A feasibility study on low-enriched uranium fuel for nuclear thermal rockets - I: Reactivity potential

This paper is concerned with the possibility of implementing Low-Enriched Uranium (LEU) fuels in NERVA (Nuclear Engine for Rocket Vehicle Application) type Nuclear Thermal Rockets (NTR). It presents a detailed study of the requirements for implementing LEU in a NERVA type NTR revolving around the softening of the neutron spectrum. This work has been done to demonstrate the possibility to enhance the proliferation resistance of these nuclear space systems in the hope of fostering the groundwork for their eventual commercial use. The necessity of thermalizing the neutron spectrum is discussed along with a detailed study of various methods by which this can be achieved. The effect of minimizing non fission neutron loss through the selection of appropriate structural materials is then presented along with a cursory study of various options. Finally a reference conceptual reactor configuration is proposed and compared with previous NTR designs where its relative shortcomings and obvious advantages are presented and discussed. It is concluded that an LEU-NTR is not only a definite possibility, but also offers distinct advantages over existing Highly-Enriched Uranium (HEU) NTR designs, particularly the increased proliferation resistance of the system and the reduction of the fuel cost and development schedule. Finally, some suggestions are made for future work that would enable the progression of the current conceptual design to a more finalized reactor design.