Advanced Zirconium Carbide Tie-Tubes for NTP

Nuclear Thermal Propulsion (NTP) has been identified as a critical technology needed for human missions to Mars due to its increased specific impulse (Isp) as compared to traditional chemical propulsion systems. To achieve this high Isp, NTP reactors must operate at extremely high temperatures (i.e., >2400K) for long periods of time. However, many of the best materials for some reactor components (i.e., support rods, control drums, and the reflector) cannot operate at these high temperatures. Therefore, high temperature insulators that are chemically inert, neutronically acceptable, and structurally stable are desired. The Rover and Nuclear Engine for Rocket Vehicle Application (NERVA) program identified zirconium carbide (ZrC) as a leading candidate for NTP insulator materials. However, the inherent brittleness and high melting temperature of ZrC make fabrication of complex components such as long, hexagonal tie-tubes extremely difficult. Recently, advanced Vacuum Plasma Spray (VPS) forming techniques have been developed for producing near-net-shape components from Ultra High Temperature Ceramic (UHTC) materials such as tantalum carbide (TaC) and hafnium carbide (HfC). Building on this success, advanced VPS processing techniques will be developed for producing long, hexagonal ZrC based tie-tube support rods for NTP.