Chemical compatibility of silicon carbide in molten fluoride salts for the fluoride salt-cooled high temperature reactor

Functional Requirements for the Modeling and Simulation of Advanced (Non-LWR) Reactor Mechanistic Source Term

“…Additionally, many fission products are chemically reactive with fluoride ion and soluble in fluoride salts, thereby potentially increasing the circulating activity of a FHR relative to a HTGR. Recent studies on the chemistry of fluoride salts in FHR have highlighted additional gaps in knowledge such as the impact of impurities on reactor chemistry and corrosion [82], and the compatibility of fluoride salts with silicon carbide in TRISO fuel [83]. Although corrosion does not always directly impact the source term, the addition of new compounds into the molten salt coolant changes the chemistry, which could have a considerable effect on source term analysis.…”

Development of an Open-source Alloy Selection and Lifetime Assessment Tool for Structural Components in CSP

“…Corrosion products such as CrF 2 can further drive corrosion by forming Cr-rich carbides on the SiC surface and consequently dissolving Si from SiC into the salt. The effect of SiC microstructure on the corrosion and susceptibility to form localized attack are additional factors to consider [79].…”

Survey and Assessment of Computational Capabilities for Advanced (Non-LWR) Reactor Mechanistic Source Term Analysis.

“…Depending on the core design, FHR coolant salt will be in direct contact with SiC layers in certain regions of the fuel matrix holding the TRISO fuel. These carbon-based materials are generally inert towards fluoride salts but can corrode when in contact with metal impurities (e.g., Ni and Cr) that may be present in the coolant salt as well as oxygen [236,237]. In addition, the molten salt structure at the solid-liquid interface may differ from the bulk.…”

“…Considering the potentially larger surface area-to-volume ratio of FHRs for carbon-molten salt, surface interactions could affect the overall chemical behavior of the salt. Additionally, SiC has been shown to corrode in the presence of oxygen impurities and higher temperatures, entering the melt as a silicon fluoride complex [236]. Thus, the chemical behavior of FHR molten salts may differ from MSR salts due to interactions with the SiC surface.…”

“…Slight changes in the environment to which the FHR coolant salt is exposed during a transient (i.e., exposure to O2) could lead to large changes in salt redox potential and hence radionuclide behavior. Similar to MSRs, tritium production will have a large impact on redox potential with FHRs [236] and so tritium modeling capability is important [220], as will be discussed further in Section 4.2.7.…”