[pfdietz]

It requires chlorine isotope separation or else you make Cl-36, a beta emitter with a half-life of 300,000 years.

Moltex got around this in their concept by only using chloride salts inside the fuel tubes; the surrounding sterile molten salt was a fluoride. Being sterile, the oxidation potential of the fluoride salt could be kept low enough to be compatible with stainless steel.

(Moltex ran out of money last year, I've read, and has been selling its IP as distressed assets.)