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Post by alias72 on Apr 15, 2017 22:34:31 GMT
Hello. I was messing around with methane NTR's, constantly hitting that annoying Uranium dioxide melting point when a thought occurred. why do I care if the Uranium Dioxide melts? It's not like the nuclear properties of Uranium change when it liquefies. If the Uranium Dioxide is contained within some other material than its temperature is irrelevant. It turns out I was not the first to come up with this idea. childrenofadeadearth.boards.net/thread/518/encapulated-liquid-uranium-capsulesThis thread details something similar. If the UO2 is allowed to melt but it is contained in a solid matrix than we can increase core temperatures by another 1000k. This comes with a sacrifice. We need to encapsulate our moderator as well or use a less effective moderator. another design for a Liquid or semi solid NTR is the Liquid Annular Reactor System. ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19910012832.pdfif I am not mistaken the only thing preventing nuclear fuel from exiting the reactor is the centripetal force of the spinning fuel. Other than these I haven't really found much else. It appears that people either want to look into solid core NTR's because of the established literature or gas core NTR's because of the insane theoretical performance. Has anyone found additional information on liquid core or semi solid core concepts? It seems like an interesting way to boost the performance of traditional solid cores without abandoning a mostly fixed core design. |
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Post by bigbombr on Apr 16, 2017 5:45:21 GMT
I'm not sure were you can find it, but someone modded a 'U-233 encapsulated in tantalum hafnium carbide'. Methane NTR's have an exhaust velocity about 1 km/s higher. Someone else also modded Cermet (with is another fissile with ahigher melting point). But they're not just useful in NTR's, it's in fission reactors with a graphene/vitreous carbon thermocouple where they truly shine.
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Post by The Astronomer on Apr 16, 2017 7:50:06 GMT
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Post by ash19256 on Apr 16, 2017 7:54:29 GMT
Although, I wonder how difficult it would be to simulate Graphene coated fuel canisters, for an extra 320-400 K in terms of melting point. Granted, at that point it would probably have to be set up as something on the order of 99% encapsulated material, 1% Graphene, but it would allow for further increases in engine temperature and efficiency.
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Post by RiftandRend on Apr 16, 2017 11:33:16 GMT
Although, I wonder how difficult it would be to simulate Graphene coated fuel canisters, for an extra 320-400 K in terms of melting point. Granted, at that point it would probably have to be set up as something on the order of 99% encapsulated material, 1% Graphene, but it would allow for further increases in engine temperature and efficiency. The difficult part would be determining how much structural strength the graphene coating adds. Not really relevant for our purposes though. |
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Post by ash19256 on Apr 16, 2017 22:47:34 GMT
Although, I wonder how difficult it would be to simulate Graphene coated fuel canisters, for an extra 320-400 K in terms of melting point. Granted, at that point it would probably have to be set up as something on the order of 99% encapsulated material, 1% Graphene, but it would allow for further increases in engine temperature and efficiency. The difficult part would be determining how much structural strength the graphene coating adds. Not really relevant for our purposes though. Yeah. I've actually got some mockups of that concept working, I'll post them here: Ceramics.txt Material Graphene Boron Nitride Cermet
Elements N B C
ElementCount 1 17.6 1
Density_kg__m3 4946
YieldStrength_MPa 1000
UltimateTensileStrength_MPa 1850
YoungsModulus_GPa 550
ShearModulus_GPa 223.9
MeltingPoint_K 4900
SpecificHeat_J__kg_K 5162
ThermalConductivity_W__m_K 1500
ThermalExpansion__K 6.76e-7
Resistivity_Ohm_m 2.9e-7
RefractiveIndex Graphite
RoughnessCoefficient 0.9Fissiles.txt Material Graphene U-233 Cermet
Elements U-233 C
ElementCount 21 1
Density_kg__m3 18210
YieldStrength_MPa 1000
UltimateTensileStrength_MPa 1850
YoungsModulus_GPa 550
ShearModulus_GPa 223.9
MeltingPoint_K 4900
SpecificHeat_J__kg_K 5162
ThermalConductivity_W__m_K 1500
ThermalExpansion__K 6.76e-7
Resistivity_Ohm_m 2.9e-7
RefractiveIndex Graphite
RoughnessCoefficient 0.9
Material Graphene U-238 Cermet
Elements U-238 C
ElementCount 21 1
Density_kg__m3 18210
YieldStrength_MPa 1000
UltimateTensileStrength_MPa 1850
YoungsModulus_GPa 550
ShearModulus_GPa 223.9
MeltingPoint_K 4900
SpecificHeat_J__kg_K 5162
ThermalConductivity_W__m_K 1500
ThermalExpansion__K 6.76e-7
Resistivity_Ohm_m 2.9e-7
RefractiveIndex Graphite
RoughnessCoefficient 0.9
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Post by alias72 on Apr 17, 2017 1:14:53 GMT
Where did you find those cermet material properties?
I know they have to be somewhere because I keep seeing them.
Also if the melting points of those cermets is really that high then that completely negates the advantage of the semi-solid reactor (in which the fuel is allowed to melt but encapsulated in a solid matrix).
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Post by ash19256 on Apr 17, 2017 17:59:08 GMT
Where did you find those cermet material properties? I know they have to be somewhere because I keep seeing them. Also if the melting points of those cermets is really that high then that completely negates the advantage of the semi-solid reactor (in which the fuel is allowed to melt but encapsulated in a solid matrix). Actually, these are meant to simulate that, it's just that calling it a Graphene U-233 Cermet is shorter than putting in some variation on U-233 clad in Graphene. It's not really accurate, and if you can come up with a name that's about as short that's just as accurate, that would be nice. Otherwise, the properties are mostly just adjustments of the Tantalum Hafnium Carbide clad fuel/control rod materials bouncing around on the forum. |
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Post by RiftandRend on Apr 17, 2017 18:13:27 GMT
Pure boron encased in graphene should be a more effective and cheaper control rod material than encased boron nitride.
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Post by ash19256 on Apr 17, 2017 18:19:36 GMT
Pure boron encased in graphene should be a more effective and cheaper control rod material than encased boron nitride. I'll run some tests on that when I get the chance. |
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Post by Enderminion on Apr 17, 2017 18:20:37 GMT
wait whats a "semi-solid" its solid or its not right?
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Post by ash19256 on Apr 17, 2017 18:22:05 GMT
wait whats a "semi-solid" its solid or its not right? Basically, it's a reactor where the fuel rods have solid exteriors but molten interiors, ie. an outer layer of Graphene or Tantalum Hafnium Carbide containing molten U-233. |
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Post by alias72 on Apr 18, 2017 2:16:19 GMT
It would also include composite fuel rods in which the matrix of the composite remains solid thus containing the fuel in pockets.
I made the term up to describe the concept. I am not sure if there is an official usage somewhere.
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Post by Crazy Tom on Apr 28, 2017 1:07:06 GMT
You mean something like a pebble bed NTR?   Except the pellets are high tech enough to let the uranium melt? |
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Post by alias72 on Apr 28, 2017 1:42:08 GMT
You mean something like a pebble bed NTR? Except the pellets are high tech enough to let the uranium melt? I specifically avoided the particle bed reactor concept. In a pebble bed the pebbles can move. This makes performing analysis of the geometry difficult. Furthermore tests of the pebble bed reactor revealed dangerous heat buildup in areas within the pebble bed. The increased heat reduced the neutron absorption cross section of the moderator as well as its density causing heat damage. I heard this information from william emrich Principles of Nuclear rocket propulsion. |
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