Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[bytepirate]

Why ? To slow down vaporization of water from sfp ? Fresh fuel which was removed from core has bigger temperature than old fuel, so if they believe that they can restore cooling systems they want to slow down vaporization by removing some fuel from overpacked sfp...

but wouldn't that be putting out a fire with gasoline? they have to cool it anyway...

maybe they were just about to reinsert the core (scheduled). quite unlikely, but the whole disaster is quite unlikely too (one in a million years for a core melt with containment failure, i have been told). add (or rather multiplicate) this new unlikeliness and the http://en.wikipedia.org/wiki/Infinite_Improbability_Drive#Infinite_Improbability_Drive" can travel quite a bit...

 

[Jorge Stolfi]

Does anyone know what is the topscale reading of the Fukushima Daiichi CAMS meters (100 Sv/h?) (I cannot find that info with Google.) Thanks...

 

[Cyberspace]

Also this is strange that tepco only tell us about fire, there was no pictures, videos or news about explosion, only about fire...

This has bothered me too, but I did find a reference to an explosion buried in one of the TEPCO press releases for March 15th:

"At approximately 6:00am, a loud explosion was heard from within the
power station. Afterwards, it was confirmed that the 4th floor rooftop
area of the Unit 4 Nuclear Reactor Building had sustained damage."

http://www.tepco.co.jp/en/press/corp-com/release/11031504-e.html"

Lack of pictures/video might be attributable to the early hour, ie before the press had their cameras set up for the day. Sunrise time was about an hour before the stated explosion time.

 

[bytepirate]

Also this is strange that tepco only tell us about fire, there was no pictures, videos or news about explosion, only about fire...

that's strange indeed. the explosion was *not* at night, as has been stated here before.

at 2:31 you can see the intact building, blown away one frame later.

EDIT:

Lack of pictures/video might be attributable to the early hour, ie before the press had their cameras set up for the day. Sunrise time was about an hour before the stated explosion time.

i have been working for the television. that is *very* hard to believe under these circumstances. but still possible...

 

[cphoenix]

Responding to my question about whether aftershocks could have damaged building 4:

that none of the aftershocks was even remotely strong enough to so effectively destroy something that withstood original quake?

I looked at an aftershock graph, and the strongest aftershocks in the relevant time period (March 14 to 27) were under 6.4. So you're probably right. http://aebrain.blogspot.com/2011_04_01_archive.html

So what was it then? The recent JAIF Reactor Status sheets list it as "hydrogen explosion." But I don't see how it could have been an internal hydrogen explosion, given the wall panels still attached near the roof.

Could #4 have been damaged that much by #3 blowing up?

I can't even find a source that tells what day the damage happened. From video of #3 blowing up, #4 appears intact before the #3 explosion. Wikipedia lists the first "observation" of #4 damage on March 27. http://en.wikipedia.org/wiki/Timeline_of_the_Fukushima_I_nuclear_accidents

The JAIF reactor status updates give some clues: The 19:00 March 15 update lists reactor 3 building integrity as "severely damaged" but building 4 as "partially damaged". http://www.jaif.or.jp/english/news_images/pdf/ENGNEWS01_1300189582P.pdf
So does the 8:00 March 16 update, which describes multiple fires in, and increased radiation readings around, building 4.
The 12:30 March 16 update changes 4's status to "severely damaged".
(Updates can be found at http://jaif.or.jp/english/news_index.php )

I had assumed that the damage to 4 was related to the fires. But the more I think, the less likely it seems. A fire severe enough to buckle the steel framework, but not discolor the paint?

I don't have a theory to push - just a big question mark. Surely I'm not the only one wondering? Surely someone has figured out what must have happened?

 

[Borek]

But I don't see how it could have been an internal hydrogen explosion, given the wall panels still attached near the roof.

Long ago I started to wonder why they are where they are. Perhaps there is something inside of the building that shielded them from the blast.

 

[bytepirate]

Responding to my question about whether aftershocks could have damaged building 4:



I looked at an aftershock graph, and the strongest aftershocks in the relevant time period (March 14 to 27) were under 6.4. So you're probably right. http://aebrain.blogspot.com/2011_04_01_archive.html

So what was it then? The recent JAIF Reactor Status sheets list it as "hydrogen explosion." But I don't see how it could have been an internal hydrogen explosion, given the wall panels still attached near the roof.

Could #4 have been damaged that much by #3 blowing up?

I can't even find a source that tells what day the damage happened. From video of #3 blowing up, #4 appears intact before the #3 explosion. Wikipedia lists the first "observation" of #4 damage on March 27. http://en.wikipedia.org/wiki/Timeline_of_the_Fukushima_I_nuclear_accidents

The JAIF reactor status updates give some clues: The 19:00 March 15 update lists reactor 3 building integrity as "severely damaged" but building 4 as "partially damaged". http://www.jaif.or.jp/english/news_images/pdf/ENGNEWS01_1300189582P.pdf
So does the 8:00 March 16 update, which describes multiple fires in, and increased radiation readings around, building 4.
The 12:30 March 16 update changes 4's status to "severely damaged".
(Updates can be found at http://jaif.or.jp/english/news_index.php )

I had assumed that the damage to 4 was related to the fires. But the more I think, the less likely it seems. A fire severe enough to buckle the steel framework, but not discolor the paint?

I don't have a theory to push - just a big question mark. Surely I'm not the only one wondering? Surely someone has figured out what must have happened?

#4 was undamaged after #3 exploded: http://www.digitalglobe.com/downloads/featured_images/japan_earthquaketsu_fukushima_daiichi_march14_2011_dg.jpg

 

[georgiworld]

Would someone like to comment on these images
http://www.houseoffoust.com/fukushima/fukushima.html

 

[Escapekey]

Here, quell some of the useless speculation. See press releases and Kyodo news releases.

http://enenews.com/

Reactor 4 is worsening. The contamination AND evacuation zone is expanding.

http://english.kyodonews.jp/news/2011/04/85295.html

 

[Jorge Stolfi]

Updated my plots of #Fukushima reactor variables to NISA release 91 (13/apr 13:00) : http://bit.ly/gAuxse

(Note that release 89 merely repeated the data of release 88 for units #1 and #2, which were measured at 06:00 on apr/12.)

 

[Jorge Stolfi]

The Alvarez et al document about re-racking claims that

"The standard spacing for new dense-pack racks today is 23 cm—barely above the 21.4 cm spacing in reactor cores. This “dense-packed” fuel is kept sub-critical by enclosing each fuel assembly in a metal box whose walls contain neutron-absorbing boron [...] the cross-section of the portion of a densepack box that is not obstructed by fuel rods would be about 0.032 m2

Assuming that this "standard dense packing" was used at Fukushima Daiichi, we get 1/0.23^2 = 18.9 assemblies per square meter. Then 1535 assemblies in a single layer would use 81.2 square meters. What are the dimensions of the #4 pool?

In the absence of any cooling, a freshly-discharged core generating decay heat at a rate of 100 kWt/tU would heat up adiabatically within an hour to about 600C, where the zircaloy cladding would be expected to rupture under the internal pressure from helium and fission product gases, and then to about 900C where the cladding would begin to burn in air. [...] Steam cooling could be effective as long as the water level covers more than about the bottom quarter of the spent fuel. [...] When the water [level falls to near] the bottom of the fuel assembly, it appears doubtful that [steam flow through the assemblies] could keep the peak temperature below 1200C for fuel less than a hundred years post discharge.

However, the claim that steam cooling would be effective with 75% of the fuel uncovered seems to assume that the whole assembly is at the same temperature, i.e. that heat generated in the top part is efficiently transported down the assembly to the water-covered part. Is my reading correct? Is that claim valid?

 

[Astronuc]

And, while spontaneous fission is an insignificant source of heat, even a momentary sub-critical chain reaction could cause a steam explosion, could it not?

I recall that famous accident where someone was trying to demonstrate a sub-critical chain reaction with two chunks of plutonium...

A subcritical (k < 1) system decreases in power to some low level which is that left by spontaneous fissions or other neutron sources. A subcritical system would not cause a steam explosion.

Only if a system went supercritical and achieve a certain power density very rapidly, would there be a possibility of a steam explosion, and likely the system would have to be prompt critical with a significant amount of positive reactivity (i.e., k >> 1.006), which is not the case at Fukushima.

The famous bare critical sphere demonstration, e.g., the one in which Louis Slotin died, was a supercritical assembly with nearly pure fissile material. Such material is not used in power reactors.

 

[Dotini]

Such material is not used in power reactors.

You don't suppose they were above fooling around with forbidden materials?

Respectfully submitted, seeking correction
Dotini

 

[StrangeBeauty]

Would someone like to comment on these images
http://www.houseoffoust.com/fukushima/fukushima.html

Seriously though, the images the above link do not match my (perhaps faulty) recollection of most recent mapping the service floor layout to the buildings done by our esteemed colleagues here. It places the reactor in a different place in the building (not next to the east wall, but in the mid-south part of the building), and the SFPs slightly west of the middle of the south wall in building #4. Can someone please check my memory as this seems like new/revised info to me. Thanks.

 

[jmelson]

from the link above...
Beta particles are just electrons from the nucleus, the term "beta particle" being an historical term used in the early description of radioactivity. The high energy electrons have greater range of penetration than alpha particles, but still much less than gamma rays. The radiation hazard from betas is greatest if they are ingested.

so is it possible to say that beta particle derived from plutonium and uranium are indistinguish from normal "electricity in the air"? and therefore unmeasurable?

No, they are certainly measurable, and the high energy distinguishes them from static electricity.
They have energies of hundreds of KeV to several MeV, and that allows them to penetrate at least some layers of the skin. When these electrons are stopped, the energy from their momentum is given off as gamma rays. So, in fact, if the Betas have something like a thin metal foil to stop them, then any sensitive (to low energies) gamma detector will detect their presence.

Jon

 

[razzz]

Would someone like to comment on these images
http://www.houseoffoust.com/fukushima/fukushima.html

Nice work georgiworld, that took some time and effort. Can't add much. Looks like entombment looks impossible due to debris having to be removed first. Everything contaminated and not approachable doesn't help.

'Pit' looks like it took a direct hit to the lid from falling object.

Always wondered how the working deck/platform was constructed. Need a drawing to see how it is assembled and what supports it. Is it anchored down or 'float' independently?

Many weak points when your vessel/capsule is glowing red and venting, ready for takeoff. Flange and pass-through(s) just for starters besides overheating leading to a stress crack qualify as weak points.

 

[razzz]

http://af.reuters.com/article/energyOilNews/idAFTFD00673420110413

http://www.welt.de/vermischtes/weltgeschehen/article12901818/Schickt-Tepco-Obdachlose-ins-AKW.html

 

[StrangeBeauty]

Would someone like to comment on these images
http://www.houseoffoust.com/fukushima/fukushima.html

Adding onto my post above -- slogged through many past pages and found several posts from Fred that were good in trying to overlay the reactor floor layout on the existing destroyed buildings -- see this one for example:

https://www.physicsforums.com/showpost.php?p=3235798&postcount=3302

The images above disagree with the placement of the SPF here. I found compelling the combination of the photo of the #4 reactor room (is this really an actual picture of that exact room as is claimed?) then _flipped_ (which is odd), which then matches up with the other images showing the yellow, removed containment cap. Second opinions?

 

[TCups]

Would someone like to comment on these images
http://www.houseoffoust.com/fukushima/fukushima.html

g-

I will risk a comment. The mark-ups in many cases don't match the pre-earthquake pictures or the building schematics.

If this were indeed is a picture of the inside of Unit 4, Fukushima Diiachi, then there is an important clue to what has happened at Unit 4:

http://www.houseoffoust.com/fukushima/reactor4_insideplain.jpg

The mark up of the SFP4 stops short. The mark up should include an accessory pool in the corner of the SFP used for cask transfer. The elevator shafts have to be in the southwest corners to mate with the external access tunnels at the south end of the west walls of Units 3 and 4.

At Fukushima Diiachi, the reactor core, RPV and primary containment are located in the center line of the building on the east-west axis but are located to the east of the center line of the north-south axis, I believe. I suspect "Unit 4" here refers to Fukushima Diana not Fukushima Diiachi.

The floor plan layout that seems to match both the schematic drawings and the actual photography is much closer to this:

http://i306.photobucket.com/albums/nn270/tcups/Picture63.png

http://i306.photobucket.com/albums/nn270/tcups/TopFloor-Floorplan.jpg

http://www.houseoffoust.com/fukushima/reactorcutaway.jpg

That leaves the bulk of the floor storage space to the west side of the access floor, which is where the yellow drywell cap can be seen. I had assumed the pressure vessel's cap would be radioactive enough that after its removal, it would be transferred and placed in the equipment pool to the north of the reactors primary containment plug.

There are pictures that seem to support this in several of my earlier posts.

It has not been conclusively confirmed, at least to me, but I believe that the cask pool for the Bldg 3, 4 design was not incorporated into the corner of a larger SFP as in your marked up photo, but rather was a separate, smaller pool, gated and located between the fuel cask elevator shaft and the SFP of Units 3, 4. If so, then the cask pool may have great significance in the apparent pattern of explosion damage at Unit 4.See also:

http://i306.photobucket.com/albums/nn270/tcups/aerial-floorplan.gif

http://i306.photobucket.com/albums/nn270/tcups/FHM.jpg
Note the absence of an accessory cask pool in the corner of the SFP, and also the concordant location of the yellow drywell cap. Compare to the inside view of Fukushima Diana here, which does have the cask pool in the corner of the SFP

http://i306.photobucket.com/albums/nn270/tcups/Picture38.png

And compare to what I believe to be the layout of the Fukushima Diiachi core and pools seen in this shot. The red arrow indicates the path of transfer of fuel rods through the transfer chute into the SFP, the cutaway detail and green arrow show the access through a much larger gate to the equipment pool and, I believe, the RPV cap in the equipment pool.

http://i306.photobucket.com/albums/nn270/tcups/Picture2-4.png

PS: See also this recent video

http://www.youtube.com/watch?v=_L5cc8yNvDA&feature=youtu.be

 

[AtomicWombat]

The real question is: How the hell would it reach detonation limit, 18%, without getting ignited first? You can explain it when it's leaking from the reactor, having cooled down sufficiently, but there's zirconium burning in steam (and air) there, at more than 1000 degrees Celsius or so, I'd guess hot pieces of oxide flying around, etc.
From 4% to 18% it is deflagration, not detonation.
See this:
http://www.iaea.org/ns/tutorials/regcontrol/appendix/app9344.htm
and check wikipedia etc:
http://en.wikipedia.org/wiki/Hydrogen_safety

I'm really kind of confused. I just can't believe in hydrogen detonation in reactor 4. Does not compute. I don't believe in nuke steam explosion in SPF either.

Very good point. I'd forgotten about the difference between flammability and explosive limits.

Hydrogen is lighter than air so it will tend to accumulate near the ceiling of the reactor buildings and could build beyond the explosive limit provided no source of ignition was present.

Whether it would burn in air as soon as it is produced above the SFP would presumably depend on the H2 production rate and the air supply - given the temperature is likely high enough.

This video demonstration - where hydrogen is produced in a steam-zirconium reaction - shows that the hydrogen is not necessarily immediately burnt in air.
http://vimeo.com/22209827"

 

[AtomicWombat]

http://search.japantimes.co.jp/cgi-bin/nn20110413x1.html"

"The radiation level 6 meters above the spent-fuel storage pool at the crippled Fukushima No. 1 nuclear plant was measured at 84 millisieverts per hour Tuesday. Normally, it's 0.1 microsievert.

Tepco used a robot to take a water sample from the pool Tuesday to analyze the radioactive materials in it, which can tell them in greater detail what is happening to the spent fuel rods."

If they can measure radiation 6 metres above SFP 4 and sample it with robots, why can't they take a decent high resolution photo!

I feel more like a mushroom every day.

 

[hbjon]

I bet you didn't know that the garbageake mushroom has elevated levels of vitamin D when exposed to brief amounts of UV radiation. Much like the workers on site in Fukushima. They will probably see their vitamin D levels increase as well. Vitamin D is a beneficial nutrient the human body cannot store for long periods of time. Go easy Borek, go easy.

 

[densha_otoko]

Thanks for the updates. BTW, according to some Japanese documents I read a few days ago (cannot find now) the 4/08 R1 Drywell radiation reading was actually 187 Sv/h, not EXACTLY 100 as reported in some places. A Japanese source said 100 was the max limit reportable for some reason, but a conversion of the raw readings data released by Tepco translated to 187 Sv/h.

It bugs me that they delayed reporting #1 data right after the nitrogen injections started and then stopped reporting Drywell radiation after it started to go wild this week. And in your chart today we see a Torus radiation spike in #1. #1 is not looking stable indeed.

Also trying to find #4 fuel pool data trends. I think #4 pool has MOX fuel rods as well. Kyodo news says #4 has 204 unused/new fuel rods in addition to the 1,331 rods stored there. (http://english.kyodonews.jp/news/2011/04/85295.html)

Does the presence of unspent fuel rods make the situation more volatile or dangerous?

Updated my plots of #Fukushima reactor variables to NISA release 91 (13/apr 13:00) : http://bit.ly/gAuxse

(Note that release 89 merely repeated the data of release 88 for units #1 and #2, which were measured at 06:00 on apr/12.)

 

[Reno Deano]

You run the effluent out of the reactors into the water processing facility/ship then pump it back to the plant. Depending on temperatures you run it through appropriate radiator/coolers before it gets to the ship.

Have experience with one of those systems (cobalt 60 removal) they would soon be such a high radiation hazard (due to fuel particle buildup on the filtration system) that it would need to be towed out to sea to reduced area radiation levels. Also, the inplant radwaste system is not designed (shielded) for fuel particle removal.

Dean

 

[Reno Deano]

I notice from the NEI reports that Unit 1 is having water continously injected! Why not recirculated? Where is the water going? Seems to indicate that the RPV and primary containment are breached, and they cannot keep the core covered. If hydrogen is being generated in such a large scale to need a Nitrogen blanket, then the core must be uncovered or cycling through covered and uncovered. Your thoughts folks.

Dean

 

[PietKuip]

Does the presence of unspent fuel rods make the situation more volatile or dangerous?

Unspent fuel produces less decay heat, but it is more likely to go critical.

 

[Dmytry]

Unspent fuel produces less decay heat, but it is more likely to go critical.

what the hell is unspent fuel doing in the pool? It doesn't need to be cooled, and in fact there's garbageton of precautions in transportation to prevent it from going critical if truck falls off bridge into a river.

 

[Samy24]

Updated my plots of #Fukushima reactor variables to NISA release 91 (13/apr 13:00) : http://bit.ly/gAuxse

(Note that release 89 merely repeated the data of release 88 for units #1 and #2, which were measured at 06:00 on apr/12.)

There is a jump in the Csupc readings (1930) of unint 1 in your plot regardng release 91. Where did you get this data?

 

[razzz]

I notice from the NEI reports that Unit 1 is having water continously injected! Why not recirculated? Where is the water going? Seems to indicate that the RPV and primary containment are breached, and they cannot keep the core covered. If hydrogen is being generated in such a large scale to need a Nitrogen blanket, then the core must be uncovered or cycling through covered and uncovered. Your thoughts folks.

Dean

One would have to conclude at the least that the plumbing is broken, crack or missing to all three cores whether or not the cores remain inside some kind of containment due to the fact all the cooling liquid going in comes out contaminated. So, like unit 4, the fuel rods are all exposed to the environment without watering. A description like 'containment' would be a misnomer as far as I'm concerned.

 

[bidou]

Hello everyone.
First I want to thank you all. I follow this discussion since 10 days and its really interesting.
Big Kudos!

I have some questions about the Corium.
We know that the Fuel is in pretty bad shape.
Some says Corium may be present.
Others are more confident and says that Corium IS present.
(I've read that after 10 hours without cooling everything is potentialy melting).
So what do you think? Are Corium ponds present in Fukushima?

Second question.
IF Corium is present. Can it go critical?
Corium is an indistinct molten mass of a little bit everything.
Is it possible that it goes critical? Or hardly?
IF Corium is present and it can go critical.
What are the risks? Does this "only" throw radiation everywhere or can it heat so rapidly to explode?

Yes I know there is many IF and many questions :/
Thank you in advance.

 

[georgiworld]

Nice work georgiworld, that took some time and effort. Can't add much. Looks like entombment looks impossible due to debris having to be removed first. Everything contaminated and not approachable doesn't help.

I must clarify that these images are not my work. I noticed new images and a different interpretation of old ones and wanted feedback from the experts on this forum. The website is quite comprehensive and deserves attention. There are probably errors in the analysis, which I hope the members here can point out.

I have thanked the author for her work and in no way want to take credit for the fine job done.

 

[georgiworld]

I wonder if someone can clear something up for me. From the beginning I thought Reactor 4 posed the most danger since the fuel in it, both spent and unspent, were outside of containment. Since then most attention has focused on the three other reactors and the possible breaching of the RPV with a concomitant oozing of corium .

There have now been reports of fires at number 4, which has refocused attention on it and which concerns me greatly.

As I understand it, the decay heat that is emanating from the spent fuel has created the need for a great deal of water to be added in order to remain cool. While this effort appears to have worked since there remains water in the pool, the amount of heat generated maybe too much to deal with and the excess heat has found another outlet.

Now what I'd like to know is could this heat be melting the unspent fuel rods? Is that what is on fire?

Are we looking at an open-air reactor with widespread dissemination of radiation?

Can anyone reassure me that this is not the case.

 

[Arm_Chair_QB]

Hello everyone.
First I want to thank you all. I follow this discussion since 10 days and its really interesting.
Big Kudos!

I have some questions about the Corium.
We know that the Fuel is in pretty bad shape.
Some says Corium may be present.
Others are more confident and says that Corium IS present.
(I've read that after 10 hours without cooling everything is potentialy melting).
So what do you think? Are Corium ponds present in Fukushima?

Second question.
IF Corium is present. Can it go critical?
Corium is an indistinct molten mass of a little bit everything.
Is it possible that it goes critical? Or hardly?
IF Corium is present and it can go critical.
What are the risks? Does this "only" throw radiation everywhere or can it heat so rapidly to explode?

Yes I know there is many IF and many questions :/
Thank you in advance.

There is the saying: never say never. Certainly this recent tragedy is once again a testament to this philosophy and a stark reminder to all engineers and scientists.

Given that disclaimer, these civilian nuclear reactors are designed with contingency in place to ensure they (for the most parts) do not go critical when they aggregate into a lumped mass corium at the bottom of a reactor containment and beyond. This is because firstly the nuclear fuel is of low purity in terms of fissile elements. Secondly, neutrons generated directly from fission of say uranium have too high energy - this results in a low probability of causing other fission events of other uranium atoms thereby eventually freezing out a chain reaction.

These reactors are purposely designed to have neutron moderators placed between fuel rods to slow down and reduce the energy of these neutrons from fission, so that they can cause fission and sustain a chain reaction. In other words, when fuel rods are melted down into a corium, there is presumably no more neutron moderators between the fuel rods and fuel elements (that is, the water), thereby from that point on you are primarily concerned with high energy neutrons generated from fission which have low probability of sustaining a chain reaction while thermal neutrons (lower energy) that can sustain a chain reaction are reduced in a hypothetical corium configuration.

This is the best case scenario of course. If it so happens that the civil structure of the plant itself unknowingly had neutron reflecting material nearby, it may be able to sustain a reaction to a degree. Theres also the possibility that the corium achieves localized critical mass configurations within the corium that can sustain a reaction (though not likely as the fuel is purposly designed to have low purity and is assumed to be homogenous in composition). All of this is purely hypothetical of course as are any other plausible scenarios people can draw up.

That is also not the end of the story of course, as life is never that perfect: it is not just 100% fuel configuration with control rods in place or 100% corium lump mass. If it is partially melted with a corium and some spent fuel assembies, presumably with neutron moderating water inbetween, this can again lead to criticality, especially since control rods that would have otherwise prevented criticality may be ineffective to block neutrons between the corium and the fuel assemblies though they will be far away in distance and the reaction rate should not be very high.

 

[elektrownik]

New thermal images, very bad, so hot: http://www.mod.go.jp/j/approach/defense/saigai/tohokuoki/kanren/230414.pdf

 

[bidou]

Thank you for the answer.