Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[jim hardy]

""" So an external emergency freshwater tank, a backup suppression chamber if you must, sounds like a very elegant solution to the issue, particularly in the case of drywell venting.

NPP engineers, is there any reason from an engineering point of view why that might not be be feasible or effective? On the face of it it does seem to be "cheap insurance" for this type of NPP. """


these things come to a practical limit.
it is always initial reaction to add something, seems natural enough to do that


some thoughtful deliberation necessary to figure out whether more would be gained from improving what's already there.

certainly the fresh water tanks could be moved up the hill so they'd be immune to flooding and feed by gravity,,,

and perhaps made bigger

then one should figure out whether that might relieve need for another layer of suppresion around existing suppression pool. that'd be a mighty big structure...

not shooting at your sugestion, just questioning where's most gain for effort expended.

every added complexity brings with it new failure mechanisms. Take Windows, for example...

 

[NUCENG]

Thank you for a very coherent and cogent response.
The comments about depressurizing the reactor as a means to allow more easily feasible emergency cooling make great sense. Presumably there would still be noticeable emissions as the reactors would essentially be boiling in the open, but if the fuel rods remain intact, the contamination damage is relatively minute. Indeed, if the reactors are depressurized, water could be injected by a hydraulic or pneumatic pressurizer, somewhat similar to the existing emergency cooling systems but with more backup. Is there a good reason such an approach is not already SOP?

The basic response I outlined is implemented under Emergency Operating Procedures (EOPs) at US NPPs. The real key is that the reactor must be depressurized before signicant damage occurs and before the suppression pool loses its pressure suppression capacity. Containment must be vented before it is overpressurized and fails. That may not have been the plan of attack at Fukushima. Perhaps this is one reason that TEPCO has been reluctant to release their emergency procedures under the idea that they are proprietary.

The latest designs for the Economic Simplified BWR carry this further with passive (AC Power Independent) design for safety systems.

See: http://www.nrc.gov/reactors/new-reactors/design-cert/esbwr.html .

 

[Rive]

And now you have re-invented the suppression chamber, haven't you?

Only if what he is thinking about is pressurized and within the containment.

If not, then it's called 'condensing tower' and used on some VVER reactors (instead of a full featured containment).

 

[westfield]

""" So an external emergency freshwater tank, a backup suppression chamber if you must, sounds like a very elegant solution to the issue, particularly in the case of drywell venting.

NPP engineers, is there any reason from an engineering point of view why that might not be be feasible or effective? On the face of it it does seem to be "cheap insurance" for this type of NPP. """


these things come to a practical limit.
it is always initial reaction to add something, seems natural enough to do that


some thoughtful deliberation necessary to figure out whether more would be gained from improving what's already there.

certainly the fresh water tanks could be moved up the hill so they'd be immune to flooding and feed by gravity,,,

and perhaps made bigger

then one should figure out whether that might relieve need for another layer of suppresion around existing suppression pool. that'd be a mighty big structure...

not shooting at your sugestion, just questioning where's most gain for effort expended.

every added complexity brings with it new failure mechanisms. Take Windows, for example...

Indeed complexity adds complexity.

However I believe the idea was presented by the OP as primarily a simple, passive, cost efficient, filtering method for the hardened vent system emissions rather than something that makes it a true "backup suppresion chamber" which certainly would add complexity as you point out.

Making it seem a more complex idea than that was my fault. I got carried away and was thinking of additional alternate uses for a mega tank of freshwater onsite apart from just scrubbing the vent emissions.

Its a giant tank of freshwater between the hardened vent system and the stack.
I'd best shut up and let the OP run with it ;)

 

[gnasch]

Venting to the athmosphere seems to pollute a max. How about putting the venting tube directly into the harbour, and make a 'door' for the harbour? On an other note, what is the sense of introducing all kinds of valves into the vent path when there is a rupture disc?

 

[jim hardy]

"Making it seem a more complex idea than that was my fault."

no fault ascribed... it's just that quiet contemplation is the way to figure out one's long term path.

it's the difference between firefighting and building in fire resistance.

i certainly don't know what to do.
seems like they might've used up all the heat storage capacity that their suppression pool had,,,

so as you suggest percolating the vent would clean it up considerably.
I was at fault for not realizing OP was suggesting a tank for cleanup not heat removal. Thanks for your kind and polite correction.

how could one stretch the ability of torus to handle heat so the hardened vent remains unnecessary??
I'd say flood the basement to submerge the whole darn thing but you'd have to fill torus completely lest it float...and move all equipment above high water mark.

old jim

 

[NUCENG]

Venting to the athmosphere seems to pollute a max. How about putting the venting tube directly into the harbour, and make a 'door' for the harbour? On an other note, what is the sense of introducing all kinds of valves into the vent path when there is a rupture disc?

The vent path is a direct path from the containment to atmosphere bypassing primary containment. After venting is complete valves reestablish containment. Class A containment isolation requires 2-valve protection. Rupture disk ensures that the containment has pressure that needs to be vented and allows isolation valve testing without defeating containment.

 

[gnasch]

Nuceng, thanks for your response. It seems Tepco had big problems using these 2 valves. How about making them fail open, would this assure that venting can take place even in station blackout and with operators unable to act?
In the course of the accident the sea seemed more resilient than the atmosphere in coping with all the fission products - that is why I thought about the harbour.

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20111018/index.html Tepco has made a probabilistic risk assessment of the present water injection system based on 7 scenarios. The highest risk is from the large tsunami scenario. Because it is located outdoors, the new system is 10 times more risky than the original cooling system that was available before the accident.

http://www.tepco.co.jp/cc/press/betu11_j/images/111017i.pdf Water injection system probabilistic risk assessment (Japanese only for now)

http://www.tepco.co.jp/cc/press/betu11_j/images/111017b.pdf A new Tepco document: Policy on the mid and long term security for the Units 1 to 4, part 1: Water injection equipments. On the diagrams on pages 1-37, 1-38, 1-39 (pdf pages number 42,43 and 44) one can see blue equipments marked with "lines to be started in the future". In particular on the diagram for unit 1 on page 1-37 (pdf page 42) some blue equipments read "to be started in the last decade of November". The red color items read "to be installed in the last decade of November" or "to be installed in the middle decade of December".

An English version of this attached document will be posted soon after we translate it.
http://www.tepco.co.jp/en/press/corp-com/release/11101711-e.html

 

[etudiant]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20111018/index.html Tepco has made a probabilistic risk assessment of the present water injection system based on 7 scenarios. The highest risk is from the large tsunami scenario. Because it is located outdoors, the new system is 10 times more risky than the original cooling system that was available before the accident.

http://www.tepco.co.jp/cc/press/betu11_j/images/111017i.pdf Water injection system probabilistic risk assessment (Japanese only)

http://www.tepco.co.jp/cc/press/betu11_j/images/111017b.pdf A new Tepco document. On the diagrams on pages 42,43 and 44 one can see blue equipments marked with "lines to be started in the future". In particular the diagram for unit 1 on page 42 reads "to be started in the last decade of November".

While it is surely true that the current jury rig system is at least 10x more vulnerable to a tsunami than the original installation, back to back tsunamis are absent from the historical record afaik. Should that not be factored in?

 

[Shinjukusam]

Tsutsuji, as always, I'm very thankful for your links.

Just a quick comment, for most English speakers a phrase like "the last decade of November" sounds very confusing, as decade usually implies a ten year span. Maybe it would be better to translate 下旬 as "last 1/3rd of the month"

Not meaning to nitpick, just thought I'd try and contribute. Really appreciate your work.

 

[tsutsuji]

Tsutsuji, as always, I'm very thankful for your links.

Just a quick comment, for most English speakers a phrase like "the last decade of November" sounds very confusing, as decade usually implies a ten year span. Maybe it would be better to translate 下旬 as "last 1/3rd of the month"

Not meaning to nitpick, just thought I'd try and contribute. Really appreciate your work.

http://ejje.weblio.jp/content/旬 has two Japanese-English dictionaries translating the word as "decade" : the Japan River society dictionary and the Japan Science and Technology Agency dictionary.

The 1913 Webster Dictionary http://machaut.uchicago.edu/?resource=Webster%27s&word=decade&use1913=on defines "decade" as "A group or division of ten; (...) as, a decade of years or days;"

"Temperatures warmed markedly during the final decade of December, and the year ended with much warmer than usual weather across the Country except for the central and northern Plains".

Dr. Richard E. Felch, climatologist
General summary of weather conditions, year 1973
Climatological data: National summary, Volume 24, No. 13, p.11
US National Atmospheric and Oceanic Administration
http://books.google.com/books?id=9i...ook_result&ct=result&resnum=1&ved=0CC0Q6AEwAA

So perhaps my English sounds as strange as a 1973 or 1974 US document. Or a 1995 British journal. If fits so well the Japanese word that I would like to keep this translation, even if it sounds a bit old fashioned or an outright archaism to some ears.

 

[NUCENG]

Nuceng, thanks for your response. It seems Tepco had big problems using these 2 valves. How about making them fail open, would this assure that venting can take place even in station blackout and with operators unable to act?
In the course of the accident the sea seemed more resilient than the atmosphere in coping with all the fission products - that is why I thought about the harbour.

My initial reaction is that I still want containment isolation valves to fail closed (Yes, that's the way we've always done it, but that is sometimes actually corrrect). Remember that the Fukushima scenario is only one of the possible events and accidents that must be mitigated. I would want to get detailed information from operators and examine the valves to figure out what went wrong and fix those problems. If the investigation demonstrates that the valves should fail open, then that should be done.

From memory, the hardened vent system valves are pretty big and, if I am correct, butterfly type valves. Depending on how they are oriented, and the delays in trying to initiate venting, the valves could have failed due to pressure locking, thermal binding, loss of power, or, if pneumatic, loss of pressure to the operators. Pressure Locking or Thermal Binding could explain why the operators had problems with manual operation. Or there could be other explanations.

I understand wanting to vent under water or through a filter, but either of those increase the differential pressure for the vent path and slows venting of pressure. That is not something that can simply be tacked on. The whole system would need to be resized to ensure sufficient flow rate.

Another point that we haven't discussed is that the current design vents from the stack - an elevated release point which causes a very large dispersion effect compared to the ground releases from containment failure. The difference in near field radiation levels can be as much as a factor 1000 to 10,000. Analysis assumptions for carcoal filtration systems have no effect on the release of noble gases, a factor of about 90 to 99.9 percent for other fission products and particulates. The filter holds the released products and the remainder would still get elevated release so the total reduction with a filter can be a factor of one million. Either of those scenarios is better that the loss of containment and ground release that happened in Japan.

I am watching this forum closely and discussing it with friendsa and colleagues in the nuclear industry. There are some good ideas here and a lot of good questions. If I had to point to a single reason that the internet is valuable, I would point to this forum. Unlike many of the cynics I am amazed at how much information has been made available so quickly. That is obvious compared to TMI and Chernobyl, but even things like the Air France Crash, the California Gas Pipeline Explosion, are available for examination and public comment. To the PF team and mentors and every poster and lurker. Thank you.

 

[Rive]

...

Tsutsuji, can you please check if there was any released information about cleaning up U4 top levels, or covering U4 SFP? All I can recall are just plans, but in http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/111017e6.pdf"document they have photos of the ongoing/finished works.

It would be interesting to see more related photos or vids about this.

While it is surely true that the current jury rig system is at least 10x more vulnerable to a tsunami than the original installation..

Well... I think it has just a very limited meaning. As I see the photos, the main unit doors are open now: any tsunami (high enough) would wash out all the turbine building and unit basements, so the whole site would be inaccessible, possibly for months.

 

[tonio]

In order to visualize things: a picture of a Fukushima vent in action.

 

[Astronuc]

In order to visualize things: a picture of a Fukushima vent in action.

The white plume that seems to start at the top of the stack and curves downward to the right (south) is the water being dropped from the helicopter, which was trying to get water into the spent fuel pools.

 

[tonio]

Suppose you're right. I already wondered what the black object above the stack was. Are there any photos of the vents in action?

 

[SteveElbows]

Suppose you're right. I already wondered what the black object above the stack was. Are there any photos of the vents in action?

The original TEPCO webcam seems to show venting on certain occasions.

Archive here:

http://gyldengrisgaard.dk/tepcowebcam/

The most obvious examples are a number of shots taken on March 13th:

http://gyldengrisgaard.dk/tepcowebcam/tepweb20110313.html

Ive also often wondered exactly what I am looking at on this shot from March 12th at 3pm. Is there any find of flammable gas flaring feature built into the stacks?

 

[tsutsuji]

Tsutsuji, can you please check if there was any released information about cleaning up U4 top levels, or covering U4 SFP? All I can recall are just plans, but in http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/111017e6.pdf"document they have photos of the ongoing/finished works.

It would be interesting to see more related photos or vids about this.

http://www.tepco.co.jp/cc/press/betu11_j/images/111017d.pdf is about the safety of the four spent fuel pools, and some pages are about unit 4, but it does not seem to address the covering issues of unit 4 or unit 3. I have not heard about the covering of unit 4 SFP since it was last discussed on https://www.physicsforums.com/showpost.php?p=3528287&postcount=11378 and https://www.physicsforums.com/showpost.php?p=3526548&postcount=11372 (september 27). The pictures of debris removal on the top of unit 3 and unit 4, including the "curing for spent fuel pool, oct 14" picture shown in http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/111017e6.pdf are new to me.

 

[SteveElbows]

I've been looking at the October update of TEPCO's roadmap. Before it was published it was mentioned in translated news on this thread that there would be an update of release estimates.

Pages 13-15 of the following roadmap document detail this stuff.

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/111017e3.pdf

There seem to be two main differences compared to the September roadmap. They have updated the source of the March 15th peak release rate estimate, it was previous the 31st NSC meeting report. They have now used the 63rd meeting NSC report instead. The main difference this makes to TEPCOs report is that the time period for the March 15th release peak is now said to be 1pm-5pm rather than 9am-3pm. But there appear to be a couple of errors in this section of the TEPCO document, such as sea area estimate being written as 0.07 Bq/hr in the text, but shown as 0.7 Bq/hr on the graphic, and a different error in Septembers version involving 8.0 x 10¹⁴ Bq/hr being written as 'Approx two quadrillion Bq/hr'. So Id rather look at the original source documents, especially as they contain more detail. More on that in a moment.

The 2nd difference is that they have updated the release estimates to include a recent period of October, which will form the new estimated current release rate. Its down from approx 0.2 billion Bq/hr in September to approx 0.1 billion Bq/hr in October. I cannot say that I am a big fan of how they have rounded these estimates though, it looks like there is a desire to show the emissions have halved in a month.

Here is the relevant September roadmap document for comparison with Octobers:

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110920e3.pdf

In September their calculation is described as follows:

The current release rate for both Unit 1 and 2 is estimated at approx. 0.04 billion Bq/h using dust concentration at the upper parts of the reactor buildings. The rate for Unit3 is now being re-estimated.
・ The current total release rate is estimated at approx. 0.13 billion Bq/h using dust concentration at the sea area, and there might be little effect of radioactive materials that released previously.
・ Therefore, the current total release rate is assessed at 0.2 billion Bq/h, which is 1/4,000,000 of that at the time of the accident.
・ The radiation exposure per year at the site boundaries is assessed at 0.4mSv/ year provisionally (excluding the effect of the radioactive materials already released up until now.)

And here is Octobers:

The current release rate for each Unit is estimated at, Unit 1: approx. 0.04 billion Bq/h, Unit 2: approx. 0.01 billion Bq/h and Unit 3: approx. 0.04 billion Bq/h, respectively, using dust concentration at the upper parts of the reactor buildings. The total release rate from Units 1 to 3 is estimated at approx. 0.08 billion Bq/h (Release rate for each Unit is rounded up.)
・ The current total release rate from Units 1 to 3 is estimated at approx. 0.07 billion Bq/h using dust concentration at the 2km offshore from the site, and there might be little effect of radioactive materials that released previously.
・ Therefore, the current total release rate from Units 1 to 3 is assessed at approx. 0.1 billion Bq/h at the maximum (provisional figure), which is 1/8,000,000 of that at the time of the accident.

The radiation exposure per year at the site boundaries is assessed at approx. 0.2 mSv / year provisionally (The target is 1 mSv / year, excluding the effect of the radioactive materials already released up until now.)

Specifically I am not keen on the rounding down of Octobers total, and then comparing that to the peak release and being able to say 'look its about 8 millionth of the peak release rate, last month it was 4 millionth'. Especially as the underlying data from above the reactors and in the sea has some vagueness attached to it (e.g. in September the reactor 3 emissions were being re-estimated). Mind you some of the data may be showing actual trends accurately, e.g. unit 2 estimated release rates are down from 0.04 billion Bq/hr in September to 0.01 billion Bq/hr in October. And we have possible explanations for such a trend, namely the reduction of various measured temperatures at reactor 2 due to increased water injection rates, and absence of steam in video of upper reactor building floor compared to the previous video.

Returning to the original source documents for the March release estimates, I looked at the document from the 31st NSC meeting in the past, as it contained the release estimates graph which I posted to these forums a number of times and so will not repeat again now.

Im not sure as I had looked at the 63rd meeting document before. Here it is, some kind of translation of any part of it would be most helpful. I believe that some of its conclusions have likely already been seen by us in some other documents, such as the last time that official release estimates were tweaked, but would still be keen to learn more about the methodology behind such estimates, and changes to them between 31st and 63rd meetings.

http://www.nsc.go.jp/anzen/shidai/genan2011/genan063/siryo5.pdf

 

[SteveElbows]

A document was given to the press in June, which included estimates of radioactive releases in the 1st 100 hours of the crisis.

On page 13 a table is given with the following header:

解析で対象とした期間での大気中への放射性物質の放出量の試算値

"Estimated amount of radioactive material released into the atmosphere over the time period covered by the analysis" {google translate}

It shows 1.2254x10^12 becquerels of Plutonium 238, 239, 240, 241 combined, 99% of which was Pu-241

This document is available in English, and has come up before since it is one of the main publications with detail of both TEPCO and government agency estimates of reactor 2 & 3 core damage and associated consequences.

http://www.nisa.meti.go.jp/english/press/2011/06/en20110615-5.pdf

The table you refer to has long been of interest to me because I've always been interested in the reasons why this sort of data seems to show reactor 2 being responsible for a large chunk of the total. As part of this I have sometimes wondered whether such estimates included water, considering reactor 2 building survived and this reactors highly-radioactive water made headlines when first discovered. But most March release estimate data seems to involve methods that use data such as radiation levels at site boundaries, and levels detected on land at a variety of locations, which tends to suggest to me that at last some of the numbers we see are for 'air only'. But other grand totals, such as the ones I've just been going on about in my previous post, also add on water estimates. Its been quite hard for me to form highly detailed conclusions about some estimates though, sometimes down to translation issues or sparse/ambiguous use of language, but also because stuff such as MELCOR analysis of what may have happened is involved, and I don't actually know the full detail of how this model works.

I doubt it contains the full answers to the questions you have asked, but for some additional talk about this kind of release estimate data, you may also find the thread about Unit 2 of some use, especially since it is not very long so its not hard to pick out the posts that discuss this sort of data:

https://www.physicsforums.com/showthread.php?t=507252

 

[tonio]

Ive also often wondered exactly what I am looking at on this shot from March 12th at 3pm. Is there any find of flammable gas flaring feature built into the stacks?

I understand what you mean. See the added details of photos. In the left photo, a steam plume seems to come from the top of the stack. In the other photo (from the quoted message), a steam-like plume emerges from a lower level and changes from whitish to faint black (soot?).

 

[tonio]

forgot the photo.

 

[LabratSR]

At the bottom of page 10 they state they covered the Unit 4 SFP on Oct 14

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/111017e3.pdf

 

[Astronuc]

. . . . Its been quite hard for me to form highly detailed conclusions about some estimates though, sometimes down to translation issues or sparse/ambiguous use of language, but also because stuff such as MELCOR analysis of what may have happened is involved, and I don't actually know the full detail of how this model works.

I doubt it contains the full answers to the questions you have asked, but for some additional talk about this kind of release estimate data, you may also find the thread about Unit 2 of some use, especially since it is not very long so its not hard to pick out the posts that discuss this sort of data

An analysis is only as good as the input. If one assumes no cooling whatsoever (i.e., purely adiabatic condition), then certainly core melting is only a matter of time. Only by knowing the exact cooling history can a reasonable analysis be performed.

Otherwise, one has to wait to see what the core looks like, then perform parametric studies with cooling time histories in an attempt to match predictions with results.

This might be of help - MELCOR Application of Selected Design Basis Accident Analyses.
Accession Number: ML111570055
Date Released: Thursday, June 9, 2011

http://pbadupws.nrc.gov/docs/ML1115/ML111570055.html - Enclosure 1 & 2 contain the details.

 

[westfield]

I understand what you mean. See the added details of photos. In the left photo, a steam plume seems to come from the top of the stack. In the other photo (from the quoted message), a steam-like plume emerges from a lower level and changes from whitish to faint black (soot?).

I have no idea about the colour of the emissions but it's two different stacks, one almost obscured by the other.

There is a stack each for Units 1 & 2, 3 & 4, 5 & 6, and the radwaste treatment building stack.

4 stacks all up at F1.

edit : At a glance the "lower down" emissions may be from the Units 1 & 2 shared stack, with units 3 & 4 stack obscuring it.

The documents intimate that the majority of the emergency venting from Unit #2 came from the drywell hardened vent which may or may not have something to do with the colour of the plume. ( I.e. completely unfiltered from the drywell hardened vent vs somewhat scrubbed if done via wetwell\S\C direct venting)

 

[westfield]

Tsutsuji, can you please check if there was any released information about cleaning up U4 top levels, or covering U4 SFP? <snip>

It would be interesting to see more related photos or vids about this.


<snip> .

Yes it would be interesting to see more of the work at Units 3 & 4. It would be even better if they moved the webcam over there now that Unit 1 RB is fully "tented". But I would understand if we don't get to see much. I'm not sure TEPCO would want to show us exactly how they have been tackling the debris cleanup near units 3 & 4. Debris which was mapped as significantly contaminated to highly contaminated in spots.

They have been extremely busy around units 3 & 4.

Actions like ripping open the large ducting between Units 2 & 3 leading to the common radwaste treatment building in order to get crane access and sorting and crushing concrete and steel as if it's being prepared for recycling on a conventional demolition site like here right next to RB 3 makes me wonder if TEPCO are doing a "rush job" on the debris without what would be considered "best practice", understandable I guess if that's the case, but not something good for the public's eyes.

http://i1185.photobucket.com/albums/z360/fukuwest/misc/demolitionexample01f1.jpg

http://i1185.photobucket.com/albums/z360/fukuwest/misc/110825_1_crop_removedpiping.jpg

Does anyone here work on Superfund sites or similar that may care to comment on the cleanup methods being deployed at F1?

 

[MadderDoc]

<..>At a glance the "lower down" emissions may be from the Units 1 & 2 shared stack, with units 3 & 4 stack obscuring it.

Indeed the plume seen in the webcam from 15:00 on March 12th is most likely from the 1+2 shared stack. This emission event appears to have been captured also in a video taken from a helicopter overfly in the afternoon on March 12th, here's a frame from that video.

Also, Tepco has reported that on March 12th at 14:00 a makeshift air compressor was installed such that the unit 1 AO valve for S/C venting could now be operated, and an hour later, that emission of radioactivity from the S/C vent was ongoing. Pressure data too indicate that the S/C and D/W pressure decreased over that period, from about 0.75 MPa to 0.5 MPa.

 

[Rive]

...Actions like ripping open the large ducting between Units 2 & 3 leading to the common radwaste treatment building in order to get crane access and sorting and crushing concrete and steel as if it's being prepared for recycling on a conventional demolition site like here right next to RB 3 makes me wonder if TEPCO are doing a "rush job" on the debris without what would be considered "best practice", understandable I guess if that's the case, but not something good for the public's eyes.

The 'rush job' is correct, but while they are just collecting the debris and deploy it in an on-site storage area, IMHO it's OK. I think they will try to cover U3 and U4 before the end of the year, and to remove all that debris from the top levels of the units will take some time.

I don't think that any of this part is 'non public'. In fact, it's a kind of victory. I can't understand why is it not presented with more publicity.

http://www.tepco.co.jp/cc/press/betu11_j/images/111017d.pdf is about the safety of the four spent fuel pools, and some pages are about unit 4, but it does not seem to address the covering issues of unit 4 or unit 3. I have not heard about the covering of unit 4 SFP since it was last discussed on https://www.physicsforums.com/showpost.php?p=3528287&postcount=11378 and https://www.physicsforums.com/showpost.php?p=3526548&postcount=11372 (september 27). The pictures of debris removal on the top of unit 3 and unit 4, including the "curing for spent fuel pool, oct 14" picture shown in http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/111017e6.pdf are new to me.

Very thanks. So it's just another 'we just did it, you don't have to know much about it' thing :(

---------------------------------------------------

What 'soundness' could be originally?
http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111019_01-e.pdf

 

[SteveElbows]

The documents intimate that the majority of the emergency venting from Unit #2 came from the drywell hardened vent which may or may not have something to do with the colour of the plume. ( I.e. completely unfiltered from the drywell hardened vent vs somewhat scrubbed if done via wetwell\S\C direct venting)

Given that reactor 1 building suffered an explosion about half an hour after the webcam image was taken, I was tentatively working on the basis that it was reactor 1 venting seen in the image. And so I was wondering if hydrogen was coming out of the stack during the period leading up to the explosion.