A few years ago I chanced upon an article in a Sunday supplement regarding the building of a small scale Thorium Reactor which was very interesting, because these reactors don't go into meltdown, don't explode and the fuel is abundant. There are also some great Youtube videos showing notable engineers espousing the merits of these reactors, but there doesn't appear to be any mainstream take up, when in the future of massive demand these reactors could safely take up the shortfalls that take wind and solar have. I am wondering why this maybe as this is way beyond my engineering know-how as to any drawbacks that these reactors may have. Perhaps there is someone on this website who could elucidate?
I will try to explain some of the main problems with Thorium Reactors and give you a link to some more detailed information.
First problem, Thorium 232 is not 'fissile', it cannot form a chain reaction. It is however 'fertile' and can be bred into Uranium 233 which is fissile.
Second problem, to use Thorium as a reactor fuel you have to start with something fissile, typically Uranium 235 or Plutonium 239. The fission of these materials generates the neutrons to breed the Thorium 232 to Uranium 233 (via a couple of decay steps).
Third problem, how do you use the U233? Do you keep it in the same reactor and use some clever physics to keep the fission under control as the amount of fissile material in the reactor will increse over time? Do you take it out, process it and put it in another reactor? U233 is an effective bomb material.
Thorium can be and is being used in conventional design reactors, especially the Heavy Water CANDU types, with all there attendant problems with reprocessing and waste. Experiments have been carried out with various high temperature reactors but these required highly enriched Uranium (HEU) as a seed which is no longer acceptable on anti -proliferation grounds. The reactors you are thinking of are the molten salt type where the fissile seed material and the Thorium are disolved in a molten salt a several 100°C. The salt is circulated through the system and is used as the heat transfer medium. Online chemical processing is used to remove the fission products (these still have to be dealt with like conventional reactors). Experiments are being carried out but there are some very significant materials problems to solve, molten salts (especially the favorite fluoride salts) are very corrosive at high temperatures.
Thank you Roger for your informative comment. I had thought there had to be some downside or we would be seeing a rush to make thorium reactors mainstream.
