Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[Jorge Stolfi]

Let's please stop this discussion about "double layers" of fuel in the SFP. The depth of the fuel pool is about 40 ft and the height of a fuel assembly in the SFP racks is about 14 ft. Plant technical specifications require a minimum water level of about 20 ft above irradiated fuel in the SFP. This technical specification requirement could never be met if two fuel assembilies were stacked on top of each other. The very idea of such a thing would be impractical.

Er, just because something is against the rules, it does not mean that it wasn't done.

They may have assumed that very old and/or fresh fuel did not need 20ft water. After all, while the fuel is in transit between reactor and SFP, I believe it is carried above the top of the spent fuel in the SFP, and therefore under less than 12 feet of water. Is this correct?

When a utility increases the capacity of the SFP, they do it by replacing the exisiting used fuel storage racks in the SFP with racks that allow the fuel to be placed closer together (higher density).

I understand that re-racking had already been done at Fukushima Daiichi. If the new packing is like that described in the re-racking articles previously posted, then the capacity cannot be increased without going to a second layer.

Someone quoted a capacity for 1444 fuel assemblies for the SFP in each unit. Is that before or after re-racking? The same sources said that 1535 were currently stored in #4. How can we square these numbers?

The geometry is analyzed and possible change to the neutron absorber panels in the fuel racks are changed to preclude criticality of the assemblies in the SFP.

But the neutron absorbers used in the SFP (unlike those used in the reactor core) will melt or decompose before the temperature reaches 670C, which seems to be well below the threshold for significant zirconium+steam=H2.

 

[Jorge Stolfi]

It seems to me that if the geometry of the fuel cells is maintained, even without the boron, criticality would require return of the water as a moderator. I may be wrong.

Well, I assume that the boron baffles are there because they are needed.

Interleaving fuel and moderator seems to be the most efficient design, but if I understand correctly it is not necessary. Suppose the fuel gets compacted into a solid mass surrounded by water, away from absorbers. Most of the neutrons that escape the mass will scatter around the surrounding water and eventually find their way back to the mass. In other words the water should behave like a diffusing "mirror", just as a cloud cover eventually "reflects" most of the incident sunlight back to space.

If the fuel is in layer at the bottom of the pool, with water on one side only,
then almost 50% of the neutrons that are produced in it should be scattered back to it.

 

[Dmytry]

I've been wondering about that too. Lately they indicate that the nitrogen injection is causing the pressure increase. I don't remember exactly when the nitrogen injection started but I seem to remember the pressure rising well before that.

EDIT: from the 4/7 IAEA report: "Instrumentation "B" for Reactor Pressure indicates that the pressure in the RPV is increasing and instrumentation "A" indicates that it has stabilized. NISA has indicated that some instruments in the reactor vessel may not be working properly. "

it would imply that they cannot relieve the pressure (they would want to keep pressure low as the vessel may have been damaged). The re-criticality, I would not expect it to run nicely, i'd expect some oscillations.

Void coefficient is bad, folks. Positive void coefficient (as in RBMK) is obviously bad, negative void coefficient (as in BWR) is less obviously bad. Sudden power increase on one side collapses bubbles on other side (given the thermal lag between rods and water), resulting in larger power excursion that can collapse bubbles elsewhere even better, etc.

Then the BWR core. Ever thought about that: the fuel has to react on the top, where there's a lot of voids? Where the water density is a lot lower.
BWR control rods are inserted upwards, so that the top which has voids and less moderation also has less neutron absorption. The RBMK (Chernobyl's reactor) control rods were graphite tipped on the bottom so that the fuel on the bottom (where there's less voids) could react. Those are the kind of very dangerous design decisions that you have to do to increase fuel burnup when you have coolant that is also the moderator boiling inside the reactor, and when the void coefficient is not zero.
Entire BWR idea is on par with RBMK in terms of cutting the safety to make things cheaper, increase fuel burnup, etc. Boiling water and nonzero void coefficient = no good. In BWR, the fuel obviously has to be able to react on top where there's a lot of voids. A lot of excess reactivity is required. PWR is a much more reasonable design, but also more expensive.

When it comes to safety, the burden of proof is not on me that something scary can happen, but on designer that it can't happen.

Safety design (dangerous until proven safe) is an opposite of legal process (safe until proven dangerous), but everyone tends to debate in the 'safe until proven dangerous' way.

 

[AtomicWombat]

Tks-tsk-tsk.

Is it possible that the replacement process was in 'dry' phase in the time of the earthquake?

What if the pool gates were broken during the EQ and the pool water flooded the empty RPV - leave the pool with only a limited amount of water, barely covering the rods? That could explain the hydrogen buildup. And this flow can explain the weird thermal image too (the water injected to the pool is still flowing to the RPV and beyond).

Which reminds me. ON the UCS site they mention a failure mode whereby the seals around the gates on the SFP fail when there is a power loss. If the primary containment and rector were "dry" due to the shroud replacment the SFP water would leak there when the power failed.
http://allthingsnuclear.org/post/3964225685/possible-source-of-leaks-at-spent-fuel-pools-at"

 

[AtomicWombat]

I guess that will be the third or fourth time I'm asking this...

In hope that I'll get an answer this time:

http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/plots/cur/plot-un1-full.png

In this plot (provided by Stolfi, thx) you can see that the pressure in the core of Unit 1 is rising and rising. Furthermore, a couple of days ago the drywell radiation sensor topped 100 Sv/h and then went AWOL.

I have no idea of reactor physics, so I'm asking you: What could that imply? What's the meaning of this data? Recriticality? Especially with these heightened I-131 measurements in the trenches of Unit 1 and 2? Or nothing?

The radiation measurment rose after the start of N2 injection. N2 injection will do 2 things 1) stir up the contents of wherever it's being injected; and 2) create void space.

Void space in the water will reduce shielding from the radiation sources. Stirring could spread the radiation around.

All this is speculation. I don't even know whether the N2 is injected into the RPV or dry-well.

 

[Joe Neubarth]

There's no question Stolin's configuration was supercritical. It could hardly be mathematically anything else:
http://en.wikipedia.org/wiki/Demon_core"
It seems that criticality incidents can have quite different time courses. With nuclear weapons criticality accidents appear prompt and self-limiting - the burst of energy restores sub-criticality. With lesser enriched material, it appears criticality can sometimes be sustained without those nearby noticing. Astronuc can probably give more reliable information.
http://en.wikipedia.org/wiki/Criticality_accident"

It seems to me that if the geometry of the fuel cells is maintained, even without the boron, criticality would require return of the water as a moderator. I may be wrong.

You are quite right. Thank heavens when they frantically tried to refill the cement reservoirs alongside the Reactor, most of the fuel assemblies were gone. Basically, it was a self correcting transient of power.

 

[AtomicWombat]

Well, I assume that the boron baffles are there because they are needed.

The water is there for colloing and as a radiation shield. The boron baffles are there to avoid criticality in water.

Interleaving fuel and moderator seems to be the most efficient design, but if I understand correctly it is not necessary. Suppose the fuel gets compacted into a solid mass surrounded by water, away from absorbers. Most of the neutrons that escape the mass will scatter around the surrounding water and eventually find their way back to the mass. In other words the water should behave like a diffusing "mirror", just as a cloud cover eventually "reflects" most of the incident sunlight back to space.

If the fuel is in layer at the bottom of the pool, with water on one side only,
then almost 50% of the neutrons that are produced in it should be scattered back to it.

I agree. If the fuel ended up in a solid mass surrounded by water I suspect it would be hard to avoid at least transcient criticality events.

I understood from your original proposal that the criticality was occurring above the water layer where the boron was lost. But if the water was lost here as well I don't see how criticality could occur.

 

[TCups]

AFAIK fuel casks are used only when the fuel is ready for dry storage / has no dangerous heat output which can damage the fuel or the assembly. That's why the SFPs exists.

Rive - sure, understand. There was an excellent post earlier about dry cask fuel storage. But I was not sure that is the same thing a a fuel transfer cask. It may be. But I do know at the Fukushima Daiichi facility, a 7th spent fuel storage pool for the older, colder fuel exists and that it contains a substantial portion of the 40 year old spent fuel on site. As it it still stored in a pool, under water, it logically follows that there is some mechanism in place to transfer rods from one pool to another, and that in principle, though older and colder, those might still be hot enough to require immersion cooling, except for the short-term transfer process. This, however is an educated guess. Also, there must be a process for transferring into the SFP and subsequently into the reactor core, new fuel rods and fuel rod assemblies

I had not considered the existence of a fuel preparation machine in the SFP4 or how it might be used, but perhaps its size and placement in the diagram . . .

http://i306.photobucket.com/albums/nn270/tcups/FuelPrepMachine.jpg

. . . suggest one. Again, this is an educated guess on my part. Is the specific purpose of the fuel preparation machine to take new (ie, not highly radioactive individual fuel rods) and insert them into fuel rod assemblies while under water in the SFP, and conversely perhaps, to allow removal of individual fuel rods, perhaps damaged fuel rods, from a fuel rod assembly and thus repair the fuel rod assembly?

If so, then it would appear that the FHM would need to be all the way to the far edge of the SFP to access the fuel preparation machine, and that there may even be guide channels to allow new fuel rods to be lowered into the individual fuel rod assemblies from the service floor level at the south end of the SFP.

That is a lot to infer from a very basic diagram, but given the amount and quality of information forthcoming from TEPCO, inferential analysis of the photographs and diagrams is, unfortunately, most of what is available.

 

[Krikkosnack]

I'm trying to analyze more in detail this video to get some information about what flew in the sky ... mainly on its mass. Maybe someone can help me too.
http://energheia.bambooz.info/index.php?option=com_content&view=article&id=170%3Areactor-3-explosion-enhanced-view&catid=60%3Avideo&Itemid=85&lang=it

Some notes:
Take a look on the right side of the reactor 3 and follow the hard material falling down near the tower

1) at the time 0:16 there is an explosion of flammable material that expands almost sideways
2) immediately something shoot oneway directed upward the material as a recoil of the weapon (very strange, like a cannonball!)
3) about the time 0:21 comes to its maximum height
4) at the time 0:32 comes around on the ground near the tower under the law of gravitation http://en.wikipedia.org/wiki/Equations_for_a_falling_body

 

[biffvernon]

At approx 1:38 - what was flying overhead - repeated also?

I wondered that but then thought it was a bit of muck on the vehicle window; it reappears again a little later on.

 

[ceebs]

I wondered that but then thought it was a bit of muck on the vehicle window; it reappears again a little later on.

I was thinking Insect myself

 

[dinorobo]

There's new footage of inside reactor 4's building in this news report. You can see them taking a sample from the spent fuel storage pool:

http://news.tbs.co.jp/20110415/newseye/tbs_newseye4701752.html

I don't know if you can watch it outside of Japan though

 

[Rive]

I don't even know whether the N2 is injected into the RPV or dry-well.

To the drywell. One of my forum-mates made a calculation based on the data provided here: http://www3.nhk.or.jp/daily/english/07_37.html

The company says that after injecting 413 cubic meters of nitrogen gas until 5 PM on Thursday, the pressure reading inside the vessel was 1.76, up 0.2 from before the injection started.

For the volume of the drywell he got 3634.5m³: the 'factory data' of an MK1 containment is 3700m³ (don't ask for calculation details, it wasn't my work).

- As far as I know the drywell of unit 1 were injected with considerable amount of seawater.
- the JAIF reports refers to water injection to drywell of unit 1 as ' to be confirmed'.

Where is the water? Or is the calculation wrong?

...educated guess...

Mine was an kind of educated guess too.

About http://www.freepatentsonline.com/y2010/0232564.html" .

Side effect of googling that machine was this: http://www.aws.org/w/a/wj/2003/09/048/index.html

 

[Rive]

http://www.youtube.com/watch?v=gWzPU5fgThA&feature=youtu.be

Video of fire engine almost getting its water to the right place.

I've tried to 'deshake' that video with VirtualDub and Deshake filter but I have not enough bandwidth to upload the result...

 

[tsutsuji]

A new batch of pictures (some of them taken on April 14, 2011) is available at http://cryptome.org/eyeball/daiichi-npp8/daiichi-photos8.htm

 

[biggerten]

Because nothing says everything is under control like the government doing a runner

http://www.novinite.com/view_news.php?id=127294"

ITAR-TASS is not quite the AP. And furthermore, I'd be surprised if the US Government doesn't have plans in place to relocate DC if trouble arises, I'd bet most developed countries do.

 

[Borek]

I'm trying to analyze more in detail this video to get some information about what flew in the sky ... mainly on its mass. Maybe someone can help me too.

You can't calculate the mass from known trajectory. Every object having the same initial speed will behave identically (well, ignoring air resistance, but in the case of high density objects and not too high speeds that's quite good approximation).

 

[tsutsuji]

ITAR-TASS is not quite the AP. And furthermore, I be surprised if the US Government doesn't have plans in place to relocate DC if trouble arises, I'd bet most developed countries do.

The plans for relocating the capital of Japan is an old story. The timeline at http://www.mlit.go.jp/kokudokeikaku/iten/English/background/index.html starts in the 1950s, but in old times, emperors changed the location of their capital quite often : http://en.wikipedia.org/wiki/Capital_of_Japan

It is obvious that the occurrence of a major earthquake or any other large-scale disaster in the Tokyo Metropolitan area, where political and economic activities and population are concentrated, would dramatically impact not only Japan’s economy but also the global economy, as well as destroy lifeline services essential to people’s lives, disrupt the transportation network such as Shinkansen (bullet trains) and airports, and cause deterioration in public security. In preparation for such circumstances, it is becoming increasingly important to relocate the Diet and other organizations—the core functions of our country—outside the Tokyo Metropolitan area as a measure of risk management.

December 22, 2004
Inter-party Conference Committee of Both Houses on the Relocation of the Diet and Other Organizations
http://www.mlit.go.jp/kokudokeikaku/iten/English/reports/report_1222_2004.html

 

[clancy688]

The radiation measurment rose after the start of N2 injection. N2 injection will do 2 things 1) stir up the contents of wherever it's being injected; and 2) create void space.

Okay, thx.

There's new footage of inside reactor 4's building in this news report. You can see them taking a sample from the spent fuel storage pool:

http://news.tbs.co.jp/20110415/newse...ye4701752.html

I don't know if you can watch it outside of Japan though

Interesting video. Doesn't look as if there's much damage inside of Unit 4... oO

 

[triumph61]

The same Video but better . Sorry for my English

 

[cphoenix]

I wrote:

While I'm at it, let me float a new hypothesis for building 4:

1) Fuel abruptly went critical near the bottom of the pool. (Even a mild aftershock might have shifted geometry.)

(list continues, describing a steam bubble and water hammer causing steam explosion in the building below the pool.)

Assuming that http://www.asahi.com/english/TKY201104140125.html is correct, and the water sample rules out any disintegration of fuel rods, then this is no longer plausible. I've added that note to the original post.

 

[Jorge Stolfi]

I understood from your original proposal that the criticality was occurring above the water layer where the boron was lost. But if the water was lost here as well I don't see how criticality could occur.

I do not have a definite proposal; I am just looking for ways that chain fission could have happened in the SFP (which could explain why the explosion happened earlier than predicted by decay heat alone).

Suppose the top half of the assemblies got hot enough to melt the top half of the boral baffles. Then we got a layer of 1535 half-assembles, densely packed without neutron absorbers, sitting above a layer of water. By the above reasoning, that water would behave like a neutron moderator+reflector, with somewhat less than 50% efficiency (for being on one side only of the fuel).

The problem with this idea is that the still-intact lower halves of the boral plates would absorb a large part of the neutrons that enter the water, before they had the chance to emerge. Would enough of them survive to produce significant fission?

The idea may have a better chance if the assemblies got completely uncovered for a while, lost the entire boral baffles, then got partly or totally submerged again. But that did not happen, did it? Water injection into the SFP only began after the explosion, right?

Or perhaps the explosion of #3 jostled the seals of the SFP door in #4, allowing water to flow from the reactor pool to refill the SFP, where the assemblies had already been exposed...

Anyway, note that the water-around-is-enough observation applies also to a molten fuel mass in a reactor core. Will the molten absorbers (steel?) float over the molten/compacted fuel? Or sink below it? Or get mixed with it?

 

[AntonL]

A new batch of pictures (some of them taken on April 14, 2011) is available at http://cryptome.org/eyeball/daiichi-npp8/daiichi-photos8.htm

and these solve the mystery of the "ballistic" fuel handling machinery in unit 3, submerged in SPF3
[PLAIN]http://k.min.us/imMKhK.JPG

 

[ottomane]

and these solve the mystery of the "ballistic" fuel handling machinery in unit 3, submerged in SPF3

Any idea what the half round concrete plate may be (top half of the pic, left of the middle)?

 

[Dmytry]

I do not have a definite proposal; I am just looking for ways that chain fission could have happened in the SFP (which could explain why the explosion happened earlier than predicted by decay heat alone).

Suppose the top half of the assemblies got hot enough to melt the top half of the boral baffles. Then we got a layer of 1535 half-assembles, densely packed without neutron absorbers, sitting above a layer of water. By the above reasoning, that water would behave like a neutron moderator+reflector, with somewhat less than 50% efficiency (for being on one side only of the fuel).

The problem with this idea is that the still-intact lower halves of the boral plates would absorb a large part of the neutrons that enter the water, before they had the chance to emerge. Would enough of them survive to produce significant fission?

The idea may have a better chance if the assemblies got completely uncovered for a while, lost the entire boral baffles, then got partly or totally submerged again. But that did not happen, did it? Water injection into the SFP only began after the explosion, right?

Or perhaps the explosion of #3 jostled the seals of the SFP door in #4, allowing water to flow from the reactor pool to refill the SFP, where the assemblies had already been exposed...

Anyway, note that the water-around-is-enough observation applies also to a molten fuel mass in a reactor core. Will the molten absorbers (steel?) float over the molten/compacted fuel? Or sink below it? Or get mixed with it?

what if an aftershock makes a wave. then the water in the wave boils violently, pushing water down, and amplifying the wave. That can be expected to happen even without criticality. Would take numerical simulation to demonstrate, of course.

 

[ian_scotland]

From the latest cryptome images, http://cryptome.org/eyeball/daiichi-...hi-photos8.htm

Is it just me, or does the semicircular item with a stepped edge look a bit like the half of the concrete plug that usually sits over over the reactor?

It is of course difficult with possible perspective and scale unknowns

Edit1... AntonL you beat me to it !

Edit 2 the actual plug appears to be approx 6.5m radius. Can anyone identify something to scale from in the photo?

 

[rowmag]

Okay, thx.
Interesting video. Doesn't look as if there's much damage inside of Unit 4... oO

That's what the professor is saying at the end of the video. "What kind of explosion destroyed the building, but left the crane looking relatively unscathed? Very surprising."

Edit to add: Watching the video again, the term he uses is "fuel exchanging machine" (I guess what folks here call the "FHM"), not "crane."

 

[Dmytry]

That's what the professor is saying at the end of the video. "What kind of explosion destroyed the building, but left the crane looking relatively unscathed? Very surprising."

the same kind of explosion that blew all the wall panels from the floor 1 but left 2 out of 4 panels standing on floor 4? (western wall) The kind of explosion that didn't happen where the crane is?

 

[TCups]

and these solve the mystery of the "ballistic" fuel handling machinery in unit 3, submerged in SPF3
[PLAIN]http://k.min.us/imMKhK.JPG[/QUOTE]

Sure looks like part of a big green machine in SPF. Maddening that there isn't a wider field of view. The round thing looks to be too small to be part of the primary containment plug, but it's hard to get an absolute scale from this perspective.

 

[ottomane]

Edit 2 the actual plug appears to be approx 6.5m radius. Can anyone identify something to scale from in the photo?

The white roof panels - aren't they 70cm wide? Not sure anymore.

I have problems to correlate this pic with the other areal pics of R3.

 

[TCups]

The white roof panels - aren't they 70cm wide? Not sure anymore.

I have problems to correlate this pic with the other areal pics of R3.

Funny, too that exposed rebar seems to be partially in and partially out of the pool. How does that happen?

Hey Anton! I've got it! The FHM broke in two pieces and one of them fell back into the SFP! Amazing!

 

[Dmytry]

What is the chimney height and reactor height? We can estimate velocity of rising air there, in reactor 3 explosion video. Hell, we can probably estimate blast energy in kt.

 

[TCups]

What is the chimney height and reactor height? We can estimate velocity of rising air there, in reactor 3 explosion video. Hell, we can probably estimate blast energy in kt.

Dmytry:

http://www.houseoffoust.com/fukushima/blueprint.html

Take your pick. The "chimney" is either the depth of the SFP or the "neck" of the reactor's primary containment, depending on whether one believes the vertical blast originated from the SFP or the primary containment, I suppose.

Surprisingly, in the drawing, they are about the same size, so it may not be that much different.

 

[M. Bachmeier]

What is the chimney height and reactor height? We can estimate velocity of rising air there, in reactor 3 explosion video. Hell, we can probably estimate blast energy in kt.

You could also look at the audio file to try and confirm the energies.

This is my best guess alignment of audio to video with the middle blast corresponding to the visible explosion. Best estimate of camera distance 2.25 KM.

Video Link :

Audio wave table :

 

[M. Bachmeier]

You could also look at the audio file to try and confirm the energies.

This is my best guess alignment of audio to video with the middle blast corresponding to the visible explosion. Best estimate of camera distance 2.25 KM.

Video Link :

Audio wave table :

Also audio file in ac3 format: