High-Temperature Ferrofluids Based on Molten Salts

[NNadir]

6. Someone once asked me to consult - for free - to make an MSR with lithium free BeF2 as the coolant.

To be a nice guy, I looked at it. The reason for so doing was concern about the accumulation of tritium. (It turns out that tritium will be in short supply if all those fusion toys start running.)

To be perfectly honest, I have lots of plutonium/salt phase diagrams, and I'm sure somewhere in my files, the Flibe/ThF₄, UF₄ phase diagram, but I don't seem to have a UF₄/LiF phase diagram. If they're doing this at 700°C there must be a eutectic since this is lower than the melting point of pure LiF.

From my perspective, fluoride is the preferred halide anion in fission settings because of it is monoisotopic, has a very low neutron capture cross section, and no long lived radioisotopes. Both bromine and iodine have high neutron capture cross sections, and as mentioned above in the OP and posts, chlorine has two isotopes and a long lived radioactive isotope between them.

That said, cesium iodide and rubidium iodide have some remarkable physical properties which suggest to my mind many nuclear applications, bromides not so much. Both CsI and RbI are fission products, which makes them fun; the former being more fun because it will always be highly radioactive in the form fission product, which to my mind suggests a tremendous value.

Can the Copenhagen thing work? Sure, I'd guess, I don't see a reason it wouldn't. But a five year test is a long time, given the scale and magnitude of the crisis of extreme global heating. (This is triply true for the magical success of fusion reactors.) I think better options are currently available for immediate or near term build.

I hope this helps.