particle bed engine?

[Brycesv1]

i just heard about what was called a particle bed reactor (wikipedia came up with nothing so i think he meant pebble bed) that could be used by spacecraft for thrust by pumping any inert gas through it and venting the plasma as thrust. leaving behind a radioactive gas cloud in the process but i think its nothing compared to the background radiation.

i was wondering if this is actually a viable system and if so, exactly how would it work? pros/cons?

 

[T.Neo]

Sounds like a version of a nuclear thermal engine. Generally hydrogen, which has the lowest particle mass, offers the best exhaust velocity, but it isn't exactly inert.

How radioactive your exhaust is, depends on how much radioactive isotopes react with your fuel or are carried out of the engine.

I think [ame="http://en.wikipedia.org/wiki/Project_Timberwind"]Project Timberwind[/ame] was based on a particle-bed arrangement, though I may be wrong.

Timberwind achieved better performance than NERVA.