Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[biffvernon]

Note that the map is dated 8th April. Up until then the wind had been almost totally out to sea. On Sunday last and Tuesday 19th when it rained, the wind was from the east, blowing the plume inland. They have been very lucky with the westerly winds so far. If the power-station is still leaking into the air as we move into the typhoon season those numbers could get much higher.

 

[Jorge Stolfi]

I was just referring to the fact there is no flash point for hydrogen peroxide. I know it is a dangerous stuff.

Biological control should not require large quantities of H2O2 of KMnO4. The typical dose (e.g. for sanitizing vegetables) is a few drops per gallon. A few tens of kg should be enough for years.

 

[Rive]

Note that the map is dated 8th April. Up until then the wind had been almost totally out to sea. On Sunday last and Tuesday 19th when it rained, the wind was from the east, blowing the plume inland. They have been very lucky with the westerly winds so far. If the power-station is still leaking into the air as we move into the typhoon season those numbers could get much higher.

The actual aerial release rate is not high enough to cause any radical change on that map.

The sea and the groundwater is a different story, of course.

 

[Caniche]

Why is Speedi not giving any info when it costs 12.8 million yen pa ; why is Rimnet not communicating; why has Radnet crashed? For Speedi ,2 published forecasts out of 2000 produced, since 11/3 seems a poor return . I'm sure there is a perfectly acceptable explanation(- :

 

[biffvernon]

The actual aerial release rate is not high enough to cause any radical change on that map.

The sea and the groundwater is a different story, of course.

Hmm... It's not sea or groundwater that produced the map pattern but stuff blown on the wind on the very few days that the wind has blown onshore. That map may need revision when the wind changes.

 

[jlduh]

new data from Tepco website on underground water contamination:

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110419e11.pdf

and pdf with time curves for all reactors samples:

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110419e12.pdf

 

[Dmytry]

Just because you have Cs and I in the water, it does not mean that they will stick together as CsI. Each ion (Cs⁺ and I^-) will go is way and interact with all the other crud in the pool.
Fresh seawater is slightly alkaline, but boric acid was added to it. It is a weak acid, but presumably enough to allow the much smaller amount of iodide to form HI and leave with the steam.

However it seems that iodide in water easily reacts with oxygen to form neutral iodine I2, which is volatile too. The pH does not seem to matter in this case.

On the other hand cesium has no volatile compounds that I know of, so it can only leave the liquid carried by droplets, as you say --- which will only form if the water if boiling or blasted away.

In summary, if hot water containing Cs and I is kept in an open container (like the #4 SFP, but unlike a normal reactor), I guess that the Cs:I ratio will gradually get skewed towards the former. Would that effect be enough to confuse the interpretation of the analysis, e.g. with regard to old x recent fission?
They took the sample with a bucket suspended from the concrete pump by a cable. The camera was mounted on the crane too. Radiation presumably was a bigger obstacle to human intervention than any heat level would be.

Yea. Two things to note about CsI :
a: in solution there is no such thing as CsI
b: CsI has approximately 1360 Bq of I to 1Bq of Cs ratio, i.e. the role of CsI in the transport of Cs is small. It's role in the transport of iodine might be big or not, but very little Bq of caesium get carried along with iodine as CsI .
The ratio being skewed over time towards Cs would make it look like criticality ended longer ago.

 

[MiceAndMen]

MARK

T plus 1,000 hours

1 x 10³ hours since TEPCO reported failure of the Emergency Core Cooling Systems to NISA, as reported here:
http://www.nisa.meti.go.jp/english/files/en20110416-9-1.pdf

A key benchmark value for many graphs I've seen that use log(time) for the abscissa.

 

[Dmytry]

on topic of criticality in SFP... why are we all (myself was a little guilty of that before in other forum) so sceptical about that? There's those boral plates
http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr0933/sec3/196.html
which presumably are required to prevent criticality (or so NRC says). Is it a big stretch that aluminium would start melting if spent fuel gets uncovered? Possibly even before any zirconium fire, massive fuel damage, etc. Is it a big stretch that if enough of the boral plates fail, it would go critical if water is re-introduced (or even just having water nearby) ?
Then there's the issue of heavy stuff falling into SFP and damaging everything in unpredictable way. It is a safety issue, right? Shouldn't the burden of proof to be on whoever claims that re-criticality is impossible ? And shouldn't it be like this - if it can't be shown impossible, the water has to be borated more?
Then, the isotope analysis - was it not a priority to make sure there is no criticality? Why no short living isotopes data was released?

also, read the article about boral. It can make hydrogen quite well, according to that page.

 

[Dmytry]

Well, maybe i should have written maximal ALLOWED dose for general population (defined by french safety coden but that is the limit in many countries for artificial radiation). Which i expect is a "safe limit" by the way ;o)

The fact is that we see on the map that outside of a certain perimeter, the measures (in grey) are below 1 mSv/year (100 mrem/year).

So maybe you have an example Jarvik about who is leaving with a dose of less than 1 mSv/year on this planet ;o) . In fact, this last remark let me conclude that we don't know if this study is separating artificial radioactivity from "natural" one?

A whole body scanner gives you even more than 10 mSv, the measured values go up often to 20 mSv, which is the maximal equivalent dose of a worker in nuclear industry in France!

But this doesn't mean that there is no risk, in 2010 the president of the french ASN indicated that the radiation doses received by people from medical examinations (mostly X rays and Scanners) increased by 50% in the last 5 years! He was considering this as a scary trend and was insisting in investing more in MRI equipment than scanners to reduce this tendency.

So i don't think that giving that kind of comparison -with doses coming from medical exams- is also very relevant, because one can also say that medical examination is not a normal process for everybody, it is a process with a benefit/risk consideration when somebody has a significant disorder.

Here we are talking about average doses (the real doses have to be better assessed, taking into account food and water ingestion, and many other parameters) for a COMPLETE population, including old and youngs, healthy and sick people.

And in their case, they have absolutely not benefit in taking these extra doses, right?

Coming back on the map showed (and this sketch was already the general tendency 4 weeks ago) I don't undertsand why japanese government stayed with a basic 20 or 30 kms circular zone. Data are available to show that the risk area could be more finely tuned (especially at the north west side)...

Very low tech method, to say the least...

Yes, I've been wondering about that. Also, how many people did this 'stay indoors' order kill? It's just irresponsible to give stay indoors order and keep it in place for weeks. They had to map it properly (don't you map radiation from a plane?)

 

[default.user]

I found this article today.

http://www.glgroup.com/News/After-5...137-Suggests-Ongoing-Criticalities-53599.html

I used the google translator.

So, sorry my bad english. But a few people thinking, that Tepco has a lot of problems with the reactors.

http://www.businessweek.com/news/2011-03-31/tepco-workers-threatened-by-heat-bursts-sea-radiation-rises.html

At this week i saw this blue light often.
Is it possible that the neutron light can see through concrete?

 

[Joe Neubarth]

Yes, I've been wondering about that. Also, how many people did this 'stay indoors' order kill? It's just irresponsible to give stay indoors order and keep it in place for weeks. They had to map it properly (don't you map radiation from a plane?)

I believe most of the countryside was mapped from a plane or helicopter. I think Greenpeace or some organization like that was driving around into contaminated areas and taking measurements that were considerably higher that previously posted.

 

[Joe Neubarth]

I found this article today.

http://www.glgroup.com/News/After-5...137-Suggests-Ongoing-Criticalities-53599.html

I used the google translator.

So, sorry my bad english. But a few people thinking, that Tepco has a lot of problems with the reactors.

http://www.businessweek.com/news/2011-03-31/tepco-workers-threatened-by-heat-bursts-sea-radiation-rises.html

At this week i saw this blue light often.
Is it possible that the neutron light can see through concrete?

When high speed neutrons hit the nucleus's of large atoms they bounce off sort of like a ping pong ball does off of a bowling ball. Neutrons can make it through concrete and some air but it is difficult for them to travel far. The experts on radiation attenuation probably have charts that they can refer you to.

 

[TCups]

Regarding the radioactive contaminated underground water in the basements of Unit 5 and 6:

I have just read a very interesting post regarding this matter in a german Fukushima board - http://fukushima.physikblog.eu/discussion/33/radioaktivitaet-im-grundwasser-noch-so-ein-thema

It's very large, so I'll try translating the most vital parts. All thoughts come frome user Silene in the german forum, I'm only reciting. But I think it's very plausible.

Here is an image of the sweetwater/saltwater levels at coasts:

Notice that the saltwater is forming a wedge which's pressing inland. Since saltwater is more dense than sweetwater, sweetwater is pushed upwards near the coast, it's floating on the saltwater.
The water leak which was sealed earlier this month can't be responsible for the big seawater contamination which was measured since there was only a release of 7m³/h. It's more likely that the saltwater, which was previously used to cool the reactors, seeped through the ground, passed through the sweetwater (because it's denser) and mixed with the saltwater. That way, it could have gotten into the ocean.
Now the reators are cooled with sweetwater. The sweetwater is staying with the groundwater and the overall groundwater level is rising -> radioactive groundwater begins seeping into Units 5 and 6.

REGARDING GROUND WATER CONTAMINATION AT FUKUSHIMA - IS THIS RIGHT?!

After taking a day off just to step back and think about all of this, I am catching up. In that time and several pages of posts, I find the post from Clancy688 to be the most interesting and most alarming new information. If I understand the concept correctly (please correct me if I got it wrong) this is why:

1) the ongoing efforts to cool the reactor cores and the SFP4 are going to continue to release massive volumes of contaminated water for months to come.

2) the density gradient between the denser saltwater and lighter, fresh ground water forms, effectively, a dam-like barrier to the active mixing of fresh ground water with the ocean (though presumably there must be diffusion (osmosis) across the gradient based on the concentration of NaCl)

http://upload.wikimedia.org/wikiped...r_Intrusion.gif/440px-Saltwater_Intrusion.gif

3) The switch to using fresh water for cooling means that the waste water from the ongoing cooling is now differentially contaminating ground water more so than ocean water. So forget seepage into the basement of Units 5 and 6 -- as bad as the ongoing contamination of the ocean would be, contamination of the ground water in terms of long term adverse consequences to the Japanese population is going to be even worse and long lasting.

4) As long as the fuel remains "hot" and requires cooling, the water used to cool it is going to be contaminated at high levels.

5) The rate of that ongoing water-borne contamination will continue at the same rate at the flow of cooling water unless an effective containment, precipitation and filtration system for the waste water is devised.

Yikes!

 

[jlduh]

to come back to the groundwater subject, even if i didn't find any precise map of the area around the plant, but because of the proximity of ocean, it is very probable that the direction of flow of the fresh water table is towards the sea (discharge path). This is the normal case in costal areas at least. So it is IMHO very probable that ground water (and so radioactive contamination through it) won't move far inland (which would be a good news), but will finish in the ocean, like the direct leaks from the plant...

The sketch below is summarizing this process:

http://www.netimago.com/image_191926.html

So the sketch for the contamination move through groundwater could be close to this one:

http://www.netimago.com/image_191927.html

 

[TCups]

to come back to the groundwater subject, even if i didn't find any precise map of the area around the plant, but because of the proximity of ocean, it is very probable that the direction of flow of the fresh water table is towards the sea (discharge path). This is the normal case in costal areas at least. So it is IMHO very probable that ground water (and so radioactive contamination through it) won't move far inland (which would be a good news), but will finish in the ocean, like the direct leaks from the plant...

The sketch below is summarizing this process:

http://www.netimago.com/image_191926.html

So the sketch for the contamination move through groundwater could be close to this one:

http://www.netimago.com/image_191927.html

@jlduh

Thanks for that. Amazing all the stuff you can learn from a really big nuclear accident, isn't it? But in broad strokes, it would seem to me that the groundwater contamination problem will be just as big or bigger and just as complex if not more complex than the airborne contamination problem in the wake of the Fukushima events. Is that how you assess things as well? PS, welcome back. Hope you had a great holiday.

 

[jlduh]

Hi TCups, thanks, yes vacations were fine (and isolated)!

Well, ground water contaminations are always complex matters (treating them is uneasy because they are... underground!). But obviously, the contaminations have to be assessed regarding what they can directly impact in the short to long term timeframe: so basically, 1) what will be their path and 2) what will they encounter along these path (in terms of usage of the water resource for example). In other words, which "targets" will the contamination hit in the next weeks, months, years, decennies...

If the flow of the groundwater is a discharge flow towards the sea at Fukushima, the targets won't be numerous because the path will be short. Of course, I'm only talking about ground water. Ocean water is an other department (of importance). In the Fukushima disaster, I'm afraid that the ocean is going to be the big garbage can of the contamination. To be more precise, ocean is big, BUT the coastal areas will be in my opinion the biggest target of the pollution. It seems that the currents are going south in this area of the Japan sea, so I wouldn't be surprise that the plume of contamination follow this costal line... But it is to early to be sure of that.

Don't forget also that with the typhoon season, huge amount of rain water is going to "wash" the big mess on the Fukushima plant (soils, buildings, reactors, etc.). And this water is going to finish its trip into... the ocean.

At Tchernobyl it has been estimated that because of the 1000m2 or so of cracks in the cover of the shelter (sarcophagus), around 10 000 m3 of rain water enter every year the sarcophagus, and that there is still 3000 m3 of water in the basements of the plant.

You can read also this article which treats this subject and come to a similar conclusion it seems:

http://www.groundwatergo.com/blog/nuclear-disasters-and-groundwater/

 

[rowmag]

Blueprints would be helpfulbut not certain. Any estimate of the leakage rate required as per your idea?

Good question, and maybe that is the one that can put this to rest.

Don't know proper dimensions, but a quick back of the envelope calculation of what kind of wind is needed to replace the air in a reactor building through, say, a 10 m^2 cross-section trench in one day suggests wind-tunnel-like air flow. So not likely, unless concentrated hydrogen were piped through, but
a) why would it be? and
b) in any case, robot videos of the inside of Unit 3 show the lower floors in pretty good shape, no obvious signs of hydrogen explosion down there, suggesting that the hydrogen in Unit 3 was largely confined to the top of the building, far from any underground conduit.

 

[Jorge Stolfi]

I've updated my plots of #Fukushima reactor variables, up to #NISA release 106 (21/apr 15:30) :

http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/plots/cur/Main.html

No big news. The drop by a factor of 10 in the CAMS (A) reading in the Unit #1 torus persists. Presumably it is the previous values that were wrong by 1 in the exponent. It is hard to tell
because the (B) redings are intermediate between the two (A) values, old and new, and both have
been changing a lot recently.

In release 103 there was another similar drop, by a factor of 100, in the CAMS (B) reading of Unit #3 torus. Here it is clear that it was a typo in the exponent, since the (A) and (B) readings were previously off by factor of 100 (exponent 1 instead of -1), and now they agree. The question is, are they now both correct, or both wrong?

In their release packet 105, NISA messed up their file names, so intead of the raw TEPCO fax we got a second copy of the redacted NISA press release. The latter does not give the CAMS readings, water pump flows, and core and drywell temperatures. But release 106 was OK.

 

[MiceAndMen]

I've updated my plots of #Fukushima reactor variables, up to #NISA release 106 (21/apr 15:30) :

http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/plots/cur/Main.html

No big news. The drop by a factor of 10 in the CAMS (A) reading in the Unit #1 torus persists. Presumably it is the previous values that were wrong by 1 in the exponent. It is hard to tell
because the (B) redings are intermediate between the two (A) values, old and new, and both have
been changing a lot recently.

In release 103 there was another similar drop, by a factor of 100, in the CAMS (B) reading of Unit #3 torus. Here it is clear that it was a typo in the exponent, since the (A) and (B) readings were previously off by factor of 100 (exponent 1 instead of -1), and now they agree. The question is, are they now both correct, or both wrong?

In their release packet 105, NISA messed up their file names, so intead of the raw TEPCO fax we got a second copy of the redacted NISA press release. The latter does not give the CAMS readings, water pump flows, and core and drywell temperatures. But release 106 was OK.

What do people think here? Is TEPCO/NISA sloppy with their reporting, or are the inconsistencies due to translation? I've seen plenty of Japanese electronics' users' guides in my day, and it seems there are plenty of Japanese - ostensibly employed as professionals - who do not read and write English as well as they think they do. Not to say all Japanese in general are like that; I know several who are fluent in English and they would not make such grievous errors. But it seems to be common that the first person who raises their hand when the boss asks, "Who can translate this into English?", always gets the job regardless of their actual level of fluency.

On the other hand it would not surprise me if they're just sloppy and careless with the numbers for Japanese consumption, too.

 

[Jorge Stolfi]

MARKT plus 1,000 hours [...] A key benchmark value for many graphs I've seen that use log(time) for the abscissa.

... and for certain data files and scripts which had naively allocated 3 digits for the "hours since accident" column.

 

[dh87]

I've updated my plots of #Fukushima reactor variables, up to #NISA release 106 (21/apr 15:30) :

http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/plots/cur/Main.html

No big news. The drop by a factor of 10 in the CAMS (A) reading in the Unit #1 torus persists. Presumably it is the previous values that were wrong by 1 in the exponent. It is hard to tell
because the (B) redings are intermediate between the two (A) values, old and new, and both have
been changing a lot recently.

In release 103 there was another similar drop, by a factor of 100, in the CAMS (B) reading of Unit #3 torus. Here it is clear that it was a typo in the exponent, since the (A) and (B) readings were previously off by factor of 100 (exponent 1 instead of -1), and now they agree. The question is, are they now both correct, or both wrong?

In their release packet 105, NISA messed up their file names, so intead of the raw TEPCO fax we got a second copy of the redacted NISA press release. The latter does not give the CAMS readings, water pump flows, and core and drywell temperatures. But release 106 was OK.

Thank you for maintaining this record of the data and for trying to deal with the inconsistencies in the reporting. I have been watching your graphs for weeks. There is a NISA document here (http://www.nisa.meti.go.jp/english/files/en20110406-1-1.pdf ) that parallels your graphs, but I don't know whether it's been updated since this version. The graphs are consistent with yours.

 

[|Fred]

Well, maybe i should have written maximal ALLOWED dose for general population (defined by french safety coden but that is the limit in many countries for artificial radiation). Which i expect is a "safe limit" by the way ;o)

It would have be a equally failing understanding. It is not a safe limit it is the threshold that we do not want to exceed for artificial if possible.

The fact is that we see on the map that outside of a certain perimeter, the measures (in grey) are below 1 mSv/year (100 mrem/year). In fact, this last remark let me conclude that we don't know if this study is separating artificial radioactivity from "natural" one?

Nope, this map is for dose induce by radioactive matériel from Fukushima, it take into account decay, external ionization and internal inhaled particule. it assume one is standing outside 247. and does not take into account that radiation exposition would be mitigated by the time you spend indoor (as requested).

As for the 1 mSv you get it from the ²²²Rn present in the air every one breath .. You also get 0,2mSk from your own potassium etc ..
http://www.rchoetzlein.com/theory/wp-content/uploads/2011/03/radiation.jpg

A whole body scanner gives you even more than 10 mSv, But this doesn't mean that there is no risk

Here again this is a miss understanding, on the "no risk concept". Of course there is a risk, every time you take some medication there is a risk, I almost die the first time I toke penicillin, every time you do something there is a risk.. There is no such thing as risk free, But what is commonly admitted is that when the probability of something bad to hapen is low enough or lower that a lot of other thing we consider it risk free. Call in un "abut de language" or convention..

So i don't think that giving that kind of comparison -with doses coming from medical exams- is also very relevant

I mentioned different annual dose for different country France + Dose from this map < annual dose from the states or Sweden..

And in their case, they have absolutely not benefit in taking these extra doses, right?

As low as possible is the word, unless you are Tcup's mice ( I have yet to read the paper), now if you do a proper assessment you have to take into account other choice you make and pose superior threat.

 

[Jorge Stolfi]

... there are plenty of Japanese - ostensibly employed as professionals - who do not read and write English as well as they think they do.

That is irrelevant since the TEPCO faxes and NISA releases are all in Japanese.

Godzilla only knowns how how many hands separate the readings on the instruments to the faxes sent by TEPCO to NISA. Someone along that path seems to be unfamiliar with scientific notation; that would explain the exponent errors (and why the numbers are not being converted to ordinary decimal notation).

I have this old theory that (a) TEPCO has no nuclear experts in their payroll, and (b) their sub-contractors, who actually run the plant, have only technical-level expertise, not engineering- or science-level --- namely, they know standard procedures, but cannot understand or react to situations that are are not in the manuals. I would love to be proved wrong...

I watched a documentary on Chernobyl the other day. One lesson that Japan could have learned from that incident is: do not let the the plant operators remain in charge of disaster contol. At Chernobyl, precious days were lost while the operators (and their bosses and bosses' bosses, up to cabinet level) insisted that "everything was under control". Real action began only after Gorbachev pushed those people aside and put a committee of the country's top nuclear scientists in charge.

Unfortunately it seems much harder to do that in Japan, given the constraints of capitalism (Fukushima-I is still the private property of TEPCO) and the fact that the State is in many ways subordinated to big corporations like TEPCO, GE, Toshiba, etc. So here we are, 1000 hours after the accident and we are still wondering whether there is any real cook in the kitchen.

 

[AntonL]

Has the freshwater supply at Fukushima dried up? Or has SFP 1,3 & 4 always been replenished with seawater.

http://www.tepco.co.jp/en/press/corp-com/release/11042203-e.html"

Previous reports just stated water spraying

On March 25 and 26 reactor cooling was switched from sea water to freshwater.

Unit 2 SFP was regularly filled with fresh water according to Tepco reports. Unit 1, 3 and 4 SFP replenishing is always referred to as water spraying with concrete truck.

 

[rowmag]

Has the freshwater supply at Fukushima dried up? Or has SFP 1,3 & 4 always been replenished with seawater.

http://www.tepco.co.jp/en/press/corp-com/release/11042203-e.html"

Previous reports just stated water spraying

On March 25 and 26 reactor cooling was switched from sea water to freshwater.

Unit 2 SFP was regularly filled with fresh water according to Tepco reports. Unit 1, 3 and 4 SFP replenishing is always referred to as water spraying with concrete truck.

It is a mistake.

The Japanese version just says water spraying with concrete truck, not seawater.

http://www.tepco.co.jp/nu/f1-np/press_f1/2011/htmldata/bi1456-j.pdf

 

[Dmytry]

That is irrelevant since the TEPCO faxes and NISA releases are all in Japanese.

Godzilla only knowns how how many hands separate the readings on the instruments to the faxes sent by TEPCO to NISA. Someone along that path seems to be unfamiliar with scientific notation; that would explain the exponent errors (and why the numbers are not being converted to ordinary decimal notation).

I have this old theory that (a) TEPCO has no nuclear experts in their payroll, and (b) their sub-contractors, who actually run the plant, have only technical-level expertise, not engineering- or science-level --- namely, they know standard procedures, but cannot understand or react to situations that are are not in the manuals. I would love to be proved wrong...

I watched a documentary on Chernobyl the other day. One lesson that Japan could have learned from that incident is: do not let the the plant operators remain in charge of disaster contol. At Chernobyl, precious days were lost while the operators (and their bosses and bosses' bosses, up to cabinet level) insisted that "everything was under control". Real action began only after Gorbachev pushed those people aside and put a committee of the country's top nuclear scientists in charge.

Unfortunately it seems much harder to do that in Japan, given the constraints of capitalism (Fukushima-I is still the private property of TEPCO) and the fact that the State is in many ways subordinated to big corporations like TEPCO, GE, Toshiba, etc. So here we are, 1000 hours after the accident and we are still wondering whether there is any real cook in the kitchen.

Excellent overview, that's precisely what I was feeling. Also, so much was done in Chernobyl in very short time... getting the water out of meltdown's way, etc. All forgotten by the public, Chernobyl made look as the absolute worst case most ineptly handled.

In any case, why would tepco have enough nuclear experts for accident handling on staff before accident? That wouldn't even make sense for each single utility, they should of created a company jointly, ala KHG, so that they together pool for such a team. But they didn't do that, there is no Japanese equivalent of KHG or INTRA.

 

[rowmag]

Don't forget also that with the typhoon season, huge amount of rain water is going to "wash" the big mess on the Fukushima plant (soils, buildings, reactors, etc.). And this water is going to finish its trip into... the ocean.

They have this big, triangular seawall. Can they block off the entrance, and make the whole thing into a giant containment tank? Won't prevent all the contaminated groundwater from leaking out, but couldn't they at least reduce some of the marine pollution that way?

http://upload.wikimedia.org/wikipedia/commons/e/e8/Fukushima_I_NPP_1975.jpg

Seems like it could be a useful next step after the silt fences etc. that they have installed closer in.

 

[tsutsuji]

It seems that the currents are going south in this area of the Japan sea, so I wouldn't be surprise that the plume of contamination follow this costal line... But it is to early to be sure of that.

http://sirocco.omp.obs-mip.fr/outils/Symphonie/Produits/Japan/SymphoniePreviJapan.htm has an "animation of surface currents" and a simulation of the dissemination of the pollutants into the sea through direct release and atmospheric release.

 

[jlduh]

Finally, japanese government starts to move from its original position about evacuation zone and expands it north-west, as we were talking about yesterday on this thread !

http://www3.nhk.or.jp/daily/english/22_20.html

Edano said that due to the possible impact on residents' heath, the government is now urging them to evacuate within about a month.

So is this 20 mSv a "threshold" or a "safe limit"?
(a lit bit of irony inside, i admit ;o))

I think it is now accepted by many specialists that any increase of artificial radiation is also an increase in diseases risks, like it is also with many chemical products that act on health of living organisms WITHOUT ANY THRESHOLD MECANISM. This is called "excess risk" and "relative excess risk":

http://cat.inist.fr/?aModele=afficheN&cpsidt=1886907

http://www.rerf.or.jp/radefx/late_e/cancrisk.html

So in fact you were right and i was wrong: there is probably no "safe limit" for radiation, there is only a threshold for evacuation decision...