Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[Jorge Stolfi]

Another beautiful theory slain by ugly facts.

Well, OK, I will shut up. For now.

 

[clif]

REF 4177;


I don't KNOW, but I seriously doubt that this is about Unit 3.

According to the top of the page the entire photo section is about;

このレポートは、東京電力株式会社、福島第一原子力発電所、広報部の取材協力を受けております。 This report, Tokyo Electric Power Company, Fukushima Daiichi Nuclear Power Station, we received the cooperation of the public relations coverage.

and

2000.5.19 tour interview at the Fukushima Daiichi Nuclear Power Station Toukyoudenryoku

according to the webpage it is Fukushima #3

 

[|Fred]

where the floor control rooms gone ? supose to be in the south west corner but the remains do not seems to fit the structure

 

[MiceAndMen]

Thank you for this: it's very useful.

Oyster Creek is BWR2/MK1 as the Unit 1. Unit 2 to 4 are BWR3/MK1 as like Dresden NPP, Monticello, Quad Cities, Santa María de Garoña or Pilgrim NPP.
http://en.wikipedia.org/wiki/List_of_boiling_water_reactors

I've actually started to search, but it's too much, it'll be slow (days).

It does take a long time to search and you need some luck also. Many older documents have not been scanned into PDF format yet, and all you get for results are small 320-byte references to physical document numbers. I don't have the time or inclination to actually go in person to the NRC's reading room to look at physical documents or worse (microfiche), but if I did there are a few plants' drawings I would like to have a look at. You listed a few. Vermont Yankee and Millstone I are another two that I think are close to the Fukushima Daiichi designs.

There is a search option that's not listed there for minimum document file size that I worked out through trial and error (I think it's called $size:xxx) but it times out on most searches I tried. An option for "only downloadable PDF documents" would be very handy, but alas, it does not exist. Additionally, you are supposed to be able to check the boxes for several files on the left and download a .zip file that contains your selections. That doesn't work either; you have to download each one individually. It's got some bugs and quirky behavior, but overall I think they did a good job with the web-ADAMS search site. I'd rate it a solid 8 out of 10.

I suspect someone needed the Oyster Creek drawings in PDF form for some task in recent years and that's why they are available online.

 

[NUCENG]

Stacking in a SFP?

ＭＯＸ燃料を真上から (Fuel from right above)

MOX would mean reactor #3

The objects on the right appear to be a level higher then those on the left.

Image from here

http://www.newcs.futaba.fukushima.jp/05-20000519/index41.html"

What that appears to be to me is two fuel racks to the right and left at the same level, but empty. In the center are two short sections consisting of two rows filled with control rods. The lifting handles of fuel bundles and control blades are different and these look like control blades to me.

 

[Jorge Stolfi]

I've updated my plots of Fukushima Daiichi reactors #1--#3 variables to NISA relase 102 (apr/19 15:00).
http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/plots/cur/Main.html

These two reseases maintain the puzzling drop by an exact factor of 10 in the CAMS reading (A) of the #1 suppresion chamber. I still think it is a typo in the exponent that is being retained through copy-and-paste. (The reading dropped from "9.92×10⁰" Sv/h to "1.07×10⁰" on release 98)

 

[Giordano]

Nuclide analysis of water in SFP 2:
http://www.tepco.co.jp/en/press/corp-com/release/11041805-e.html

 

[NUCENG]

It does take a long time to search and you need some luck also. Many older documents have not been scanned into PDF format yet, and all you get for results are small 320-byte references to physical document numbers. I don't have the time or inclination to actually go in person to the NRC's reading room to look at physical documents or worse (microfiche), but if I did there are a few plants' drawings I would like to have a look at. You listed a few. Vermont Yankee and Millstone I are another two that I think are close to the Fukushima Daiichi designs.

There is a search option that's not listed there for minimum document file size that I worked out through trial and error (I think it's called $size:xxx) but it times out on most searches I tried. An option for "only downloadable PDF documents" would be very handy, but alas, it does not exist. Additionally, you are supposed to be able to check the boxes for several files on the left and download a .zip file that contains your selections. That doesn't work either; you have to download each one individually. It's got some bugs and quirky behavior, but overall I think they did a good job with the web-ADAMS search site. I'd rate it a solid 8 out of 10.

I suspect someone needed the Oyster Creek drawings in PDF form for some task in recent years and that's why they are available online.

After 9/11 many plant and site drawings were removed from ADAMS and were considered as Safeguards information. These drawings may have been missed or a mistake. Or maybe somebody finally figured that this wouldn't really help a terrorist.

 

[tsutsuji]

For what it's worth, here is a model of Hamaoka NPP's unit 3 (BWR-5 type, according to http://en.wikipedia.org/wiki/Hamaoka_Nuclear_Power_Plant" so it might fit Fukushima daiichi's unit 6 ?)

[URL]http://mrneko.huu.cc/sannsaku089/13.jpg[/URL]

From http://mrneko.huu.cc/sannsaku089/013.html

http://blog-imgs-30-origin.fc2.com/g/e/o/geo555/w800DSC02328s.jpg"

A http://blogs.yahoo.co.jp/kin_sugiya.../folder/79764/img_79764_2616016_0?1301230802"

 

[|Fred]

I've updated my plots of Fukushima Daiichi reactors #1--#3 variables to NISA relase 102 (apr/19 15:00).
http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/plots/cur/Main.html

I would like to formally thank you for maintaining this page, It is really help full to have some reference, one could get back to rather that trust his memory of the event, and it allow to get a better picture of the time lined event

 

[NUCENG]

Nuclide analysis of water in SFP 2:
http://www.tepco.co.jp/en/press/corp-com/release/11041805-e.html

1. Ratio of Cs-137 and I-131 consistent with fuel that has been shut down for a while.

2. Still much lower concentrations than can be achieved with only minor damage (gap release) to fuel in the pool.

3. Significantly higher readings than for Unit 4 which also tends to support little damage to the fuel in the unit 4 SFP as claimed by TEPCO.

 

[clancy688]

Interesting thoughts by Arnie Gundersen on SFP of Unit 4:

http://vimeo.com/22586794 (Around 4:25)

TEPCO measured around 250 Bq/cm³ I131 in the SFP of Unit 4. Since Unit 4 is in shutdown since four months, I131 can't come from its fuel. So TEPCO blames it on aerial deposition.
Now Gundersen did a little calculation with these numbers and got an I131 deposition of 30.000.000.000 Bq/m² I131.
Which seems a little bit much... so he thinks, that there may have been a criticality in the SFP.

What are your thoughts on this? To me it sounds plausible...Unit 4 SFP measurements by TEPCO:

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110414e20.pdf

 

[TCups]

Embryo Proposition for unit 3 chain of event, aka Bang Bang Bang
(nothing to do with the audio track that I'm I'm not taking into consideration)


Bang 1 : First explosion, is a regular "clean" explosion with an horizontal plan main component. Walls gave out

Bang 2 : Is not explosion it's the hudge heavy top crane falling down on the operating floor, and likely damaging the concrete slab /shield / cookie and link to the pool

Bang 3: Its the second explosion the vertical component.


Missing all the ins and out, the implosion or sucking in that happened after bang 1

RE: THE EXPLOSIONS AND PATTERN OF DAMAGE AT BLDG 3 & 4 -- SIMILARITIES AND DIFFERNECES


@Fred:
M. Bachmeir did extensive analysis of the sound frequencies and concluded that Bang 1 and Bang 2 were similar and were explosions and that Bang 3 was fundamentally different from the first two, as I recall. Maybe he would comment again about the possibility of one of the audible bangs being a mechanical transient from a large falling object.

If FHM 3 is in the pool, (yes Fred, mea culpa, my initial scenario proposal was wrong and I do believe the FHM is mostly in the SFP), then the blast still had to be strong enough to lift it, de-rail it, and let it fall with enough force to hit and submerge completely in the pool, else part of it would have been visible above the water level. And if it is in the pool, then something either had to break or bend significantly on one or both ends for it to fit.

There is a lot of complex-looking green equipment in all of the reactor buildings, though, and fragments and various damaged parts of them are tough to identify visibly.

OBSERVATIONS ABOUT THE EXPLOSIONS AND DAMAGE PATTERNS


Whether FHM 4 is in its normal position or down by a meter or two is really less the point than that the overriding fact that the explosion at Unit 3 was much more powerful than the explosion at Unit 4. Whether it was none or part of the FHM3 that went ballistic is also not strongly relevant at this point, because, whatever it was that went ballistic, a lot of stuff did go ballistic, both vertically and horizontally, much more so at Bldg 3 than Bldg 4.

If one accepts the possible scenario of the damage at Bldg 4 being due to the asphalt roof, then it follows that the same mechanism was likely in play at Bldg 3, given a similar epicenter of the apparent explosion, over the SFP.

I am not so sure it was reinforced concrete, having red a bit last night about commercial industrial roofing. I believe the roofing material was flexible and water proof (concrete is neither), and that it was laid on corrugated metal which peeled off the roof girders, partially lifted, and then from a more vertical position, plunged into the north end of the building. Actually the analogy of the mechanics of a folding convertible car top coming up and over the interior of the car before folding back into the trunk space is a pretty good analogy, if you have ever had a convertible. Something very similar might have happened at Unit 3 with some variations.

The stronger explosion at Bldg 3 initially blew more of the roof apart and straight up. The stronger explosion more forcefully blew the more northern section of the roof higher and further back. The more northern portion of the roof, instead of crashing in a more or less large, intact slab, just into the norther end of the building as at Bldg 4, took out the north-facing upper wall completely, and much more extensively damaged the north end of Bldg 3 and the building below.

Step back and take an overall "big picture" look at the pattern of damage done to the roof and upper structures at Bldg 3 and 4. I believe that there are some pretty strong similarities in the damage patterns, except that, again, the blast at Bldg 3 was much more powerful.

Though I can offer no credible technical explanations for the "why and how" of hydrogen and steam explosion being involved at both Bldg 3 and 4, I can and do offer my revised scenario that the difference in total energy at Bldg 3 vs Bldg 4 was that of a hydrogen explosion coming from the primary containment at Bldg 3, and then, for whatever reason, to a much greater degree, the water in the SFP at 3 turning to steam than at Bldg 4, and that the visible damages were due in significant part to portions of heavy roof segments, not falling machinery.

 

[|Fred]

No need to beat your self up I liked and concurred to the Balistic FHM and at the time , given the information at hand it was plausible. Now that we have the Bolt Machine, the FHM is less plausible.

I'm not so keen on the soundtrack , it may be exploited as an evidence but with it's low level I'll prefer to stay away from it until it is properly sourced, actually, this video I one of the less reliable piece of info that we have.. ( I see the face of a man in the smoke don't you ?)

"There is a lot of complex-looking green equipment .."
I think with all the pictures we have we can start counting:
unit 3
1) top crane center
3) FHM and FHM crane (somewhere initially on the south part eat middle)
3) Cast Crane south west wall
4) Bolt machine (initially on the north west center)


If one accepts the possible scenario of the damage at Bldg 4 being due to the asphalt roof
Could you please clarify I did not understood that scenario .. I'm probably failing at English there

 

[artax]

Yes I do... or did, was it unit 4, middle window west side?... er wall panel

I don't like the sound at all on the video, there must be somehwere to ask about the source of that video>

 

[tsutsuji]

Fukushima 1 Nuclear Power Plant_38

This picture was taken at Fukushima Daiichi in 1999. More pictures available at http://www.flickr.com/photos/hige2/sets/72157626327994523/

 

[artax]

Beginning to sound promising... actual plan with numbers in!

from the new york Times:-

"Anne Lauvergeon, the chief executive of Areva, France’s nuclear power equipment provider, said at a news conference in Tokyo on Tuesday evening that it would take at least until the end of May to set up a water treatment station at the Fukushima nuclear plant and begin purifying water. Once running, the water treatment facility should be able to handle 50 metric tons of water an hour and will be able to reduce the radiation in the water by 99.9 percent to 99.99 percent.

Ms. Lauvergeon said that even having the system up by the end of May would pose a big challenge. “It is a fight against time, but we are doing everything in our power” to meet this timeline, she said. "

 

[artax]

new pictures for ya.

http://cryptome.org/eyeball/daiichi-npp10/daiichi-photos10.htm

 

[Giordano]

1. Ratio of Cs-137 and I-131 consistent with fuel that has been shut down for a while.

2. Still much lower concentrations than can be achieved with only minor damage (gap release) to fuel in the pool.

3. Significantly higher readings than for Unit 4 which also tends to support little damage to the fuel in the unit 4 SFP as claimed by TEPCO.

Thank you for comments.

1. Maybe it is consistent, but don't you think that the ratio is "too" high, suggesting significant release of I-131 to the atmosphere (in the order of PBq) ? Also it the pool has been diluted due to cooling operations the release of I-131 to atmosphere could be even higher.

2. ?

 

[NUCENG]

Interesting thoughts by Arnie Gundersen on SFP of Unit 4:

http://vimeo.com/22586794 (Around 4:25)

TEPCO measured around 250 Bq/cm³ I131 in the SFP of Unit 4. Since Unit 4 is in shutdown since four months, I131 can't come from its fuel. So TEPCO blames it on aerial deposition.
Now Gundersen did a little calculation with these numbers and got an I131 deposition of 30.000.000.000 Bq/m² I131.
Which seems a little bit much... so he thinks, that there may have been a criticality in the SFP.

What are your thoughts on this? To me it sounds plausible...


Unit 4 SFP measurements by TEPCO:

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110414e20.pdf

In a previous post (#4111) I calculated the concentration of a 5% gap release of Iodine-131 into the pool from just the last core offloaded. Unfortunately I only accounted for a 30 day decay. Mr. Gunderson correctly indicated that the unit was shutdown 4 months before the accident. It has been a month since. So I repeated my calculation accounting for 180 days (6 months) of decay.

From an ORIGEN2 calculation of a BWR the core inventory of I-131 at 6months after shutdown is 5.03E-3 Ci per MW. Assuming 760 MW Electric and a 33% efficiency for Unit 4 leaves a total I-131 at the time of the accident of 5.23E5 Ci. In Taking 5% (gap release) and converting to Bq leaves 9.67E14 Bq.

I assumed a Fuel Pool of 40' by 20' by 40' deep. That converts to 1.81E9 cm^3.

Possible concentratiion of I-131 after 6 months in the fuel pool with only 5% of the source term released is up to 5.34E5 Bq/cm^3.

Personally I think Mr. Gunderson is absolutely correct when he ridicules TEPCO's explanation of Iodine deposition. But you do not need criticality to explain the concentration of I-131 they reported.

I try to keep reminding people that just because an isotope has a short half life does not mean it disappears in a few half lives. Half of a big number is still a big number. I-131 will likely be detectable beyond a year after shutdown.

 

[Dmytry]

How thick is the containment vessel? And what's the temperature difference across it (inside to outside)? I'd guess that the thickness of the steel doesn't matter much relative to the (probably low) heat transfer coefficients at the inner & outer surfaces.

yes and the thermal conductivity of the fuel lava is a lot lower than thermal conductivity of steel.
http://www.lenntech.com/stainless-steel-304.htm
thermal conductivity at 500 celsius = 21 W/m*K

http://www.ati.ac.at/fileadmin/files/research_areas/ssnm/nmkt/06_BWR.pdf
the wall at bottom of rpv is reported as 23 centimetres.

I think as long as the RPV has water on outside, fuel (non-critical) can only partially melt through. Of course afterwards, stupid operator actions (e.g. raising the pressure) can blow it out.
Suppose the outer stainless steel is at temperature 100 Celsius, the inner stainless steel at 1300 Celsius (almost molten), and the thickness is 23cm. The temperature gradient is 1200/0.23=5200 K/m , and the heat flow is 21 W/m*K * 5200 K/m = 21*5200 = about 0.1 MW/m^2 .
Now on to thermal conductivity of uranium dioxide
http://en.wikipedia.org/wiki/File:ZrUthermalcond.png
around 4 W/m*K meaning that for same heat flow it has 5x the thermal gradient of stainless steel = meaning that thermal gradient through first 12 centimetres of fuel will be 2.5*1200 = 3000 kelvin or so. From the orders of magnitude alone it is obvious that fuel cooled from the bottom (no convection) will be literally boiling off inside before it can melt through RPV.

Thus the worst case scenario of reactor accident: the RPV is cooled from outside, a little water is getting into RPV, the steam (with literally fuel aerosol in it) is vented out, plus the people in charge are measuring just the I and Cs and telling all the time how it is getting better and putting stress on comfort words such as containment and intact.
I really hope that did not happen. This sort of fuel vaporization might make you wish it just melted down and vent all over the place due to steam explosion, rather than cooked itself silently.

The awesome thing about decay heat is that it doesn't care how hot the fuel already got. It will just keep heating itself, and a lump of fuel in a pot can literally boil itself off and re-condense as fine aerosol.

 

[NUCENG]

Thank you for comments.

1. Maybe it is consistent, but don't you think that the ratio is "too" high, suggesting significant release of I-131 to the atmosphere (in the order of PBq) ? Also it the pool has been diluted due to cooling operations the release of I-131 to atmosphere could be even higher.

2. ?

1/ Latest research and lessons learned from TMI2 indicated that th largest part of Iodine release is in particulate form (mostly CsI) It is hygroscopic (if I remember the term) so it likes to be in water. It will plate out and loves to setle on horizontal surfaces. They have been adding seawater to the SFP which has probably maintained the pH of the pool in the basic category so the Iodine woukd not likely had significant re-evolution as I2 gas. The change of the ratio of Cs and I over time is not a fixed rate because of things like chemical reactions, settling, and reevoltion can be be differeny for the Cs and the I. The only direction you don't want to see is a sudden increase in I-131 in air that could indicate the pool has become acidic and is releasing I2 or, in water indicating, less likely, recriticality.

2. See post #4200.

 

[Jorge Stolfi]

Possible concentratiion of I-131 after 6 months in the fuel pool with only 5% of the source term released is up to 5.34E5 Bq/cm^3.

From the photos taken by the sampling camera, it looks as if the water in #4's SFP is hot and stirring. Could it be boiling? (The infrared pics show rather low temperatures --- but perhaps the IR camera does not have a direct view to the liquid?)

If the water is boiling, and the pool water is slightly acidic, wouldn't the iodine evaporate as I2 or HI? (I suppose that the cesium would remain in solution in any case).

 

[Krikkosnack]

What about this strange idea ?
[PLAIN]http://img864.imageshack.us/img864/770/7d39a2e665024e3f8856f31.jpg[/QUOTE]

https://www.physicsforums.com/showpost.php?p=3249305&postcount=3870")

 

[TCups]

No need to beat your self up I liked and concurred to the Balistic FHM and at the time , given the information at hand it was plausible. Now that we have the Bolt Machine, the FHM is less plausible.

I'm not so keen on the soundtrack , it may be exploited as an evidence but with it's low level I'll prefer to stay away from it until it is properly sourced, actually, this video I one of the less reliable piece of info that we have.. ( I see the face of a man in the smoke don't you ?)

"There is a lot of complex-looking green equipment .."
I think with all the pictures we have we can start counting:
unit 3
1) top crane center
3) FHM and FHM crane (somewhere initially on the south part eat middle)
3) Cast Crane south west wall
4) Bolt machine (initially on the north west center)


If one accepts the possible scenario of the damage at Bldg 4 being due to the asphalt roof
Could you please clarify I did not understood that scenario .. I'm probably failing at English there

@Fred:

You are testing my Illustrator skills perhaps like I am testing your language skills.

Think of the roofing material as a large, thick, heavy but flexible sheet of material backed with corrugated steel resting on top of the building (A)

The explosion rips off the roof from the southeast corner, and probably blasts some fragments of the roof upward (B)

The expanding gas from the explosion continues to lift the roof slab off of the girders and billow it like a sail full of air. More fragments of the roof are blasted away (C)

As the gas escapes, the weight of the what is left of the roof slab is borne by the north wall of the building. It begins to fall back into the building, dragging part of the north wall inward and downward (D)

 

[NUCENG]

From the photos taken by the sampling camera, it looks as if the water in #4's SFP is hot and stirring. Could it be boiling? (The infrared pics show rather low temperatures --- but perhaps the IR camera does not have a direct view to the liquid?)

If the water is boiling, and the pool water is slightly acidic, wouldn't the iodine evaporate as I2 or HI? (I suppose that the cesium would remain in solution in any case).

Boiling doesn't mater. CsI may get attached to droplets carried off with steam but most will remain in the water. The use of seawater to keep the pools full should prevent acidic conditions in the pool.

If operators were able to get close enough to the pool to take a sample it must be well short of boiling.

If you've ever brought a large pot of water to a boil (e.g., home brewing) you see a lot of motion and stirring well before bubbles start to form. That is convection. When bubbles do start to form on the hot surfaces they may grow and break off but don't reach the surface because the bulk temperature is still below boiling. That is the onset of nucleate boiling (ONB). In a reactor when the surface reaches a high enough temperature a layer of steam covers the surface of the fuel and heat transfer is cut drastically. This dryout is the Departure from Nucleate boiling (DNB). That is the big difference between a PWR and a BWR.

PWR's have design limits to prevent ONB. BWR's worry about DNB. They don't start making money until they achieve ONB.

 

[rowmag]

And the containment part of the drawing is square shaped, with the core at the centre. The Unit3 has the RPV on the side closest to the turbines.

I don't KNOW, but I seriously doubt that this is about Unit 3.

http://translate.google.hu/translat....futaba.fukushima.jp/05-20000519/index41.html

At the foundation level, in the basement (where the torus is), the reactor is centered in the square. The upper elevations of the reactor building are not centered on the reactor, though. So the diagram probably shows the foundations.

 

[TCups]

https://www.physicsforums.com/showpost.php?p=3249305&postcount=3870")

(sigh)

Didn't happen. These are not the droids you are looking for. Move on.

Look closely at the horizontal debris tracks, the impacts on the front and rear facades of the turbine buildings, the horizontal debris tracks on the west side of the buildings, the damage to the buildings on the west side of the reactors, and the pieces of the wall slabs still laying about on the photographs. ALL of that came from horizontal outward blast of the wall panels. None of the wall panels went upward.

The only good candidates for vertical "ballistic" objects, IMO, were the FHM directly over SFP3 (now disproved) and portions of the buildings roofs (which seems a likely scenario at least for now).

Go way back to around to posts in the low #600's a few weeks ago and you will find lots of pictures and analysis.

 

[rowmag]

In a previous post (#4111) I calculated the concentration of a 5% gap release of Iodine-131 into the pool from just the last core offloaded. Unfortunately I only accounted for a 30 day decay. Mr. Gunderson correctly indicated that the unit was shutdown 4 months before the accident. It has been a month since. So I repeated my calculation accounting for 180 days (6 months) of decay.
[...]

What are the implications for hydrogen generation under the new scenario?
Can pool emissions explain the building explosion?

 

[StrangeBeauty]

What were they trying to do in unit #4 before it exploded/burned and after #3 exploded? In this picture, #3 has exploded, #4 has not, but I do not see the truck halfway into the access bay where they load/unload fuel and other supplies for the building:

http://www.digitalglobe.com/downloads/featured_images/japan_earthquaketsu_fukushima_daiichi_march14_2011_dg.jpg

Am I missing it? The truck is clearly visible in all subsequent overhead pictures of #4 after it burned/exploded:

http://cryptome.org/eyeball/daiichi-npp/pict12.jpg

Also I wish people would abandon the idea that there is any good data in the soundtrack of the video of #3 exploding that has the 3 added (and heavily processed) explosion sounds -- it's clearly faked (for many reasons previously stated here). Here's another one with faked added sound:

 

[clancy688]

I try to keep reminding people that just because an isotope has a short half life does not mean it disappears in a few half lives. Half of a big number is still a big number. I-131 will likely be detectable beyond a year after shutdown.

Thanks for the reminder. I often forget how big the numbers are we're using here... ^^;

I tried to calculate it myself and got a similar outcome. But could you please do me a favor... please use SI-units and not feet / curie... :(

It's so hard to think in these units, and since official releases are all in SI, I think we should use them, too.

From an ORIGEN2 calculation of a BWR the core inventory of I-131 at 6months after shutdown is 5.03E-3 Ci per MW. Assuming 760 MW Electric and a 33% efficiency for Unit 4 leaves a total I-131 at the time of the accident of 5.23E5 Ci. In Taking 5% (gap release) and converting to Bq leaves 9.67E14 Bq.

Uh, so when the Tsunami hit there were around 2E16 Bq in all (used core) fuel assemblies? Where can I find this calculation?

 

[rowmag]

Very interesting photos, thank you for that link. Trivially, perhaps, note that picture 4 has the Kanji symbol for "North" on the column. http://hararie-japan-tokyo-tokyo.co...ws-direction-of-japanese-element-symbols.html

That is for the crane operators. Their control pad will have the same directional markings (North, South, East, West, Up, Down).

 

[Rive]

At the foundation level, in the basement (where the torus is), the reactor is centered in the square.

OK, then if it's the basement where the torus is, where is the torus on the picture?

 

[artax]

Boiling doesn't mater. CsI may get attached to droplets carried off with steam but most will remain in the water. The use of seawater to keep the pools full should prevent acidic conditions in the pool.

If operators were able to get close enough to the pool to take a sample it must be well short of boiling.

If you've ever brought a large pot of water to a boil (e.g., home brewing) you see a lot of motion and stirring well before bubbles start to form. That is convection. When bubbles do start to form on the hot surfaces they may grow and break off but don't reach the surface because the bulk temperature is still below boiling. That is the onset of nucleate boiling (ONB). In a reactor when the surface reaches a high enough temperature a layer of steam covers the surface of the fuel and heat transfer is cut drastically. This dryout is the Departure from Nucleate boiling (DNB). That is the big difference between a PWR and a BWR.

PWR's have design limits to prevent ONB. BWR's worry about DNB. They don't start making money until they achieve ONB.

They didn't get close to the pool, There's a video of them using the concrete pump with a sample tube (looks like stainless steel) hanging on a wire/rope from the tip.
I also think the pool would be more of a radiation hazard than a heat/steam hazard.

 

[NUCENG]

What are the implications for hydrogen generation under the new scenario?
Can pool emissions explain the building explosion?

The mechanisms for hydrogen generation due to metal water reactions, primarily zirconium) are the same in the core or in the fuel pool. If fuel is uncovered and heats up enough the reaction will start producing hydrogen. In a spent fuel pool this may also generate zirconium fires due to air.

If the damage is slight it may only perforate cladding. This can release the fission product gasses and particulates located in the fuel gap during operation. Approximately 5% of the core source term is estimated to be in the gap. This level of release would not necessarily indicate a major release of hydrogen.

If more of the cladding is consumed, it will begin to rupture and release greater amounts of fission products to the vessel. This is called the early in-core release phase of an accident. Significant hydrogen generation is expected.

As long as we can see levels of radioactivity that could be explained by gap release, it is reasonable that hydrogen releases from fuel pools are also limited. The hydrogen released into a large volume like secondary containment or the refueling floor would be at levels for deflagration but probably below detonation. If the hydrogen release were somehow contained, however, then detonation might be possible.

As for the cores inside units 1, 2, and 3, however, it is pretty clear there was major damage, and a lot of hydrogen.

My best guess is that the buiding explosions came from the containments of units 1, 2, and 3. and that includes the damage to unit 4.