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There is a lot of work going on at the moment into nuclear gas turbines (e.g. the PBMR & GT-MHR reactors). Both of these use fuel pellets to heat helium gas, which is then used to drive a turbine.
But how about using a highly enriched fissile gas, not only to drive the turbine but also to act as the
fuel. UF6 would be ideal as it has a very high coefficient of volume expansion, boils at 56C and has a critical temp of 230C.
You could use a compressor to squeeze the gas through a narrow aperture (increasing it's density), surrounded by neutron reflectors (and maybe moderator & neutron injectors). As gas passes through this aperture it becomes critical and heats up. As a result the gas expands and is forced through the turbine, which is in turn linked to the compressor (very similar a turbojet) and of course a generator. In this way you get a continuous flow of gas though the reactor.
Ideally you could have down stream separation of the fission products after the gas has left the turbine. Add a little more fuel to replace whats been used and return the remaining gaseous fuel to the compressor.
As there's no need to transfer the heat to some secondary medium, this should be a very efficient power plant.
The total inventory (amount of RA material) in this kind of plant would be quite small. Also this concept would continuously cycle the fuel and so get close to 100% consumption of the fissile materials (unlike current reactors) and so the volume of irradiate nuclear fuel (high level waste) being remove would be small.
And finally the reaction is only sustained by active input. So if anything goes wrong it cant runaway (although I realize that this problem is pretty much solved in modern reactors).
The US's contribution to nuclear gas turbines [vaccumac, Jul 16 2006]
And south africa's [vaccumac, Jul 16 2006]
Wiki's description of gas turbines [vaccumac, Jul 16 2006]
See slides 10-12 for gaseous reactors [vaccumac, Jul 17 2006]
||It's "highly toxic, reacts violently with water and is corrosive to most metals"--not the best working fluid. (Most of the depleted uranium stored in the US is in this form, and there have been several accidental releases.)
An additional problem is that you'll be working at fairly low temperatures, so the thermal efficiency will also be low. Other problems: it breaks down with intense radiation, and it can solidify, blocking pipes and causing the pressure in the reactor to build up, possibly resulting in a runaway reaction.
||I knew it was a tricky substance to handle, but i didn't know it easily broke up in radiation fields (kinda puts a dampener on things). Anyone know of a stable fissile gas?
||As for running at a low temperature, I kinda though the reverse would happen and if anything the temperature and pressures involved would be pushing boundaries. Why would it run at a low temperature?
||Alright I found the answer to a stable gas UF4. Plus I also found that gaseous reactors have been studied before(though not quite a turbine). See link