Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[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?

 

[jim hardy]

here's from a real old Oak Ridge report. sounds like they'll be okay if they keep it wet.
I wouldn't even worry about temp somewhat above boiling - like a stove burner heating water from below, it has to be hotter than the pot

http://www.osti.gov/bridge/servlets/purl/6124656-R8y05j/6124656.pdf
cover page says distribution unlimited so i guess it's okay for us to read.
moderator scrub post if it violates anything, I'm still learning my way here.

[q]After structural deformation and downward relocation of molten control
blade, channel box, and candling clad material (in that order) onto the
dry core plate [2], local creep rupture failures of the core plate would
introduce relocating material into the lower plenum water and begin the
accumulation of quenched debris in the reactor vessel bottom head
[3,4]. Relocation of the metal structure of the core is expected to
leave the fuel pellet stacks standing until weakening, by overtemperature,
of the ZrO2 sheaths surrounding the fuel pellets and similar loss
of strength by the previously molten material that tends to weld the fuel
pellets together. It should be noted, given the progressive relocation
methodology outlined above, that the majority of the debris entering the
lower plenum is expected to be in the solid state when it enters the
water.
As the relocated core material accumulates in the 3WR reactor vessel bottom
head, it is expected that the composition of the quenched debris bed
would vary with height. Lowermost in the bed would be the mostly metallic
debris (control blades, canisters, candled clad and dissolved fuel)
that had either accumulated on the core plate before local core plate
failure or had subsequently relocated downward above the core plate failure
locations before fuel pellet stack collapse. Higher, within the
middle region of the bed, would be the collapsed fuel and ZrO2 from the
central region of the core. The initial local core plate structural
failures would cause temporary bursts of steaming as the relocated
metallic debris was quenched; however, with the collapse of the central
core fuel pellet stacks, a constant heat source (the decay heat
associated with the pellets) would be introduced to the lower plenum
reservoir, initiating a rapid continuous boiloff of the lower plenum
water.[/q]

stuff at bottom of pile protects vessel from the corium in middle of pile?

it's only a flesh wound...

 

[IowaNewbie]

it's only a flesh wound...

That's how gangrene starts ...

 

[rmattila]

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

Large amount of cladding failures, yes. But concerning the max temperature of the core, information regarding the quantities of elements that evaporate between 1000 and 1500 degrees Celsius would be really important. It would help to see the results (besides the easily-evaporating I and Cs nuclides) of the analyses of the water found at different locations at the plant buildings (or even better, the raw gamma spectra) in order to see what has come out and how much.

Soil and air samples found at the site can be largely explained by the explosion at unit 3 service floor and don't thus tell much about the condition of the cores.

 

[rowmag]

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.

We have had such an insane number of aftershocks (still ongoing, though no large ones recently), that it may be an embarrassment of riches to look for a likely culprit. But if such an attempt is made, it may be useful to filter on shindo rather than magnitude. Shindo shows how much shaking a particular location felt. This might be a place to start to look for such data:

http://www.jma.go.jp/en/quake/quake_singendo_index.html

I think they are calling shindo "seismic intensity."

I would filter out anything below a shindo 5 for starters.

 

[TCups]

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.

Excellent! Now, add the overlay of the floor plan of the top floor. BTW, you should be marking this kind of work "copyright, 2011" and put your name on it, MadderDoc. There may be a publication in your future.

 

[MadderDoc]

I've overlay and added some labeled

I do believe that we can see an original steel structure between A and B

Nice job, |Fred. That conclusion about A and B is tempting, seeing there _is_ apparently a traverse in what appears to be the original position.

From a plausibility viewpoint one could say, why should it be in the orginal position considering the utter damage around it. However, more to the evidential, the interpretation leaves another structure unexplained, which I have marked in blue here:

I believe what is marked in light blue there is in fact the sorry remains of the original steel traverse between A and B.

In that interpretation the traverse that gives the illusion of being the original AB-traverse, is a loose traverse from uphill the roof structure further east, which has come to rest in this position - not quite incidentally, seeing that the trusses at both point A and B are kinked downwards, producing the nearest low resting position for it to come to rest in after having come loose. The high resolution photos looking in from the west also indicates that the traverse we see between A and B, may actually not be affixed to point A, but rather is resting close to and on top of it.

 

[RealWing]

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

This link shows a basic layout of the level circuit. 2 taps into the vessel connected to a differential pressure (DP) cell and transmitter. http://www.pbnc2010.org.mx/pdfs/technical/tuesday/14.00_ModelingLevelInstrumentation.pdf

The released TEPCO photo shows the techs at a whole panel of DP cells.
I don't think anyone knows for sure where these taps actually sense level in the RPV. Is the bottom tap in the shroud region or acually in the vessel itself (ie below the downcomer)??
It is also not clear if they blew back the sensing lines to make sure they were clear of any obstruction. They also should have pumped water back up to the upper condensate pot to ensure the reference leg was full. Without doing these 2 steps - the readings may still be wrong!

 

[mscharisma]

TEPCO has responded that the photos from the previous time was steam from the spent fuel pools of reactor #3 and #4.

http://www.digtriad.com/news/national/article/174708/175/Japan-New-Smoke-At-Nuclear-Plant

The linked article here may also hold the answer/confirm what the memos/emails were about discussed here a few pages back.

"TEPCO also decided to open the reinforced door of the troubled No. 1 reactor building on Sunday, making way for engineers to work inside to stabilize it."
"We are trying to be as courteous as possible, so we will directly call our neighboring countries to let them know and the countries that are assisting us, such as the United States," Hosono told reporters at the joint news conference."

 

[jlduh]

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.

Well you are right: the control rods are inside the RPV so the bottom of fuel rods must have been at a minimum 4m above the very bottom of RPV which is spherical, and in fact probably more so the peripheral rods can still enter 4m inside the core.

But on the other hand, we must add in the inventory of masses the mass of all the push rods mecanism (control rod drives = stainless steel?) as the core has been scrammed (control rods inserted).

Anyway, with a density of between 5 and 9 for the main materials, i think it is obvious that there must be enough room at the bottom to locate a fully melted core below the initial core position, or even 1m below it.

Assuming that the bottom of fuel rods was:

-> 5m above bottom of RPV, we get roughly (pi d2/4 * h) = 90 m3, one meter below gives 72m3,

and if I start with:

-> 4m above bottom of RPV, i get 72m2 and 54m3 one meter below.

So 58m3 is a possible number (even removing the volumes of the pushing rods but I don't know how big they are in dia?)

58 m3 with a density of 5 to 9 enables something like 290 to 522 tons of corium if fully liquid (lava) which is much more than we could imagine the inventory of molten material is (my guess is around 80/90 tons with the fuel assemblies, some plates, the control rods and their push rods and some other small stuff) . But this is assuming of course 100% liquid corium filling every space available, which can hardly be the case of course.

So based on what tepco said, it's possible that damaged core is still inside the RPV in an "undertermined" (but BAD) state.

 

[M. Bachmeier]

Please Note:

I understand that this thread is being monitored for political content, and I don't want to start sifting through soap boxes or diatribes, but the politics (corporate & nationalistic) are impacting directly on the effort to bring some scientific understanding.

I assert that political criticism, where it applies to the data and possible reasons for obfuscation, should have greater latitude in this thread with links to the more political thread for expression in detail. My reasoning is that the questionable political control of data flows is a legitimate reference when attempting to form hypothesis and speculation on substitute data.

I think it would make for a more concise presentation of hypothesis' if a persons primary reasoning were contained in the same block of statements. If another member wishes to argue they can state their primary objection with link to external thread (if needed) for more verbose communication. There's no mistaking that the politics have become a factor in the science of understanding and corrective action.

I have a second point...

Speculation:

The term 'unprecedented' seems wholly inadequate to describe these crisis' and the attempts to control them. I also believe this thread has enjoyed a greater latitude than nearly any other on this forum WRT speculation. I advocate even more speculation, provided unwarranted conclusions are not bandied about in that effort.

I've had ideas offered to me (while looking for a technical solution) by customers or friends that appeared to be utterly stupid (revealing their shear lack of technical understanding), only to realize that their ideas have lead to a completely new approach to the problem and the solution. "Brainstorming" is one thing I love about this thread and think it too needs more latitude from moderators and members alike.

I realize moderators have been working overtime to try and justly allow elements of political consideration and speculation, so I apologize for asking them to go further, but believe the asserted direction to be of value and the correct approach.

 

[Rive]

This link shows a basic layout of the level circuit. 2 taps into the vessel connected to a differential pressure (DP) cell and transmitter. http://www.pbnc2010.org.mx/pdfs/technical/tuesday/14.00_ModelingLevelInstrumentation.pdf

The released TEPCO photo shows the techs at a whole panel of DP cells.
I don't think anyone knows for sure where these taps actually sense level in the RPV. Is the bottom tap in the shroud region or acually in the vessel itself (ie below the downcomer)??
It is also not clear if they blew back the sensing lines to make sure they were clear of any obstruction. They also should have pumped water back up to the upper condensate pot to ensure the reference leg was full. Without doing these 2 steps - the readings may still be wrong!

So, we have a reactor with probably a decent amount of solid salt, peppered with some debris and corium, boiled in unknown amount of water against an unknown reference pressure/level to calibrate some differential pressure sensor.

Bummer.

 

[pdObq]

This link shows a basic layout of the level circuit. 2 taps into the vessel connected to a differential pressure (DP) cell and transmitter. http://www.pbnc2010.org.mx/pdfs/technical/tuesday/14.00_ModelingLevelInstrumentation.pdf

The released TEPCO photo shows the techs at a whole panel of DP cells.
I don't think anyone knows for sure where these taps actually sense level in the RPV. Is the bottom tap in the shroud region or acually in the vessel itself (ie below the downcomer)??
It is also not clear if they blew back the sensing lines to make sure they were clear of any obstruction. They also should have pumped water back up to the upper condensate pot to ensure the reference leg was full. Without doing these 2 steps - the readings may still be wrong!

Yes, I was also thinking that, how can they be sure their recalibration is correct...

And I don't understand, why they don't have a whole armada of specialized remote controlled robots like the KHG ones on site checking every corner of the buildings?

Maybe they don't want to know? I mean it really leaves the impression that they are not trying hard enough.

So, as to face wild hypothetical worst-case scenarios, if the one of the cores was on its way to "China" (in some sense taking care of its own long-term waste storage facility), would there be any easily detectable signs for that? How could one tell, apart from plausibility arguments based on reactor sensor readings, that it would not be happening?

 

[pdObq]

The linked article here may also hold the answer/confirm what the memos/emails were about discussed here a few pages back.

"TEPCO also decided to open the reinforced door of the troubled No. 1 reactor building on Sunday, making way for engineers to work inside to stabilize it."

Why can't they say more specifically which one they are talking about. The one of the refuelling tunnel/entrance on the SW corner? That would be most likely from their plan, I guess.

 

[clancy688]

Lets just get the facts straight, http://k.min.us/ikop60.JPG" that 200GJ of energy is required for a melt through 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 through 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.

I don't think that "200 GJ" figure is about "melt through" but rather "melt down" - the energy needed to totally transform a normal core into corium. Failure of the RPV would be another issue.
And there is failure, otherwise it's unplausible as to where the water goes. They pump 6 tons water per hour, yet the water level is still 1 m below the fuel rods. There must be some kind of big leak at the very bottom of the core.

I've come across a very interesting Caltech presentation, here it is:

http://www.galcit.caltech.edu/~jeshep/fukushima/ShepherdFukushima30April2011.pdf

One thing to mention is that Unit 1 has, according to this source, a different passive emergency cooling system than Unit 2 and 3. Unit 1 has an "isolation condenser", which's using a water pool on the fuel loading deck as heat exchanger. Once the pool is boiled dry, cooling is gone. 2 and 3 are using an RCIC which's working with a steam turbine and the condensation chambers. Emergency cooling in Unit 2 and 3 was probably more effective than in Unit 1!

So, now we know that the water level sensor was "lying". We don't know when he began sending bogus data, but I think it probably happened when the readings got frozen. That would be 12/3, 15:28 ( http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/plots/cur/wlev-un1.txt ). The explosion was at 15:36. What a coincidence...
At 11:20, the core was uncovered 90 cm already. Seawater injection started with 2 tons per hour at 20:20. According to IAEA-TECDOC-955, you need around 20-15 tons/h to cool a 3000 MWt plant during days 1-10 after shut down. Unit 1 is half the size, let's make it 10-7. So, the water level gauge started malfunctioning at -1,7m and first seawater injection started five hours after this, but with not enough water.

On page 120 of the presentation I posted there's a paragraph about pressure vessel failure by molten core.
The time given for RPV penetration / rupture is 4-10 hours if the drywell is NOT flooded. And TEPCO told us today that it isn't.

So I think it's totally possible that during the time Unit 1 was not cooled or not cooled appropriate, the whole core could've molten down and failed the pressure vessel.

 

[maddog1964]

Please Note:

I understand that this thread is being monitored for political content, and I don't want to start sifting through soap boxes or diatribes, but the politics (corporate & nationalistic) are impacting directly on the effort to bring some scientific understanding.

I assert that political criticism, where it applies to the data and possible reasons for obfuscation, should have greater latitude in this thread with links to the more political thread for expression in detail. My reasoning is that the questionable political control of data flows is a legitimate reference when attempting to form hypothesis and speculation on substitute data.

I think it would make for a more concise presentation of hypothesis' if a persons primary reasoning were contained in the same block of statements. If another member wishes to argue they can state their primary objection with link to external thread (if needed) for more verbose communication. There's no mistaking that the politics have become a factor in the science of understanding and corrective action.

I have a second point...

Speculation:

The term 'unprecedented' seems wholly inadequate to describe these crisis' and the attempts to control them. I also believe this thread has enjoyed a greater latitude than nearly any other on this forum WRT speculation. I advocate even more speculation, provided unwarranted conclusions are not bandied about in that effort.

I've had ideas offered to me (while looking for a technical solution) by customers or friends that appeared to be utterly stupid (revealing their shear lack of technical understanding), only to realize that their ideas have lead to a completely new approach to the problem and the solution. "Brainstorming" is one thing I love about this thread and think it too needs more latitude from moderators and members alike.

I realize moderators have been working overtime to try and justly allow elements of political consideration and speculation, so I apologize for asking them to go further, but believe the asserted direction to be of value and the correct approach.

Thank You !