From an engineering standpoint any chemical reaction that changes the properties of a metal in an unwanted way will be called corrosion. It is something to prevent and/or monitor that will inevitably shorten the lifespan of the metal part. (Non-metals like fiberglass can also "corrode".)

You need an oxydizer whatever it is. Oxygen is only one oxidizer. Chlorine, fluorine and the other halogens are oxidizers too.

Fluoride (with a 'd') is not fluorine (with a 'n'). The difference is as big as that between sodium and sodium chloride. You can eat one, but not the other.

The most powerful oxidizer in MSR fuel salt is the U(IV) ion.

IIRC fluorine is/can be a more potent oxidiser than oxygen.

"Corrosion is a natural process that converts a refined metal into a more chemically stable form".

Oxidation is the most well known form of corrosion, but there are many other corrosive reactions out there.

https://en.wikipedia.org/wiki/Sulfide#Corrosion_induced_by_s...