Thorium fuel cycle

The thorium fuel cycle is a nuclear fuel cycle that uses an isotope of thorium,
Th, as the fertile material. In the reactor,
Th is transmuted into the fissile artificial uranium isotope
U which is the nuclear fuel. Unlike natural uranium, natural thorium contains only trace amounts of fissile material (such as
Th), which are insufficient to initiate a nuclear chain reaction. Additional fissile material or another neutron source is necessary to initiate the fuel cycle. In a thorium-fuelled reactor,
Th absorbs neutrons to produce
U. This parallels the process in uranium breeder reactors whereby fertile
U absorbs neutrons to form fissile
Pu. Depending on the design of the reactor and fuel cycle, the generated
U either fissions in situ or is chemically separated from the used nuclear fuel and formed into new nuclear fuel.

The thorium fuel cycle has several potential advantages over a uranium fuel cycle, including thorium's greater abundance, superior physical and nuclear properties, reduced plutonium and actinide production, and better resistance to nuclear weapons proliferation when used in a traditional light water reactor though not in a molten salt reactor.