Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[zapperzero]

http://www.jnes.go.jp/content/000119688.pdf confirmation of the presence or absence of core recriticality: Study of the causes of neutron measurement data above the detection level revealed at Fukushima Daiichi monitoring points.

http://www.jnes.go.jp/content/000119689.pdf About the neutron leak at unit 4 storing pool: From 14 March to 15 March, neutron measurement data above detection level have been revealed at the Fukushima Daiichi monitoring points. Study of the causes of these measurements.

Thank you for your great and selfless work.

Now it only remains for jnes to translate these into English. I am very curious as to why neutrons were detected "at unit 4 storing pool". I had no idea that there was such a detection. I only remember the talk about neutron beams detected at the plant perimeter.

 

[zapperzero]

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

I have 3 questions:

1.) Is there a way to convert the 1,225,400,000,000 becquerels into number of grams of Plutonium released?

FWIW, wolframalpha says 1 g of Pu-241 is 3.84E+12 Bq. So roughly 0.3 grams.

EDIT: perhaps when comparing this with the total inventory of a NPP it is easier to understand the seemingly cavalier attitude of some industry insiders who are dismissing Fukushima as "not a big deal". It's not so big a deal, in truth, from that perspective. Could have been orders of magnitude worse, easy.

 

[tsutsuji]

Thank you for your great and selfless work.

You are welcome.

Now it only remains for jnes to translate these into English. I am very curious as to why neutrons were detected "at unit 4 storing pool". I had no idea that there was such a detection. I only remember the talk about neutron beams detected at the plant perimeter.

In my previous post I merely translated the titles and summaries on the main menu page at http://www.jnes.go.jp/jyohou/kouhyo/kaiseki_published.html without having a look at the pdf documents themselves.　

Now, if I try to look a them, I find at the bottom of http://www.jnes.go.jp/content/000119689.pdf (dated 27 April 2011) that the last sentence is "Concerning the reason why neutron data above detection level were measured at Fukushima Daiichi monitoring points from 14 March to 15 March, for unit 4 SFP to be the cause, it is necessary that the water level declines below top of fuel".

The last sentence on page 2 of http://www.jnes.go.jp/content/000119688.pdf (dated 13 April 2011) is "Concerning measurement data above neutron detection level at Fukushima Daiichi monitoring points from 14 March to 15 March, there is almost no possibility that they are caused either by core recriticality or pool water level decline. Also, under the hypothesis that those measurements are valid, the possibility of neutron discharge from volatile substances of delayed neutron precursors caused by venting of units 1, 2, 3, can be thought".

http://www.sfgate.com/cgi-bin/article.cgi?f=/n/a/2011/10/15/international/i025338D61.DTL English article about the JNES documents.

 

[Astronuc]

From the translation of the JNES documents provided by tsutsuji, it is still not clear about the 'neutron source'.

The delayed neutron precursors have very short half-lives, less than one minute as shown below:

Nuclide Half-life
         (sec)
 Br-87    55.7
 Cs-141   24.9
 I-137    24.5
 Te-136   19.0
 Br-86    16.0
 I-138     6.5
 Rb-93     5.86
 Br-89     4.38
 Te-137    3.5
 Rb-94     2.76

At 10 minutes from shutdown, they have decreased by a factor of 1000, and in a half-hour, they have decreased by a factor of 1 billion from shutdown, so all but the longest lived have decayed away, and the longest is less than 1 billionth of a small amount to begin with. In the SFPs, the fuel hadn't operated for months, so essentially, there are no delayed neutron sources. The only possible neutron sources would be transuranics, e.g., Pu, Am, Cm, Cf

Draining of the SFP would reduce moderation, so criticality would be rather impossible. However, neutrons could escape without the shielding of the water, but the source would rather weak.

 

[nikkkom]

The short answer is that US BWR hardened vent systems, that I have studied, are not filtered. These systems were classified for use in a beyond design basis event. That is the last ditch effort to minimize releases to the environment in a severe accident once it is impossible to prevent those releases. Now, your turn. Keep it respectful.

To me, this is one of Fukushima "lessons learned".

IIRC Sweden constructed a 10000 m^3 filtration/buffer in their hardened vent with the goal of capturing most of emissions, and up to F1 disaster it was not clear whether this effort makes (economic) sense.

Today we can say that it definitely does make sense. In F1, it could have captured a large fraction of release, saving tens or even hundreds of billions of dollars.

If NRC would have proposed adding systems like this one to NPPs in US, I'd have reasons to think NRC took F1 disaster seriously enough.

So far I don't see it.

 

[etudiant]

To me, this is one of Fukushima "lessons learned".

IIRC Sweden constructed a 10000 m^3 filtration/buffer in their hardened vent with the goal of capturing most of emissions, and up to F1 disaster it was not clear whether this effort makes (economic) sense.

Today we can say that it definitely does make sense. In F1, it could have captured a large fraction of release, saving tens or even hundreds of billions of dollars.

If NRC would have proposed adding systems like this one to NPPs in US, I'd have reasons to think NRC took F1 disaster seriously enough.

So far I don't see it.

It does seem that the idea of hardening the vent without also making provisions for filtering the possibly extreme emissions is a possibly damaging half measure. A severe accident plume clearly exceeds the natural dilution capacity of the environment and it seems ill advised to raise the emission point several hundred feet on top of that.
In this context, the UK experience in the 1950s with the Windscale accident deserves more attention. Filters were installed on that site and saved the country from an enormous disaster when the nuclear pile (graphite moderated) caught fire. Filtering a reactor accident in a water moderated reactor with massive steam generation will however be a much more challenging task.

 

[Bodge]

...

2.) Is this estimate referring to "releases into the environment" or "releases into the atmosphere", i.e. air or water or both?

Google translate suggests that this is just for the first 100 days into the air only.​

3.) What will happen to the 7.6x10^13 becquerels of Neptunium-239 shown on the same table - what mass of Plutonium-239 will result?



http://www.meti.go.jp/press/2011/06/20110606008/20110606008-2.pdf

Anyone help?

 

[NUCENG]

The decision to add filtration to a hardened vent is not so simple. The purpose is to protect containment by releasing pressure from containment. Protection of the coolant piping and vessel barrier, and the cladding barrier keeps the plant out of a major release and generation of significant hydrogen concentrations.


Charcoal filtration requires a fairly low velocity of the filter stream to permit it to work. Having sufficient flow for the period immediately after shutdown requires a large surface area. The larger the system is physically, the more likely is its need for force ventilation flow (fans that require emergency power).


Activated charcoal is quickly saturated if the humidity id too high. So filtration systems heat the stream to lower humidity. That requires emergency power or some form if heat source. Failure of either of these design requirements will result in backpressures that could result in containment overpressure.I have not studied the Finnish or Swedish filtration systems designs so I can't say they have solved those problems (particularly the power issue). In any case, those systems have the same experience level as US and Japanese hardened vents up until March 11, 2011. They have not been tested by a real severe event.


Let's turn to Fukushima specifically. Possibly due to operator error in securing isolation condenser flow early in the event, Unit 1 quickly wound up with no makeup and fuel was uncovered. Fuel damage and hydrogen generation were well underway within hours of the SBO - even before batteries were exhausted. Containment pressures were more than twice design limits so containment leakage was probably significant even before the venting was attempted.


Units 2 and 3 also had significant problems attempting to vent. I can't confirm this from the information I have seen here or released by TEPCO, but it is possible that attempts to keep the cores covered were unsuccessful and fuel damage was underway before attempting to vent those units as well. They maintained the reactors at pressure longer in order to use the RCIC and HPCI steam driven systems despite knowing that they would be lost when the batteries died.


Basically, I believe Fukushima units 1, 2, and 3 were already leaking and already building explosive levels of hydrogen before they attempted to vent. They had already lost the war.


The alternative is that in an extended SBO where it is clear the plant will not regain AC systems for makeup and cooling, the reactor should be manually depressurized early. This will permit external low pressure makeup sources (fire pumps, fire trucks, or, in the US, B.5.b systems) to be used to keep the core covered, reducing or preventing fuel damage and oxidation. Priority should be to use the core spray system for injection since it is the most direct path to the core. Pressure relief from the reactor to the torus should be maintained via the SRV system. Containment pressure relief by the hardened vent system. Preventing or reducing core damage reduces the need for hardened vent filtration.


Now, for my caveats. This discussion is based on current knowledge and understanding of Fukushima. It is not carved in stone. At a minimum we need to learn more about why the operators had trouble venting and ensure that won’t happen again. It is clear that the duration of SBO coping periods should be reevaluated and possibly lengthened. Unit 1 problems with reinitiating isolation condenser operation needs to be examined to see if it is more than operator error. In view of the reports that other countries have Filtration systems on the hardened vent systems, this potential should be considered. I believe US BWRs need to reconsider the need for hydrogen ignition systems to prevent explosive concentrations.


The international nuclear industry needs to continue to support Japanese recovery efforts to ensure we can mine every possible lesson that this accident can teach. I don’t think we know anywhere near enough about what happened yet, and that is why it is important that we don’t get bored and quit watching and discussing. That process will only be useful as long as the discussion stays respectful.

 

[etudiant]

The decision to add filtration to a hardened vent is not so simple. The purpose is to protect containment by releasing pressure from containment. Protection of the coolant piping and vessel barrier, and the cladding barrier keeps the plant out of a major release and generation of significant hydrogen concentrations. ...

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?

 

[nikkkom]

Charcoal filtration requires a fairly low velocity of the filter stream to permit it to work. Having sufficient flow for the period immediately after shutdown requires a large surface area. The larger the system is physically, the more likely is its need for force ventilation flow (fans that require emergency power).

Activated charcoal is quickly saturated if the humidity id too high. So filtration systems heat the stream to lower humidity. That requires emergency power or some form if heat source. Failure of either of these design requirements will result in backpressures that could result in containment overpressure.

Charcoal filters are probably not what's needed when you plan to vent hundreds of tons of steam relatively quickly.

To my non-specialist eye, a bubbler tank with mass of cold water no less than five times the mass of total reactor coolant inventory should be sufficient.

If F1 would vent their contaminated and overheated coolant through such a bubbler tank, most of Cs-134/137 would be that tank now instead of hundreds of square miles of Japan territory.

Such tank would be a large, but relatively simple, low-tech construct. How much can it cost?

 

[zapperzero]

Anyone help?

2) Np-239 decays to Pu-239 with a half life of 2.3 days. Starting quantity is 0.009 grams, again according to wolframalpha (makes sense, shorter half life means higher activity).

 

[zapperzero]

Charcoal filters are probably not what's needed when you plan to vent hundreds of tons of steam relatively quickly.

To my non-specialist eye, a bubbler tank with mass of cold water no less than five times the mass of total reactor coolant inventory should be sufficient.

If F1 would vent their contaminated and overheated coolant through such a bubbler tank, most of Cs-134/137 would be that tank now instead of hundreds of square miles of Japan territory.

Such tank would be a large, but relatively simple, low-tech construct. How much can it cost?

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

 

[zapperzero]

The delayed neutron precursors have very short half-lives, less than one minute

At 10 minutes from shutdown, they have decreased by a factor of 1000, and in a half-hour, they have decreased by a factor of 1 billion from shutdown, so all but the longest lived have decayed away, and the longest is less than 1 billionth of a small amount to begin with. In the SFPs, the fuel hadn't operated for months, so essentially, there are no delayed neutron sources. The only possible neutron sources would be transuranics, e.g., Pu, Am, Cm, Cf

Draining of the SFP would reduce moderation, so criticality would be rather impossible. However, neutrons could escape without the shielding of the water, but the source would rather weak.

Now, if I try to look a them, I find at the bottom of http://www.jnes.go.jp/content/000119689.pdf (dated 27 April 2011) that the last sentence is "Concerning the reason why neutron data above detection level were measured at Fukushima Daiichi monitoring points from 14 March to 15 March, for unit 4 SFP to be the cause, it is necessary that the water level declines below top of fuel".

The last sentence on page 2 of http://www.jnes.go.jp/content/000119688.pdf (dated 13 April 2011) is "Concerning measurement data above neutron detection level at Fukushima Daiichi monitoring points from 14 March to 15 March, there is almost no possibility that they are caused either by core recriticality or pool water level decline. Also, under the hypothesis that those measurements are valid, the possibility of neutron discharge from volatile substances of delayed neutron precursors caused by venting of units 1, 2, 3, can be thought".

So, it is either uncovered fuel in SPF #4 or recriticality in 1, 2 or 3, but probably the former?

 

[jim hardy]

""" the possibility of neutron discharge from volatile substances of delayed neutron precursors caused by venting of units 1, 2, 3, can be thought"."""

i spent a LOT of time back then trying to figure that out.

from plant logsheets those measurements co-incided with water injection and venting

so i assumed particulates went up the vents

looking for my old link to those plant logsheets
seems they had wind direction also and i decided nasty particulates wafted by measuring point which was main gate.
fuel probably was crackling and sputtering good - ever pour water on hot coals? you get covered with ashes.

had to be an awful scary time for those fellows.

 

[westfield]

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

Only if emergency venting was exclusively from the suppression chambers which it certainly wasn't at F1.

From my laymans perspective it seems like a great solution to enable emergency scrubbing from the hardened vent. Additionally, we know that venting from the drywell\s took place at F1, bypassing the torus completely, so its not reinventing the S\C, it's actually putting an adhoc one in line. We also know that the torus of at least F1-2 exceeded its capacity to shed pressure and heat which would seem to add another possible use for an additional standby volume of water.

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.

 

[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