Anisotropy measurement of pyrolytic carbon layers of coated particles
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otropy Measurement of Pyrolytic Carbon Layers of Coated Particles Ju. A. Vesyolkina *, A. S. Ivanova **, and T. V. Trushkinab a
National Research Center Kurchatov Institute, pl. Akademika Kurchatova 1, Moscow, 123182 Russia Research Institute of Inorganic Materials (VNIINM), ul. Rogova 5a, Moscow, 123098 Russia email: *[email protected]; **[email protected]
b AllRussia
Received December 23, 2013
Abstract—Equipment at the National Research Center Kurchatov Institute intended for the anisotropy determination of pyrolytic carbon layers in coated particles (CPs) of the GTMGR reactor is tested and cal ibrated. The dependence of the anisotropy coefficient on the size of the measurement region is investigated. The results of measuring the optical anisotropy factor (OPTAF) for an aluminum mirror, rutile crystal, and available CP samples with the known characteristics measured previously using ORNL equipment (United States) are presented. In addition, measurements of CP samples prepared at VNIINM are performed. A strong dependence of the data on the preparation quality of metallographic sections is found. Our investiga tions allow us to make the conclusion on the working capacity of the existing equipment for measuring the anisotropy of pyrolytic carbon CP coatings using the equipment at the Kurchatov Institute with the relative error of about 1%. It is shown that the elimination of the errors caused by the stochastic fluctuations in a mea suring path by mathematical processing of the signal allows us to decrease the relative error of OPTAF mea surements to ~0.3%. Keywords: microfuel, pyrolytic carbon, anisotropy, layers, measurement error. DOI: 10.1134/S1063778815110174
INTRODUCTION Fuel elements based on coated particles (CPs) with the TRISO (triisotropic) coating are used as the fuel of hightemperature reactors. A spherical core (kern), which contains the fission material, is arranged in the CP center. The kern is coated by a shell consisting of several layers, which is intended to hold fission prod ucts, Fig. 1. The first layer, which immediately adjoins the kern, is the socalled buffer zone, which consists of low density pyrolytic carbon PyC (porous carbon). The next layer is the inner layer of pyrolytic carbon (Inner PyC), or simply IPyC. The third layer, which coats the kern, consists of silicon carbide and plays the role of the force shell. The last layer consists of dense pyro lytic carbon PyC and is called outer pyrolytic carbon layer (Outer PyC) or OPyC. The large amount of attention to the investigation into the microstructure of pyrolytic carbon CP coat ings is associated with the necessity to hold fission products at large fuel burnups and neutron radiation fluence. The variations in the structure under the effect of irradiation and accumulation of fission prod ucts can substantially affect the properties of PyC coatings. The fact is that one of the main causes of degradation of the force CP shell is the corrosion interaction of SiC with kern components.
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