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Pu-238 shipment quantity 'opens the tap' for space missions

Plutonium oxide is loaded onto a truck for shipping. Adam Parkison/ORNL, U.S. Dept. of Energy



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.

NASA funded equipment for packaging Pu-238 at ORNL. Genevieve Martin/ORNL, U.S. Dept. of Energy
NASA funded equipment for packaging Pu-238 at ORNL. Genevieve Martin/ORNL, U.S. Dept. of Energy

Shortly afterward, ORNL produced 50 grams of Pu-238, demonstrating it was capable of making the high-demand isotope. A small amount of ORNL-produced Pu-238 oxide was even present on the Perseverance rover sent to Mars in 2020 — though it alone wasn’t anywhere near enough to power Perseverance’s instruments and systems.

But the quantity shipped in June, 550 grams, is nearly enough to fill a coffee cup — and significantly help power an RTG, Parkison said. It keeps ORNL on track to meet its production goal: 1.5 kilograms annually by 2026.

“This is no longer an experiment,” he said. “We’re now able to produce significant amounts. These types of shipments are going to become routine.”

ORNL ships the plutonium oxide to Los Alamos National Laboratory, which turns it into fuel clads. Those clads are then sent to Idaho National Laboratory to be loaded and assembled into the RTG before being shipped to Kennedy Space Center in Florida.

Although Pu-238 was produced at the Savannah River Site until the early 1990s, ORNL had to build its own processes for Pu-238, since both the current facilities at ORNL and the national regulatory environment differ greatly.

“We had to start nearly from scratch,” Parkison said. “This has been a research and development effort. We leveraged the legacy of ORNL, and all of the work that’s come prior, and invented a flow sheet of the activities needed for production. Over the past decade, we’ve been inventing and reinventing aspects of the process, molding and shaping it, and now we have a process that’s able to generate production-scale quantities.”

That quantity multiplies when combined with lower-quality material from the Savannah River stockpile, which has been decaying for 30 years, Parkison said.

“The material we’re making is very, very high quality,” he said. “It will be blended with the stockpile material to bring even more material back on the table that wasn’t previously accessible.

ORNL-produced Pu-238 will account for a significant portion of the Pu-238 used to power Dragonfly, a rotorcraft NASA plans to launch in 2026 to Titan, one of Saturn’s moons. Scientists want to study the icy moon because they think it can provide clues to how life developed on Earth.

And it gives NASA many more options for missions.

“The Decadal Strategy for Planetary Science and Astrobiology from the National Academies lists missions it recommends NASA consider, and some subset of those are enabled or limited by Pu-238,” Parkison said. “Now that we have opened the tap, that subset is on the table. This is a big deal for ORNL, but it’s also a big deal for the nation.”

Parkison praised the resiliency and dedication of the teams involved with Pu-238 production who overcame technical challenges, organizational changes, and the uncertain climate of the COVID-19 pandemic.

“Bringing this packaging capability online at Oak Ridge National Laboratory demonstrates the DOE’s commitment to our partnership with NASA,” said Kathryn Huff, assistant secretary for Nuclear Energy. “Together, we are working to ensure that a viable end-to-end capability to produce radioisotope power systems for deep space use exists within the U.S. for decades to come.”

UT-Battelle manages ORNL for the Department of Energy’s Office of Science, the single largest supporter of basic research in the physical sciences in the United States. The Office of Science is working to address some of the most pressing challenges of our time. For more information, please visit