Conceptual Design of a Particle Bed Nuclear Reactor for Aerospace Application

Nuclear Thermal Propulsion (NTP) was actively studied between the 1950s and 1970s, with several reactors tested. These early experiments demonstrated the feasibility of this technology, which has the potential to improve rocket performance, allowing faster travel to the Moon, Mars, and even the outer planets. After decades of inactivity and only some theoretical studies, interest in NTP has been reignited. With the development of NASA's Artemis program and the growing need for more power in space hubs and propulsion systems, attention has returned to using nuclear reactors in space. The renewed focus has led to projects such as DRACO and KRUSTY, both developed by NASA. Such an interest has also spread to Europe, with both industry and research fields showing enthusiasm for nuclear technologies in space. This thesis work stems from these recent developments but with a particular focus on sustainability. The proposed reactor design features a particle bed core and uses ammonia as the propellant. The particle bed design was chosen to increase the exhaust gas temperature above 3200 K while maintaining reactor safety. Ammonia, on the other hand, was selected because it can be produced in-situ from lunar and Martian regolith. This approach supports long-term sustainability efforts in space missions and compared to more traditional propellants like hydrogen and methane, ammonia is easier to store and handle in space environments, making it particularly well-suited for missions to the Moon and Mars. The ammonia stability and ease of transport provide a strategic advantage for long-term missions, where efficient and safe storage is crucial. From a technical perspective, the reactor design addresses key neutronic and thermal-hydraulic challenges. Neutronics, which deals with the behavior of neutrons in the reactor, is critical for ensuring efficient and safe operation. In this project, the open-source Monte Carlo code OpenMC was used to model the reactor’s neutronic behavior. This tool allows detailed simulations of fuel performance and the reactor’s geometry, helping to understand how neutron interactions affect overall reactor efficiency and safety. On the thermal-hydraulic side, a custom MATLAB code developed by the Aerospace Department of the University of Pisa simulates the reactor’s heat transfer. In conclusion, this thesis introduces a new approach to nuclear thermal propulsion. By focusing on sustainability, efficiency, and adaptability, this reactor design represent a promising concept for future space missions, enabling faster and safer journeys to the Moon, Mars, and beyond.