Life Prediction of SiC/SiC Composites in Advanced Nuclear Reactors

Some Generation IV nuclear reactor designs call for the employment of high reactor core temperatures, in order to improve the thermodynamic efficiency of the power generation and efficiently produce process heat. Materials are required that are capable of sustaining temperatures approaching 1000C and also are stable in a high radiation environment. The outer containment of the control rod material is one such application, where the sheath material is subjected to large thermal gradients and thermal cycling in addition to high temperature and high radiative fluxes. A silicon-carbide-fiber-reinforced, silicon-carbide matrix composite, which is stable under high neutron fluxes, would address the requirements for the control rod sheaths. However, the low part-per-million oxygen level, anticipated in the reactor, may limit allowable stress levels. This project will utilize life prediction methods along with experimental stress rupture data to define acceptable stress levels that are consistent with the low oxygen levels anticipated in the reactor. Phase I will perform stress rupture testing with a range of oxygen concentrations and stress levels. The data will be incorporated in a life prediction model that will allow extrapolation to the long stress-rupture times targeted for nuclear grade composites. Commercial Applications and Other Benefits as described by the awardee: The technology should be an enabling materials technology that would contribute to the database of properties of high temperature materials for nuclear applications. The core conditions of the Very High Temperature Reactor (VHTR) reactor are a challenge for materials developers, and a nuclear grade SiC/SiC is a prime candidate for control rod sheaths.