Why is thorium not used in a nuclear reactor?

Answer 1

: Main article: Thorium fuel cycle Thorium, as well as uranium and plutonium, can be used as fuel in a nuclear reactor. Although not fissile itself, 232Th will absorb slow neutrons to produce (233U), which is fissile. Hence, like 238U, it is fertile. Problems include the high cost of fuel fabrication due partly to the high radioactivity of 233U which is a result of its contamination with traces of the short-lived 232U; the similar problems in recycling thorium due to highly radioactive 228Th; some weapons proliferation risk 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 commercialised, and the effort required seems unlikely while (or where) abundant uranium is available. Nevertheless, the thorium fuel cycle, with its potential for breeding fuel without fast neutron reactors, holds considerable potential long-term benefits. Thorium is significantly more abundant than uranium, and is a key factor in sustainable nuclear energy. One of the earliest efforts to use a thorium fuel cycle took place at Oak Ridge National Laboratory in the 1960s. An experimental reactor was built based on Molten Salt Reactor technology to study the feasibility of such an approach, using thorium-fluoride salt kept hot enough to be liquid, thus eliminating the need for fabricating fuel elements. This effort culminated in the Molten-Salt Reactor Experiment that used 232Th as the fertile material and 233U as the fissile fuel. Due to a lack of funding, the MSR program was discontinued in 1976.

Answer 2

Thorium is quite widespread and could be a useful part of the nuclear fuel cycle. It is not itself fissile, but if it is irradiated in a reactor it will produce uranium 233 which is fissile. To separate out the U233 would require processing of irradiated material which is not done on any large scale in the US at the present time. Some countries such as India are interested because they have plenty of thorium and not so much uranium. In the US and Europe supplies of uranium are not a problem and we have the enrichment facilities required to raise the level of U235, so there is no need to go down the thorium route, but I am sure this will be kept under review in the future.

Answer 3

Thorium is a possible source of fissile Uranium 233. This would require thorium to be irradiated in a reactor, and the resulting product to be chemically treated to separate out the U233. This might sound simple, but there are complications due to other products like U232. In any case I believe at the present time there is a ban in the US on treating irradiated fuel, so this would require legislation.

Problems include the high cost of fuel fabrication due partly to the high radioactivity of the traces of the short-lived 232U that contaminates the 233U fuel; the similar problems in recycling thorium due to highly radioactive 228Th; some weapons proliferation risk 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 commercialised, and the effort required seems unlikely while (or where) abundant uranium is available. The conclusion is that it is much easier and cheaper to enrich natural uranium, and this is likely to continue until uranium becomes difficult to find or too expensive to refine from low grade ore. Since we are probably at least 50 years and maybe 100 years from that point in time, use of thorium will stay a theoretician's dream for many years yet.

Answer 4

Uranium-238, which makes up 99.3% of natural uranium, is not fissionable by slow neutrons. U-238 has a small probability for spontaneous fission and also a small probability of fission when bombarded with fast neutrons, but it is not useful as a nuclear fuel source.

Answer 5

The most important disadvantage of thorium is the radioactivity; but fortunately this radioactivity is not so dangerous for thorium.

Answer 6

Thorium is not fissile, hasn't a critical mass, can't sustain a nuclear chain reaction.