Synthesis and Properties of Reaction-Bonded SiC Ceramic with Embedded UO₂ - TRISO Coated Particles

Abstract

Ceramics based on SiC are characterized by extreme hardness, high thermal conductivity, relatively low thermal expansion and chemical durability. In principle, SiC ceramics can be considered as a long-term stable matrix for final disposal of radioactive waste, such as coated fuel particles (CP) separated from the graphite matrix from spent HTR (high-temperature gas-cooled reactor) fuel pebbles. In the present work, SiC-based ceramic with the embedded UO2 - TRISO (tristructural-isotropic) coated particles was synthesized by the reaction-bonding process. The synthesis was performed in standard SiC crucible. Several physico-mechanical properties of the synthesized samples were investigated. It was shown that the coated particles in the reaction-bonded silicon carbide (RBSiC) matrix are distributed homogeneously. The amount of pores is insignificant and the crippling of the coated particles is not observed. Besides, the junction between CP and RBSiC matrix and between RBSiC matrix and the SiC crucible is very good. For all ceramic components of the synthesized samples, namely, for the UO2-kernels, SiC-layers, SiC crucible wall and for the synthesized RBSiC ceramics, the values of microhardness and fracture toughness were measured and compared with the reference data. The strength properties, such as tensile strength of the synthesized samples, failure mechanism of the reaction-bonded SiC ceramic with embedded UO2 - TRISO coated particles, microstructure of the fracture surfaces, the peculiarities of the coated particles fracture were investigated in detail. Moreover, the diffusion of radioactive tracers (137Cs, 241Am, 36Cl, 3H) across synthesized ceramic was studied and the high safety characteristics of the synthesized ceramic were demonstrated.

Nanocrystalline silicon carbide thin films by fluidised/packed bed chemical vapor deposition using a halogen-free single source

“…1,2 The SiC layer on the nuclear fuel acts as a diffusion barrier and prevents radioactive fission products from migrating into the coolant circuit. [3][4][5] SiC is prepared by the thermal decomposition of various source gases including methyltrichlorosilane (CH 3 SiCl 3 ; MTS) and methane, acetylene or propane at temperatures above 1773 K. This high deposition temperature results in the introduction of structural defects in the layers and difficulties with using the system in the field. [6][7][8][9][10][11][12][13][14][15] Besides the above constraint, MTS decomposes under typical SiC CVD conditions producing corrosive HCl, SiHCl 3 , SiCl 3 , SiCl 4 , and CH 4 as well as other silanes and hydrocarbons.…”