If I recall correctly 90 pounds of Pu238 are needed to produce 10 kilowatts in a RTG = radioactive thermonic generator. Strontium 90 would likely be used if it produced more power. A steam turbine powered by the same heat might apply 50 kw to the wheels of a typical SUV, which may be enough to give acceptable performance. I can't imagine 90 pounds of either metal in a car, especially at the prices suggested in this thread. Likely much of the cost is refining from high level nuclear waste. Perhaps the high level nuclear waste can power the car, without the cost of processing the waste. The main problem would be neutrons and gamma radiation which would be difficult to shield properly. This system may have application for unmanned vehicles which don't need shielding. Vehicle repairs would have to be done by waldo or robot. Neil