The solution is to replace the reactor chamber far more often than you would in other reactor designs. It's not actually an insurmountable problem because fluoride chemistry is extremely common in nuclear engineering - most of our nuclear waste is stored as uranium hexafluoride after all - and there is a lot of expertise in dealing with exotic corrosive materials. It's just that replacing your entire reactor every year is astronomically expensive. Just because the technology exists to do it, doesn't mean that it can be done economically when competing against natural gas, solar, and wind.