Japan Earthquake: nuclear plants


by gmax137
Tags: earthquake, japan, nuclear
Rive
Rive is offline
#6823
May12-11, 06:48 AM
P: 337
Quote Quote by htf View Post
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:
Inspection Status of the Indicator (Water level indicator A, fuel area) at Unit 1, Fukushima Daiichi Nuclear Power Station

- Does anybody knows how are those indicators works? Pressure difference, maybe?
- yeah, some more rods
yakiniku
yakiniku is offline
#6824
May12-11, 06:56 AM
P: 30
Quote Quote by AntonL View Post
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.
Attached Thumbnails
photo.jpg  
|Fred
|Fred is offline
#6825
May12-11, 06:59 AM
P: 312
Quote Quote by jlduh View Post
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
TCups is offline
#6826
May12-11, 07:05 AM
TCups's Avatar
P: 494
Quote Quote by MiceAndMen View Post
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
Borek is offline
#6827
May12-11, 07:07 AM
Admin
Borek's Avatar
P: 22,708
Quote Quote by AntonL View Post
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
jlduh is offline
#6828
May12-11, 07:11 AM
P: 468
Quote Quote by jlduh View Post
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 N1 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 N1 as total BS? Then i have to admit that one of the "proofs" that N3 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 N1, 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.







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 N1, 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 1811%."

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



-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 100C 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/fukushi...1/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???)



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

yakiniku
yakiniku is offline
#6829
May12-11, 07:21 AM
P: 30
Quote Quote by Borek View Post
"Reactors are very susceptible" sounds a little bit too general to me.
I read it that way at first too. Without putting words in to AntonL's post it had the article "the" before "reactors" which would indicate the particular reactors that are being discussed at Fukushima.
MadderDoc
MadderDoc is offline
#6830
May12-11, 07:21 AM
MadderDoc's Avatar
P: 698
Quote Quote by TCups View Post
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
ihatelies is offline
#6831
May12-11, 07:24 AM
P: 45
Quote Quote by |Fred View Post
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


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
|Fred is offline
#6832
May12-11, 07:28 AM
P: 312
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
rmattila is offline
#6833
May12-11, 07:28 AM
P: 242
Quote Quote by jlduh
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
BlueCactus is offline
#6834
May12-11, 07:52 AM
P: 5
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
Dmytry is offline
#6835
May12-11, 07:54 AM
P: 505
Quote Quote by jlduh View Post
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
Luca Bevil is offline
#6836
May12-11, 07:58 AM
P: 87
Quote Quote by BlueCactus View Post
TEPCO said, it is about 58 Cubic meter that the RPV can contain water without being detected by sensors.
looks reasonable
robinson
robinson is offline
#6837
May12-11, 08:08 AM
P: 201
Didn't the amount of radionuclides found outside the plant area show massive damage to fuel early on?
jim hardy
jim hardy is offline
#6838
May12-11, 08:15 AM
Sci Advisor
jim hardy's Avatar
P: 3,149
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/...5j/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
IowaNewbie is offline
#6839
May12-11, 08:18 AM
P: 10
Quote Quote by jim hardy View Post
it's only a flesh wound......
That's how gangrene starts ...
rmattila
rmattila is offline
#6840
May12-11, 08:22 AM
P: 242
Quote Quote by robinson View Post
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.


Register to reply

Related Discussions
8.9 earthquake in Japan: tsunami warnings Current Events 671
New Nuclear Plants Nuclear Engineering 9
Gen IV Nuclear Plants Nuclear Engineering 10
New Nuclear Plants Nuclear Engineering 14
Astronomer Predicts Major Earthquake for Japan General Discussion 65