All right, I'll offer a serious reason why it wouldn't work. Cost. What you are proposing is very costly to build, very costly to maintain.
I seriously doubt that there will be developed a safe, reliable, and small enough nuclear power plant to operate at the single car level, or even at the single train level. Since you wanted to get away from fossil fuel, that leaves nuclear electric generation and distribution to the motors (engines, but electric engines are called motors). That much juice needs to travel by Catenary or third rail from the sub-station to the motor.
Electric powered trains perform much better, and last longer than their diesel-electric brethren. They out accelerate them hands down, their weight-hp ratio is much better, they don't have to carry their power source with them.
The big problem is the power distribution system. It is not trivial to build and maintain. And it's susceptible to things like weather knocking down lines, flooding third rails, etc. All these make to an expensive system. You'll notice that in the USA, electrified tracks are concentrated in high population density areas where these high costs can be spread out over a larger population.
Rail does have it's part to the solution. As capacity grows, so will the amount of fright that gets transported, probably via containerizes freight.
Pbuttenger rail can compete with airlines where total door to door travel times are close, but cross-country pbuttenger rail at this time is in trouble. It will take separate rights of way and very high speeds.
Don't get me wrong I love trains, and I want to see a greater share of the transportation problem go to them. But there are some very serious obstacles to overcome.
Doug
