To generate all US electricity from nuclear we'd need about another 400 1GW reactors, whose total cost would be approximately $1 trillion, given how much plants have cost to build historically. For comparison, that is about a third of the estimated total economic cost of the Iraq war, and about 20% more than what congress has spent so far to fight the Iraq war. On 1GW coal plant costs about $2 billion to build today, by the way. If we could at last overcome construction delays caused by people crying NIMBY (who then end up with a coal plant in their backyard instead), it would cost still less. And seeing how living near coal plants exposes you to more radiation than living near nuclear plants, I don't understand why we haven't already made this choice. Oh wait, I remember, it is because of misinformation playing on the fears of people who don't understand the science and technology involved.

To get all of our energy from non-fossil fuel sources would take a lot more reactors, though how many I can't say, as it depends on what kinds of technology (new and old alike) we adopt for homes, offices, transportation, farming, manufacturing, and so on.
The easiest and cheapest carbon-free energy mix that we could achieve in the short term would be comprised of nuclear, wind, and solar, with maybe a smattering of wave, tidal, and geothermal where appropriate. Nuclear fuel is cheap enough that the reactors need never be turned off, so during the times when the production of electricity from renewables exceeds consumption we should manufacture synthetic fuels- hydrogen or otherwise. If demand exceeds supply we can consume these fuels for electricity. Excess fuel produced can be used in vehicles, including cars, trucks, ships, and planes. Ideally our ships would be nuclear, our cars and trucks will be PHEV and so use little fuel, and our planes will be more efficient than they are today. In that case, we could imagine most of the remainder of our fuel needs being met by biodiesel or nth generation biofuels. None of these goals would be particularly difficult to achieve if the political will is there.

"Residents in the Vaucluse, a popular southern French tourist destination, were banned yesterday from drinking well-water or swimming or fishing in two rivers after a uranium leak from one of France's nuclear power plants."

"embarrassed the government."

http://www.guardian.co.uk/environment/2008/jul/10/nuclearpower.pollution

Total lifecycle cost of Solar, Wind & Geothermal is better & safer. Look at all the private money lined up for wind & solar projects. So many that the BLM was trying to hide them and then block them entirely. Compare that to the constant scamming for public money to build nuclear plants and nuclear waste dumps.

There is no reason to use nuclear for grid power except to make a bunch of rich government contractors even richer.