Nuclear start-ups Oklo and Flibe Energy both announced this week that they have been selected by the Department of Energy for advanced negotiations under the department’s Surplus Plutonium Utilization Program, which aims to make surplus U.S. plutonium available to the nuclear industry for advanced reactor fuels.

According to multiple reports, three other companies—Exodys Energy, Shine Technologies, and Standard Nuclear—have also been selected for advanced negotiations under the program, which is being led by the DOE’s Office of Nuclear Energy.