Towards Controlling Corrosion of Structural Alloys for Molten Salt Reactors with Surface Modifications

Candidate Fe- and Ni-alloys for next generation molten salt reactors (MSRs) often corrode by the selective dissolution of less noble alloying elements (Cr, Fe) when exposed to molten salt mixtures, which is due to impurities, notably moisture and oxygen. Materials used in current nuclear reactors, as well as those in consideration for MSRs, often require corrosion control strategies, such as surface modification. This study determines the viability of two surface modification combinations to control corrosion in molten Cl salt mixtures: (1) physical vapor deposited (PVD) Ni coating on Type 304L stainless steel and (2) pre-oxidized Al2O3 coating on Alloy 214. Bulk immersion coupled with post-immersion surface characterization by electron microscopy was used for this purpose. Both coatings show promise in controlling (reducing) corrosion (Cr dealloying) in each case. However, coatings are prone to defect formation, which compromise corrosion protection and, thus, requires further research and development.