Trade-Offs Between Space Nuclear Systems Fueled with Highly Enriched Uranium and Low-Enriched Uranium

Whether to use highly enriched uranium (HEU) or low-enriched uranium (LEU) in space reactors is a highly debated topic. Most analyses focus on performance as the principal determinant of use, where HEU has inherent advantages. This paper identifies seven dimensions along which rigorous comparisons must be made to evaluate whether HEU or LEU is an appropriate enrichment level for space nuclear systems. These dimensions are performance, safety, security and nonproliferation, timeliness of a system to come to fruition, fuel availability, cost, and ability to include commercial partners. Our analysis shows that HEU and LEU systems provide different advantages depending on the dimension of interest, and whether the United States continues to use HEU or switches to LEU is ultimately a policy decision, not a technical one.