Jacob Stonehill | Engineering Papers

NASA NTRSDate not supplied

Reactor Parametric Assessments for Alternative Propellant Nuclear Thermal Propulsion Engines

This work focuses on the implications of alternative working fluids for nuclear thermal propulsion (NTP) reactors. To perform this analysis, NASA’s Testing Reference Design (TRD) is altered using parametric studies with selected alternative propellants to determine the reactor modifications required to enable an operable system. This research investigates ammonia, water, methane, helium, and enriched diborane as feasible options to enable a specific impulse (𝐼 𝑠𝑝 ) greater than the chemical propulsion alternatives. Frozen and dissociated 𝐼 𝑠𝑝 for each propellant is shown for variable chamber temperature conditions. Geometrical sensitivities are performed to observe the impact on the neutron multiplication factor (k eff ), system mass, and HALEU loading. Control drum worth curves are included for 5- degree increments of rotation. The base TRD configuration does not enable a critical system for ammonia and enriched diborane, thus these propellants will be highlighted in the final results. Equivalent study results for hydrogen will be included as a point of comparison to the performance of the other options.

Nuclear Thermal Propulsion↗

NASA NTRSDate not supplied

Reactor Parametric Assessments for Alternative Propellant Nuclear Thermal Propulsion Engines

This work focuses on the implications of alternative working fluids for nuclear thermal propulsion (NTP) reactors. To perform this analysis, NASA’s Testing Reference Design (TRD) is altered using parametric studies with selected alternative propellants to determine the reactor modifications required to enable an operable system. This research investigates ammonia, water, methane, helium, and enriched diborane as feasible options to enable a specific impulse (Isp) greater than the chemical propulsion alternatives. Frozen and dissociated Isp for each propellant is shown for variable chamber temperature conditions. Geometrical sensitivities are performed to observe the impact on the neutron multiplication factor (keff), system mass, and HALEU loading. Control drum worth curves are included for 5- degree increments of rotation. The base TRD configuration does not enable a critical system for ammonia and enriched diborane, thus these propellants will be highlighted in the final results. Equivalent study results for hydrogen will be included as a point of comparison to the performance of the other options.

Nuclear Thermal Propulsion↗

NASA NTRSDate not supplied

Mini-Nozzles for Individual Fuel Elements for NTP Systems NETS

The Testing Reference Design (TRD) reactor and engine for Nuclear Thermal Propulsion (NTP) systems typically use a large single nozzle with regenerative cooling which contributes a significant portion of the engine mass. Furthermore, if a fuel element is damaged or the flow is otherwise compromised, stagnant or backflow is expected which would further damage the reactor and engine. Therefore, the current analysis attempts to solve this potential issue by considering individual, smaller nozzles allocated for each individual fuel element while also neglecting regenerative cooling flow due to lower hoop stresses from the chamber pressure. However, a material that can withstand the chamber temperatures should be considered such as molybdenum or tungsten or a mixture of the two.

Daria Nikitaeva↗

NASA NTRSDate not supplied

Coupled Reactor and Engine Nuclear Thermal Propulsion Modeling Methodology

The design and development process of a Nuclear Thermal Propulsion (NTP) system requires extensive multiphysics modeling to couple the neutron physics and thermal feedback effects to determine the reactor’s power shape. Propulsion system performance codes utilize this power shape to determine NTP key performance parameters. While the power shape is heavily dependent on the temperature profile and geometry of the reactor, many analyses either assume a constant power shape, or use neutronics analysis to determine a power shape for a specific reactor configuration. The development of a coupling interface for a propulsion system performance code and a Monte Carlo neutron transport code (OpenMC) allows for the reactor power shape to be calculated in a Picard iteration.

Jacob Stonehill↗

NASA NTRSDate not supplied

Coupled Reactor and Engine Nuclear Thermal Propulsion Modeling Methodology

The design and development process of a Nuclear Thermal Propulsion (NTP) system requires extensive multiphysics modeling to couple the neutron physics and thermal feedback effects to determine the reactor’s power shape. Propulsion system performance codes utilize this power shape to determine NTP key performance parameters. While the power shape is heavily dependent on the temperature profile and geometry of the reactor, many analyses either assume a constant power shape, or use neutronics analysis to determine a power shape for a specific reactor configuration. The development of a coupling interface for a propulsion system performance code and a Monte Carlo neutron transport code (OpenMC) allows for the reactor power shape to be calculated in an iteration loop. The interface utilizes a file share system to transfer geometry dimensions, temperatures, and material identifiers to OpenMC, which is used to perform a neutron transport simulation of a design like the government Testing Reference Design reactor. The interface is then able to post-process the results from OpenMC and use the same file share system to share a power shape and other important neutron transport parameters to the system performance code. Initial results show that neglecting the changes to power shape when comparing reactor configurations can yield inaccurate results. Furthermore, utilizing propellants other than hydrogen gas can cause significant changes to the power shape, and thus, the thermal performance of a specific reactor design. This methodology is being expanded to allow for multiple families of NTP reactors to be analyzed, including block moderator, particle bed, and NERVA-derived reactors.

multiphysics coupling↗

NASA NTRSDate not supplied

Coupled Reactor and Engine Nuclear Thermal Propulsion Modeling Methodology

The design and development process of a Nuclear Thermal Propulsion (NTP) system requires extensive multiphysics modeling to couple the neutron physics and thermal feedback effects to determine the reactor’s power shape. Propulsion system performance codes utilize this power shape to determine NTP key performance parameters. While the power shape is heavily dependent on the temperature profile and geometry of the reactor, many analyses either assume a constant power shape, or use neutronics analysis to determine a power shape for a specific reactor configuration. The development of a coupling interface for a propulsion system performance code and a Monte Carlo neutron transport code (OpenMC) allows for the reactor power shape to be calculated in an iteration loop. The interface utilizes a file share system to transfer geometry dimensions, temperatures, and material identifiers to OpenMC, which is used to perform a neutron transport simulation of a design like the government Testing Reference Design reactor. The interface is then able to post-process the results from OpenMC and use the same file share system to share a power shape and other important neutron transport parameters to the system performance code. Initial results show that neglecting the changes to power shape when comparing reactor configurations can yield inaccurate results. Furthermore, utilizing propellants other than hydrogen gas can cause significant changes to the power shape, and thus, the thermal performance of a specific reactor design. This methodology is being expanded to allow for multiple families of NTP reactors to be analyzed, including block moderator, particle bed, and NERVA-derived reactors.

multiphysics coupling↗

NASA NTRSDate not supplied

High-Fidelity Modeling Approach for Coupling Thermal, Fluid, and Neutronic Analysis in an NTP Engine

Nuclear thermal propulsion (NTP), with its increased efficiency compared to traditional rocket engines, is a potentially enabling technology for space missions of higher complexity, such as delivering heavy machinery or crew to the moon or other planets. Thus, exploring modeling approaches that can effectively couple the thermal, fluid, and neutronic behaviors of NTP reactors is essential to mitigate cost and schedule challenges with hardware development. This paper details one such approach which utilizes Cardinal to unify reactor physics analysis performed using OpenMC, heat transfer analysis performed using the MOOSE framework, and thermal hydraulic analysis performed using the MOOSE Thermal Hydraulic Module. This approach is demonstrated with a proof of concept that focuses on a legacy reactor geometry from the historic NERVA program. This preliminary model found an overprediction in, when compared to the reference data, axial power peaking and the temperatures of both solids and fluids by roughly 20%. It is clear, however, that the model conserved a number of broad trends, and a few model refinements should reduce the observed error. This approach has definite merit and should enable the production of informative results for more modern NTP systems. This work is a first step in creating a transient reactor model that can be updated across a sequence of time steps based on continually fluctuating, time-dependent boundary conditions.

Nuclear Thermal Propulsion↗