Could nuclear submarines be powered indefinitely by extracting Uranium from seawater?

I believe that raw Uranium ore can be extracted from seawater. I'm not so sure about tapwater. And, I've read that this process of extraction can be done as cheaply as 100 dollars a pound. This is three times as expensive as Uranium can be obtained from mining, but, it seems to me that it still might be rather convenient under some circumstances. Wouldn't this allow for the possibility of having nuclear powered submarines travel indefinitely by simply refueling themselves, rather along the lines of Jules Verne's 20,000 Leagues under the Sea? Now, I realize, of course, that modern nuclear reactors are not powered directly by raw Uranium ore, but require specifically the refined isotopes U-235 or U-238. Would it be impossibly expensive, awkward or time-consuming to refine the Uranium ore obtained from seawater to obtain the needed U-235 or U-238 in a nuclear powered submarine? Does anyone have any specific experience with these Uranium extraction technologies from water, and does this sound like a practical possibility now, or in the future? https://www.sciencedirect.com/science/article/abs/pii/S0149197017300914