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.

Fast breeder reactors, using uranium from the ground

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.”

Once-through, using uranium from the oceans

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,

Figure 24.4. Three Mile Island nuclear power plant.
Figure 24.5. Dounreay Nuclear Power Development Establishment, whose primary purpose was the development of fast breeder reactor technology. Photo by John Mullen.