I don't know the current situation but older Chrysler and Jeep diesels used to be VM Motori units and those in current Jeep Cherokee - debadged Mercedes Benz 320CDis.
Nuclear fuel rods would probably be cheaper than gas HA!
I am sure they already are and by a multitude. And you wouldn't have to fill up or charge batteries. Your car would probably last it's service lifetime as it came from factory.
Here's an old blueprint for nuclear powered locomotive.
Biggest problem for nuclear reactor in small vehicles is the amount of mass needed for radiation shielding.
Well, no, I actually take that back. The biggest problem would be dealing with health and safety environmental protection agencies convincing them that idea of thausands of nuclear reactors wizzing past apartment buildings and occasionally crashing into each other wouldn't pose danger of any kind to inhabitants or environment. :D
Unless you're going to North pole or Moon or Mars, you don't need a mobile nuclear reactor. All you need is a good battery...