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

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).