Thorium fuel cycle

The thorium fuel cycle is a nuclear fuel cycle that uses an isotope of thorium, ²³²
Th
, as the fertile material. In the reactor, ²³²
Th
is transmuted into the fissile artificial uranium isotope ²³³
U
which is the nuclear fuel. Unlike natural uranium, natural thorium contains only trace amounts of fissile material (such as ²³¹
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, ²³²
Th
absorbs neutrons to produce ²³³
U
. This parallels the process in uranium breeder reactors whereby fertile ²³⁸
U
absorbs neutrons to form fissile ²³⁹
Pu
. Depending on the design of the reactor and fuel cycle, the generated ²³³
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.