A method developed at Oak Ridge National Laboratory is allowing the Department of Energy to cull promethium-147 from plutonium-238 produced for space exploration. Under an ORNL project for the DOE Isotope Program that began last year, the lab has been mining Pm-147, a rare isotope used in nuclear batteries and to measure the thickness of materials, from the fission products left when Pu-238 is separated out of neptunium-237 targets. The Np-237 targets are irradiated in Oak Ridge’s High Flux Isotope Reactor, a DOE Office of Science user facility, to produce the Pu-238.
According to the DOE, the primary goal of the project is to reestablish the domestic production of Pm-147, which is in short supply. As a side benefit, the project is reducing the concentrations of radioactive elements in the waste so that it can be disposed of safely in simpler, less expensive ways, both now and in the future.
“In the process of recovering a valuable product that the DOE Isotope Program wants, we realized we can reduce our disposal costs,” said Richard Mayes, group leader for ORNL’s Emerging Isotope Research. “There’s some synergy.”
The process: The ORNL efforts are tied to the Pu-238 production schedule, which is currently between two and four processing cycles a year. It is estimated that there are hundreds of curies of Pm-147 in each batch. Working in around-the-clock shifts for several days, the project team uses hot cells in ORNL’s Radiochemical Engineering Development Center (REDC) to isolate a concentrated batch of Pm-147 from the solution of Pu-238 byproducts.
That batch is then transferred into a shielded cave at the REDC, where it is purified and readied for shipment to DOE Isotope Program customers. The process involves a few months of effort and around 20 people.
The team will spend the next year demonstrating whether the recovery of Pm-147 from Pu-238 by-products is sustainable. If so, the project should grow alongside the Pu-238 program. The lab’s goal is to produce enough Pu-238 to yield 1.5 kilograms of plutonium oxide annually to meet NASA’s demands for deep space travel.
“Currently, we’re the only producers of Pm-147 in the U.S., and there’s a market for it,” Mayes said. Research indicates it could have additional applications in medical imaging and as a radioisotope to generate power for space probes.
The program: While the Pu-238 Supply Program is funded by NASA and managed through DOE’s Office of Nuclear Energy, the recovery of Pm-147 is funded by the DOE Isotope Program within the DOE’s Office of Science.
Pm-147 is one of about a dozen elements the DOE is looking to mine from the Pu-238 production waste stream. Successful efforts with Pm-147 may lead to the extraction of other materials at ORNL, Mayes said.