Evaluation of Non-Oxide Fuel for Fission-Based Nuclear Reactors on Spacecraft

Abstract

This project investigated the use of uranium nitride (UN) and uranium carbide (UC) reactor fuel and compared their performance to uranium oxide (UO₂) in a nuclear reactor for space-based applications. As a baseline for analysis, the Prometheus Project reference reactor module was considered: a gas-cooled fast reactor using highly enriched UO₂ fuel with 1 MW of thermal power output and a 15-year core life. An estimate of the temperature feedback effect on reactivity was made for each fuel type at the beginning, middle, and end of core life; results for each fuel were compared. This analysis indicates that UN-fueled reactors may exhibit a stabilizing negative reactivity feedback for increasing temperatures and that this benefit persists in the face of fuel composition changes over core life. The benefit of increased uranium loading density was assessed through a quantitative estimate of overall core weight for each fuel. It was found that weight savings on the order of 1000 kg can be realized for a reactor of this size by using either UC or UN rather than UO₂.

Keywords:

• Prometheus Project
• uranium oxide
• uranium nitride
• uranium carbide
• gas-cooled reactor

Acknowledgments

This work was partially supported by funding from the Defense Threat Reduction Agency. The authors would like to thank Mark Natale from Naval Reactors who facilitated an internship for the first author at Bettis Atomic Power Laboratory and the assistance and mentorship provided by Szelim Kong, Dave Sottosanti, and Adam Daniels from Bettis Atomic Power Labs. In addition, the authors acknowledge the mentorship provided to the first author by Dave Poston and Tim Goorley from Los Alamos National Laboratory.