Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[NUCENG]

My nuclear power theory was all taught to me in naval nuclear power school half a century ago so I am asking a question that we were not taught an answer to. We were taught to operate plants, not deal with theory of glowing radioactive blobs.

At Fukushima we have heard talk of recriticality.

How is it possible for those melted cores to go critical again when the normal operating process was for neutrons from fission to slow down in water and thus interact with Uranium 235. If the water ain't there, are the neutrons becoming thermal (lower energy state) by bouncing off of the entrained impurities in the melted blob? Does the size of the blob provide for reflection of energy (Neutrons) back towards the center?

We know that Reactor One is melted down, yet it sure looks like it is "breathing" (as some call it) with increases in temperature coming in long waves that would seem to indicate increases in criticality and then decreases.

NucEng, can you or somebody else with experience answer this?

Has any institution done any research in Blob criticality theory?

I am looking at everything I can find on this event. I just checke my download directory related to Fukushima and I am approaching 7 GB. I've at least skimmed most of it, and I just don't know whether the remaining core, debris, corium, blobs are or have been critical since rods were inserted on 3/11.

My position is that Recriticality is possible. I have seen anomalies in sub-drain I-Cs ratios that are exactly that - anomalies. The data limitations to just a few isotopes make it impossible to disprove recriticality, but the same limitations prevent proving recriticality has occurred. As a Navy nuc, you probably remember the term subcritical neutron amplification as the reactor approaches criticality. Oscillating generation of neutrons could explain detection of increased neutron "beams" and blue flashes of light. But criticality is a self-sustaining condition and I haven't seen proof of that.

A hot glowing blob is an interesting image as in imagination. If a hot blob exists it is deficient in moderator so would be difficult to support criticality. At the edges of the blob the presence of water moderator would likely be oscillating between a steam layer and rewetting, that again could produce an oscillating neutron amplification effect, but again, that is not my understanding of criticality.

Destruction of boral or boraflex inserts in a dense packed fuel pool without soluble boron could cause criticality, but at least pictures from unit 4 and pool radioactivity levels are inconclusive.

Part of wisdom is alleged to be knowing what you don't know and I am much wiser now than on March 11. It amazes me how many people can be so certain of what is going on inside all that concrete and steel. We are like six blind men "seeing" the elephant. It is only when we share information and listen to each other that a clear picture will emerge.

We will all now sit in a circle, hold hands and sing "Kumbaya!" ;-}

 

[NUCENG]

But if they are going out of the core to hit the water, who sends the neutrons back into the core?

I remember in Nuc Pwr Sch they did tell us that the reactor vessel does act to redirect the neutrons back in the direction of the core if they try to escape. Gotta herd them little doggies in the right direction or they might get lost.

But if the Blob is out of the reactor, the neutrons would be free to wander in the cement and mortar around them until the blob hits bedrock.

Hummmmm? Blob Criticality Theory. Somebody has to be writing a thesis on this for a doctorate. Right?

"It's Alive! It's Alive!"

If the neutron comes out of the blob its direction is "outward", if there is water around the blob the neutron begins to collide or bounce off the hydrogen nuclei losing a lot of energy in each collision or bounce. Hitting something heavier like an Oxygen nucleus also deflects the neutron, but does not absorb as much of the energy as would a target about the same size as the neutron. In any case the neutron gradualy slows down and due to allthose deflections is now going in a completely random direction (even inwards back into the blob).

Thus water can be both a moderator and a reflector. At some point the neutron will hit a target at the right energy and be absorbed. If that happens to be a fissile atom, the story starts all over again. And they all lived happily ever after.

 

[Quim]

.....criticality is a self-sustaining condition

Is a criticality which causes its own end by rearranging the physical proximity of the supporting material still a criticality? even if it only lasts a couple of milliseconds?

 

[Borek]

Thus water can be both a moderator and a reflector. At some point the neutron will hit a target at the right energy and be absorbed. If that happens to be a fissile atom, the story starts all over again. And they all lived happily ever after.

I don't doubt it is possible that a single neutron gets back, but the main question is whether it can be a self sustaining process? k close to 1?

 

[GJBRKS]

I just saw a white and black spotted DOG walk past the TEPCO webcam , it stopped and even looked into the cam for a sec !

( unfortunately no screenshot)

 

[MadderDoc]

Is a criticality which causes its own end by rearranging the physical proximity of the supporting material still a criticality? even if it only lasts a couple of milliseconds?

I think so. There seems to be nothing in the definition of criticality that implies that the k=1 clause for criticality could not be changed into k>1(supercritical) or k<1 by something rearranging the physical proximity of the supporting material. Cf. a supercriticality might elevate the temperature such as to become critical, or selfdestruct into something subcritical. It would still have been a supercriticality until that happened.

 

[Quim]

It would still have been a supercriticality...

Next question:

Is it possible to calculate the joules of heat produced by the smallest possible self sustaining reaction - stated as Joules per millisecond?

TIA

 

[thehammer2]

I think so. There seems to be nothing in the definition of criticality that implies that the k=1 clause for criticality could not be changed into k>1(supercritical) or k<1 by something rearranging the physical proximity of the supporting material.

snip

Changing a core's surroundings can be of extreme importance. During the Manhattan project, the "demon core" that most people associate with killing Louis Slotin actually killed Harry Daghlian first.

Daghlian was doing experiments on neutron reflectors with the subcritical assembled core. He was stacking tungsten carbide bricks around it in a controlled manner and taking measurements when he accidentally dropped a brick onto the assembly. The brick gave enough reflectivity to the core's surroundings and it went critical and gave Daghlian a massive dose.

This is not to say at all that I think there are suddenly shifts in the surroundings that are making the Fukushima cores critical. This is just to say that when calculating the criticality of a core the surroundings must be considered. During the Manhattan project, if I remember correctly, one of Richard Feynmann's jobs was to maintain safety, including developing protocols for moving materials into and out of areas with consideration of what might be contained in the room next door.

In related news, during the Manhattan Project, these guys worked in the same room with and basically barehanded plutonium bomb cores regularly.

 

[MadderDoc]

Next question:

Is it possible to calculate the joules of heat produced by the smallest possible self sustaining reaction - stated as Joules per millisecond?

TIA

That would come out close to zero, I think. It is indeed a borderline case, but the smallest imaginable critical mass would have consumed fissionable material such as to become subcritical after just one 'neutron generation'.

 

[tsutsuji]

The test of the cesium absorption facility of the water decontaminating system was started with low level contaminated water at 3:45 AM this morning (June 14th). The test of the whole facility will be started on June 16th.

On the other hand, the harbour purifying system is started again with only 30% of the cesium being removed. The presence of oil in the water prevents to reach the expected 60~70%. The flow is 30 tons/hour but more units could be installed.

http://mainichi.jp/select/jiken/news/20110614ddm002040156000c.html
http://www.tv-asahi.co.jp/ann/news/web/html/210614003.html

 

[Quim]

That would come out close to zero, I think. It is indeed a borderline case, but the smallest imaginable critical mass would have consumed fissionable material such as to become subcritical after just one 'neutron generation'.

That sounds more like NUCENG's "subcritical neutron amplification."

If it become subcritical after just one neutron generation how could you consider it self-sustaining?

 

[maddog1964]

You guys do realize that there's a thread which deals specifically with the Unit 3 explosion? How about you talk about that topic over there?

could you please list the link to that thread. ty

 

[MadderDoc]

That sounds more like NUCENG's "subcritical neutron amplification."

If it become subcritical after just one neutron generation how could you consider it self-sustaining?

I did say, this is a borderline case.

 

[Bioengineer01]

@ Bioengineer01


Fine, go and do the exploration... I would suggest you first explore the possibility that there is NO inconsistency in the thermal signatures of the SFP versus the visible surface of water in the reactor vessel.
.

Absolutely agree and I am not wasting any time on conspiracy theories. That is why I am reading the thread and enjoying the discussion and trying to make sense and find an explanation to the apparent inconsistency. I've done myself lots of IR for biological reasons, it is an extremely useful tool, in my post, I was just trying to explain why people are still discussing this. Nothing less, nothing more.

 

[robinson]

http://www.tepco.co.jp/nu/f1-np/camera/index-j.html

While it would be hard to imagine a worse camera set up, even so you can still see the constant steam coming out of the buildings. Is there any plan to do anything to even find out what is happening inside building three?

Like stick some cameras in there? How long do you simply just let a nuclear pile of crap steam away? With out even knowing where the steam is coming from. or what is in it.

 

[Bioengineer01]

I note your tremendous artistic talent in replying. Thank you.

I have always thought of is as ping pong balls and bowling balls. Ping pong balls (neutrons) will bounce off of heavier atoms (bowling balls) without losing energy, but will bounce off of Hydrogen atoms and impart some of their energy to the Hydrogen. I guess eventually they can be turned around.

I read early on that the salt produced by the evaporation of sea water could have a significant effect on this interaction from experts at the NRC that advised Japan to stop the seawater injection. But I never found it in written news, my assumption was that it could help form a crust around the Corium and any cracks or fissures that it may develop and make the process of heat extraction more difficult, but now I wonder if that same crust of salt would not participate in neutron slowdown and reflection. Just a thought, anybody? Can anybody add clarity to this?

 

[MadderDoc]

Absolutely agree and I am not wasting any time on conspiracy theories. That is why I am reading the thread and enjoying the discussion and trying to make sense and find an explanation to the apparent inconsistency. I've done myself lots of IR for biological reasons, it is an extremely useful tool, in my post, I was just trying to explain why people are still discussing this. Nothing less, nothing more.

I agree the heat signature from the reactor well is 'strange'. Generally this signature has had an IR measured temperature close to 30^oC, and this even on early mornings where ambient temperature has been only 0-5^oC.

Naturally under such circumstances we are unlikely to be measuring the temperature of the water surface, but rather the temperature of condensed steam hanging over it. And this would imply that the water surface must be even _warmer_ than 30^oC. I too cannot imagine how water can be kept this warm in the reactor well throughout many days during March and April, with cold nights and never a ray of sunlight hitting it. I certainly would like to know how I can keep the roof of my house cosily warm throughout winter without a considerable heat source underneath it ..

 

[Jorge Stolfi]

If it become subcritical after just one neutron generation how could you consider it self-sustaining?

By that criterion criticality is impossible, since as the fuel is consumed the value of k will decrease until the chain reaction stops.

The k parameter and the critical/subcritical distinctions are drastic simplifications of reality. If you look too closely, the k parameter is not a well-defined quantity, and criticality becomes a fuzzy concept.

On the other hand, note that some chain fissions should occur at a steady rate even if k < 1, and should boost the spontaneous neutron emission rate by the factor 1/(1 - k). For k = 0.8, for example, the total neutron production (spontaneous + fission) should be ~5 times the spontaneous rate. That is "sustained" in the sense that the fission reactions keep happening at the same rate as long as one can consider the composition of the mass constant.

I would guess that even with a boost of x5 or x20 over the spontaneous rate, the heat generated by fission will be negligible compared the normal decay heat of half-used fuel. But what about the radiation hazard?

 

[Pu239]

Conditions in the night are such that it looks steaming every day. My bet is that is mostly a matter of local weather - humidity and temperature changes. Fog clouds are moving in and out of the light, which makes the picture dramatic.

I have looked at the live feed at several occasions, never longer than just a few minutes, usually after someone raises alarm - and each time it looks the same to me.

Edit: it occurred to me that compression artifacts look like a dynamic smoke/steam cloud as well. Thats typical in low light conditions - dark, large spots with slight color gradient look like moving even if the image is still. It can look as a dynamic steam motion, even if the real situation is quite stable.

I gather nobody actually saw the large release of steam - very large - last night. We know it is steaming every day but this was far above the normal. Definitely not fog or clouds. This was a large, fast moving vertical plume of smoke coming directly from #4 - top of roof. It eventually billowed out and clouded everything - then, at that stage it was mistaken by many observers for fog or rolling cloud. Not. (Think of looking at a smoking chimney in cloudy or possibly foggy conditions - smoke is grey, fog is white).

Just before that everything was clear (but dark) with the usual lit-up reactors. The plume was studied carefully [by myself and others] as it grew from a whisp at the top of #4 to a massive all-engulfing cloud. Emergency vehicles arrived soon after, with flashing lights.

Have heard nothing since.

TEPCO LIVE CAMERA

http://www.tepco.co.jp/en/nu/f1-np/camera/index-e.html

 

[StrangeBeauty]

I just saw a white and black spotted DOG walk past the TEPCO webcam , it stopped and even looked into the cam for a sec !...

Could it be that the white spots are neutron reflectors and the black spots neutron absorbers creating a moderating field for recriticality?!

I did say, this is a borderline case.

Yes! It must have been a borderline collie!








Apologies for the physics humor. ;)

 

[robinson]

http://flyingcuttlefish.wordpress.c...-fire-right-now-live-cam-shows-lots-of-smoke/

Second video shows a time lapse where the steam.smoke is obvious. Not from last night, but still, this is a regular event at night.

 

[StrangeBeauty]

I gather nobody actually saw the large release of steam - very large - last night...

A lovely sequence of a marine fog bank rolling in with lots of video compression artifacts thrown in.

http://flyingcuttlefish.wordpress.c...-fire-right-now-live-cam-shows-lots-of-smoke/

Second video shows a time lapse where the steam.smoke is obvious. Not from last night, but still, this is a regular event at night.

Yes lots of "steam" whenever the dewpoint gets close to the air temperature (as it often does at night).

I realize that something (more) horrible could happen with SPF4 or any of the other units, but these frequent steam displays are not it. The building is not on fire. The building is not smoking. At least not now or all the other times that such has been claimed.

This is just the same, constant steaming of the SPF made more visible by local weather conditions. I am not saying to drop vigilance in observing, but I think we're getting way too many false alarms now. I imagine that most of our esteemed thread readers and participants are just skipping over the constant stream of "fire/smoke at SPF4/#3" posts and will skip over a legitimate problem if it should arise.

 

[Morbius]

The k parameter and the critical/subcritical distinctions are drastic simplifications of reality. If you look too closely, the k parameter is not a well-defined quantity, and criticality becomes a fuzzy concept.

Jorge,

Yes - it's fuzzy when you're just hand-waving about the definition.

However, in terms of the mathematical definition of "k", the k parameter is very well defined. It is as well defined as any other eigenvalue of an eigenvalue equation which is what the critical problem really is.

Dr. Gregory Greenman

 

[robinson]

Yes lots of "steam" whenever the dewpoint gets close to the air temperature (as it often does at night).

No, when the dewpoint is right you can see it, but there is always steam/water vapor coming out of all four buildings. 24/7

If only there was a way to measure what is in it. It could give a clue as to what is happening.

 

[StrangeBeauty]

No, when the dewpoint is right you can see it, but there is always steam/water vapor coming out of all four buildings. 24/7

Of course it's 24/7. I meant it becomes more visible under those conditions and that's when people have been "crying wolf" about fires/smoke.

If only there was a way to measure what is in it. It could give a clue as to what is happening.

I completely agree with that. The compressed video is just too misleading/imprecise to tell anything definitive.

 

[Pu239]

A lovely sequence of a marine fog bank rolling in with lots of video compression artifacts thrown in.

Yes lots of "steam" whenever the dewpoint gets close to the air temperature (as it often does at night).

I realize that something (more) horrible could happen with SPF4 or any of the other units, but these frequent steam displays are not it. The building is not on fire. The building is not smoking. At least not now or all the other times that such has been claimed.

This is just the same, constant steaming of the SPF made more visible by local weather conditions. I am not saying to drop vigilance in observing, but I think we're getting way too many false alarms now. I imagine that most of our esteemed thread readers and participants are just skipping over the constant stream of "fire/smoke at SPF4/#3" posts and will skip over a legitimate problem if it should arise.

Have a look at the following videos. I'll drop this topic very shortly, but I do want some kind of corroboration, given that this board's topic is: Physics Forums > Engineering > Nuclear Engineering > Japan Earthquake: nuclear plants.

This was not

- a false alarm
- one of the many false alarms
- one of the many frequent steam displays

It was a *massive* and significant steam/vapour display that started with a clearly visible vertical emission of vapour, then blotted out all the other reactors - starting around 2:15 in the first video below. Also look at the 10 second mark in the second video. They look very much like explosions to me:

Here's the video:
2011.06.14 00:00-01:00 / 福島原発ライブカメラ (Live Fukushima Nuclear Plant Cam)
http://www.youtube.com/fuku1live#p/u/9/k-EDceWFovc

2011.06.14 01:00-02:00 / 福島原発ライブカメラ (Live Fukushima Nuclear Plant Cam)
http://www.youtube.com/fuku1live#p/u/8/fg8yGBhoLxU

 

[Pu239]

You'll notice that actually #3 and #4 are steaming in those videos.

 

[biggerten]

I think you saw three things -

1) SFP 4 steaming.
2) Followed by a fog bank rolling in.
3) The arrival of a wide load caravan with one of those oversized tanks they're bringing in at the rate of 4 or 6 per day.

 

[Pu239]

No fog that day. We checked the weather - realtime. Conditions were cloudy.

Unless fog starts inland from the top of a building and rolls out to sea?

Also, you'll see two vertical plumes - one from #3 and one from #4.

You'll also see flashes of light within those plumes - but, have to watch all of the video.

You'll also notice an explosion 10 sec in on the 2nd video from #4, or the shared spent fuel area.

I see no caravan. Or gypsies.

Time to drop this topic I guess.

 

[quark42]

I live along the central California coast. I'm very acquainted with the behavior of fog and lights at night. I also have years of photography experience (an avocation along with an engineering vocation). Also, being a pilot with com/inst ratings, I have a very good understanding of what happens when the temp/dew point spread narrows and its affect on water vapor visibility, i.e. clouds.

My opinion on the "visible vertical emission of vapor" is an illusion caused by the lighting of the exhaust tower behind forming fog. The tower is exactly behind where the column of vapor "appears".

Just my two cents worth, anyway.

It does, however, bare repeating the importance of checking the temp/dewpoint spread when considering the possibility of anomalous emmisions from the reactor buildings.