Date of Award

2022

Degree Type

Capstone Project

First Advisor

Dr. Bahram Nassersharif

Abstract

Team 20 was charged with the responsibility of developing solutions to produce high speed rotations (up to 5000 RPM at full scale) of nuclear fuel rods within a centrifugal nuclear thermal rocket (CNTR) under the guidance of NASA Marshall Space Flight Center. With Mars as the next space frontier, NASA is continuing to pursue nuclear capability within their aerospace fleet in order to accomplish the travel distances associated with the red planet (approximately 200x further than the Moon). The current CNTR designs house nineteen nuclear fuel rods within a reactor, providing a continual supply of heat for the rocket’s hydrogen propellant which ultimately produces thrust. High-speed rotation of the nuclear fuel rods essentially improves nuclear fuel efficiency – centrifugal motion of the fuel elements inhibits the escape of nuclear fuel from the rocket as pressurized hydrogen is heated (by the fuel) and exits as a thrust-producing propellant.

The proposed design called for an electric motor to offset nuclear fuel rod rotation as a safety backup system, with turbine-driven rotation by the flow of pressurized hydrogen propellant as the primary rotation source. 12V motors were utilized in conjunction with Arduino microcontrollers to produce rotation of a single, scaled 3D printed nuclear fuel rod, contained within a frame structure of extruded 80/20 aluminum. Motor-drive rotational speeds of up to 3700 RPM were attained and measured via an infrared sensor and viewed in real-time by a liquid crystal display (LCD). Experimental pneumatic and bearing housings were designed in SolidWorks and incorporated within the experimental apparatus, and a building-supplied 50 psi steady source and basic venturi splitter were used to test high-speed, turbine-driven rotation. Here, compressed air was intended to simulate high-pressurized hydrogen. During testing, turbine-driven pneumatic rotations were accomplished, yet persisting bearing frictional constraints limited rotational speeds to 1000 - 2000 RPM. Despite these constraints, this represented a significant improvement over early designs.

Furthermore, nuclear fuel rod stability and inertia during the high-speed operation were evaluated and mechanisms to minimize vibration were computed and carried out during testing. Inertial rods - inserted through the 3D printed nuclear fuel rod element - with opposing point masses were shown to improve system stability from startup through approximately 1000 RPM. Computational fluid dynamics (CFD) simulations in SolidWorks were also developed to gain a visual understanding of propellant flow through the turbine and over the exterior of the fuel element, and Abaqus Finite Element Analysis (FEA) software was employed to investigate the mechanical behavior of the fuel rod. The final designs presented in this report build upon the previous semester’s efforts, meeting the specific aims determined in the Preliminary Design Report, including a rebuilt dimensionalized testing apparatus; stable operation handoff between motor and pressure-driven modes; and further development of the control system.

Comments

Team Name: Team 20, Astro0

Sponsor: NASA

Project Funding: The Rhode Island Space Grant Consortium

Document Reference: URI-MCE-402-20H-2022

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