Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[Joe Neubarth]

I was talking somewhere else about control rods, in other designs I was reading if the power is cut as the control rods are attached at the top by electromagnets, the rods will fall back into the reactor and shut the reaction down, whereas on BWR's the rods are inserted from underneath by gas pressure. I assume that the control rods must be mounted fairly rigidly to enable them to line up with the fuel assemblages. If these things are true, let us say you have a partial core meltdown, now I was reading somewhere else that the melting point of the fuel rods is about 1800 C whereas the melting point of the control rods is around 2500 C, So in another type of reactor, the detached control rods would fall into the molten fuel mix as the structure of the rods melted and collapsed. but in A BWR if all is as I've put together, as the fuel melts you'd get less and less of the control rods moderating the reaction as the fuel slumps around the vertical rods.

Am I missing something obvious? or will the molten fuel start to react more readily as the moderation gradually disappears due to height and distance?

As the fuel puddles at the bottom of the reactor in the BWR, there is less water between the fuel molecules and thus most of the neutrons that are racing through the Uranium Lava are not slowed down enough to interact with the Uranium.

 

[Astronuc]

I was talking somewhere else about control rods, in other designs I was reading if the power is cut as the control rods are attached at the top by electromagnets, the rods will fall back into the reactor and shut the reaction down, whereas on BWR's the rods are inserted from underneath by gas pressure. I assume that the control rods must be mounted fairly rigidly to enable them to line up with the fuel assemblages. If these things are true, let us say you have a partial core meltdown, now I was reading somewhere else that the melting point of the fuel rods is about 1800 C whereas the melting point of the control rods is around 2500 C, So in another type of reactor, the detached control rods would fall into the molten fuel mix as the structure of the rods melted and collapsed. but in A BWR if all is as I've put together, as the fuel melts you'd get less and less of the control rods moderating the reaction as the fuel slumps around the vertical rods.

Am I missing something obvious? or will the molten fuel start to react more readily as the moderation gradually disappears due to height and distance?

The BWR control rods are inserted hydraulically or pneumatically - with presserurized water. There is a latching mechanism that locks them in place. Below the core there is a guide tube that orients the blade vertically, and the tip of the blade is guided through a stainless steel fixture on which four assemblies sit. The control rod tip also has some rollers which roll along the surface of the channels, and that helps guide the control rod up into the core.

The stainless steel melts at aroudn 1400 C, while Zircaloy melts at 1850 C. The concern is that the stainless steel would melt before the fuel, or would crack and leach boron. If the control rods melted to the bottom or the core, or the boron was lost, then the concern would be criticality. This is one reason that when the operators lose the ability to cool the core, they would have to inject borated water into the core to ensure that there is sufficient boron to prevent criticality.

Well before the cladding and channels melt, they would undergo oxidation/corrosion by the steam. If the cladding fails, then the fuel rods can balloon or split open and the fuel pellets can start disintegrating. Then bits of fuel can drop out into the coolant. In contact with the coolant (water or steam), some fuel can oxidize into particles, and some can dissolve.

The UO2 ceramic melts at 2800 C, well above the cladding and steel melting temperatures.

As long as there is water in the core, the fuel does not melt.


For general interest - http://www.tec-sim.de/images/stories/severe-accident-phenomenology.pdf (~7 Mb, so use save target as)

 

[Joe Neubarth]

The BWR control rods are inserted hydraulically or pneumatically - with presserurized water. There is a latching mechanism that locks them in place. Below the core there is a guide tube that orients the blade vertically, and the tip of the blade is guided through a stainless steel fixture on which four assemblies sit. The control rod tip also has some rollers which roll along the surface of the channels, and that helps guide the control rod up into the core.

The stainless steel melts at aroudn 1400 C, while Zircaloy melts at 1850 C. The concern is that the stainless steel would melt before the fuel, or would crack and leach boron. If the control rods melted to the bottom or the core, or the boron was lost, then the concern would be criticality. This is one reason that when the operators lose the ability to cool the core, they would have to inject borated water into the core to ensure that there is sufficient boron to prevent criticality.

Well before the cladding and channels melt, they would undergo oxidation/corrosion by the steam. If the cladding fails, then the fuel rods can balloon or split open and the fuel pellets can start disintegrating. Then bits of fuel can drop out into the coolant. In contact with the coolant (water or steam), some fuel can oxidize into particles, and some can dissolve.

The UO2 ceramic melts at 2800 C, well above the cladding and steel melting temperatures.

As long as there is water in the core, the fuel does not melt.

As long as there is water "covering" the core the fuel does not melt.

 

[ceebs]

Thanks gents, that connects my thoughts up properly and points them in the right direction :)

 

[JustGuessing]

I've also been trying to understand this "Minimum Debris Retention Injection Rate (MDRIR)" terminology from the NRC report.

I found this slide show from Wolfgang Hoesel and Peter Keller for the Leibstadt Nuclear Power Plant, that covers Severe Accident Management Guidelines:

http://www.docstoc.com/docs/38671644/Folie-eins

Does any of these accident scenarios apply to Fukushima?

Thanks

 

[Astronuc]

As long as there is water "covering" the core the fuel does not melt.

Even if the water doesn't cover the core, the fuel does not melt. Only if there is stagnant steam with essentially no heat transfer (i.e., more or les adiabatic) would the fuel melt.

METI/NISA overview of the events at Fukushima -
http://www.nisa.meti.go.jp/english/files/en20110406-1-1.pdf

 

[Astronuc]

I've also been trying to understand this "Minimum Debris Retention Injection Rate (MDRIR)" terminology from the NRC report.

I found this slide show from Wolfgang Hoesel and Peter Keller for the Leibstadt Nuclear Power Plant, that covers Severe Accident Management Guidelines:

http://www.docstoc.com/docs/38671644/Folie-eins

Does any of these accident scenarios apply to Fukushima?

Thanks

I took a quick look at the document, and it really doesn't apply to Fukushima. For one, KKL has a Mk-III containment, and one will not that the spent fuel pool is in a separate area.

The accident at Fukushima is unique in that the lost off-site power AND their back up power, so they had no cooling of the core or SFPs. It's also possible that there is damage to the containment structure.

I don't believe that KKL has the same seismic risk as Fukushima.

 

[shogun338]

The government is preparing to raise the legal radiation limits to adjust to the fact that people near the plant are sustaining cumulative exposure. The original policy was set to cover reactor workers briefly sustaining high doses in an accident. WHAT ! This is how there government thinks . http://www.reuters.com/article/2011/04/07/us-japan-idUSTRE72A0SS20110407

 

[Jorge Stolfi]

Updated my plots of #Fukushima reactor temp, pressure, water level, CAMS to NISA/METI release 78 (apr/07 08:00) :

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

No big news.
Reactor #1: RPV pressure still rising (last 859 kPa ~ 8.5 bar) and rising faster.
CAMS in suppr. chamber (SC) broke the slow exponential decay trend and increased a bit.
Reactor #2: RPV, DW, SC at ~1 bar; but temp ~150C, how come?
Reactor #3: RPV and DW at ~1bar, ~100C; SC at ~1.7 bar, why?

 

[TCups]

REGARDING THE INITIAL EXPLOSION OF BLDG 3

1) |Fred's earlier observation that the roof of Bldg 3 seems to implode before the blast is correct
2) The initial fireball (Boom) isn't a fireball -- it is a pure, white puff of steam or smoke that only ignites after entering the outside air. After that, it doesn't expand or blow outward, it just seems to burn up and consumes itself. The building explodes next. The vertical plume of dense smoke is the final visible event. I haven't matched each of these to the boom, boom, boom sounds, though.

Each frame = 1/30th of a second (--15.png is at 15/30ths, or 1/2 second after --1.png)

http://i306.photobucket.com/albums/nn270/tcups/Fukushima%20Foto%20Files/Picture1.png

http://i306.photobucket.com/albums/nn270/tcups/Fukushima%20Foto%20Files/Picture2.png

http://i306.photobucket.com/albums/nn270/tcups/Fukushima%20Foto%20Files/Picture3.png

http://i306.photobucket.com/albums/nn270/tcups/Fukushima%20Foto%20Files/Picture5.png

http://i306.photobucket.com/albums/nn270/tcups/Fukushima%20Foto%20Files/Picture15.png

There is much more information in this audio and video to be extracted! Wish I had better video skills.

 

[michael200]

Minimum debris retention rate (MDRIR) is the lowest RPV injection rate at which it is expected that core debris will be retained in the rpv when rpv level cannot be determined to be above the bottom of active fuel. It is utilized to ensure that injection into the Rpv is sufficient to remove decay heat from the core debris.
This is scary stuff. Essentially trying to cool corium so that it doesn't fail the reactor pressure vessel.

 

[shogun338]

Wikipedia page of all criticality accidents . A criticality accident, sometimes referred to as an excursion or a power excursion, is an accidental increase of nuclear chain reactions in a fissile material, such as enriched uranium or plutonium. This releases a surge of neutron radiation which is highly dangerous to humans and causes induced radioactivity in the surroundings.http://en.wikipedia.org/wiki/Criticality_accident

 

[Jorge Stolfi]

... the roof of Bldg 3 seems to implode before the blast ...

You must be aware that MPEG and JPEG compression add very complicated artifacts to the frames. Roughly, each 8x8 pixel block is "simplified" independently of the other blocks. So one gets blurring and/or spurious streaks within each block, and spurious sharp edges between the blocks. For MPEG there are also complicated tricks to simplify apparent motion, that generate more artifacts when you try to grab a single frame. The video was recorded at high compression (= low quality) so these artifacts are quite strong. To make things worse, an edge-enhancement filter was used before compression --- which adds its own artifacts, such as spurious "grains" and "echoes" along sharp light/dark boundaries. Unfortunately, most of this damage is irreparable, since no filter can restore the information that was lost in the encoding.

For example, although the reddish flash spans a dozen pixels across, the video does not record any detail about its position, shape, and texture. The flash basically got simplified to one or two very bright 8x8 squares, with no internal detail; and that is all we are ever going to get.

What seems to be "the roof caving in" could also be a ring of black dust being blown horizontally al around the building, along the edge of the tar/cement roof, as the latter begins to be lifted off the underlying metal framework. This ring of dust becomes wider in the succeeding frames, covering more and more of the wall, from the top down.

The vertical plume of dense smoke is the final visible event.

I believe the rising column and mushroom is just a late convection artifact (i.e. not thrown out by the explosion, but lifted by buoyancy.) Like the mushroom of a nuclear bomb, or of a large gas tank explosion.

 

[AntonL]

pdf pages 46 to 55 of "[URL assessment procedures for determining protective actions during a reactor accident
IAEA-TECDOC-955[/URL] gives the method to asses core damage from CAMS radiation data that is published regularly



http://www-pub.iaea.org/MTCD/publications/publications.asp" do not be put of by price - that is for the paper copy - pdf can be downloaded

 

[razzz]

REGARDING THE INITIAL EXPLOSION OF BLDG 3

1) |Fred's earlier observation that the roof of Bldg 3 seems to implode before the blast is correct...

Without knowing the distance the camera is from the blast it would be hard to re-adjust the sound track to the video explosion by eliminating the delay-distance factor. As I read comments to the video, some complained that the sound was not played during the first showing of the video and later aired with a soundtrack, making commenters suspicious that a soundtrack was added in. I think the distance causing delay in sound travel was confusing to viewers.

Here I'll link Unit 1's explosion again, not for the sound but lack of a noticeable flash, also notice towards the middle of the explosion where a dark rise, contrasting against the white surrounding clouds, begins to balloon upwards but quickly recedes and a link to Unit 3 without sounds.

http://www.youtube.com/watch?v=9oNEIj7EmNo&feature=related"

http://www.youtube.com/watch?v=9oNEIj7EmNo&feature=related"

 

[shogun338]

REGARDING THE INITIAL EXPLOSION OF BLDG 3

1) |Fred's earlier observation that the roof of Bldg 3 seems to implode before the blast is correct
2) The initial fireball (Boom) isn't a fireball -- it is a pure, white puff of steam or smoke that only ignites after entering the outside air. After that, it doesn't expand or blow outward, it just seems to burn up and consumes itself. The building explodes next. The vertical plume of dense smoke is the final visible event. I haven't matched each of these to the boom, boom, boom sounds, though.

Each frame = 1/30th of a second (--15.png is at 15/30ths, or 1/2 second after --1.png)

http://i306.photobucket.com/albums/nn270/tcups/Fukushima%20Foto%20Files/Picture1.png

http://i306.photobucket.com/albums/nn270/tcups/Fukushima%20Foto%20Files/Picture2.png

http://i306.photobucket.com/albums/nn270/tcups/Fukushima%20Foto%20Files/Picture3.png

http://i306.photobucket.com/albums/nn270/tcups/Fukushima%20Foto%20Files/Picture5.png

http://i306.photobucket.com/albums/nn270/tcups/Fukushima%20Foto%20Files/Picture15.png

There is much more information in this audio and video to be extracted! Wish I had better video skills.

I have converted video to different formats and went frame by frame . What I think your seeing is the walls expand at the same time the fireball starts to eject . The roof seems to travel down at this point then explodes upwards with everything else and fireball is sucked back into upward explosion . A lot of the dust in this explosion is pulverized concrete. Thats why you don't see more of it laying around. Some of the large pieces fell between Unit 2 and Unit 3 onto the building attached to Unit 3. There is a mirage also in the video because it was taken at such long range that makes the structure move some .

 

[|Fred]

The government is preparing to raise the legal radiation limits to adjust to the fact that people near the plant are sustaining cumulative exposure. The original policy was set to cover reactor workers briefly sustaining high doses in an accident. WHAT ! This is how there government thinks . http://www.reuters.com/article/2011/04/07/us-japan-idUSTRE72A0SS20110407

are you sure you linked to the right article ? Where did you read that

 

[clancy688]

pdf pages 46 to 55 of "[URL assessment procedures for determining protective actions during a reactor accident
IAEA-TECDOC-955[/URL] gives the method to asses core damage from CAMS radiation data that is published regularly

I have a question there... the table on page 49 states, that a core will melt completely if it's uncovered for more than one hour. If I remember, the core in unit 2 was dry for a couple of hours a few days after the tsunami (I believe it was around 13th-16th).
Doesn't that mean, that it's possible for the core being completely gone? Or for which time after shut down of the reactor does this table apply to? I couldn't identify informations regarding the time...

http://news.xinhuanet.com/english2010/world/2011-03/14/c_13778395.htm

 

[georgiworld]

NRC suspects RPV 2 has been breached.

http://www.nytimes.com/2011/04/07/world/asia/07japan.html?_r=1

If true, can anything be done to arrest the process?

 

[AntonL]

REGARDING THE INITIAL EXPLOSION OF BLDG 3

1) |Fred's earlier observation that the roof of Bldg 3 seems to implode before the blast is correct
2) The initial fireball (Boom) isn't a fireball -- it is a pure, white puff of steam or smoke that only ignites after entering the outside air. After that, it doesn't expand or blow outward, it just seems to burn up and consumes itself. The building explodes next. The vertical plume of dense smoke is the final visible event. I haven't matched each of these to the boom, boom, boom sounds, though.

Each frame = 1/30th of a second (--15.png is at 15/30ths, or 1/2 second after --1.png)

http://i306.photobucket.com/albums/nn270/tcups/Fukushima%20Foto%20Files/Picture1.png

http://i306.photobucket.com/albums/nn270/tcups/Fukushima%20Foto%20Files/Picture2.png

http://i306.photobucket.com/albums/nn270/tcups/Fukushima%20Foto%20Files/Picture3.png

http://i306.photobucket.com/albums/nn270/tcups/Fukushima%20Foto%20Files/Picture5.png

http://i306.photobucket.com/albums/nn270/tcups/Fukushima%20Foto%20Files/Picture15.png

There is much more information in this audio and video to be extracted! Wish I had better video skills.

When looking at frames 3, 5 and 15 I realize we are not looking at an explosion extending to the left of the picture but at a well known problem of an overexposed and saturated CCD pixel effecting the next pixels that are read out serially. Therefore the explosion extending to the right of the building could very well be a electronic recording artifact.

Further you will note the black line next to white surfaces - this is an electronic artifact from the image sharpening process and these are one or two pixels wide.

That a hydrogen explosion is followed by an implosion I have speculated in https://www.physicsforums.com/showpost.php?p=3199497&postcount=641"

I now have found the proof in this document http://www.gexcon.com/doc//PDF files/Middha_Hansen_CFD_09.pdf see pressure graphs page 3 of 8

 

[shogun338]

Without knowing the distance the camera is from the blast it would be hard to re-adjust the sound track to the video explosion by eliminating the delay-distance factor. As I read comments to the video, some complained that the sound was not played during the first showing of the video and later aired with a soundtrack, making commenters suspicious that a soundtrack was added in. I think the distance causing delay in sound travel was confusing to viewers.

Here I'll link Unit 1's explosion again, not for the sound but lack of a noticeable flash, also notice towards the middle of the explosion where a dark rise, contrasting against the white surrounding clouds, begins to balloon upwards but quickly recedes and a link to Unit 3 without sounds.

http://www.youtube.com/watch?v=9oNEIj7EmNo&feature=related"

http://www.youtube.com/watch?v=9oNEIj7EmNo&feature=related"

Razzz you can look at the layout of the plant and see from where this was filmed the camera had to be a least 2 miles away . Some say it was 5 miles from plant . At 2 miles it would have taken around 10 seconds for that sound to reach the camera and on the one video it reached the camera at 2 seconds . That is why I say they sound was added to that video . On the video that is zoomed in more you can see the walls expand then a split second later the fireball explodes out upper right side facing turbine building .

 

[|Fred]

FK-I Units 1-5 are MK I containment, but FK-I Unit 6 is Mk II.

Unit 1 is a BWR/3, Units 2-5 are BWR/4 and Unit 6 is a BWR/5.

Unit 4 containment is the advanced type (this is not necessarily the case of the other BWR/4 unit in the plant, and likely not the case)

 

[TCups]

You must be aware that MPEG and JPEG compression add very complicated artifacts to the frames. Roughly, each 8x8 pixel block is "simplified" independently of the other blocks. So one gets blurring and/or spurious streaks within each block, and spurious sharp edges between the blocks. For MPEG there are also complicated tricks to simplify apparent motion, that generate more artifacts when you try to grab a single frame. The video was recorded at high compression (= low quality) so these artifacts are quite strong. To make things worse, an edge-enhancement filter was used before compression --- which adds its own artifacts, such as spurious "grains" and "echoes" along sharp light/dark boundaries. Unfortunately, most of this damage is irreparable, since no filter can restore the information that was lost in the encoding.

For example, although the reddish flash spans a dozen pixels across, the video does not record any detail about its position, shape, and texture. The flash basically got simplified to one or two very bright 8x8 squares, with no internal detail; and that is all we are ever going to get.

What seems to be "the roof caving in" could also be a ring of black dust being blown horizontally al around the building, along the edge of the tar/cement roof, as the latter begins to be lifted off the underlying metal framework. This ring of dust becomes wider in the succeeding frames, covering more and more of the wall, from the top down.
I believe the rising column and mushroom is just a late convection artifact (i.e. not thrown out by the explosion, but lifted by buoyancy.) Like the mushroom of a nuclear bomb, or of a large gas tank explosion.

'tiz true -- resolution won't improve, and compression sucks detail out of the image. I am much more in tune with the effects of lossy compression in still photos and high resolution digital gray-scale images than I am with video that is low resolution stuff from the start, but I suggest that if not the detail, then the overall general motion and time frame of the motion are preserved in the context of a frame to frame analysis at 1/30 rate.

Also, compression artifact isn't what turns the initial white puff into red. Only heat does that. And though shadow and compression artifact play hell with the fine details of what is in the vertical smoke plume, there is very little doubt that a whole pile of garbage is falling out of it, streaking ground-ward in later frames.

Convection may cause billowing mushroom clouds and waft smoke and dust and water vapors aloft -- some of that is certainly going on; however I, for one, doubt rising heat alone will casually toss large, heavy chunks of debris almost straight and then quickly drop them on and around the building. It takes significant mechanical force and the impulse of a blast to accomplish that.

As for the "imploding" roof effect, I suggest (agree with you that) it seems equally plausible, and perhaps even likely, that the apparent downward roof movement is neither compression artifact nor implosion, but perhaps instead the visual effect of the sides of the top floor being blown outward and down, surrounded by dark smoke. When examined very carefully, there almost seem to be some horizontal contrails coming from that blast, too.

All great fun to sift through and speculate over. It is going to be even more interesting if I can get the audio track, pitch adjusted for slow motion, synched with the video. There are a bunch of very weird mechanical noises coming from that clip, too.

PS: I tried as best I could to hold to on-screen resolution when I grabbed the individual frames so as not to degrade the image further. I confess that I not too familiar with the .png format or loss of detail from a screen grab in .png format being re-displayed at the same on screen resolution. Side by side with the original video on screen, the reproduction seems true.

PPS: wiki says .png is lossless, bitmapped

 

[shogun338]

are you sure you linked to the right article ? Where did you read that

That was copy and pasted from the news report then link added . I just went back and read it and its not there now. It was on page # 2 of this report and they have changed it . I will look and see if its reported anywhere else .

 

[shogun338]

Fred here is another link with the same statement .The government is preparing to raise the legal radiation limits to adjust to the fact that people near the plant are sustaining cumulative exposure. The original policy was set to cover reactor workers briefly sustaining high doses in an accident. http://www.publicbroadcasting.net/weos/news.newsmain/article/0/0/1785774/World/Japan.tackles.hydrogen.buildup..cumulative.radiation

 

[TCups]

REGARDING COMPRESSION ARTIFACT AND RESOLUTION

Just for grins, here are the actual pixels I am able to resolve, not from the video, but from the links to the frame grabs I posted. ROI is the initial white puff and red fire ball.

http://i306.photobucket.com/albums/nn270/tcups/Fukushima%20Foto%20Files/Picture2-1.png

http://i306.photobucket.com/albums/nn270/tcups/Fukushima%20Foto%20Files/Picture3-1.png

http://i306.photobucket.com/albums/nn270/tcups/Fukushima%20Foto%20Files/Picture4-1.png

Not great, but more than 8 pixels for sure. Plus the tower just to the left will give an idea of edge artifact and contrast resolution.

 

[|Fred]

I've google it as well and the quote was edited out from a number of media, might be an interpretation mistake that was cut out

 

[shogun338]

I've google it as well and the quote was edited out from a number of media, might be an interpretation mistake that was cut out

Yes . I hope so . I have been searching news sites for more info on that statement and have found nothing official yet .

 

[Jorge Stolfi]

the overall general motion and time frame of the motion are preserved in the context of a frame to frame analysis at 1/30 rate.

The MPEG format encodes motion in a complicated way. Extracting a frame requires non-trivial interpolation and may add motion artifacts. (For instance, in extreme cases a spot that moves steadily at 2 pixels per frame may be encoded as a spot that moves 6 pixels in one frame and 2 pixels backwards in the next frame. When played at normal speed the eye sees only the average.) Saving each frame as a .png file prevents *additional* loss but does not recover what was lost in the JPEG/MPEG encoding, and retains all the artifacts of the latter.

Also, compression artifact isn't what turns the initial white puff into red. Only heat does that. ... there is very little doubt that a whole pile of garbage is falling out of it, streaking ground-ward in later frames. ... rising heat alone will [not] casually toss large, heavy chunks of debris almost straight and then quickly drop them on and around the building. It takes significant mechanical force and the impulse of a blast to accomplish that.

I think so too.

 

[shogun338]

TEPCO should have heeded the warnings of the stone slabs . http://news.yahoo.com/s/ap/as_japan_earthquake_warnings_in_stone