Molten salts are a promising high temperature heat transfer fluid in part due to their high specific heat, and ability to operate at close to ambient pressure. This has incited interest for their use in molten salt nuclear reactors and solar thermal power plants. Molten salt reactor (MSR) feasibility was demonstrated in the Molten Salt Reactor Experiment at Oak Ridge in the 1970’s. Since then, corrosivity has been identified as a key remaining hurdle to widespread adoption of MSRs. In response, numerous corrosion-resistant, Ni-based alloys such as the Hastelloy series have been developed, but these alloys are prohibitively expensive and lacking in high temperature strength. It has been shown in complex Ni-based alloys, Cr depletion is a main observation of corrosion. However, the precise mechanism of this corrosion is not fully understood. Here we explore Ni and Ni-Cr alloy corrosion in pure KCl:MgCl<sub>2</sub>, with a focus on the metal-salt interface. The three-dimensional morphological structure and chemical constitution of Ni and Ni-Cr microwires has been probed using X-ray nanotomography and transmission electron microscopy with energy dispersive X-ray spectroscopy and electron energy loss spectroscopy.. With Ni-only the system seems to be dominated by corrosion along interfaces and defects such as grain boundaries, contrasted with the Ni-Cr system where differing diffusivities lead to porosity potentially created by Kirkendall effects, and surface rearrangements occur. Both systems ended with a shell only structure. These results further the fundamental understanding of Ni and Ni-Cr interactions with molten salts. This will help build a foundation for the development of more complex alloy systems for containment of molten salts.

Morphological and chemical evolution of Ni and Ni-20Cr microwires in molten KCl:MgCl<sub>2 </sub>

2019 Fall National Meeting

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Morphological and chemical evolution of Ni and Ni-20Cr microwires in molten KCl:MgCl2

Morphological and chemical evolution of Ni and Ni-20Cr microwires in molten KCl:MgCl₂