Insights into the chemical speciation of chromium corrosion products in molten salt fuel mixtures using XANES

Fluoride and chloride molten salts are currently the reference fuel for Molten Salt Reactor technologies. But the use of these highly corrosive mixtures exposes the structural materials to high risks of degradation and failure over the lifetime of the reactor. Ni-based alloys have shown the best resistance to molten salts at high temperatures. However, chromium present in these alloys at a relatively high content, is the most likely to dissolve in the fuel salt, leading to chromium depletion in the structural material, and concomitant formation of corrosion products within the salt. The objective of this work is to experimentally determine the chemical speciation of chromium, i.e., as divalent or trivalent species, in key fuel salt mixtures, using static corrosion experiments followed by post-characterization using XANES spectroscopy at the ROBL Beamline. Such study is essential to gain insights into the corrosion mechanisms and for the development of corrosion mitigation strategies.