Now, thanks to [i]SCIENCE. [/i]
Now you're probably thinking "HA YOURE DUMB URANIUM HAS TO BE MINED AND THERES ONLY SO MUCH WE CAN MINE!!!1!!1" Well, that [b][i]used to be[/i][/b] the case.
Seawater holds literally billions of tons of uranium. It's in the ppm when you're looking at a gallon of seawater, (parts per million) but because there's at least hundreds of epic butt tons of sea water (yes that's an exact measurement) the amount of uranium adds up.
So how is that renewable? Well to keep it as layman as possible basically the amount of uranium in seawater maintains a natural equilibrium, so when it's extracted it's naturally replenished by the rocks and ground exposed to seawater. And since there's way more epic butt tons of uranium in the rocks, were talking hundreds of millions of years worth if we relied on nuclear and nuclear only for the entire worlds energy, its considered renewable, like the sun is.
So why does this matter?
Well the Department of Energy (your tax dollars at work) initiated a program involving a multidisciplinary team from national laboratories, universities and research institutes to address the fundamental challenges of economically extracting uranium from seawater. Within five years this team has developed new adsorbents that reduce the cost of extracting uranium from seawater by three to four times.
And now it's more cost effective (as well as much more environmentally friendly) to extract it from seawater than than through mining.
You can read about the process itself here:
http://www.pnnl.gov/news/release.aspx?id=4271
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It's not renewable, just really -blam!-ing abundant.