It’s in interesting article, thanks for posting it Lorianne.
It looks like they’re putting all their eggs in the Liquid Floride basket; is there any reason they are bypassing Sodium? (I read about it being used as the thermalizer/coolant for some reactors; in the same book, it said that it was ideal for breeder-reactors.) {Yes there is the water/air thing.}
A book titled The Radioactive Boyscout was an interesting read and the titluar character was interested in building his own breeder reactor. While reading it, I was struck with the thought that perhaps cold-welded components would be more ideal for the internals of a nuclear reactor... this article’s excitement about the floride-solution being self-regulating [w/ proper engineering] brought to mind the idea of a hydraulic-piston where the working fluid is moved from one chamber to another; couldn’t this be also used with the Thorium reactor as a control mechanism?
{The cold-welding comes to mind specifically for the materiel in the heat exchanger, which could (and arguably should) be a closed system. Perhaps the heat-exchanger’s and reactor’s thermalizer’s volume/pressure couldbe linked like in the example of the hydraulic-piston as a means of automatically regulating it.}
Sodium is used as coolant for Uranium to Plutonium breeder reactors.
Sodium is heavy enough that the neutrons released from fissions are not thermalized too quickly, thereby giving the Uranium 238 a better chance of absorbing a neutron and being converted to Plutonium 239. (These breeder reactors are referred to as Intermediate Reactors, vs. Thermal reactors - and both terms refer to neutron energy levels.)
Uranium fissioning releases, on average, 243 neutrons per 100 fissions - and when at power, steady state - you want every “life cycle” to have 100 fissions for every 100 fissions in the previous life cycle, and you want as many of the remaining 143 neutrons to be absorbed by U-238 to create Pu-239. Realistically, there is leakage, neutron capture by other materials - but to optimize reactor design - you want to maximize fuel breeding.
For this article - Thorium is an easier breeder at Thermal neutron energy levels - so water moderator is okay. Other fluids are okay, if they have suitable heat conduction, minimal corrosion characteristics, etc.
(US civilian reactors were never used for weapons production of Plutonium. Some Plutonium production reactors use Graphite as the moderator - not as efficient as sodium, but far better than water. The Soviets used graphite moderated reactors in the civilian realm, but diverted Plutonium produced to weapons use. Think Chernobyl!)
Mike