Since September 11, 2001, the U.S. government has sought to remove weapons-useable highly enriched uranium (HEU) containing 20 percent or more uranium-235 from as many locations as possible because of concerns about the possibility of nuclear terrorism.
President Barack Obama worked to make this effort a global priority with biennial nuclear security summits between 2010 and 2016.
The primary focus of this HEU cleanout strategy has been on replacing HEU civilian research reactor fuel and uranium “targets” used in the production of medical radioisotopes with non-weapons-usable low-enriched uranium (LEU) fuel and targets. Eliminating the use of HEU in naval fuel was not on the agenda. Yet, naval reactors account for more than half of global HEU use and most of the global stockpile of HEU for nonweapons use. As the phase-out of other uses continues, naval reactors will become increasingly dominant among nonweapon users of HEU unless actions are taken to convert them as well.
S. Philippe and F. von Hippel, "The Feasibility of Ending HEU Fuel Use in the U.S. Navy," Arms Control Today, November 2016.