Researchers at a nuclear research facility in the Netherlands are working on building up molten-salt nuclear reactors that would use thorium as a fuel, according to New Scientist. Using thorium to produce nuclear power is considered to be much more stable than using uranium to power nuclear reactors, but using uranium is more common.
That may be due to Cold War strategic decisions: uranium-based reactors can produce plutonium, which has been desirable for making nuclear weapons. Another reason may be cost: fuel fabrication costs using thorium are driven up due to the high level of radioactivity built up in U-233, the fissile fuel material that thorium can get transformed into when it's bombarded with neutrons, according to the World Nuclear Association.