Nuclear Thermal Propulsion

Abstract

This chapter will cover the fundamentals of nuclear thermal propulsion systems, covering basic principles of operation and why nuclear is a superior option to chemical rockets for interplanetary travel. It will begin with a historical overview from early efforts in the early 1950s up to current interests, with respect to fuel types, core materials, and ongoing testing efforts. An overview will be provided of reactor types and design elements for reactor concepts or testing systems for nuclear thermal propulsion, followed by a discussion of nuclear thermal design concepts. A section on system design and modeling will be presented to discuss modeling and simulation of driving phenomena: neutronics, materials performance, heat transfer, and structural mechanics, solved in a tightly coupled multiphysics system. Finally, it will show the results of a coupled physics model for a conceptual design with simulation of rapid startup transients needed to maximize hydrogen efficiency.

Automated Control for Nuclear Thermal Propulsion Start-Up using MOOSE-based Applications

“…The design is based on the BWX Technologies NTP concept shown in Figure 1 and is largely identical to the one further presented in [1]. An overview of the active core design can be found in Figure 2.…”

“…Indeed, while Doppler feedback effects are strictly local, the multigroup condensation process uses the neutron spectrum to compute cross-sections which depends significantly on conditions elsewhere in the core [1]. A significant approximation in this work-which will have to be addressed in the future-is that the cross-sections can be tabulated by assuming fixed axial profiles for all state variables, as was done in [12].…”

“…Whenever an element of the mesh contains both the absorber and non-absorber segments, proper weighting is performed to avoid cusping, which manifests in non-smoothness of the reactivity curve. Figure 7 illustrates a typical reactivity curve obtained for temperatures matching a state point: the procedure ensures the eigenvalue matches the reference eigenvalue at grid points (vertical dotted lines), and the cusping treatment gives a smooth behavior between Figure 6: Full-core neutronics mesh (picture courtesy of [1]).…”

“…To convert the homogeneous power density computed by the neutronics model into the heterogeneous power density to be applied in each representative 30-degree slice, the average power density p assm,r,i was computed 1 for each assembly ring (of index r) over a given axial layer (of index i, with the total number of layers being set to 10). Next, a volume correction factor was applied to account for volume changes between homogeneous and heterogeneous power densities, and a fixed fraction χ-defined by Equation ( 12)-was assumed to be deposited in the fuel, while the remaining amount was assumed deposited in the moderator.…”

“…Nuclear thermal propulsion (NTP) systems for interplanetary travel (e.g., manned missions to Mars) rely on nuclear reactors, rather than a more conventional chemical rocket, to heat the propellant and create the required thrust. This enables the use of molecular hydrogen (H 2 ) in lieu of gaseous H 2 O, thereby increasing the specific impulse by a factor of two [1] and reducing the travel time (or, alternatively, increasing the payload) by that same amount.…”