the water to be from tsunami because that way they can minimize their estimates for the loss of cooling water. Here Mr. Yoshida seems to confirm this thought.

 

[rowmag]

#3 temp increasing, now it is 222c, bigger water injection doesn't help, also water level for one of sensor drop, so it look that crack in rpv is bigger, and #2 torus is now 76Sv

Where did you get this data? Newest on meti is report 125.

I think elektrownik got it from the TEPCO site:
http://www.tepco.co.jp/nu/fukushima-np/index-j.html
http://www.tepco.co.jp/nu/fukushima-np/f1/images/00_05050600.pdf

 

[MadderDoc]

If what they are saying in this is really based on TEPCO's speculations...

http://www.yomiuri.co.jp/dy/national/T110428006723.htm

<..>even if the article is not based on TEPCO's speculations it is still a good theory. So what would be the worst case adverse effects if they tried to pump some fresh water into the RPV?

I take it that these are based on Tepco's speculations. Tepco like us must be trying hard to find out what has happened. and has the benefits of being much closer to the situation, so I think the theory should be taken seriously, and at face value. And, it is plausible --looking at unit 4, it indeed appears to have been subjected to an explosion, followed by a wet hiccup from the pool.

The worst case adverse of pumping in water, I guess would be it's overflowing. Pumping water in excess erodes margin for further pumping when it it might be needed. Room for extra water is a limited resource, so to speak.

 

[jpquantin]

Soon we will have so many estimates that no matter what your theory is you can always pick an approriate decay heat estimate for it.

Well we can go further than that.

rmattila estimates and AESJ estimates converges.

Moreover, using formulas mentioned on Cambrige slide by AntonL, assuming one year burn for 548 assemblies and then 156 days of decay, one year burn for the other ones and 522 days of decay for the 783 other ones, I find: 1.2 MW + 0.6 MW = 1.8 MW today, 1.6 + 0.7 MW = 2.3 MW at time of earthquake. So back again to AESJ estimate.

This methods does not assume infinite burnup, which seems really to make a BIG difference. Simply taking same formula with infinite burnup would give 6 MW + 6.3 MW ! MIT has a footnote explaining this (*Values for the decay heat were calculated based on assuming an infinite reactor operation time prior to shutdown. Infinite operation is a conservative assumption, and actual values may be significantly lower than those that are shown in the figure and table.).

Finally using "Nuclear Heat Transport" El-Wakil formula:

P(t) = 0.095 Po ts ^ -0.26

Po = power before shutdown
ts = shutdown time is seconds

Assumes also infinite burning. This would give 3.1 MW today. Maybe IRSN used this one ?

The more accurate estimate so far seems to be AESJ one, I would personnally go for 1.8 MW.

 

[MadderDoc]

From the viewpoint of this photo one can see right through the building, through a blown out wall panel at the 4th floor west, to one of the blown out panels east above the sfp. So, in its present state, the service floor of unit 4 is not intact at the west edge of the pool.
http://www.houseoffoust.com/fukushima/tv/vid9.jpg

 

[rmattila]

Can you explain what simulation tool did you use, and which tool or formula did you use for cooldown calculation ? Just to know about the background of the figures.

The actual burnup/cooldown calculations were made by a colleaque of mine, using the Monte Carlo burnup code Serpent (http://montecarlo.vtt.fi/) and Jeff 3.1 decay heat data. Single-assembly 2D burnup calculation with constant power density of 39.8 W/gU, and then an explicit decay calculation of 1800 days, all with the same code and in the same calculation. Burnup calculations were made with three different void histories to burnups 5, 10, 15, 20, 25, 30, 35, 40, 45 and 50 MWd/kgU, and as I said, each of them was followed with its own decay cooldown calculation.

What I did then was an Excel sheet, where I tried to guesstimate the probable burnup distribution of the cores, and based on this distribution, I calculated the core averaged decay heat values from the aforementioned Serpent single-assembly results.

So, lots of hand waving there - no account taken for the cooldown periods at refueling outages etc. - but some kind of an estimate in any case.

Edit: And note that the burnup distribution of the 2381 MWth core was estimated at 138 EFPD (corresponding to unit 2), not at EOC, which is the case for the fuel at unit 4 SFP. At EOC the core average burnup (and thus the decay heat) would be somewhat (but not much, taking into account the metdhod used in the burnup calculation) higher - see attachment. And that "581" I just noticed in the plot is a typo - the actual number of assemblies used in the estimates is the correct 548.

 

[Rive]

From the viewpoint of this photo one can see right through the building, through a blown out wall panel at the 4th floor west, to one of the blown out panels east above the sfp. So, in its present state, the service floor of unit 4 is not intact at the west edge of the pool.

Both U3 and U4 has a hole on the service floor at that position for moving the fuel casks. FOr normal operation it's covered, but after the explosion... So it's not necessarily a structural damage.

Ps.: I could find nothing useful for this in the other videos (T-Hawk).

 

[AntonL]

From the viewpoint of this photo one can see right through the building, through a blown out wall panel at the 4th floor west, to one of the blown out panels east above the sfp. So, in its present state, the service floor of unit 4 is not intact at the west edge of the pool.

Top beam = roof level
followed by Crane girder beam
followed by top floor or service floor
view is as expected when wall panels are removed

 

[AntonL]

#3 temp increasing, now it is 222c, bigger water injection doesn't help, also water level for one of sensor drop, so it look that crack in rpv is bigger, and #2 torus is now 76Sv

I think elektrownik got it from the TEPCO site:
http://www.tepco.co.jp/nu/fukushima-np/index-j.html
http://www.tepco.co.jp/nu/fukushima-np/f1/images/00_05050600.pdf

Also note how the water level has dropped to 2 metres below top of fuel, this is the first time I have seen such a low level

 

[elektrownik]

Also note how the water level has dropped to 2 metres below top of fuel, this is the first time I have seen such a low level

Yes, and note that water injection is 50% bigger...

 

[TCups]

Thanks, TCups. I guess what has me puzzled is that in areas on the NSC map which show an estimated cumulative external dose for adults of 1mSv, the estimated internal thyroid dose for 1yr olds is estimated at 100mSv. Most of what I have read suggests however that, despite bioaccumulation and possibly higher relative health risk, internal doses themselves will almost always be significantly less than external doses. The NSC estimates are based on constant outdoor exposure between 3/12 and 3/24, reduced to 1/4 -1/10 if the person remained indoors. I wish the statements referenced the relevant standards (i.e. BEIR VII, ICRP, etc) on which the estimations were made. Do you think these estimates are reasonable, in a ball-park way at least?

I do not know. Exposure rates, dose rates, and total absorbed dose would vary widely, I should think, just as the distribution of the radioactive contaminants do. There is also a fairly broad range of "normal" measured RAIU% (radioactive iodine uptake) of I-131 -- about 5-15% at 6 hr if my memory serves. The total thyroid "dose" would be a combination of both internal absorbed (beta) dose from I-131 primarily, and external external absorbed (gamma, x-ray) dose secondarily. So, even a "reasonable" ballpark estimate seems almost meaningless on an individual, case by case basis (my best guess).

 

[rowmag]

Yes, and note that water injection is 50% bigger...

Something like this happened in mid-April, too:
https://www.physicsforums.com/showpost.php?p=3252132&postcount=4033

Temperature rose on the Unit 3 RPV bellows seal, to which they responded by increasing the water injection rate. Seemed to work then. Hope it does again.

(That is also when they started reporting the RPV bellows seal temperature in the daily status reports.)

 

[MadderDoc]

Top beam = roof level
followed by Crane girder beam
followed by top floor or service floor
view is as expected when wall panels are removed

OK, I see that now, thanks AnthonL, Rive. Through that 'by design' hole in the servicefloor, I would be looking up through the far end of the roof, I reckon.

Attached in another crack in a floor, I hope I am more lucky with that one :-)
See attachment, left frame:

Looking down from the west on unit 3 on a sunny day, there is an unusual bright speck visible, looking though the fuel transfer hole, apparently a speck of sunlight inside the building at 4th floor, next to the SFP.

Alternatively the speck of light could be formed by something closer up to the fuel transfer hole, something hanging out in the air within its frame and being lit by sunlight falling through the transfer hole.

However, in that case the speck of light should be also visible in the photo from the same occasion, that is looking straight down in the hole, and it is not, see attachment right frame.

So I am left with my immediate impression that sunlight must coming in through a crack in the servicefloor. I can't think of any other explanation.

Sunlight is coming in from the SSE, so the crack would seem to be somewhere about the area of the floor I have encircled in the right frame.

(That there is a crack in the servicefloor of unit 3 may not be exactly breaking news, but personally I had sort of ticked this particular part of the concrete deck as 'likely undamaged'.)

 

[jlduh]

PF forums seem to have problems today (I couldn't access for more than 4 hours...). So i finally post this message below:

Where did you get this data? Newest on meti is report 125.

You can have some updated plots of the various parameters of the reactors on this speadsheet, and jump at the bottom of the spreadsheet from one plot to an other one or the different reactors.

https://spreadsheets.google.com/spr...DZDbX39YK-iFb0Iw&hl=ja&authkey=CP6ewJkO#gid=2

Concerning reactor 3:

This is apparently (japanese translation to confirm this) the plot for the two temps that are followed on the sketches of the Meti report.

https://spreadsheets.google.com/spr...ZDbX39YK-iFb0Iw&hl=ja&authkey=CP6ewJkO#gid=13

We see that they are increasing in the last week in a trend which is a little bit scary...

There is this other plot which shows that the rise that Electrownik reported earlier in this thread is accelerating also: the "D/W RPV temp" (dry well/ Reactor pressure vessel "bellows seal" TEMP) is rising very quickly (228°C last reported, and the rise is almost 1°C per hour):

https://spreadsheets.google.com/spr...ZDbX39YK-iFb0Iw&hl=ja&authkey=CP6ewJkO#gid=40

So "something" is going on inside this reactor right now...

And this doesn't sound good to me. The bellows seal which temp is measured is the seal between the outside of the RPV at the top of it and the wall of the dry-well, it is a seal used to seal this area in order to fill the well with water, above the reactor, when this one is opened for fuel maintenance. If no seal, the water would drop into the dry-well (the containment vessel around the reactor vessel).

So what we see here is that the temps are rising inside the reactor 3. This bellows seal which is at the top of the reactor gained a 100 degrees in 5 or 6 days (from a level at around 120 °C: so this is almost a doubling of the temp in less than a week, and the trend seems exponential...

We can think that this is a result of a global increase of the temps inside the reactor 3, based on the other plot and the fact that this seal is at the top so probably receives the uprising heat by convection in addition to the one by conduction through the metal of the RPV.

What is happening inside N°3 right now? Do people with access to live feed of TBS see something special on the images (more steam for example?).

 

[Rive]

Alternatively the speck of light could be formed by something closer up to the fuel transfer hole, something hanging out in the air within its frame and being lit by sunlight falling through the transfer hole.

There is something shiny on the 'tour' video, but I will not say that they are the same.

 

[artax]

some unit 3 explosion analysis on here.

http://www.youtube.com/watch?v=9PHQ3IJHJbw&feature=related

 

[mikefj40]

It's a matter of resources, and the US has the resources to take this burden off the Japanese with a flick of the wrist.

A US Marine anti-radiation contingent arrived in Japan on April 5th. http://www.japantoday.com/category/national/view/u-s-marine-anti-radiation-team-to-leave-japan-next-week-after-not-being-called-in

They held a drill with Japanese SDF forces that seemed more of a PR stunt than anything else. Their departure from Japan was announced on April 19th.

"U.S. forces appeared to have come to a conclusion that the nuclear crisis would not deteriorate further now that the plant operator, Tokyo Electric Power Co, announced Sunday its schedule to bring the situation under control over a period of six to nine months, the official said."

They are experts at decontamination. One wonders why they weren't called on to provide temporary showers for the workers.

 

[mikefj40]

I have the impression that more than once people were calling for Japanese voices.

Your impression is correct as far as I'm concerned. Good idea about moving rather than deleting, too.

 

[pdObq]

Its approximately the right size, and its in a place that would make sense.

However, looking at an image taken from a different angle clearly shows that its actually some sort of ground vehicle/crane that has an arm extending into the sky (the small one near bottom of this picture, not the larger more obvious crane):

Ah, yes, I should have looked at other pictures from different angles before posting. Attached is again the overhead view but including the unit 3 reactor building as well. (A) is what I thought could be the FHM, but on the other picture one can see that it is clearly a crane (You also had that view attached, which I just saw now, because last time I checked I was not logged in and therefore could not view it).

I also had some comments on the deformed roof girders (C) (yellow, rusty) and the other deformed objects (B) (gray), and had written a response earlier but then I got timed out before sending it... argh. Anyway, I agree that (B) must be some kind of panels from the roof (aluminum?), as such objects can be seen also on the much more intact roof of unit4. While I first thought their spaghetti-like deformation might be due to heating, I now tend to think that these panels are probably thin and can easily be deformed simply by the forces during the explosion. The steel roof girders (C) also seemed deformed due to melting to me around where the reactor should be. But that could in principle also be due to the forces during the explosion, not necessarily due to the heat. Concerning the rust on them, I think it makes sense that that comes from the steam from the reactor. The third attached picture shows that the rusty areas coincide more or less with where the steam from the reactor poured out. (All three images are taken from the houseoffoust site.)

A slightly unrelated question: Why are the SFPs in these kind of reactor designs not at least covered with a concrete block like the reactor is during normal operation (that might not have helped at unit4...) ? It almost seems like the SFP was some kind of afterthought in the containment design.

 

[jlduh]

some unit 3 explosion analysis on here.

http://www.youtube.com/watch?v=9PHQ3IJHJbw&feature=related

This second video with the second theory (hydrogen explosion reflected from the stronger walls of Unit 3 into the SFP triggering a prompt critical explosion is interesting. http://www.youtube.com/watch?v=2onC01URt9c&feature=iv&annotation_id=annotation_31501

I found the full study mentionned in this video concerning the possibility that there was a Nuclear explosion at Chernobyl , it is here:

Estimation of Explosion Energy Yield at Chernobyl NPP Accident
SERGEY A. PAKHOMOV and YURI V. DUBASOVhttp://www.springerlink.com/content/d71710g0012116x4/fulltext.pdf

 

[Samy24]

PF forums seem to have problems today (I couldn't access for more than 4 hours...). So i finally post this message below:

You can have some updated plots of the various parameters of the reactors on this speadsheet, and jump at the bottom of the spreadsheet from one plot to an other one or the different reactors.

Thanks. That is a good and actual source.

All the temperature readings are going up. So we can asume not all the instruments have the same failure. Even TEPCO does this interpretation and increased the water flow by a very big amount.

Interesting is, that the amount of water did not help to lower the temperature till now.

 

[jlduh]

Thanks. That is a good and actual source.

All the temperature readings are going up. So we can asume not all the instruments have the same failure. Even TEPCO does this interpretation and increased the water flow by a very big amount.

The readings of these sensors don't seem erratic and they haven't been reported faulty by Tepco as far as i know. Plus there is some coherence.

 

[elektrownik]

Interesting is, that the amount of water did not help to lower the temperature till now.

Also water level is not increasing, it drop litle on one of sensors.

 

[pdObq]

Updated sub-drain isotope measurements through 5/3:
http://www.tepco.co.jp/cc/press/betu11_j/images/110503o.pdf

(For criticality-watch fans.)

I guess the only one going up is the unit 3 sub-drain. Iodine increase seems to slow down, but Cs isotopes are increasing. So, what does that change in the ratio of Iodine vs Cesium mean?
I.e. recriticality or just the slow inflow of more contaminated water with Iodine starting to decay away?

 

[|Fred]

For plot I kind of prefer the one made by Jorge Stolfi from the forum, nicer looking non google, and closer to us (lot easier to discuss and source his work since he is here :) )
http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/plots/cur/Main.html
the current temp rise is somewhat analog to the temp decrease from the 18th April

 

[pdObq]

Although I have been following this thread for a while, I have one question which I haven't seen addressed yet, although it might already have been discussed somewhere in the 5000+ posts. Sorry, if that is the case.

As far as I understand, in unit 1 the wall panels from the service floor upward are designed as blowout panels, i.e. they are meant to blow out easily in case of a hydrogen explosion on the service floor. That the explosion at unit 1 went relatively graceful thanks to these panels can be seen from the fact that the wall steel structure is basically still standing. Unit 2 also seems to have blowout panels, as the whole in the wall looks rather clean (see first attached picture).

At unit 3&4 however, they apparently changed the construction of the walls above the service floor, and used reinforced concrete pillars instead of the steel structure and reinforced concrete "panels" in between (see second attached picture of unit 4). Now, I am wondering if those were still supposed to have the function of "blowout panels", or if they just thought "oh, let's make those upper walls a bit more sturdy" without taking into account that a hydrogen explosion on the service floor will be much more devastating, as there is no easy way out any more. Indeed the explosion at unit three was much worse than at unit 1, destroying the walls completely on three sides of the building, and even kicking out concrete panels below the service floor. In addition, the stuff flying around was much heavier and caused more damage than in case of unit 1.

So, my question is basically if the upper walls in unit 3 had been the same as in unit 1, would the damage have been less severe? And are those reinforced concrete panels a Japanese "upgrade", which turned out to actually make things worse? Do other reactors of this type built e.g. in the US still have blow out panels like unit 1 (From the cut out drawings from GE it looks like both Mark I and Mark II containments have blowout-able upper wall structures).

[Both images taken from houseoffoust]