exploration and little uranium exploration has been undertaken since the
1980s; so maybe more mineable uranium will be discovered. Indeed, one
paper published in 1980 estimated that the low-grade uranium resource is
more than 1000 times greater than the 27 million tons we just assumed.
Could our current once-through use of mined uranium be sustainable?
It’s hard to say, since there is such uncertainty about the result of future
exploration. Certainly at today’s rate of consumption, once-through reac-
tors could keep going for hundreds of years. But if we wanted to crank up
nuclear power 40-fold worldwide, in order to get off fossil fuels and to al-
low standards of living to rise, we might worry that once-through reactors
are not a sustainable technology.
Uranium can be used 60 times more efficiently in fast breeder reactors,
which burn up all the uranium – both the 238U and the 235U (in contrast to
the once-through reactors, which burn mainly 235U). As long as we don’t
chuck away the spent fuel that is spat out by once-through reactors, this
source of depleted uranium could be used too, so uranium that is put in
once-through reactors need not be wasted. If we used all the mineable
uranium (plus the depleted uranium stockpiles) in 60-times-more-efficient
fast breeder reactors, the power would be 33 kWh per day per person.
Attitudes to fast breeder reactors range from “this is a dangerous failed
experimental technology whereof one should not speak” to “we can and
should start building breeder reactors right away.” I am not competent
to comment on the risks of breeder technology, and I don’t want to mix
ethical assertions with factual assertions. My aim is just to help understand
the numbers. The one ethical position I wish to push is “we should have a
plan that adds up.”
The oceans’ uranium, if completely extracted and used in once-through
reactors, corresponds to a total energy of
|4.5 billion tons per planet
|= 28 million GW-years per planet.
|162 tons uranium per GW-year
How fast could uranium be extracted from the oceans? The oceans circulate
slowly: half of the water is in the Pacific Ocean, and deep Pacific
waters circulate to the surface on the great ocean conveyor only every 1600
years. Let’s imagine that 10% of the uranium is extracted over such a
1600-year period. That’s an extraction rate of 280 000 tons per year. In
once-through reactors, this would deliver power at a rate of
2.8 million GW-years / 1600 years = 1750 GW,