LTFR reactor would minimize potential radiation issues
I don't know if they would work as well as Uranium reactors, but if a nuclear rocket could be based on the LTFR molten salt reactor, nearly all the fissile material could be Thorium, which presents a much smaller risk of radioactive contamination in the event of a catastrophic failure. This might obviate one of the major objections to nuclear rockets.
If I understand correctly, the ability of a nuclear reactor to provide the necessary energy for a long period of time with a small fuel mass means that a much larger amount of propellant (the stuff shipped out the back) could be carried instead of chemical fuel. This means that a long, slow thrust could be used instead of the present method of maximum thrust for a very short time.