Development of a Prototypic Tie-Tube for Low-Enriched Uranium Nuclear Thermal Propulsion

摘要

Nuclear thermal propulsion (NTP) is under consideration for future human missions to deep space destinations such as Mars. NTP will be capable of providing a specific impulse (I_(sp)) nearly double that of the highest performing chemical engines, which significantly reduces the amount of propellant required for to complete a mission and with reduced transit time. NASA in collaboration with external partners is investigating development a low-enriched uranium (LEU) engine concepts for future mission needs. The current point design calls for an array of in-core tie-tube, which function in part to pre-heat the hydrogen propellant that will drive the turbo-pump and house the zirconium hydride (ZrH_(1.8)) moderator to thermalize the neutron spectrum. A small development team was tasked to mature a tie tube concept by considering detailed mechanical design and materials selection based upon specific design constraints. The material and thermo-mechanical response of the system was evaluated through the construction of a sub-scale tie-tube test rig. An experimental test apparatus was developed in order to determine temperature gradients across the tie-tube, variations in inlet and outlet pressure, and potential material degradation. Nitrogen, argon, and hydrogen was used over a range of mass flow rates and furnace temperatures (-200 - 500°C). The project culminated in the construction and preliminary testing of the test rig in addition to the creation and quantification of ZrH samples. Future work aims to scale the test rig to effectively test full-length tie-tube elements.