Properties and Design of a Nuclear Grade SiC/SiC Control Rod Sheath for Generation IV Nuclear Plants

Some Generation IV nuclear reactor designs call for employing high reactor core temeratures to improve the thermodynamic efficiency of the power generation and to efficiently produce process heat. Materials are required that are capable of sustaining temperatures approaching 1000°C and also are stable in a high radiation environment. One such application is the outer containment of the control rod material, where the sheath material is subjected to large thermal gradients and thermal cycling in addition to the high-temperature high-radiative-flux environment. This project will develop a silicon-carbide-fiber/reinforced-silicon-carbide matrix composite that is stable under these high neutron fluxes and addresses the requirements for control rod sheaths. In Phase I, a nuclear grade SiC/SiC composite was made by using braided preform architectures, which are well suited for the fabrication of axisymmetric control rod sheath tubes. Preliminary mechanical and thermal testing was performed, and a preferred braid architecture was identified. In Phase II, material property data, including mechanical and thermal properties, will be acquired. The data will cover the range of use temperatures anticipated under normal and off-normal operating conditions of a high temperature gas reactor. The data will be used to develop a viable design concept for a nuclear grade SiC/SiC control rod sheath. The design approach will be validated through structural element testing and subcomponent testing. A prototype composite will be fabricated to demonstrate producibility. Commercial Applications and other Benefits as described by the awardee: The nuclear grade SiC/SiC composite should benefit the Department of Energy efforts to develop Generation IV fission reactors, and also benefit the longer range development of fusion power. Both of these energy generation approaches could substantially reduce dependence on foreign sources of fossil fuels as well as reduce greenhouse gas emissions.