Implementation of LEU fuels in NERVA type nuclear thermal rockets

Abstract

In this master thesis we present our study regarding the possibility of implementing Low Enriched Uranium (LEU) fuels in NERVA type Nuclear Thermal Rockets (NTR). This work was done to demonstrate the possibil-ity to enhance the proliferation resistance of these nuclear space systems, in the hope of fostering the ground-work for their eventual commercial use. First, we present a background on NTR technology as well as how their performance is measured and how it differs from traditional nuclear and rockets systems. We then give a detailed description and discussion of legacy NTR designs. We then present our detailed studies related to the requirements for implementing LEU in a NERVA type NTR. Here we discuss the necessity of thermalizing the neutron spectrum and provide a detailed study of various methods by which this can be achieved. We then examine the effect of minimizing non fission neutron loss through the selection of appropriate structural ma-terials and provide a cursory study of various options. Once the different studies regarding how to implement LEU fuels are concluded, a finalized conceptual reactor configuration is proposed. This reactor is generated using the parameters determined from the LEU implementation studies and a minimum mass optimization. This optimization takes into account both neutronic and thermal effects, including a first iteration of tempera-ture dependent reactivity effects. The finalized reactor configuration is then characterized in terms of operat-ing performance, thermal, hydraulic, and neutronic parameters including operating life, cycle burn up, power and temperature distributions, and flow characteristics. Finally, the proposed reactor concept is compared with previous NTR designs where its relative shortcomings and obvious advantages are presented and dis-cussed. Furthermore, possibilities for the further improvement of the reactor design are suggested in order to make up for the current issues in the design. We then c...