Re: Ooooo, aren't we feeling arrogant today What's ridiculous? Ok: Scale, stability (there is none), spikes of energy dissipated out from the core, fuel burnout, reaction poisons. Why would there be any low Z elements in the core when they would've, according to you and suggestions of buoyancy, floated to outside the core? This is a BIG point. It wouldn't be steady state because steady state is not the nature of nuclear reactions. Given conditions suggested here, you'd have a giant supercritical reactor that would reach some ridiculously large power output in a matter of nanoseconds. This is because power increases in a fission reactor exponentially. This is why it'd be a giant bomb. This is true for a man-made reactor. Our reactors are carefully constructed and don't have the right geometry or material distribution to be a bomb. That's why they melt down instead of exploding. For the scale we're talking about, such considerations go out the window. The limiting factor in how big we can make a fission bomb is how big a mass (well, two masses) of concentrated fissile nuclei (Pu-239, U-235, et al) we can make before the masses are bombs themselves. Eventually they would, but they would be a poison for as long as they're there, and that could be awhile. Creation of such poisons on such a scale would (at best) yield some seriously squirrley (spikey) behavior that would be violently shaking the planet quite often. I have no reason to believe that there would be anything but VERY uniform material distribution in the core, given how old the earth is. Heat and material movement might matter on a human scale reactor, but not this size. I'm sure there's some very interesting natural mechanisms for material transport, but nothing that would regulate the reactor as you're suggesting. It really all depends on if and how you mix waste. Generally, nuclear power doesn't generate much besides some high level waste (spent fuel) and some short lived low level wastes from reactor operation. The reason it is impossible to exactly determine what's in those mixes is because decay chains have more than one possible path. However we can tell with pretty good certainty what should and shouldn't be there. There are a shitload of rules for doing this and they're followed quite rigidly. Don't get these ideas of leaky barrels of waste killing children at playgrounds get to your head. The only irresponsible waste disposal done that I know of was by the government (for weapons development and production during the cold war) before people started getting on their asses. Such messes have nothing to do with present nuclear power production and are nothing I wish to associate myself with. No problem. How's this: Please Register or Log in to view the hidden image! This is me.
Re: Re: Ooooo, aren't we feeling arrogant today And here I thought your 20 years in Los Alamos and 15 years at GE....Please Register or Log in to view the hidden image!
Re: Re: Ooooo, aren't we feeling arrogant today Scale: you ought to know that no sustained fission reaction can occur across kilometers of molten iron. Obviously, most of the fission hot-spots (when there are any) will be localized and would coalesce/dissipate in a random way. The rest would take the form of a constant, low-level radiation/heat background. And as for stability, in the long term the noise averages out. That's stability. If there were no convection, turbulence and other hydroelectrodynamic currents induced by Earth's rotation, then you would be correct. Why supercritical? Why giant? This assumes there is a sufficient density of fissile material to begin with. If, as soon as the density reaches critical levels, there is an exponential build up of heat, then this heat will prevent the density becoming critical to begin with. You keep assuming some artificial initial conditions; newsflash: there's nothing artificial about our planet's core. Conditions in the core at any instant in time must have been generated causally by immediately preceding conditions in the core. You are proposing naturally impossible conditions as the starting point of your analysis. That is baloney, and I would have expected better from a so-called nuclear engineer. Our reactors do not contain the right fuel to be a bomb; bomb-grade material is highly enriched and purified -- conditions one would definitely not expect in nature and that take some pretty esoteric machinery and a lot of effort to achieve. Unless the material is bomb-grade, it won't sustain a runaway chain reaction no matter how much of it you put together. Fill the oceans with it; all you'll get is a massive meltdown but no nuclear blast. And you should know this is not applicable in a natural setting. Which is yet another argument against your catastrophic visions. Do you seriously propose that such tiny spikes of energy would be sufficient to be felt through thousands of kilometers of turbulent liquid rock of varying compositions and densities? Then again, the surface of our planet is constantly, incessantly shaking. The vibrations are just too week for us to feel, but they do present a noise background with which seismologists must cope. Besides, keep in mind that the inside of our planet is always in motion, and it would be pretty hard to create some steady-state nuclear phenomenon in such an environment. At best all you'd get is transient spikes. Ah, now you want to consider long-term trends for a change. But this time, you ignore the dynamism of the core. Just answer these questions: where does the geomagnetic field come from, and how does it manage to reverse itself every few thousand years? Why not "this size"? It would take longer to assemble a local inhomogeneity of a "reactor", than it would take to blow it apart. Last I checked we weren't talking about human management of nuclear plants, but about the natural mixtures and transmutations that would occur under intense pressure and temperature deep in the Earth's core that together are hardly attainable in a laboratory for any significant period of time. The point was that a great many nuclear pathways would play a role, and there would be many different avenues for producing heat through nuclear reactions. Congratulations. But the guys who wrote the original article at the start of this thread are PhDs; one of them working at Oak Ridge National Laboratory. So it seems you're screwed. Please Register or Log in to view the hidden image! Besides, if I didn't know better I would have concluded that you were attempting to argue from authority. That would have been very bad form.
May I introduce a couple of moderators namely Zirconium and Hafnium that may play major roles in the reactor too. And we have plenty of them.
Re: Re: Re: Ooooo, aren't we feeling arrogant today I just read the whole article (skimmed it last time) and I can say that I'm still quite comfortable with my position. They made too many assumptions and used a very limited simulation method(s). Ah ah ah... the article you're so vehemently defending suggest a core mass spread across several km of core. Further more it insisted on modeling for constant operation during the past 2 billion years. THAT is why is said scale. The article mentioned outward movement of the lighter elements, poisons and such, but ADMITTED that if their ASSUMPTION was wrong that much of their argument goes to shit. Supercritical: k (k_eff in this case) > 1.0000 The graph on the first column of the third page suggests constant supercriticality. Giant: compared to the reactors we build and the codes they're using that were designed with man-made sized reactors in mind, this scale is gigantic. There has to be sufficient density of fuel to begin with for there to be a reactor. That's not an assumption, it's a given. There's no artificial condition here, having a sufficient amount of material is necessary for there to be any nuclear reactor. Oh for pete's sake. I said: Material distribution AKA number density AKA fuel enrichment. I understand perfectly well the enrichment differences between reactor grade fuel and bomb grade fuel. Quit splitting fine hairs with this crap, you're wasting your time and mine. Why? As far as reactor (or bomb) function is concerned, a concentrated mass of Uranium made by man is no different than one that forms naturally. You can only screw around with varying density and size so much before you reach the limits. TINY?!?!?! When you're talking about a reactor that is forced (by gravitational pressure) to remain a relatively constant volume undergoing the HUGE power spikes that occur in nuclear reactors (power can vary by as much as 3 orders of magnitude in MAN-MADE reactors left unchecked) left unchecked. This thing is (supposedly) operating in the range of anywhere from 3-45 TW in their assumed normal conditions, the spikes would release several times that much energy over a short period of time. I'm not claiming to know exactly what would happen, but dissipating that much energy (especially when it's still at the core) is bound to cause problems. Like I said before, if you want to argue for the article, you have to keep along their position that the reactor operates over a period of some 2 billion years. You don't know enough about nuclear energy to just take their idea and run with it. From the National Geophysical data center: a. the Earth's conducting, fluid outer core (~90%); b. magnetized rocks in Earth's crust; c. fields generated outside Earth by electric currents flowing in the ionosphere and magnetosphere, d. electric currents flowing in the Earth's crust (usually induced by varying external magnetic fields), and e. ocean current effects (I actually was able to think of a, c, and e beforehand thanks to all those fusion classes I took. Please Register or Log in to view the hidden image! ) I think that, given those conditions (variables), the appropriate question would be "why would it remain constant?" Easy answer: it doesn't. Because size here also has to deal with scale and number density. On a human scale, such concentrations get blown apart; on this scale, everything is pretty much stuck in place because of the immense pressure. Rapidly rising criticality would be a big problem AKA nasty spike in k. As my first neutronics professor would say (he's Korean) "you just turn your reactor into bomb... only result will be boom!" We're not talking about human management of nuclear plants, however, periodic comparison is useful for certain considerations. We obviously cannot replicate such conditions and that brings around all the assumptions they made with modeling. Simply put, there were too many. They made enough assumptions to reduce a vastly complex problem to something out of an introductory neutronics class. The codes they used were not meant for this scale or environment and 1-D analysis doesn't hold much weight for any real considerations even where relative homogeneity can be attained. They made too many assumptions and simplified the problem too much to make it anything more than a HW assignment for a dual level class. Hey pal, there's no need to be rude. You asked me to show why I'm qualified to get in this debate with the certainty I have and I showed you. Also, just because they have Ph.Ds in something doesn't automatically make them experts. Based on their paper, I'd say it's likely that my neutronics education is on par with or possibly even exceeds theirs. The difference between a B.S. and a Ph.D is a thesis that proves the Ph.D. can do research. Another consideration is what those Ph.Ds are in. A physicist's Ph.D is pretty different from a nuclear engineer's Ph.D. I'd be pretty surprised if their Ph.Ds were nuclear engineering because nukes should know better. I don't quite follow what you're trying to say.
Well, now that I have also read the article carefully Please Register or Log in to view the hidden image!, I won't support it so strongly. However, I think their general approach is valid. You can't create ultra-complex models right away without going through simpler stages first. Simplified models help you get a grip on what's going on, and then ratcheting up complexity gradually might show predictable trends that would allow extrapolation or at least constrain the possibilities. Now, I would think it pretty much indisputable that heavier elements sink. Further, it ought to be a no-brainer that most of the Uranium/Thorium/whatever would have sunk to the center and what we see at the surface is mere traces compared to concentrations at/near the core. What exact shape this would take and what the equilibrium would look like or how stable it would be may be up for debate, but it is pretty obvious that old (crystallized iron core) models don't take the radiological elements seriously at all. Moreover, with estimated 10 TW still escaping the Earth (what is it, hourly?) today, one has to wonder how it's overwhelmingly molten after 4 billion years. The authors admit the limitations of their model, and they would clearly like to include more accurate transport and hydrodynamics into it. I'm sure that's the next step. But I think their <sup>3</sup>He observation is intriguing, and their suggestions for further empirical testing are quite reasonable. I think they overdid the supercriticality bit; I find it easier to imagine that k<sub>eff</sub> would approach 1 from below, not above, as the "reactor" oscillates between activation due to gravitationally driven diffusion and shutdown due to thermal expansion/convection/accumulation of moderators/poisons. That's probably what they'll see when they make their model more realistic. Concerning magnetic field, you did mention that 90% is attributed to the core. Any other contributions hardly could destabilize the field; major changes can only be due to the dynamics of the core one way or some other. To consider dissipation of energy, let's say a 300 kiloton nuclear device dissipates roughly 10<sup>12</sup> J of energy. That's 1 TJ. For convenience, suppose all this energy is released within 1/10th of a second; then it's 10 TW of power. Then it would take the energy of, say 10 300 kiloton nuclear devices to output 100 TW. Crude, I know, but bear with me. In 1953, I believe, the Russians tested a 5 megaton fission bomb. That's the equivalent of 10 500 kiloton nuclear devices. The world would have been none the wiser if it weren't for sensitive seismometers and, of course, spies. Parenthetically, typical fusion bombs today can reach upward of 50 megaton output, which is another factor of 10 larger. Now, even 100 TW spikes in the core would happen some 5000 kilometers down under ground or so, and would be masked by multiple inhomogeneous layers of liquid, semi-liquid and solid rock of various compositions. Let's just assume this extra energy would take the shape of a sound wave (note: in a typical earthquake, only 10% of the energy is manifested as seismic waves; the rest goes into actually deforming the crust.) Assuming losses due to friction, reflection/refraction, and simple heat absorption, how much of that explosive energy would actually reach the surface? Over how large a surface area would it be spread? Would it be at all detectable on the surface? What do you think? A magnitude 8 (Richter scale) earthquake releases energy equivalent of roughly 1 gigaton of TNT. At 100 km depth it is devastating. At 1000 km depth it is barely detectable. At 5000 km depth it is a whimper buried in the noise. To compound the problem, for shockwaves originating that deep I'd expect most of the energy to reflect back into the core from the various liquid/solid boundaries, so that only a tinsy fraction of that energy would reach the surface as a sound wave (the rest would eventually reach the surface as heat.) So to sum up, you need to put the "enormity" of the "reactor" into perspective. Earth is a pretty enormous planet, and it takes some truly titanic energies to rock it (horrible pun not intended.) Plus, take the dynamism of the core into account. Things might be easier to model as symmetrical and static, but in real life hardly anything ever is that simple.
im not really on the side of the article........ but 2 points in the inanity of this 'my dick is bigger than yours' contest......... since when is the earth @ steady-state? ...... and more importantly......... haven't you ever solved the actual spherical PDE's on autocatalytic phenomena by hand? (since you supposedly have a degree in N.E.)..... i mean hell, i did it just as a math exercise.... clearly, the assumed density profile would not allow for a bomb effect, perhaps however, you have some refined first hand knowledge of core composition etc that you aren't revealing........
More stuff to think about. Quoted from http://www.nuclearplanet.com/ Eos, Transactions, American Geophysical Union, Vol. 79, No. 38, September 22,1998, Pages 451,456 QUOTE: Unlike traditional, globally important energy sources, which change gradually and in only one direction overtime, planetary-scale nuclear fission reactors may be capable of variable or intermittent operation like the Oklo reactors. As inferred from Oklo and reactor technology, changes in nuclear reactor energy production can result from changes in composition and/or position of fuel, moderators, and neutron absorbers. Paleomagnetic investigations (augmented by geological, paleobiological, and geochronological studies) and magnetometer measurements of the ocean floor have established that the Earth's magnetic field reverses polarity frequently, but quite irregularly, with an average time between reversals of about 200,000 years. The cause of geomagnetic reversals has not yet been established. Herndon [ 1993] has suggested that the variable and intermittent changes in the intensity and direction of the geomagnetic field have their origin in nuclear reactor variability. Significantly, the geomagnetic field has been in existence at least 3000 million years and certainly during the time period natural reactors could begin to operate and breed fissile material. The following schematically illustrates one possible mechanism for geomagnetic field reversals and excursions: Nuclear fission consumes actinide fuel and produces fission fragments, some of which have high neutron capture cross-sections. Fission products may be removed from the reactor sub-core region by diffusion and gravitational layering based on density at the prevailing pressures. One might imagine instances in which the rate of production of fission fragments exceeds the rate of their removal. In such instances, the power output of the reactor would decrease and the reactor might shut down, eventually shutting down the Earth's magnetic field. After a period of time had elapsed for fission fragments to diffuse to regions of lower density, the reactor output would increase, and the Earth's magnetic field would reestablish itself either in the same direction or in the reverse direction.
Ok... people are sounding more reasonable now. Please Register or Log in to view the hidden image! I think these guys have an interesting idea, but their assumptions and limited modeling are the limiting factors as far as any real validity is concerned. I think the idea that OCASSIONAL, short lived, natural critical masses could form is worth considering, but the idea that the core is a big reactor just raises too many questions that nobody can really answer. Good discussion. Please Register or Log in to view the hidden image!
Where's the beef Let's assume it's true. Wouldn't it continually breed plutonium? If so, where'd it go? If we assume as some here do that it would “float” to the center – well, that doesn’t seem like too pretty a picture. If we more appropriately assume that most heavy elements more or less mix proportionately at or near the center (due to the equal or almost equal effect of gravity originating from all sides) then the theory goes completely out the door as there would be no gravity driven conjugation of the uranium in the first place. I gotta pour me a nice tall glass of skepticism here.
Surely there needs only to be gravity driven conjugation of fissionable materials, those are ones that can be "split" by neutrons for this theory to be important. This site, http://www.isis-online.org/publications/fmct/primer/Section_I.html, mentions that such materials include plutonium 239 and uranium 235. According to www.environmentalchemistry.com, Plutonium is more dense than Uranium. So it would be expected to move more easily towards the centre in the case where the nuclear material actually differentiates as Herndon has suggested, and as participants here were inclined to agree about to a limited extent. However also I have noted that according to www.environmentalchemistry.com, some Plutonium nuclides are parent nuclides for Uranium isotopes. According to that site this means that by radioactive decay they turn into Uranium nuclides. However bobbapink seems to have a confident criticism. What is the basis of confidently claiming that there the set of high density substances in the core of the earth is not likely to have higher concentration of fissionable materials than normal? Presently Chalko's article at www.nujournal.net/core.pdf is not available because it is being revised, however it suggested that if you consider the conditions for the stability of the solid inner core in the fluid outer core, it is clear that the density of the inner core should be about 26grams/cm^3. This is higher than the densities of Uranium and Plutonium, and I think Chalko suggested that materials of such density may not have been discovered yet. If this is true, then the way Uranium and Plutonium and substances of similar densities would be likely to intermix and interact in the core may not be important. My main point is that for these reasons, I am not sure that you should dismiss these theories.
Re: Ooooo, aren't we feeling arrogant today The OKLO reactors only worked since the concentration of U-235 was high enough to permit a light water reactor to function. This was several billion years ago IIRC and since then the U235 concentration of natural uranium has decayed below the critical level. U235 has a half life of about 700 MY while U238 is 4500 MY so the ratio 235/238 must decrease over time. These reactor also occured at the bottom of lakes and rivers which supplied the moderator. They were also supposed to only have run intermitantly when conditions were ideal over a couple million years. They may have run for 100 years and then shut down for 25000 before starting again. Mr Nuke is refering to the six factor formula for critcality and I agree I don't see how it could happen at the core. For one thing the 235 concentration has dropped there too. Density considerations might overcome that I don't know. I have to figure out the quoting system here.
Re: Re: Ooooo, aren't we feeling arrogant today Finally someone who knows what I'm talking about!!! Please Register or Log in to view the hidden image! To quote someone, use the hyperlinked 'quote' at the lower right of the post of the person you want to quote. It's standard vBulletin, just trimmed on graphics to save bandwith.
Sir, uranium has too short a half-life. We barely have any today for this reason. Why nuclear radiation? There are simpler explanations.
Indeed, the amount of energy lost by the earth's surface is balanced by the energy it receives and produces -- an equilibrium. Much of the earth's internal energy is released through radioactive decay. When it's all considered, the amount of energy produced by spontaneous decay is pretty much exactly what's needed to explain the equilibrium we now enjoy. There's no need to invent a giant nuclear reactor. - Warren
This would not be the only force at work pushing towards a more equal mix. Convection must also be considered as a force to move the core material around. On another note, Emfuser is proud of his newly earned BS in nuclear engineering. I don't blame him, I am sure he worked hard to get it.
Plainly there is now possible way the the earths core can be soild, this concept comes from little boys that play with rocks on the surface of the earth. 1.) universal attraction of the cosomos will not allow any body to be soild not even a rock, this is also know as the second law of thremal dynamics. 2.) it is well know that the llayers of earth must be seperated by relief or pressure or the earth would be a buring ball, this is record of tempture to depth ration, the event of a solid earth would result in temptures in excess of the suns surface. 3.) the event of a magnetic field also known as electromotive force, is one that is derived from focused energy, that exist in uniform, spartic eneryg dispersal results in sparatic and un unifed magnetic force, the event of uranium as a core simliy in themal emmision(spectrum emmision would be too hot to maintain a uniform magnetic field. the earth has a hollow cors about 11 to 50 miles thick, surrounding this hollow core are helium and hydrogen about 137 miles thick, from there on out the denstiy of mass increases. the event or barriers of the earth core after this magnetic field shell of helium and hydrogen are layers of rings that have points where ther is nothing at all but gases, or void, this layering barriere proccess are repeated over and over again until one reaches the surface. in understanding the core of earth, hydrogen and helium are the only abundant elements in the universe, that have the energy freguency and coversion to feed the heat sink of the univsese 2degrees kelivn, the rest of the element that are know take to long to convert energy from the background constant of the universes or solar sysytmen, ther fgore they are just suck up by the endless spcae with the ablity to maintain a stable postion to congergate, this is why we have cosmic particles, and endless cloud bodies of hydrogen and helium in the universe, cosmic particle can con group and therfore are flying aroung hrdrogen and helium which can convert the background constants to feed its heat sink can group and therfore form clouds, these clouds are the beging of planets suns ect...,once these stable gases beging to form other element can find stblity near them and revolve aorund them. these heavy elements can not take the center of the hydrogen and helium mass as the are attracvted by the univese therfore thay float on the gases, as the mass grows and heats up heavy elements become more stable, however they can not take the center due to the event of unversal attraction, like wise hydrogen and helium can not tkae the center, this leave the center hollow with the gases revovling around the hollow, creating unifired motion such as rotation, ones mass forms a shell, the gaseous are and where polarized by the universe, this causes a magnetic field, and every planet has had one, or has one. the reason that all bodies seen thorugh a telescope known as stars, suns, planets, are round is due to the event of universal attraction of the cosmos, called the background constant 2 degrees kelvin, as theis attracts on all side at all points the heavanly bodies are all round, and hollow, meaning that the attraction of the universe is so great that no object can have a soild center. not a even a atom. DWAYNE D .L.RABON
universal attraction of the cosomos will not allow any body to be soild not even a rock, this is also know as the second law of thremal dynamics. Hmmm... I thought the second law of thermodynamics says that the entropy of the universe increases. Silly me. the event of a solid earth would result in temptures in excess of the suns surface Therefore, all planets, moons, asteroids, etc., must be hollow. the reason that all bodies seen thorugh a telescope known as stars, suns, planets, are round is due to the event of universal attraction of the cosmos, called the background constant 2 degrees kelvin, as theis attracts on all side at all points the heavanly bodies are all round, and hollow, meaning that the attraction of the universe is so great that no object can have a soild center. not a even a atom. Please Register or Log in to view the hidden image!
Uranium isn't exactly a trace element on the Earths surface. On the other hand it isn't abundant either. We should be asking ourselves why this is. Doesn't it seem logical to assume the heaviest Elements sank to the Earth's core during its early liquid state. It was nothing more than a smelting furnace back then and as most people will realise, heavy elements sink in a furnace. Why do you think its hot downstairs? It's not friction or trapped heat from billions of years ago. That high temperature is trapped radioactive heat from the natural halflife of Uranium and other natural fissionable elements. Earth is a nuclear reactor and that heat has moved continents, created mountain ranges and generally shaped our world. Without it's violent upheavals the surface crust wouldn't have solidified with any heavy Elements in it at all. Including Gold and other dense metals. Natural reactors make life possible in this universe. The Sun is a reactor too as you all know. A massive fusion reactor. We should study nuclear technology to the fullest of our ability if only to better comprehend the natural universe around and below us.
