Measurement of Optical Anisotropy Factor for PyC Layer of Simulated TRISO-coated Fuel Particles

The TRISO(tri-isotropic)-coated fuel particle for a HTGR(high temperature gas-cooled reactor) is composed of a nuclear fuel kernel with a diameter of 0.5 mm and coating layers. The coating layers consist of a buffer PyC(pyrolytic carbon) layer, inner PyC(I-PyC) layer, SiC layer and outer PyC layer(O-PyC). The coating layers protect the kernel and prevent the release of fission products. The anisotropy of I-PyC layer and O-PyC layer plays an important role of the safety of TRISO fuel. The anisotropy of PyC layers can be optically measured by a photometer. The photometer is composed of a polarization microscope, data processing computer, light source and detector. The photometer measures the optical anisotropy factor(OPTAF) of PyC layer by analyzing the polarization of the reflected light on the surface of PyC layer. In this study, the OPTAF of PyC layers were measured for TR-64 simulated TRISO-coated fuel particles based on the optical characteristics of light source. The general objective lens was used for the magnification of 200 and 500. The objective lens for oil was used for the magnification of 500. In the experiments, the OPTAF of buffer PyC layer was about 1.06, the OPTAF of I-PyC layer ranged from 1.05 to 1.09, the OPTAF of O-PyC layer ranged from 1.06 to 1.08. The OPTAF was not affected by the change of magnification ratio or the use of oil