[acidburnNSA]

For seawater extraction, you just put enough uranium capture fibers in a few places and the uranium is delivered to you slowly over billions of years via ocean currents. This is well supported by the various articles and entire scientific issue featured in the See Also section.

But if you don't buy seawater extraction, check out the Weinberg 1959 reference (https://doi.org/10.1063/1.3060564), which contains a calculation for how much earth would need to be moved to power the entire world on granite. They calculate that we'd need granite mining from the crust about the same order of magnitude of the fossil fuel mining operations at that time. Of course, mining granite is far less destructive than mining fossil fuel, so it's totally acceptable.

Recall that there is 20x more nuclear energy in average crustal rock than there is chemical energy in coal, per kg. So to a breeder reactor, it's literally as if the entire earth's crust is made of pure coal, 20x over.

Will that last long enough for ya? :)

And with that kind of energy density, it's all economical to extract.

[adgjlsfhk1]

this has some serious problems in the analysis. First of all, about half of the earth's crust is under an ocean. Second, of the remaining half, it is on average about 10 miles deep. There is no way that digging up 10 miles of rock to get to some scattered uranium atoms is net positive from an energy perspective. The deepest mines in the world are 2.5 miles under ground, and is in a location with a very high concentration of gold. Most of the uranium in the earth's crust is at concentrations of less than 1 part in 1 million, and one ton of uranium can only (being maximally optimistic) lift 1 million tons of rock by about 1 mile, so any uranium lower than that (not in a major vein) will produce negative energy to mine. Also, just because it's technically net energy positive, doesn't mean it's efficient at all. If we want mining to be at least somewhat efficient, we will only be getting roughly 1/3rd of that (since by the time you are lower, you will be losing too much energy to be cost competitive).

This very basic analysis suggests that your link is off by at least a factor of 100, which doesn't inspire much confidence in their results.

[pfdietz]

Ocean floor bedrock is basalt, which has much lower U/Th content than granite. Granites are continental rocks.

Geologically, U and Th have been concentrated over the billions of years by about a factor of 1000 in the minerals that have accumulated in continents. Were this not the case, fission power would be completely impractical.