Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[Astronuc]

@Astronuc:

What type(s) of scattered debris following a hydrogen explosion might have a 900 mSv/hr activity? It would seem to me something from the SFP of Unit 3 would be at the top of the suspect list, but perhaps not so. Your opinion? Thanks.

Bearing in mind 1 rem = 1000 mrem = 10 mSv = 0.01 Sv

and 1 rad ~ 1 rem when referring to gamma and X rays.
http://www.ndt-ed.org/EducationResources/CommunityCollege/RadiationSafety/theory/Measures.htm

I've seen pieces of fuel rod, underwater with activities on the order of 1000s of rad/hr, or 10000s mSv/hr. I suspect that rebar was contaminated with Cs and I, so it had a count in air of ~ 900mSv/hr.

 

[RealWing]

Bearing in mind 1 rem = 1000 mrem = 10 mSv = 0.01 Sv

and 1 rad ~ 1 rem when referring to gamma and X rays.
http://www.ndt-ed.org/EducationResources/CommunityCollege/RadiationSafety/theory/Measures.htm

I've seen pieces of fuel rod, underwater with activities on the order of 1000s of rad/hr, or 10000s mSv/hr. I suspect that rebar was contaminated with Cs and I, so it had a count in air of ~ 900mSv/hr.

The big unknown for me as a former plant guy is - at what distance from the hot spot was the radiation measurement taken. The number is meaningless without this info. I'm sure they didt get too close to a 90 R/hr hot spot (at least I hope not!)

 

[Astronuc]

The big unknown for me as a former plant guy is - at what distance from the hot spot was the radiation measurement taken. The number is meaningless without this info. I'm sure they didt get too close to a 90 R/hr hot spot (at least I hope not!)

That's one of the many unknowns. How did they measure it - by robot or remote control vehicle, and how did the apply geometric factors?

 

[MiceAndMen]

Sorry if this has been discussed earlier.

France's IRSN has calculated that SFP 4 would lose max 115 tons per day.

http://www.world-nuclear.org/info/fukushima_accident_inf129.html

An extensive report with some highly suspect "factual information". They state that hydrogen was vented to the service floors intentionally.

Excess pressure from the wetwell (above 300 kPa) can be vented through the 120 m emission stack via a hardened pipe or into the secondary containment above the reactor service floor of the building.

The esteemed AREVA report by Matthias Braun makes the same claim on page 21. http://www.fairewinds.com/sites/default/files/AREVA%20Fukushima.pdf

Has it been established that there is a direct vent path from the primary containment to the reactor building service floor?

Or is this yet more bad information we'll just have to live with until the experts sort it all out for us after having collected data for a few more years?

The wno report also claims the explosion at Unit 4 further damaged Unit 3. That's a new one on me.

 

[rowmag]

rowmag really is example of the reason why government feels free to keep secrecy... a citizen who, in absence of data, would come up with his own explanations along the lines of how correct the government actions were. That is very convenient. Simple lack of specific data becomes effective positive propaganda in such cases.

First of all, I am not a citizen. Second of all, I have never said I thought the government actions were all correct. But there is another thread for that discussion.

 

[pdObq]

I am sure you have noticed that a part of the metal roof structure is missing on the roof in the south end. That's because in the course of the blast it ended up in the yard between units 3 and 4. Fortunately its attachment to the south edge of the roof has been that much retained that one can see that one end has been torn apart, while the other end appears to have been affected by a similar heat-damage what we are talking about effect. Are we to assume three separate fire/blast events, two on the roof and one in the yard?

Detail from one end of the roof structure landed in the 3/4 yard:

A few pages back there has been some discussion about where the refueling crane (FHM = Fuel Handling Machine?) of unit 3 has gone, and if it could be below the big crane...

Looking at this image, I noticed that brownish-greenish structure with something that looks like a bent metal pole sticking out in the middle-left part of the image. There is some gray debris on its lower part, likely concrete pieces. Is it possible that this object is the unit 3 fuel crane that has maybe been ejected from the service floor in the unit 3 explosion? Would the size and its current position make any sense? The brownish color might be rust, and maybe we are seeing the bottom of the crane.

 

[ranchorelexo]

Sorry if this has been discussed earlier.

France's IRSN has calculated that SFP 4 would lose max 115 tons per day.


http://www.world-nuclear.org/info/fukushima_accident_inf129.html

MIT has calculated that even after 1 year the decay heat for units 2 & 3 after scram would be 5 MW per unit. Units 2 & 3 contain the same amount of reactor fuel assemblies that SFP 4 has spent/partially fuel assemblies (4 months old).
http://mitnse.com/2011/03/16/what-is-decay-heat/

(MIT is stating that their calculation is conservative, though.)

How was this 71 tons calculated? And can we be absolutely sure about it?

I don't know if this has been mentioned, but what about the new fuel assemblies stored in each SFP
Reactor 1 SFP contains 100 new fuel assemblies
Reactor 2 SFP contains 28 new fuel assemblies
Reactor 3 SFP contains 52 new fuel assemblies
Reactor 4 SFP contains 204 new fuel assemblies

 

[Zallia]

Have you all seen the live cam?

http://www.youtube.com/watch?v=Ck_KEILBLlU&feature=player_embedded

Looks like fires breaking out in #3 and #4.

 

[MiceAndMen]

I don't know if this has been mentioned, but what about the new fuel assemblies stored in each SFP
Reactor 1 SFP contains 100 new fuel assemblies
Reactor 2 SFP contains 28 new fuel assemblies
Reactor 3 SFP contains 52 new fuel assemblies
Reactor 4 SFP contains 204 new fuel assemblies

Please cite your source for this information.

 

[jlduh]

Did somebody knew that tepco seem to have vented through the stack on this timelapse video at a moment indicated as the 13th of March at around 14h00 (see at t=around 0:30' on this video)



There may be (but I'm not sure) an other small venting at t=0:29' (13th of March at 10h00) and previously one at t=0:24' which is indicated as the 12th of March at 15h00.

I believed that there was no possibility to vent directly to the outside through the stack because this had to be actuated through a valved requiring electricity and there was total blackout at the plant at this date after the tsunami?

That's the reason that was presented by some on this forum to explain why they were venting manually inside the buildings, leading to the H2 explosions.

Any explanation?

 

[jlduh]

Have you all seen the live cam?

http://www.youtube.com/watch?v=Ck_KEILBLlU&feature=player_embedded

Looks like fires breaking out in #3 and #4.

Hi please clarify your post, the link is towards a missing video and probably not "live"!

The live cam is here:
http://www.tepco.co.jp/nu/f1-np/camera/

 

[ranchorelexo]

Please cite your source for this information.

Status of the fuel as of march 11, 2011. Theres a table about half way through the pdf.

http://www.nisa.meti.go.jp/english/files/en20110406-1-1.pdf

 

[Zallia]

Hi please clarify your post, the link is towards a missing video and probably not "live"!

The live cam is here:
http://www.tepco.co.jp/nu/f1-np/camera/

Sorry! Try this site:
http://lucaswhitefieldhixson.com/fukushima-i-nuke-plant-live-video-feed-tbs

Not the still cam. Live video. You can see planes fly over and the change to night. Seems to be the real deal.

 

[jlduh]

The second link is not working either...

 

[jlduh]

More analysis and data around the release of the SPEEDI simulations and measurements:

http://ex-skf.blogspot.com/2011/05/japanese-government-finally-divulges.html

On Toshizo Kosako adviser's resignation, especially based upon the fact that children may have received to much radiation per government decisions:

http://menknowpause.fooyoh.com/news/6075624
http://online.wsj.com/article/SB10001424052748704167404576294343071646176.html

http://ecocentric.blogs.time.com/2011/05/03/japan-are-kids-being-exposed-to-too-much-radiation/
http://mdn.mainichi.jp/mdnnews/news/20110503p2g00m0dm017000c.html

Pressure is increasing, outside of the reactors...

 

[Zallia]

Am I doing something wrong or are they just not loading for you?
I've got one more:
http://news.tbs.co.jp/newsi_sp/youtube_live/

 

[StrangeBeauty]

The second link is not working either...

I can see the streams at both URLs without a problem (using google chrome) - both urls are the same stream.

Translation on the TBS/JNN youtube channel says:
Live camera JNN Fukushima Daiichi nuclear power plant (Live)
Live streamed on 2 May, two thousand and eleven by Tbsnewsi
--hmm should be 4 May now

I couldn't absolutely confirm it's a live feed, but the weather appears similar between the tepco still camera and this feed. TBS/JNN appears to be a legit news organization in Japan.

I'm seeing significant white smoke/steam coming intermittently from units 2, 3 and 4. I'm really not sure this is unusual considering the large amounts of water that people here have projected must be steaming off.

Hmm they've zoomed out now to include units 5 and 6, so it's much harder to see the smoke/steam. Now they're zooming again...

Also find the feed here:
http://ex-skf.blogspot.com/2011/05/fukushima-i-nuke-plant-live-video-feed.html

 

[Zallia]

Good, I was starting to worry. :) When it zooms in, there are flashes on the building on the far right, supposedly no. 4. They've been appearing and disappearing in different places, so it seems to be fire. There was some on the pile of rubble building next to it as well, but it was ground level so looks like they got it out? Hard to say for sure at the distance though.

I can see the streams at both URLs without a problem (using google chrome) - both urls are the same stream.

Translation on the TBS/JNN youtube channel says:
Live camera JNN Fukushima Daiichi nuclear power plant (Live)
Live streamed on 2 May, two thousand and eleven by Tbsnewsi
--hmm should be 4 May now

I couldn't absolutely confirm it's a live feed, but the weather appears similar between the tepco still camera and this feed. TBS/JNN appears to be a legit news organization in Japan.

I'm seeing significant white smoke/steam coming intermittently from units 2, 3 and 4. I'm really not sure this is unusual considering the large amounts of water that people here have projected must be steaming off.

Hmm they've zoomed out now to include units 5 and 6, so it's much harder to see the smoke/steam. Now they're zooming again...

Also find the feed here:
http://ex-skf.blogspot.com/2011/05/fukushima-i-nuke-plant-live-video-feed.html

 

[jlduh]

well sorry, all the links return a message "This video is not available". tried it with Chromium and Firefox with the same result, don't know why...

Maybe a restriction of rights for certain areas in the world? (I'm from France). Anybody else have trouble or only me?

I'm going to check if this is not a problem with Flash Player for 64bits system (Windows 7) causing the trouble.

EDIT: updated to the latest flash player release but no improvement. Tried Chromium, Explorer, Opera, Safari and Firefox... Quite strange.

 

[Zallia]

well sorry, all the links return a message "This video is not available". tried it with Chromium and Firefox with the same result, don't know why...

Maybe a restriction of rights for certain areas in the world? (I'm from France). Anybody else have trouble or only me?

Just keep refreshing. It's taken other people several attempts to connect as well. They are all the same feed, but not sure if any site will work better than the others. I hope it's not a restriction issue...

 

[AntonL]

Have you all seen the live cam?

http://www.youtube.com/watch?v=Ck_KEILBLlU&feature=player_embedded

Looks like fires breaking out in #3 and #4.

Hi please clarify your post, the link is towards a missing video and probably not "live"!

The live cam is here:
http://www.tepco.co.jp/nu/f1-np/camera/

@Zallia thanks for that link, This is exactly the same point from which explosions 1 and 3 where recorded from and this confirms my believe that the position is a fixed point weather cam

@jlduh this is live cam the tepco site is an hourly snapshot

a lot of steam can still be observed and the bird song is rather pleasing

[PLAIN]http://k.min.us/inr320.JPGThe videos of the explosion, in my opinion, were taken from this point http://watchizu.gsi.go.jp/watchizu.html?b=372016&l=1405540 which is 13km from fukushima and at an elevation of 582metres. This point also seems to be TV or radio station as a mast and a building is visible on google earth.

Using Google Earth one can draw site lines and check features like the high voltage line towers (vertical lines in the middle of the foreground)
[PLAIN]http://k.min.us/inr1us.JPG[/QUOTE]

below reactor 2 corner is a white vertical line (a mast in the landscape), both on live cam and explosion video above
[PLAIN]http://k.min.us/iniKbg.JPG

 

[jlduh]

Well that's a pity i cannot get the live feed...

I just found this page with extracted pictures trying to show what may be going on on reactor 4:

http://lucaswhitefieldhixson.com/fukushima-daiichi-reactor-4-fire-may-3-2011

 

[AntonL]

Well that's a pity i cannot get the live feed...

I just found this page with extracted pictures trying to show what may be going on on reactor 4:

http://lucaswhitefieldhixson.com/fukushima-daiichi-reactor-4-fire-may-3-2011

I cannot agree with lucaswhitefieldhixson to a fire in reactor 4, what he refers to as water streams moving side to side could just as well and most likely be mobile cranes clearing rubble.

These live pictures confirm that a lot watre is being boilded as a lot of steam is visible

 

[Zallia]

Look just off-center of the right-hand building on the ground floor. There's an orangeish-yellow flashing that wasn't there earlier. Seems to change size. Do you think that's fire or could it be something else? I think the May 2 is probably just the date when they started the streaming and that's why it's not current.

And you're welcome. :) Since most everyone seems content to ignore this problem entirely, it's nice that there are a few places where people are trying to obtain and spread as much information as possible. Seems best to share info when possible.

@Zallia thanks for that link, This is exactly the same point from which explosions 1 and 3 where recorded from and this confirms my believe that the position is a fixed point weather cam

I cannot agree with lucaswhitefieldhixson to a fire in reactor 4, what he refers to as water streams moving side to side could just as well and most likely be mobile cranes clearing rubble.

These live pictures confirm that a lot watre is being boilded as a lot of steam is visible

 

[MiceAndMen]

Status of the fuel as of march 11, 2011. Theres a table about half way through the pdf.

http://www.nisa.meti.go.jp/english/files/en20110406-1-1.pdf

Yes, the NISA reports have been discussed here. The number of new and used fuel assemblies has also been discussed. The new fuel that has not been activated gives off less heat than the used fuel.

 

[razzz]

I was following the live video link, which worked for me, and found more links...

http://ex-skf.blogspot.com/2011/05/highly-radioactive-sewage-sludge-in.html"

Fukushima, May 1 (Jiji Press)--High levels of radioactive cesium have been found in sewage sludge in Fukushima Prefecture, northeastern Japan, the prefectural government said Sunday.

The sludge at a treatment center in Koriyama had 26,400 becquerels of radioactive cesium per kilogram. Slag made by reducing the volume of sewage sludge had 334,000 becquerels per kilogram.

http://jen.jiji.com/jc/eng?g=eco&k=2011050300567"

The installation of the ducts, slated for Thursday, will be done by four pairs of plant workers. They are required to finish the job quickly because a high radiation level of 1,120 millisieverts per hour was detected at one place in the reactor building in a recent unmanned survey.

Newer news links after the article.

 

[|Fred]

More analysis and data around the release of the SPEEDI simulations and measurements:

there is a hudge disparity between the document found there
http://www.mext.go.jp/a_menu/saigaijohou/syousai/1305747.htm
and the one found there http://www.nsc.go.jp/mext_speedi/

Translation help is needed to know exactly what we are reading about

 

[PietKuip]

I don't know if this has been mentioned, but what about the new fuel assemblies stored in each SFP
Reactor 1 SFP contains 100 new fuel assemblies
Reactor 2 SFP contains 28 new fuel assemblies
Reactor 3 SFP contains 52 new fuel assemblies
Reactor 4 SFP contains 204 new fuel assemblies

Ok, so there was fresh enriched uranium in the pool.

Gundersen's theory of a prompt criticality as the cause of the unit 3 mushroom cloud is a possibility.

 

[~kujala~]

Please cite your source for this information.

http://www.nisa.meti.go.jp/english/files/en20110406-1-1.pdf (page 36)
New fuel is heat negligable.

 

[elektrownik]

Why they put fresh fuel in pool ? It don't need to be in water until it is loaded into core, but anyway, I didnt saw any place in reactor building where they could store fresh fuel... I don't know if it is normal in bwr reactors to keep new fuel in pool...

 

[artax]

Have you all seen the live cam?

http://www.youtube.com/watch?v=Ck_KEILBLlU&feature=player_embedded

Looks like fires breaking out in #3 and #4.

That's a nice find that is.
looks as if it's a day or two behind according to some text on the screen... would be nice to know.
And yes it looks like it's from the same vantage point as the explosion vids... my concern is the wind direction... It looks on shore now.

 

[zapperzero]

New fuel is put in the pool for safety, but also because it can only be put in the reactor one way: by being picked up from the pool, moved through a trough, underwater, between the pool and the reactor and inserted, while still underwater, in the reactor core.

 

[jpquantin]

Sorry if this has been discussed earlier.

France's IRSN has calculated that SFP 4 would lose max 115 tons per day.


http://www.world-nuclear.org/info/fukushima_accident_inf129.html

How was this 71 tons calculated? And can we be absolutely sure about it?

71 tons is calculated from estimating heat generation from SFP4 to 1,600 kCal/hour / 2MW. Was estimated by Atomic Energy Society of Japan (AESJ), source if here (http://www.aesj.or.jp/en/release/chousacom_EN_01_110418.pdf).

Both are estimates ...

 

[jpquantin]

At 27. Tepco said the Pool is leaking. At 28. Tepco said the Pool is NOT leaking.

Do you have links towards this leaking / then not leaking announcements?

Whats happend? Did they find the leaked? Perhaps they also restore the cooling?

Perhaps, but most probably they would have made announcements on these good news, don't you think?

 

[jpquantin]

I will probably still try to keep somewhat of an open mind about this data and what it means, just in case there is some factor we are missing, or for example if they have already tried to convert the raw skimmer water temperature into a pool temperature before publishing the data. I doubt this but its just one example of things I cannot be sure about.

We would need to know what is the exact shape of the FPC skimmer surge tank in unit 2 to check, based on its level and announced temperature. If of cylinder shape, then it seems to me it may be the deduced (calculated) temperature of the SFP.

They could also estimate temperature of SFP thanks to infrared aerial measurements, or also a thermocouple attached to the concrete truck arm.

 

[artax]

Radiation levels in unit 1 "far higher than tepco expected"

http://www.telegraph.co.uk/news/worldnews/asia/japan/8491624/Robot-sends-back-footage-from-inside-Fukushima-plant.html

I'll try to correct that link

 

[PietKuip]

http://www.nisa.meti.go.jp/english/files/en20110406-1-1.pdf (page 36)
New fuel is heat negligable.

Yes, until it goes critical.

Criticality is supposed to be prevented by boron in Boral sheets. Aluminum is stable in water only when the water is at neutral pH.

So when cooling gets lost, the spent fuel is boiling off the water, fuel rods get exposed and really hot, zircalloy is reacting with water, H2 is developed, and the water becomes alkaline (I think). This eats away Boral really fast in hot water. The boral sheets drop to the bottom of the pool.

Anything that can go wrong, will go wrong. If aluminum can dissolve in water when it is alkaline or acidic, it is just bound to happen somewhere sometime. From a safety point of view, the choice of aluminum as a matrix for boron is just incredibly stupid.

But the company says: http://www.ceradyneboron.com/products/nuclear-power/neutron-absorbers/boral/
"currently used at seventy nuclear power plants and eleven research reactors worldwide"
"It is well suited to many nuclear applications including storage of spent nuclear fuel, "

 

[Jim Lagerfeld]

Do you have links towards this leaking / then not leaking announcements?

April 27th:
TEPCO: Water may be leaking from No. 4 reactor fuel pool
http://www3.nhk.or.jp/daily/english/27_09.html

April 28th
TEPCO: Water isn't leaking from No. 4 reactor pool
http://www3.nhk.or.jp/daily/english/28_05.html

 

[MadderDoc]

<..>
i am curious about the orange flash at beginning of #3 video, and if you find the right youtube there was one in first fraction of a second of unit 1 as well. <..> Does anybody know of a frame by frame?

You can have a peek here:
http://gyldengrisgaard.dk/fuku_expl1/
http://gyldengrisgaard.dk/fuku_expl3/

(I would be happy for someone else to mirror this stuff
I do not really have the bandwidth to serve properly)

And is there anything to be gleaned from the burst of orange flame?
Orange is the color of burning salt but they weren't spraying seawater into the pools yet, as best i could find.

I don't think much can be gleaned from the color of the explosions. Hydrogen does burn ideally, like in a test tube, with an almost invisible flame, however in a real world hydrogen explosion, other stuff, e.g. dust, soot, will be present or be produced and be heated by it, producing a yellowish or reddish glow.
see:

 

[jpquantin]

The attached capture shows smoke over unit 2, 3 and 4.

I would go for steam - all same color for all units.

Also I do not see the red arm of the concrete truck near unit 4, but maybe this is too small to be visible ?

 

[rowmag]

there is a hudge disparity between the document found there
http://www.mext.go.jp/a_menu/saigaijohou/syousai/1305747.htm
and the one found there http://www.nsc.go.jp/mext_speedi/

Translation help is needed to know exactly what we are reading about

The first link only gives instantaneous simulations up to 3/16.
More recent updates are found here: http://www.nsc.go.jp/mext_speedi/past.html , which URL is found on the second link you gave above.

The second link you gave is the one I briefly explained in the post below:
https://www.physicsforums.com/showpost.php?p=3280525&postcount=5596

I'm not up for translating the whole thing, but if there are particular plots or other bits you are curious about, I can try to explain those (if someone else doesn't first).

 

[artax]

The attached capture shows smoke over unit 2, 3 and 4.

I would go for steam - all same color for all units.

Also I do not see the red arm of the concrete truck near unit 4, but maybe this is too small to be visible ?

Yes it is certainly steam as it soon disappears... however it is probably radioactive and the wind is now on shore so it will be falling inland and I expect TEPCO's radiation readings to rise considerably.

 

[ernal_student]

http://www.nsc.go.jp/mext_speedi/

On that site, you may be interested in this page with daily report collections:

http://www.nsc.go.jp/mext_speedi/past.html

Each collection has hourly reports, each showing a wind direction map and a plume flow map

 

[~kujala~]

71 tons is calculated from estimating heat generation from SFP4 to 1,600 kCal/hour / 2MW. Was estimated by Atomic Energy Society of Japan (AESJ), source if here (http://www.aesj.or.jp/en/release/chousacom_EN_01_110418.pdf).

Both are estimates ...

Thank you, now I have seen at least three different estimates, MIT estimate is conservative, AESJ seems to be quite optimistic, IRSN is somewhere between.

Is there any reasons to believe that some of these estimates could be questioned?

 

[Borek]

the wind is now on shore so it will be falling inland

Can be, but doesn't have to. Please remember there is an elevated terrain just behind the plant. It can be a horizontal whirl just on the shore, the air higher can be going in the direction of the sea, and sucking air from the sea over the buildings.

 

[jpquantin]

April 27th:
TEPCO: Water may be leaking from No. 4 reactor fuel pool
http://www3.nhk.or.jp/daily/english/27_09.html

April 28th
TEPCO: Water isn't leaking from No. 4 reactor pool
http://www3.nhk.or.jp/daily/english/28_05.html

Thanks !

From http://www3.nhk.or.jp/daily/english/27_09.html" :

TEPCO has poured in 140 to 210 tons of water over each of the last few days. The company found that water levels in the pool were 10 to 40 centimeters lower than expected despite the water injections.

Means they monitor water level at SFP4, but does not tell us when and how. Also 10 cm of water in SFP4 is 12 tons, 40 cm is 48 tons (if pool gate still there, more if not). Without knowing the time of measurement, no conclusion is possible. Would be soon after injection, I guess ...

From http://www3.nhk.or.jp/daily/english/28_05.html" :

But the company said on Wednesday that it now believes that the water has been evaporating at a rate in line with calculations by experts.

We come back to the boiling rate. I'd really love to have these experts calculations. Until now ...

If we take IRSN figure, we cannot tell for sure the SFP is leaking. The latest average loss is close to this figure (114 compared to my 124).

If we take AESJ figure, there MUST be leaks to explain the losses, because the boiling rate (70) is far below the average rate of loss (my 124).

Unless I'm incorrect, or data are corrupted, or calculation false, or FPC skimmer level not working correctly, or ... (etc).

Also what is surprising is that during video snapshot of Apr 28 I could not see evidence of a completely boiling pool. But this was just after the latest "full" signal, pool had just been refilled. And I must admit that I have not see many boiling SFP in my life ...

Any data on boiling rate estimates, based on number and "age" of rods in SFP4, would be appreciated ...

 

[jlduh]

Did somebody knew that tepco seem to have vented through the stack on this timelapse video at a moment indicated as the 13th of March at around 14h00 (see at t=around 0:30' on this video)



There may be (but I'm not sure) an other small venting at t=0:29' (13th of March at 10h00) and previously one at t=0:24' which is indicated as the 12th of March at 15h00.

I believed that there was no possibility to vent directly to the outside through the stack because this had to be actuated through a valved requiring electricity and there was total blackout at the plant at this date after the tsunami?

That's the reason that was presented by some on this forum to explain why they were venting manually inside the buildings, leading to the H2 explosions.

Any explanation?

I quote myself because i didn't get any comments on this right now and i find this confusing based on what was considered until now...

If venting through stack could be operated (i don't see very well on the frames which stacks are the plumes coming from: i think the N°3/N°4 stack for the plume the 13th March at 14h00, right?), why did they changed to Inside buildings venting with H2 risks of explosion if it was NOT because there was no other option because black out?

 

[zapperzero]

Why did they changed to Inside buildings venting with H2 risks of explosion if it was NOT because there was no other option because black out?

There is no way to intentionally vent inside. Hydrogen escaped into the building, then went boom.

 

[MadderDoc]

<..>
Has it been established that there is a direct vent path from the primary containment to the reactor building service floor?

Or is this yet more bad information we'll just have to live with until the experts sort it all out for us after having collected data for a few more years?

That would be over my cold crumbled curiosity.

From reading the document, link below, don't know it it has been previously posted, I get the impression that BWRs are by design meant to vent the primary containment through to the secondary then to filtering/scrubbing and final to exhaust.

http://www.sumofallfears.com/m/OCRDocuments:Role_of_BWR_Secondary_Containments_in_Severe_Accident_Mitigation

 

[Rive]

AFAIK it's the torus what's vented through some chimneys near the reactor (these are the high towers between U1&U2, U3&U4). The system is called 'Direct torus vent system', DTVS.

Of course I don't know if the vent path was 'official' or not - there was that blackout...