DOE digs up molten salt nuclear reactor tech, Los Alamos to lead the way back

“However, as the Oak Ridge National Laboratory found during the Molten Salt Reactor Experiment, fluoride salts are incredibly corrosive and required hardened materials to safely contain them.”

Is it a given that fluoride salts would be very corrosive, I assume this is down to its electro-negativity?

But what makes fluoride salts so useful in this context over other halides?