An experimental system for in situ high temperature measurements of spectral emissivity of VHTR materials has been designed and constructed. The design consists of a cylindrical block of silicon carbide with several machined cavities for placement of test samples, as well as a black body cavity. The block is placed inside a furnace for heating to temperatures up to 1000°C. A shutter system allows for selective exposure of any given test sample for emissivity measurements. An optical periscope guides the thermal radiation from the sample to a Fourier Transform Infra Red (FTIR) spectrometer which is used for real-time measurements of spectral emissivity over a wavelength range of 0.8μm to 10μm. To specifically address the needs of VHTR applications, the system has been designed for studies with VHTR grade helium environments and air transients. Inlet and outlet gas compositions are measured using a gas chromatograph, which in conjunction with ex situ analysis of the samples by electron microscopy and x-ray diffraction will allow for the correlation of surface corrosion of the materials and their spectral emissivities under different operating and accident conditions.
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