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Post by matterbeam on Jul 24, 2017 13:32:37 GMT
I think the issue in this case becomes finding components or reactors that run even hotter than this, so that the radiator can cool them. There was an idea bounced around on the Discord channel for a boiling uranium reactor. Reactor chamber is liquid uranium at its boiling point; as it reacts and generates heat it boils. Gaseous uranium gets run through a steam turbine or MHD generator. Then it gets cooled and condensed back to liquid and returned to the reactor chamber. The boiling point of uranium is 4111 K according to CoaDE, so the vast majority of materials cannot contain this. A nice feature is that a criticality incident would just cause more vigorous boiling, instead of melting through the pressure vessel. Excessive pressure can, at worst, get vented. Having steamships in space is funny. I believe this design would be second only in craziness to the Zubrin NSWR. Even if we have materials that can survive molten uranium temperatures, note that we would be operating at nearly 90% of their melting point. What sort of strength would they retain at such temperatures? And its not even static forces you can reinforce with clever designs. Its thin blades you're spinning at extreme temperatures. I'm not sure active cooling of the blades if possible here, as making them hollow is another cut to their already compromised strength. Finally, you're dealing with uranium fluid. Any pressure wave or flow disturbance might cause it to be compressed somewhere down the line to a critical density. The fission rate spikes, lots of of energy is released and now you've got a hole jetting out out a voracious, radioactive gas into your ship. This is all disregarding pesky annoyances such as neutron embrittlement and vibrations caused bubbling and condensation. ... Wait. Gaseous uranium?!
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Post by apophys on Jul 24, 2017 14:06:32 GMT
And its not even static forces you can reinforce with clever designs. Its thin blades you're spinning at extreme temperatures. [...] Any pressure wave or flow disturbance might cause it to be compressed somewhere down the line to a critical density. A turbine is one option for extracting work from the expanding gas. Pistons on a crankshaft should also be possible. An MHD generator has no moving parts, so it may be the only choice if material is too weak. Future material science and/or clever engineering may help here. Routing the gas through small tubes (maybe parallel tubes if you need higher flow) would keep the uranium from reacting where you don't want it to, by virtue of separation and low density of gas.
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Post by matterbeam on Jul 24, 2017 15:30:27 GMT
And its not even static forces you can reinforce with clever designs. Its thin blades you're spinning at extreme temperatures. [...] Any pressure wave or flow disturbance might cause it to be compressed somewhere down the line to a critical density. A turbine is one option for extracting work from the expanding gas. Pistons on a crankshaft should also be possible. An MHD generator has no moving parts, so it may be the only choice if material is too weak. Future material science and/or clever engineering may help here. Routing the gas through small tubes (maybe parallel tubes if you need higher flow) would keep the uranium from reacting where you don't want it to, by virtue of separation and low density of gas. The ionization temperature of uranium is much lower than the temperatures we're dealing with, so an MHD will have a decent working fluid to draw energy from. But still... it's like playing with fire.
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Post by Enderminion on Jul 24, 2017 16:26:23 GMT
A turbine is one option for extracting work from the expanding gas. Pistons on a crankshaft should also be possible. An MHD generator has no moving parts, so it may be the only choice if material is too weak. Future material science and/or clever engineering may help here. Routing the gas through small tubes (maybe parallel tubes if you need higher flow) would keep the uranium from reacting where you don't want it to, by virtue of separation and low density of gas. The ionization temperature of uranium is much lower than the temperatures we're dealing with, so an MHD will have a decent working fluid to draw energy from. But still... it's like playing with A armed shock sensitive nuclear weapon
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Post by treptoplax on Jul 24, 2017 17:47:15 GMT
And its not even static forces you can reinforce with clever designs. Its thin blades you're spinning at extreme temperatures. [...] Any pressure wave or flow disturbance might cause it to be compressed somewhere down the line to a critical density. A turbine is one option for extracting work from the expanding gas. Pistons on a crankshaft should also be possible. An MHD generator has no moving parts, so it may be the only choice if material is too weak. Future material science and/or clever engineering may help here. Routing the gas through small tubes (maybe parallel tubes if you need higher flow) would keep the uranium from reacting where you don't want it to, by virtue of separation and low density of gas. Maybe put a neutron absorber on that piston plate, and reflectors for the cylinder? I'm not sure the math works, but it might, and the closed-cycle nuclear diesel engine is certainly pleasingly steampunk!
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Post by Enderminion on Jul 24, 2017 17:49:20 GMT
A turbine is one option for extracting work from the expanding gas. Pistons on a crankshaft should also be possible. An MHD generator has no moving parts, so it may be the only choice if material is too weak. Future material science and/or clever engineering may help here. Routing the gas through small tubes (maybe parallel tubes if you need higher flow) would keep the uranium from reacting where you don't want it to, by virtue of separation and low density of gas. Maybe put a neutron absorber on that piston plate, and reflectors for the cylinder? I'm not sure the math works, but it might, and the closed-cycle nuclear diesel engine is certainly pleasingly steampunk! that would be diesel or atompunk then
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Post by apophys on Jul 24, 2017 19:30:37 GMT
Maybe put a neutron absorber on that piston plate, and reflectors for the cylinder? I'm not sure the math works, but it might, and the closed-cycle nuclear diesel engine is certainly pleasingly steampunk! I don't see why you would want neutron absorber on the pistons. The pistons' purpose would be the same as in a conventional internal combustion engine - to extract usable work from an expanding gas. There isn't any nuclear reaction required in that section, so sub-critical masses of gas would be used (with as many pistons as needed). An MHD generator is looking to be a simpler and more likely method of generating the electricity.
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Post by Durandal on Jul 24, 2017 19:45:40 GMT
Boiling uranium internal combustion engines...
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Post by matterbeam on Jul 24, 2017 21:10:38 GMT
Maybe we'd want to make a new thread, but nuclear diesel engines... Working fluid is some kind of superfluid seeded with uranium. It gets transported through pipes as a cool, subcritical mass. In the piston, it is compressed to critical uranium densities, causing a short spike in fission activity. The heat released causes the gas/fluid to expand back to subcritical densities. The expanding gas efficiently expands inside the piston, converting its thermal energy into kinetic motion. The gasses pipe out at the top of the compression cycle, to be re-seeded and adjusted for the next cycle. Boom boom boom your nuclear reactor now has an RPM rating and spaceships have shaft horsepower.
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Post by Enderminion on Jul 24, 2017 21:15:25 GMT
you still need heat to move the ship
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Post by treptoplax on Jul 24, 2017 21:23:55 GMT
Problem with the non-steady-state schemes, if I understand correctly (not a sure thing), is that a significant portion of the heat energy is from secondary steps on the decay chain; all you can cut off (mostly) with expansion/control rods/diffusion is the uranium splitting. As a result a significant part of the energy output can only be cycled up and down on a timescale of days (weeks?) a problem that CoaDE ignores in general.
(It also follows that getting two thirds of your radiators shot off will mean not less power but the reactor core vaporizing, unless you're going to just eject it into space Star Trek style.)
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Post by thorneel on Jul 28, 2017 20:31:40 GMT
Boiling uranium internal combustion engines... Maybe we'd want to make a new thread, but nuclear diesel engines... Working fluid is some kind of superfluid seeded with uranium. It gets transported through pipes as a cool, subcritical mass. In the piston, it is compressed to critical uranium densities, causing a short spike in fission activity. The heat released causes the gas/fluid to expand back to subcritical densities. The expanding gas efficiently expands inside the piston, converting its thermal energy into kinetic motion. The gasses pipe out at the top of the compression cycle, to be re-seeded and adjusted for the next cycle. Boom boom boom your nuclear reactor now has an RPM rating and spaceships have shaft horsepower. Sounds like a Molten Salt reactor if someone asked Zurbin to invent the concept
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Post by srbrant on Nov 23, 2017 10:21:11 GMT
Can the hull itself be used as a low-grade auxiliary radiator for the habitat module? Also, I've been thinking about fin-shaped radiators that can fold up like fans, though they'd likely need to be quite flexible in order to do so.
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Post by shiolle on Nov 23, 2017 11:08:03 GMT
Well, now I know how science fiction writers in the fifties arrived to those brilliant ideas about nuclear campfires and nuclear washing machines. Gloss over enough details of controlling nuclear chain reactions and there is nothing you can't achieve.
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Post by srbrant on Nov 23, 2017 11:15:54 GMT
Well, now I know how science fiction writers in the fifties arrived to those brilliant ideas about nuclear campfires and nuclear washing machines. Gloss over enough details of controlling nuclear chain reactions and there is nothing you can't achieve. And atomic cars, which is probably the closest thing ISIS has to pornography.
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