Date of Award
2026
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Aerospace Systems Engineering
Committee Chair
Robert Frederick Jr.
Committee Member
James Baird
Committee Member
Jason Cassibry
Committee Member
William Emrich
Committee Member
D. Keith Hollingsworth
Committee Member
L. Dale Thomas
Research Advisor
Robert Frederick Jr.
Subject(s)
Space vehicles--Propulsion systems, Nuclear propulsion, Fission products--Diffusion rate--Computer simulation, Computational fluid dynamics
Abstract
Centrifugal nuclear thermal rockets (CNTR) are an advanced concept engine first proposed in the 1950’s that would allow for specific impulses of up to 1800 seconds. A major difference in this engine is that the liquid fuel allows for fission products to move through the fuel layer and even exit out of the reactor completely. This dissertation seeks to answer the question, how does the migration of fission products within a centrifugal nuclear thermal rocket affect its operation and performance?” To accomplish this a reduced order model was developed to simulate and track the fission products generated during the firing of a centrifugal nuclear thermal rocket. This model was backed by higher fidelity 2D multiphase CFD analysis of a multi-injector uranium hydrogen bubbly mixing system. The reduced order model simulated the fission product formation, diffusion, decay, and exhaust for the entire length of an engine burn (120 minutes). From this data modified yield fractions were found for the standard six delay groups. These modified delay groups were used to solve the additional post burn heat rejection and propellant mass required. These results showed a moderate reduction of additional cooling required and a propellant mass fraction reduction of 15.9%, or roughly 36.34 kg of propellant for a scientific mission to Uranus This contribution to the study of CNTR is significant as it demonstrates that exhausting fission products meaningfully reduces cooling propellant mass while simultaneously impacting controllability by altering delayed neutron behavior. The results are a conservative estimate of the propellant reduction needed to cool a centrifugal nuclear thermal rocket post firing; however, it also identifies concerns with reactor controllability as a considerable portion, 25.73% of the delayed neutrons are also exhausted out of the engine, particularly those with longer half-lives significantly reducing the frequency response of the reactor.
Recommended Citation
Schroll, Mitchell, "Diffusion behavior of uranium fission products in a centrifugal nuclear thermal rocket" (2026). Dissertations. 496.
https://louis.uah.edu/uah-dissertations/496