The spectacularly-named physicist Friedwardt Winterberg of the University of Nevada has long studied nuclear propulsion and nuclear explosives. He has just published a paper describing a nuclear explosive that uses chemical explosives (HMX, specifically) to drive a Deuterium-tritium fusion reaction, without the use of a fission element. If it could be made to work, it would result in a nuclear explosion with very little in the way of radioactive fallout… no radioactive heavy elements, mostly just a giant BANG and gamma rays, X-rays and some neutrons. Nothing you’d want to stand too close to, but also nothing that would cause any real environmental harm.
The explosions themselves are not described as being particularly spectacular by H-bomb standards. A sphere of HMX 60 centimeters in diameter, with a chemical yield equivalent to about 1/4 of a ton of TNT, would set off a small core of liquid D-T, producing a nuclear yield of about 25 tons of TNT (0.025 kilotons). By enriching the outermost 1 cm of the high explosives with 20% boron, the bulk of the neutrons generated by the fusion would be captured; the boron itself would explode due to the sudden addition of the neutron energy, sending a shockwave inwards which would aid in burning the D-T. Theoretically the radius of the high explosive could be reduced by about half and would still produce the same nuclear BANG. So a thirty-centimeter (11.8 inch) diameter ball would produce a 25-ton explosion… a gain of a factor of about 1000 from the yield of the chemical explosive alone.
Winterberg suggests using these devices to generate electrical power in MHD generators 60 meters in diameter. But their utility for space propulsion seems fairly obvious. Given the spherical nature of the bomb and the resultant blast, these would seem to be perfect fits for Johndale Solems “Medusa.” They would also work for propulsion systems with parabolic “pusher plates,” though the structures would have to be either very rugged, or (like Medusa) extremely flexible, or equipped with extremely powerful magnetic fields. For use in a more conventional Orion vehicle, something would have to be done to turn them into more effective shaped charges. Perhaps wrapping them in carbon fiber or graphene cylinders… hmmm…