ORNL achieves milestone in producing plutonium-238 for space missions

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An Oak Ridge National Laboratory employee uses a remote-manipulator to move a vial of plutonium-238 oxide inside a shielded hot cell at ORNL’s Radiochemical Engineering Development Center. (ORNL photo/Jason Richards)

Oak Ridge National Laboratory announced Tuesday it had achieved production of 50 grams of plutonium-238. That’s roughly the mass of a golf ball, according to the Department of Energy, but it’s considered an important milestone in re-establishing a U.S. stockpile of Pu-238 for use as a power source on deep-space missions.

ORNL has been developing the capability over the past couple of years with funding that NASA provided via the DOE’s Office of Nuclear Energy. The lab uses the High Flux Isotope Reactor for production of the plutonium isotope and then processes and purifies the radioactive material in a series of shielded hot cells.

Pu-238, which is different isotope than the plutonium-239 used in nuclear weapons, is used as fuel in space power systems known as radioisotope thermoelectric generators or RTGs. The radioactive material produces heat as it decays, and that heat is then converted to electricity for vital tasks on spacecrafts.

ORNL and the Department of Energy, which issued separate announcements, said the infrastructure is now in place to provide a steady and growing supply of plutonium-238 for future space missions. According to NASA, the next mission with plans for using an RTG is the Mars 2020 Rover, which is tentatively scheduled for launch in July 2020.

“The mission seeks signs of life on Mars and will test technology for human exploration and gather samples of rocks and soil that could be returned to Earth,” the statement said.

The Department of Energy said the work at ORNL, in conjunction with Idaho National Laboratory (which provides the inventory of neptunium-237 that’s used for targets to produce the plutonium inside the Oak Ridge reactor) has restored a domestic capability for the first time in nearly 30 years. According to the statement, the previous U.S. source was shut down at DOE’s Savannah River Plant in South Carolina in the late 1980s.

Bob Wham, who headed the project at Oak Ridge, said in a statement, “Once we automate and scale up the process, the nation will have a long-range capability to produce radioisotope power systems such as those used by NASA for deep-space exploration.”

If funding continues, the lab expects to ramp up production to 300 to 400 grams of Pu-238 per year and eventually provide an annual supply of about 1.5 kilograms.

“We have demonstrated that our process works, and we are ready to move on to the next phase of the mission,” Wham said.

After the neptunium targets have been irradiated in the High Flux Isotope Reactor to form Pu-238, the pellets are removed and dissolved to chemically separate the plutonium from what’s left of the neptunium.

“The plutonium product is converted to an oxide and shipped to Los Alamos National Laboratory (in New Mexico), where it’s stored until needed for a space mission.

The current U.S. inventory of plutonium-238 is only about 35 kilograms, according to DOE. That reportedly includes material that’s leftover from the Savannah River production decades ago, as well as some Pu-238 that was procured from Russia.

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