Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[elektrownik]

Unit 3 is 283C now and increasing...
Also 2nd unit 3 sensor jump from 156 to 203C

 

[PietKuip]

I think the questions to be focused on in the case of reactor 1 are not "where is the water and where is it going" but rather "where is the corium and how hot is it" if we are to get a reasonable picture of what happens next.

The water must have leached an enormous amount of radioactive isotopes from the fuel, so its path is also interesting. And if the outflow is in the bottom, the current could also have carried pieces of corium with it.

 

[|Fred]

i see that "moderate" members start to be upset by what they discover weeks after weeks... Stay scientific and have a rational approach of things as much as possible, this understandable desire would be, as things will developped, undermined by the fact that the infos, on which we base most of our efforts and reflexions.
So my point is: how can people like us think of being able to do a good or even satisfactory scientific work based on sources that are in fact so unreliable and weak? I have my own answer from the beginning (time will prove if I was wrong or right) but I let people here meditating about this...

I do not think that a rational approach is undermined by weak data. As I use to be told geometry is the art of thinking out of false drawing. The idea not to make the theory fit the data. Does the actual adjustment, makes more sens ? Explain a gray area in the formally postulated hypothesis leading to and other hypothesis or does it makes thicken the plot ?
I think better usually comes from decisions based on reasoning (although the reasoning might be wrong) rather than on a 50/50 bet.

 

[GJBRKS]

Unit 3 is 283C now and increasing...
Also 2nd unit 3 sensor jump from 156 to 203C

Could you please provide links to your source when announcing these data ? (As there are 13 temp readings per unit)http://www.tepco.co.jp/nu/fukushima-np/f1/images/032_1F3_05121300.pdf

 

[zapperzero]

The water must have leached an enormous amount of radioactive isotopes from the fuel, so its path is also interesting. And if the outflow is in the bottom, the current could also have carried pieces of corium with it.

I could not care less. The sea is where the fishes and a couple dozen discarded nuclear reactors live (I'm not talking only subs, the Russians dumped massive amounts of effluent from their plutonium separation plants into the sea). Plankton won't die from a few pCi/l more, the whales could use a 60-year moratorium on fishing. We live on land. A big fire or steam explosion means China gets a sizeable dose, while Japan gets cut in half.

Corium flowing into that lagoon? Meh. Think corium coating 80% of the world's chip foundries.

 

[AntonL]

Can low water level can be connected to radiation spike and sensor faliture in unit 1 ? Some days ago sensor jump to 80Sv/ and then die (or they don't give data because it is too bad)

some days ago it was 8th April, Cams peaked to over 180Sv/h before falling and then discarded. That same day was also a temperature peak see https://www.physicsforums.com/showpost.php?p=3291622&postcount=6305"

Evidence of Earthquake Susceptibility of the Reactors


Evidence 1
On 7th April there was a reported 7.1 (some say 7.4) north of Fukushima that also shook Tokyo. http://earthquake.usgs.gov/earthquakes/recenteqsww/Quakes/usc0002ksa.php
[PLAIN]http://k.min.us/ilcuMS.JPG

and look what happened to the CAMS reading from 30 to 100 to 187
[PLAIN]http://k.min.us/ikY1Ys.jpg
Now with all the information we have today leak sprung in the reactor vessel releasing very radioactive water.

Evidence 2
On May 1^st, 11.48AM A 4.8 earthquake struck 9.5km from Fuskushima NPP
http://neic.usgs.gov/neis/bulletin/neic_kjal.html
[PLAIN]http://k.min.us/ikXLzM.JPG

after that the temperature in the reactor 3 rose, something changed!
[PLAIN]http://k.min.us/ilcVfi.JPG

I believe two earthquake events and two changes from the steady state reactor parameters is proof enough to make the statement that the damaged Fukushima reactors are susceptible to Earth quakes, and is a very worrying thought for trying to get fukushima under control.

Edit: After Borek's comment https://www.physicsforums.com/showpost.php?p=3297660&postcount=6831"

 

[clancy688]

Unit 1 remains a mystery for me. During the last few hours, some questions popped up...

Here's the NHK news regarding the Unit 1 water leak: http://www3.nhk.or.jp/daily/english/12_23.html

On Thursday morning, it was found that the water level was more than one meter below the bottom of the fuel rods, suggesting a large volume of water is leaking into the containment vessel.

The utility company also believes that the water is leaking from the containment vessel into the reactor building. This is because the estimated volume of water inside the containment vessel appears to be less than what leaked into it from the reactor.

Tokyo Electric says temperatures at the bottom of the reactor are between 100 and 120 degrees Celsius, suggesting that the fuel has fallen and is being cooled in the water below.

The utility says it does not believe the fuel has completely melted and spilled through the bottom of the reactor. It adds that instead, the fuel appears to be being cooled inside the reactor.

I didn't thought about it first, but that means that not only the water level sensor is malfunctioning, but another sensor as well - the pressure sensor.
Stolfis Plots ( http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/plots/cur/plot-un1-full.png ) were showing contant water levels and rising pressure for Unit 1.
Now we've learned that Unit 1 is leaking, both RPV and containment. If there's a leak, the RPV pressure will very unlikely rise significantly over atmosphere level.

A user raised doubts that the whole molten core could relocate in the bottom of the pressure vessel. I have no idea how big (in m³) the area 1m below the bottom end of the fuel rods is, and I also have no idea how much space (in m³ again) the whole core in corium form needs. It would be nice if someone, who has the needed numbers, could calculate this.
Even if there would be enough space for a fully molten core, it would be impossible to cool it down. The water could only reach the corium's surface, not the hot core.

Moreover, TEPCO stated that the bottom of the RPV is only slightly over 100 degree °C hot. But if the core's really relocated to the bottom, there's nothing between the hot corium and the steel. And then it's only 100 degrees hot? I can't believe that.

Since today we know that the RPV and the containment are breached. Water's disappeared and TEPCO doesn't know where it went. Perhaps the Houdini Unit 3 is getting acquaintance. If it went to the sides, TEPCO would have discovered it, as with the water leaks from Units 2 and 3.
So in my opinion, that leaves the only direction where TEPCO has no eyes - down.
What, if part of Unit 1s fuel got uncovered and melted, dropping to the bottom and compromising the RPVs integrity. It burned a hole into the RPV, which's now leaking. Water is escaping and the overall water level is sinking, more fuel is uncovered and melts as well. But those parts are not settling down at the bottom of the RPV, but washed out with the water flow - since there is always water supply from above.
Parts of this fuel gather at some point in the containment and burn another hole in the bottom, sinking through the basement and into the ground. Now the water can escape into the ground as well.

There's also a probability of sudden fuel cladding failure. The fuel was uncovered for a certain amount of time, but did not melt. But the zircalloy was very severely damaged. It's highly oxidated and unstable. Everything seems fine, water flow is resumed. Then, a violent afterquake hits, shaking all assemblies.
This sudden stress could result in rupturing and breaking of the cladding, releasing the fuel pellets to the ground. And if that happens in enough places, it could trigger a chain reaction (mechanical, not nuclear... ^^;), leading to a similar outcome as described above. I don't find them anymore, but sometime during the last weeks I saw assessments of Mark I containments and BWR pressure vessels during accidents. They stated that the RPV would likely be breached by corium in less than one hour.

 

[PietKuip]

Evidence of Earthquake Susceptibility of the ReactorsEvidence 1
On 7th April there was a reported 7.1 (some say 7.4) north of Fukushima that also shook Tokyo. http://earthquake.usgs.gov/earthquakes/recenteqsww/Quakes/usc0002ksa.php

and look what happened to the CAMS reading from 30 to 100 to 180
[PLAIN]http://k.min.us/ikY1Ys.jpg
Now with all the information we have today leak sprung in the reactor vessel releasing very radioactive water.

Interesting analysis. And that "100.0" reading, was not that a code for "off scale"?

 

[elektrownik]

I also think that core is in drywell science radiation jump in drywell...

 

[artax]

Sorry... simple question but what does CAMS stand for?

 

[MadderDoc]

Find attached my assessment of the state of the roof structure of unit 3, after the explosion.

Based on visual inspection of photos, each field in a 16x24 matrix covering the entire roof structure was assessed to one of five categories of damage, see legend. The method used gives the assessment a resolution of about 1.5 meter.

Fragments found on the roof of unit 3 were assessed, as were fragments of the roof structure locatable to the south and the east side of the building. Due to poor photo coverage and their inter-mixture with other debris fragments which ended to the north of the building could not be inspected. Those parts of the structure from the N end and from the SE corner which could not be inspected were assessed based on plausibility, judging from visually inspected close-by or bordering fields.

 

[jlduh]

Just wanted to remember everyone that Tepco just recalculated 2 weeks ago the amount of fuel damaged in the cores:

http://www.powermag.com/POWERnews/3678.html

For Unit 1 it was revised from 70% to 55%...

All this gave the impression of precision and control of what was going on, isn't it?

Now it's 100%. Finally, we could call it a "50/50 bet" , after all. With much "scientific" (maybe pseudo?) reasoning though.

Which credit should we give to the numbers for the other units, now?

 

[PietKuip]

Just wanted to remember everyone that Tepco just recalculated 2 weeks ago the amount of fuel damaged in the cores:

http://www.powermag.com/POWERnews/3678.html

For Unit 1 it was revised from 70% to 55%...

Indeed. Based on the CAMS readings (Containment Atmospheric Monitoring System). But Michio Ishikawa never believed it.

 

[artax]

Thanks Piet, have these images been discussed, particularly the ones of the surveying helicopter at the bottom?

http://cryptome.org/eyeball/daiichi-npp14/daiichi-photos14.htm

 

[htf]

Moreover, TEPCO stated that the bottom of the RPV is only slightly over 100 degree °C hot. But if the core's really relocated to the bottom, there's nothing between the hot corium and the steel. And then it's only 100 degrees hot? I can't believe that.

If the temperature readings are correct then the corium is not at that location. This would be my conclusion. So, where is the core?

 

[AntonL]

Unit 1 remains a mystery for me. During the last few hours, some questions popped up...


I don't find them anymore, but sometime during the last weeks I saw assessments of Mark I containments and BWR pressure vessels during accidents. They stated that the RPV would likely be breached by corium in less than one hour.

Correction - All units remain a mystery.

Lets just get the facts straight, http://k.min.us/ikop60.JPG" that 200GJ of energy is required for a melt a large civil core we can then calculate using the formulas provided that the time for melt through is using Po=1380MW
0 minutes after shut down - 4hours
01 hours after shut down - 5 hours
02 days after shut down - 11 hours
30 days after shut down - 26 hours
60 days after shut down - 36 hours

So it is very unlikely that the core has melted completely and is digging itself to the centre of the earth. We can forget that.

Reactors 2 and 3 Po=2380MW and the times will be proportionally less.

EDIT: as per Clancy688 https://www.physicsforums.com/showpost.php?p=3297899&postcount=6855"

 

[PietKuip]

Thanks Piet, have these images been discussed, particularly the ones of the surveying helicopter at the bottom?

http://cryptome.org/eyeball/daiichi-npp14/daiichi-photos14.htm

The Ministry of Defense has released the thermal images taken by the helicopter in April.

I have not seen any data about radiation levels from those helicopter flights. Anyway, that was at a height of 3000 meters if I remember correctly. They did not have equipment to do any gamma imaging.

 

[AntonL]

Thanks Piet, have these images been discussed, particularly the ones of the surveying helicopter at the bottom?

http://cryptome.org/eyeball/daiichi-npp14/daiichi-photos14.htm

Wearing lead suit to protect body and testicles is a good precaution, but surely they should also wear helmets to protect the most vital organ - the brain

 

[SteveElbows]

Regarding earthquakes, perhaps have to be slightly cautious about stuff that changed at reactor 1 around April 7th because they started injecting nitrogen a day earlier. I find it quite plausible that earthquakes can change things though, not ruling it out, just want to consider other factors too.

I think the April 11th earthquake is the one TEPCO tend to mention in reactor history, but that's because it knocked out power to the site for a while.

 

[MadderDoc]

Now we've learned that Unit 1 is leaking, both RPV and containment. If there's a leak, the RPV pressure will very unlikely rise significantly over atmosphere level.<..>

Yes that's a mystery. Both RPV pressure meters give readings considerably above atmospheric, and both meters appear to be 'alive', picking up an upward trend, rather than just static.

<..>TEPCO stated that the bottom of the RPV is only slightly over 100 degree °C hot. But if the core's really relocated to the bottom, there's nothing between the hot corium and the steel. And then it's only 100 degrees hot? I can't believe that.

If that's the temperature at the outside of the vessel (I believe it is), and the readings from the drywell pressure/temperature are valid, it may not be entirely incredible. Readings show the drywell to be at close to atmospheric pressure, and below 100 deg. C. This would be consistent with liquid water interfacing with the bottom outside of the reactor vessel, in which case that could not get much above 100 C.

 

[Rive]

If the temperature readings are correct then the corium is not at that location. This would be my conclusion. So, where is the core?

I think the data collected right after the accident is more reliable than this new one... IMO the lower parts of it are still in place, with the upper parts melted/collapsed, as were estimated on basis of the early water levels. Of course, I can't be sure.

New TEPCO media release:
http://www.tepco.co.jp/en/news/110311/images/110512_1.jpg"

- Does anybody knows how are those indicators works? Pressure difference, maybe?
- yeah, some more rods

 

[yakiniku]

I believe two earthquake events and two changes from the steady state reactor parameters is proof enough to make the statement that the reactors are very susceptible to Earth quakes, and is a very worrying thought for trying to get fukushima under control.

Very interesting. Particularly the timing between the magnitude 7.1 earthquake and the CAMS d/w data. Keep in mind that there have been a large number of aftershocks/earthquake ongoing near Fukushima.

I've attached a screenshot from the QuakeZones iOS app which I've filtered to earthquakes of magnitude greater than 5 and within the last 30 days. The red pins are earthquakes greater than magnitude 6. Sorry, I am sure there is an online resource to achieve the same but this was easily within reach.

If you would like the data for further analysis and there isn't an easy way online to pull the date/time and intensity of each of these occurrences, I'd be happy to manually transcribe.

 

[|Fred]

Just wanted to remember everyone that Tepco just recalculated 2 weeks ago the amount of fuel damaged in the cores

The other day I had AK that gave me a 60+% chance to win then the flop came and those odds dropped to 35%. One could think that considering that there is two outcome "win" or "lose" he had a 50/50% and play without looking at his card. :)

 

[TCups]

This has been my feeling all along: that a compromised drywell cap seal allowing gas or steam to escape would result in that gas diffusing upward through the non-pressure-sealed shield plugs and into the upper reaches of the secondary containment, i.e. the reactor building. That makes more sense to me than jetting sideways through the fuel transfer chute blocks and whatever seal might be present there. The pressure increase, to me, seems more likely to seat the tongue-and-groove shield blocks leading to the fuel chute even more firmly in place, making it less, not more, likely to get through there. Not when there's a path out through the plugs above that were never designed to hold pressure at all.

There are other scenarios studied over the years that result in containment breach that do not involve the drywell cap being displaced or breached. A structural failure of the torus is just as likely to be the release point for an overpressurized containment as the drywell cap. So are the seals for electrical conduit drywell penetrations. So are the emergency cooling systems' pump seals. So are leaks in the venting ductwork. All these potential pathways could leak substantial amounts of hydrogen into the building.

Occam's Razor leads me to believe that a burping drywell cap jetting burning hydrogen sideways at the exact spot where the fuel chute blocks/gates/seals might be weak is less likely to be the release path for hydrogen into the secondary containment than any number of other, simpler explanations. I'm not claiming the idea is totally without merit, but until we learn more I don't see how it can be given more credence than any of the other equally credible scenarios.

The pathway for hydrogen from the RPV to the primary containment through the drywell cap seal, into the upper primary containment and then into the upper floor has been the likely scenario since the beginning, as was the presence of a large amount of leaked hydrogen in the upper building. I agree that concrete slabs would not be hydrogen tight, and, that neither would a failed seal on either of the transfer gates. What I don't see is why a lifting force on the concrete slabs would reinforce the strength of the underlying tongue-in groove arrangement of the concentric segments of the upper primary containment. Further, a slow leak of hydrogen is entirely a different thing from a large explosion originating in the drywell. I am no expert here, but if the pressure within the primary containment suddenly reached explosive levels, then it would seem that that explosion will tend to first vent through, and then, literally destroy the weakest part of the containment. A small rupture will very rapidly become a large rupture. In that regard, the structure of the fuel transfer gate would seem a likely spot for the weakest portion of the upper drywell structure, and the forces needed to rip it open, once the explosion occurred are likely less than those needed to displace the 8 semicircular concrete segments of the upper containment plug (just my guess). Also, the vector of the initial blast seems to match. But a blow out of the chute is not mutually exclusive with partial lifting of the concrete plug above.

As for the persistent leakage of steam, I had thought that the source of the hydrogen and steam was leakage from some damage (not a catastrophic rupture) to the RPV or more likely, through one of the pipes into/out of the RPV resulting from the lateral forces of the initial quake, which exceeded the design limits. If that were the case, then, I suggest that the drywell cap seal (in fact, perhaps the entire drywell cap) may have been destroyed. I don't think this is in terms of minor or fairly limited damage to the cap seal, although damage to the RPV cap seal, if present, might be less extensive. The explosion from within the drywell probably opened up large cracks in the upper primary containment at both the general area of the drywell's fuel transfer chute and equipment transfer gate, and probably partially displaced the concrete plug.

The rate of persistent venting steam seems most likely determined by the rate of steam leaking from the RPV, not the absolute size of the cracks in the damaged upper drywell.

In any case, the scenario of hydrogen leakage from the RPV, through the upper drywell containment, into the upper building, followed by an explosion originating from within the drywell venting into the upper building, with a secondary explosion of the hydrogen therein and, possibly vaporization of part of the water content of the SFP3 remains consistent and very plausible to me, at least.

 

[Borek]

I believe two earthquake events and two changes from the steady state reactor parameters is proof enough to make the statement that the reactors are very susceptible to Earth quakes, and is a very worrying thought for trying to get fukushima under control.

"Reactors are very susceptible" sounds a little bit too general to me. "Damaged reactors that are out of control and their standard work parameters are very susceptible to shaking" sounds more like goo evaluation.

I am not stating earthquakes don't matter, what I am aiming at is the fact that normally working reactor _slightly_ shaken will probably still work OK, while reactor that is a mess inside can react to the same shake in an unpredictable way.

 

[jlduh]

Ok now let's list what new questions are raised IF WHAT TEPCO REVEALED IS TRUE AND IF THEY DON'T COME BACK TO APOLOGIZE FOR A NEW MISTAKE ABOUT THIS (who knows?):

1- if what used to be the core in N°1 has totally relocated at the bottom of the RPV, how can all the parameters given by TEPCO be interpreted? Total BS?

2- the same question applies to the 2 other reactors (2 and 3): are this parameters relevant to assess the situation or can it be considered like for N°1 as total BS? Then i have to admit that one of the "proofs" that N°3 reactor was still there in a "close to normal shape" is clearly weakened because of this revelation...

3- based on the amount of fuel initially inside the reactor N°1, plus the volume of the "other stuff" inside (control rods, etc.), is it even physically possible, from the volume standpoint, based on the dimensions of the RPV and its layout, that ALL the fuel has enough room to relocate below the "1m below the bottom of fuel rods" level? This calculation has to be done to assess if what TEPCO says is consistent with reality and IF WE CAN THEN ASSUME that NO MELTED FUEL/LAVA LEAKED OUTSIDE OF THE BOTTOM OF THE RPV. If there is not enough room, then at some point it would probably mean that some lava leaked outside.

4- considering what is below the RPV, the drawings and sketches we have indicate that there is below it what is called sometimes "reactor cavity" where sits all the control rods mecanisms and some other stuff.

http://www.netimago.com/image_199258.html

http://www.netimago.com/image_199265.html

http://www.netimago.com/image_199266.html

The question is: do we think this cavity is now full of water coming from:

A) the containment vessel around (which is supposedly flooded to some level) whatever path the water folllowed (leaks, etc.)

or

B) the leaked RPV (bottom) especially through control rods bores or any other leakage there.

5- If this cavity has water in it, and if it is a quite closed cavity (concrete around) then any drop of lava from RPV could create a new feared steam explosion.

But who knows, maybe there is already some lava there? The calculation of point number 3- is a first check for this assessment.

6- how can such a mass of melted/damaged fuel relocated at the bottom of the RPV can still be "cooled" by only sitting water above it? In TMI meltdown, only half of the core was melted and relocated, but more than 1 meter below the bottom of fuel rods levels, this is a 100% damage and relocation.

As a first try to assess the point that i listed above (3-), i mean the volume of the possibly melted fuel at N°1, we could start with the TMI corium data, especially densities:

"The bulk density of the samples varied between 7.45 and 9.4 g/cm3 (the densities of UO2 and ZrO2 are 10.4 and 5.6 g/cm3). The porosity of samples varied between 5.7 and 32%, averaging at 18±11%."

http://en.wikipedia.org/wiki/Corium_(nuclear_reactor )

Of course it's a little bit difficult to be sure of the accuracy of this approach because:

-TMI was a pressurized reactor, so the core is substantially different.
-the TMI core was only around 50% damaged

http://www.netimago.com/image_199327.html

-There can be some void/porosities in various combinations inside
-AND, last but not least, we still don't know if part of it melted, or just got damaged, and in which percentage. I even saw in an article (don't remember which sorry) that the fuel has been "sliding" below (i don't know how to interpret this!).

Anyway, the 100% corium hypothesis can be calculated to assess the minimum volume it would occupy assuming it's at the bottom of the RPV (which seems strange IF the temp of 100°C is confirmed, but i don't trust to much these readings now i must say...).

Any hypothesis with only a part of the core melted (partial corium) would result in a global lower density for the destroyed core, so a bigger volume. So let's see if the minimum volume hypothesis (100% corium) fits the actual volume at the bottom of he RPV, 1m below the bottom level of fuel rods.

1- we have some possible densities for corium between 7.45 and 9.4 g/cm3 (the densities of UO2 and ZrO2 are 10.4 and 5.6 g/cm3).

2- we need the core mass in unit 1, including all the "stuff" around, and the mass of the control rods.

3- we need the volume of this part of the RPV for Unit 1 (around 5m diameter I think, but we need more precise data). The key data is also how high were located the bottoms of fuel rods from the very bottom of RPV.

Any sources of infos?

EDIT1:
Found this from tepco site:
http://www.tepco.co.jp/en/nu/fukushima-np/outline_f1/index-e.html

--> So inner diameter of RPV is indicated "around 4,8m"
--> 400 fuel assemblies, 69 tons of uranium (but do they include the total weight of fuel rods or just uranium content?)
--> 97 control rods (which unit weight?)EDIT2:

i add this picture and sketch of BWR RPV:

This one was called BWR800 (800 MWatts?) on the page i found it; it shows the bottom of the RPV with the peripheral flange on which it seats over its concrete piedestal, and the many holes into which the control rods are entering (damn how can this thing not leaking?)

http://www.netimago.com/image_199334.html

these sketches of RPV are from BWR4 and 6 designs, but i think the global layout is the same so it gives some ideas:

http://www.netimago.com/image_199335.html

 

[yakiniku]

"Reactors are very susceptible" sounds a little bit too general to me.

I read it that way at first too. Without putting words into AntonL's post it had the article "the" before "reactors" which would indicate the particular reactors that are being discussed at Fukushima.

 

[MadderDoc]

In any case, the scenario of hydrogen leakage from the RPV, through the upper drywell containment, into the upper building, followed by an explosion originating from within the drywell venting into the upper building, with a secondary explosion of the hydrogen therein and, possibly vaporization of part of the water content of the SFP3 remains consistent and very plausible to me, at least.

Just to add, assuming this scenario, it would seem implausible if water was not also expelled from the drywell/RPV, partly as liquid, partly as steam. There is unfortunately very little vital data for the reactor up to the time of the explosion, but what we have indicates that RPV and containment were both at about 5 bar a few hours before the explosion.

 

[ihatelies]

I've overlay and added some labeled

I do believe that we can see an original steel structure between A and B
It is my perception the "arc" aka green path between A and B is not a deformed formely mention AB steel structure.
But my main point of attention is in the bottom view , I've highlighted white metalic structure, perspective might be a bit hard to see from this angle but the right picture might help you

[AD] and [BC] are part of the double layered East West metallic structure the double layer is Pink on top blue at the bottom with some reinforcement in white between the Two layer
[AD] and [BC] are link by dual layer cross bars

I think that the pictures show that [BC] is twisted and is falling abruptly to the pool, I also think that there are remains of the cross bars covering . I do not believe that the damage we see could have been cause by a circular exiting object . I do believe that some of the damage to the crossbar was done by the [BC] structure . I do not know what cause the [BC] structure to twist / break /wall , might have been by an interaction between FHM and its Crane


[PLAIN]http://i.min.us/ikY3PY.jpg[/QUOTE]

Excellent.
My thoughts: If AB is still attached at both ends, then the round hole theory is pretty hard to justify. I believe it may not be attached at B however. There's some metal roofing debris on top of it near this joint, but looks to be separated. If so, it could have simply bent vertical during the ejection and flopped back down.

Regarding the twisting of the double rails or roof trusses. I discount the twisting of them somewhat. Remember they were installed into the roof 5-7 meters up from where they sit now. They were subject to a very large blast of some type, then collapsed to where they are now. Then they were subject to whatever residual heat has occurred since then.

If I recall correctly, there has been some discoloration and possibly heat deformation of the rails since the explosion. Certainly there have also been many aftershocks that could have moved things somewhat.

I'm gone for a few days. Thanks for the analysis.

 

[|Fred]

before you go check on youtube the US HAwk helicopter drone footage (part 3)
I grabbed the bottom picture from that , the moving picture gives a better sens of the 3 dimensional aspect that support my twisting theory

ps: I'm not sure [AB] is attached but the vector of the metal part linking A to B is rather consisted with a no deformation applied from a round object to this segment

 

[rmattila]

is it even physically possible, from the volume standpoint, based on the dimensions of the RPV and its layout, that ALL the fuel has enough room to relocate below the "1m below the bottom of fuel rods" level?

In a BWR, there's plenty of room below the core to accommodate the control rods (which are as high as the core and are completely withdrawn during operation). Thus, if the core would melt, it would easily fit in the region below the core bottom plate.

However, taking into account there seems to be no instrumentation qualified to withstand the post-accident conditions at the Fukushima plants, I would be very careful in interpreting any information based on the instruments. In my opinion, the only reliable direct data to evaluate the core status would be information regarding the quantity and isotopic composition of the water/steam/air releases coming out of the plant units. As long as this information is not available, I'm afraid there's very little we can do to reliably evaluate the status of the cores.

 

[BlueCactus]

2- we need the core mass in unit 1, including all the "stuff" around, and the mass of the control rods.

3- we need the volume of this part of the RPV for Unit 1 (around 5m diameter I think, but we need more precise data). The key data is also how high were located the bottoms of fuel rods from the very bottom of RPV.

Any sources of infos?

TEPCO said, it is about 58 Cubic meter that the RPV can contain water without being detected by sensors.

 

[Dmytry]

Just wanted to remember everyone that Tepco just recalculated 2 weeks ago the amount of fuel damaged in the cores:

http://www.powermag.com/POWERnews/3678.html

For Unit 1 it was revised from 70% to 55%...

All this gave the impression of precision and control of what was going on, isn't it?

Now it's 100%. Finally, we could call it a "50/50 bet" , after all. With much "scientific" (maybe pseudo?) reasoning though.

Which credit should we give to the numbers for the other units, now?

it was clear right away that the core damage percentage estimating based on CAMS is utter nonsense / inapplicable in the situation.

The "core damage %" itself is an utterly nonsensical concept. There's % of the fuel tubes that ruptured, % of fuel that reached this temperature, % that reached that temperature, % that melted, % that ended up on the bottom, etc.
A case of abstract thought gone wrong. Like abstract painting of a sunny day at the beach - consisting of a light gray rectangle, 1 pixel, painted from a two pixel 'photo'.

I think TEPCO, for all the things they done wrong, actually did a better job at understanding that those core damage estimates are entirely meaningless, than did many posters in this thread.

 

[Luca Bevil]

TEPCO said, it is about 58 Cubic meter that the RPV can contain water without being detected by sensors.

looks reasonable

 

[robinson]

Didn't the amount of radionuclides found outside the plant area show massive damage to fuel early on?