The main safety concern with this would be in getting the nuclear fuel to the space craft. Initially, at least, it would have to be transferred from earth. Full containment is very heavy. A nuclear fuel container, as used for road transport weighs 20 tonnes not including the fuel. Uranium is also one of the densest materials on earth, with a density of 19.1 g/cm^2.

How would they mitigate a disaster during launch and the subsequent potential nuclear material dispersal?