| A computational model of an open-cycle Gas Core Nuclear Rocket (GCR) is developed. The model evaluates the rocket performance of an open-cycle GCR as a function of design and operational parameters. The primary output of the model is the specific impulse and thrust of the rocket.; The solution is divided into two distinct areas--thermal-hydraulics and neutronics. To obtain the thermal-hydraulic solution, a computer code is written which solves the Navier-Stokes, energy, and species diffusion equations. A spatially implicit solution is obtained by a direct solver that is developed specifically for the code. The two-dimensional transport code TWODANT is used to obtain the neutronics solution. The important requirements of the neutronics model are the ability to handle neutron upscattering and a highly inhomogeneous mesh. The thermal-hydraulic and neutronic models are coupled, and the solution proceeds in an iterative manner until a consistent power density profile is obtained.; Various open-cycle gas core nuclear rocket designs are evaluated. First, it is assumed that the fuel and propellant do not mix. In this ideal case, it is found that the limiting factor in determining thrust and specific impulse is the maximum allowable wall heat flux. Next, a neutronic study is performed on a simplified homogeneous open-cycle GCR design. The effect of changing the fuel/propellant densities and temperatures on the multiplication factor k-eff is studied, as is the use of alternate fuels and propellants. Following this simplified neutronic study, the results from a complete thermal-hydraulic/neutronic solution are presented. The thermodynamic and nuclear properties of the reactor are studied in detail, particularly density and neutron flux. These results provide insight into the underlying physics of an open-cycle GCR, as well demonstrate the capabilities of the model. Next, a parametric design study is conducted which examines the rocket performance of the open-cycle GCR as a function of various design and operational parameters. It is found that fuel containment is very adversely effected by high reactor power or rocket acceleration. Finally, some innovative concepts are discussed that could help improve fuel containment. |
