Thorium + Computation = new solutions
As mentioned, the main reason thorium was neglected as an energy source from 1945-1960 was that uranium was the better "dual use" fuel for making weapons and for civilian energy. Hence uranium is where all the government research dollars went. However, as Alvin Weinberg pointed out in Annual Reviews of Nuclear Science (1972) pp 327-333, there was a major economic+technical obstacle for thorium as well: the basic heavy water and graphite reactor designs up until 1972 did not conserve neutrons sufficiently well to keep a thorium breeder operating, unless the fuel were reprocessed frequently--too frequently to be cost effective. Hence Weinberg invented the liquid-fueled reactor where the dissolved thorium fuel passes through a continuous fuel-reprocessing step. In theory, this could be more cost-effective, and possibly safer
for some of the reasons mentioned above.
Today we have computing power that Weinberg could not have imagined in 1972, and this allows us to model a wide variety of reactor core configurations that could not have been computed in that era. One result is that we can now show--while the liquid fuel thorium reactor has a higher breeding ratio than any practical solid-thorium fueled reactor--it is ALSO possible to operate a heavy water or graphite reactor thorium breeder at substantially higher efficiency than Weinberg was able to calculate. This is an area of active research in India.
While the Molten Salt (dissolved liquid thorium) reactor is a likely future technology for thorium energy and should be developed, there are also nearer-term thorium breeder solutions in the graphite and heavy water moderated (solid thorium fueled) design space that should be of great interest in Asia in the next few years. My colleagues and I will be publishing an example later this year.
