one-ton car and a dedicated parking place for it.” A large investment, yes,
but not absurdly off scale. And that was the calculation for once-through
reactors. For fast breeder reactors, 60 times less uranium is required, so
the mass per person of the uranium collector would be 0.5 kg.


Thorium is a radioactive element similar to uranium. Formerly used to
make gas mantles, it is about three times as abundant in the earth’s crust as
uranium. Soil commonly contains around 6 parts per million of thorium,
and some minerals contain 12% thorium oxide. Seawater contains little
thorium, because thorium oxide is insoluble. Thorium can be completely
burned up in simple reactors (in contrast to standard uranium reactors
which use only about 1% of natural uranium). Thorium is used in nuclear
reactors in India. If uranium ore runs low, thorium will probably become
the dominant nuclear fuel.

Thorium reactors deliver 3.6 billion kWh of heat per ton of thorium,
which implies that a 1 GW reactor requires about 6 tons of thorium per
year, assuming its generators are 40% efficient. Worldwide thorium re-
sources are estimated to total about 6 million tons, four times more than
the known reserves shown in table 24.7. As with the uranium resources, it
seems plausible that these thorium resources are an underestimate, since
thorium prospecting is not highly valued today. If we assume, as with ura-
nium, that these resources are used up over 1000 years and shared equally
among 6 billion people, we find that the “sustainable” power thus generated
is 4 kWh/d per person.

An alternative nuclear reactor for thorium, the “energy amplifier” or
“accelerator-driven system” proposed by Nobel laureate Carlo Rubbia and
his colleagues would, they estimated, convert 6 million tons of thorium to
15 000 TWy of energy, or 60 kWh/d per person over 1000 years. Assuming
conversion to electricity at 40% efficiency, this would deliver 24 kWh/d
per person
for 1000 years. And the waste from the energy amplifier would
be much less radioactive too. They argue that, in due course, many times
more thorium would be economically extractable than the current 6 million
tons. If their suggestion – 300 times more – is correct, then thorium and
the energy amplifier could offer 120 kWh/d per person for 60 000 years.

Land use

Let’s imagine that Britain decides it is serious about getting off fossil fuels,
and creates a lot of new nuclear reactors, even though this may not
be “sustainable.” If we build enough reactors to make possible a significant
decarbonization of transport and heating, can we fit the required
nuclear reactors into Britain? The number we need to know is the power

Country Reserves
(1000 tons)
Turkey 380
Australia 300
India 290
Norway 170
USA 160
Canada 100
South Africa 35
Brazil 16
Other countries 95
World total 1580
Table 24.7. Known world thorium resources in monazite (economically extractable).
Figure 24.8. Thorium options.