Last month, Oak Ridge National Laboratory hit a milestone not seen in more than three decades: shipping a production-quantity amount of plutonium-238.

“This marks what I consider to be the reestablishment of the nation’s ability to make Pu-238,” said ORNL’s Adam Parkison, program manager for Pu-238 production.

That’s important because NASA needs this high-power, long-lasting isotope for missions into deep space. The heat it produces as it decays is the primary source of power for the radioisotope thermoelectric generators, or RTGs, that provide electricity to spacecraft.

In 2015, NASA contracted with the Department of Energy and ORNL to find a process to again produce Pu-238. The last time large quantities were made in the United States was about 30 years ago at the Savannah River Site in South Carolina. NASA funded the effort to restart production at ORNL, using the High Flux Isotope Reactor at ORNL and the Advanced Test Reactor at INL to irradiate the targets from which Pu-238 is produced, install a neptunium pellet and target fabrication production line, invent a chemical separations flowsheet, and install equipment at ORNL for packaging Pu-238 for shipment.