Thorium Energy Fuel Cycle
Like 238U, 232Th is not fissile itself, but it is fertile: it will absorb slow neutrons to produce, after two beta decays, 233U, which is fissile. The preparation of thorium fuel does not require isotopic separation, unlike the preparation of uranium fuels.
The thorium fuel cycle creates 233U, which, if separated from the reactor's fuel, could with some difficulty be used for making nuclear weapons. This is one reason why a liquid-fuel cycle (e.g. Molten Salt Reactor or MSR) is preferred — only a limited amount of 233U ever exists in the reactor and its heat-transfer systems, preventing any access to weapons material; however the neutrons produced by the reactor can be absorbed by a thorium or uranium blanket and fissile 233U or 239Pu produced. Also, the 233U could be continuously extracted from the molten fuel as the reactor is running. Neutrons from the decay of uranium-233 can be fed back into the fuel cycle to start the cycle again.
The neutron flux from spontaneous fission of 233U is negligible. 233U can thus be used easily in a simple gun-type nuclear bomb design. In 1977, a light-water reactor at the Shippingport Atomic Power Station was used to establish a 232Th-233U fuel cycle. The reactor worked until its decommissioning in 1982. Thorium can be and has been used to power nuclear energy plants using both the modified traditional Generation III reactor design and prototype Generation IV reactor designs. The use of thorium as an alternative fuel is one innovation being explored by the International Project on Innovative Nuclear Reactors and Fuel Cycles (INPRO), conducted by the International Atomic Energy Agency (IAEA).
Unlike its use in Molten salt reactors, when using solid thorium in modified light water reactor (LWR) problems include: the undeveloped technology for fuel fabrication; in traditional, once-through LWR designs potential problems in recycling thorium due to highly radioactive 228Th; some weapons proliferation risk due to production of 233U; and the technical problems (not yet satisfactorily solved) in reprocessing. Much development work is still required before the thorium fuel cycle can be commercialized for use in LWR. The effort required has not seemed worth it while abundant uranium is available.
Read more about this topic: Thorium Compounds, Applications, Thorium As A Nuclear Fuel
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