Comparison of properties of CX-270G and DACC C/C composites for the development of structural materials in HTGRs

Carbon-carbon (C/C) composites have been widely used for high-temperature structural applications because they possess excellent mechanical properties such as high specific strength and thermal shock resistance. In the nuclear industry, the composites have been also considered for plasma facing materials in fusion reactors and high-temperature structural parts in gas cooled reactors. In the high-temperature gas cooled reactor (HTGR) designs such as GT-MHR and HTTR, the reactor core temperature can approach 1600 .deg. C during severe loss of coolant accidents. A high temperature control rod is therefore desirable, and assures control rod availability under all conceivable reactor conditions. With this goal in mind, efforts have been directed in the USA and Japan toward the development of C/C composite control rods. Recently, the C/C composites have also been considered for the application of high-temperature structural parts such as upper core restraint blocks, upper plenum shroud, hot duct insulation cover sheets, and floor blocks. In this study, we evaluated basic properties of the C/C composite fabricated by a domestic company, aiming at the development of core components in HTGR. The nuclear grade CX-270G composite, which has been developed by JAERI for the control rod components of the HTTR, was also tested for comparison purpose. Through the comparison of the microstructure, flexural strength, and thermal conductivity of the two composites, we tried to bring up some directions for an improvement of the domestic composite