Fluoride salts, like all salts, cause corrosion in most metals and alloys. FliNak is different from FLiBe in the sense that is a basic melt—or it has an excess of fluorine ions.  As FLiNak melts, all three components are alkali fluorides and therefore disassociate into positive and negative ions.  The concentration of molten fluorine ions are able to corrode any metallic structures if it is energetically favorable.  This is in contrast to FLiBe, which in a 66-34 mol% mixture will be a chemically neutral mix, as fluorine ions from LiF are donated to BeF to create the tetrafluoroberyllate ion BeF.