Net Energy and Uranium
According to Robert Palgrave, a commenter on Stewart Brand's environmental heresies (seen via NEI Nuclear Notes):
There is only a finite supply of uranium ore containing reasonable concentrations of uranium 235. When this concentration falls below 0.01%, the costs of energy production from nuclear power can no longer cover the costs of extraction of uranium from the earth, at which time the nuclear fuel cycle will produce no net energy. In other words: below a certain uranium content, nuclear power produces less energy than is needed to build, fuel, and operate the reactor and to repair the environmental damage.Robert Palgrave can be so certain presumably because rarer minerals are at a higher-entropy state and MUST take more energy to extract.
There is a counterexample to that. Uranium is 4 parts per million of the Earth's crust, the same concentration as a typical gold ore. Since gold mines don't run at a loss, gold can be extracted from such a concentration of gold ore at a cost of roughly $20 per gram. Even if we assume that all of that $20 goes to pay for energy, 1 gram of uranium can produce far more than $20 worth of energy if breeder reactors are used.
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