France comes the closest (about 95% of consumption) and while they've certainly benefited from it, they still run into problems having too much generation from a single source. If they didn't have fairly significant hydro/fossil (exporting the excess), they would have even more trouble.
Do we have enough fuel for that increased number of NPP?
Absolutely. There are multiple possible fuel cycles and the most likely involve very plentiful resources (uranium and thorium are quite common). The price would certainly have to rise significantly in that demand scenario, but fuel costs are a tiny proportion of the cost of nuclear power.
Considering much of the energy that is used to mine and process the ore now is fossil
That's really not a relevant consideration. You're not properly appreciating how substantial the mass-energy conversion is. The actual carbon emissions related to the mining of nuclear fuel is incredibly tiny on a per kWh basis. All of the major clean generation technologies (hydro/solar/wind/nuclear) involve fossil-powered heavy equipment for steel/concrete/construction/etc... but in all of those cases, the amount is quite comparable (and more importantly, negligible).
Is it even possible to be at 100% saturation nuclear energy?
Not really. And it would be incredibly wasteful. While the newer designs are much more flexible, you would still need to build enough of them to cover peak demand plus a margin to account for refueling and maintenance. A high percentage of the year you would have way too much excess capacity.
But again, why would you even try? For instance... we get 8% of our electricity from hydro power. I can't think of any reason why you would shut those down.
With those questions asked wouldn't it be smart to increase our reliance on renewables?
That's not really logical. First of all... asking questions doesn't imply conclusions. It's the answers to those questions that matter. Second, just from a logical perspective, nuclear and renewables aren't the only alternatives. So saying that you can't see one of them providing 100% of demand doesn't imply that the other necessarily needs to grow. It would be, for instance, much harder for renewables to provide 100% of demand... do you therefore conclude that we need to increase out reliance on nuclear? Of course not.
But the answer is still yes. It would be smart to increase out reliance on renewables. It's also smart to increase our reliance on nuclear power. Because that unmentioned category (coal/gas) is still the 900 lb gorilla that needs to be slain. There's lots of room for growth in both areas before we ever have to choose between one or the other.
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