As californium-252 demand continues to climb, ORNL is increasing production

A new process, nearly a decade in development, could shave a week or more off Oak Ridge National Laboratory's californium-252 production schedule - and it couldn't have come at a better time.

The Department of Energy lab, which is the only producer of californium-252 (Cf-252) in the western world, expects to see a jump in demand for the neutron-emitting radioisotope, which is used to start up nuclear reactors and assay fresh reactor fuel, as well as for oil well logging, national security and other applications, said ORNL Cf-252 Program Manager Samantha Schrell.

Funded by DOE's Office of Isotope R&D and Production, ORNL produces Cf-252 and provides it to an industrial consortium that fabricates and distributes the finished, sealed sources to customers worldwide.

Federal priorities, industrial applications

Federal policy has increasingly emphasized expanding nuclear energy in the United States. Recent federal direction calls for increasing domestic nuclear capacity, including initiating construction of 10 new large reactors by 2030 and increasing the maximum power level at which existing reactors can operate.

In addition, several companies are developing small fission reactors, which will use Cf-252 for startup, and an executive order instructs the military to deploy a reactor on a domestic Army base in the next two years.

Add that to the amount of the radioisotope used for national security applications such as fuel rod scanners and port security, as well as industrial uses including coal analysis, oil well logging and instrument calibration, and Schrell said the lab hopes to significantly increase its Cf-252 production output.

"This is an exciting new chapter in Cf-252 production," Schrell said. "We're raising the bar internally while pushing the boundaries of heavy-element production."

More efficient processing

ORNL makes Cf-252 every two years. Schrell investigated whether having a Cf-252 campaign every year would make sense and concluded it wouldn't, for reasons including cost, limited hot cell time and the radioisotope's short half-life (in 2.6 years, it will have decayed to half its original amount).

But other changes will boost the lab's output, including increasing the number of HFIR cycles with curium targets each year, and making radiochemical processing more efficient.

Ten years ago, radiochemist Lætitia Delmau walked into the Radiochemical Engineering Development Center (REDC) during a Cf-252 separations campaign.

Delmau's prior experience in solvent extraction led her to a theory: Switching to a neutral solvent in a step during processing irradiated targets could be just as effective - and much faster.

"One hour inside the specialized nuclear facility where we produce Cf-252 is extremely expensive," Delmau said. "If you can save time, it saves you a lot of money."

For decades, ORNL's Cf-252 separation process used bis-diethyl hexyl phosphoric acid (HDEHP) to extract trivalent actinides and lanthanides - other isotopes formed during fission at the same time as Cf-252 - from the solution in which the targets had been dissolved.

For that to work correctly, the solution's acidity first needed to be significantly decreased - which took about a week.

Delmau, a distinguished R&D staff member in ORNL's Isotope Science and Enrichment Directorate, theorized that researchers could use a neutral molecule that would capture the desired elements in a very acidic solution, instead of using a molecule that releases extra acid to capture those elements but needs the less acidic environment to work.

So, in 2015, Delmau received a "tiny drop" of waste solution from the ongoing campaign to study, diluted so that its radioactivity was reduced enough to allow for handling in a glovebox rather than the heavily shielded hot cell.

After the next campaign, two years later, she was able to work in the hot cell with a little bit of the actual solution of dissolved targets to test. Two years after that, she received more campaign solution and adjusted the concentration of the ligand she was using for the separation.

She received 6 percent of material from the 2023 campaign to scale up her testing, which validated her glovebox work. During the 2025 campaign, she performed a full-scale test.

Ultimately, with Delmau's revised process, one cycle was enough to extract 95 percent of other isotopes produced during fission - americium, curium and cerium - from the Cf-252 solution. It provided the same result as the older process, but in significantly less time.

"It worked well," she said. "We were very happy."

With some further improvements for next year's campaign, Delmau's new process will be used going forward.

Opportunity for innovation

With the new one-cycle process, separation takes about a week less - cutting time in half without any change in quality.

Delmau said such an innovation couldn't have happened without the support of Schrell and past ORNL Cf-252 program manager Julie Ezold, her colleagues at the REDC, and the lab environment.

"The beauty of being at ORNL is that you can work on sizable amounts," she said. "When you're developing a process, being able to work with even 5 percent to 6 percent of the campaign gives you a different perspective than working with sub-microgram levels in the glovebox. You cannot do that anywhere else, period."

UT-Battelle manages ORNL for DOE's Office of Science, the single largest supporter of basic research in the physical sciences in the United States. DOE's Office of Science is working to address some of the most pressing challenges of our time. For more information, visit energy.gov/science. - Kristi Bumpus