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I'm no chemist, but if uranium salts can be disolved in water, then how about some boron compound at the same time? That would act as a neutron absorber, so the tank could be just be thin aluminum or composite, uless those are netron reflectors, but composite should be alright at least. Then when you want to fire up the engine, you have small centrifugal pumps, so it can't go critical in them, and the diferance in the densitys of Boron salts and Uranium salts seperates them. Then most of the water is used as normal, and the boron water can be added to the edges for extra reaction mass.
http://www.npl.washington.edu/AV/altvw56.html
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This won't work, and I do happen to be a chemist
Its a neat idea, but the problem is getting the boron (or other neutron absorber) out of the solution before injecting it into the reaction chamber/tube.
In a true solution, all ions (which the Uranium and Boron would exist as) are surrounded by water molecules, which are continuously in random motion due to thermal energy of the water, which would likewise push the ions around at random. This force is a great deal stronger than any concieveable centrifuge I imagine, plus the ions with like charge (either Uranium or Boron) would strongly repel each other, thus preventing concentration. The cumulative effect of these two forces means that the ions are more-or-less evenly distributed through the water regardless how much acceleration it is under.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
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Oh well, how about using cobalt though? Then magnets could pull it out, if cobalt formed a solution. Or, perhaps there is something that could be added to the boron solution that would make it precipitate? Is there any thing that would bind to boron but not uranium at a reasonable temperature?
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When you talk about a salt being dissolved in solution, it always exists as the ion and no longer a solid particle. Even if the ions themselves were magnetic, which they likely aren't due to preferred electronic structure, they still repel each other very strongly. Much more strongly than could overcome by magnets in any event, plus you would have the substantial entropic loss too.
Precipitation reactions would have to occur awfully fast and very completely to ensure the nuclear reaction is efficient, which will demand an excess of the precipitation agent. You must pump the Uranium-laced solution out of the rocket pretty fast to prevent it from going supercritical inside the engine you know. Removing the solid after precipitation will also be a trick, filtration is definitely out since the now inhibitor-free solution would slow down (and blow up) if the filter were clogged. Removal by centrifuge would be a tricky process, and some of the Uranium solution would be wasted in separation too.
Overall its not worth it, NSWR fuel is already pretty dense, and the fuel tanks won't be that big. All the stuff and cost of the stuff you need to get the inhibitor compound out of the fuel can't compete with just bringing more fuel.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
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You're probably right that just brining a bigger fuel tank would be better for the short runs, but on a long trip like to the kupier belt, were peak thrust isn't as important, you might want to reduce the tankage mass by making the engine smaller. The main tank, has no neutron absobtion, but the pumps do, so you could take the absorbing salts out as slowly as was practical, by precipitating them or with a magnet. Or, when the solution goes into the engine it turn to steam because of the low presure, so maybe a large magnet could pull the cobalt to the edges then, when it wouldn't be in solution but just suspeded in the gas. If it could be made to work it would be a lot safer, as with a boron tank, if there is a small spill or leak, the whole thing blows up.
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No I don't think so. It would still be cheaper just to build a bigger tank. Like how Boeing built a big, dumb rocket (Delta-IV) with a big cheap engine but still gets the same performance as a smaller rocket with a really nice SSME-class engine.
I think you really overstate the chance of a disaster with an NSWR engine in zero gravity, that any potential spill will simply not be a problem, because if there is a leak the solution will either freeze solid (block the leak) or vaporize (disperse the solution) and no explosion would occur. The "leak problem" is only really when the thing is sitting on a launch pad.
Anyway, I fail to see how any kind of precipitation mechanism will work very well at any rate, first you will have to carry a substantial mass of the precipitating agent to ensure complete reaction, then you have to have a fully shielded, hyper-reliable, self-cleaning filtering mechanism. Remember, if the flow is blocked while the engine is running, the result could be catastrophic.
Again, Cobalt or other salts dissolved in the solution exist as ions. They aren't Cobalt anymore, but rather a distinctly different sort of particle, its electronic state (which defines its physical properties) is entirely different. It does not in any shape form or fashion behave like a solid suspended in liquid (eg fine sand and water).
Say that you did find a Cobalt salt that did retain some magnetic character, there are still some problems: when you boil a salt solution, the attractive forces with the ions to the remaining water is still quite strong, so rather than having a vapor of water and Cobalt salt, instead you have some water vapor and more concentrated salt solution. The concentration in the remaining fuel would increase, and the amount of salt being pushed out the nozzle is small. The same thing will occur with the Uranium salt.
Ultimately the solution keeps getting more and more concentrated and less and less water vapor can escape as the salts start to form a solid. It will just clog up the engine at best, or at worst go critical inside the nozzle. Vaporizing the water prior to carrying out the nuclear reaction is a bad idea.
I also think that the water is crucial to making the reaction work, normally the neutrons released from Uranium are traveling quite fast, and hence for efficient reaction you would want to slow them down. I bet that the liquid water doubles as this "moderator" (the proper term) as well as reaction mass and coolant. A little steam is not an acceptable substitute.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Okay, there's another example of how ignorat of chemistry I am, I didn't know that salts could be disolved in steam. In the intressests of economics, you're right, since there's no way any one is going to build one of these for a long time, building a bigger tank will be cheaper with the next generation launch systems.
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