Thorium is a more abundant material than Uranium. It has a half life or 14 billion years, older than the universe. It is regarded as fertile, not fissile. That means it needs to be hit with a stream of neutrons to transmute it from Thorium 232 then into Uranium 233 which is fissile.Once the U233 has built up it can supply most of the neutrons to keep the reaction going.
It becomes a breeder reactor where the non fissile Thorium or Uranium 238 is transmuted to fissile atoms
The Neutrons for this reaction can come from bomb grade or enriched Uranium or Plutonium, or the neutron stream can come from a spallation source. This is an accelerator bombarding a pool of mercury. Many research reactors use spallation sources and use no Uranium.
Arguments for Thorium fission
Thorium is more abundant than Uranium. There are large known deposits in Australia, India, Idaho in the U.S, and Norway.
Higher MP and chemically more stable than Uranium
Thorium is a byproduct of most “rare-earth” mining around the world and with a 14-billion year half life, constitutes no danger when treated properly. Thorium has been stockpiled by US Dept of Energy in sufficient pure-metal quantities to meet all US energy needs for about a decade.
..not only can Th232 be easily bred to U233 in molten salt, but the resulting U233 (which doesn’t occur in nature) fissions far more completely than other U or Pu isotopes, leading immediately to lower waste production.
There would never be any “enriched fuel” sitting around for theft – it would all exist as, say, Fluoride salts, dissolved into the simple MSR chemistry. The Th232-U233 transmutation can even be started with a medical proton-accelerator, as the Japanese have done.
Dr. Alexander Cannara
Spallation can be used to supply the neutrons to start a fission reactioni. It is a process in which fragments of material (spall) are ejected from a body due to impact or stress.
In nuclear physics, spallation is the process in which a heavy nucleus emits a large number of nucleons as a result of being hit by a high-energy particle, thus greatly reducing its atomic weight.