Comparing low enriched fuel to highly enriched fuel for use in nuclear thermal propulsion systems

Abstract

Low enriched uranium (LEU) is an economically and politically friendly alternative to highly enriched uranium (HEU) that can enable the use of nuclear thermal propulsion (NTP) systems. Historically, only HEU reactors were considered for NTP due to need of minimum mass systems and the common perception that HEU nuclear cores will always make smaller reactors than LEU cores. However, recent studies have shown LEU NTP systems can be created to enable human Mars missions. These studies do not show the performance losses or gains when using an LEU system rather than an HEU system. The goal of this paper is to present four optimized NTP systems designed for the same 16,000 lbs-f thrust, with a combination of minimum mass and high specific impulse. The four designs differ in the nuclear fuel type; two contain a carbide composite fuel that is derived from historical experiments and two contain tungsten cermet fuel, which has become a good fuel choice given advances in manufacturing techniques. Within each fuel type, LEU or HEU will be used. Core design methods and details such as fuel dimensions, enrichment profiles, fuel layout and thermal design details including core pressure drops and hydrogen outlet conditions are presented here. Similar performances are found between all designs.