The Thorium is a naturally-occurring,slightly radioactive metal discovered by Swedish chemist Jons Jakob Berzeliusin 1828.
Country | Reserves (tonnes) |
---|---|
Australia | 300 000 |
India | 290 000 |
Norway | 170 000 |
USA | 160 000 |
Canada | 100 000 |
South Africa | 35 000 |
Brazil | 16 000 |
Other countries | 95 000 |
World total | 1 200 000 |
Thorium as a Nuclear fuel
Thorium, as well as uranium, can be used as a nuclear fuel. Although not fissile itself, thorium-232 (Th-232) will absorb slow neutrons to produce uranium-233 (U-233), which is fissile. Hence like uranium-238 (U-238) it is fertile.In one significant respect U-233 is better than uranium-235 and plutonium-239, because of its higher neutron yield per neutron absorbed. Given a start with some other fissile material (U-235 or Pu-239), a breeding cycle similar to but more efficient than that with U-238 and plutonium (in slow-neutron reactors) can be set up. The Th-232 absorbs a neutron to become Th-233 which normally decays to protactinium-233 and then U-233. The irradiated fuel can then be unloaded from the reactor, the U-233 separated from the thorium, and fed back into another reactor as part of a closed fuel cycle.
Over the last 30 years there has been interest in utilising thorium as a nuclear fuel since it is more abundant in the Earth's crust than uranium. Also, all of the mined thorium is potentially useable in a reactor, compared with the 0.7% of natural uranium, so some 40 times the amount of energy per unit mass might theoretically be available (withouit recourse to fast breeder reactors
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