Nuclear Turbine

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 what’s 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 can’t runaway (although I realize that this problem is pretty much solved in modern reactors).