Saw something on the history channel (I think) that said the biggest danger comes from the spent fuel since it remains highly dangerous for a couple thousand years. Is that true? I mean if its totally safe and there's nothing to worry about then why all the fuss over Yucca mountain?
Picking the "biggest danger" is kind of like asking the ETS folks what the best survival knife is. It depends on what you're concerned about.
Did you know that a fuel rod is low-grade enriched uranium pellets contained in a welded tube of some other metal (like stainless steel)?
Spent fuel rods do contain bad stuff in the form of fission products (that's what's left after you break the uranium atoms to get the energy) some of which have very long half-lives (the time it takes for half of the material to undergo radioactive decay and change to some other isotope) and give off some strong radioactive particles or energy when they do. Some of the fission products are bad poison in a chemical sense.
Yucca mountain is all about storing the result of re-processing the fuel rods by separating the remaining uranium (like the 95% that wasn't consumed) for re-use in new fuel rods from the genuinely nasty fission products for safe storage. Many similarities to reusing motor oil with Yucca mountain being where the nasty sludge goes.
Yes, things can go wrong. But the fear-mongers emotionally and vastly overstate the risks. They are in far more danger driving to the rally to protest the plant than they are from the plant itself.
I sat thru the classes. I'm an engineer and I'm a nuclear trained former US Navy submariner. But this is the internet where everyone's opinion is equally weighted.