I'm not a genius im only an engineer.
But why not build a car using nuclear decay to power a generator
which powers an electric motor to drive the car
Many people have suggested plutonium 238 not sutable for clean bombs but great for a dirty bomb .
how about strontium 90 never been assosiated with weapons has a halflife 32 years (most people do keep cars that long) and can reach a temp of 800 celcius and its called a waste product which they just end up storing in underground vaults.
Its is a beta decay which requires more sheilding than alpha decay
so why not put the pellets in a sythetic diamond case to sheild the radiation before it even reaches the liquid but not insulate the heat (because diamond is the best know conductor of heat) the strontium will heat liquid helium to the critical point 176 celcius. the steam turns a turbine and generates electricity
the helium then passes through a thermal electric cooler making it easily compressable equiring less energy
the helium is then recommpressed into a tank to a pressure of 5000psi then strontium in the tank reboils the liquid helium.
people have suggesteed solar powered cars and puting turbines to charge a battery but how about using solar to only power the 10 hp compressor and a dozen mini tubine to power the thermal electric cooler.
so this would be a closed circuit the helium never leaves lasts minimum of 20 years
also this type of rtg would be more efficent compared to regular rtg which convert heat dirrectly to electricity