Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[~kujala~]

The trouble with general terms like 'sandstone' and 'mudstone' is that they tell you approximately nothing about the strength and probably nothing about the permeability of the rock.

As far as I understand the velocity of the S-waves are dependent on the strength of the rock ie the harder the rock the faster the S-waves. Faster is better.

So as we know that S-wave velocity in two different earthquakes has been around 520 m/s in Fukushima I think we can make some assumptions based on that. Or can we?
http://varasto.kerrostalo.huone.net/lietekivi_4.png

This would be quite normal S-wave velocity for mudstones/sandstones when compared to those in San Fransisco:
http://varasto.kerrostalo.huone.net/lietekivi_2.png

Actually it's a little on the slow side because the borders are 350 m/s - 750 m/s so in the middle it would be 550 m/s and it's 520 m/s. But I suppose this is something to be expected because we also know that sandstone/siltstone in Fukushima is young (Quaternary).

On the other hand the soil amplification for class C in the above chart is considered not to be as significant as for classes D/E. But it's not the same as for classes A/B where no significant soil amplification is considered.

Some other hints might be found from these drawings - according to Astronuc the numbers in the first one might be pressure gradients. What about the velocities in the second one? Could they be P-wave velocities (1,600 m/s - 1,700 m/s for mudstone):
http://varasto.kerrostalo.huone.net/lietekivi_5.png
http://varasto.kerrostalo.huone.net/lietekivi_6.png

 

[zapperzero]

Could they be P-wave velocities (1,600 m/s - 1,700 m/s for mudstone):
http://varasto.kerrostalo.huone.net/lietekivi_5.png
http://varasto.kerrostalo.huone.net/lietekivi_6.png

So it seems.

 

[Borek]

All 4 videos are now hosted on my site

Are you sure they are properly described?

 

[desertlabs]

Could it be that the white spots are neutron reflectors and the black spots neutron absorbers creating a moderating field for recriticality?!

Yes! It must have been a borderline collie!
Apologies for the physics humor. ;)

Thanks so much for the humour...I needed the comic relief!

 

[desertlabs]

Have a look at the following videos. I'll drop this topic very shortly, but I do want some kind of corroboration, given that this board's topic is: Physics Forums > Engineering > Nuclear Engineering > Japan Earthquake: nuclear plants.

This was not

- a false alarm
- one of the many false alarms
- one of the many frequent steam displays

It was a *massive* and significant steam/vapour display that started with a clearly visible vertical emission of vapour, then blotted out all the other reactors - starting around 2:15 in the first video below. Also look at the 10 second mark in the second video. They look very much like explosions to me:

Here's the video:
2011.06.14 00:00-01:00 / 福島原発ライブカメラ (Live Fukushima Nuclear Plant Cam)
http://www.youtube.com/fuku1live#p/u/9/k-EDceWFovc

2011.06.14 01:00-02:00 / 福島原発ライブカメラ (Live Fukushima Nuclear Plant Cam)
http://www.youtube.com/fuku1live#p/u/8/fg8yGBhoLxU

Not an expert, however, just because the dew-point may enable better visualization of the "steam" does that mean the ongoing release is not "important"?

 

[quark42]

Not an expert, however, just because the dew-point may enable better visualization of the "steam" does that mean the ongoing release is not "important"?

No, it doesn't necessarily mean the releases aren't important. It just means there probably isn't as drastic a change in the amount being released as some interpretations of the visible vapors have suggested (as seen in the videos being discussed above).

I'd also like to see some measurements taken from within the releases (as others have mentioned).

 

[Orcas George]

Tepco plans to create the first nuclear powered Zeppelin:

http://www3.nhk.or.jp/daily/english/15_07.html

The operator of the Fukushima Daiichi nuclear plant will begin to cover the No.1 reactor building with polyester sheets this month to prevent the dispersal of radioactive substances.

The buildings of the No.1, 3, and 4 reactors were severely damaged by explosions and radioactive elements are still being released into the atmosphere. There are fears that heavy rain may hamper the workers' activities and that the rainwater may become contaminated with radioactive materials.

To prevent these situations, Tokyo Electric Power Company, or TEPCO, plans to enclose the reactor buildings with polyester sheets. The covering of the No.1 reactor building will begin later this month.

I hope that this plan makes more sense than it seems to. If the purpose is to contain the gasses and they do in fact make a leakproof covering, they will have created a Zeppelin. If hydrogen is still being produced, they will have made the Hindenberg.

Of course, if they vent the gasses to keep this from happening, then what was the point of exposing all of those workers?

All of this is aside from the fact that 1mm thick polyester is not going to survive a good gale, let alone a typhoon. I have some experience with this, having had a large expensive product shipped from China nicely wrapped in heavy-duty heat shrink poly. The captain of the container ship said that the covering barely made it out of the harbor before being ripped to shreds.

I think that the upshot of this exercise is that Tepco is now going to have to figure out how to dispose of hundreds of meters of shredded, highly contaminated polyester. This will not be easy, to say the least.

Edit: Oh by the way, that stuff floats...

 

[NUCENG]

Tepco plans to create the first nuclear powered Zeppelin:

http://www3.nhk.or.jp/daily/english/15_07.html


I hope that this plan makes more sense than it seems to. If the purpose is to contain the gasses and they do in fact make a leakproof covering, they will have created a Zeppelin. If hydrogen is still being produced, they will have made the Hindenberg.

Of course, if they vent the gasses to keep this from happening, then what was the point of exposing all of those workers?

All of this is aside from the fact that 1mm thick polyester is not going to survive a good gale, let alone a typhoon. I have some experience with this, having had a large expensive product shipped from China nicely wrapped in heavy-duty heat shrink poly. The captain of the container ship said that the covering barely made it out of the harbor before being ripped to shreds.

I think that the upshot of this exercise is that Tepco is now going to have to figure out how to dispose of hundreds of meters of shredded, highly contaminated polyester. This will not be easy, to say the least.

Edit: Oh by the way, that stuff floats...

Might they possibly include hydrogen recombiners and filtered venting? I don't know but that might help!

 

[etudiant]

Tepco plans to create the first nuclear powered Zeppelin:

http://www3.nhk.or.jp/daily/english/15_07.html I hope that this plan makes more sense than it seems to. If the purpose is to contain the gasses and they do in fact make a leakproof covering, they will have created a Zeppelin. If hydrogen is still being produced, they will have made the Hindenberg.

Of course, if they vent the gasses to keep this from happening, then what was the point of exposing all of those workers?

All of this is aside from the fact that 1mm thick polyester is not going to survive a good gale, let alone a typhoon. I have some experience with this, having had a large expensive product shipped from China nicely wrapped in heavy-duty heat shrink poly. The captain of the container ship said that the covering barely made it out of the harbor before being ripped to shreds.

I think that the upshot of this exercise is that Tepco is now going to have to figure out how to dispose of hundreds of meters of shredded, highly contaminated polyester. This will not be easy, to say the least.

Edit: Oh by the way, that stuff floats...

Are there not several stadiums and even Denver Airport covered with some sort of fabric?
I assume this is not shrinkwrap that they plan on using.

In general, surely it is better to keep the dirt collected and try to deal with it immediately than to allow it to waft all over and then to try to clean some of it up as is the case presently.

 

[etudiant]

Edit:
Just read the NHK writeup with the 1 mm poly detail in the story.
That does seem quite inadequate, especially as this is a flat structure, the wind pressure on it will be material.

Apparently this is a temporary initial version which is supposed to be replaced in the longer term by a more robust enclosure to shelter the eventual dismantling of the reactor building.

 

[joewein]

All of this is aside from the fact that 1mm thick polyester is not going to survive a good gale, let alone a typhoon. I have some experience with this, having had a large expensive product shipped from China nicely wrapped in heavy-duty heat shrink poly. The captain of the container ship said that the covering barely made it out of the harbor before being ripped to shreds.

I think that the upshot of this exercise is that Tepco is now going to have to figure out how to dispose of hundreds of meters of shredded, highly contaminated polyester.

No, that really won't be a problem, because:

TEPCO aims to complete the covering operation in late September

...which is the usual time of the year the typhoon season ends in Japan.

But seriously, a lot of commercial greenhouses here in Japan use plastic sheets over a metal frame, instead of glass sheets. It does seem to work for the local climate. I wouldn't totally dismiss it as being unsuitable because of wind. It really depends on how it's done.

 

[joewein]

Now 15 days without update.

Since the figures seem to already have dropped by about 4 orders of a magnitude during the published interval, we should consider the possibility that figures since the end of updates have been below detection level:

[PLAIN]http://www.bfs.de/de/ion/imis/spurenmessstellen_caesium.jpg

The data published since May 10 has only been sampled weekly.

I am expecting the pattern of I-131 spikes to continue into June.

It's been 95 days since the reactors were scrammed on March 11. That's almost 12 half lives for I-131. All but 1/4096 of it should have decayed by now. Cesium is another matter of course.

EDIT: Yes, it looks like worldwide samples (except in Japan) are falling below detection thresholds (shaded in gray at the bottom):

Iodine-131:
[PLAIN]http://www.bfs.de/de/ion/imis/ctbto_aktivitaetskonzentrationen_jod.gif

Cesium-137:
[PLAIN]http://www.bfs.de/de/ion/imis/ctbto_aktivitaetskonzentrationen_caesium.gif

The dashed orange lines are German maximum daily averages after the Chernobyl disaster.

 

[etudiant]

Initial test runs using low level contaminated water showed the Kurion cesium removal process did cut the cesium level in the treated water to 1/3000th of the initial value, in the middle of the predicted performance range.
The NHK report is here: http://www3.nhk.or.jp/daily/english/14_37.html
Note that the full train including the Areva coprecipitation and desalination treatment has not yet been run, nor is there any data on flow rates or test duration for this test.
These kind of columns can be somewhat sensitive to channeling, which would reduce efficiency.
So the performance needs to be monitored on an ongoing basis.

 

[etudiant]

No, that really won't be a problem, because:



...which is the usual time of the year the typhoon season ends in Japan.

But seriously, a lot of commercial greenhouses here in Japan use plastic sheets over a metal frame, instead of glass sheets. It does seem to work for the local climate. I wouldn't totally dismiss it as being unsuitable because of wind. It really depends on how it's done.

There is a big difference between a greenhouse, usually a smooth wind cheating structure close to the ground
and this square sided tower. Ask any sailor what the stress on a sail maybe 100 feet high and equally wide will be.

 

[Azby]

The trouble with general terms like 'sandstone' and 'mudstone' is that they tell you approximately nothing about the strength and probably nothing about the permeability of the rock.

Sandstone is any sedimentary rock composed of sand grains; mudstone is a sedimentary rock made of much finer particles; siltstone is a sedimentary rock made of particles finer than sand but coarser than mud.

Sandstone may be very weak, crumbling in your hand, if the matrix that holds the sand grains together is weak. At the other extreme a metaquartzite is a rock made of grains of quartz sand cemented together by quartz that has crystallised in conditions of relatively high temperatures and pressures. It's harder and stronger than granite.

In the Fukushima case we seem to be dealing with something not so extreme. It is probably safe to assume that the sandstones and siltstones at the site are quite adequate to build power plants upon (the area of alluvium to the north and to the south has been avoided) and that for most practical purposes the siltstones can be regarded as impermeable to the flow of water while the sandstones will allow the passage of water albeit it at very slow rates. There is likely to be a net flow of water through the rock towards the sea, pressured by rainwater descending from the higher ground inland. Over a period of years one might expect contaminated water to move down and out and released to the Pacific Ocean.

There may be other pathways, joints and bedding planes, even cracks caused by earthquakes, that allow faster flow in complex directions but one needs more site-specific data to judge that.

I just got another email from the geologist concerning groundwater flow:

"The ground water generally flow from elevated part of the aquifer to the structual low of the aquifer. In the plain, it is usually from the mountain (catchment area of the rain) to the sea, unless the flow makes a short-cut to a nearby river/stream or lake. As the cross-section of the aquifer in the paper you showed me showed that they are inclined to the sea, it is likely that the overall flow is from the land to sea, even though it might locally flow to different directions (i.e., landwards), notably from the source of the contamination for a few km. But in a general rule, aquifers located far landward of the nuke plant is safer.

It is ironic that scientists/engineers use radioactive source called Tracer to check the underground movement of water within aquifer - after a few months, the movement of the Tracer is checked in nearby wells, rivers, seas, surface reservoir (ponds/lakes). This is the most powerful and reliable way to determine the flow pattern of an aquifer in a given region (other way is to measure pressure gradient within the area, but it is less reliable). Tracer usually exhibits a negligible amount of radioacitvity and is harmless to health, but, this time, gigantic amount of "tracer" has been injected within the hydrologic system in both surface and underground waters. So the best way to check the movement of the ground water is simply to measure radioactivity of waters from the wells/streams/ponds, etc. around the nuke plant."

 

[biffvernon]

Actually it's a little on the slow side because the borders are 350 m/s - 750 m/s so in the middle it would be 550 m/s and it's 520 m/s. But I suppose this is something to be expected because we also know that sandstone/siltstone in Fukushima is young (Quaternary).

Correct me if I'm wrong, but I think the Quarternary deposits are to the north and to the south of the plant. The sandstones and siltstone below the plant are much older (and stronger).

How a rock behaves in an earthquake is very complicated and how a building sitting on top behaves is even more so. A hard rock will transmit the earthquakes energy quickly with high frequency small amplitude movements. You get high acceleration but small linear movement. A soft rock will move more slowly but further and that is often more damaging to a building, particularly when it sways in resonance.

Here's an analogy. Take three coins placed on a smooth table. Hold one down firmly with a finger, place the second touching the first. Flick the third into the held down coin hitting it on the side opposite the second coin. The held down coin will not move but the second coin will shoot off across the table.

The held down coin is like the hard rock, transmitting the shockwave without visibly moving. The second coin is like the soft rock, it experiences a large magnitude acceleration. Don't build your nuclear power plant on the second coin.

 

[~kujala~]

Correct me if I'm wrong, but I think the Quarternary deposits are to the north and to the south of the plant. The sandstones and siltstone below the plant are much older (and stronger).

I don't know. I tried to find geological maps for Daiichi area and I found maps quite near the plant but that's not enough. If I remember correctly in some earlier discussions some maps were also presented. You never find anything when you really want to...

Could you show your source for the above claim so we could all see it?

 

[westfield]

Tepco plans to create the first nuclear powered Zeppelin:

http://www3.nhk.or.jp/daily/english/15_07.html


I hope that this plan makes more sense than it seems to. If the purpose is to contain the gasses and they do in fact make a leakproof covering, they will have created a Zeppelin. If hydrogen is still being produced, they will have made the Hindenberg.

..

The plan makes perfect sense if we regard it as simply TEPCO attempting to hide what is going on. I won't be surprised if TEPCO "discover" that hydrogen is lighter than air and "unfortunately" they will have to allow venting from their "greenhouse", but still not allow us to peek in there.

 

[biffvernon]

Could you show your source for the above claim so we could all see it?

LOL There was a map posted here several pages ago! The anonymous professor gave the name of the Sandstone/siltstone formation. This is the 'bedrock' that the power plants are built on. The Quarternary deposits cover this bedrock just north and south of the site. The builders were not completely daft!

See post 9753:
" it has been long known that around the Fukushima Daiichi Plant is sedimentary rock Taga Group; around the plant this rock is called the Tomioka Formation, whch is made of coarse sandstone (or Grit) and tuffaceous siltstone."

 

[westfield]

The number of posts here regarding the non-events observed while glued to the Fukushima Webcam Entertainment Network is getting annoying.

I would second a motion to create a photo interpretation thread, or the renaming of the Unit 3 explosion thread to become general photo interpretaion.

It has it's place but it takes up lots of forum inches. If this is anything like the Macondo deal then the discussions will go on long after the cameras have stopped rolling.

 

[biffvernon]

Oh dear, I've just found a paper about the geology written in English:https://ir.kochi-u.ac.jp/dspace/bitstream/10126/2261/1/N022-04.pdf

The Taga Group and its Tomioka Formation are indeed Quarternary - Late Miocene/Early Pliocene. Much younger than I had assumed and so likely to be much softer and more wobbly in an earthquake. Deary me.

 

[Azby]

Oh dear, I've just found a paper about the geology written in English:


https://ir.kochi-u.ac.jp/dspace/bitstream/10126/2261/1/N022-04.pdf

The Taga Group and its Tomioka Formation are indeed Quarternary - Late Miocene/Early Pliocene. Much younger than I had assumed and so likely to be much softer and more wobbly in an earthquake. Deary me.

Great find! I've passed it on for comment. It's from 1973 it seems, not long in geologic time for sure but maybe the region is better understood now.

 

[SteveElbows]

OK so we now have some results from air sampling above reactor 3, like we previously got for 1 & 4.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110614_03-e.pdf

As withthe previous tests, I am not sure whether their methods are very good for doing a decent estimate. And I've no idea how to convert the numbers shown into something a bit more useful, such as estimated release rate.

 

[MiceAndMen]

I would second a motion to create a photo interpretation thread, or the renaming of the Unit 3 explosion thread to become general photo interpretaion.

It has it's place but it takes up lots of forum inches. If this is anything like the Macondo deal then the discussions will go on long after the cameras have stopped rolling.

Thank you for exactly reading between the lines. A separate thread is called for IMO. I have all but stopped following this thread; I see 3, 4, 5 posts in a row regarding the webcam and I just "page down, page down, page down ... next page". Very bad for the signal to noise ratio. Can anyone point out ONE post mentioning any of the webcams post-unit-3-explosion that was newsworthy? Explosion here, vapors there, steam and smoke over there, but hyperventilating viewers everywhere.

TV viewers like to think they are seeing things that are worthwhile. Entertainment, news, current events, paparazzi, bread and circuses... it's all the same. Worthless speculation ensues. News at 11.

 

[Borek]

Feel free to start a new thread, you don't need Admin privileges to do so

 

[~kujala~]

See post 9753:
" it has been long known that around the Fukushima Daiichi Plant is sedimentary rock Taga Group; around the plant this rock is called the Tomioka Formation, whch is made of coarse sandstone (or Grit) and tuffaceous siltstone."

Yes, but the professor is also saying:

I have talked with some of my colleagues (geology professors) today, and some of them knew for many years/decades that the bed rock of the Fukushima Daiichi Nuke Power Plant is soft sedimentary rock.

Why would he (they) be worried about geological issues if it would only concern some areas outside the plant area? It makes no sense.

I think it is this very mixture of siltstone/sandstone that they think is "soft". And I think it is also this "soft" siltstone/sandstone that they believe is below the Daiichi plant.

I also noticed that in the first sentence he is using the word "around" which might be some kind of translation issue. Or perhaps he means that the geological structure outside the plant area is known for sure and inside the plant area only TEPCO knows it absolutely sure?

BTW, I am referring to discussions about 1 - 2 months ago. I remember that some documents were presented that contained detailed geological information. But I don't remember what the conclusion was back then.

 

[biffvernon]

Oh dear, I've just found a paper about the geology written in English:


https://ir.kochi-u.ac.jp/dspace/bitstream/10126/2261/1/N022-04.pdf

The Taga Group and its Tomioka Formation are indeed Quarternary - Late Miocene/Early Pliocene. Much younger than I had assumed and so likely to be much softer and more wobbly in an earthquake. Deary me.

That should have read Tertiary rather than Quaternary (but it doesn't change the argument very much).

The basement rock of granite type material starts about 800 meters below the power plant and is overlain by the Tomioka Formation of Late Miocene/Early Pliocene sedimentary rocks upon which the the plant is built.

This paper: Granitoids with 300 Ma in the Joban coastal region, east of Abukuma Plateau, northeast Japan. Journal of Mineralogical and Petrological Sciences Vol. 105 (2010) , No. 6 December 320-327 Yukiyasu TSUTSUMI et al.

http://www.jstage.jst.go.jp/article/jmps/105/6/105_320/_article

describes a deep borehole into the basement from a site pretty close to Fukushima Daiichi. It also has a map that shows a couple of big lines marked Futaba Shear Zone and Hatakawa Shear Zone.

Now will somebody please tell me that these do not represent any kind of earthquake hazard.

 

[~kujala~]

Oh dear, I've just found a paper about the geology written in English:

https://ir.kochi-u.ac.jp/dspace/bitstream/10126/2261/1/N022-04.pdf

The Taga Group and its Tomioka Formation are indeed Quarternary - Late Miocene/Early Pliocene. Much younger than I had assumed and so likely to be much softer and more wobbly in an earthquake. Deary me.

Yes, I also found this paper (and couple of others) but...
If you look carefully the map (figure 3) on page 106, the area of the study only goes as far as Yamadahama in the north.
Both Fukushima I and II NPP:s are both further away to north. So the proof is still not absolute.
Also in the figure 1 on page 104 it is said that Taga group goes as far as Tomioka but Fukushima I is still not covered.

But if the professor says Taga group also covers Fukushima I perhaps we should believe him?

http://www.boston.com/news/world/asia/fukushima_nuclear_plant/
The pin A is near Tomioka. It's Daini.
The pin B is located further away to north. It's Daiichi. It's located near Futaba.

 

[biffvernon]

Why would he (they) be worried about geological issues if it would only concern some areas outside the plant area? It makes no sense.

Right, to summarise, I think what we now know is that we have some soft, Quaternary, deposits, maybe fluvial or marine alluvium, to the north and south of the site. That would not be sensible to build anything very heavy upon.

The plant itself is built on the Tertiary Sandstone/siltston/mudstone complex known as the Tomioka Formation. It's perhaps not ideal but was judged strong enough to support heavy buildings.

800 metres below is the granitic basement. This outcrops at the surface a few kilometres inland.

That granitic basement has a couple of major shear zones trending NNW-SSE a few km west of the plant.

And to speculate, rather than what we know, if those shear zones are potentially active (and the fact that there has not been a major earthquake on them for 400 years does not mean they aren't potentially active) then building a nuke on Tertiary sediments a few km away might be judged, generously, as hoping for the best.

 

[~kujala~]

describes a deep borehole into the basement from a site pretty close to Fukushima Daiichi. It also has a map that shows a couple of big lines marked Futaba Shear Zone and Hatakawa Shear Zone.

Now will somebody please tell me that these do not represent any kind of earthquake hazard.

I guess it was these fault lines that the professor described:

So people thought the region is relatively safer in terms of bed rocks and fault systems. But after the 3-11 earthquake, many "inactive" fault systems moved, causing some problems such as landslides or forming sink holes. Some of these faults CUT through these hard rocks, which people, including many geologists, thought quite unusual (if not impossible) utill they saw the consequence of the 3-11 Earthquake in Tohoku.

... and there are a few active faults around*the plant*(they have been recently*found to be active after the 3-11 Earthquake)

I don't know how much harm they could cause for Daiichi, though.

 

[biffvernon]

Yes, I also found this paper (and couple of others) but...
If you look carefully the map (figure 3) on page 106, the area of the study only goes as far as Yamadahama in the north.
Both Fukushima I and II NPP:s are both further away to north. So the proof is still not absolute.
Also in the figure 1 on page 104 it is said that Taga group goes as far as Tomioka but Fukushima I is still not covered.

But if the professor says Taga group also covers Fukushima I perhaps we should believe him?

http://www.boston.com/news/world/asia/fukushima_nuclear_plant/
The pin A is near Tomioka. It's Daini.
The pin B is located further away to north. It's Daiichi. It's located near Futaba.

Yes, you're right.

 

[MadderDoc]

<..>Can anyone point out ONE post mentioning any of the webcams post-unit-3-explosion that was newsworthy? <..>

To be newsworthy in the common sense of that word, I reckon such webcams would have to show something like explosions, fires, or at the very least some dramatic evolution of smoke or steam. I think I have mentioned in some of my posts the 7am webcam from March 15th (explosion in unit 4), and the webcams from March 21st and March 24th (dramatic smoke events at unit 3). They were all, I think, newsworthy.

However, 'newsworthy' is hardly a criterium for what can be mentioned in this thread. In fact preciously little of what is being mentioned here would have the interest of the general public.

 

[swl]

The plan makes perfect sense if we regard it as simply TEPCO attempting to hide what is going on. I won't be surprised if TEPCO "discover" that hydrogen is lighter than air and "unfortunately" they will have to allow venting from their "greenhouse", but still not allow us to peek in there.

Indeed. Otherwise, why would they be saying on one hand that they need to open the doors to lower the internal radiation levels for workers, while on the other hand they are saying they need to build a tent to contain the contamination within the work area.

In Japan, blue vinyl sheets are often used by the police to hide crime scenes from cameras.

 

[NUCENG]

Indeed. Otherwise, why would they be saying on one hand that they need to open the doors to lower the internal radiation levels for workers, while on the other hand they are saying they need to build a tent to contain the contamination within the work area.

In Japan, blue vinyl sheets are often used by the police to hide crime scenes from cameras.

I guess I have to say it again. If you contain the buildings, it allows you to filter the venting instead of letting it drift down wind. That is justification enough. As to hiding what is going on iside a containment "tent," don't you think by now that we already know something bad happened there? If offsite dose rates decline or increase isn't that good enough to tell whether their efforts are working?

Other than speculation about steam and fog and light flashes what has anybody seen while there is no tent? One big gain of installing a tent might be to let all of the looky loos sitting staring at the live webcam to get back to their lives.

 

[MadderDoc]

Interesting video filmed on June 9 (during sampling and radiation measurement) in Unit 3 (53MB zip, unzips with no problems):
http://www.tepco.co.jp/en/news/110311/images/110615_01.zip