http://en.wikipedia.org/wiki/
Maybe you were like me and assumed that expanded nuclear fission power could help humanity wean itself off fossil fuel derived electricity, and reduce greenhouse gas emissions. As of 2009, it supplied 20% of all US electricity, which is greater than all renewable sources combined. It seems like a perfectly "clean" technology: radioisotopes react in a controlled manner, creating heat that evaporates industrial water into steam that turns giant turbines, which powers our homes, businesses, and eventually cars too. The only major waste produced is heat and water. There are plenty of pro-nuclear "data" and persuasive marketing out there (http://www.world-nuclear.org/
Apart from the obvious and still legitimate concerns for plant accidents and waste disposal, nuclear power is a lot dirtier and inefficient than the industry and their political allies would admit, because we have to take the entire "nuclear fuel cycle" into account. First of all, as anyone following the Iranian uranium enrichment saga would know, fuel-grade material doesn't magically seep out of the ground like oil (and even oil must be refined before it is more useful). Uranium and plutonium isotopes have to be processed, concentrated, and separated from non-fissile material in a huge series of centrifuges, which of course requires lots of power to run and therefore have a big carbon footprint. Uranium mining and transportation is also energy-intensive, and any nuclear power plant must have adequate security in the post-9/11 world, which also adds to the cost of every KW produced. Also, high quality uranium is the least carbon-intensive, but quality ore mostly comes from Canada, and some of their major mines are nearing depletion. All other global uranium deposits in the US, Australia, and elsewhere have lower quality material and therefore higher pollution potential.
Obviously the up-front costs of plant construction are huge (maybe $10B, like the recent estimate for a new South Carolina project), also taking into account very generous government subsidies and tax breaks that the renewable energy industry doesn't even come close to enjoying. To be fair, nuclear's gross subsidies are huge vs. renewables, but appear much more reasonable on a per-MW basis ($24 for solar vs. $1.56 for nuclear), though this is partly due to the huge scale of nuclear plants vs. renewable projects. And let's remember that part of renewables' subsidies is a premium we're paying to avoid pollution. It's not meant to be the most economical energy source, though some renewables proponents would argue that it can be with proper government support, less superfluous aid to dirty energy, and consideration of the indirect costs of emissions (such as the BP spill, and health/productivity losses due to respiratory diseases).
With current technology, nuclear plants are built for a service life of 15-60 years, and must be decommissioned in a complex and even more costly process (maybe 2-10X construction cost, taking waste storage into account also). Therefore, many of the plants that were built by the G20 during the Cold War are aging, and half of the world's 443 large-scale reactors will be considered for retirement by 2012. So if the nuclear industry wants to boost their slice of the energy pie, they will need to invest in many new plants that they probably can't afford, and couldn't find the real estate for anyway, since they can't just build on top of a former plant site for 30-100 years, due to possible contamination from decommissioning. Also, an MIT study estimates that the Earth has enough uranium for 1,000 gigawatt-scale reactors for at least 50 years. Sounds great, but actually our ability to discover, mine, and produce fuel-grade material will not be able to keep up with the industry's hopes for growth. Each GW-size plant requires about 200 metric tons of uranium per year. Multiply that over all plants, and fuel production can't keep up: in 2004 plants needed 68,000 metric tons of fuel, but mines only produced 39,000, with the remainder coming from Cold War inventories, recycling, conversions of weapons-grade material. But our stockpiles are due to run out by 2020, possibly leading to a nuclear fuel shortage. That's why the IAEA expects nuclear power production to peak around 2015 and then taper off by 2030 to below-present levels. Nuclear currently supplies 6% of global energy, and may only peak at 10-14%, despite about $2T in total global investment since the technology became available. Just imagine if we spent that much on renewables.
The US hasn't built a new nuclear plant since 1978, and although (even more) new plant constructions subsidies are in Obama's energy plan, I don't know how it's going to pan out, because it's hard enough to get approval to build a much safer and smaller natural gas power plant. Plus with more nuclear plants comes more fuel waste to store in giant steel/concrete tanks at guarded facilities. Already 50% of Americans live within 75 miles of an above-ground nuclear spent-fuel site (whether they know it or not, according to the Federation of American Scientists), so probably the "not in my backyard" mentality will obstruct nuclear's growth (especially with the $50-100B Yucca Mountain waste repository project still in limbo and many logistical issues still unresolved).
All things considered, the DOE estimates that the economic and environmental costs of nuclear power (using current data) make it dirtier and less efficient than all other renewable energy sources but solar (due to very expensive photovoltaics), and in some cases, worse than traditional coal or natural gas power plants (8-13 cents/KWH for nuclear, vs. 6-12 cents/KWH natural gas, 6-23 cents/KWH coal, 3-9 cents/KWH wind/hydro). The DOE also estimates that nuclear's net energy (output divided by all energy inputs needed for the entire nuclear fuel cycle) is about 0.3 to heat a home, meaning we're actually taking an energy LOSS going nuclear (as in, 100 KW must be spent for every 30 KW of electric heating created). Compare this to passive solar home heating with a net energy of 5.8, or a natural gas furnace at 4.9 (which also creates CO2 unfortunately).
Then there's the old hope that technology will save us. New nuclear plant designs do have improved safety and economics, but probably won't make a big enough difference to make nuclear a more attractive energy source. New breeder plants actually produce plutonium while they consume uranium, supposedly making them nearly "renewable", but the technology is unproven, and fuel is not the major cost concern of nuclear power (though as I mentioned above, fuel supply shortage is a concern which breeder plants could potentially mitigate). Nuclear-friendly France experimented with a breeder plant that opened in 1986, but was closed just 12 years later due to operating cost overruns (in addition to the $13B to build it). Consequently, other nations have canceled breeder projects before breaking ground.
Humans will always tinker with clever ways to generate energy, but of course it takes energy to make energy. If you believe the climate scientists, we don't have a lot of time to counteract major climate change, if it's not already too late. The days of cheap oil are over, but drops in supply will be gradual, and maybe slow enough to prevent major public outcry forcing politicians to enact energy reform. We don't have the resources to invest in ridiculously expensive energy sources like nuclear that may not even provide much benefit over hydrocarbons. Obviously the best way to create new energy is to not waste what we already have, so improvements in CAFE standards, greening buildings, and more sustainable consumption habits will be like creating a new Saudi Arabia in the long run. And what do we have to lose by giving renewables a fair chance, and at least as much government support as dirty energy has enjoyed over the years? I know there are still socioeconomic and environmental costs associated with wind farms and dams, but at least failures there don't compare with Chernobyl or Valdez. Every venture has risk, but the upside of large-scale renewable power is much better than nuclear, "clean coal", or other alternatives.