Paul Weisz’s article on long-term energy supplies (Physics Today, Physics Today 0031-9228 57

7
200447July 2004, page 47 ) states that uranium resources with breeder reactors could provide the world’s energy needs for “hundreds of years.” That is a gross underestimate. The world’s energy needs could be provided by uranium-fueled breeder reactors for the full billion years that life on Earth will be sustainable, without the price of electricity increasing by more than a small fraction of 1% due to raw fuel costs. 1  

The error in Weisz’s calculation is that he is referring to uranium available at its present price, $10–20 per pound. But in breeder reactors, 100 times as much energy is derived from a pound of uranium as in present-day light water reactors, so we could afford to use uranium that is 100 times as expensive.

The cost of extracting uranium from its most plentiful source, seawater, is about $250 per pound—the energy equivalent of gasoline at 0.13 cent per gallon! The uranium now in the oceans could provide the world’s current electricity usage for 7 million years. But seawater uranium levels are constantly being replenished, by rivers that carry uranium dissolved out of rock, at a rate sufficient to provide 20 times the world’s current total electricity usage. In view of the geological cycles of erosion, subduction, and land uplift, this process could continue for a billion years with no appreciable reduction of the uranium concentration in seawater and hence no increase in extraction costs.

1.
B. L.
Cohen
,
Am. J. Phys.
51
,
75
(
1983
).