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 Post subject: Crazy idea
PostPosted: Jun 26, 2013 4:35 pm 
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What if you had a giant stirling engine using UF6 and He as the working gases and trigger fission with neutron reflecting materials or a particle accelerator when the gas is on the "hot" side, while poisoning it and conducting heat away on the "cold" side. The reactor and power generating device would be the same compact unit.

I've read the section on gaseous homogenous reactors in Fluid Fuled Reactors and it seems they are possible, just very difficult, and I have no idea how you could make this arrangement breed thorium

Just wanted to put this idea out there. I don't have near enough knowledge of physics to figure out if it is even remotely possible.


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 Post subject: Re: Crazy idea
PostPosted: Jun 27, 2013 1:12 am 
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I seem to remember a Popular Mechanics article showing a nuclear piston engine for ship applications that would be a close analogue. Piston top dead center would get hot (I think the working fluid was water/steam with the piston head and cylinder head forming effectively a flash boiler). Nuclear fuel was in the piston I believe, though in practical terms having it in the cylinder head and the neutron reflector in the piston seems more workable.

Unfortunately, a lot of the high performance stirling engines use a thin metal diaphragm so it would be hard to put the neutron reflector into the diaphragm itself.

Oddball idea would be a thermoacoustic engine setup where the compression of the standing wave is sufficient to cause criticality in the UF6 gas mix in the area of the engine with sufficient neutron reflectors. Shutting down the engine would be done either by stopping the acoustic drivers, or dropping total gas pressure by dumping gas to a relief tank so the drivers can't compress enough.


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 Post subject: Re: Crazy idea
PostPosted: Jun 27, 2013 6:17 pm 
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I was thinking of the beta or gamma Stirling engine where there is a big displacer piston separating the hot and cold zones, and an equally robust power piston at the end, the neutron reflector would be in the displacer. http://www.animatedengines.com/stirling.html
UF6 corrosion would defiantly be a problem with the cylinder seals, but I'm more interested in if a fission reaction emitting lots of heat can be started and stopped within a few seconds.


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 Post subject: Re: Crazy idea
PostPosted: Jun 28, 2013 9:49 pm 
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After I saw it being mentioned in this discussion,-http://energyfromthorium.com/forum/viewtopic.php?f=2&t=3357&p=42239&hilit=organic#p42239

I found out about DuPont's "krylox" perfluorocarbon lubricant -http://www2.dupont.com/Lubricants/en_US/tech_info/Index.html. This stuff is stable up to 400C and reacts with almost nothing, including UF6, and seems like it could help with corrosion in gaseous homogenous reactors.


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 Post subject: Re: Crazy idea
PostPosted: Jun 28, 2013 10:10 pm 
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Joined: Feb 05, 2013 5:24 am
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J Perry wrote:
What if you had a giant stirling engine using UF6 and He as the working gases and trigger fission with neutron reflecting materials or a particle accelerator when the gas is on the "hot" side, while poisoning it and conducting heat away on the "cold" side. The reactor and power generating device would be the same compact unit.

I've read the section on gaseous homogenous reactors in Fluid Fuled Reactors and it seems they are possible, just very difficult, and I have no idea how you could make this arrangement breed thorium

Just wanted to put this idea out there. I don't have near enough knowledge of physics to figure out if it is even remotely possible.


Seems like an enormous challenge. I thought about UF6 reactors, but gas reactors are so low power density, corrosion would be tough, what happens with the fission products as they won't all be gasses, having the energy conversion basically in the core seems like a lifetime/maintenance issue, conversion from UF6 to UF4 would allow fissile fuel plateout and concentration on the cooling surface causing hot spots and excess local reactivity, an ultimately burn through and loss of gaseous fuel and fission products. The latter is why ORNL gave up on aqueous homogeneous reactors.


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 Post subject: Re: Crazy idea
PostPosted: Jun 29, 2013 9:30 am 
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Ed P wrote:
J Perry wrote:
What if you had a giant stirling engine using UF6 and He as the working gases and trigger fission with neutron reflecting materials or a particle accelerator when the gas is on the "hot" side, while poisoning it and conducting heat away on the "cold" side. The reactor and power generating device would be the same compact unit.

I've read the section on gaseous homogenous reactors in Fluid Fuled Reactors and it seems they are possible, just very difficult, and I have no idea how you could make this arrangement breed thorium

Just wanted to put this idea out there. I don't have near enough knowledge of physics to figure out if it is even remotely possible.


Seems like an enormous challenge. I thought about UF6 reactors, but gas reactors are so low power density, corrosion would be tough, what happens with the fission products as they won't all be gasses, having the energy conversion basically in the core seems like a lifetime/maintenance issue, conversion from UF6 to UF4 would allow fissile fuel plateout and concentration on the cooling surface causing hot spots and excess local reactivity, an ultimately burn through and loss of gaseous fuel and fission products. The latter is why ORNL gave up on aqueous homogeneous reactors.


A good summary of precisely why this idea is "crazy". Add the fact that everything is at much higher pressures than molten salt reactors can operate at, and it's not hard to see why gaseous fuel reactors haven't caught momentum.

Incompressible, stable liquid, high heat capacity, and low pressure, are among the chief advantages of the molten salt fuelled and cooled reactor concepts.


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 Post subject: Re: Crazy idea
PostPosted: Jun 30, 2013 7:34 am 
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Joined: Jun 22, 2013 2:38 pm
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I think I figured out the answer to my question
J Perry wrote:
I'm more interested in if a fission reaction emitting lots of heat can be started and stopped within a few seconds.

A fission reaction starting up and producing a lot of energy in a few seconds is what happens in a nuclear bomb.


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 Post subject: Re: Crazy idea
PostPosted: Jun 30, 2013 12:21 pm 
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J Perry wrote:
I think I figured out the answer to my question
J Perry wrote:
I'm more interested in if a fission reaction emitting lots of heat can be started and stopped within a few seconds.

A fission reaction starting up and producing a lot of energy in a few seconds is what happens in a nuclear bomb.

Actually a bomb does this in milliseconds. In a scram situation you shut down power production rapidly in a reactor (seconds). In the ARE they cycled the power rapidly. In a production reactor you would prefer to be more gradual to reduce wear and tear on turbine etc. As far as the nuclear core goes it will happily change power rapidly - less happily change temperature rapidly.


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 Post subject: Re: Crazy idea
PostPosted: Jul 02, 2013 4:24 am 
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Joined: Feb 05, 2013 5:24 am
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Lars wrote:
J Perry wrote:
I think I figured out the answer to my question
J Perry wrote:
I'm more interested in if a fission reaction emitting lots of heat can be started and stopped within a few seconds.

A fission reaction starting up and producing a lot of energy in a few seconds is what happens in a nuclear bomb.

Actually a bomb does this in milliseconds. In a scram situation you shut down power production rapidly in a reactor (seconds). In the ARE they cycled the power rapidly. In a production reactor you would prefer to be more gradual to reduce wear and tear on turbine etc. As far as the nuclear core goes it will happily change power rapidly - less happily change temperature rapidly.

And a TRIGA reactor goes supercritical and shuts Down
In 10microseconds.


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 Post subject: Re: Crazy idea
PostPosted: Jul 02, 2013 10:34 am 
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Location: NoOPWA
Ed P wrote:
And a TRIGA reactor goes supercritical and shuts Down
In 10microseconds.
One hopes?

_________________
DRJ : Engineer - NAVSEA : (Retired)


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 Post subject: Re: Crazy idea
PostPosted: Jul 02, 2013 3:23 pm 
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Joined: Jun 22, 2013 2:38 pm
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So, the only major problem is solid build-up and corrosion?


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