Improved measurement of local thermal conductivities of coatings by the steady-state Raman spectroscopy method: A case study in TRISO particles

Abstract

Tristructural-isotropic particle (TRISO) is a fully ceramic microencapsulated fuel of high-temperature gas-cooled reactors with complex microstructural morphology and heat transfer process, hindering the accurate measurement of its thermal conductivity. Here, a dual test wavelength steady-state Raman spectroscopy method (SSRS) for determining the thermal conductivities is proposed, resolving the issue of the conventional SSRS failing to measure the thermal conductivity of 3C-SiC. By demonstrating prerequisites for using the SSRS method and modeling the conductive-radiative coupled heat transfer, the thermal conductivities of all layers in TRISO have been accurately measured. It is also found that the thermal conductivity of an underlying material can be estimated by measuring the material on its top if the outer material has low absorption under the applied laser wavelength, offering the possibility of measuring the buried layers in localized structures. The work extends the usable range of the SSRS method for obtaining thermal conductivities in wide applications.