Oak Ridge lab outlines how it converts neptunium-237 into plutonium-238 to power deep-space missions

A researcher at Oak Ridge National Laboratory described the lab’s role in producing plutonium-238 (Pu-238), the isotope used in radioisotope thermoelectric generators (RTGs) that power long-duration deep-space missions. The presenter said ORNL places solid neptunium-237 into the High Flux Isotope Reactor as "targets," where neutron bombardment converts the atoms into Pu-238.

"RTGs are nuclear powered batteries which use the heat from decay of radioactive isotopes to power spacecraft," the Unidentified Speaker said, explaining why RTGs are used when solar panels and conventional batteries are unsuitable for deep-space missions. The speaker listed Mars rovers Perseverance, Curiosity, Opportunity and Spirit as examples of mobile science platforms that have relied on long-lived power supplies.

The presenter said Pu-238 has been used on U.S. spacecraft since the 1960s and that Pu-238 "can provide reliable heat and power in space for decades." According to the speaker, one ingredient in making Pu-238 is neptunium-237 and ORNL’s facilities enable production of the irradiated targets needed for conversion to Pu-238. The speaker asserted that ORNL’s facilities and capabilities "make it the only place on Earth where these targets can be produced." This assertion was presented as the speaker’s claim in the presentation.

The researcher described laboratory efforts to better understand neptunium chemistry through microscopy. "With these microscopes, I can take never before seen images of neptunium particles, many of which are smaller than the width of a single strand of human hair," the speaker said, adding that imaging particle features helps reveal how chemical reactions progressed and how particles formed.

The speaker framed that microscopic information as a path to improving production: learning how to make neptunium targets in a more cost-effective, efficient or consistent manner. The presentation also acknowledged scientific uncertainty: the speaker said neptunium was discovered in 1940, has multiple radioactive isotopes, and that "there's still a lot we don't know about its chemistry."

The talk closed by linking the laboratory work to national objectives. "Here at ORNL, we are securing the nation's supply of plutonium-238, ensuring that the U.S. stays at the forefront of exploration and discovery," the Unidentified Speaker said.

No formal policy actions, votes, or funding decisions were recorded in the presentation. The researcher described ongoing laboratory research and production activities and emphasized microscopy-driven process improvements as next steps.