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

Abstract

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.

Keywords:

• Space nuclear power and propulsion
• highly enriched uranium
• nuclear security
• space nuclear systems, uranium

Acknowledgments

This work was funded by the National Science Foundation under contract number NSFOIA0408601.

Notes

^a Source: DOE Atomic Power in Space.

^b The term “delta-v” is used in spacecraft flight dynamics to measure the impulse needed to perform a maneuver such as launch from, or landing on a celestial body, or conduct in-space orbital maneuvers.

^c Other relevant criteria not addressed here are system reliability, controllability, and scalability.

^d More information on the probe is on the Honeybee Robotics website: https://honeybeerobotics.com/portfolio/slush/.

^e Some private companies, such as BWXT, have licenses to handle HEU and will not incur any additional costs.

^f As per the Nuclear Energy Institute, estimated annual requirements for HALEU in 2030 would be 185.5 tonnes U per year; https://www.nei.org/CorporateSite/media/filefolder/resources/letters-filings-comments/letter-perry-haleu-20180705.pdf.

^g LES is owned by foreign entities (based in France), and the centrifuges are internationally sourced, meaning that it would not meet DOD requirements of “unobligated” material. Furthermore, the facility is restricted under its operating agreement to only be used for “producing enrichment for peaceful non-explosive purposes only.”

^h The resolution notes that “Nuclear reactors shall use only highly enriched uranium 235 as fuel”; https://www.unoosa.org/oosa/en/ourwork/spacelaw/principles/nps-principles.html.