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Nuclear Propulsion: Accelerator Driven Reactors (GEM*STAR)

Posted by: sanman - Thu Apr 08, 2010 5:42 am
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Nuclear Propulsion: Accelerator Driven Reactors (GEM*STAR) 
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Space Walker
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Post Nuclear Propulsion: Accelerator Driven Reactors (GEM*STAR)   Posted on: Thu Apr 08, 2010 5:42 am
http://nextbigfuture.com/2010/04/molten ... riven.html

Virginia Tech is researching accelerator-driven reactor designs with its GEM*STAR project. The idea of ADS reactors is to have a sub-critical reaction that is kept going by supplementing it with an external source of neutrons, supplied by a particle accelerator (proton beam as a spallation source, which then produces a supply of neutrons)

So a sub-critical reactor, if it can be done, is inherently safe, which would favor it for propulsion purposes. The reactor is naturally limited by sub-criticality, so there's no chance of meltdown - especially if the beam power is cut off.

This then leaves at least a couple of major problems. One is to have a spallation source which is lightweight (ie. a lightweight particle accelerator)
The other problem is characteristic of all nuclear reactors - transferring the nuclear power generated over to a propulsive flowstream, so you can get thrust. (At least with chemical fuel, that same stuff generating your energy is also shooting out the back of your rocket as your propellant. You don't want your radioactive material shooting out the back in the same way.)


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Post Re: Nuclear Propulsion: Accelerator Driven Reactors (GEM*STAR)   Posted on: Thu Apr 08, 2010 1:20 pm
VASIMR
would be a great powersource for that.


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Post Re: Nuclear Propulsion: Accelerator Driven Reactors (GEM*STAR)   Posted on: Thu Apr 08, 2010 6:54 pm
Fair enough - VASIMR is a cool propulsion system looking for a good power source. GEM*STAR or some other safe reactor would be a lot better than some large solar array.

But I find the gravity well to be the most fascinating challenge which limits our access to space and to other worlds.

To overcome gravity, you need high thrust. How to come up with a safer and more efficient high-thrust rocket, for heavy-lift purposes? VASIMR is nowhere near strong enough to take on the Earth's gravity.

I've always fantasized about using nuclear power or power from some other high-energy density material to achieve convenient low-cost access to space.

I was thinking that with a sub-critical Accelerator Driven System, you could combine it with a particle-bed reactor design. There would be a natural complementarity there, because a particle-bed system could be capable of "burst mode" operation for very high power output, while the subcriticality with beam cutoff would provide inherent safeguard against runaway reaction/meltdown. It would also allow the use of natural unrefined uranium, as well as burnup of fission products - both of which would mean a much reduced threat of environmental contamination.

I think that ADS and particle-bed are a natural fit for each other, to combine their advantages. The main challenge then is to address the weight issue, and to find a way to effectively transfer power to the propellant flowstream. The nice thing about chemical rockets is that your combustion reaction is literally taking place with the propellant itself, which is as intimate a coupling as you can get.

Maybe if someone ever figures out the link between electromagnetism and gravity, we'll see the problem licked for good.


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Post Re: Nuclear Propulsion: Accelerator Driven Reactors (GEM*STAR)   Posted on: Fri Apr 09, 2010 12:40 pm
You need to read "The Nuclear Rocket" by James Dewar from Apogee Books. Also "To the End of the Solar System" by the same author. These are awesome and inspiring books and have every iota of information you need to know about these kinds of systems.

Don't speculate. Go get the info.

http://www.apogeebooks.com/Books/solarsystem.html
http://www.apogeebooks.com/Books/breaking.html

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