Mechano-Chemical Degradation of Metallic Cylindrical Microwave Resonant Cavity Transducer in High Temperature Molten Salt

We are investigating transduction of high temperature fluid kinematic property with a metallic cylindrical microwave resonant cavity. The flat wall of the cylinder is flexible enough to undergo microscopic deflection due to dynamic fluid pressure, which leads to a shift in the microwave resonant frequency. We have conducted a preliminary computational investigation of relevant mechano-chemical damage mechanisms, creep and corrosion, of a stainless steel 316 cylindrical resonator immersed in FLiBe (a mixture of lithium fluoride and beryllium fluoride) salt for a temperature range 500oC to 700oC. Creep was investigated computationally with combined Nabarro-Herring and Coble continuum mechanics models, which were implemented using COMSOL Nonlinear Structural Mechanics Module. Intergranular corrosion was modeled in 2D with COMSOL Corrosion Module. These models predict significant inelastic deformation at most temperatures due to creep, and qualitatively predict chromium depletion both along the liquid/solid interface and along the grain boundaries. This work has applications for flow sensing in the vessel of a high temperature fluid advanced reactor (AR), such as a molten salt cooled reactor (MSCR) or a sodium fast reactor (SFR).