Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[MadderDoc]

Do we know if the bottom of the RPV is still dry on the containment side? If so, we might expect it to be very hot.

Dr. Michio Ishikawa, Chief Adviser(Former President & CEO)
Japan Nuclear Technology Institute(JANTI)
http://www.gengikyo.jp/english/shokai/Tohoku_Jishin/article_20110413.htm"

I suggest that cooling the hot RPV is going to create a lot of steam, and that could be what they are expecting.

I may be way off here and stand to be corrected.

EDIT - clarified the question about the RPV being dry on containment side

The experiment that was conducted with increased injection rates April 27th-29th indicates to me that Tepco quickly achieved temperature below boiling and atmospheric pressure in the containment, while the readings from the RPV reacted promptly displaying a decrease in pressure and temperature. So perhaps a steam surge from a quick submersal of the PV is not that much of a worry, such a surge would seem liable to condense and dissipate into the water present in the containment. Certainly inside the RPV must be very hot, but if the pressure and temperature readings from the drywell can be trusted, I can't see the outside of the vessel as glowing hot.

 

[Rive]

http://atomicpowerreview.blogspot.com/"

There is that schedule:

What's the 'big equipment hatch' they want to open? All I could find is the big containment plug which cannot be relevant.

 

[GJBRKS]

http://www.tepco.co.jp/nu/fukushima-np/f1/images/00_05061300.pdf
#3 243C water level decreasing
#2 torus 130Sv/h
#1 Water injection now 8m^3/h

What else can it be with #3 ? I see 2 options: recriticality or bigger crack/leak in RPV...

3rd option : reduced flow and pathways because of salt accretion

Also , when watching the lhttp://www.youtube.com/watch?v=Ck_KEILBLlU&feature=player_embedded" , I don't see as much steam rising from #3 as from #2 and #4.

Less steam might imply less cooling

 

[jensjakob]

130 Sv/h in no 2 torus - that is quite a lot?

How can that be?

 

[elektrownik]

130 Sv/h in no 2 torus - that is quite a lot?

How can that be?

If the core or part of core melt from RPV and drywell to torus, but sensor can be damaged also

 

[elektrownik]

3rd option : reduced flow and pathways because of salt accretion

but they don't use salt water science many days...

 

[AntonL]

http://www.tepco.co.jp/nu/fukushima-np/f1/images/00_05061300.pdf
#3 243C water level decreasing
#2 torus 130Sv/h
#1 Water injection now 8m^3/h

What else can it be with #3 ? I see 2 options: recriticality or bigger crack/leak in RPV...

4th Option - 9m³/h water not reaching the reactor, a leak could have sprung somewhere or the flow meter is faulty.

130 Sv/h in no 2 torus - that is quite a lot?

How can that be?

electrowink has been looking at his computer screen too much and needs new glasses :)
it is 12.4 Sv/h and water injection rate is 9m³/h

 

[Rive]

I don't think unit1 upper wall panels are from concrete, but rather are some sort of steel panels just as on the roofs, see the quote from an earlier post of rive below.
...
Thanks, I am looking forward to your findings.

Actually, I made a mistake: the roof had some concrete-like upper cover over the steel. But the walls are steel.

Judging by the pictures:
Browns Ferry: steel.
Brunswick: steel.
Cooper: steel.
Duane: steel.
Monticello: steel.
Santa Maria de Garoña (not in the US): possibly concrete.
Vermont Yankee: steel.

Those are which I have pictures about - there are many other such NPP. Maybe Google Earth can provide some pictures (at least, uploaded by users?), I don't know. Ps.: I could find a picture of the 'Fuel prep machine' in use. Maybe it would be interesting to compare it with the south edge of U4 where Nancy of Houseoffoust suspects that shattered fuel assembly.

3rd option : reduced flow and pathways because of salt accretion

We can turn this upside down: as the freshwater solves the accreted salt maybe the core 'restructures' itself?

 

[GJBRKS]

electrowink has been looking at his computer screen too much and needs new glasses :)
it is 12.4 Sv/h and water injection rate is 9m³/h

hmmm... using his glasses ? ( he refers to #2 S/C (B) CAMS data , it's indeed 1.3E2 there )

 

[GJBRKS]

but they don't use salt water science many days...

true , not since 25th of March , so that seems unlikely unless some salt has reshifted

 

[artax]

anyone know why that live webcam is down, can anyone get anything?

http://lucaswhitefieldhixson.com/fukushima-i-nuke-plant-live-video-feed-tbs

 

[AntonL]

hmmm... using his glasses ? ( he refers to #2 S/C (B) CAMS data , it's indeed 1.3E2 there )

OK time that I visit the optician

 

[PietKuip]

I agree with you guys, something was different about unit 3. Way more energetic.

I too have looked for a mechanism to cause criticality in the pool but can't find one. It'd take something to remove the poison to let it go critical. and they weren't spraying the pools yet i believe.

There was also fresh fuel in the same pool.

So a possible scenario might be the spent fuel boiling away the water, zirconium oxidation making the water alkaline, hot alkaline water eating away the aluminum of the Boral absorbers between the fresh fuel rods -> criticality.

A chemical explosion could have triggered prompt criticality.

A Tepco worker has said that radiation readings in the emergency control room bunker went up by a factor of 12 at the time of the #3 explosion.

 

[AntonL]

anyone know why that live webcam is down, can anyone get anything?

http://lucaswhitefieldhixson.com/fukushima-i-nuke-plant-live-video-feed-tbs

I hear the birds and see lots of fog just a grey screen

 

[artax]

That was live the other day... and it's night-time now,...but even at night you could see the buildings/ tree line against the sky, I think it's down.
I know it's serious but this made me laugh!

 

[PietKuip]

As the experts have pointed out, it is a complicated situation with water from different sources being mixed and added to and drained from at various rates, and with various transport and filtering mechanisms in play, in some configuration that is not well understood because it is all happening underground and out of sight... BUT, what I am naively hoping to see is that the long-term trend of the I-131/Cs-137 ratio is going down.

The measurements in air are showing a downward trend consistent with the 8-day halflife of I-131:
https://spreadsheets.google.com/spr...tEdE5IbzlocmczREZ2Z3Y0TEk2WVdwUVE&hl=en&gid=1

 

[jlduh]

http://www.tepco.co.jp/nu/fukushima-np/f1/images/00_05061300.pdf
#3 243C water level decreasing
#2 torus 130Sv/h
#1 Water injection now 8m^3/h

What else can it be with #3 ? I see 2 options: recriticality or bigger crack/leak in RPV...

The RPV D/W bellows seal temp is now close to its highest since recorded. But it was still a bit higher in mid April (253°C). What has to be watched is the rate of increase of this TEMP (around 1°C per hour) and especially if the the rate continues to be like that in the next days.

https://spreadsheets0.google.com/sp...ZDbX39YK-iFb0Iw&hl=ja&authkey=CP6ewJkO#gid=40

Concerning the water level decrease, it's not so obvious i think for the moment, because when you look at time series you see that it's fluctuating (depending on which reading you take), but lf you take reading A it has long been at around -1800/-1850mm and this changed the 5th of May (yesterday) when it dropped to -2000/2050mm. So there has been a sudden drop of 20cms of the water level in the RPV (if the readings are accurate and reliable, which is unsure) but the trend is not so clear than the temps, which started to rise about one week ago before the change in water level.

As a reminder here are the datas:
https://spreadsheets0.google.com/sp...DZDbX39YK-iFb0Iw&hl=ja&authkey=CP6ewJkO#gid=2

So it's difficult to draw based on these data a correlation between the two, and to find out what is causing what...espacially with the poor infos we get from Tepco on what they are actually doing!

Maybe i missed some infos from tepco (plus i was out of internet connection for 2 weeks beginning of April) but do we know for sure how and precisely where tepco is injecting the water into the reactor pressure vessel in N°3? Are they using the nozzles at the top? Didn't see any sketch on this.

The leaks in the RPV can be at various places, and they can be numerous. It's a high possibility that there are leaks at the bottom where there are a lot of insertions (around 250 insertions holes if I'm not wrong) from control rods and various measuring equipements coming out of the core. We heard about i think a long crack in the side wall of the vessel, but no confirmation. What is sure is that water will take, under gravity, the easiest path to go out, from top to bottom.

If my understanding is correct, if i consider the way the reactor is now "cooled", there couldn't be no flow (and so no cooling) inside the core if there was no leakage from the RPV, right?

If it is so, we can be very happy that these babies are heavily leaking otherwise we would have had very quickly some BIG BOOOOMs if this cooling of last resort couldn't be established through the leakages? After the story of SFP N°4 being saved by the miraculous explosion which opened not the Red Sea but the gate in between the SFP and the well (still to be confirmed i think), we are very lucky again with these reactors in some kind of "stable mode" for weeks now only beacuse there are leaks everywhere! Again this should be integrated in the design parameters when they start to "think the unthinkable" (sarcasm inside! but this is related to my yesterday post on the future new guidelines in France for safety in case of severe accident ).

Considering this very empirical way of cooling the stuff, there can be various reasons explaining why temperatures are changing, independently from the flow injected. The core is damaged and the geometry is lost, you have probably debris, crust or melted stuff inside, and this is evoluating. Some debris can obstruct some canals inside the core fuel rods, which will reduce locally the flow, or stop it, and then local temp will rise, and so one. So this is very difficult to know what is going on inside. But one thing is sure: this thing is very alive and its "stable mode" is an appearance from the outside.

And chance doesn't last for always...

 

[rowmag]

As the experts have pointed out, it is a complicated situation with water from different sources being mixed and added to and drained from at various rates, and with various transport and filtering mechanisms in play, in some configuration that is not well understood because it is all happening underground and out of sight... BUT, what I am naively hoping to see is that the long-term trend of the I-131/Cs-137 ratio is going down. There seem to be hints that Unit 2 and/or Unit 3 is making at least sporadic efforts to be difficult (from a simple-minded reading of these plots, and with no knowledge of typical measurement errors).

And here's the sub-drain isotope update through 5/5:
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110505e13.pdf

The measurements in air are showing a downward trend consistent with the 8-day halflife of I-131:
https://spreadsheets.google.com/spr...tEdE5IbzlocmczREZ2Z3Y0TEk2WVdwUVE&hl=en&gid=1

That's true. And the internal reactor parameters don't all seem to point the same direction, either. (#3 temperature goes up, but drywell radiation readings continue down. #2 radiation reading goes up in one monitor, but not in the others nor in temperatures...)

Maybe it's all just garbage readings.

 

[yakiniku]

That's a good point, of course. I'm just looking at the other slides like "Monitoring of Radiation Dose when opening the airlock to implement the work" and "Environmental Impact Assessment caused by opening the airlock to implement the work," and sensing that the officials are covering their hindquarters with the anouncement. Plus the "opening of airlock" is the only thing marked in red on the schedule!

Thanks for the attachment. I had not seen it. I agree it corroborates with the information in the blog post. It is interesting to see the estimate of opening the airlock is an airflow of 22,000m3/h. That's based on an assumption of no wind on the outside of the building.

 

[MadderDoc]

There is that schedule:

What's the 'big equipment hatch' they want to open? All I could find is the big containment plug which cannot be relevant.

And there would be need for clearing 'debris under the big equipment hatch'. This would seem to indicate opening a hatch somewhere below the level of the service floor in one of the walls. The north and the west wall seem the likely candidates since the east and the south walls have attached buildings.

In the west wall there is a clear signature of a small hatch above service floor level and a faint signature of a larger rectangular shape below it, with two pipes? sticking out from the wall above it. Otoh, below there is rather more equipment and small buildings than debris.

The north wall is hard to come by good photos of, from what I have seen no signature of any openings in the wall can be discerned. Otoh at the foot of this wall there is not much but debris, and probably relatively high activity debris to boot.

See attachments

 

[jpquantin]

About unit 4 explosion breaking gate theory ...

This theory is interesting, but it relies on the assumption that the pool was quite empty at the time of the explosion, in order to explain that in the days after there were no signs of a dry pool, like for instance zirconium fire. I've even seen drawings with uncovered fuel assemblies at the time of the explosion.

Now looking at SFP4 losses rates, there are still missing pieces to me to explain such a point of departure.

Explosion happened Mar. 15th around 6 AM. If fuel assemblies were uncovered at this time, this means that all water above it would have boiled, leaked or splashed before the explosion. According to my calculation, this is about 870 tons of water. Without considering splashing, this means 217 tons losses per day. Losses of water due to splashing in SFP in other units (5 & 6) would help know the impact of it. Splashing may be one missing piece. Any information anyone?

Then: they put 1554 tons of water afterwards in order to reach the "pool is full" signal, which was first reached on Apr. 13 14:55. This is an average 46 tons per day loss. There are a few injections / spray for which we lack volumes (two helicopter drops, and one injection between Mar. 26 06:05 and Mar. 26 10:20). Even considering a big injection for the missing one (180 tons), and 2 drops of 20 tons each, one gets an average loss rate of 52 tons. Even splitting calculations between period with or without skimmer surge tank levels, you got roughly a rate about 50 - 60 tons per day loss.

So the situation would have been the following:
- prior to explosion, they suppose SFP4 had an average 217 tons per day loss
- after it, data only gives 50 to 60 tons per day.

Well, not only explosion saved SFP4 from a zirconium fire, and fuel melt, but it also stopped leaks apparently! How can you explain that? Rubbles filling the pool? But the pool is full of casks, and it may be very difficult for rubbles to go the places where there are leaks.

Moreover last video did not show that much rubble in the pool (attach1). Which seems weird also, as in another picture (attach2) shows SFP4 surrounded by a LOT of rubbles.

Next, looking at a http://www.youtube.com/watch?v=AUx7lIUsogA&NR=1", there is a view that is I think of the reactor wel (see circle in attach3). No steam above it, while lot of steam left of it (red / green circles in attach4), above SFP. We would expect at least some steam above reactor wel is gate would be broken, wouldn't we?

The gate broken theory is interesting, but it seems to contradict with other observations.

Pictures of unit 4 before and after explosion clearly qualify an hydrogen explosion. The key to me would be to estimate the amount of hydrogen with different water level drop rates, and see with this volume if one can explain the damages in unit 4. I've heard here and there that there were models to calculate hydrogen release from zirconium-steam reaction, maybe it would help qualify one or the other assumption. Maybe still covered assemblies, but surrounded by boiling water, can produce enough hydrogen to explain damages to unit 4? I don't know. I've seen a post on this question, quite interested in it.

Additionnally, we can also quantify the volume of water brought through the broken gate. It has to be significant in order to "save SFP4".

Well if the gate broke during the explosion it brought water that was above the reactor wel in the SFP. My own estimate of this volume is 1200 m^3, using this input:

- Top of RPV is at 31660
- Service floor is at 38900
- This is 7.24 meters height
- Assuming width identical to SFP, 12.2 meters
- Third length is 2 times distance between 2 pillars: 2 x 6.76 = 13.52 meters
- Estimated volume: 1200 m^3

Any remark anybody on this volume estimate?

NB: Some part of this providential water may have turned into steam due to the heat of the explosion, reducing its benefits...

 

[jpquantin]

Last attachement for previous post

 

[jlduh]

Maybe it's all just garbage readings.

That's a possibility that cannot be dismissed! That's why i mentionned several weeks ago that doing some "scientific analysis" on datas that are not confirmed reliable (to say the least) or that are coming from sources which are not scientifically neutral (Tepco for example to say the least) is more "educational guess" than science anyway!

But let's live with this without forgetting about it, you are right!

 

[fluutekies]

[...]
(Several days ago I tweeted @tep_co about the CAMS drop and got back a reply that they would look into it "later".

Please be advised that @tep_co is some sarcastic parody...

 

[artax]

There's a new update at all things nuclear.

http://allthingsnuclear.org/

 

[jlduh]

About unit 4 explosion breaking gate theory ...

This theory is interesting, but it relies on the assumption that the pool was quite empty at the time of the explosion, in order to explain that in the days after there were no signs of a dry pool, like for instance zirconium fire. I've even seen drawings with uncovered fuel assemblies at the time of the explosion.

Now looking at SFP4 losses rates, there are still missing pieces to me to explain such a point of departure.

Explosion happened Mar. 15th around 6 AM. If fuel assemblies were uncovered at this time, this means that all water above it would have boiled, leaked or splashed before the explosion. According to my calculation, this is about 870 tons of water. Without considering splashing, this means 217 tons losses per day. Losses of water due to splashing in SFP in other units (5 & 6) would help know the impact of it. Splashing may be one missing piece. Any information anyone?

Then: they put 1554 tons of water afterwards in order to reach the "pool is full" signal, which was first reached on Apr. 13 14:55. This is an average 46 tons per day loss. There are a few injections / spray for which we lack volumes (two helicopter drops, and one injection between Mar. 26 06:05 and Mar. 26 10:20). Even considering a big injection for the missing one (180 tons), and 2 drops of 20 tons each, one gets an average loss rate of 52 tons. Even splitting calculations between period with or without skimmer surge tank levels, you got roughly a rate about 50 - 60 tons per day loss.

So the situation would have been the following:
- prior to explosion, they suppose SFP4 had an average 217 tons per day loss
- after it, data only gives 50 to 60 tons per day.

Well, not only explosion saved SFP4 from a zirconium fire, and fuel melt, but it also stopped leaks apparently! How can you explain that? Rubbles filling the pool? But the pool is full of casks, and it may be very difficult for rubbles to go the places where there are leaks.

Moreover last video did not show that much rubble in the pool (attach1). Which seems weird also, as in another picture (attach2) shows SFP4 surrounded by a LOT of rubbles.

Next, looking at a http://www.youtube.com/watch?v=AUx7lIUsogA&NR=1", there is a view that is I think of the reactor wel (see circle in attach3). No steam above it, while lot of steam left of it (red / green circles in attach4), above SFP. We would expect at least some steam above reactor wel is gate would be broken, wouldn't we?

The gate broken theory is interesting, but it seems to contradict with other observations.

Pictures of unit 4 before and after explosion clearly qualify an hydrogen explosion. The key to me would be to estimate the amount of hydrogen with different water level drop rates, and see with this volume if one can explain the damages in unit 4. I've heard here and there that there were models to calculate hydrogen release from zirconium-steam reaction, maybe it would help qualify one or the other assumption. Maybe still covered assemblies, but surrounded by boiling water, can produce enough hydrogen to explain damages to unit 4? I don't know. I've seen a post on this question, quite interested in it.

Additionnally, we can also quantify the volume of water brought through the broken gate. It has to be significant in order to "save SFP4".

Well if the gate broke during the explosion it brought water that was above the reactor wel in the SFP. My own estimate of this volume is 1200 m^3, using this input:

- Top of RPV is at 31660
- Service floor is at 38900
- This is 7.24 meters height
- Assuming width identical to SFP, 12.2 meters
- Third length is 2 times distance between 2 pillars: 2 x 6.76 = 13.52 meters
- Estimated volume: 1200 m^3

Any remark anybody on this volume estimate?

NB: Some part of this providential water may have turned into steam due to the heat of the explosion, reducing its benefits...

Your explanations are interesting, especially the significant difference in loss rate of water before and after the explosion at N°4.

I've been surprised also to see the underwater images at the bottom of the pool (only a small part of it though) with very few debris indeed. That's not what I would imagine after such destructions around, but Tepco may have selected a clean spot!

 

[GJBRKS]

That's true. And the internal reactor parameters don't all seem to point the same direction, either. (#3 temperature goes up, but drywell radiation readings continue down. #2 radiation reading goes up in one monitor, but not in the others nor in temperatures...)

Maybe it's all just garbage readings.

In my view ,garbage readings do not follow real world dynamics.
I see some correlation , and I do not consider this a closed system , so there will be a lot of interconnected and unknown differentials.

But of course not all is well

 

[jlduh]

There's a new update at all things nuclear.

http://allthingsnuclear.org/

Thanks, but nothing really new i think.

But i saw just below an interesting article on SFPs, which describes the real flaws (and even gaps!) in the safety issues and scenarios retained for assessing them by NRC.

http://allthingsnuclear.org/post/4814761753/susquehanna-spent-fuel-pool-concerns-and-how-i-ended

Lochbaum is refererencing excerpts of his book already posted here:

http://www.ucsusa.org/assets/documents/nuclear_power/nuclear-waste-disposal-crisis-excerpts.pdf

 

[SteveElbows]

Latest updates mention 58t of water added to number 2 pool today, and a hefty 270t added to unit 4 pool on the 5th, think that might be the most they have stuck into that pool in one go.

 

[bytepirate]

130 Sv/h in no 2 torus - that is quite a lot?

How can that be?

it can not...
according to the graphs here: http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110427e19.pdf
130Sv/h would mean a core damage rate of above 100%

but as the readings of A and B differ by magnitudes, i would assume, that the readings are almost meaningless.
as long as we don't know, what exactly these monitors *see*, we simply don't know what these readings mean.

 

[Jorge Stolfi]

Here is an annotated version of the Air Photo Service snapshot of reactor #3, from nearly above:

[PLAIN]http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/povray/blueprint/foto/edited/out/reactor3-Z-3-c-A-i.png

To the best of my knowledge:

(A) Outline of the service floor, out to the outer surface of the building.
(B) Stairwell (?).
(C) Elevator shaft.
(D) Spent-fuel pool. The North edge is guessed, the East edge may be a bit off.
(E) Steam-dryer storage pool (= equipment pool). The South edge is guessed.
(F) Overhead crane (outline of upper surface).
(G) Winch box of the overhead crane.
(H) E-W and N-S cuts through the reactor axis (as in blueprints).
(I) Estimated broken edge of service floor slab.
(J) Grappling attachment for the containment cap?

Now, where is the Fuel Handling Machine? In orbit perhaps?

The tracks of the FHM allow it to travel only between the spent-fuel pool and the reactor opening. Perhaps it was over the reactor, and was squashed into the refueling pit by the falling crane? Were the concrete plugs in place at the time of the explosion?

Higher resolution images:
http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/povray/blueprint/good/un3_foto_exploded_Z_1.png
http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/povray/blueprint/good/un3_foto_exploded_Z_2.png
http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/povray/blueprint/good/un3_foto_exploded_Z_3.png
http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/povray/blueprint/foto/edited/out/reactor3-Z-3-c-A-e.png (annotated version of the latter)

 

[jim hardy]

piet

"A chemical explosion could have triggered prompt criticality."

can you explain the mechanism for that?

 

[artax]

piet

"A chemical explosion could have triggered prompt criticality."

can you explain the mechanism for that?

Well I assume they're considering the possibility that the chemical explosion changed the geometry of the nuclear fuel in such a way that the number of neutrons escaping was less or close to that causing fission.

The first atomic bombs used a chemical explosion to compress a 'sub critical' sphere of fissile material into a critical one of same mass but slightly samaller volume.

The following is from wikipedia

TEPCO claimed that there was a small but non-zero probability that the exposed fuel assemblies could reach criticality.[243][244] The BBC commented that criticality would never mean a nuclear explosion, but could cause a sustained release of radioactive materials.[243] Criticality is usually considered highly unlikely due to the low enrichment level used in light water reactors.[245][246][247]

There was, however, speculation on Russia Today by low-dose radiation researcher and anti-nuclear activist Christopher Busby that the explosion that destroyed the reactor 4 building was a "nuclear explosion" of some kind in the spent fuel pool.[248] Similarly, as noted above, Arnie Gundersen surmised a prompt criticality for the 13 Mar 2011 explosion at the spent fuel pool located on top of the Reactor-3 (see Reactor-3 above). [249]

Visual inspection of the spent fuel rod pool on reactor 4 on April 30 has however shown that that there is no significant visible damage to the fuel rods in the pool. This observation is inconsistent with speculation of prompt criticality

 

[jlduh]

piet

"A chemical explosion could have triggered prompt criticality."

can you explain the mechanism for that?

See an hypothesis (without any calculation though) in this video that I posted in this previous message:

https://www.physicsforums.com/showpost.php?p=3284941&postcount=5890

As i understand it the principle would be the same than the one for the first Nuke bombs (despite with far than "optimum" conditions resulting in a low energy nuclear explosion).

Have not enough knowledge to assess if this is a stupid idea or a possible one.

See also these wiki:
http://en.wikipedia.org/wiki/Prompt_critical#Critical_versus_prompt-critical
http://en.wikipedia.org/wiki/Critical_mass

Gunderson says that the answer is probably is the Xe data which could indicate the occurence of this phenomenon (don't ask me how).

Which Xe data do we have on hand for Daichi?

 

[elektrownik]

it can not...
according to the graphs here: http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110427e19.pdf
130Sv/h would mean a core damage rate of above 100%

but as the readings of A and B differ by magnitudes, i would assume, that the readings are almost meaningless.
as long as we don't know, what exactly these monitors *see*, we simply don't know what these readings mean.

I saw table, but I can't find it now with information how long reactors were without water, tahere was: 2,5h for 1&3 and 12,5h for 2 (because they were not able to open some valve) and then additional 50min after one of aftershocks, I think that 12,5h is enought to melt 100% of core ?